Plasma descumming

LINEWIDTH CONTROL Lens imperfections Source stability Mask dimensions Beam shape Mechanical stability Developing Etching Baking Plasma descum Film thickness Film uniformity Swelling... 

Process Developer and conditions Pre and Postbake temperature Pre and Postbake time Plasma descum Etching technique C min. 

PLASMA DESCUMMING Gas composition Reactor configuration Time Temperature Power Frequency Gas flow rates... 

Postdevelopment Treatment. Descum. A photoresist plasma descum step is typically but not always used after development. This step removes unwanted resist residues that were not cleared out during development and, in effect, increases the process latitude of the occasionally troublesome exposure-development sequence. Likewise, the descum step can smooth out minor irregularities of the resist side wall. This mild plasma treatment is done with 02 or 02-CF4 gases with low power and pressure settings, short process times, or both. The same plasma under more-vigorous conditions may be used later to strip the resist at the end of the masking operation. 

It has been found, however, that the etch rate of PBS can be reasonably controlled in both oxygen and CF4/O2 plasmas if the substrate temperature is kept below room temperature (9). This fact has been utilized to reduce the defect density in the manufacture of chrome photomasks by exposing the developed PBS pattern to a low-temperature oxygen plasma (descum) prior to wet-etching the chrome. We have now found that the plasma-etch resistance of PBS in a CF4/O2 plasma can be markedly enhanced at room temperature simply by exposing the resist to a short oxygen plasma pretreatment prior to exposure to the fluorinated plasma. This effect can be used in a variety of pattern transfer processes to controllably generate submicron features on wafers and masks. This paper examines the parameters associated with this effect, proposes a mechanism to account for the results and delineates some possible pattern transfer processes. 

PSiPI Film Preparation. A cleaned (acid washed or oxygen plasma descummed) silicon wafer is spincoated with PSiPI and dried at 100°C for 1 hour. The wafer is then masked and exposed. Typical times are 30 sec on the PPG Ultraviolet Processor and 5 min under RS Sunlamps. The unexposed area is then developed typically using 0.5N NaOH. The patterned film is then thermally tempered at 200°C for 1 hr followed by 300°C for 1 hr to convert it to the imide. 

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