# An Exploration into Damage Repair and Manufacturing Technology of Photomask Glass Substrates
## 1 Introduction  
The integrated circuit (IC) is the core and forerunner of modern high technologies. It shall be highlighted that photo-etching technology plays a crucial role in making ICs [1]. In recent years, the integration of semiconductor technology has developed rapidly, and the photo-etching technology for manufacturing semiconductor devices has also been improved, which proposes increasing higher requirements for the accuracy of photomask glass substrates [2]. The surface-shape accuracy, local tiny bubbles, cracks, scratches, subsurface damage, and other defects of photomask glass substrates would deteriorate their imaging effects and cause serious errors in the pattern layout. The fabrication requirements for the photomasks are shown in Table 1. Hence, it is necessary to propose higher requirements for the quality of photomask glass substrates, including high ultraviolet transmittance, high optical uniformity, high intrinsic quality, and high surface processing quality [3, 4]. \begin{table}
\begin{tabular}{c c} \hline
**Item** & **Value** \\ \hline Surface shape errors Surface roughness (RMS) & Less than 1 wave \\ Cracks, ripples, pitting & Not allowed \\ \hline \end{tabular}
\begin{tabular}{c} Not allowed for sizes larger than 1 \(\upmu\)m \\ 0.031/cm\({}^{2}\) allowed for sizes less than 1 \(\upmu\)m \\ \end{tabular}
\end{table} 
Table 1: Photomask manufacturing requirements. Photomask glass substrates can be mainly divided into quartz glass substrates and soda glass substrates according to different substrate materials [5]. With quartz glass as substrate materials, the quartz glass substrate has a high optical transmittance and low thermal expansion rate. Compared with the soda glass substrate, the quartz glass substrate is smoother and wear-resistant, with a long service life. Thus, it is mainly used for high-precision photomask substrates [6]. The processing quality of quartz glass substrate directly determines the quality of photo-etching technique [7]. Due to some limitations in equipment or technology during manufacturing, the pattern on the photomask substrate cannot be completely consistent with the design image. Further, the manufacturing defects and errors on the photomask substrate will be introduced into the chip manufacturing by photo-etching technology in the subsequent silicon wafer manufacturing process. Therefore, the surface and subsurface quality of the photomask substrate will directly affect the yield rate and stability of chip. At present, chemical mechanical polishing (CMP) is the main method for processing photomask quartz glass substrates. In CMP, free abrasive particles and grinding discs are utilized to remove materials via a chemical and mechanical composite method, through which a surface with low surface roughness can be obtained [8]. However, it is difficult to control the free polishing particles in the polishing process, which would cause failure to realize higher surface-shape accuracy of the machined component surface. In addition, the mechanical removal method would leave some subsurface damage and surface scratches. Many scholars have carried out research on the manufacture of photomask glass substrates and nondestructive processing of quartz materials. [PERSON] et al. proposed a full-aperture polishing method based on the application requirements of photomask substrates. They improved the equipment according to the technological requirements, which significantly reduced the surface-shape error of the polishing pad [9]. [PERSON] et al. conducted an exploration into the chemical mechanical grinding method of quartz glass. The machining of large-diameter workpieces with high surface quality and high shape accuracy can be realized by actively enhancing the chemical reaction in the grinding process, weakening the bonding potential energy of quartz glass, and eliminating the surface damage caused by brittle removal [8]. [PERSON] et al.