In-poor IGZO: superior resilience to hydrogen in forming gas anneal and PBTI

TL;DR

This paper presents an In-poor IGZO transistor design that exhibits superior hydrogen resilience during forming gas anneal and PBTI, enabling better integration with silicon technology and scaling.

Contribution

Demonstrates that In-poor IGZO channels significantly improve hydrogen resilience compared to In-rich ones, facilitating fabrication processes compatible with silicon technology.

Findings

In-poor IGZO shows minimal threshold voltage shift after FGA

Enhanced resistance to H-induced PBTI in In-poor IGZO

Resilience to H effects differs between FGA and PBTI processes

Abstract

Integrating In-Ga-Zn-oxide (IGZO) channel transistors in silicon-based ecosystems requires the resilience of the channel material to hydrogen treatment. Standard IGZO, containing 40% In (metal ratio) suffers from degradation under forming gas anneal (FGA) and hydrogen (H) driven positive bias temperature instability (PBTI). We demonstrate scaled top-gated ALD transistors with an In-poor (In $\le$ 17%) IGZO channel that show superior resilience to hydrogen compared to the In-rich (In=40%) counterpart. The devices, fabricated with a 300-mm FAB process with dimensions down to $W_\mathrm{CH} \times L_\mathrm{TG} = 80 \times 40 \mathrm{nm}^2$, show excellent stability in 2-hour 420$^\circ$C forming gas anneal ($0.06 \le \left| \Delta V_{\mathrm{TH}} \right| \le 0.33\mathrm{V}$) and improved resilience to H in PBTI at 125$^\circ$C (down to no detectable H-induced $V_{\mathrm{TH}}$ shift) compared to In-rich devices. We demonstrate that the device degradation by H in the FGA is different from the H-induced VTH instability in PBTI, namely oxygen scavenging by H and H release from a gate-dielectric into the channel, respectively, and that resilience to H in one process does not automatically translate to resilience to H in the other one. This significant improvement in IGZO resilience to H enables the use of FGA treatments during fabrication needed for silicon technology compatibility, as well as further scaling and 3D integration, bringing IGZO-based technologies closer to mass production.