Effects of varying the parameters in witness-sample-based photoresist outgas testing: dependence of the carbon growth on pumping speed and the dose, time, and area of resist exposure

In this work, we discuss several parameters influencing extreme ultraviolet (EUV) resist qualification test results. The witness sample resist qualifications test is implemented on several different instruments world wide. The original protocol for the test developed by the tool manufacturer requires that a 300 mm wafer be exposed to a dose to clear in one hour. Also required is that the carbon contamination rate on the witness sample be mass limited, i.e., that the rate be saturated with respect to the EUV or e-beam intensity. Simple arguments have been presented in the past to show that the thickness of the carbon growth should be inversely proportional to the pumping speed and proportional to the area exposed if dose and duration were held constant. The present experiments demonstrate the real-life limitations of these arguments and provide validation to our area scaling procedure to equate test results done with 200 mm wafers to results expected for 300 mm wafers. In the process of studying the dependence of carbon growth on pumping speed, we encountered the important effect of increased partial pressure on the degree of intensity saturation.