Overview
The dose.dat file can be used to verify whether the pressure compensation value is accurate for production wafers in Axcelis ion implantation systems [1]. This technique allows process engineers to calculate and optimize PCOMP values through data analysis rather than solely relying on experimental trial methods.
Step-by-Step Procedure
Step 1: Data Preparation
Extract the following two key parameters from the dose.dat file generated during implantation into photoresist-coated wafers [1]:
| COLUMN | DESCRIPTION | SOURCE |
|---|---|---|
| Disk Faraday Current (Imeasured) | The measured beam current readback value recorded by the disk faraday cup [1] | dose.dat file |
| IG3 Pressure Reading (P) | Vacuum pressure reading from Ion Gauge 3 located in the end station [1] | dose.dat file |
Create two new calculated columns:
- Natural logarithm of the disk faraday current: ln(Imeasured) [1]
- Normalized IG3 pressure value P (in appropriate units) [1]
Step 2: Create Scatter Plot
Using spreadsheet software or data analysis tools, plot your processed data as follows [1]:
- X-axis: End station vacuum pressure (P, from IG3 gauge) [1]
- Y-axis: Natural logarithm of beam current ln(Imeasured) [1]
- Chart Type: Scatter plot to show individual measurement points during the implantation cycle [1]
Step 3: Linear Fitting to Extract k-Factor
Fit a straight line through your plotted data points using linear regression. The slope of this fitted line represents the pressure compensation coefficient k [1].
Mathematical Foundation
The underlying physics is described by the following pressure compensation formula for standard Axcelis systems [1]:
Iactual = Imeasured · e(k − P)
Taking the natural logarithm of both sides transforms this into a linear equation:
ln(Iactual) = ln(Imeasured) + k − P
Where:
| SYMBOL | DESCRIPTION | SOURCE |
|---|---|---|
| Iactual | Pressure-compensated beam current (appears as pcompI in the Dose.dat file) [1] | Formula derivation |
| Imeasured | Raw measured beam current from disk faraday readback [1] | dose.dat column “diskI” |
| P | Pressure reading from IG3 ion gauge [1] | dose.dat pressure columns (e.g., end_hcig) |
| k | Linear fitting slope = Pressure Compensation Factor [2] | Calculated result |
Step 4: Convert k-Factor to PCOMP Recipe Value
After obtaining the k-factor from your linear fit, convert it to the actual recipe parameter using this formula for standard pressure compensation mode [1]:
PCOMP = 100 × (ek − 1)
Important Technical Notes
Pressure Compensation Modes
| MODE | COMPLEXITY | RECOMMENDATION |
|---|---|---|
| Standard PCOMP | Linear fitting is valid [1] | Use above formula |
| Gamma Pressure Compensation | Fitting becomes significantly more complicated due to non-linear response | Requires alternative methods or vendor consultation [1] |
Physical Mechanism Behind the Data Pattern
The dose.dat file reveals a characteristic pattern that validates this calculation method:
- As the ion beam hits wafers with photoresist, outgassing begins and vacuum pressure rises immediately [2].
- Simultaneously, measured beam current decreases due to charge-exchange neutralization reactions (ions capture electrons from gas molecules) [1][3].
- When implantation continues beyond peak outgassing, the effect gradually diminishes as resist desorption slows down.
Verification
After calculating PCOMP using this method:
- Compare your calculated pressure-compensated beam current (Iactual or
pcompI) against expected values [2]. - Verify that compensated current shows minimal standard deviation during implant (ideally constant throughout) rather than varying with end station pressure fluctuations [3].
Recommended Resources for Further Study
For more detailed information on Dose.dat analysis and PCOMP determination, refer to these Axcelis documentation sources:
- Best Methods and Practices for Determining Pressure Compensation Factors Using Dose_dat Software (Part Number 9510721) [1]
- Dose Theory and Pressure Compensation on Axcelis GSD High Current Implanter – Published paper by Infineon Technologies AG, IEEE Proceedings [3]
References
- Axcelis Dose_dat Training Documentation, File ID: 150d0f20-2e1e-440d-8506-e684b7f7355d
- most detail for IMPL training.pdf – Axcelis Process Lab Documentation, File ID: 21a3f7ab-a105-4906-8372-3660bd997da7
- Kraupner J., Kyek A., Vogl J., Weiss S. “Dose Theory and Pressure Compensation on Axcelis GSD High Current Implanter” – IEEE Proceedings, 2002
Summary for Students
When explaining this to your students, emphasize these key teaching points:
- PCOMP is necessary because photoresist outgassing causes variable pressure, which creates neutralization reactions that distort dose uniformity.
- The disk faraday cup measures electric charge (current), but not the actual particle flux of dopants reaching the wafer surface.
- Dose.dat analysis provides a data-driven, non-destructive method to validate or optimize PCOMP without splitting production lots for experimental measurements.