Inside/outside morphology changes due to RTP non-uniformity
Last week, I used a 6-inch thermocouple wafer to profile the temperature uniformity (outside the susceptor) in the RTP. I measured four points: center, front, back, and center-right (positions relative to the RTP door e.g. front means closer to the door). The center-right position was chosen to verify side-to-side uniformity of the lamps.
Below is a chart showing the before and after tuning temperature profiles and differential. The tuning involved changing the lamp power in the three banks (upper front, upper back, lower).
Before tuning, the center to back temperature was similar but center to front differed by 30 C! After tuning, the temperature at the edge of the wafer was very similar (front minus back) but the center to edge temperature differed by 15 C. I’ve contacted the vendor to try and get some tips on tightening up the uniformity.
Using the newly tuned RTP, I annealed a series of four wafers at three temperatures. Below are histograms comparing center and egde samples.
What’s interesting is that the non-uniformity is exaggerated in the lower temperature anneals (900 C, 925 C). The porosity is higher at the center (as based on the temperature profile – hotter at the center). The higher temperature anneals are closer in porosity and avg size.
Here’s a plot of the four histograms (center samples) on the same chart.
