Various deposition and etching processes and tools are used in semiconductor wafer processing such as for integrated circuits, solar photovoltaic cells and micro-machining. Two predominant types of reactors used in semiconductor processing are the tube-type reactor and the showerhead-type reactor, which are discussed in “Principles of Chemical Vapor Deposition” by Daniel M. Dobkin and Michael K. Zuraw, 2003, Kluwer Academic Publishers.
Typically, a chemical vapor deposition (CVD) showerhead reactor operates on a single wafer per chamber and thus has much lower wafer throughput than a CVD tube reactor, which handles many wafers in parallel in a single load. In a showerhead reactor, gases are distributed to a wafer from a showerhead (alternately, shower head). In a tube reactor, gases are distributed to a parallel-spaced set of wafers in a boat, with the gases traveling from an inlet at one end of the tube to an exhaust at the other end of the tube. Showerhead reactors are often run at a higher deposition rate in order to improve throughput for commercial viability.
Tube reactors and showerhead reactors are often known as hot-wall and cold-wall reactor designs respectively, with the tube reactor normally operated as nearly isothermal and the showerhead reactor having large temperature gradients from one part of the reactor to another. Generally, for plasma generation, showerhead reactors are preferred as compared to tube reactors, as tube-type plasma reactors have difficulties in mechanical design, particle control, electrical design and wafer handling. Tube reactors are suitable for processes requiring good temperature uniformity and high temperatures, such as polysilicon deposition. Showerhead reactors are suitable for lower temperature plasma-based processes including deposition of various materials and etching.
Plasma reactors often use a metallic showerhead as one plasma electrode, and a wafer in electrical connection with a chuck as the other plasma electrode. Walls of the chamber in which the showerhead and the wafer are mounted are generally held at ground potential for safety reasons. Electrons in the plasma lose energy to the chamber walls upon collision with the walls. Plasma enhanced chemical vapor deposition (PECVD) is often preferred in semiconductor processing as compared to physical vapor deposition (PVD), as films deposited by PECVD conformally cover processed wafer topographies, filling trenches or holes, and have superior electrical properties and lower defect densities.
Plenum dimensions and diameter, angle, and placement of holes in the showerhead affect flow of process gases. Generally, the showerhead has a diameter that is approximately the same as or is slightly larger than the silicon wafer or substrate being processed, as does the chuck supporting the wafer or substrate. Multiple gas plenums may be arranged in circumferential rings in or above the showerhead, for dispensing multiple gases without mixing in the plenum.
US Patent Application Publication No. 2010/0233879 A1 discloses a single-wafer, multiple-showerhead, multiple-chuck reactor. A wafer is moved to four or five different chucks for deposition of a portion of a film at each chuck. Each showerhead introduces its own random nonuniformities. Using several chucks averages out the random nonuniformities.
Improvements in showerhead reactors are sought. It is a goal of the present invention to improve processing throughput in showerhead reactors.