Semiconductor Etching Equipment Industry In-depth Research: Domestic Etching Machine Future Can Be Expected
etching is the key link of IC manufacturing, complex process to build industry barriers
1.1. etching is the precise scalpel to carve the chip
Integrated circuit (integrated circuit) is the use of a variety of processes, a circuit required transistors, resistors, capacitors and inductors and other components and wiring interconnected in a small piece or several small pieces of semiconductor wafers or media substrates, and then packaged in a shell to achieve the required circuit function of the micro structure. Modern integrated circuits can be divided by function into four main categories: memory, processor, logic IC, and analog IC.
The manufacturing process of a complete IC is usually divided into two parts: Front-End and Back-End. The traditional packaging (back-end) test process can be roughly divided into eight major steps, including backside thinning, wafer dicing, placement, lead bonding, molding, plating, rib forming, and final testing. Compared to front-end wafer fabrication, back-end packaging is relatively simple and requires less process environment, equipment, and materials. Front-end wafer fabrication is much more complex than back-end packaging, involving lithography, etching, thin-film deposition, development and coating, cleaning, doping and oxide diffusion, and measurement. Etching is one of the three most important processes in wafer fabrication, along with photolithography and thin film deposition.
The structure of an integrated circuit is not simply a flat figure, but a three-dimensional structure with layers of structures superimposed. The role of etching as one of the core processes is to physically and chemically engrave the three-dimensional microstructure required for ICs on the substrate and other materials on the wafer surface, transferring the pattern from the previous mask to the wafer surface. On etching the newly formed structure, 𝑆𝑖𝑂2, SiN dielectric film deposition or metallic Al, Cu, W film deposition can be performed, as well as multiple exposures or the next etching step, resulting in the correct pattern on each layer and proper connectivity between the different layers to form the complete integrated circuit.
The importance of etching equipment is increasing. This is because lithography equipment is limited by the wavelength of the light source (193 nm for DUV or 13.5 nm for EUV) and there are limits to resolution; when transistors are miniaturized to a certain size, it is very difficult to advance the process with the accuracy of the lithography machine alone. The industry barriers for the equipment, process, and core components of the etching step are very high. This is mainly because: (1) etching, as a key step in pattern transfer, requires different structures to be carved out; (2) etching needs to be performed on different material surfaces, and the process methods involved vary greatly; (3) etching, as a major step, takes up a lot of process time and factory space, and its productivity and yield have a great impact on the efficiency of the production line; (4) etching requires (4) the etching step requires precise and smooth coordination of multiple subsystems, such as RF source, gas circuit, electrode, hot and cold source, vacuum, etc., which requires a lot of process data accumulation.
NAND flash memory has entered the 3D era, with 128-layer 3D NAND flash memory now in mass production, and 196-layer and 200-layer+ flash memory chips being released. 3D NAND manufacturing processes increase integration not by reducing the line width of a single layer, but by increasing the number of stacked layers. 3D ICs are placing greater demands on etching equipment.
1.2. Evolution of etching methods from wet to dry
After the 1980s, with the upgrading of IC processes and the continuous reduction of chip structure size, the limitations of wet etching in terms of line width control and etch directionality gradually emerged and were gradually replaced by dry etching. Wet etching is now mostly used for back etching, removal of special material layers, and cleaning of residues.
1.2.1 Wet etching technology applications
Wet etching is the original etching technology, using the chemical reaction between the solution and the film to remove the part of the film not covered by the protective mask, so as to achieve the purpose of etching. The reaction product must be a gas or a substance soluble in the etchant, otherwise there will be a problem of precipitation of the reactant, which will affect the normal etching. Usually, the materials treated by wet etching include silicon, aluminum and silica, etc.
1) Wet etching of silicon
Silicon is generally oxidized by strong oxidizing agents, and then silicon dioxides are removed by reacting hydrofluoric acid with silicon dioxide to achieve the purpose of silicon etching. The most commonly used etching solvent is a mixture of nitric acid with hydrofluoric acid and water. In addition, a solution containing KOH can also be used for etching.
2）Wet etching of silicon dioxide
The wet etching of silicon dioxide can be performed using hydrofluoric acid (HF) as the etching agent, but the reaction rate decreases as the hydrofluoric acid is continuously consumed during the reaction. To avoid this phenomenon, ammonium fluoride is usually added to the etching solution as a buffering agent, resulting in an etching solution called BHF, which produces hydrofluoric acid by decomposition and maintains a constant concentration of hydrofluoric acid.
3）Wet etching of silicon nitride
Silicon nitride is a chemically stable material, and its role in semiconductor manufacturing is mainly as a cover layer and a protective layer after the completion of the main process. Wet etching is mostly used to remove the whole layer of silicon nitride, and for small area etching, dry etching is usually chosen.
4) Wet etching of aluminum
In integrated circuits, most of the electrode leads are made of aluminum or aluminum alloy. Aluminum etching methods are many, the production of commonly heated phosphoric acid, nitric acid, acetic acid and a mixture of water solution. The role of nitric acid is to increase the etching rate, and acetic acid is used to improve the etching uniformity.
1.2.2 The use of dry etching technology
With the development of ICs, wet etching presents the following limitations: it cannot be used for patterns below 3 microns; wet etching is isotropic and can easily lead to distortion of the etched pattern; potential toxicity and contamination of liquid chemicals; additional rinsing and drying steps are required, etc.
The emergence of dry etching technology has solved the challenges faced by wet etching. Dry etching uses gas as the primary etching material and does not require liquid chemical rinsing. Dry etching is mainly divided into plasma etching, ion sputtering etching, and reactive ion etching, which are used in different process steps. (1) Plasma etching involves ionization of the etching gas to produce charged ions, molecules, electrons, and chemically active atomic (molecular) groups, which then react with the material to be etched to produce volatile substances that are evacuated by vacuum equipment.
