Improving the etching uniformity of plasma etching machines can be achieved by optimizing equipment design and adjusting process parameters. The specific methods are as follows:
Equipment design optimization
Installation of Focus Ring: The focus ring is installed around the edge of the wafer to fill the height difference between the wafer edge and the electrode, making the sheath layer flatter and ensuring that ions can vertically bombard the wafer surface, avoiding etching distortion and improving etching uniformity.
Optimize the distribution of reactive gases: Improve etching uniformity by optimizing the injection method of reactive gases. For example, the silicon etching chamber can gradually evolve from injecting gas from the periphery of the wafer to injecting gas from above the center of the wafer.
Adjusting the distance between the upper and lower plates: In a capacitively coupled plasma (CCP) chamber, the gap between the cathode and anode is a key parameter that affects the uniformity of ion flux. The smaller the gap, the better the uniformity of the plasma. Adjustable gap technology can be used to optimize the ion flux distribution according to different process conditions.
Adopting zone temperature control: Wafer temperature is a key factor affecting etching uniformity, and electrostatic chuck (ESC) can optimize temperature uniformity by introducing different heating or cooling zones, such as developing from early single zone temperature control to dual zone temperature control, four zone temperature control, and even deploying more than 100 local heating elements to further improve temperature control accuracy.
Process parameter adjustment
Optimize gas composition and injection method: Adjust the injection position of the main reaction gas, or inject regulating gas at different positions to control the gas-phase chemical environment on the wafer and improve etching uniformity.
Increasing RF power: Appropriately increasing RF power can increase the energy of incident particles, making them bombard the target surface more vertically, thereby reducing the difference in etching rate of sidewalls, which is helpful for reducing micro groove effects and improving etching uniformity.
Implementing intermittent etching: By periodically interrupting the etching process and giving electrons enough time to escape, the charging effect can be significantly reduced, thereby improving etching uniformity.
Compensatory process control: When the etching rate of a certain step is faster in the central area, compensation can be achieved by increasing the edge etching rate, such as using the BevleEtch machine for precise control.