Plasma etching pattern delineation

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. 

Polymeric resists (1) are utilized widely in the electronics industry to lithographically delineate circuit patterns onto normally non-patternable inorganic substrates. As device dimensions shrink, an increasing number of the levels of these devices will have to be etched by dry-process (e.g., rf plasma) etching techniques (2). As a... 

After pattern delineation, the next step in a production process is e.g. etching (wet or plasma), ion implantation or metal deposition. Some of these techniques result in heating of the resist above 200 °C. Although novolak resins start to crosslink from a temperature of 120 °C, crosslinking cannot prevent thermal flow of a resist pattern because the flow occurs at a lower temperature already. Several solutions to this problem have been found, and are described below. 

The etch resistance of poly (butene-1 sulfone) in fluorocarbon-based plasmas can be enhanced by prior treatment of the surface in an oxygen plasma. This pretreatment inhibits or retards the depolymerization reaction that characterizes normal etching in fluorocarbon plasmas, thereby permitting formation of a surface-modified layer which exhibits a substantially reduced etch rate. Pretreating PBS in an oxygen plasma enables it to be used subsequently in selective reactive-ion etch processes involving fluorocarbon plasmas to delineate submicron, anisotropically etched patterns. 

Reactive ion etching is now very widely used for delineating fine patterns in the fabrication of VLSI circuits. Recently, fluorine atoms produced in CF plasma have been used in the etching of Si wafers, generating SiF2 (8). As an alternative dry etching approach, a photo-excited etching has been reported by... 

After the resist pattern has been delineated, it has to withstand processes like etching (wet or plasma) or ion implantation. A high thermal flow stability and low... 

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