Two-layer deep-UV PCM

The schematic processing steps for the two-layer deep-UV PCM system are shown in Table III for near-UV and e-beam exposures, resulting in capped and uncapped profiles respectively. Step 5a is required only for near-UV exposures to average out optical interference effects discussed in Section 6.2.a. Step 6a is used to enhance the AZ to PMMA adhesion and cap retention. Figure 15 shows uncapped 1 - nm lines in a 2 - /im thick PMMA layer. Figure 16 shows the capped image with 0.3 fim AZ on 2 -iLim PMMA. The AZ layer was delineated by a 30 - /iC/cm 25 - keV e-beam in both cases. 

TABLE III. Processing Steps for the Two-Layer Deep-UV PCM Systems... 

Figure 15. Uncapped resist image obtained with a two-layer deep-UV PCM system. The 0.85-um wide PMMA lines were 1.9-fim thick separated by 2.4 ixm. A 0.2-um AZ1350J PCM was used.

Figure 16. Capped resist image obtained with an identical two-layer deep-UV PCM system as in Figure 13. The AZ layer was 0.3-fim thick on...

Such a pinhole density test was performed on the AZ/PMMA two-layer deep-UV PCM system (26). The result is shown in Table IX where a pinhole density of 8 and 6 per cm was obtained for the capped (A) and uncapped (B) systems. Because only three wafers were used for each test, the result should be taken only qualitatively and the numerical difference between 6 and 8 pinholes/cm should be taken as being indicative of measurement fluctuations only. It should not be attributed to the use of different developers or O2 plasma because in the subsequent tests of batches C and D in which the DUV exposure was omitted, the numbers were 0 and 1 pinhole/cm with the capped system giving the smaller pinhole density. The low pinhole density in batch E in which the AZ development step was omitted suggests that the pinholes arise during the development of the AZ layer. Presumably, a small portion of the AZ base resin molecules were not linked up with the photoactive compound and therefore still exhibited their intrinsic high solubility in the AZ developer. After development, these high solubility spots became pinholes. These pinholes are apparently larger than the diffraction - limited sizes so that they can be transferred into the PMMA film by deep-UV exposure. 

TABLE XI. Pinhole Test Results of the AZ/PMMA Two-Layer Deep-UV PCM System... 

Deep-UV resists are used in two principal modes as surface resist in single layer mode, or as the thick planarizing layer in portable conformable mask (PCM) bilayer mode. In the single layer mode, the use of deep-UV resists provides improved resolution, while in the PCM mode, a deep-UV resist is used in combination with a conventional resist to make use of the wavelength selectivity of the two types of resists. The PCM process (Figure 5.47) first exposes and develops the conventional novolac-based thin top resist using a 436 nm masked exposure. A second full exposure is then made in the deep-UV, which is... 

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