Expand the scope of RTP use

Mattson’s goal is focused on two RTP technologies-especially the formation of super shallow junctions. “We need very shallow bonding and a high degree of activation.” Timans said, “The technology of choice today is the high-temperature spike annealing technology, which has the largest impurity activation and minimum diffusion, as well as good defect annealing. Repair characteristics, the formation of high quality joints, low leakage current. This technology will be very important up to the 65nm process-it can minimize diffusion while ensuring a high degree of activation. In the era of advanced devices, improve activation The contradictory trade-off between degree and diffusion control will become increasingly difficult. “Advanced devices-especially logic products-will be manufactured using NiSi technology. However, NiSi brings more complex problems, especially it requires RTP equipment to be capable of low temperature control.

The process temperature of Ni is lower than that of cobalt, so temperature measurement and control are the most interesting issues when expanding the use range of RTP. “Our users want to be able to maintain the metal silicidation process in the RTP equipment.” Axcelis company Hebb said, “but also need to be able to measure and control low temperature. In order to broaden the scope of the process, the current development direction is how to control the RTP temperature at 250 ℃.”

When the temperature decreases, the radiation intensity emitted by the object will decrease exponentially. Since the wafer cannot emit enough energy at low temperatures, it is difficult to measure and control the temperature with a pyrometer. “Light interference is another problem. The light emitted by the heating source will also pass to the pyrometer, but what we need to measure is the radiation or light emitted by the wafer.” The higher the heating source temperature, the worse the situation.

Using hot walls instead of light tubes for heating can help. “We have launched a system with 250°C temperature control capability that can be used for NiSi development,” Hebb said. “Users can use a one-step process to anneal NiSi, while cobalt has always used a two-step process. Although nickel can be treated in a one-step process in theory, the two-step process has its own advantages. We found that a two-step annealing process (the first step) Below 300°C) there will indeed be some positive results.”

A serious problem encountered by Ernst Granneman, manager of the RTP division of ASM International, is that more than 90% of the RTP systems currently use lamps for heating. “For these systems, the most critical issues are temperature control, reliability, processing speed, cost of consumables and lack of low-temperature processing capabilities.” Granneman added that replacing radiant heating with continuous heating is an effective way to solve these problems.

USJ (Ultra shallow junction) formation technology blueprint includes ion implantation spike annealing and solid-phase epitaxial structure re-growth. As for bonding contacts, the blueprint is expected to transition from CoSi2 to NiSi. As Granneman said, “The process in the technical blueprint requires RTP equipment to have extremely excellent performance: heating and cooling speeds of several Baidu per second, independent of wafer surface pattern/emissivity, precise temperature control and application To form NiSi’s low-temperature working ability (starting at 200°C). We believe that the use of conduction rather than radiant heating is the solution to the problem, so that the USJ formation technology can maintain continuity in the current and future process era. Its temperature rise/fall speed It can be selected in the range of 300-900°C/sec, and the operating temperature range is 100-1100°C, with precise temperature control capabilities.”

For Yasuo Kunii, general manager of Hitachi Kokusai Electric’s Technology Development Center, thermal budget is the main process problem, and he believes that this problem can be solved by new chemistry and plasma processes. “As the semiconductor process developed from 130nm to 45nm, the thermal budget gradually became a serious problem. For the CVD process, the thermal budget can be reduced by changing the reaction precursor. For example, when the SiN film is deposited with SiH2Cl2 and NH3, the reaction temperature is 700°C. If SiH2Cl2 is changed to BTBAS, the SiN film deposition temperature can be reduced to 600°C or even lower, thereby significantly reducing the thermal budget

With the progress of the process, the thermal budget requirement for SiN reaction is getting higher and higher. By the 65nm process (45nm is more certain), in order to meet the process and production needs, we must adopt new technologies. (Source: Hitachi Kokusai) Laser processing

Sandeep Mehta, Director of Application Strategy and Process Development, Varian Semiconductor Equipment Association, believes that metal silicidation is the most common use of RTP. “In the past few process eras, RTP has been widely used in source/drain activation and ion implantation.” He said, “The need to reduce thermal budget has led to the transition from traditional high-temperature furnace annealing to RTP process. New Technology development has maintained this trend. For example, the spike annealing technology that can quickly heat up and cool down can further reduce the thermal budget.”

In order to keep the bonding depth shallow, the traditional spike annealing method will become an obsolete technology. A few years ago, it was thought that laser annealing was the best solution to form shallow junctions. “The advantage of laser annealing is that you don’t need to use a filament for heating. You can use the laser to quickly increase the temperature until it is enough to melt the silicon crystal to make it highly activated.” Mehta said, “However, from a mass production perspective, this One technology still has a key integration problem. From a technical point of view, there are also leakage current and residue defects, which will affect the performance of transistors. Although research in this field is still active, laser heating technology is integrated It is not feasible to form USJ.

People have also tried dynamic surface annealing, which is a laser treatment process whose working temperature is lower than the melting point of silicon crystals. This technique is expected to become an advanced spike annealing technique. Flash annealing is another option, which is an extension of the RTP spike annealing technique. During flash annealing, the wafer is first heated to an appropriate temperature, about 600-800°C, and then irradiated with high-intensity radiation for a short time pulse to make the wafer reach the required high temperature. Once the temperature peak reaches the requirement, the system will immediately turn off the radiation.

Mehta said. “Although the research work in the above two fields is very active, no one has successfully integrated laser heat treatment or flash annealing technology into the USJ process. So far, the RTP spike annealing process is still the only technology available for production. ”

Device manufacturers will have to adopt some alternative technologies. Regardless of the changes in device structure, materials, and impurity types, or the combination of the above methods, the purpose is to continuously improve the junction characteristics and improve transistor performance.