The Key Role of Laser Pointing Stability in the Application of Lithography Systems

Lithography is one of the core processes in semiconductor manufacturing, and extreme ultraviolet lithography technology, as a new generation lithography technology, is also in a rapid development stage. The basic principle is to use photoresist (also known as photoresist) to form corrosion resistance due to photochemical reactions after being photosensitive, and to engrave the patterns on the mask onto the processed surface. The main steps of photolithography of silicon dioxide in semiconductor chips include coating photoresist, aligning the mask and exposing it, dissolving the photosensitive photoresist layer with developer, dissolving the unprotected silicon dioxide layer with etchant, and removing the photosensitive photoresist layer.

In lithography systems, stable laser pointing is crucial as it directly affects the accuracy and consistency of the lithography pattern. There are three main factors that affect the stability of beam pointing, namely the displacement of the laser itself, the vibration differences between lasers and lighting systems on different bases, and the disturbances of the optical system during transmission. These disturbances will have a serious impact on the quality of lithography.

Firstly, the stability of laser pointing is crucial for ensuring precise etching of the pattern. During the lithography process, the laser beam needs to be precisely irradiated onto a specific area on the silicon wafer to achieve accurate transfer of patterns. If the laser pointing is unstable, it can cause problems such as displacement of the graphic position and size changes, seriously affecting the quality and performance of the product.

Secondly, the stability of laser pointing is also related to the repeatability and consistency of lithography. In semiconductor manufacturing, it is often necessary to perform photolithography on a large number of silicon wafers, which requires a high degree of repeatability and consistency in the photolithography process. If the laser pointing is unstable, the results of each photolithography will vary, resulting in inconsistent performance between product batches, increasing manufacturing difficulty and cost.

Therefore, the stability of laser pointing is particularly important under the constantly improving accuracy requirements.

We can achieve relative stability of the beam by reducing vibration and temperature changes, but this is only a passive compensation method and cannot completely avoid these interferences. In this regard, an active compensation system can be used to adjust the optical path and turn the beam back when it deviates, making the environmental requirements less stringent.

The Aligna laser beam pointing stabilization system from TEM company can effectively solve and achieve the above functions. The system consists of two Fast Reflecting Mirrors (FSMs), a Position Detector (PSD), and a Control Cabinet. The deflection of FSM can be achieved by combining electric motors and piezoelectric ceramics, ensuring both wide range and high accuracy of the fast reflector. Coupled with a high-resolution position detector (PSD), the total accuracy of the system can reach the sub micron level. In addition, response time is also crucial for systems that require real-time stability of laser beams, and excellent algorithms can limit it to the range of 0.2ms with a closed-loop bandwidth exceeding 5KHZ.

The following diagram is a schematic diagram of the beam detection and stabilization system. After passing through two fast reflection mirrors R1 and R2, the laser is incident on the beam splitter BS1. The transmitted light is used for subsequent experiments and normal use, and a small amount of reflected light will enter the PSD for beam detection. PSD is a photoelectric device based on the transverse photoelectric response of a semiconductor PN junction. According to the output voltage of the centroid of the incident light spot, two PSDs are used to detect the position deviation and angle deviation of the beam, respectively. After the controller detects the deviation information, it passes the feedback information to the FSM through an algorithm, controls the rotation of the FSM, and realizes the pointing correction of the main beam.

The following figure shows the displacement of the spot position before and after using the system. It can be clearly seen that the spot position is unstable and has a significant displacement before the system works; After the system starts working, the position of the spot is basically controlled near the origin, and the stability of the position is significantly improved.

Source: Yangtze River Delta Laser Alliance