What is the uniformity of thin film deposition?
Thin film uniformity refers to the consistency of the thickness distribution of the thin film across the entire wafer. Good uniformity means that the thickness of the thin film is very close at every position on the wafer.
What are the types of thin film uniformity?
Generally, the following types are considered:
●Within-wafer uniformity: Uniformity within a single wafer.
●Wafer-to-wafer uniformity: Uniformity between different wafers.
●Lot-to-lot uniformity: Uniformity between different batches of wafers.
How is uniformity calculated?
Taking within-wafer uniformity as an example, its standard deviation is calculated using the formula:
This formula calculates the square root of the average of the squared differences between each data point and the mean of the data.
σ (standard deviation): Represents the degree of dispersion of the data; the larger the standard deviation, the greater the dispersion.
N: The total number of data points measured.
ti: The thickness value of the ith data point.
Mean: The average value of all data points.
(ti−Mean)^2: The squared difference between each data point and the mean.
∑: Summation.
The formula is somewhat difficult to understand, so here is an example:
Assume we have a set of thin film thickness data points: 55.1, 54.8, 55.3, 54.9, 55.0, 54.7, 55.2, 54.9, 55.1, 54.8.
●First, calculate the mean of these 10 points: Mean = 54.98.
●Then, calculate the squared difference between each thickness and the mean: 0.0144, 0.0324, 0.1024, 0.0004, 0.0004, 0.0784, 0.0484, 0.0004, 0.0144, 0.0324.
●Sum these squared differences and find the average: (0.0144 + 0.0324 + 0.1024 + 0.0004 + 0.0004 + 0.0784 + 0.0484 + 0.0004 + 0.0144 + 0.0324) = 0.3996.
●Finally, calculate the standard deviation: σ = 0.193.