Depending on the method of plasma generation, dry etching is divided into capacitive plasma etching and inductive plasma etching. Capacitive plasma etching mainly deals with hard dielectric materials and etches microstructures such as through-holes, contact holes, and trenches with high aspect ratios. Inductive plasma etching is mainly used for softer and thinner materials. These two etching devices cover the main etching applications.
(2) Reactive Ion Etching (RIE) physically bombards the substrate with reactive ions and simultaneously performs a chemical reaction. It is a combination of sputter etching and plasma etching with the advantages of anisotropy and good selectivity. The surface of the etched material is first bombarded with ions to break the atomic bonds and enhance the chemical reaction, and then the products deposited on the surface of the etched material are knocked off.
(3) Ion beam sputtering etching is also called ion beam etching or ion milling. Unlike plasma etching systems, which rely primarily on chemical reactions, ion beam etching is a physical process. The wafer is placed on a holder in a vacuum reaction chamber, and a stream of argon gas is introduced into the reaction chamber; the argon gas is influenced by a stream of high-energy electrons coming from a pair of cathodes, and the argon atoms are ionized into a positively charged, high-energy state and sucked toward the holder. As the argon atoms move toward the wafer holder, they accelerate and impact the exposed wafer layers and bombard a small portion of the wafer surface.
1.3. Silicon, metal, dielectric, CCP and ICP, multiple etching processes working together
Metal etching is mainly used to etch aluminum alloys for metal interconnects and to make tungsten plugs; dielectric etching is mainly used to make contact holes, vias, and grooves; silicon etching is mainly used to make gate and device isolation trenches. Dielectric etching is generally capacitively coupled plasma etching machine; silicon, metal etching is generally inductively coupled plasma etching machine.
1.3.1. CCP etching and ICP etching differences
(1) Capacitively Coupled Plasma (Capacitively Coupled Plasma) etching
Capacitively coupled plasma etching (CCP) is generated by applying an RF voltage to two parallel flat electrodes through a matcher and a spacer capacitor to discharge the two electrodes and the plasma to form an equivalent capacitor. This discharge is maintained by an ohmic heating and sheath heating mechanism. Due to the introduction of the RF voltage, a capacitive sheath is formed near the two electrodes and the boundary of the sheath is rapidly oscillating. When electrons move to the sheath boundary, they are reflected by this fast moving sheath and gain energy. Capacitively coupled plasma etching is often used to etch materials with high chemical bonding energy such as dielectrics, and the etching rate is slow.
(2) Inductively coupled plasma ICP (Inductively Coupled Plasma) etching
The principle of inductively coupled plasma etching (ICP) is that an AC current is passed through a coil to generate an induced magnetic field, which generates an induced electric field, and the electrons in the reaction cavity are accelerated in the induced electric field to generate plasma. The ionization rate generated by this method is high, but the ionophore homogeneity is poor, and it is often used to etch materials with low chemical bonding energy, such as silicon and metals. Inductively coupled plasma etchers can control the electric field independently in the horizontal and vertical directions, allowing a true De-couple, independent control of plasma density and bombardment energy.
1.3.2. Single-crystal etching
Single crystal etching is used to form shallow trenches (STI) and deep trenches for capacitors. The breakthrough process uses SiF4 and NF gas to remove the oxide layer from the single-crystal silicon surface by strong ion bombardment and fluorine chemistry; the main etch uses hydrogen bromide (HBr) as the main etchant, which decomposes in the plasma to release bromine radicals that react with the silicon to form volatile silicon tetrabromide (SiBr4). (SiBr4). Monocrystalline silicon etching is usually performed using inductively coupled plasma etchers.
1.3.3 Polysilicon etching
Polysilicon etching is one of the most important etching processes because it determines the gate of the transistor, and the control of the gate size largely determines the performance of the IC. The etching of polysilicon requires a good selection ratio. Usually halogen gases are used, chlorine for anisotropic etching with a good selection ratio (up to 10:1), bromine based gases for a 100:1 selection ratio, and a mixture of HBr with chlorine and oxygen to increase the etching rate. Moreover, the reaction products of halogen gas and silicon are deposited on the sidewalls, providing protection. Polysilicon etching is usually done by inductively coupled plasma etching machines.
1.3.4 Metal Etching
The etching requirements are: high etching rate (greater than 1000nm/min); high selection ratio, greater than 4:1 for the mask layer and greater than 20:1 for the interlayer medium; high etching uniformity; good control of critical dimensions; no plasma damage; few residual contaminants; no corrosion of the metal, etc. Metal etching is usually done with inductively coupled plasma etching machines.
1) Aluminum etching
Aluminum is the most important wire material in semiconductor preparation, with the advantages of low resistance, easy deposition and etching. Etching of aluminum is done by using plasma generated by chloride gas. Aluminum reacts with chlorine to produce volatile aluminum trichloride (AlCl3), which is drained from the cavity as the gas is pumped out. Generally, aluminum is etched at a slightly higher temperature than room temperature (e.g., 70°C), and the AlCl3 is more volatile, reducing residues. In addition to chlorine gas, halides such as SiCl4, BCl3, BBr3, CCl4, CHF3, etc. are often added to aluminum etching, mainly to remove the oxide layer on the surface of aluminum and to ensure the normal etching process.
2) Tungsten etching
In multilayer metal structures, tungsten is the main metal used for hole filling, and other metals such as titanium and molybdenum are also used. Fluorine-based or chlorine-based gases can be used to etch tungsten metal, but fluorine-based gases (SiF6, CF4) are less selective for silicon oxide, while chlorine-based gases (CCl4) have a good selection ratio. Usually, nitrogen is added to the reaction gas to obtain a high etchant selectivity ratio and oxygen is added to reduce carbon deposition. Anisotropic etching and high selectivity ratios can be achieved by etching tungsten with chlorine-based gases. The gases used for dry etching of tungsten are mainly SF6, Ar and O2, where SF6 can be decomposed in isotropes to provide fluorine atoms for chemical reaction with tungsten to produce fluoride.
