Technical Field
The disclosure concerns a chamber or reactor for processing a workpiece such as a semiconductor wafer using microwave power.
Description of Related Art
Processing of a workpiece such as a semiconductor wafer can be carried out using a form of electromagnetic energy, such as RF power or microwave power, for example. The power may be employed, for example, to generate a plasma, for carrying out a plasma-based process such as plasma enhanced chemical vapor deposition (PECVD) or plasma enhanced reactive ion etching (PERIE). Some processes need extremely high plasma ion densities with extremely low plasma ion energies. This is true for processes such as deposition of diamond-like carbon (DLC) films, where the time required to deposit some type of DLC films can be on the order of hours, depending upon the desired thickness and upon the plasma ion density. A higher plasma density requires higher source power and generally translates to a shorter deposition time.
A microwave source typically produces a very high plasma ion density while producing a plasma ion energy that is less than that of other sources (e.g., an inductively coupled RF plasma source or a capacitively coupled RF plasma source). For this reason, a microwave source would be ideal. However, a microwave source cannot meet the stringent uniformity required for distribution across the workpiece of deposition rate or etch rate. The minimum uniformity may correspond to a process rate variation across a 300 mm diameter workpiece of less than 1%. The microwave power is delivered into the chamber through a microwave antenna such as a waveguide having slots facing a dielectric window of the chamber. Microwaves propagate into the chamber through the slots. The antenna has a periodic power deposition pattern reflecting the wave pattern of the microwave emission and the slot layout, rendering the process rate distribution non-uniform. This prevents attainment of the desired process rate uniformity across the workpiece.
A limitation on processing rate is the amount of microwave power that can be delivered to a process chamber without damaging or overheating the microwave window of the chamber. Currently, a microwave window, such as a quartz plate, can withstand only low microwave power levels at which DLC deposition processes can require hours to reach a desired DLC film thickness. The microwave window provides a vacuum boundary of the chamber and is consequently subject to significant mechanical stress, rendering it vulnerable to damage from overheating.