Characterization and removal of polysilicon residue during wet etching

•We presented 2 models on the residues generated at the Si wet etching.•The residues of tornado shape make on hydrophobic surface due to poor wettability.•We found the optimized surface through the contact angle.•Hydrogen bubble generated during silicon wet etching causes significant residues.•Ultrasonication or adding IPA is effective for preventing the bubble effect.

Process optimization of polysilicon removal by wet etching with alkaline chemicals in a gate-last device integration scheme was investigated. Initial surface condition of the polysilicon layer, spreading properties of wet etching chemicals, and generation of hydrogen bubbles during wet etching were revealed as key parameters affecting the degree of polysilicon residue after wet etching both in patterned structures and on non-patterned bare wafers. Wet etching starting from a hydrophilic polysilicon surface showed successful polysilicon removal (no residues) compared with a hydrophobic polysilicon surface, indicating that the spreading and wetting properties of the wet etching chemical on polysilicon surface is very important in the polysilicon wet etching process. Therefore, it is believed that chemicals showing lower contact angles on the polysilicon surface may be suitable to enhance process efficiency. Furthermore, hydrogen gas generated during silicon wet etching can hinder polysilicon removal, causing significant residues after processing. Ultrasonication or addition of IPA in the wet etching solution can be an alternative method for preventing the hydrogen bubble effect.

Graphical abstractThe summarized graph (left) shows the measured contact angles changing toward different chemicals. This was carried out on the proper conditions for complete wet etching of polysilicon without any patchy residues. Also the results of the bubble removal evaluation after adding IPA and using ultrasonic waves (right) are mentioned as schematic and images for definite comparison.Figure optionsDownload full-size imageDownload as PowerPoint slide