title = "Advanced Process Control (APC) in Lithography"

content = """
Advanced Process Control (APC) is a closed-loop control system used to 
maintain process stability and minimize variability in lithography.

**Feedback Control:**
Metrology data (CD and overlay) from processed wafers is fed back into 
the APC system. The system then calculates corrections (offsets) for 
the scanner's dose, focus, and alignment settings for the next batch 
of wafers. This compensates for slow drifts in the scanner's 
performance or changes in the incoming wafer characteristics.

**Feed-Forward Control:**
Data from previous process steps (e.g., film thickness measurements 
from deposition) can be "fed forward" to the lithography step. The 
APC system can then adjust the lithography parameters (e.g., exposure 
dose) to compensate for variations in the incoming material.

**Run-to-Run (R2R) Control:**
R2R control is a type of APC that adjusts process parameters on a 
batch-by-batch or even wafer-by-wafer basis. It uses statistical 
models to predict the process outcome and then optimizes the 
parameters to achieve the target result.

**Process Window Monitoring:**
APC systems also monitor the process window (the range of dose and 
focus within which the process is stable). If the process window 
shrinks or shifts, the APC system can alert engineers to a potential 
problem.
"""

version = "0.0.1"
