Preparation of 3-inch Diamond Film on Silicon Substrate for Thermal Management

doi:10.15541/jim20230476

Abstract

Abstract:

The diamond film material holds great potential as a heat sink for GaN electronic devices. The diamond film layer with low stress, large dimensions, high quality, and an atomically smooth surface is crucial for enhancing the overall heat transfer capacity of GaN devices. This study presents a technique for growing and polishing polycrystalline diamond films on 3-inch(1 inch=2.54 cm) silicon substrates to facilitate the use of large-sized diamond film materials in radiator applications. Firstly, the study carries out multi-physical field self-consistent modelling of plasma in a microwave resonator. It then analyses the feasibility of depositing large diamond films using a microwave plasma chemical vapour deposition (MPCVD) device with a 2.45 GHz multi-mode ellipsoid resonator through simulation technology. The growth process parameters are optimized accordingly. After that, the diamond film is polished to meet the bonding requirements of GaN devices. The simulation results show that under the same microwave power input, the increase of chamber pressure leads to the increase of number density of plasma core electrons and H atoms, but the uniformity of radial distribution becomes worse. Diamond film is deposited under optimized conditions and mensurates that the thickness inhomogeneity of diamond film is 17%. In this process, methane at high concentration leads to pyramidal morphology of diamond grains dominated by (111) planes, accompanied by formation of twins. Full width at half maximum (FWHM) of the first-order characteristic peak of diamond in Raman spectrum is 7.4 cm⁻¹. After polishing, the surface roughness reaches 0.27 nm, the average bending degree of diamond film on silicon substrate is 13.84 μm, and the average internal stress is −40.7 MPa. Silicon substrate diamond wafers with large size, high crystal quality, low internal stress and atomically smooth surface are successfully prepared by the above method.

Key words: diamond film, MPCVD, wafer level polishing

CLC Number:

O484

YANG Zhiliang, YANG Ao, LIU Peng, CHEN Liangxian, AN Kang, WEI Junjun, LIU Jinlong, WU Lishu, LI Chengming. Preparation of 3-inch Diamond Film on Silicon Substrate for Thermal Management[J]. Journal of Inorganic Materials, 2024, 39(3): 283-290.

Figures/Tables 9

Fig. 1 Three-dimensional resonance mode diagram of microwave electric field in MPCVD device

Table 1 Set of collision reactions [21]

Num.	Electron collision reaction	Collision type	Energy loss/eV
1	$e+{{\text{H}}_{2}}\to e+{{\text{H}}_{2}}$	Elastic collision	-
2	$e+{{H}_{2}}\to e+H_{2}^{\text{*}}$	Excitation	14
3	$e+{{H}_{2}}\to e+H+H$	Dissociation	8.9
4	$e+{{H}_{2}}\to e+e+H_{2}^{+}$	Ionization	15.4

Table 2 Collection of surface reactions

Num.	Surface reaction	Adhesion factor
1	$H_{2}^{\text{*}}+wall\to {{H}_{2}}$	1
2	$H+H+wall\to {{H}_{2}}$	1
3	$H_{2}^{+}+wall\to {{H}_{2}}$	1

Fig. 2 Group distribution in the axial direction of the reactor under different microwave power/chamber pressure conditions (a) Electron number density distribution; (b) Atomic H number density distribution

Table 3 Electron number density ne and atomic H number density nH at the center (r=0, z=0.5) and edge (r=38.1, z=0.5) of the substrate under different chamber pressures

Chamber pressure/kPa	n_e/m⁻³		n_H/m⁻³
Chamber pressure/kPa	r=0, z=0.5	r=38.1, z=0.5	r=0, z=0.5	r=38.1, z=0.5
6	1.14×10¹⁷	1.96×10¹⁵	2.83×10²¹	1.26×10²¹
8	2.09×10¹⁷	3.18×10¹⁵	6.00×10²¹	2.02×10²¹
10	3.44×10¹⁷	4.63×10¹⁵	1.05×10²²	2.21×10²¹
12	4.97×10¹⁷	5.31×10¹⁵	1.51×10²²	1.67×10²¹

Fig. 3 Surface morphology, cross-sectional morphology and thickness distribution of the diamond film (a) Surface topography of a silicon substrate diamond film with inset illustrating the ideal diamond crystal profile when the growth parameter α is 2.9; (b) Surface profile of silicon substrate diamond film obtained by laser confocal microscope; (c) Cross-sectional morphology of the edge of the diamond film; (d) Thickness distribution of diamond film

Fig. 4 Raman spectrum (a), PL spectra (b) and XRD pattern (c) of diamond films on silicon substrate

Fig. 5 Actual photographic and AFM morphology of polished diamond films on silicon substrate (a) Actual photographic; (b) AFM image

Fig. 6 Results of film bending and stress test (a) Test area of the film stress test system; (b) Bending test results of the monocrystalline silicon substrate; (c) Bending test results of the polished silicon substrate diamond film; (d) Internal stress of the diamond film calculated by the Stoney formula

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