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Thermal SiNx Using NH3 and Anhydrous Hydrazine as Nitriding Agents

Su Min Hwang‚ Dan Le‚ Arul Ravichandran‚ Aswin Kondusamy (University of Texas at Dallas); Dan Alvarez‚ Jeffrey Spiegelman (RASIRC); Jiyoung Kim (University of Texas at Dallas)

Silicon nitride (SiNx) is perceived as a quintessential component in microelectronics for scaling next generation ultra-large-scale integration (ULSI) technology with possible applications as a passivation layer‚ sidewall spacer‚ and contact etch stop liner.1 Deposition of ultrathin and uniform SiNx films with high conformality is required for ULSI due to application restrictions‚ such as thickness and complicated surface areas.2 In general‚ the plasma-enhanced ALD (PEALD) process allows a low temperature process for such film deposition‚ but potentially results in poor conformality‚ creates surface damage‚ and is not applicable on sensitive substrates. The thermal ALD (tALD) process can overcome these issues; however‚ it requires a higher deposition temperature range for SiNx films.1 In this study‚ we focus on establishing a high quality SiNx tALD deposition process at relatively low temperatures (350 °C – 650 °C) for ammonia (NH3) and evaluate the properties of films deposited using hydrazine. Furthermore‚ films grown by hydrazine will be compared to films grown with ammonia with the same process conditions‚ silicon precursor‚ and temperature range.

In this experiment‚ hexachlorodisilane (HCDS) is used as the source of silicon‚ along with BRUTE hydrazine and ammonia as the precursors for nitrogen. A PEALD/ tALD chamber (Rocky Mountain Vacuum Tech Inc.) is employed to deposit SiNx films with a working pressure between 150 – 160 mTorr. Furthermore‚ to eliminate the possibility of condensation of precursor or residual products‚ the chamber walls and precursor delivery lines are heated to 120 °C and 100 °C‚ respectively. The experimental temperature range is established from 350 °C to 650 °C. At the temperature range of 450 °C – 550 °C‚ the index of refraction (R.I.) of SiNx films deposited using hydrazine is up to 2.0‚ which further coincides with the earlier reported result‚ with a R.I. as high as 2.1.2 Additionally‚ the atomic force microscopy (AFM) indicates that films grown with hydrazine have a smooth surface‚ with an RMS as low as 0.14 nm. It is further determined that the SiNx films roughness is independent of temperature. Moreover‚ the GPC of SiNx films deposited using ammonia is less than half of the GPC of films grown with hydrazine at a temperature range of 500 °C – 550 °C. The experiment details and detailed results will be presented.

We thank RASIRC Inc.‚ for sponsoring this project and supplying the BRUTE hydrazine source.

1 X. Meng et al.‚ Mater. 9 (12)‚ 1007 (2016).

2 S. Morishita et al.‚ Appl. Surf. Sci. 112‚ 198 (1997).

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