Why the side wall bend during dry etching

Dry etching is a process that combines both physical and chemical effects, with ion bombardment being a key physical etching method. During this process, the angle and energy distribution of the incoming ions can be uneven. If the ion incident angle varies across different points on the sidewall, the etching effect will also vary accordingly. In areas where the ion incident angle is larger, the ions exert a stronger etching effect, leading to increased material removal and causing the sidewall to bend. Additionally, an uneven distribution of ion energy can contribute to this effect. Ions with higher energy are more effective at removing materials, resulting in inconsistent etching levels along the sidewall, which further exacerbates the bending issue.

 

Photoresist acts as a mask in dry etching, protecting areas that do not need to be etched. However, photoresist is also affected by plasma bombardment and chemical reactions during the etching process, and its performance may change. If the thickness of the photoresist is uneven, the consumption rate during the etching process is inconsistent, or the adhesion between the photoresist and the substrate is different in different locations, it may lead to uneven protection of the sidewalls during the etching process. For example, areas with thinner photoresist or weaker adhesion may make the underlying material more easily etched, causing the sidewalls to bend in these locations.

 

The etched substrate material itself may have different properties, such as different crystal orientations and doping concentrations in different regions. These differences will affect the etching rate and etching selectivity. Taking crystalline silicon as an example, the arrangement of silicon atoms in different crystal orientations is different, and their reactivity with the etching gas and etching rate will also be different. During the etching process, the different etching rates caused by the difference in material properties will cause the etching depth of the sidewall at different locations to be inconsistent, ultimately leading to sidewall bending.

 

The performance and status of the etching equipment also have an important impact on the etching results. For example, problems such as uneven plasma distribution in the reaction chamber and uneven wear of the electrode may lead to uneven distribution of parameters such as ion density and energy on the wafer surface during the etching process. In addition, uneven temperature control of the equipment and slight fluctuations in gas flow may also affect the uniformity of etching, thereby causing sidewall bending.

 

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