DUV Blank Mask Edition: the next domestic substitution opportunity at the “photoresist” level

In the grand chain of semiconductor manufacturing, the lithography machine is the star under the spotlight, photoresist is the market’s hot topic, and the blank mask—this seemingly ordinary "coated glass"—has long been relegated to a neglected corner. Yet, it is precisely this "blank photomask" without any circuit patterns that serves as the physical origin of lithography precision, determining the ultimate conversion efficiency from design blueprints to wafer yield.

I. What Happened? — DUV Blank Masks Embark on the Path of Domestic Substitution

1. What is a blank mask?

A blank mask, also known as a mask substrate or photomask blank, is the base material used to manufacture photomasks. If we compare wafer fabrication to printing, the lithography machine is the printer, the photomask is the printing plate, and the blank mask is the "blank steel plate" used to make the printing plate.

From a physical composition perspective, a blank mask is made by combining a precision-polished high-purity substrate (such as synthetic quartz or soda-lime glass) with nanoscale functional thin-film layers (including light-shielding films and photoresist layers). During the lithography process, the blank mask undergoes exposure, development, etching, and other processes to be fabricated into a photomask with specific patterns, which are then transferred to the wafer. Key indicators such as the flatness, film uniformity, and defect density of the blank mask directly determine the accuracy of lithographic pattern transfer, thereby having a decisive impact on chip process yield and performance.

2. How are blank masks classified?

Based on lithography wavelength, blank masks are mainly divided into three categories:

The first category is Binary Blank Mask, primarily used in g-line, i-line, and KrF (248nm) processes, making it the most widely used type for mature nodes. It typically adopts a quartz substrate + chromium (Cr) absorber layer structure.

The second category is Attenuated Phase Shift Blank Mask, mainly corresponding to ArF (193nm) and some advanced processes. Compared to traditional Binary Masks, it adds phase-shift materials such as MoSi (molybdenum silicon), improving pattern imaging contrast through interference principles, with significantly higher difficulty in film layer control.

The third category is EUV Blank Mask, representing the industry's highest technological frontier, suited for 7nm and below advanced processes. It requires an ultra-low thermal expansion substrate (LTEM) and a multilayer reflective film structure of approximately 40–50 Mo/Si layers.

By application field, blank masks can be further divided into semiconductor Blank Masks, FPD (flat panel display) Blank Masks, and PCB photomask blanks. Among these, semiconductor Blank Masks have the highest technical barriers and added value.

3. Why is the domestic substitution of DUV blank masks particularly important amid the AI wave?

The market often directly links AI with advanced EUV processes, but this perception overlooks the much larger demand for mature processes in the AI supply chain.

First, the bulk of China's semiconductor industry demand still comes from DUV processes. Currently, the main processes of most domestic 12-inch fabs remain concentrated at nodes such as 28nm, 40nm, 55nm, 65nm, and 90nm, all relying on KrF and ArF lithography. Even for some more advanced logic products, due to restrictions on EUV equipment, domestic manufacturers still depend on ArF immersion lithography combined with multiple patterning to achieve higher precision manufacturing. This not only does not reduce the demand for DUV Blank masks but actually increases the usage of high-end ArF Blank and PSM Blank masks due to the higher number of mask layers.