Ultrahigh-resolution pattern using electron-beam lithography HF wet etching

Abstract

The authors have developed sub-6nm electron-beam lithography using a high-resolution inorganic resist, hydrogen silsesquioxane (HSQ). The results are obtained using a 100KeV VB6 ultrahigh-resolution Leica Gaussian beam equipment. Because HSQ is a flowable silicon oxide, it can be converted to SiO2 at an elevated temperature. This allows the process flow to be modified by removing the hard mask etching and resist stripping and using HSQ directly when structuring silicon. In addition, the dissolution of SiO2 in HF solution is well known as a fundamental step in fabricating integrated circuits. To obtain sub-5nm HSQ patterns, they developed resist trimming, using this similarity between HSQ and SiO2. The first step of the study is done on full-sheet 200mm Si. After the coating, the wafers are hard baked at different temperatures (from 350to550°C) and for different lengths of time. In a second step, HSQ e-beam patterns are trimmed by HF etching. The choice of pH and concentration of HF solution allow them control the etching rate. In summary, they demonstrated an ultrahigh-resolution pattern using electron-beam lithography HF wet etching. Such performance is suitable for nanoscale device processes.