Formation of a-Si:H Film by p-CVD Method with SiH 4 -He Mixture and its Opto-Electronic Properties
- PDF / 316,940 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 95 Downloads / 214 Views
Table I Growth Conditions of a-Si:H Parameter Rf Power (13.56 MHz) Volume of bell-jar Diameter of anode electrode
Value 2.5-30 W 100 1 160 0
Reactive gas
SitH4-He, Silt4-1-2 mixture 30 - 100 SCCM
Gas flow rate
Concentration of SiH4
10%
Substrate temperature
250 'C
Gas pressure Distance between electrodes
0.5 Torr 20.0 mm
Growth time Substrate materials
60 min glass, Si wafer
electric conductivity. The n-type silicon wafer substrate having 1000 Qrm of resistivity was used for FT-IR. Substrate temperature was kept at 250 OC. Photo-conductivity of a-Si:H film was measured at the exposure intensity of 50 mW/cm 2 with a light source of tungsten-iodine lamp. Measurement of FT-IR was done within accuracy of 2 cm-1 in the region from 400 to 4000 cm"'.The absorption spectrum corresponding to the intensity due to the stretching modes of SiH at 2000 cm-1 and SiH2 at 2090 cm 1 was separated into the two components to gain the ratio of [Sill] to [SiH] +[SiH 2 ] and also hydrogen content in a-Si:H film. Optical band gap, Eop, was calculated applying Tauc's equation from the absorbance obtained by VIS spectro-photometer. Optical emission spectra were observed by a photonic multi-channel analyzer made by Hamamatsu Photonics Co, Ltd. RESULTS AND DISCUSSION Deposition rate of a-Si:H at 0.5Torr for the mixtures of SiH4(20%)-He(80%) and SiH4(40%)-He(60%) increased proportionally near to 3[tm/hr with the supplied rf power and had a tendency to saturate in the upper region than 10W. On the other hand, as shown in 3.0 I -12,2base
2.5
2.0 0
1.5
ID
C)
.= 1.0 0
0
0
0.5
I...I...1-
nV 0
20
1...1-
40 60 80 Gas flow rate (SCCM)
100
120
Figure 1. Gas flow rate dependence on deposition rate. Reactive gas pressure : O.5Torr Rf power : 10 w SiH4(10%) - He(90%) Sill4(10%) - HA(90%)
22
Figure 1, deposition rate of a-Si:H for the mixture of SiH4(10%)-H2(90%) was about 0.8ttm/hr at the deposition condition of 0.5Torr and 1OW, while that for the same concentration of silane diluted with helium was about 2jim/hr. In order to investigate deposition process in the glow discharge in the reactive gas system, optical emission spectrum was observed. Figure 2 shows a typical optical emission spectrum in SiH4(10%)-He(90%) mixture and Figure 3 shows that in SiH4(10%)-H 2 (90%) mixture. Figure 4 shows the experimental result of gas flow dependence on optical emission intensity for silane concentration of 10% in the both dilution of helium and hydrogen at constant gas pressure of 0.5Torr. From these figures the intensity of SiH*at 414nm for helium dilution was stronger than that for hydrogen in the whole region. Higher deposition rate for helium dilution corresponds with the intensity of SiH* which was reported as a good indicator for deposition rate 5 . Intensity ratio of SiH* at 414 to Ha at 656 for hydrogen dilution decreased drastically from 5 to 1 with decrease of gas flow rate, while that for helium dilution decreased from 8 to 3. As the gas pressure is maintained at constant, decrease of gas flow rate indicates the increase o
Data Loading...
