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Sub-Lithography Imaging Method

IP.com Disclosure Number: IPCOM000034931D
Original Publication Date: 1989-May-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 54K

Publishing Venue

IBM

Related People

Chesebro, DG: AUTHOR [+2]

Abstract

A process sequence is shown which produces line structures which are much smaller than possible using conventional lithography. The following process sequence is capable of defining lines with precise dimensions which are less than 500 angstroms wide, and in the width of one lithographic dimension (0.5 microns, for example), it is possible to produce two lines and one space. Fig. 1 shows an imaged layer of nitride over a layer of oxide on a substrate. Using the nitride as a mask, some of the oxide is isotropically etched, undercutting the nitride, as shown in Fig. 2. Next a conformal film of the desired type, i.e., chemical vapor deposition (CVD) of polysilicon, tungsten etc., is deposited over the structure, as shown in Fig. 3.

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Sub-Lithography Imaging Method

A process sequence is shown which produces line structures which are much smaller than possible using conventional lithography. The following process sequence is capable of defining lines with precise dimensions which are less than 500 angstroms wide, and in the width of one lithographic dimension (0.5 microns, for example), it is possible to produce two lines and one space. Fig. 1 shows an imaged layer of nitride over a layer of oxide on a substrate. Using the nitride as a mask, some of the oxide is isotropically etched, undercutting the nitride, as shown in Fig. 2. Next a conformal film of the desired type, i.e., chemical vapor deposition (CVD) of polysilicon, tungsten etc., is deposited over the structure, as shown in Fig. 3. By reactive ion etching (RIE) anisotropically through the conformal layer, using nitride as the etch-stop, narrow rails or filaments are formed under the nitride overhang, as shown in Fig. 4. Finally, the masking layer of nitride is selectively etched, leaving pairs of lines (rails) separate by a space element, as shown in Fig. 5. To precisely control the rail thickness relative to its width, the deposition of the oxide layer shown in Fig. 2 can be placed over a nitride layer, as shown in Fig. 4a. This variation of the process utilizes the nitride layer under the oxide as an etch stop for the isotropic etch step. The patterned nitride on top of the oxide is used as an etch-stop when reactive ion etching anis...