Toray Develops New Material to lower Costs of SiC Devices
Toray Industries Inc has developed a material that is designed to lower the manufacturing cost of SiC- based power devices, which feature lower loss but are more expensive than Si-based power devices. The material is a highly heat-resistant photosensitive resist that can simplify the ion implantation process in the manufacturing process of SiC power devices. By using the resist, it is possible to simplify the conventional ion implementation process for SiC power devices and reduce the time required for the process by more than 40%.
SiC power devices using the material have already been commercialized, but the company plans to start volume production of them in 2017. And it is planning to be ready for volume production of the resist in fiscal 2015. Compared with the ion implantation process for Si power devices, that for SiC power devices has a larger number of processes, increasing the cost of SiC power devices. With the new resit, the ion implantation process can be as simple as that for Si power devices. The conventional ion implantation process for SiC power devices consists of the following processes. First, an oxide (SiO2) film is formed on a SiC wafer with CVD equipment. Then, a photosensitive resist is applied to it for exposure. It is dry-etched, and the unnecessary part of the SiO2 film is removed. Also, the remaining resist is peeled off. After that, ions are implanted, and the oxide film used as a mask is removed. This process is repeated several times. On the other hand, with the new photosensitive resist, it is applied to a SiC wafer by spin coating. Next, the resist is exposed and, then, calcined. By using it as a mask, the ion implantation is performed. Finally, the mask is removed. The number of processes is almost the same as that required for Si power devices. The new resist not only simplifies the ion implantation process but also eliminates the needs for CVD and dry etching equipment, enabling to reduce equipment cost and maintenance time.
The volume production models of CVD and dry etching equipment cost about ¥100 million (approx USD 918,864) per unit. The photosensitive resist meets the following four property requirements of the ion implantation process for SiC power devices. First, a pattern with a width smaller than 1.5 m can be formed. Second, it features ion stopping capability. Third, it has a thermal resistance of 450° C. Fourth, it can be peeled off. In regard to the thermal resistance, the company plans to improve it to 500° C within 2014. Also, the company aims to reduce the pattern width to 1 m or smaller.
