Enhancing Si1-XGex/Si Etch Rate Selectivity Using Etching Inhibitor in Radical Oxidation By Halide-Based Oxidant
Authors: Lee Changjin , Lee Ji-Eun , Jang Eun-Woo , Kim Ji-Hoon , Park Jea-Gun 
Published: August 2024

As the technology node shrinks, innovation in the metal-oxide-semiconductor field-effect transistor (MOSFET) architecture has been required to mitigate the short-channel effects (SCE). Thus, planar FET had changed to FinFET and now gate-all-around FET (GAAFET) has been introduced with entering the 3-nm-generation. To fabricate GAAFET, selective etching of Si1-xGex- to Si-film is a key technology. According to the International Roadmap for Devices and Systems (IRDS™), the gate width of GAAFET is around 30 nm. Therefore, higher than 30 nm/min of etch rate for throughput and more than 400:1 of selectivity for acquiring a uniform Si-channel layer are required.
As is well known, the etch rate in wet etching strongly depends on the standard reduction potential (SRP) of the oxidant. Our research group previously revealed the radical oxidation mechanism of sodium periodate (NaIO4) oxidant. In an acidic medium, NaIO4 can exist in periodate ion (IO4
-) form capable of generating hydroxyl radical (•OH). The high SRP value of hydroxyl radical (2.80 eV) compared to conventional oxidant, hydrogen peroxide (H2O2, 1.76 eV) and peracetic acid (PAA, 1.75 eV), resulted significantly high etch rate. In subsequent research, we introduced inhibitors reducing the Si-film etch rate to enhance Si1-xGex/Si etch rate selectivity when using sodium periodate as an oxidant.
Acetic acid is commonly used as an additive in wet etchants to maintain uniform pH and control the etching of Si-film. However, it has several issues, strong vinegar odor, relatively large concentration to act, etc. Therefore, other additives are needed to substitute acetic acid. In selecting inhibitors, 2 factors are considered, i) scavenging effect for hydroxyl radical, and ii) hydrophobicity, as shown in Figure 1. Because the concentration of hydroxyl radical influences not only the Si1-xGex-film etch rate, but the Si-film etch rate, the scavenging effect of an inhibitor can reduce the film etch rate to enhance etch rate selectivity. Furthermore, the hydrophobicity part of inhibitors can build a hindrance layer on Si-film. Generally, Si-film has more hydrophobicity than Si1-xGex-film, inhibitors having hydrophobicity part are more prone to form a hindrance layer on Si-film than Si1-xGex-film. This results in the enhancement of Si1-xGex/Si etch rate selectivity by reducing Si-film considerably than Si1-xGex-film. The qualitative comparison of hydroxyl radical concentration depending on inhibitors and characterization methods to confirm the hindrance layer will be presented in detail.

Acknowledgement

This work was supported by the Technology Innovation Program (20022475, Development of wet Etchant capable of high selection etching in microprocesses below 10 nm) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea)

References

[1] Lee, Seung-Jae, et al. "Extremely high selective Si1−xGex-film wet etchant generating highly dissolved oxygen via peracetic acid oxidant for lateral gate-all-around FETs with a logic node of less than 3-nm." Chemical Engineering Journal 475 (2023): 146257.

Figure 1