# Improved MSRN-Based Attention Block for Mask Alignment Mark Detection in Photolithography
## 2 Related Work  
### Semiconductor Mask Aligner  
The most important factors that a machine vision algorithm uses in various industrial fields are fast computation time and the reliability of object recognition. In the field applied over several cycles along the feedback loop, the importance of fast computation time and algorithm stability is increasing. In photolithography, a mask aligner is equipment that accurately aligns the wafer and then irradiates the light to draw the circuit pattern on the mask on the wafer [16]. Figure 1 shows the photolithography process workflow. The photolithography proceeds as follows: First, surface preparation is performed prior to photolithography. There are three processes: wafer cleaning, dehydration baking, and wafer prime. The second is the spin coating process, which is the process of applying photoresist. Third, the soft bake process removes the remaining solvent along with the applied photoresist. Fourth, alignment and exposure are performed. The fifth is Post Exposure Bake (PEB), which is a process of heating and drying the PR after exposure and before development. The sixth is development, which removes the PR from a certain area in order to realize a pattern by separating the necessary and unnecessary parts using the developer. The seventh is a hard bake. This is a process that removes residual solvent, dries PR, and increases adhesion to the substrate. After the last inspection, if the PR is properly applied, the etching process is carried out. Figure 2 shows the overall structure of  
Figure 1: Workflow of the photolithography process. the mask aligner in photolithography. Several photolithography processes are repeated as a stacked structure while manufacturing a semiconductor chip. Mask alignment is an important process at this time, and the horizontal position between each layer must be precisely aligned. A grayscale image processing technique is used in the visual image to separate the object from the mark [17]. This is a method for objects to be detected based on their threshold values. Setting the threshold value changes the quality of the image depending on the lighting and the environment and introduces a lot of noise [18]. Therefore, dynamic binarization that adjusts the threshold value based on the existing image contrast distribution and object contrast has been studied [19]. The alignment process proceeds as follows: Extract the feature value of the mark before performing mark recognition and alignment. Analyze the geometric shape of the mark, extract the pixels obtained from the pattern, and find the pattern matching within the area. Then, check the markings on both sides of the Mask Alignment (MA) and check whether the alignment of the mask is well achieved through this marking. Next is Global Alignment. Check that both sides of the wafer are marked, and check whether the alignment of the wafer is correct throughout this marking. Finally, Fine Alignment checks whether the print and the reticle are the same. After the mask is properly aligned with the wafer, patterning should be performed sequentially. For this confirmation, various marks exist on the wafer. Photolithography performance factors include resolution, depth of field, field of view indicating viewing angle, modulated transfer function, spatial coherence, alignment accuracy, and throughput factors for semiconductor production yield [20]. There is no tolerance in the exact position when each layer of the wafer is stacked. The measure of the value stacked vertically is called the overlay, and it refers to the alignment state of each layer. Precise alignment technology can increase the overlay value; otherwise, misalign problems will occur. Thermal run-out error, translational error, and rotation error are types of overlay errors. If there is misalignment, there is a very high possibility that the device will malfunction or an electrical defect will occur, resulting in a loss.