Silicon carbide SiC is a compound mainly formed by the covalent bond between silicon (Si) and carbon (C). Its basic unit is si-C tetrahedron, in which Si atom is located in the center and C atom is around. All structures of SiC consist of Si-C tetrahedrons piled up in different ways. Now have found the silicon carbide homogeneity of different crystal structure has more than 200, including the structure of the six-party 4 h SiC (4 h – SiC) with high critical breakdown electric field, the advantages of high electron mobility is manufacturing high pressure, high temperature, anti irradiation power semiconductor device of semiconductor materials, is also the best comprehensive performance, the highest degree of commercialization, technology the most mature of the third generation of semiconductor materials, it has:
(1) The critical breakdown electric field intensity is nearly 10 times that of silicon materials;
(2) High thermal conductivity, more than 3 times of silicon material;
(3) The saturated electron drift velocity is high, twice that of silicon material;
(4) Good radiation resistance and chemical stability;
(5) Like silicon materials, silicon dioxide insulation layer can be directly grown on the surface by thermal oxidation process. Pure SiC is colorless, industrial silicon carbide appears brown to black due to iron content, etc., and the rainbow luster on the crystal is caused by the passivation layer of silicon dioxide produced on the surface.
The development of power semiconductor has gone through the following development process: the first generation semiconductor materials represented by single crystal materials such as germanium and silicon, the second generation semiconductor materials represented by compounds such as gallium arsenide and indium phosphide, and the third generation semiconductor materials represented by silicon carbide and gallium nitride.
In recent years, with the rapid development of semiconductor technology, the performance of traditional Si-based devices has approached the theoretical limit in terms of low energy consumption, high energy efficiency and miniaturization. Compared with SI-based semiconductor materials, SiC has attracted much attention for its low energy consumption, high efficiency and miniaturization. Sic MOSFET has become one of the most rapidly developing power semiconductor devices due to its advantages of low on-off resistance, good thermal stability, fast switching speed and high blocking voltage.
Development status of silicon carbide industry
Since the 1990 s, Japan Europe and other countries have invested a lot of money and manpower to silicon carbide materials and devices were studied, the device performance improvement and shrinkage has made a major breakthrough, in this regard, domestic also spend a lot of money and technology, to now also has achieved good results. For example, the international substrate has been done to 8 inches, domestic also can be done to 6 inches, 8 inches is also in the research and development, we are gradually narrowing the gap between the international leading level.
Production process of silicon carbide
Silicon carbide power semiconductor industry chain mainly includes single crystal materials, epitaxial materials, devices, modules and applications. Among them, single crystal materials are the basis of silicon carbide power semiconductor technology and industry, epitaxial materials are the key to realize device manufacturing, devices are the core of the entire industrial chain, modules are the bridge to realize device application, and applications are the source power of silicon carbide power semiconductor devices and industrial development.
SiC single crystal growth method
1. PVT, Physical vapor transport
High-purity sic powder at the bottom of the graphite crucible as a source of growth, the seed crystal is fixed at the top of the graphite crucible, in more than 2000 ℃ high temperature heat the polycrystalline silicon carbide powder into Si atoms, gas phase material such as Si2C and SiC2 molecules, under the drive of temperature gradient, the gas phase material will be transported by low temperature specific is formed on the silicon carbide seed crystal silicon carbide crystals. SiC crystal can be formed by controlling the temperature field, airflow and other process parameters of PVT. Silicon carbide monocrystalline materials mainly consist of two kinds of conductive substrates and semi-insulating substrates. High quality and large size silicon carbide monocrystalline materials are the primary problem to be solved in the development of silicon carbide technology. Continuous increase of wafer size and reduction of defect density (microtubules, dislocation, stratification, etc.) are its key development direction.
2. High Temperature Chemical Vapor Deposition (HTCVD, High Temperature Chemical Vapor Deposition)
In a closed reactor, appropriate reaction temperature (2000-2300℃) and pressure (40kPa) are maintained, and SiH4 and C2H4 loaded by H2 or He are fed into the reactor. The reaction gas is decomposed into silicon carbide at high temperature and attached to the substrate surface. By controlling the reaction volume, reaction temperature, pressure and gas composition, the optimum process conditions were obtained.
