Optimization Design of MPCVD Single Crystal Diamond Growth Based on Plasma Diagnostics

doi:10.15541/jim20230164

Abstract

Abstract:

Microwave plasma chemical vapor deposition (MPCVD) technology is an ideal way to prepare large size and high-quality single crystal diamonds. However, the complexity of MPCVD single crystal diamond growth and the diversity of crystal growth requirements make it difficult to optimize the growth process. To address this issue, a systematic design method for MPCVD single crystal diamond growth based on plasma diagnostic technology was proposed, using plasma imaging and spectral analysis to quantitatively diagnose microwave plasma. The physical coupling characteristics and quantitative relationship between pressure, microwave(MW) power, plasma properties, and substrate temperature were studied by using home-made MPCVD system. And the size of major axis, precursor group concentration and distribution, energy density, and other data of the plasma under different parameters were obtained. Based on experimental data, the growth process map of single crystal diamond was obtained. According to this map, we selected process parameters by growth temperature and growth area. Through experimental verification, it is shown that this map is usful for guiding prediction with parameter error of less than 5%. Simultaneously, based on the predicted map, growth of single crystal diamond under different plasma energy densitiesis studied. At lower power (2600 W), a higher energy density (148.5 W/cm³) was obtained, and the concentration of carbon containing precursors was higher than that of the other parameters, resulting in a higher growth rate (8.9 μm/h). By this method system, effective plasma control and process optimization can be carried out meeting for different single crystal diamond growth.

Key words: MPCVD, single crystal diamond growth, plasma, optimization of growth parameters

CLC Number:

TQ174

LI Yicun, HAO Xiaobin, DAI Bing, WEN Dongyue, ZHU Jiaqi, GENG Fangjuan, YUE Weiping, LIN Weiqun. Optimization Design of MPCVD Single Crystal Diamond Growth Based on Plasma Diagnostics[J]. Journal of Inorganic Materials, 2023, 38(12): 1405-1412.

Figures/Tables 10

Fig. 1 HITLH-2450M diamond growth system and plasma diagnostic system (a) Diagrammatic sketch; (b) Photograph of the system

Fig. 2 Pressure-microwave power parameter curves (a) and Hα intensity of plasma central region (b) under three matching modes The abscissa in (b) corresponds to the 10 parameter observation points in (a)

Fig. 3 At a certain pressure, change of reflected power (a) and change of Hα intensity (b) with input power The data at 17 kPa are selected for display, and the variation trend is similar under the other pressures

Fig. 4 Atomic hydrogen concentration distributions in plasma at various observation parameter points under optimal absorption matching mode with similar distribution pattern changes in other modes

Fig. 5 Quantitative analysis of plasma in uniform increase and optimal absorption matching mode (a) Sizes of major axis and minor axis; (b) Eccentricity; (c) Volume; (d) Energy density

Fig. 6 Changes in plasma major axis and minor axis (a), eccentricity (b), volume (c), and energy density (d) with input power under constant pressure with data at 16 kPa showing the selected display, and variation trends being similar under different pressures

Fig. 7 Prediction map of MPCVD single crystal diamond growth process HITLH-2450M system, seed at 0.5 mm in thickness, under the conditions of 20 ℃ water-cooling, 9-17 kPa pressure, and 1600-4200 W microwave power

Table 1 Parameter points selection based on the predicted map and growth parameters of actual single crystal diamond

Parameter	Sample 1	Sample 2	Sample 3
Preset growth temperature/℃	850	850	850
Preset major axis/mm	48	42	53
Predicted pressure- microwave power	14.2 kPa- 3140 W	15.6 kPa- 2600 W	12.8 kPa- 3500 W
Actual growth temperature/℃	867	860	835
Actual major axis/mm	47.5	41.2	52.8
Energy density/ (W·cm^-3)	121.3	148.5	115.2
Growth rate/(μm·h^-1)	8.5	8.9	8.2

Fig. 8 Photos of plasma growth environment of three samples (with Hα filter) and the surface optical micrographs after 10 h of growth (a, b) Sample 1; (c, d) Sample 2; (e, f) Sample 3

Fig. 9 Plasma emission spectra in the growth of single crystal diamond #1, # 2 and # 3 correspond to samples 1, 2, and 3, respectively

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