Plasma enhanced selective area microcrystalline silicon deposition on hydrogenated amorphous silicon: Surface modification for controlled nucleation

Abstract

Selective deposition of μc-Si on hydrogenated amorphous silicon is demonstrated using time-modulated silane reactant flow in a low temperature plasma enhanced process. Alternating cycles of thin silicon layer deposition and atomic hydrogen exposure result in silicon layers on receptive surfaces, with no net deposition on nonreceptive areas of the substrate. Selective deposition could be useful to form self-aligned contacts in hydrogenated amorphous silicon (a-Si:H transistor applications. However, a problem commonly observed in low temperature selective deposition is that the selective process tends to etch amorphous silicon, harming the devices. We describe a technique involving Mo metallization that stabilizes the a-Si:H surface with respect to hydrogen plasma exposure and allows selective μc-Si deposition on a-Si:H in device structures, while avoiding deposition on the top SiNx insulator material. Surfaces and subsequent selective nucleation and growth were characterized using atomic force microscopy, x-ray photoelectron spectroscopy, and Auger electron spectroscopy, which revealed the presence of Mo incorporation in the a-Si:H surface remaining after complete removal of the metal layer. A direct comparison of selective deposition experiments on films prepared with and without Mo treatment demonstrate that the metallization stabilizes nucleation of microcrystalline silicon on amorphous silicon surfaces.

Microcrystalline Silicon Tunnel Junctions for Amorphous Silicon-Based Multijunction Solar Cells

“…They have proposed that the low mobility gap of the gtc-Si:H and the high defect density at the oxide junction are critical to obtaining high recombination rates. Although recent studies have characterized the nucleation and growth of intrinsic, p, and n type lic-Si:H on aSi:H i-layers [3][4][5][6][7], few studies have characterized the deposition of •tc-Si:H layers on underlying .tcSi:H either with plasma termination or with intervening interface layers. In this study, we have applied real time spectroscopic ellipsometry (RTSE) to characterize the nature of itc-Si:H p/n interface formation.…”

Self-aligned gate and source drain contacts in inverted-staggered a-Si:H thin-film transistors fabricated using selective area silicon PECVD

“…We find that amorphous silicon could be passivated to etching by atomic hydrogen by a multiple step process including metal deposition, metal stripping, BOE dip, and hydrogen and helium plasma exposure steps. After this treatment, even without post-deposition annealing, surface analysis shows evidence for metal silicide formation on the amorphous silicon, with no metal remaining on the dielectric surface [7]. Immediately before loading the patterned substrates into the PECVD reactor for selective deposition, a BOE dip was used to remove native oxide.…”

“…In the deposition chamber, the substrate surface is first exposed to a 150 W helium plasma with a flow rate of 1000 sccm for 5 min. Selective deposition was achieved using timemodulated flow of 10 sccm silane (with 1% phosphine) into a hydrogen plasma with a flow rate of 1500 sccm [7]. Processing pressure was 1.5 Torr and the substrate temperature was 250 C. The silane and hydrogen flow cycle times were 20 and 50 s, respectively.…”