3) Titanium Nitride Etching
Titanium nitride hard masks replace conventional silicon nitride or oxide masks for double damascene etching processes. The poor selection ratio between the conventional mask and the low-k dielectric layer leads to a circular profile on top of the low-k dielectric layer and an enlarged trench width after etching, and the spacing between the deposited metal lines is too small, which makes it easy for bridging leakage or direct breakdown to occur. Titanium nitride etching is usually used in hard mask opening process, and the main reaction product is TiCl4.
1.3.5. Dielectric etching
Dielectric etching uses silicon dioxide, silicon nitride and other dielectrics as the main etching objects, which are widely used in chip manufacturing. Dielectric etching is mainly used to form contact holes and channel holes to connect different circuit layers. In addition, the process steps covered by dielectric etching are hard mask etching and solder pad etching (partial). Dielectric etching is usually performed using an etching machine based on the capacitively coupled plasma etching principle.
1) Plasma etching of silica films
Etching of silica films usually uses etching gases containing fluorinated carbon, such as CF4, CHF3, C2F6, SF6 and C3F8. CF4 is the most commonly used etching gas, and when CF4 collides with high energy electrons, various ions, atomic groups, atoms and free radicals are generated. Fluorine free radicals can chemically react with SiO2 and Si to produce volatile silicon tetrafluoride (SiF4).
2) Plasma Etching of Silicon Nitride Film
Plasma etching of silicon nitride films can be performed using CF4 or a mixture of CF4 gases (plus O2, SF6 and NF3). For Si3N4 films, etching with CF4-O2 plasma or other gas plasma containing F atoms can achieve etching rates of up to 1200Ă…/min for silicon nitride with etching selectivity ratios as high as 20:1, with the main product being volatile, easily extracted silicon tetrafluoride (SiF4).
1.4. etching process indicators are complex and difficult industry barriers are high
Etching is the most important IC manufacturing step other than photolithography, and there are several key process indicators that have a great impact on chip yield and capacity. In order to achieve the relevant process indicators, etching equipment needs long-term experiments and chip runs to accumulate experience and knowhow, and constantly debug the corresponding parameter settings of each subsystem of the equipment. Therefore, there are high barriers in the etching equipment industry. (1) The etching rate is the speed of removing the surface material from the wafer during the etching process, and the etching rate needs to be increased in order to improve the yield in actual production. It is a very important parameter in the equipment using single wafer process. (2) Etch profile refers to the shape of the sidewall of the etched pattern. There are two basic etch profiles, namely isotropic and anisotropic. The isotropic etching profile is etched at the same etching rate in all directions (transverse and longitudinal). 3) Etching deviation The etching deviation is the change in line width or critical dimension after etching.
(4) Selection ratio The selection ratio refers to the ratio of the etching rate of two different materials under the same etching conditions. An etching process with a high selection ratio will not etch the next layer of material and will not etch the protective photoresist. In the most advanced processes, high selection ratios are necessary to ensure critical dimensions and profile structures. The smaller the size, the higher the selection ratio required. As shown in the figure below, SiO2 is the desired etchant and photoresist is the avoided etchant, a high selection ratio means etching as much SiO2 as possible and as little photoresist as possible.
(5) Uniformity is a parameter that measures the ability of the etching process to etch on a single wafer, or between different wafers. Uniformity is closely related to the selection ratio, since non-uniform etching produces additional over-etching. The etch rate is slower in small window patterns, and even in small size patterns with high aspect ratios, etching stops completely, a phenomenon known as deep aspect ratio dependent etching (ARDE), also known as the micro-load effect. In order to improve uniformity, the ARDE effect on the wafer surface must be minimized.
Other indicators such as residues, polymers, plasma-induced damage and particle staining, reaction chamber start-up time, etc. are also key technical parameters to be met by the etching equipment in actual production.
2. Production expansion overlapped with technology iteration, and the share of etching equipment sales is rising
2.1 Global production expansion will drive the demand for equipment, and the etching equipment market will reach $24.2 billion
Integrated circuit manufacturing requires a wide range of semiconductor equipment, etching machine is one of the core equipment. From 2020, the global semiconductor market will enter a boom cycle due to the increase in demand for electronic products caused by the epidemic, the increase in penetration of new energy vehicles, and panic stockpiling. According to IC Insights, the global semiconductor market is expected to grow from $492.6 billion to $654.8 billion in 2020-2022. Driven by the surge in demand for semiconductor products, fabs are actively expanding capacity, with capital expenditures from 2020 to 2022 of $113.1 billion, $153.1 billion, and $185.4 billion (estimated). Equipment procurement spending accounts for the vast majority of fabs' capital expenditures. Strong downstream demand has significantly boosted the market size of semiconductor equipment such as etching equipment.
2.2. 5nm logic chip manufacturing etch steps climb to 160
Driven by Moore's law, transistor integration has increased significantly, corresponding to the IC line width is shrinking, which directly leads to the IC manufacturing process more complex. According to SEMI, the 20nm process requires about 1,000 steps, while the 10nm and 7nm processes require more than 1,400 steps. Especially when the line width to 10, 7, 5 nanometers or even smaller direction, the need to use multiple stencil process, repeated multiple film deposition and etching process to achieve smaller line width, which makes the number of etching significantly increased. According to SEMI, 20 nm processes require about 50 etching steps, while 10 nm and 7 nm processes require more than 100 etching steps. The significant increase in the number of etching steps in the logic process means that the number of etching equipment market demand continues to grow.
