Toray Industries Inc developed a material that enables 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%, the company said.
Toray is currently delivering samples of the resist to some of its customers. 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, Toray said.
According to Toray, 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, Toray said.
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 US$918,864) per unit, the company said.
New resist validated with devices
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, Toray plans to improve it to 500°C within 2014. Also, the company aims to reduce the pattern width to 1?m or smaller.
At TPEC, in which Toray has been participating since 2012, the company has been testing the manufacturing of power devices using the new resist in collaboration with Japan's National Institute of Advanced Industrial Science and Technology (AIST), Fuji Electric Co Ltd and Ulvac Inc. In fact, it confirmed that SiC transistors and SiC schottky-barrier diodes (SBDs) (withstand voltage: 1,200V) made with the resist have electrical properties equivalent to those made with the conventional ion implantation process.
Toray will announce the details of the new technology at the 10th European Conference on Silicon Carbide and Related Materials (ECSCRM 2014), an academic conference on SiC technologies, which will take place from Sept 21 to 25, 2014, in France.