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...

The three-layer deep-UV PCM system of Lin and Chang 34) used A1 as a deep-UV PCM instead of Si02 as the RIE PCM. This eliminates the need for an RIE system but still requires a large number of processing steps. Figure 20 shows a 0.3 - pm thick A1 deep-UV PCM on 1.6 pm of PMMA. 

C The Improvement Era. The improvement era started in 1980 following major discoveries between 1978 and 1979. The siloxane system of Hat-zakis (7), though reported in 1981, is a unique and promising system. Therefore it was included in the renaissance era. The MLR systems have evolved into either RIE PCM or deep-UV PCM by this time and many of the researchers in this period have been more concerned with applying the MLR principle to improve lithographic performance. A list of the MLR systems reported in this period is shown in Table VIII. Because of the increased volume of publication in this period, the list is meant to be representative rather than exhaustive. 

Figure 24. Uncapped images delineated with the Novolak/PMMA deep-UV PCM system. A GCA Mann DSW4800 aligner with 0.28-NA and 436-nm wavelength was used. The smallest openings are of 0.8 /iw nominal dimension. (Reproduced with permission from Ref. 46.)...

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... 

Both the deep-UV-and the RIE PCM-delineated resist structures can be used for electroplating which was successfully demonstrated by Satini and Viswanathan 45) as shown in Figure 22 for the deep-UV PCM case. In this case the control of the image in the planarizing layer is critical. Because of the unique anisotropic characteristics of RIE, this control should also be feasible for RIE PCM. In such cases linewidth variations include the contribution from the planarizing layer as well as top layers. The consideration of resist removal after plating is similar to the case for lift-off. 

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