In the front-end process of logic circuits (FEOL), etching steps include isolation slot etching, sidewall etching, and polysilicon gate etching; in the back-end process (BEOL), through-hole etching, trench etching, and wire etching are the main processes involved. The logic chip involves the etching of a variety of materials, including: single crystal silicon etching for the formation of shallow trench isolation, polysilicon etching for the gate and local connection, dielectric etching is mainly used for contact hole etching, through-hole etching, trench etching, sidewall etching.
Polysilicon gate fabrication is the core step of IC production, which requires high etching requirements and therefore requires equipment with high selection ratio, high anisotropy, and high control accuracy. In addition, due to the extremely small size of polysilicon gate and shallow slot isolation, the accuracy requirement is very high, and the selection ratio should be about 150:1. At the same time, the small size brings an increase in the depth to width ratio, silicon etching in the 14nm below the depth to width ratio will reach about 30:1 and above, etching more difficult.
The importance of etching is also enhanced by the adoption of new FinFET architectures, called finFETs, in which the gate is designed as a fork-like 3D structure resembling a fin. The advantages over planar structures are: (1) better channel control, (2) lower leakage current, (3) lower threshold voltage, and (4) significantly reduced gate length.
In the 2D structure MOSFETs, the "gate length" is about 10nm, which is the smallest and most difficult of the left and right structures. When the gate length is reduced to less than 20nm, a "short-channel effect" occurs: the source and drain are too close to each other, the oxide layer below the gate becomes thinner and thinner, and electrons may "leak". The FinFET structure replaced the old MOSFETs and has successfully solved this problem with its excellent characteristics, and has gradually become the mainstream of the market since 2013.
The etching steps and difficulty of FinFET structures have increased compared to conventional structures. For FinFET upper interconnect layer fabrication, as circuit density increases, the interconnect structure becomes more complex, increasing the number of etching steps; at the same time, the losses associated with complex interconnect layers gradually increase, and the process yield of etching equipment places higher demands.
Double exposure technology (LELE) is in the same wafer, according to the sequence of lithography - etching - lithography - etching process in turn, making the graphics density doubled. The main steps are: Lithography 1: Expose the first layer of pattern to the mask plate. Etch 1: Etch the first layer onto the mask. Lithography 2: Expose the second layer to double the pattern density. Etch 2: The final double-density pattern is etched onto the wafer. The original layer of photolithography is split onto two or more masks, enabling the superimposition of image density. Self-aligning multiple patterning (SADP) is a dual patterning process that replaces the traditional LELE method. The dual patterning scheme is achieved by a sidewall self-alignment process: the axial pattern is formed by a single lithography and etching process, and then the sidewall pattern is formed by an atomic layer deposition and etching process on the sidewall, and the axial layer (i.e., sacrificial layer) is removed, resulting in a sidewall hard mask pattern with half the pattern size.
The SADP technology increases the number of etchings and the difficulty of etching, which drives the development of etching equipment. On the one hand, since the SADP process involves etching of multiple layers of masks, multiple etching lines need to be matched, increasing the number of etchings. On the other hand, the main difficulties of this technology are: (1) the selection ratio problem: SADP technology with more repetitions requires more layers of sidewalls and masks, which makes the etching process more complicated; to ensure the accuracy of pattern transfer, the etching selection ratio is also more demanding for different layers of materials, spacers, substrates, etc. (2) the control of sidewall shape: sidewall shape is the key mask for pattern transfer, and the difficulty of etching is also a major factor in the development of etching equipment. The difficulty of etching increases with the increase of the number of sidewall layers.
2.3. Deepening reliance on etching equipment for memory manufacturing
The development of integrated circuits is not only reducing the line width, but also the device structure is becoming more complex and multi-layer. For example, memory DRAM is mainly progressing towards size reduction and introducing 3D structures such as concave grids and buried word lines. NAND flash memory has entered the 3D era, and by increasing the number of layers in the stack, the layer level of 3D NAND has also developed from 64 layers, 128 layers, to 192 layers and more than 200 layers.
2.3.1. DRAM structure shrinking and multi-layered at the same time
The core structure of DRAM memory cell can be divided into two parts: deep-slot capacitor and transistor; DRAM transistor miniaturization progresses mostly similar to logic process, relying more and more on self-aligned multiple patterns and multiple exposures, requiring more and more advanced etching equipment; while capacitor slot etching is the main technical difficulty in DRAM iteration. DRAMs can be divided into trench DRAMs and stacked DRAMs according to the position of the capacitance groove. 1) Trench DRAM: The capacitance groove is etched on the silicon first, and then a dielectric layer is deposited in the groove to form the capacitance, with the gate on top of the capacitance. This type of DRAM has fewer applications at present. (2) Stacked DRAM: The memory cell is formed on top of the gate and is mainly used for manufacturing stand-alone high-density DRAM. The formation of the capacitive structure is mainly dependent on dielectric etchers and single crystal silicon etchers with high aspect ratio function. Currently, most DRAMs use stacked structures.
The accuracy of the capacitance slot etching is directly related to the subsequent dielectric material deposition process. As the DRAM process evolves from 2Y to 1X,1Y,1Z, the width of each DRAM cell is shrinking, and the depth to width ratio of the capacitance slot inside the DRAM cell is increasing.
In addition to miniaturization, DRAMs have adopted new technologies, including buried word lines and concave grids, to further reduce the volume per unit of memory cell, which places new demands on etching equipment. The main structure of buried word lines and concave grids is distributed on monocrystalline silicon substrates; the monocrystalline silicon etching process required to engrave them requires better control of key dimensions, depths, and profiles; and the need to achieve nearly identical etch rates for monocrystalline silicon and STI-positioned silicon oxide.
2.3.2 NAND manufacturing etching equipment expenses far exceed those of photolithography
The core structure of 3D NAND includes a channel hole between layers, a contact hole, a saircase for each layer, and a scribe for each layer. The core structure of 3D NAND includes channel hole, contact hole, staircase, slit, etc. As the number of stacked layers increases, the number of microstructures increases and the technical difficulty of etching increases. Compared with DRAM memory, 3D NAND involves more number of hole etching steps and more difficult etching, so it requires a large number of more advanced etching equipment. In addition, the formation of step structure and slit structure in 3D NAND also requires a lot of advanced etching equipment.
