Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
1998-12-02
2001-01-09
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S313000, C216S041000
Reexamination Certificate
active
06171763
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to etching metal using an ultra-thin resist. In particular, the present invention relates to etching extremely fine patterns in metal preferably using an extreme UV ultra-thin resist and an oxide/silicon nitride hard mask.
BACKGROUND ART
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down the device dimensions on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller features sizes are required. This includes the width and spacing of interconnecting lines and the surface geometry such as corners and edges of various features. Since numerous interconnecting lines are typically present on a semiconductor wafer, the trend toward higher device densities is a notable concern.
The requirement of small features, such as metal lines, with close spacing between adjacent features requires high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as optical light, X-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the photomask, for a particular pattern. The lithographic coating is generally a radiation-sensitized coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive of the subject pattern. Exposure of the coating through the photomask causes a chemical transformation in the exposed areas of the coating thereby making the image area either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
Projection lithography is a powerful and essential tool for microelectronics processing. However, lithography is not without limitations. Patterning features having dimensions of about 0.25 &mgr;m or less with acceptable resolution is difficult at best, and impossible in some circumstances. This is because photoresist layers used in lithography have thicknesses on the order of 7,000 Å and higher. Such relatively thick photoresist layers are not conducive to making small patterned dimensions with good resolution. In other words, critical dimension control for features having dimensions of about 0.25 &mgr;m or less is poor with relatively thick photoresist layers.
However, corner rounding problems and insufficient etch protection are associated with using thinner photoresists (less than 7,000 Å). In particular, corner rounding of layers underneath thin photoresists is caused by insufficient etch protection and results in poor definition/resolution. Improved lithography procedures providing improved resolution and improved critical dimension control are therefore desired.
SUMMARY OF THE INVENTION
The present invention generally provides methods that lead to improved critical dimension control in patterning metal lines. Since it is possible to patterning openings in ultra-thin photoresists on the order of about 0.1 &mgr;m or less, the present invention provides methods for forming hard masks with adequate stop capability for metal etching having improved resolution and to methods of forming metal lines of small width having improved resolution due to use of ultra-thin photoresists and hard masks having improved resolution. As a result, the present invention effectively addresses the concerns raised by the trend towards the miniaturization of semiconductor devices.
In one embodiment, the present invention relates to a method of forming a metal line, involving the steps of providing a semiconductor substrate comprising a metal layer, a silicon nitride layer over the metal layer, and an oxide layer over the silicon nitride layer; depositing an ultra-thin photoresist over the oxide layer, the ultra-thin photoresist having a thickness less than about 2,000 Å; irradiating the ultra-thin photoresist with electromagnetic radiation having a wavelength of about 250 nm or less; developing the ultra-thin photoresist exposing a portion of the oxide layer; etching the exposed portion of the oxide layer exposing a portion of the silicon nitride layer; etching the exposed portion of the silicon nitride layer exposing a portion of the metal layer; and etching the exposed portion of the metal layer thereby forming the metal line.
In another embodiment, the present invention relates to a method of etching metal to form metal lines, involving the steps of providing a semiconductor substrate comprising a metal layer, a silicon nitride layer over the metal layer, and an oxide layer over the silicon nitride layer; depositing an ultra-thin photoresist over the oxide layer, the ultra-thin photoresist having a thickness from about 500 Å to about 2,000 Å; irradiating the ultra-thin photoresist with electromagnetic radiation having a wavelength of about 200 nm or less; developing the ultra-thin photoresist exposing a portion of the oxide layer, wherein the exposed portion of the oxide layer has a width of about 0.1 &mgr;m or less; etching the exposed portion of the oxide layer exposing a portion of the silicon nitride layer; etching the exposed portion of the silicon nitride layer exposing a portion of the metal layer; and etching the exposed portion of the metal layer thereby forming metal lines.
In yet another embodiment, the present invention relates to a method of processing a semiconductor substrate, involving the steps of providing a semiconductor substrate comprising a metal layer, a silicon nitride layer over the metal layer, and an oxide layer over the silicon nitride layer, wherein the metal layer comprises aluminum; depositing an ultra-thin photoresist over the oxide layer, the ultra-thin photoresist having a thickness from about 500 Å to about 2,000 Å; irradiating the ultra-thin photoresist with electromagnetic radiation having a wavelength of about 200 nm or less; developing the ultra-thin photoresist exposing a portion of the oxide layer; etching the exposed portion of the oxide layer exposing a portion of the silicon nitride layer; etching the exposed portion of the silicon nitride layer exposing a portion of the metal layer; and etching the exposed portion of the metal layer thereby forming a metal line having a width of about 0.1 &mgr;m or less.
REFERENCES:
patent: 5710067 (1998-01-01), Foote
patent: 5962346 (1999-10-01), Shue
patent: 5989776 (1999-11-01), Felter
patent: 6013582 (2000-01-01), Ionov
patent: 6020269 (2000-02-01), Wang
patent: 6057219 (2000-05-01), Cho
Bell Scott A.
Levinson Harry J.
Lyons Christopher F.
Nguyen Khanh B.
Wang Fei
Advanced Micro Devices , Inc.
Barreca Nicole
Huff Mark F.
Renner , Otto, Boisselle & Sklar, LLP
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