Microcrystalline Silicon Growth: Deposition Rate Limiting Factors
- PDF / 429,045 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 102 Downloads / 232 Views
05 Mat. Res. Soc. Symp. Proc. Vol. 507 01998 Materials Research Society
Table I: deposition conditions used in the layer-by-layerprocessfor an inter-electrode distance
d=
3.6 cm.
Silane plasma
Gas flow (sccm) 5 SiH 4
Pressure (Pa) 13
RF power (W) 10
Time (sec) Tsi = 20
Hydrogen
85 H2
33
30
TH = 95
plasma
85 H 2
92
30
TH =
50
In the case of hydrogen dilution, the films were deposited at a constant RF power of 50 W at d = 3.6 and 2 cm. The pressure was varied between 92 and 500 Pa and three hydrogen dilution ratios (99%, 98%, and 97%) were studied. The growth kinetics of the samples was monitored in-situ by spectroscopic ellipsometry (SE), and their crystalline fraction was deduced from the fit of the SE data using the Bruggeman
Effective Medium Approximation (B-EMA) model [10]. RESULTS AND DISCUSSION Layer-by-layer growth (dilution in time)
As shown in table I, the increase of the pressure during the hydrogen plasma exposure sequences allows a significant decrease of the hydrogen plasma treatment time (TH) necessary to achieve lac-Si growth. The value of TH decreases from 95 sec to 50 sec while the crystalline fraction at steady-state remains the same (Fig la). This result confirms the better dissociation of hydrogen at high pressure and the key role played by the ratio of atomic hydrogen to silicon radicals ( R = [H] / [Si] ) in the jic-Si growth. The kinetics of the crystallization, as a function of the number of LBL cycles (thickness), is also largely affected by R. Indeed, as shown in figure la, the increase of the pressure during the hydrogen plasma exposure has resulted in a faster kinetic of crystallization. If we consider a growth model based on the chemical annealing i.e, the release of energy in the growing film resulting from the recombination of atomic hydrogen [11], this later result suggests that the nucleation process strongly depend on the density of energy released by hydrogen per unit of time. 70 ... •"60 ,_,
..........
a
2PlO
120
....
,• D
..
. '80."
.. '34 Pa
50
63..3Pa '-30
T
2P
•"
60
S20
S40 )
0
d
92Pa
20
. d
0
20
40
60
80
100
0
120
0
20
40
60
80
100
120
Number of LBL cycles Number of LBL cycles Figure 1: Evolution of the crystallinefraction a) and the film thickness b) during the layer-bylayer growth of pc-Si:H silicon on corning glass at an hydrogen pressure of 33 and 92 Pa. The thickness of the films as a function of the number of LBL cycles is displayed in figure lb. For any number of cycles, the thickness of the film deposited at high hydrogen pressure is higher than that of the film deposited at low hydrogen pressure. This thickness dependence of the number of LBL cycles associated with the reduction of TH from to 95 sec to 50 sec results in an increase of the average deposition rate, estimated at steady state, from 0.lAds to 0.21,A/s. 506
This result shows that a faster kinetic of crystallization can be obtained with increasing deposition rate. A further increase in the average deposition rate up to 0.4 A/s was obtained by redu
Data Loading...
