Analysis of Radical Reaction on Growing Surface During Si Epitaxy by Photo-Cvd
- PDF / 302,846 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 38 Downloads / 190 Views
Mat. Res. Soc. Symp. Proc. Vol. 507 © 1998 Materials Research Society
summarizes the main growth conditions. The crystallinity of the films was confirmed by high energy electron diffraction (RHEED) and Raman scattering spectroscopy. Figure 1 shows a schematic diagram of the photo-CVD reactor used in the calculation. We assumed that the UV light with the wavelength of 254 nm is irradiated uniformly. Table I. Growth conditions
window
substrate
UVE liv
Substrate Back pressure Growth pressure Growth temperature Gas flow rate SiH 4 H2
10 sccm 0 - 100 sccm
2 40 mW/cm Lamp Power Hg bath temperature 40 *C
x-L
x=0
Si(100) 1 k Q cm 2x10- 7 Torr 0.5 Torr 90 - 280 TC
Figure 1. Idealized diagram for the theoretical analysis of the gas phase reaction. Surface reaction model of SiH3 and H The following three reactions are taken into account for the reaction model on the growing surface. SiH3 + D.B. + -H -- =SiH2 + H2 SiH3 + -H -- SiH4 H + D.B. -- -H
Film growth Abstraction of bonding hydrogen Hydrogen termination
The first reaction is the film growth; SiH3 radical migrates on the hydrogen-terminated Si(100) surface, then the radical is chemisorbed at a dangling bond resulting in the growth of Si. Second reaction is the abstraction of bonding hydrogen by SiH3 radicals. Third reaction is the dangling bond termination by atomic hydrogen. From these surface reactions, the equation for the change in the hydrogen surface coverage ratio "0 " is given by Ns d 0//dt =
j3 SiII3 J(SiI-13 ) Ns(1- 0 ) Lsiih Ur Sir[ /3 Si1J(SiH 3) Ns 0 Lsi 5 3 O 'Sil + 83 iJ(H) Ns (1-0) Lit Yii. -
(1)
In steady state, d 0 /dt goes to zero. In eq. (1), L is a migration length of each radical and a is a two-dimensional cross section of each reaction. 13is a reaction probability of radicals and the 2 Values of /3 Sill 3 and 3 11are reported to be 0.1 and 0.8, respectively [2]. Ns (6.8x1014 cm- ) is the surface atomic density of Si(100). J(SiH 3) and J(H) are the flux of SiH 3 radical and atomic H, respectively. The flux of radicals can be obtained by the analysis of gas phase
reactions [4]. 424
The equation of the growth rate is also given by
Growth rate =
1 silh J(SiH3)Ns(1- 0 ) Lsiti
G siI3
(2)
Mi/p
where m (4.66x10- 23 g) is the mass of Si atom and P (2.329 g/cm 3) is the atomic density of Si. The eq. (2) is transformed into following equation by using eq. (1) with the steady state condition: Growth rate = /3sirt3 J(SiH 3 )Lsillu30'sil3 Nsm/P)
a
aLlll
+ + 'sYii 3 +O"Sil3(3
LSills30 rSil 3
5rSil
3
where "a"is a radical flux ratio on the surface and given by S3 J(H) 11 /3sinl3 J(SiH 3 )
Gas phase reaction model of Hg-sensitized photo-CVD In our photo-CVD system, the 254 nm resonant radiation was used as a light source, and the photons excite the Hg atoms from the ground state Hg('So) to the excited state Hg( 3 p,). Then the SiH4 molecules are decomposed by the collisions with the excited Hg atorns [6]. As a result of the Hg-sensitized reaction of H 2 and SiH 4 molecule, SiH 3 radical and atomic H are generated. h v(A = 253.7 nm)
Data Loading...
