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2022
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Pre-treatment of Seed Crystals Prior to Single-Crystal Diamond Growth in MPCVD Equipment
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During the MPCVD growth of diamond, in addition to process parameters such as power, gas pressure, temperature, leakage rate, and the types and ratios of gas sources, the quality of the seed crystal itself is also a critical process parameter. Currently, the primary crystallographic orientations used for diamond growth are (100), (110), (111), and (113). Among these four orientations, the (100) face exhibits a relatively low probability of defect and twin formation during growth, making it well suited for producing high‑quality, large‑area single‑crystal thick films. Moreover, seed crystals with this orientation are easier to polish than those with other faces and can readily yield substrates with few defects.
Pre-treatment of Seed Crystals Prior to Single-Crystal Diamond Growth in MPCVD Equipment
During the MPCVD growth of diamond, in addition to process parameters such as power, gas pressure, temperature, leakage rate, and the types and ratios of gas sources, the quality of the seed crystal itself is also a critical process parameter. Currently, the primary crystallographic orientations used for diamond growth are (100), (110), (111), and (113). Among these four orientations, the (100) face exhibits a relatively low probability of defect formation and twinning during growth, making it well suited for producing high‑quality, large‑area single‑crystal thick films. Moreover, seed crystals with a (100) orientation are easier to polish and more readily yield low‑defect substrates. Consequently, most MPCVD systems today grow diamond by epitaxial deposition on the (100) face.
During diamond growth, surface damage to the seed crystal and the presence of impurities can both degrade the quality of the single-crystal diamond. Therefore, prior to growing single-crystal diamonds, the seed crystal must undergo appropriate pre‑treatment, which typically involves the following steps:
First, the polycrystalline material at the seed crystal’s edge is cut away. This is because the edge effect causes the growth rate of the polycrystalline regions around the seed crystal to be significantly higher than that of the single-crystal diamond in the central region, leading to the polycrystalline material spreading toward the center and thereby compromising the growth of the single-crystal diamond.
Step two involves polishing the seed crystal, performing both rough and fine polishing, so that the diamond acquires a flat, smooth surface, thereby reducing the diffusion barriers for impurity groups during the growth process.
Step three involves acid‑washing the seed crystal. This is necessary because the polished surface of the seed crystal may still contain metallic impurities, which must be removed through acid treatment. The dilute acid solution is prepared by mixing nitric acid, concentrated sulfuric acid, and water in a specific ratio. Once the solution is ready, the seed crystal is immersed in the dilute acid and subjected to boiling in a heating furnace.
Step four is the deionization process, which serves to remove organic impurities and inorganic ions from the diamond surface.
MPCVD equipment
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