John Daugherty

Maintaining reproducible plasma reactor wall conditions: SF6 plasma cleaning of films deposited on chamber walls during Cl2/O2 plasma etching of Si

Silicon oxychloride films deposited on plasma etching reactor walls during the Cl2/O2 plasma etching of Si must be removed to return the reactor to a reproducible state prior to etching the next wafer. Using multiple surface and plasma diagnostics, we have investigated the removal of this silicon oxychloride film using an SF6 plasma. In particular, a diagnostic technique based on the principles of multiple total internal reflection Fourier transform infrared spectroscopy was used to monitor the films that formed on the reactor walls. The silicon oxychloride film etching proceeds by incorporation of F, which also abstracts and replaces the Cl atoms in the film. If the SF6 plasma is not maintained for a sufficiently long period to remove all the deposits, the F incorporated into the film leaches out into the gas phase during the subsequent etch processes. This residual F can have undesirable effects on the etching performance and the wafer-to-wafer reproducibility. The removal of the silicon oxychloride fil...

Current capabilities and limitations of in situ particle monitors in silicon processing equipment

By enabling real time monitoring and control of particle levels in integrated circuit process equipment, in situ particle monitors (ISPMs) have the potential to reduce dramatically the dominant source of yield‐killing defects, i.e., process induced particles. However, there are also significant limitations to their use for on‐line monitoring. A survey of the ISPM literature shows that the greatest benefit provided by ISPMs for most applications is their immediate indication of high‐particle excursions. In only a few applications described in the literature do the sensor data correlate with wafer surface scans and show enough sensitivity to baseline particle levels to control process maintenance cycles. Scaling arguments show that at gas pressures below about 100 mTorr, gravitational settling and particle inertia typically prevent particles from being carried efficiently to exhaust sensors, in spite of experimental evidence that bouncing significantly aids particle transport. Combined with the low sampling...

Formation and removal of composite halogenated silicon oxide and fluorocarbon films deposited on chamber walls during plasma etching of multiple film stacks

In the shallow trench isolation process, a stack of thin films on a Si wafer must be etched using different gas discharges. During plasma etching of a thin-film stack consisting of an organic antireflection coating, Si3N4 and Si with Cl2, CHF3/CF4 and Cl2/O2 discharges, respectively, halogenated silicon oxide and fluorocarbon films form on the chamber walls. The chemical nature of these films and the methods for removing them were studied using multiple plasma and surface diagnostics. We find that the film which deposits on the chamber walls is a composite consisting primarily of two components, a halogenated silicon oxide film—created during Cl2/O2 etching of Si—and a fluorocarbon film formed during CF4/CHF3 etching of Si3N4. The halogenated silicon oxide film can be removed by etching with F formed by dissociation in SF6 plasma, while the fluorocarbon film is etched by O atoms created in O2 plasma. A sequential SF6 and O2 plasma process can be used to etch the composite film, but even an O2 plasma maint...