Method of forming small transistor gates by using self-aligned reverse spacer as a hard mask

The present invention relates generally to fabrication of semiconductor devices, and more specifically to methods of fabricating transistor gates used in semiconductor devices.

The current practice to form small transistor gates uses increasingly smaller wavelengths of light in the lithography step(s). The current practice places increasingly stringent requirements on lithography.

U.S. Pat. No. 4,784,718 to Mitani et al. describes a method for fabricating a semiconductor device with its gate electrode and source/drain extraction electrodes being made of the same material on a GaAs substrate and with its source/drain heavily doped regions self-aligned with both gate electrode and source/drain extraction electrodes.

U.S. Pat. No. 5,202,272 to Hsieh et al. describes a method of forming a field effect-transistor formed with a deep-submicron gate.

U.S. Pat. No. 4,931,137 to Sibuet describes a process for fabricating conductor elements on a substrate mutually spaced by a submicron dimension.

U.S. Pat. No. 4,729,966 to Koshino et al. describes a process for fabricating a Schottky FET device using metal sidewalls as gates.

U.S. Pat. No. 4,648,937 to Ogura et al. describes a method of preventing asymmetric etching of lines in sub-micrometer range sidewall images transfer.

U.S. Pat. No. 6,171,937 to Lustig describes a process for fabricating an MOS transistor having a channel length of less than 100 nm.

U.S. Pat. No. 5,336,630 to Yun et al. describes a method of making a semiconductor memory device having a storage node with a plurality of pillars capable of increasing the storage node surface and thus the cell capacitance.

Accordingly, it is an object of the present invention to provide an improved method of fabricating small transistor gates.

Another object of the present invention to provide an improved method of fabricating small transistor gates that relies less on lithography than conventional methods.

Other Objects Will Appear Hereinafter.

It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, a substrate is provided having an overlying Si 3 N 4 or an SiO 2 /Si 3 N 4 stack gate dielectric layer. A gate material layer is formed over the gate dielectric layer. A hard mask layer is formed over the gate material layer. The hard mask layer and the gate material layer are patterned to form a hard mask/gate material layer stack. A planarized dielectric layer is formed surrounding the hard mask/gate material layer stack. The patterned hard mask layer is removed from over the patterned gate material layer to form a cavity having exposed dielectric layer side walls. Masking spacers are formed on the exposed dielectric layer side walls over a portion of the patterned gate material layer. The patterned gate material layer is etched using the masking spacers as masks to expose a portion of the gate dielectric layer. The planarized dielectric layer is removed. The masking spacers are removed to form narrow gates comprising gate material.

The features and advantages of the present invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which like reference numerals designate similar or corresponding elements, regions and portions and in which:

FIGS. 1 to 6 schematically illustrate in cross-sectional representation a preferred embodiment of the present invention.

Unless otherwise specified, all structures, layers, etc. may be formed or accomplished by conventional methods known in the prior art.

Initial Structure

FIG. 1 illustrates a cross-sectional view of a wafer 10 , preferably a semiconductor wafer, having an Si 3 N 4 or SiO 2 /Si 3 N 4 stack gate dielectric layer 12 formed thereover to a thickness of preferably from about 15 to 100 Å and more preferably from about 15 to 28 Å. Si 3 N 4 or SiO 2 /Si 3 N 4 stack gate dielectric layer 12 is preferably deposited over wafer 10 and is more preferably is comprised of an SiO 2 /Si 3 N 4 stack as will be used for illustrative purposes hereafter.

Gate material 14 is deposited over SiO 2 /Si 3 N 4 stack gate dielectric layer 12 to a thickness of preferably from about 900 to 2000 Å and more preferably from about 1200 to 1600 Å. Gate material 14 is preferably comprised of polysilicon (poly), W on TiN stack or TaN and is more preferably comprised of poly.

Hard mask layer 16 may then be formed over gate material 14 to a thickness of from about 900 to 2000 Å and more preferably from about 1200 to 1600 Å. Hard mask layer 16 is preferably formed of nitride, silicon nitride (Si 3 N 4 ) or silicon oxynitride (SiON) and is more preferably formed of silicon nitride.

Patterning of Gate Material 14

As shown in FIG. 2, gate material 14 is then patterned to form patterned gate material 14 ′ having a width of preferably from about 1800 to 3200 Å and more preferably from about 1800 to 2400 Å.

Gate material 14 may be patterned as shown in FIGS. 1 and 2 to form patterned gate material 14 ′, that is patterned photoresist layer 18 may be formed over hard mask layer 16 as shown in FIG. 1 . As shown in FIG. 2, hard mask layer 16 may then be patterned using patterned photoresist layer 18 during an etch process to form patterned hard mask layer 16 ′. Photoresist layer 18 would then be stripped and gate material 14 patterned to form patterned gate material 14 ′ using patterned hard mask layer 16 ′ as a mask. If it is desired to minimize loss of the hard mask layer 16 ′ during etching of the gate material 14 , photoresist layer 18 is not stripped until after the patterned gate material 14 ′ is formed. The thickness of the patterned hard mask layer 16 ′ determines the thickness of the resist spacers 24 to be formed later (see below).

Deposition of Dielectric Layer 20

As shown in FIG. 2, dielectric layer 20 is then deposited over the structure and planarized to fill in the gaps between adjacent patterned hard mask 16 ′/patterned gate material 14 ′ stacks. Dielectric layer 20 is planarized using patterned hard mask layer 16 ′ as a polish stop. Dielectric layer 20 is preferably planarized using chemical mechanical polishing (CMP).

Dielectric layer 20 is preferably high-density plasma (HDP) oxide, PECVD oxide, LPCVD oxide or SABPSG and is more preferably HDP oxide as that provides for better gap fill between the gates.

Formation of Spacers 24

As shown in FIG. 3, patterned hard mask layer 16 ′ is removed, preferably by wet stripping or dry selective etching and more preferably wet stripping to form cavity 22 . Cavity 22 has exposed side walls 26 .

A thin layer of spacer material is deposited over the structure, filling cavity 22 , and is then etched, preferably by a blanket etch, to form self-aligned spacers 24 over exposed side walls 26 of cavity 22 . Spacers 24 are preferably comprised of photoresist.

Etching of Patterned Gate Material 14 ′

As shown in FIG. 4, patterned gate material 14 ′ is etched using spacers 24 as masks to form small transistor gate electrodes 30 . Small gate-electrodes 30 have a width of preferably from about 250 to 800 Å and more preferably from about 250 to 500 Å. It is noted that SiO 2 /Si 3 N 4 stack gate dielectric layer 12 between gate electrodes 30 are also partially etched.

It is noted that small, narrow transistor gate electrodes 30 are formed in accordance with the method of the present invention with less reliance upon lithography to form the small, narrow gate electrodes 30 . Instead the width of masking spacers 24 determines the width of small, narrow transistor gate electrodes 30 which are in turn formed by a blanket etch, without direct reliance upon lithography.

Removal of Dielectric Layer 20

As shown in FIG. 5, planarized dielectric layer 20 is removed, preferably by an oxide dip.

Removal of Masking Spacers 24

As shown in FIG. 6, masking spacers 24 are preferably removed by a resist ashing process, leaving small, narrow gate electrodes 30 .

Any unwanted connections between adjacent small, narrow gate electrodes 30 are etched off after appropriate masking.

The advantages of the present invention include:

1); non-reliance on very advanced lithography performance; and

2) deposition and etch-dependent poly critical dimensions are more controllable than lithography.

While particular embodiments of the present invention have been illustrated and described, it is not intended to limit the invention, except as defined by the following claims.