Process Parameter Control Problems

1. Insufficient Etch Selectivity
   When the etch selectivity between the material being etched and the mask or underlying material is insufficient, it can lead to excessive mask consumption or unintended etching of the underlying material, affecting pattern fidelity.
   For example, low photoresist selectivity may cause sidewall tilting or critical dimension deviations.
   Influencing factors: Improper parameter settings such as gas ratio, RF power, and pressure.

2. Non-uniform Etch Rate
   Differences in etch rates across different regions of the wafer surface may result in inconsistent pattern depths, particularly under micro-loading effects where etch rates differ significantly between dense and isolated areas.

3. Insufficient Anisotropy
   Wet etching (e.g., phosphoric acid etching of silicon nitride) is prone to undercut effects due to its isotropic nature. Dry etching may also exhibit lateral etching if plasma parameters are not properly controlled.

4. Precision Issues Due to Isotropy

• Phenomenon: Due to the inherent isotropic nature of wet etching, material is removed not only vertically but also horizontally during the etching process, leading to side etching. This affects etching precision and morphology control, making it difficult to achieve precise etching morphology for feature sizes smaller than 3 micrometers.

• Cause Analysis: The isotropic nature of wet etching is determined by the essence of chemical reactions and is difficult to alter through simple methods.

• Impact: Precision issues may result degraded device performance or failure to meet design requirements.

• Measures: To address precision issues, dry etching or a combination of dry and wet etching methods can be adopted to improve etching accuracy. Additionally, optimizing parameters such as etching solution composition, concentration, and temperature can also enhance the precision of wet etching to some extent.