Real-time etching monitor using argon quadrupole mass spectrometry for 100 nm class WSiN gate fabrication

We have developed a real-time etching monitor technique for 100 nm class WSiN gate fabrication that uses mass analysis of argon. The WSiN film absorbs argon atoms during the sputter-deposition process, and argon atoms are emitted back into the etching chamber when the WSiN film is etched in a SF6-CF4-SiF4-O2 gas mixture. By using a quadrupole mass spectrometer (QMS) to detect the emitted argon atoms, we can determine an accurate just etching time and estimate the most appropriate overetching time. This monitoring technique has sufficient signal intensity, follows etching within 1 s, has no effect on the etching reaction products, and has a small deviation in signal intensity between wafers. Using the monitor, we obtained a vertical and anisotropic etched pattern with a small GaAs loss. We compared the predictions of the QMS monitor with those of optical emission spectrometry. We demonstrated that the technique is well suited for multilayer-gate WSiN etching by using it to detect the nitrogen concentration in WSiN film