SiC epitaxial material
Different from the traditional silicon power device manufacturing process, silicon carbide power device must grow additional high-quality epitaxial materials on the on-type single crystal substrate and manufacture various devices on the epitaxial layer. The main epitaxial technology is chemical vapor deposition (CVD), which realizes a certain thickness and doped silicon carbide epitaxial material through the growth of step flow. In terms of industrialization, China’s 20 m and below sic epitaxial material product level close to the international advanced level; In terms of research and development, China has developed 100 m thick epitaxial material, which is far from the international advanced level in terms of defect control of thick epitaxial material.
Silicon carbide power device
Silicon carbide power semiconductor devices mainly include junction barrier Schottky power diode (JBS), PiN power diode and mixed PiN Schottky diode (MPS). Metal oxide semiconductor field effect transistor (MOSFET), bipolar transistor (BJT), junction field effect transistor (JFET), insulated gate bipolar transistor (IGBT) and gate turn-off thyristor (GTO).
Silicon carbide power module
In order to further improve the current capacity of silicon carbide power devices, module encapsulation is usually used to integrate multiple chips in parallel. Silicon carbide power module was first developed from the hybrid power module products composed of Silicon IGBT chip and SiC JBS diode chip. Based on the mature packaging technology and industry of silicon based power module in China, the industrialization level of silicon carbide power module in China closely follows the international advanced level.
In semiconductor technology many thermal processes are used at atmospheric pressure and at low pressure. Atmospheric processes are used for diffusion of dopands, annealing and oxidation of semiconductor materials, mainly silicon. Low pressure processes use a vacuum pump to evacuate the furnace chamber but still keep a continues gas flow of process gas. They are mainly used for deposition of dielectric layers like silicon oxide, silicon nitride or for depostion of poly-silicon films.
Doping can be achieved by solid source doping (doping-wafers), by liquid source doping as e.g. TMB (Trimethoxyboran, Trimethylborate, (CH3O)3B ) or TMP (Trimethoxyphosphine, Trimethylphosphite, (CH3O)3P) or Phosphorus Oxychloride POCl3 and by gaseous doping like Boran BH3, Phosphane PH3. TMB and TMP have gained significant acceptance. Benefits are the ease of handling a liquid source, less health hazards and improved purity levels. Anneal steps allow the activation and diffusion of dopants in the silicon. Using LGO heating elements, HAOYUE Thermo Systems can achieve excellent temperature uniformity in their furnaces and gets excellent process results for doping processes.
HAOYUE Thermo Systems has well developed furnace versions for dry and wet oxidation. Thin gate oxides can be prepared with a very high uniformity over the wafer and from wafer to wafer. Thicker field oxides or oxides used for masking can be grown faster by wet oxidation. An external torch with a very high process safety makes sure that you can run this furnace without risk. HCl can be used in order to prevent metallic contamination and helps avoiding defects in the oxidation layer. A special air tight quartz to quartz seal (see picture) avoids the leaking of corrosive materials (like HCl) and protects the scavenger from corrosion. The high performance of these furnaces can be shown especially at very thin oxides. We can send you measurement results on request for dry and wet oxidation with and without HCl.
Of course, we can also supply a TCA (1,1,1-Trichoroethane) or a trans-LC (Trans 1,2-Dichloroethylene (DCE)) bubbler as a liquid source substitute for cylinder HCl gas. TCA and trans-LC are much less corrosive compared to HCl.
HAOYUE Thermo Systems furnaces with LGO heating elements show the biggest advantages in low temperature applications. Meanwhile developed also high temperature versions of the vertical furnace for temperature up to 1350°C, using special heating elements, SiC tubes and boats .
Hydrogen can cover dangling bonds and can heal defects. These processes are operated at temperatures around 400°C. This is a rather low temperature for a semiconductor tube furnace and standard heating elements (HGC, heavy gauge coil), used in these furnaces are different to control. HAOYUE Thermo Systems has special LGO heating elements, that have a low thermal mass and can be used from 140°C already. Using these LGO heaters, you will have better temperature stability, better temperature uniformity on your wafers and from wafer to wafer and last but not least, you have no over-swing of the temperature after boat move actions or after temperature ramping.
Furnaces are available with top exhaust and bottom exhaust. A vertical furnace that combines hydrogen anneal and polyimide process is available now also .
HAOYUE Thermo Systems is a real specialist for baking of polyimide. For non-photosensitive polyimide, you can use our clean oven type CLH. A special version has been developed for polyimide baking.