The large demand for etching equipment for 3D NAND has led to a significant increase in the proportion of etching equipment in the capital expenditure required for NAND memory expansion. Tokyo Electron estimates that the proportion of etching equipment spending has increased from less than 15% for 2D memory to more than 50% for 3D memory. We expect that as 3D NAND moves to stacks of 200+ layers, the percentage of capital expenditures for etching equipment will increase.
According to Tokyo Electron, from 2015 to 2019, as the flash memory structure gradually transitions from 2D to 3D, the proportion of etching equipment required for NAND manufacturing is rising as a percentage of the etching equipment required by the entire semiconductor industry. By 2019, the scale of etching equipment used for NAND manufacturing will have surpassed that of DRAM and logic. As the construction of 3D NAND continues to progress toward higher levels, coupled with the society-wide demand for massive data storage, we expect the proportion of NAND etching equipment to the total semiconductor manufacturing industry etching equipment will further increase. 3.
3. etching equipment parts are complex, the U.S., Japan and Europe control high-value components
According to the data published in SMIC's 2021 annual report, the gross margin of etching equipment reached 44.32%, and direct materials accounted for 88.38% of the cost of semiconductor equipment products; the gross margin of Panlin Group, which focuses on etching machines, reached 46% in the latest quarter. Taking the above data together, the gross margin is estimated to be 45%, and the global etching equipment parts market size can be deduced to be 241.8 (etching equipment sales amount)*45%*88.38%, which is about USD 9.6 billion.
3.1. Structure of the main body of etching equipment
The structure of mainstream etching equipment can be divided into two major parts: the main body and the auxiliary equipment. The EFEM module is mainly responsible for loading wafers from various handling equipment (including wafer loaders, handling robots, and overhead cranes) into the etching equipment; the TM module is mainly responsible for transporting wafers inside the etching equipment; and the PM module is the module that actually performs the etching process on the wafers. The PM is the module that actually etches the wafers and performs the related physicochemical reactions. The PM is the module that actually performs the etching process on the wafer and the associated physicochemical reactions. The auxiliary equipment is designed to support the above three modules and is relatively independent of the main machine.
As the demand for individual etching equipment in IC manufacturing increases, the number of reaction chambers in a single etching machine is increasing from small to large. In the 1990s, Tokyo Electron introduced the Unity series, the world's first machine with multiple reaction chambers on a single platform; in the 2000s, the world's first machine with a parallel chamber structure, the Telius; and in the 2010s, the Tactras with 6/8 chambers. Tokyo Electron's latest Episode Series machines can mount up to 12 chambers, greatly improving the efficiency of etching equipment space utilization and reserving more space for fab expansion.
Etchers that mount multiple etch chambers are critical to fab throughput; the more chambers in a single machine, the less space a single chamber takes up on average. Reducing the space occupied by individual equipment can effectively increase the wafer capacity per unit area of the cleanroom, and reduce the depreciation and maintenance cost of the plant spread over individual wafers. Etchers (mainly dielectric etchers) with slower reaction rates and lower WPH (wafer per hour) per unit time are more likely to use ultra multi-chamber structures. However, the increase in the number of PM chambers will place new demands on the loading-transport process of EFEM front-end modules, TM transport modules.
3.2. Front End Module (EFEM) and Transport Module (TM)
The Front End Module (EFEM) and the Transport Module (TM) of the etching equipment together form the functional structure for transferring wafers from various external handling devices (including wafer loaders, handling robots, and overhead cranes) to the process module for etching processing. The front-end module consists of four main components: the casstte, the aligner, the ATM robot, and the loadport; the transfer module consists of three main components: the pre-vacuum transfer body (loadlock), the transfer platform body, and the vacuum instrument hand. The front-end market is mainly occupied by Brooks, Genmark, Kensington, and Rorze in Japan.
3.2.1 Wafer cassette and front-opening cassette (foup)
Wafer manufacturing involves many processes and steps, and wafers are placed in different external environments and equipment due to these processes or steps. Therefore, during the wafer manufacturing process, wafers are constantly transported from one location to another and sometimes must be stored for a period of time to accommodate the necessary manufacturing processes. In the front-end module of the etching equipment, the wafer boat and the front-opening cassette together form the wafer staging module, which plays a very important role in the wafer manufacturing process by providing both storage and transport functions. The external front-opening cassette (foup) protects, transports, and stores 12" or 8" wafers from damage during handling, and reduces wafer contamination from exposure to the external environment between process steps, thereby improving yield and throughput. Wafer cassettes are typically filled with protective gas during use. A cassette, also known as a wafer basket, is a special rack-like carrier for wafers in a cassette. During the loading process, wafers are usually placed into the rack piece by piece, and then the entire rack is placed inside the wafer cassette, which is called a cassette.
In semiconductor equipment, including etching equipment, most wafers are placed horizontally in the wafer cassette and the canoe. In addition, wafer cassettes and boats need to be ESD-proof, made of materials and designed to be resistant to wear and tear, low contamination, airtight, and temperature resistant (some high-temperature processes). Normally, the design parameters of wafer cassettes and wafer boats need to comply with SEMI standards to ensure that they can be transported smoothly in different manufacturers' equipment. However, in practice, some of the special equipment uses special arks, so the wafers have to be transferred from the general purpose ark to the special ark using a rewinder, and then to the special equipment.
