1. The market space for superhard materials is broad, and CVD diamonds is expected to become the next generation of semiconductor materials
1.1. Overview of superhard materials
  Superhard materials usually refer to materials with particularly high hardness and Vickers hardness greater than 40 Gpa, which are mainly used for the processing of metal and alloy materials, high hard and brittle materials, composite materials, soft and tough materials and difficult materials. At the same time, as an important functional material, it can be used in electronic appliances, equipment manufacturing, aerospace, national defense, medical testing and treatment and other high-tech fields. Superhard materials mainly include intrinsic superhard materials whose intrinsic hardness is related to their composition and non-intrinsic superhard materials whose intrinsic hardness is related to their microstructure. The intrinsic superhard materials include diamond, cubic boron nitride (PCBN), carbon nitride and B-N-C ternary compounds. Non-intrinsic superhard materials include nanocrystalline diamond aggregates, polymerized diamond nanorods, etc. At present, the common superhard materials are natural diamond, artificial diamond, cubic boron nitride and so on.

  The world's industrial superhard materials are mainly industrial diamonds, of which more than 90% are artificial diamonds. Natural diamond ore is a non-renewable resource with limited reserves, high mining cost and unfriendly to ecological environment, so it can not be widely used in the industrial field. Therefore, industrial diamond is mainly artificial diamond. The main methods of synthetic diamond preparation are high temperature and high pressure (HTHP) and chemical vapor deposition (CVD). HTHP method is to use graphite powder and metal catalyst powder as raw materials, through the current heating and hydraulic device to establish a high temperature and high pressure environment to simulate the crystal and growth environment of natural diamond, so that the graphite phase change to form diamond crystals. From the thermodynamic point of view, the growth mechanism of artificial diamond and natural diamond is similar, both make carbon atoms recombine under high temperature and high pressure environment to form a tetrahedral diamond structure with sp3 C-C bond. HTHP method is the first successful synthesis of diamond technology, is also the main production method of artificial gold corundum in our country, with low manufacturing cost, high production efficiency. During the growth of HTHP diamond, impurities in the pressure transfer medium and raw and auxiliary materials (such as iron, cobalt, nickel, etc.) will continue to enter the diamond crystal, forming various defects, and the purity is not ideal, unable to meet the high purity requirements of downstream semiconductor and optical applications. At the same time, due to the volume limitation of the six-sided top press equipment, the effective growth space of diamond is difficult to break through 100 mm, and the crystal size improvement space of HTHP diamond is limited.

  Synthetic diamond by chemical vapor deposition (CVD) means that under the conditions of high temperature and low pressure (about 1000℃, below 27kPa), the carbon-containing gas such as CH4/H2, CH4/N2, CH4/Ar is activated by a certain method. The carbon atoms in it are stripped from the carbon source gas and suoversaturated on a suitable substrate (such as Si, c-BN, SiC, Ni, Co, Pt, Ir and Pd, etc.) to obtain a high-purity, high-performance diamond film. CVD diamond growth environment mainly uses carbon source gas, the use of hydrogen at high temperature etching graphite faster than the characteristics of diamond to obtain single crystal diamond, do not need to add metal catalyst powder, so the impurities in the gold corundum is very little, can meet the high purity of downstream semiconductor and other fields. At the same time, CVD diamond can add color elements (such as nitrogen, boron, etc.) to the carbon source gas in the growth process of the seed crystal disk, and obtain pink diamonds similar to natural diamonds, yellow diamonds and blue diamonds, which is full of the diversified needs of the downstream jewelry market. At present, MPCVD method (microwave plasma chemical vapor deposition method) is the mainstream CVD method for diamond production at home and abroad because of its advantages of less pollution, large preparation area and easy control of temperature conditions.