Infrared temperature sensors of Exergen Global in the semiconductor business
Exergen Global: Non-contact thermal sensors are remarkably diverse devices that can help ensure higher process speeds, more precise accuracies, tighter tolerances, and higher yields for a wide spectrum of manufacturing processes, including semiconductor production.
Semiconductor manufacturing is a very precise and costly process and the dimensional scales in which these semiconductor manufacturers work is unprecedented, and not surprisingly, this requires exceptionally accurate measurement.
Any thermal expansion of the wafer has enormous effects on their processes. So maintaining a constant and uniform wafer temperature is essential.
Let’s look at a couple examples of how IRt/c sensors can benefit chip manufacturing.
Wafer temperature measurement
As silicon wafers move through the various stages in the manufacturing process, they are often transferred from one station to another. During that transfer, it’s essential that the wafer’s dimensions not vary more than a nanometer. Therefore, if the material’s temperature falls above or below the set tolerance level, the wafer will expand and then must be discarded—causing the manufacturer to lose both time and money.
The largest wafer manufacturers in the world have a system where after a lithography procedure, the circuitry on a wafer can be checked for errors. Once an error is detected, it can be repaired. However, we’re talking about errors on a nanometer scale here, so after an error is detected it is essential that the wafer temperature remains very stable, otherwise the wafer will expand, and the found error will be displaced. This will only be a displacement of nanometers, but that is sufficient for the system to fail.
As wafers can have different emissivity values, this is quite a challenge. Required accuracies can be met when the cone concept is applied. Wafer manufacturers work with the cone concept. See technote 36.
For several applications in PCB production, preheat of the PCB is required to help accelerate the soldering process and to prevent thermal shock.
1) Wave soldering, a bulk soldering process used in the manufacture of printed circuit boards, is one such instance. During this process, the circuit board is passed over a pan of molten solder in which a pump produces an upwelling of solder that looks like a standing wave. As the circuit board makes contact with this wave, the components become soldered to the board. The IRt/c is an excellent solution to the problem of heater control for PC board preheat. IRt/c’s work particularly well in this process, since both the heating and measuring occur right at the surface, where the solder must flow. The IRt/c reading is unaffected by reflections from the heater, since the spectral response of the 6-14 micron IRt/c lens filters out any shorter wavelengths of the radiant heater energy.
2) Coating of PCBs: the core PCB plate material consists of a copper plate, covered with a green, isolating coating. Applying the coating to the copper plate is done with heat presses (like laminating machines). This process is monitored and controlled with IRt/c’s.