3.2.2. Wafer Loadport
The wafer loadport is a mechanical device installed in the front-end module to receive wafer cassettes from the wafer handling equipment. Its main functions include loading, unloading, and securing wafer cassettes; opening or closing the doors on the cassettes. The wafer loading port is the access point for wafers to enter and exit the front-end module and the interaction between the semiconductor equipment and the production line, which is important for the automation of the fab. Wafer loading ports are required to meet SEMI standards in terms of applicable jam specifications, placement standards, opening methods, platform height standards, and communication protocols. The wafer loading port is usually equipped with RFID reading capability to identify the lot and number of the wafer cassette. Similar to other modules, wafer loading ports need to have high cleanliness to prevent wafers from being contaminated by the external environment.
3.2.3. Wafer aligner
As the IC process progresses, wafer alignment and attitude adjustment is required before almost every process. The wafer aligner is responsible for pre-aligning the wafers and is an important step in the alignment process. The alignment time of the wafer aligner has a significant impact on the speed of wafer transfer in the front-end module.
The main method of wafer pre-alignment is to use an edge detection sensor (laser sensor or image sensor) together with a rotary table to calculate the eccentric position of the wafer and to locate the notches on the wafer edges, and then to use a mechanical motion stage to correct the wafer position in preparation for the next wafer transfer.
3.2.4 Vacuum and Atmospheric Manipulators
The Atmospheric Manipulator is the core component of the EFEM and is responsible for wafer pick and place in the atmospheric environment (EFEM, inflated lockport); the Vacuum Manipulator is responsible for wafer pick and place in the vacuum environment (reaction chamber, vacuum transfer chamber, evacuated lockport). Both vacuum and atmospheric manipulators need to be protected against collisions. In addition, the precision, clamping force, balance and stability of the vacuum manipulator are very important to prevent wafer fragmentation or wafer stress deformation.
3.2.5 Pre-vacuum transfer body (Loadlock) and transfer platform body
It is used to isolate the reaction chamber from the outside atmosphere to ensure the cleanliness of the reaction chamber and reduce the probability of contamination of the chamber. When the front-end module needs to pick up and place wafers in the pre-pumped vacuum transfer body, it needs to fill with nitrogen to adjust the air pressure in the chamber to atmospheric condition, and then open the transfer valve of the pre-pumped vacuum transfer body on the front-end module side to pick up and place the wafers; when picking up and placing wafers from the transfer chamber (part of the transfer platform) to the pre-pumped vacuum transfer body, it needs to use a vacuum pump to pump the pre-pumped vacuum transfer body into the chamber. When wafers are picked up and released from the transfer cavity (part of the transfer platform) to the pre-evacuated transfer body, a vacuum pump is used to remove the gas from the pre-evacuated transfer body and adjust it to a vacuum state.
The steps of wafer transfer in the transfer system are as follows: all doors are closed → the wafer loading port opens the door of the wafer cassette → the atmospheric manipulator grabs the wafer from the wafer boat of the wafer cassette → the wafer is placed on the aligner → the wafer position is calibrated → the LoadLockA is filled with nitrogen gas → the door of the LoadLockA is opened → the atmospheric manipulator puts the wafer into the LoadLockA → the door of the LoadLockA is closed The door of LoadLockA→Evacuate LoadLockA→Open the door of the reaction chamber→Vacuum manipulator puts the wafer into the reaction chamber→The reaction occurs→Evacuate the reaction chamber after the reaction→Open the door of the transfer chamber→Vacuum manipulator moves the wafer into the transfer chamber→Close the door of the reaction chamber→Open the door of LoadLockB→Vacuum manipulator moves the wafer into LoadLockB→Close the door of LoadLockB Close the door of LoadLockB → LoadLockB is filled with nitrogen → Open the door of LoadLockB → Atmospheric manipulator moves the wafer out of LoadLockB → Close the door of LoadLockB
3.3. Process Module (PM) of etching equipment
The process module is the core module of the etching equipment and is the component where the actual etching reaction takes place. According to the functional categories, the process module of etching equipment can be divided into several main parts: reaction chamber system, RF system, electrostatic chuck and electrode system, vacuum pressure system, gas circuit system, end point detection system, etc.
3.3.1 Reaction chamber system
The reaction chamber of the etching equipment is generally made of precision machined aluminum. Because the chamber itself needs to withstand the complex and violent physicochemical environment of the etching reaction during the reaction process, the chamber needs to adopt various anti-corrosion technologies. Typically, the reaction chamber cavity is coated with a dense coating to resist ionic shock and corrosion by highly chemically active gases. Common coatings are yttrium oxide and aluminum oxide, and the aluminum parts of the chamber treated with special coatings are called coating pieces. The more important coated parts in chambers include liners, inner doors, adjustment brackets, etc. A large percentage of these parts are currently imported into China. Japan KOGA, Taiwan Jingding Precision, and the United States Super Corinne are the main overseas import sources of chamber parts.
3.3.2. RF system
RF system usually consists of two parts: RF Generator and RF Match, which is one of the core systems of etching equipment, and the market in this field is mainly occupied by AE, MKS, and Camtek. The RF power supply is a power supply that can generate a fixed frequency sine wave voltage and has a large power. After the etching gas (mainly CF4) is introduced into the reaction chamber through the gas circuit system, it is ionized by the high frequency electric field (usually 13.56MHz) generated by the RF power supply to produce a glow discharge, which completes the transformation from gas molecules to ions, forming plasma and increasing the gas reactivity. The RF power supply is directly related to the concentration, uniformity and stability of the plasma in the reaction chamber. In most etching equipment, RF power supplies are used in conjunction with DC power supplies to control the density and energy level of the ions, respectively. Due to the acceleration effect of the electric field, the ions are usually etched on the wafer in both physical and chemical form. In addition, RF systems are also an important part of thin film deposition equipment, debinding machines, ion implanters, and cleaning equipment.
