The Structural Evolution of A-SI:H Films Prepared by Pulse Rf Power Modulation with Hydrogen and Helium Dilution
- PDF / 404,578 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 83 Downloads / 212 Views
Mat. Res. Soc. Symp. Proc. Vol. 507 ©1998 Materials Research Society
Table I The deposition conditions of a-Si:H films. Wheref ton, toff, and cw are frequency, plasma-on period, plasma-off period, and continuous wave. group A No f(Hz)
(1)
(2)
5k
500
group B
cw
(3)
(4)
50
5
(5) cw
cw
(6)
1 (7)
1 (8) 1 (9)
1 (10)
500
duty cycle ton (sec)
1/10 4
1/103
1/102
1/101
1:3 1:2 1:1 2:1 3:1 1/2000 111500 1/1000 1/750 1/667
toff(sec)
1/104
1/103
1/102
1/101
1/667
1:1
1/750 1/1000 1/1500 1/2000
evolution of a-Si:H films influenced by 80% helium or by 80% hydrogen dilution with SiH 4 (He (or H2) : SiH 4 = 4 : 1) were investigated. EXPERIMENT 2 All a-Si:H films were deposited using a capacitive type PECVD system. A 10 by 10 cm Coming 7059 glass and a 4" silicon wafer were mounted on the two ground electrodes at the same deposition run. The films deposited onto Coming 7059 glasses were used for transmission measurements. The films deposited onto silicon wafers were used for infrared absorption measurements. The RF peak power, the chamber pressure and the substrate temperature were kept at 25 W, 0.75 torr, and 225 °C, respectively. All films were deposited with 4 to 1 (80%) dilution ratio of helium (He) or hydrogen (H2 ) gas to silane (SiH 4) gas. A radio frequency of 13.56 MHz RF power with square-wave pulse modulation frequency in the range of 5 Hz to 5 kHz was used to deposit the films. The duty cycle of the pulse was changed from 75% (on:off = 3:1) to 25% (on:off= 1:3). The transmission spectra of the films deposited onto the Coming 7059 glasses were measured using a Hitachi 3410 NIR-VIS-UV spectrometer in the range of 860 nm to 2600 nm. The film thickness and the refractive index were calculated from the interference pattern of the spectrum in the low absorption regime between 1000 to 2000 nm [10,11]. The bonding configuration of the films was measured through the absorption spectrum in the range of 400 to 4000 cm' with a Nicolet Magna 550 Fourier transform infrared (FTIR) Spectrometer.
RESULTS AND DISCUSSION Table I shows the deposition conditions of groups A and B and the reference sample which was deposited at continuous wave (cw) RF power. The samples from group A were deposited by tuning the pulse modulation frequency with a 50% duty cycle (1:1). The samples from group B were deposited by tuning the duty cycle with a fixed pulse modulation frequency (500 Hz). Figure 1 shows the deposition rates of all samples. For each kind of dilution gas, the deposition rate of the cw sample is higher than the value of the pulse RF power samples. The result indicates that the radical flux deposited onto the substrate surface is the highest for the cw sample. For the group A samples, the deposition rate of the pulse RE samples deposited with He
524
20 18 -
-
C
E 16
D
HA dilution
H- dilution
-
20 18-.
16 E
E
14
14
-
12-
12
C
o
.
V
-
10 -10
v C
o
8
8 5
"o 66 .. .. . . . ................
-4
4
2 0
E
2 I
I
I
I
I
0I
5k 500 50 5 cw 1/3 1/2 1/1 2/1 3/1 samples Figure 1 Th
Data Loading...
