• The reactive gas cluster injection process is an etching method that uses a neutral cluster beam without plasma. This process can avoid damage caused by energetic ion irradiation and vacuum UV light from plasma. The characteristics of etching by ClF3–Ar gas cluster injection were investigated at various target distances, pattern widths, and sample temperatures. As a result, the relationship between the etching conditions and the aspect ratio was clarified, and an equation that can predict the maximum limit of aspect ratio was derived from the ClF3 flux and pattern widths. Then high aspect etching with an aspect ratio exceeding 20 is realized. And also, 3D lever structure of 6 layers can be fabricated by double-angled etching with neutral cluster injection at the condition for high aspect etching.