Application of top-down CD-SEM metrology in measuring wafers with resist film thickness of 24 μm with various sidewall profiles

Abstract

An automated top-down CD-SEM technique, complimenting the existing high angle tilt SEM method has been developed for measuring features printed at a film thickness of 24 microns. Measurements of resist linewidth versus exposure dose were made using a KLA 8100 top-down CD-SEM. The advantage of this CD-SEM is the automated collection of a large statistical pool of data and the ability to determine the linewidth independently of operator, accurately and consistently. The technique has been applied to AZ P4000 and AZ 9000 photoresist thick films through and beyond their exposure latitude. Maintaining a sharp sidewall profile of photoresist while supporting high aspect ratios is ideal for magneto-resistive and inductive thin film recording head coil plating and many other mission-critical applications. Also a fast and non-destructive thin film recording head coil plating and many other mission-critical applications. Also a fast and non-destructive metrology technique is desired and preferred to support future more costly and larger substrates. Results are reported for 10 and 6 micron reticle linesizes, respectively, at a film thickness of 24 microns using the AZ P4620 and AZ 9262 positive photoresist over bare silicon wafers. Wafers were exposed using an Ultratech Ultrastep Stepper model 1500 system and then developed by AZ 400 K inorganic developer. Exposure dose- array fields were measured first on the top-down KLA CD-SEM and then coated and re-measured on a Hitachi scanning electron microscope with 60 degrees-tilt capability. The importance of knowledge of resist profile and choosing the proper metrology tool is discussed. Linewidth values were compared with result from the standard tilt microscope reading method. Agreement to within 10 percent is noted for profiles corresponding to most exposure doses. Profiles for higher, over-exposed fields resemble a 'coke bottle' and linewidth for bottom of resist is inferred by extrapolation based on the prior correlation found between the two SEMs. The AZ 9262 resist line features showed a smaller 'coke bottle' profile at higher doses than AZ P4620 line features. Further work is planned for other positive resists with non- traditional profiles on unconventional substrates.