In semiconductor wafer fabrication different tests and measurements are done to characterize processes, such as electrical measurements. Electrical characteristics such as resistivity and therefore the specific resistance need to be considered.
A good overview on the correlation between both can be found here:
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/resis.html
More info:
Sheet Resistance and the Calculation of Resistivity or Thickness Relative to Semiconductor Applications
How to Compare Pre- and Post Process Measurements on Semiconductor Wafers ("Pre- and Post Maps")
Different sets of wafer data (maps) can be compares by the difference and ratio method. One map can be subtracted from another map by subtracting individual measurements point by point. The resulting map will visualize the difference between the two maps.
This is a simple method, however it often requires two maps, which are identical regarding the individual coordinates of sites. In WAFERMAP such differences can be calculated without the necessity of identical grids (only the wafer diameter must be the same). This is possible because different grids will be transformed to the grid with higher density of sites before comparison.
It is also possible to calculate the ratio between two files in the same way. Using the difference method both maps should have almost the same mean value. Therefore one map must be normalized to the mean value of the second map.
Titanium was sputtered with 600Å thickness on 200mm prime wafers. Then the wafer was annealed in a RTP chamber at approximately 700°C in pure nitrogen. The sheet resistance was mapped before („premap“) and after the RTP step („postmap“).
The ratio was calculated between both maps (in WAFERMAP select „Multi-File-Operations“→ „Compare“→ select the files in the 2 windows on the left → choose „X/Y“ in the center → click on „OK”).
The result shows a „signature“ of the RTP chamber.
Mean: 14.81 Ohms/sq
Max: 15.42 Ohms/sq
Min: 14.35 Ohms/sq
Std.Dev: 2.32 %
Range: 1.07 Ohms/sq
Interval: 1.0 %
Mean: 8.99 Ohms/sq
Max: 9.38 Ohms/sq
Min: 8.6 Ohms/sq
Std.Dev: 2.35 %
Range: 0.78 Ohms/sq
Interval: 1.0%
Mean: 1.65
Max: 1.68
Min: 1.61
Std.Dev: 0.87 %
Range: 0.07
Interval: 0.5 %
This is a simple method, however it often requires two maps, which are identical regarding the individual coordinates of sites. In WAFERMAP such differences can be calculated without the necessity of identical grids (only the wafer diameter must be the same). This is possible because different grids will be transformed to the grid with higher density of sites before comparison.
It is also possible to calculate the ratio between two files in the same way. Using the difference method both maps should have almost the same mean value. Therefore one map must be normalized to the mean value of the second map.
Example:
Titanium was sputtered with 600Å thickness on 200mm prime wafers. Then the wafer was annealed in a RTP chamber at approximately 700°C in pure nitrogen. The sheet resistance was mapped before („premap“) and after the RTP step („postmap“).
The ratio was calculated between both maps (in WAFERMAP select „Multi-File-Operations“→ „Compare“→ select the files in the 2 windows on the left → choose „X/Y“ in the center → click on „OK”).
The result shows a „signature“ of the RTP chamber.
Premap after sputtering
Mean: 14.81 Ohms/sq
Max: 15.42 Ohms/sq
Min: 14.35 Ohms/sq
Std.Dev: 2.32 %
Range: 1.07 Ohms/sq
Interval: 1.0 %
Postmap after RTP
Mean: 8.99 Ohms/sq
Max: 9.38 Ohms/sq
Min: 8.6 Ohms/sq
Std.Dev: 2.35 %
Range: 0.78 Ohms/sq
Interval: 1.0%
Ratio
Mean: 1.65
Max: 1.68
Min: 1.61
Std.Dev: 0.87 %
Range: 0.07
Interval: 0.5 %
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