Photosensitive polyimide has a much better performance and can help saving several process steps and therefore reduce the costs for preparing a polyimide layer. However it creates by-products during the curing process that are very difficult to remove after the deposition. Together with one of the largest producers of photosensitive polyimide, developed this special model of a vertical furnace. Special LGO heating elements make sure that you will get an excellent temperature control and temperature uniformity at low temperatures (350°C - 400°C) that are used normally for this bake process.
The furnace is maintenance free and we can prove the superior performance of this furnace type by a very long reference list of satisfied customers. Please check also our special page, describing the polyimide cure process.
A vertical furnace that combines hydrogen anneal and polyimide process is available now also .
Due to the demand of our customers, HAOYUE Thermo Systems developed a new type of vertical furnace for the combination of hydrogen anneal and polyimide cure process. Within short time, the furnace can be switched to another process. Production peaks can be minimized with a minimum number of vertical furnaces and the backup situation for the process of polyimide cure improves a lot. It is no longer necessary to keep so much free capacity for backup reasons and production costs can be reduced finally using HAOYUE Thermo Systems’s new hybrid furnace. Several existing installation can prove the cost saving effect of this new machine already.
In the manufacturing of semiconductor devices copper lines and copper vias are used more and more instead of aluminium, although the metal contamination risk is much higher, the wall adhesion on dielectrics is worse, and the corrosion resistance of Cu is poor. However the conductivity of copper is much higher, which is an important fact for high-integrated devices. Electromigration resistance is higher for copper.
In order to improve the properties of the copper layer an anneal step is absolutely necessary. It has been found that the best conditions in order to get good copper properties are low temperature anneals (<200°C) for longer time (45s in RTP or 30 Min. in oven or furnace). It has to be considered that recrystallization in small structures takes longer time than in larger ones. You can find more details on our special page describing the copper anneal process.
Low-k materials can be deposited either by spin-on or CVD methods. Porous materials are typically spun on, with controlled evaporation of solvent providing the desired pore structure. The necessary baking of the material is normally done in a batch furnace. Today, in most cases vertical furnaces are used for this application. However, the bake temperature is typically between 350°C - 400°C, which is quite demanding to standard vertical furnaces.
HAOYUE Technology has long years experience with the similar SOG bake process and developed a special furnace with a very low thermal mass LGO heating element for this process.
Poly-silicon layers have many applications for gate electrode building, for the formation of resistors and capacitors as well as for getter layers. Doped and undoped poly-silicon processes are available from HAOYUE Technology. Using LGO heating elements, HAOYUE Technology can achieve excellent temperature uniformity in their furnaces and gets excellent process results for poly-silicon deposition. We will send you measurement results on demand.
Silicon nitride is an excellent diffusion barrier. It can be used also as a mask for oxidation, as a dielectric for capacitors and for passivation. Using LGO heating elements, HAOYUE Technology can achieve excellent temperature uniformity in their furnaces and gets excellent process results for silicon nitride deposition. Particle values can be kept low. We will send you measurement results on demand.
Deposited oxide layers do not use silicon from the wafer during growth. The silicon oxide is built completely from the gas phase. TEOS oxide is used for applications like spacer formation or grave filling. TEOS is a stable, nonpyrophoric, noncorrosive liquid, and thereby is a preferable alternative to processing technologies employing silane or dichlorsilane compounds.
Using LGO heating elements, HAOYUE Technology can achieve excellent temperature uniformity in their furnaces and gets excellent process results for CVD oxide deposition. We will send you measurement results on demand.
Phosphorous glasses can be used for doping applications and for planarization. They flow already at 1000°C and also have a good getter effect on alkaline and heavy metal contaminants. TMB and TMP can be used in order to deposit BSG, PSG or BPSG.
Using LGO heating elements, HAOYUE Technology can achieve excellent temperature uniformity in their furnaces and gets excellent process results for CVD oxide deposition. We will send you measurement results on demand.
Spin on glass (SOG) is produced by curing solved silicontetraacetate. It is used for planarization and sometimes for doping purposes. Today more common planarization technology is chemical mechanical polishing CMP.
This process is again a low temperature process that requires a very good control of the heater, installed in the furnace. The LGO heating elements have a very low thermal mass and can achieve much better results for this process, compared to other furnaces equipped with standard heaters.
Hydrogen Anneal can also be done in a low pressure furnace for special applications. Since short time, HAOYUE Technology can also offer a furnace for atmospheric and LPCVD hydrogen anneal, to be used on one machine. By changing the exhaust tube, you can switch between the two types of process.
