A furnace that processes CIGS solar cells should be capable of operating to 650°C or higher. The aim is for a wider belt with superior cross belt uniformity so that larger substrates can be contained in the future. More over, a muffle is required to ensure a cleaner operating environment because various processes in CIGS processing, such as Sulpharization, involves the introduction of different gasses at different time periods. The muffle needs to have the capability to control the gas type and gas flow in each zone. With all of this in mind, Torrey Hills Technologies has designed a furnace that is well suited to match the requirements for thin film solar applications. Figure 4 illustrates a firing furnace that is capable of processing CIGS solar cells and Table 3 lists the technical specifications for the ideal CIGS furnace.
The designed HSA furnace uses ceramic heater boards in order to achieve elevated temperatures. Aside from the standard belt size of 350 and 650mm, wider belts have been designed as well to accommodate wider glass substrates. While a 700mm wide belt has been successfully engineered, efforts are underway to build a belt as wide as 1000mm. As a standard feature, this furnace is equipped with a steel brush for cleaning the conveyor belt, however, Ultrasonic belt cleaning is available as an extra option.
A microprocessor based PID controller is what controls the furnace. Type K thermo-couples are used in determining the zone temperatures and the controls are located on the right hand side of the furnace which can be viewed from the entrance. The central processing unit (CPU) is mounted under the exit table and the CPU is primed with a Windows operating system for easy computing. The computer system is pre-installed with a program for controlling the furnace parameters, including the belt speed and the zone temperatures. Temperature profiles can be stored and retrieved as well for future purposes. Thermocouple ports are located at the entrance table for connecting the profiling thermocouple directly into the microprocessor. This feature allows for the monitoring and recording of actual temperatures experienced by the part. Software is also included with the computer to capture, display, printout and store the furnace profile. Additionally, the furnace is equipped with a redundant overheat safety protection system which incorporates an additional type “K” thermocouple in the center of each controlled zone and the multi-loop alarm.
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