RTP system uses radiant heat source to heat wafers one by one, and temperature measurement and control are completed by pyrometer. In the past, the traditional heat treatment process used batch high-temperature furnaces, and a large number of wafers were heated simultaneously in the same furnace tube. Intermittent high-temperature furnace is still widely used, which is more suitable for heat treatment process with relatively long treatment time (10 minutes or more).
RTP technology is widely used. It can be quickly raised to the temperature required by the process (200~ 1300℃) and quickly cooled, usually at the speed of 20~250℃/ s; In addition, RTP can also control the process gas well. Therefore, RTP can complete complex multi-stage heat treatment process in one recipe. The ability of RTP to rapidly heat up and treat in a short time is very important, because advanced semiconductor manufacturing requires that the heat treatment time should be shortened as much as possible, and the degree of impurity diffusion should be limited. Using RTP instead of slow thermal treatment process can also greatly shorten the growth period, so RTP technology is especially valuable for the yield improvement stage.
RTP system has many heating structures, heat sources and temperature control methods. Among them, it is the most common method to heat the wafer with multiple rows of tungsten halide lamps, because the heat source it provides is easy to control, convenient, effective and fast. In RTP system, the heat source directly faces the wafer surface, instead of heating the wafer edge like a batch high temperature furnace. Therefore, RTP system will not affect the uniformity of process treatment and the speed of heating (cooling) when processing large-diameter wafers. The general RTP system also has the function of wafer rotation, which makes the heat treatment uniformity better.
At present, the most advanced RTP system can accurately control the temperature distribution on the wafer surface within 3 s.
Another key factor of RTP is temperature measurement and control. Figure 1 is a schematic diagram of RTP system controlled by pyrometer, which measures the temperature on the back of wafer. The early RTP system has the problem of poor repeatability, because the spectral emissivity will change when the coating on the back of the wafer is different, which leads to the wrong temperature reading. At present, RTP system contains complex emissivity correction system, and the heat treatment repeatability is very good.
An important application of RTP is to activate ion implantation impurities to form ultra-thin bonds. This process requires the heat treatment system to have the function of rapid heating and cooling, because after ion implantation, the wafer must be heated to about 1050℃ for high-temperature annealing to remove the damage caused by ion implantation and activate the implanted impurities, and at the same time, the high-temperature treatment time must be shortened to minimize the diffusion of impurity ions. For this reason, people have developed a peak annealing method, so that the wafer can be heated quickly and then cooled immediately.
Another important application of RTP is the formation of metal silicide. In this process, the metal thin film reacts with silicon in the source, drain and gate regions to form metal silicide. In the advanced logic process, the commonly used metal is cobalt, and nickel is being developed for the 65 nm process. The forming process of metal silicide is usually carried out below 500℃, and the wafer must be heated in an environment protected by high purity gas, because the metal film is very sensitive to oxidation reaction. RTP system is very suitable for this process. Because the reactor of RTP is small, it is easy to introduce high-purity gas for purification, forming a very clean reaction environment.
RTP plays an increasingly important role in oxidation reaction. Because RTP can use a variety of gases for high-temperature rapid heat treatment, it can accurately control the process conditions and generate oxide films with excellent performance. Oxide films produced by RTP are usually used for gate dielectric materials, oxide films and shallow trench isolation (STI) pads. The water vapor in gas creates a new application field for RTP. For example, selective oxidation of tungsten-containing gate stacks with H2-rich steam has attracted special attention of advanced DRAM technology.