A common combination of RF system configurations for etching equipment is a fixed frequency RF power supply and an adjustable matcher. As the etching process occurs, the matcher autonomously adjusts the internal adjustable capacitor to match the output impedance of the power supply itself with the response load impedance to achieve full power output of the RF power supply. In the ideal matching condition, all RF signals are transmitted to the load location and the reflected power of its energy is reduced. When the load impedance and the impedance of the RF power supply output are not matched, a small part of the input signal will be reflected back to the RF source at the load side, and the output power of the RF power supply is not fully used, which reduces the efficiency of the etching reaction.
3.3.3 Electrostatic chuck and electrode system
With the continuous development of IC manufacturing technology, major semiconductor equipment manufacturers are gradually abandoning mechanical chucks and vacuum chucks in favor of electrostatic chuck technology. Electrostatic chucks are usually made of aluminum nitride or aluminum oxide than conventional chucks. Electrostatic chucks provide uniform wafer clamping force and reduce wear on wafer edges.
The back of the electrostatic chuck has helium (He) cooling channels. A cold pump under the electrostatic chuck drives the helium cooling fluid in the cooling channel, which, together with a cooler that is part of the ancillary equipment, provides temperature control of the wafers to avoid overheating and damage to the reaction chamber. The new electrostatic chucks generally use multi-zone cooling and temperature control technology to ensure uniform and stable wafer temperatures during the etching process, reducing the effect of temperature on the uniformity of the etching rate. The main manufacturer of cold pumps is Sumitomo Japan.
3.3.4 Vacuum pressure system
The reaction chamber of the etching equipment needs to be under a high vacuum during the reaction process, and the working pressure is usually between 1/100 Torr and 1/1000 Torr. The vacuum pressure system is responsible for maintaining this high vacuum environment and consists of dry pumps, sub-pumps, vacuum gauges, vacuum valves, etc.
The dry pumps pump vacuum, usually up to 100 milliTorr, and the molecular pumps up to 0.1 milliTorr. The two pumps are usually used in combination, the dry pump is responsible for the initial vacuuming of the chamber, while the molecular pump is responsible for pumping the chamber to a high vacuum. Some etching processes, such as atomic layer etching, require the sequential circulation of multiple etching gases to react in a short period of time. This places high demands on the pumping speed of molecular pumps. The pumping speed of new molecular pumps has also developed from 300-2200L/s to 1600-2500L/s. The market of dry pumps and molecular pumps is mainly occupied by Edwards (UK), Pfeiffer Vacuum (Germany), Shimadzu (Japan) and other companies.
The measurement of vacuum level is mainly done by vacuum gauges. Vacuum gauges are required to have the advantages of high precision and good stability. In semiconductor equipment, thin film capacitance vacuum gauges with high reliability and accuracy are usually used, and their ranges are 100mT, 1T and 10T. Metal and silicon etching mostly use 100mT vacuum gauge, while dielectric etching uses 1T vacuum gauge.
3.3.5. Gas system
The etching step requires the use of various etching gases, which are also called process media in the reaction process. The gas system of the etching equipment is responsible for the transport of the process media from the gas source to the inside of the reaction chamber and consists of a gasbox, gaspanel, flow meter (MFC), and piping.
The function of the gas box is to regulate the pressure of the gas medium from the gas source (special gas bottle or wafer fab's gas pipeline) to the gas pipeline of the etching equipment through various regulating valves. Since most of the gases used in IC manufacturing are hazardous, the cabinet of the gas circuit box is usually coated with corrosion protection, and is equipped with an external viewing window and a negative pressure inside to ensure safety. In addition, the gas circuit box is equipped with various monitoring systems that immediately cut off the gas delivery and alarm if a gas leak is detected. The gaspanel is one of the core components of the gas circuit system and is a very difficult semiconductor metal part to machine. The gaspanel is usually composed of four layers of metal discs, each of which has many small holes and complex small gas paths. The etching gas is regulated by the gas path cassette, enters the pipeline, passes through the gas leveling discs, and is finally delivered to the reaction chamber at a stable and uniform rate. The gas leveling discs need to be resistant to high temperature, low particle contamination, and corrosion, and the multi-layer metal discs need to be welded together in a special way to prevent internal leakage. Since the leveling discs are related to the core air intake step of etching, some equipment companies choose to cooperate with precision metal processing companies to develop and produce the leveling discs; in addition, Japan Fuji Gold Valve is also an important manufacturer of the leveling discs.
Etching equipment monitors and controls the rate of etching gas entering the reaction chamber by means of a mass flow meter (MFC). Because the gas inlet rate is related to the stability of the etching reaction, the etching equipment has high requirements on the flow range, control accuracy, and flow stability response time of the mass flow meter. Flowmeter can be divided into analog circuit type, digital circuit type and pressure change compensation type several. Pressure change compensation type flowmeter, can automatically compensate for fluctuations in the pressure of the gas source, to ensure that the gas output to the reaction chamber flow stability. The main manufacturer of mass flow meter is Horiba, Japan.
3.3.6. end-point detection system
End-point inspection systems are widely used in etching equipment to ensure that the depth and time of etching meet the process requirements. The etching reaction also has some loss of material that does not need to be etched (lower film, mask, etc.). During the reaction, after the layer to be removed by etching is completely stripped, the etching equipment continues to remove the next layer at a slower rate, resulting in over-etching.
The end-point detection system determines whether the etching should be finished by spectroscopy in two ways: by detecting a sudden increase in the concentration of the chemical gases involved in the reaction, and by detecting a sudden decrease in the concentration of the reaction products. The equipment can be divided into two types according to the detection wavelength range: High Optical Throughput, which can only pass a specific wavelength of light, and Monochromator, which can separate the desired wavelength of light by controlling the angle of the spectroscope with a motor.
