Deposition of Polycrystalline Silicon Thin Films by Plasma Enhanced CVD
- PDF / 366,077 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 2 Downloads / 290 Views
DEPOSITION OF POLYCRYSTALLINE SILICON THIN FILMS BY ENHANCED CVD RUSSELL E. HOLLINGSWORTH AND PAWAN K. BHAT Materials Research Group, Inc., 1241 West 49th Ave., Wheat Ridge, CO 80033-1927
PLASMA
ABSTRACT Polycrystalline silicon films have been grown using high frequency (110 MHz) rf plasma enhanced chemical vapor deposition with a hydrogen diluted silane gas. Polycrystalline growth was obtained when the silane fraction was less than 10% of the total gas mixture for all rf powers, in marked contrast to growth at 13.56 MHz where high power and more dilution are typically required for microcrystalline growth. Grains with [111] and 12201 orientations were observed to have grain sizes up to 900 Angstroms. Room temperature free carrier concentrations as low as 5 x 10" cm' for undoped films were determined by capacitance voltage measurements. Boron doped microcrystalline films were grown with conductivity as high as 8 (0cm)'. INTRODUCTION Large grain polycrystalline silicon thin films deposited at temperatures less than 500*C are sought for applications like solar cells, thin film transistors for LCD applications, and particle detectors etc. The growth of thin films of polycrystalline or epitaxial single crystal silicon, doped and undoped, by plasma enhanced chemical vapor deposition (PECVD) has received considerable interest recently. Two basic approaches have been examined: recrystallization of amorphous silicon and direct growth of polycrystalline silicon. In one approach, amorphous silicon grown by PECVD is furnace annealed at temperatures high enough to cause solid state phase crystallization, but it is anticipated that even longer annealing times may not result in larger grain size. In this communication, results on direct growth of polycrystalline films on various substrates making use of high frequency (110 MHz) rf plasmas will be reported. EXPERIMENTAL DETAILS The silicon films were grown using plasma enhanced chemical vapor deposition (PECVD) in a commercial MRG load-locked single chamber ultrahigh vacuum research reactor, Series 1000, having base pressures in the low 10.' torr range. Radio frequency power was supplied by an HP 8601A sweep generator and an Amplifier Research 150LA broadband power amplifier. Frequencies in the range 10-110 MHz were capacitively coupled to the plasma with an 'L' impedance matching network consisting of a series capacitor and inductor and a shunt capacitor, all variable. RF power was applied to the lower circular electrode, while the stainless steel substrate carrier formed the upper grounded electrode. A heater can with heating elements outside the vacuum provided indirect substrate heating. The primary heat transfer is via radiation at the operating pressures of 100-300 mtorr, although there is some conductive transfer through the gas. The surface temperature of a glass substrate has been measured to be approximately 2/3 of the heater set temperature with no more than 5"C variation from center to edge. H,/SiH, mass flow ratios in the range 10-140, heater temperatures from 300-6
Data Loading...
