Direct Nucleation and Selective Growth of Nuclei for High Crystallinity Poly-Sige Thin Films on Sio 2 Substrates
- PDF / 2,743,610 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 49 Downloads / 244 Views
Fig.1 Inhomogeneous
This is an inevitable result due to continuous nucleation and growth
crystallinity inlow-temperature
of crystallites during film growth. Several approaches to improve
CVD poly-Si thin film.
this problem have been examined, including the so-called two-step
initial growth of amorphous tissue on the substrate surface.
growth technique [4] which features an intentional treatment of the
This is characterized by an
945 Mat. Res. Soc. Symp. Proc. Vol. 507 01998 Materials Research Society
initially deposited amorphous layer on the substrate for promoting nucleation. Improved crystallinity was reported in the films treated with atomic hydrogen or heat at the early stage of film growth. These treatments, however, do not exclude the inhomogeneity in principle because of the initial growth of the amorphous layer on the substrate. To the matter worse, the improved crystallinity can not be achieved without a trade-off of reduction in grain size. Any treatments for promoting nucleation at the early stage of film growth always result in an enhanced nucleation density, leading to reduction in size of final grains in polycrystalline films. Therefore, in order to exclude the inhomogeneity and to overcome this dilemma, it is necessary to establish a new technique that allows us to form nuclei directly on the substrate surface without accompanying any amorphous tissue and to grow the resulting nuclei to the grains, independently. That is, the direct nucleation of crystallites on the substrate and their selective growth to the grains, as illustrated in Fig.2. In the reactive thermal CVD [5,6] with GeF4 and Si2H6, which react each other only when heated on substrates, leading to the film growth at temperatures lower than their pyrolytic ones, we have found that irrespective of film composition the direct nucleation of SiGe crystallites directly on Si02 substrates took place and that the selective growth of films did on Si02/Si substrate.7 ) Thus, high crystallinity poly-Sio.05Geo.95 n r ei () Direct Nucleation thin films at 375°C and polyL on susbstrate Sio.95Geo.05 thin films at 450'C could be achieved by simply Growth of tuning the growth condition for Resulting Nuclei the selective growth of nuclei after creating thesubsrate.I• nuclei on the • I• • ,• ],J High Quality Polycrystalline
a a n., a a
substrates.
EXPERIMENT
TSelective
Film with Tailored Grain Size and Uniform Crystallinity
Fig.2 Proposed new technique for high crystallinity polycrystalline thin
films by direct formation of nuclei on the substrate surface and selective The experimental apparatus growth of the resulting nuclei to grains. used for the present films growth was a typical low-pressure CVD system installed with a load-lock chamber. The CVD reactor, 40 1 in volume, was equipped with a substrate platform with a resistive heater unit, a shower-head type of gas nozzle, and two vacuum systems, i.e., mechanical booster and turbo molecular pumps backed by rotary pumps. The flow rates of source gasses, i.e., Si 2H 6 (99.99%, Mitsui Ch
Data Loading...
