Process‐induced mechanical stress in isolation structures studied by micro‐Raman spectroscopy

Micro‐Raman spectroscopy is used to study mechanical stress in local isolation structures on silicon substrates (poly‐buffered local oxidation of silicon, called PBLOCOS or LOPOS). The influence of processing parameters such as nitride film thickness and width, pad oxide thickness, and field oxide thickness is studied. Also the change of the local stress during the successive processing steps of the isolation is investigated: deposition of the nitride mask, field oxidation, and removal of the nitride mask. The results are explained using a simple analytical model. It is found that stress varies very much during the different processing stages. After deposition of the nitride film, the stress is compressive under the mask lines and tensile outside the lines, close to the line border. The stress magnitude is highly dependent on the thickness of the nitride film. It can be described by edge forces. During field oxidation, this edge‐force‐induced stress nearly completely relaxes. In LOPOS structures with fiel...