Etching of SiC Thin Films in Cl2/Ar Inductively Coupled Plasmas

C. S. Choi, Y. H. Im*, T. H. Kim*, Y. B. Hahna),

Department of Semiconductor Science and  Technology, Chonbuk National University School of Chemical Engineering and Technology, Chonbuk National University*

Chonju 561-756, Korea

Cl2/Ar 유도 결합 플라즈마를 이용한 SiC박막 식각특성

최창선, 임연호*, 김태희*, 한윤봉,

전북대학교 반도체과학기술학과, 전북대학교 화학공학과*

INTRODUCTION

The rapid advances in high power/high temperature SiC electronics for use in high voltage switches, power conditioning, electric drive trains, and utility power management has renewed interest in the development of improved processing techniques for the material. Hence, most of the previous etching studies have been focused on obtaining the relatively large etch depths typical of ridge or facet heights, where the final surface morphology on the field is less important. Moreover, ohmic contact is deposited on the etched surface, and contact resistance actually depend on roughness from this surface. In recent years the majority of the high density plasma etching has been performed using inductively coupled plasma (ICP) etch systems because of its superior uniformity, control and lower cost of ownership.1-4 However, little work has been done on the ICP etching of SiC thin films in Cl2/Ar discharges.

In this paper, a parametric study of ICP etching of SiC thin films in Cl2-based plasmas is reported. The effects of etch gas concentration, ICP source power, rf chuck power and reactor pressure on etch rates have been investigated. Results were discussed in terms of etch rates, dc bias voltage, surface morphology

EXPERIMENTAL

Dry Etching of SiC thin films was performed in a planar type Vacuum Science ICP system(VSICP-1250A), in which the ICP source operates at 13.56 MHz. The temperature of the back-side cooled chuck was held at 20 oC. The ion energy was controlled by the applied rf chuck power at 13.56 MHz excitation frequencies. The Cl2/Ar mixture with total gas loads of 20 standard

a) Author for correspondence. Email: ybhahn@moak.chonbuk.ac.kr.

cubic centimeters per minute (sccm) was injected into the reactor through electronic mass flow controllers (MFCs). For etch rate experiments, samples were masked with Apiezon wax; etch depths were obtained from stylus profilometry measurements of etched samples after removal of the wax. Surface morphology was respectively examined using Atomic Force Microscopy (AFM) operating in tapping mode with Si tip.

RESULTS AND DISCUSSION

The effect of ICP source power on the etch rates of SiC thin film and dc-bias voltage was examined with rf frequencies of 13.56 MHz for the capacitively coupled plasma source, and the results are shown in Figure 1. During these experiments the reactor pressure, rf chuck power and gas feed rate were held constant at 5 mTorr, 200 W and 10 sccm Cl2/10 sccm Ar, respectively. The etch rates increased with the ICP source power up to 700 W, and then decreased at higher ICP power the dc bias voltage was ranged from - 135 to - 270 eV when the ICP source power changed from 400 W to 800 W. The highest etch rate of 4050 Å/min was obtained at moderately high ICP power of 700 W. The decrease in dc biases with the ICP source power was mainly due to increased ion density at higher ICP source powers.

Figure 2 shows the effect of rf chuck power on the etch rates and dc bias. The etch rates and dc bias voltages increased as the rf chuck power or ion-bombarding energy increased, typical results in the ICP etching systems. The increase in etch rate with the chuck power might be explained by enhanced sputter desorption of etch products as the ion energy increased.

The effect of reactor pressure on the etch rates and dc bias is shown in Figure 3. The etch rates of the SiC thin films increased up to 5 mTorr and then decreased at higher pressures. And dc bias voltages increased with pressure. Also figure 4 shows the effect of Cl2 concentration on the etch rate and dc bias voltage. The high etch rate ( >3500 Å/min) was maintained beyond 25% Cl2. And dc bias voltage increased up to 50 % and then decreased at higher concentration.

The surface morphology of etched SiC thin films was examined using AFM. Figure 5 shows the effect of rf chuck power on the surface morphology of SiC film etched at 50 % Cl2 (10 sccm Cl2/10 sccm Ar), 700 W ICP and 5 mTorr pressure. Compared to the surface morphology of the unetched control sample (rms roughness 49.46 nm), etched sample as rf chuck power resulted in fairly good morphologies from 50.03 to 59.58 nm, respectively.

SUMMARY AND CONCLUSIONS

Dry etching of SiC thin films was carried out in Cl2-based inductively coupled plasmas. The highest etch rate of SiC thin films as ICP source power was obtained at moderately high ICP power of 700 W (4050 Å/min). The etch rate as rf chuck power increased by enhanced sputter desorption of etch products as the ion energy increased. The etch rate as pressure is highest at 5 mTorr and etch rate as Cl2 concentration is independent at injecting over 25% Cl2. The etched surface roughness showed quite smooth morphology (rms 50.03 ∼ 59.58 nm).

REFERENCES

1. J. B. Casady, A. K. Agarwal, L. B. Rowland, S. Seshadri, R. R. Siegiez, S. S. Mani, D. C. Sheridan, P. A. Sanger and C. D. Brandt, Mater. Res. Soc. Symp. Proc. 483, 27 (1998).

2. J. J. Wang, E. S. Lambers, S. J. Pearton, M. □stling, C. M. Zetterling, J. M. Grow and F. Ren, Solid-State Electron. 42, 743 (1998).

3. F. Lavois, P. Lassagne and M. L. Locabelli, Appl. Phys. Lett. 63, 171 (1996).

4. J. Hong, R. J. Shul, L. Zhang, L. F. Lester, H. Cho, Y. B. Hahn, D. C. Hays, K. B. Jung, S. J. Pearton, C. M. Zetterling, M. □stling, J. Elec. Mater. 28, 196 (1999).

Fig.1 Effect of ICP source power on etch rate and dc bias  voltage

Fig.2 Effect of rf chuck power on etch rate and dc bias voltage

Fig.3 Effect of pressure on etch rate and dc bias voltage

Fig.4 Effect of Cl2 concentration on etch rate and dc bias voltage

Fig.5 AFM image of etched SiC films as a function of rf power at 5 mTorr, 700 W ICP, and 10 sccm Cl2/10 sccm Ar.