Effect of Substrate Type on Stress and Crystallinity of Growing Polycrystalline Diamond Film

doi:10.16553/j.cnki.issn1000-985x.2025.0019

Abstract

Abstract: Various substrate materials exert distinct influences on the crystallinity and stress of polycrystalline diamond films. This study investigates the impact of three substrates （W， Si， and Mo） on the stress and crystallinity of polycrystalline diamond films synthesized using microwave plasma chemical vapor deposition （MPCVD）. Initially， to mitigate edge effects， numerical simulations and optical emission spectroscopy （OES） were employed to optimize and validate that the optimal base height for diamond film deposition is 16 mm. Growing polycrystalline diamond films under the same process conditions， the crystallinity and quality of diamond films deposited on these three substrates were evaluated via Raman spectroscopy and scanning electron microscopy （SEM）. It is found that all diamond films exhibit a （111） orientation， with the W substrate yielding superior crystallinity uniformity. X-ray diffraction （XRD） stress analysis reveals that the polycrystalline diamond film deposited on the W substrate demonstrated uniform stress distribution from center to edge， with minimal stress levels. Consequently， a polycrystalline diamond film with a diameter of 50.8 mm， thickness of 0.6 mm， and deposition time of 200 h is successfully deposited on the W substrate， featuring few impurity defects， no cracks， and a full width at half maximum（FWHM） ranging from 8.156 cm^-1 to 8.715 cm^-1 from center to edge. Transmission electron microscopy （TEM） detected a d-spacing of 0.206 nm for the （111） crystal planes. These findings indicate that the W substrate is more suitable for depositing polycrystalline diamond films intended for optical， thermal， and electronic applications compared to Si and Mo substrates. This research provides valuable insights for the deposition of large-size， low-stress， high-crystallinity polycrystalline diamond films and the application of microwave windows in nuclear fusion tokamak devices.

Key words: microwave plasma; polycrystalline diamond film; substrate; chemical vapor deposition; crystallinity; stress

CLC Number:

O484

LI Xiang, CHEN Gen, SHEN Jie, ZHU Minghui. Effect of Substrate Type on Stress and Crystallinity of Growing Polycrystalline Diamond Film[J]. Journal of Synthetic Crystals, 2025, 54(6): 986-996.

Figures/Tables 14

Fig.1 Mo support structure and the heat sink structure are described as follows

Fig.2 Schematic diagram of the relative position of sample， molybdenum substrate support， heat sink and abutment

Table 1 Nucleation and growth parameters of deposited diamond films

Parameter	Power/W	Pressure/kPa	Gas flow： H₂/CH₄	Time/h	Substrate temperature/℃
Nucleation	4 100	20.5	400 sccm/15 sccm	1	910±20
Growth	4 100	21	400 sccm/12 sccm	50	910±20

Fig.3 Electron density distribution at a height of 16 mm （a） and simulation results showing the variation in electron density from the center to the edge of the substrate surface （b） are presented

Fig.4 Light emission spectra associated with abutment heights of 12， 14 and 16 mm （a）， as well as the morphology of the plasma sphere at 16 mm （b）

Fig.5 For the diamond film deposited on a ϕ50.8 mm W substrate， Raman spectra were acquired at six points spaced 5 mm apart along a radial line from center to edge （a）， and SEM images were captured at selected locations （b）~（g）

Fig.6 For the diamond film deposited on a ϕ50.8 mm Si substrate， Raman spectra were acquired at six points spaced 5 mm apart along a radial line from center to edge （a）， and SEM images were captured at selected locations （b）~（g）

Fig.7 For the diamond film deposited on a ϕ50.8 mm Mo substrate， Raman spectra were acquired at six points spaced 5 mm apart along a radial line from center to edge （a）， and SEM images were captured at selected locations （b）~（g）

Fig.8 Variation diagram of the 1 331 cm-1 peak height of diamond deposited on W， Si and Mo substrates

Fig.9 FWHM comparison chart of diamond corresponding to six detection points from the center to the edge deposited on W， Si， and Mo substrates

Table 2 Physical properties of substrates， carbides and diamonds

Material	Lattice constant/Å	Elasticity modulus/GPa	Thermal expansion coefficient/（10^-6 K^-1）	Melting temperature/K
Si^［33］	5.431	130	2.5	1 683
W	3.165	411	4.5	3 600
Mo	3.147	327	5.8	2 888
Diamond	3.567	1 050	1.2	3 773
MoC	4.14	392	4.9	2 965
WC	2.81	710	3.8	3 143
SiC	3.1	450	4.4	3 027

Fig.10 Relationship diagram of diamond crystal face spacing and diffraction angle sin2ψ deposited on W， Si and Mo substrates

Fig.11 XRD patterns of deposited diamond

Fig.14 TEM cross-sectional image （a）， Fourier transform （FFT） diffraction pattern （b）， and inverse FFT image （c） obtained from a selected region of the diamond film deposited on a W substrate

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