More on porosity vs. position
Last week I took a series of TEM images from all but one position on wafer 638. Below are the TEMs, histograms, and porosities vs. distance from center plots. “Xpos”, “xneg”, “ypos”, “yneg” indicate which axis the images were taken from.
Positive x-axis
Negative x-axis
Positive y-axis
Negative y-axis
Wafer 638 porosity vs. position
While I was at it, I also took a look at wafer 639 for comparison.
Positive x-axis
Negative x-axis
Positive y-axis
Negative y-axis
Wafer 639 porosity vs. position
Comments
- Porosity varies 4x-5x from center to outside
- Cutoffs are consistent for all positions
- There is a slight increase in average pore size from center to outside
- The negative y-axis measurement on w639 seems anomalous. I should note that the sputtered film is deposited in such a way that film non-uniformity is centered on the wafer assuming it is a perfect circle. In reality, there is a wafer flat which is what we center our mask on. Thus I would expect that whatever non-uniformity shows up in the morphology would be more severe in the y-axis positions.
- This post highlights the importance of keeping track of what coordinate (not just radial distance) a sample comes from. Even though two samples may have the same r-value does not mean they share the same porosity!