Low temperature epitaxial silicon growth using electron cyclotron resonance plasma deposition

Abstract

The development of a process for the low temperature (< 600°C) growth of epitaxial silicon is an important technological issue. Conventional growth processes involve temperatures in excess of 1000°C. At these temperatures autodoping and impurity redistribution limit the feature size achievable in VLSI fabrication. As the typical feature sizes move into the submicron region, new processes for epitaxial silicon deposition will be needed. Another application for a low temperature growth process is the fabrication of solar cells on inexpensive metallurgical grade silicon wafers. Impurity diffusion from the wafer during conventional epitaxial silicon growth limits the quality of the solar cells if expensive high purity wafers are not used. We have used electron cyclotron resonance (ECR) plasma deposition to grow high quality epitaxial silicon films on silicon wafers. This growth technique relies on the deposition of silicon from a highly energetic hydrogen and silane plasma. The presence of the hydrogen in the plasma provides reactive etching of the silicon surface during growth. This reduces the oxygen and carbon contamination in the film as well as increasing the number of available growth sites on the surface by displacing the adsorbed hydrogen. By optimizing the growth pressure, substrate temperature, microwave power, substrate bias and silane to hydrogen ratio we have developed a process which provides enhanced growth rates and good uniformity at temperatures (425-575°C) significantly below those used in conventional processes. The structural and electrical properties of the films have been characterized using SEM, TEM, Raman spectroscopy, UV reflectance, spreading resistance profiles. Hall mobility measurements, and both four-point probe and van der Pauw resistivity measurements.

Stability and electronic properties of amorphous silicon p-i-n devices fabricated using ECR plasma enhanced chemical deposition

“…However the current density increases once again about 20mT before being reduced due to the reduced mean free path at high pressure. This is in direct contrast with H2 plasma results [41].…”

“…The plasma potential tends to decrease rapidly as the pressure is increased and it shows a linear increase with increased power of the microwave. The magnitudes in no uncertain terms were greater than that for H2 plasma [41]. This is suggestive of the fact that there may be an increase in ion energies for helium plasma.…”

“…The saturation pressure has been found to shift slightly to higher pressures as the microwave power is increased. In case of H2 plasma [41] this maximum occurs between 5mT…”

“…The first step in the design of an ECR plasma deposition system [41] is an understanding of the plasma source. There are several different possible arrangements for ECR sources.…”

“…An important step in characterization of the ECR system is the understanding of the plasma parameters [41] and the dependence of these parameters on the other system variables (microwave power and chamber pressure).…”