CD Monitoring of Critical Photo Layers in 6 Inch GaAs IC Process

摘要

In this study, a calibration was conducted on an IVS120 optical CD tool (Schlumberger) to define the measurement accuracy for the photo layers in MESFET and HBT processes. Feature sizes varied form 0.85 to 6.0(mu) and the resist film thickness between 0.9 ~ 4.3 micron. It is a challenging task to measure a thickfilm resist feature with a Coke Bottle/T shaped sidewall profile. Various sidewall profiles and the correlated focus/measurement algorithms were studied, especially for the 4(mu) thick HBT implant mask layers. Then a gauge repeatability and reproducibility (GRR) studies were conducted for the IVS120 data after matching to CD SEM to insure the precision of the CD measurements. As a result of this work, the correlation coefficients obtained between multiple runs of measurements were greater than 0.99 on both the reference CD SEM and the IVS120 tool. Standard deviation (3 sigma) was within the specification of the CD tool (1% or 15nm whichever is greater), and approximately 98% maintained within 0.01 micron. Overall GRR was as low as 5-8% in the selected layers and CD ranges.