Positive resist pattern formation through focused ion beam exposure and surface barrier silylation

• US 5,362,606 A
• Filed: 08/07/1992
• Issued: 11/08/1994
• Est. Priority Date: 10/18/1989
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Shaver, David C., Melngailis, John, Hartney, Mark A.
• Primary Examiner(s): Bowers, Jr., Charles L.
• Assistant Examiner(s): Young, Christopher G.
• Application Number:
  US07/926,971
• Time in Patent Office: 823 Days
• Field of Search: 430/325, 430/326, 430/313, 430/315, 430/302
• US Class Current: 430/315
• CPC Class Codes: G03F 7/265 Selective reaction with inorganic or organometallic reagents after image-wise exposure, e.g. silylation

Abstract

A resist exposed to a micron or sub-micron pattern of highly absorbed ion beams forms a highly crosslinked barrier layer in the exposed regions of the resist surface. The complementary surface regions are silylated in a silicon-containing reagent, and the exposed regions are then removed by a plasma etch. Pattern definition is enhanced by limiting the exposure and the silylation to the surface of the resist. The process allows feature definition below 1000 Angstroms using a relatively inexpensive single element low energy ion source.

Claims

1. A method of forming a positive resist pattern on a substrate, such method comprising the steps of

forming a film of polymeric resist material having a thickness below approximately two micrometers on the substrate,

controllably exposing the film to a pattern of focused ion beam radiation at a fluence and at an energy effective to crosslink exposed regions of the film, such that substantially all exposure radiation is absorbed by said resist and crosslinking is localized at the surface of the film without introducing chemical or thermal effects in regions adjacent or below the exposed localized surface regions, forming a crosslinked diffusion barrier layer at the surface such that said exposed surface regions become effectively impermeable to silylating ambients and prevent diffusion therethrough into the film,

controllably exposing said coated exposed substrate to diffusion of a silylating ambient under controlled conditions of pressure, temperature and time and effective to selectively incorporate silicon into only a surface portion of the unexposed regions of the resist between said exposed regions, in an amount effective to form an etch resistant barrier, and

etching the film with a plasma etch thereby selectively removing the resist material in said exposed regions.

2. The method of claim 1, wherein the step of exposing is affected by exposing through a mask.

3. The method of claim 1, wherein said radiation is heavy element ion beam radiation.

4. The method of claim 1, wherein said step of forming a film is performed by dry depositing a polymer film on the substrate in a plasma chamber, said polymer film including functionality for crosslinking upon exposure to said ion beam radiation.

5. A method of forming a positive microlithography resist pattern, such method comprising the steps of forming a polymer film on a substrate, said film being a novolac material without photoactive additive, exposing the film to a pattern of focused ion beam radiation that is written by directing the ion beam radiation against the surface of said film to form said resist pattern, said radiation being effective to crosslink only a surface exposed region of the film, said crosslinking occurring within 0.2 microns of said surface, and occurring without introducing thermal or chemical effects into adjacent regions of said film, said crosslinking further forming a diffusion barrier layer that prevents diffusion therethrough of an organometallic reagent, and contacting the coated substrate with the organometallic reageant to incorporate a barrier metal by diffusion into a surface region of the film complementary to said exposed region, and etching said film in a plasma etch, said barrier metal being etch resistant and said plasma etch being effective to remove said exposed region and underlying regions of the film to form said positive microlithography pattern.

6. The method of claim 5, wherein the step of etching includes controlling parameters of the plasma etch to achieve steep side walls.

7. A method of achieving a positive silylation resist film, such method comprising the steps of

forming a polymeric resist film of a thickness not substantially over one micron thick suitable for patterning to deposit submicron features,

determining a set of silylation conditions effective to silylate the unexposed resist film just sufficiently to prevent plasma etching,

exposing the resist film to a pattern of ion beam radiation from a focused ion beam source in a dose such that the resist film undergoes a low temperature self-reaction localized in a surface region thereof and becomes crosslinked in exposed surface regions sufficiently to resist silylation by forming a crosslinked diffusion barrier layer that prevents diffusion of a silylating ambient into the resist film through the barrier layer, and

silylating the exposed resist film under the determined set of silylation conditions so that insufficient silylation occurs in exposed regions to prevent etching, thereby achieving a positive resist pattern upon plasma etching.

8. The method of claim 7, further comprising the step of etching the exposed silylated resist film in an oxygen RIE plasma etch.

9. The method of claim 8, further comprising the step of providing a halogen-containing pre- or post-etch.

10. A method of achieving a positive silylation resist film, such method comprising the steps of

forming a polymeric resist film without photoactive compounds and of a thickness under approximately several microns but substantially greater than an absorbance path length of a given ion beam,

determining a set of low temperature silylation conditions effective to diffuse a silicon-containing reagent into and incorporate silicon in a surface portion of the unexposed resist film to prevent plasma etching,

exposing the resist film to a pattern of radiation by focusing the given ion beam without a mass separator in a dose such that the resist film becomes crosslinked only in exposed surface regions sufficiently to form a diffusion barrier layer that prevents diffusion of the silicon-containing reagent into or through the barrier layer to resist silylation yet without affecting underlying or adjacent regions of the resist, and

silylating the exposed resist film under the determined set of silylation conditions, thereby achieving a positive resist pattern upon plasma etching without introducing thermal effects during either the step of exposing or the step of silylating, thereby achieving a pattern of enhanced contrast upon etching away the exposed regions in a plasma etch.

11. A method of achieving a positive silylation resist film, such method comprising the steps of

forming a polymeric resist film without photoactive compounds and of a thickness under approximately several microns but substantially greater than an absorbance path length of a given ion beam,

determining a set of low temperature silylation conditions effective to silylate the unexposed resist film to prevent plasma etching,

exposing the resist film to a focused pattern of radiation from the ion beam source without a mass separator in a dose such that the resist film becomes crosslinked only in exposed surface regions sufficiently to form a diffusion barrier layer that prevents diffusion of a silicon-containing reagent into or through the barrier layer causing it to resist silylation yet without affecting underlying or adjacent regions of the resist, and

silylating the exposed resist film under the determined set of silylation conditions, thereby achieving a positive resist pattern upon plasma etching without introducing thermal effects during either the step of exposing or the step of silylating, thereby achieving a pattern of enhanced contrast upon etching away the exposed regions in a plasma etch.