Latent image formation: Nanoscale topography and calorimetric measurements in chemically amplified resists

Abstract

The characterization of photoresists during the image formation process has traditionally relied on bulk methods during or after development. This article shows that it is not necessary to develop the photoresist in order to obtain significant information about the image formation process in x-ray, electron beam, and UV lithography. The characterization of the image formation process in chemically amplified photoresists prior to development is difficult due to their sensitivity to electrons used in scanning electron microscopy and the weak changes in dielectric constant needed for optical microscopy. The advent and development of the atomic force microscope ͑AFM͒ have allowed local surface measurements of exposure induced changed in photoresists with sub-m scale resolution and negligible modification of the sample. A series of chemically amplified resists, positive and negative, have been studied with a variety of exposure radiation ͑electron beam, x-ray, and UV͒. The results discussed in this article focus on two of these resists: SAL 605 ͑Ϫ͒, and TOK 010 ͑ϩ͒. Both positive and negative chemically amplified resists exhibit significant changes in topography and calorimetric properties during the image formation process. Interpretation of the resist topography in negative resists is given by a semi-empirical model that assumes Fickian diffusion of resist material during post-exposure bake ͑PEB͒ and verified with AFM data. The glass transition temperature, Tg, of wafer spun thin films of SAL 605 has been measured, prior to exposure, to be 75Ϯ3°C with an ellipsometric technique. The PEB temperature, 105°C, is much greater than the Tg of SAL 605, thereby providing some justification for our Fickian diffusion model. These results are preliminary until a chemical map can be done on the resist at sub-m resolution, which at present time is not possible. The need for detecting intrinsic material property changes due to the image formation process motivates the exploration of calorimetric properties of the resist. Interpretation of the calorimetric data is still unclear. Both cases of positive and negative photoresists exhibit an increase of heat absorbed in the exposed regions. Photoacid ions produced by exposure to radiation may be considered responsible for such an increase.

Advanced Post-Irradiation Examination Capability T

“…-Ultra-large-scale integration lithography research and cellular diagnostics in biochemistry [25,28,29,30] -Detecting parameters such as phase changes in metallic alloys and ceramics [31] -Measuring material variations in semiconductor devices [32] -Near-field photothermal microspectroscopy [34] -Analyzing enthalpy in integrated circuits.…”

Hot-spot detection and calibration of a scanning thermal probe with a noise thermometry gold wire sample

“…[1][2][3][4][5][6][7][8][9][10] Temperature calibration is required for scanning thermal microscopy, where substrate temperature changes must be measured with high accuracy. A number of ways to calibrate a scanning thermal probe have been developed 11,12 and include: isothermal (hotplate) calibration, 13 melting point standard calibration, 14,15 use of the linearity of heater resistance with temperature, 16 calibration methodologies using Raman thermometry, 11 and the use of a small thermocouple in contact with the probe.…”

Secondary electron contrast modulation in SU‐8 photoresist films exposed holographically

“…The knowledge of the photoacid distribution during both exposure and PEB processes is essential for maximizing the lithographic processing and for minimizing the critical dimensions of the lithography. Some studies were carried out in undeveloped films to understand the photoacid diffusion in chemically amplified resists 14–17. AFM relief images of chemically amplified negative photoresists films before PEB have shown a light depression in the exposed areas.…”