Excimer laser exposure of Ag2Se/GeSe2: High contrast effects

Abstract

The use of an excimer laser for exposing the inorganic resist system Ag2Se/GeSe2 was recently reported (Ref. 1). One of the startling findings of that work was the dramatic (60-fold) decrease in the required dose as the pulse energy was increased; the required dose can be as low as 5 mJ/cm2. One of the questions arising out of that work was whether the high contrast and resolution of this resist system could be maintained under this form of exposure; the work reported in this paper indicates that these desirable quantities are indeed maintained. The value of contrast measured exceeded 10 (i.e., extremely high). By way of demonstrating this high value we exposed, using a KrF excimer laser operating at 249 nm, a film of Ag2Se/GeSe2 in the proximity printing mode with a Cr-on-quartz mask and observed the resulting Fresnel fringes at feature edges. Fringes with a half-period of 0.25 μm and aerial modulation of only 10% were resolved, thus indicating that even under pulsed laser beam exposure this material enjoys very desirable imaging properties both in terms of contrast and resolution. Another aspect which must be considered before the material can be regarded as practical for IC fabrication is that of possible contamination of the workpiece by the resist components—particularly silver. Experiments are currently underway involving both C–V measurements and Rutherford backscattering to determine the extent and the effect of such contaminants; preliminary results suggest that there is no significant contamination.

Chalcogenide glass resists for lithography

“…So, the main advantages of chG-ag photoresists are (Kostyukevych, 1998): uniformity of the layers, high values of contrast coefficient g (as high as 10.5 was observed for ag 2 Se/GeSe 2 system; Polasko et al, 1985), extremely high resolution capability (yoshikawa et al, 1981) and absence of shrinkage after treatment. ChG films show strong resistance to many acid solutions, such as HF, HF-nH 4 F, H 3 Po 4 , Hcl, H 2 So 4 , which are conventionally employed in the etching of Sio 2 or Si 3 n 4 in microfabrication technology.…”

Microelectronic Interconnections and Assembly

“…The necessaary elements of such media are the Ch VS layer and metal source (mostly silver or silver compounds). Schemes of IV type were succesfully used for the submicron lithography [42][43][44][45][46]. The increase of sensitivity, contrast and thermal stability can be achieved with the utilization of ill and V type of systems [20,40,41 J.…”

“…Easily dissolved in various alkaline etchants Ch VS layers after photostimulated interaction with metal have good resistive properties to this etchants [3,6,17,18,24,35,42,72,[88][89][90][91][92]. Selective etching properties ofChVS layers were investigated in detail also in many works [3,14,16,17,18,23,71,72,88,[93][94][95][96][97][98].…”

“…Possibilities in optical projection lithography were shown in [ 6,13,34,42,44,45,100 ], lines with 0.4-0.5 IUJl sizes were easily obtained ( Fig. 17 ).…”

“…Lightsensitivity of systems[21,22,42,88] and ChVS layers[16,22] depends 00. intensity of photoactive irradiatioo.. For AszS3-~ system up to irradiatioo. density l~ W/cm 2 there is no dependence from irradiation density P, then up to 10 W/cm 2 lightsensitivi~ is lowered, that is coo.nected with the growth of probability of recombinatioo.…”