Manchao Xiao

Designing high performance precursors for atomic layer deposition of silicon oxide

Conformal and continuous silicon oxide films produced by atomic layer deposition (ALD) are enabling novel processing schemes and integrated device structures. The increasing drive toward lower temperature processing requires new precursors with even higher reactivity. The aminosilane family of precursors has advantages due to their reactive nature and relative ease of use. In this paper, the authors present the experimental results that reveal the uniqueness of the monoaminosilane structure [(R2N)SiH3] in providing ultralow temperature silicon oxide depositions. Disubstituted aminosilanes with primary amines such as in bis(t-butylamino)silane and with secondary amines such as in bis(diethylamino)silane were compared with a representative monoaminosilane: di-sec-butylaminosilane (DSBAS). DSBAS showed the highest growth per cycle in both thermal and plasma enhanced ALD. These findings show the importance of the arrangement of the precursors organic groups in an ALD silicon oxide process.

In Situ Infrared Absorption Study of Plasma-Enhanced Atomic Layer Deposition of Silicon Nitride

Despite the success of plasma-enhanced atomic layer deposition (PEALD) in depositing quality silicon nitride films, a fundamental understanding of the growth mechanism has been difficult to obtain because of lack of in situ characterization to probe the surface reactions noninvasively and the complexity of reactions induced/enhanced by the plasma. These challenges have hindered the direct observation of intermediate species formed during the reactions. We address this challenge by examining the interaction of Ar plasma using atomically flat, monohydride-terminated Si(111) as a well-defined model surface and focusing on the initial PEALD with aminosilanes. In situ infrared and X-ray photoelectron spectroscopy reveals that an Ar plasma induces desorption of H atoms from H-Si(111) surfaces, leaving Si dangling bonds, and that the reaction of di-sec-butylaminosilane (DSBAS) with Ar plasma-treated surfaces requires the presence of both active sites (Si dangling bonds) and Si-H; there is no reaction on fully H-terminated or activated surfaces. By contrast, high-quality hydrofluoric acid-etched Si3N4 surfaces readily react with DSBAS, resulting in the formation of O-SiH3. However, the presence of back-bonded oxygen in O-SiH3 inhibits H desorption by Ar or N2 plasma, presumably because of stabilization of H against ion-induced desorption. Consequently, there is no reaction of adsorbed aminosilanes even after extensive Ar or N2 plasma treatments; a thermal process is necessary to partially remove H, thereby promoting the formation of active sites. These observations are consistent with a mechanism requiring the presence of both undercoordinated nitrogen and/or dangling bonds and unreacted surface hydrogen. Because active sites are involved, the PEALD process is found to be sensitive to the duration of the plasma exposure treatment and the purge time, during which passivation of these sites can occur.

Atomic layer deposition of carbon doped silicon oxide by precursor design and process tuning

Different precursors for atomic layer deposition of carbon doped silicon oxide have been investigated. The impact of precursor reactivity, the number of silicon-carbon bonds in the precursor, oxidant concentration and dosing time, and deposition temperature on deposited films carbon content are discussed. It is found that substituting the Si-H by Si-CH3 reduces precursor reactivity and decreases film growth per cycle (GPC). At temperatures higher than 225 °C, all the precursors could deposit a silicon oxide films with reasonable GPC but with very little carbon in the film (<1 at. % by X-ray photoelectron spectroscopy). At temperatures, lower than 150 °C, precursors with two or three Si-CH3 groups, e.g., dimethylaminotrimethylsilane and dimethylaminodimethylsilane, and bis(dimethylamino)dimethylsilane have almost no deposition of silicon oxide film (GPC < 0.1 A/cycle), while the monoaminosilane precursor with only one Si-CH3, e.g., di-iso-propylaminomethylsilane, could deposit silicon oxide film with rela...