Fine Lines in High Yield (Part XC) Step Tablets (Gray Scales; Step Wedges)―Part C

摘要

Tech Talk is featuring a three-part series covering the topic of Step Tablets. Part A introduced fundamental relationships between transmittance and optical density. Part B covered the relationship between different types of step tablets and how to use them in adjusting conditions to achieve the desired "step held." This Part C will compare step tablets to radiometers, and will point out pros and cons of each method to verify proper exposure conditions. In addition to step tablets, radiometers are being used to determine the proper exposure level. Radiometers (sometimes also referred to as lightmeters or photometers) contain a photocell (detector) that measures the radiation intensity (milliWatt/cm~2) from a certain wavelength range. This range should overlap with the spectral response curve of the photoresist or should at least capture the range of the greatest response. Radiometers typically can also be operated in an "integration mode," i.e., the intensity (milliwatts) is integrated over time (seconds) to give an energy reading (milliwatts x seconds = milliJoules).