Characterization of Boron Doped Amorphous Silicon Films by Multiple Internal Reflection Infrared Spectroscopy

Abstract

In this study, we employed Multiple Internal Reflection Infrared Spectroscopy (MIR-IR) to characterize chemical bonding structures of boron doped hydrogenated amorphous silicon (a-Si:H(B)). This technique has been shown to provide over a hundred fold increase of detection sensitivity when compared with conventional FTIR. Our MIR-IR analyses reveal an interesting counter-balance relationship between boron-doping and hydrogen-dilution growth parameters in PECVD-grown a-Si:H. Specifically, an increase in the hydrogen dilution ratio (H2/SiH4) was found to cause the increase in the Si-H bonding and a decrease in the B-H and SiH2 bonding, as evidenced by the changes in corresponding IR absorption peaks. In addition, although a higher boron dopant gas concentration was seen to increase the BH and SiH2 bonding, it also resulted in the decrease of the most stable SiH bonding configuration. The new chemical bonding information of a-Si:H thin film was correlated with the various boron doping mechanisms proposed by theoretical calculations.

Raman spectroscopic investigation of boron doped hydrogenated amorphous silicon thin films

“…From the infrared spectroscopy it has been reported that, with the increase of hydrogen dilution, silicon monohydride absorption peaks increase in strength whereas silicon dihydride absorption peaks decrease [13]. For fixed doping and dilution, the silicon monohydride absorption peak is significantly larger for lower growth temperature, [20] which can be attributed to additional hydrogen atoms being absorbed. On the other hand, the higher growth temperature adds surface mobility to the absorbed reactant species, which increases the likelihood of lower energy bond configurations.…”

“…It has been shown by ab initio calculations that mobile hydrogen atoms break strained silicon bonds to form Si\H and Si\H 2 [19]. From the infrared spectroscopy it has been reported that, with the increase of hydrogen dilution, silicon monohydride absorption peaks increase in strength whereas silicon dihydride absorption peaks decrease [13]. For fixed doping and dilution, the silicon monohydride absorption peak is significantly larger for lower growth temperature, [20] which can be attributed to additional hydrogen atoms being absorbed.…”

“…In plasma enhanced chemical vapor deposition (PECVD) growth, the structural configuration of a-Si depends on the hydrogen dilution of the silane precursor and the thickness of the thin film, and can yield different states such as amorphous, nano/micro crystalline and polycrystalline phases [10,11]. In addition, structural changes in a-Si:H films due to hydrogen incorporation and doping have been reported [12][13][14][15]. The addition of boron results in local structural changes resulting from the formation of chemical bonds, such as B\Si and B\H\Si, [14] resulting in an increase in bond angle and bond length, leading to a degradation of the SRO.…”

“…Specifically, it has been shown that hydrogen diluted crystallization is mediated by insertion of H atoms into Si\Si bonds through the formation of a Si\H\Si bonding configuration when H atoms diffuse in a-Si:H matrix, resulting in improved crystallinity, i.e., improvement in SRO [15]. Infrared spectroscopic results [13,16] have shown that, with the addition of boron, there is a competition between boron and silicon to form bonds with the hydrogen, resulting in an increase in B\H stretching mode bonds and a decrease in Si\H bonds as the boron concentration is increased.…”

Evaluation of Plasma Damage to Low-k Dielectric Trench Structures by Multiple Internal Reflection Infrared Spectroscopy

“…7-9 MIR-IR spectroscopy can increase detection sensitivity up to 100-fold compared with conventional FTIR because the wafer itself serves as an IR waveguide allowing for multiple detections. 10,11 In this work, a test pattern of ∼68 nm trenches with 128 nm pitch was created through oxide hard mask plasma etching followed by organic residue stripping. Damage to the dielectric in terms of silanol formation was quantified and correlated to each plasma processing step using MIR-IR complemented by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM).…”