3.4. Ancillary equipment
The auxiliary equipment mainly includes the exhaust gas treatment system (scubber), external cooler (chiller), and power supply cabinet. Among them, the exhaust gas treatment system is responsible for treating the exhaust gas extracted from the reaction chamber by the molecular pump after the etching reaction is completed. The external cooler is connected to the internal cooling components such as the cold pump under the electrostatic chuck, which forms the heat dissipation system of the reaction chamber of the etching equipment. The power supply cabinet is responsible for providing power to the etching equipment.
4. Market Status
4.1 The three overseas giants have their own expertise and occupy most of the etching equipment market
Domestic etching equipment companies started late, and most of the global market is occupied by overseas giants; the international etching equipment market shows a high monopoly pattern, with Panlin Group, Tokyo Electron, and Applied Materials as the industry TOP3, accounting for nearly 90% of the market share in 2020. Among the three giants, Panlin Group has been cultivating the etching field for many years and has the strongest technical strength and the highest market share, and its products cover almost all process types. Chinese domestic companies SMIC, North China and Eitang Semiconductor together hold 2.36% of the market share, which is not as high as Hitachi High-Tech, which ranks fourth, or Hosomax, which ranks fifth, so there is plenty of room for growth.
4.1.1 Lam Group (LAM)
LAM Research, founded in 1980, is a global leader in etching technology, with revenues of US$14.626 billion in 2021, up 45.61% year-on-year. LAM's very high aspect ratio dielectric etching equipment plays an important role in NAND production; currently LAM has a near 100% monopoly on this type of equipment.
4.1.2. Tokyo Electron (TEL)
Founded in 1963 and headquartered in Japan, Tokyo Electron (TEL) generated revenues of $14,923 million in 2021, up 22.6% year-on-year. Its etching equipment dominates the Damascus integrated etching process for logic chip production and the bench etching process for 3D NAND manufacturing; in addition, its high aspect ratio etching equipment is also important in 3D NAND and DRAM manufacturing.
4.1.3 Applied Materials (AMAT)
Applied Materials was founded in 1967 and is headquartered in the U.S. Revenues in 2021 were $23,059 million, up 34.06% year-over-year. Applied Materials is the world's largest semiconductor equipment manufacturer, but its etch equipment market position is weak. Applied Materials' 12-inch mainstay is the Producer Etch series of machines, which are used for processes such as back etching and pad etching. The strength of Applied Materials in the field of etching machines is weaker than Panlin Group and Tokyo Electron; for some of its products, domestic etching equipment has a strong substitution capability.
4.2. Historical opportunity for domestic etching equipment with focus on domestic production expansion
Based on the known expansion plans and progress of domestic fabs, we believe etching equipment and upstream components industry chain are excellent investment tracks. One of the main reasons for our judgment is the domestic bias toward mature process and memory expansion. At the same time, overseas trade restrictions have increased the urgency for domestic fabs to localize their equipment.
Semiconductor equipment in lithography, etching, thin film deposition value is the highest. According to SEMI statistics, the total size of $87.5 billion wafer manufacturing equipment market, photolithography, etching, thin film deposition accounted for 24%, 20%, 20%, respectively. As China's domestic wafer manufacturing enterprises can not smoothly purchase the latest extreme ultraviolet (EUV) lithography machine, the logic process to 7 nanometer level or more advanced level faces great difficulties, so the domestic logic process expansion mainly around the mature process of about 28 nanometers. Compared with the advanced process, domestic etching equipment enterprises have sufficient technology accumulation and process experience in the field of mature process, and are able to complete a larger scope of domestic substitution, with a larger potential market share. In terms of long-term prospects and advanced processes, the lack of extreme ultraviolet lithography equipment means that domestic foundries need to rely on multiple exposure technology or self-aligned multiple graphics technology to expand the 14nm to 7nm capacity. Multiple exposure technology requires frequent and precise etching of mask plates, while self-aligning multiple patterning involves etching of sidewalls to shape. Advanced wafer capacity using both of these technology routes will require additional procurement of etching equipment. The supply risk of overseas equipment also leads domestic fabs to rely more on domestic etching equipment, providing ample opportunities for domestic etching equipment to move to the high-end DRAM chips are currently advancing in process progress mainly through further miniaturization, which has similar impact on the etching equipment market as the logic process. In addition, the capacitor slot in DRAM and the buried word line structure also create additional demand for high depth ratio etching equipment. In 3D NAND memory, domestic foundries are advancing the process by stacking rather than miniaturizing; multi-layer 3D NAND requires a large number of etchers to perform the gouging process, so etching equipment accounts for nearly 50% of total capital expenditure. China has a huge demand for 3D NAND because of its massive data storage needs, and the nationalization of 3D NAND is crucial for information security. Although the new trade restrictions may hinder the expansion of production in the short term, in the long term, domestic 3D NAND enterprises have sufficient policy and financial support, and the gap between their technology level and that of the international majors is small, so they are determined to expand production.
4.3. Low localization rate of etching equipment and broad market demand for independent control
Domestic etching equipment is mainly sold to the domestic market. Combining with the market share of semiconductor equipment in mainland China in the past years, 25% of the global etching equipment market in 2020 is estimated to be US$13.69 billion, and the market size of Chinese etching equipment in 2020 is US$3.42 billion. If we assume that the revenue of etching equipment of North Huachuang is 1 billion yuan in 2020, the total market size of domestic etching equipment is about 2.4 billion yuan, and the corresponding market share is only about 10%.
From 2020 to 2022, domestic etching equipment companies will make breakthroughs in process validation in wafer fabs, and their share in the global market will rise to about 4%. In the public bidding projects from January to June 2022, the share of domestic etching equipment winning bids has reached 50% as shown in Table 11, but because a large number of equipment purchases for 12-inch fabs have not been publicly bid, there are some imported refurbished etching equipment among the winning bids, so the actual localization rate should be far below 50%. In the field of Damascus integrated etching, sidewall etching, contact hole etching and other high-end processes, imported equipment still occupies the absolute majority, and the potential market space for domestic substitution is still very broad.
