Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2001-07-12
2003-10-21
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S311000, C430S314000, C430S317000, C430S322000, C430S328000, C430S330000, C430S394000
Reexamination Certificate
active
06635409
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is related generally to a method of making a semiconductor device and specifically to photolithographic methods for forming submicron features including an added process step to harden photoresist material to prevent pattern collapse.
The semiconductor industry has progressively reduced the size of components and connectors on integrated circuits in the pursuit of increased computational power and device speed. State of the art semiconductor devices are approaching the limit of feature sizes that may be formed using conventional photolithography fabrication methods. One of the limits being approached involves the minimum dimension of photoresist structures that can be used during fabrication.
Photolithography employs photoresist to create a patterned structure that protects the underlying surface from subsequent fabrication steps, such as chemical etching. There are two types of photoresists in common use, positive photoresists and negative photoresists. Positive photoresists are sensitized when exposed to ultraviolet light so that exposed areas will dissolve in a developer solution leaving behind unexposed areas. Negative photoresists are hardened by exposure to ultraviolet light so exposed areas are inhibited from being dissolved by the developer solution while unexposed areas are dissolved.
Using the example of a positive photoresist process, a conventional photolithography method for producing narrow lines is illustrated in
FIGS. 1A and 1B
. Supported by a substrate
1
is provided a material layer that forms a surface
2
in which it is desired to form a first and second narrow line. A photoresist layer
3
is formed over the surface
2
. A first region
5
and a second region
7
in the photoresist layer
3
are simultaneously exposed to electromagnetic radiation
8
, such as ultraviolet or actinic light, through openings
11
and
13
in a mask or reticle
9
, as illustrated in FIG.
1
A. The mask
9
comprises a pattern of lines and spots of opaque material
10
, which prevent transmission of light
8
, and transparent openings
11
,
13
. The terms mask and reticle are used interchangeably in the semiconductor arts, with the term reticle often referring to a mask used in step and repeat exposure systems. The photoresist layer
3
is then developed wherein the exposed regions
5
and
7
are removed (when employing a negative photoresist, the unexposed areas are removed), while the unexposed region
6
remains, as illustrated in
FIG. 1B. A
gas or liquid etching medium is then permitted to reach the underlying surface
2
through the openings
15
,
17
in the photoresist layer
3
to etch narrow lines
16
,
18
in surface
2
, which are separated by an inter-lines distance
19
, as illustrated in FIG.
1
C.
In the developing step, the exposed areas of a positive photoresist are removed by a developer solution to leave the desired pattern image on the surface. At the end of the developing step, the surface must be rinsed to stop the developing reaction and remove the developer solution from the surface. Typical positive photoresist developer solutions are alkaline solutions diluted with water, which require only a water rinse. Negative photoresist developer solutions are organic solvents, which require rinsing with other organic solvents (e.g. n-butlyl acetate). After rinsing, the substrate is dried in preparation for further processing.
Developed, rinsed and dried photoresist layers are sometimes then treated with ultraviolet radiation to reduce the tendency of the photoresist to flow during subsequent process steps where the photoresist will experience high temperatures which may including bake cycles, plasma etching, ion implantation and ion milling. This treatment is typically accomplished by irradiating the dried photoresist layer with deep UV (e.g. <320 nm) while heating the layer to a high temperature (e.g. 120-190° C.) for approximately a minute.
As the width and spacing of narrow lines is reduced, the width of the photoresist structures used to create the narrow lines must be reduced. A practical limit being approached in semiconductor feature sizes results from the photoresist structures becoming so thin in the width direction, e.g. inter-lines distance
19
in
FIG. 1C
, with respect to the photoresist layer thickness that they lack the structural rigidity to withstand the forces induced by surface tension of liquid between them when the surface is dried. Referring to
FIG. 2A
, on top of a substrate
21
a material layer is provided that forms a surface
22
in which it is desired to form a first and second narrow line. A positive photoresist layer
23
is formed over the surface
22
, which is exposed to electromagnetic radiation
28
, such as ultraviolet or actinic light, through openings in opaque material
30
on a mask or reticle
24
. The photoresist layer
23
is then developed with a solution
29
wherein the exposed regions
25
and
27
are removed (when employing a negative photoresist, the unexposed areas are removed), while the unexposed region
26
remains. As shown in
FIG. 2A
, as feature sizes are reduced, the spacings between opaque regions
30
on the mask
24
are reduced, which results in exposed regions
25
,
27
, that are illuminated by light
28
, and unexposed regions
26
both having narrow widths. When developed, the photoresist features
26
are thin to provide a narrow inter-lines distance
34
, and are closely spaced to make the photoresist openings
35
,
37
narrow, as illustrated in
FIGS. 2A and 2B
. As illustrated in
FIG. 2C
, as the photoresist pattern layer dries, a meniscus
31
,
32
,
33
of developer or rinse solution forms in the narrow lines
35
,
37
between adjacent photoresist structures
26
,
38
,
39
, which pulls the structures together due to surface tension. Thin structures of relatively weak photoresist material can collapse under such meniscus forces, as illustrated by photoresist structures
38
and
39
, which renders the pattern on the surface unusable. Furthermore, thin photoresist structures may collapse under capillary forces of the liquid within narrow lines during spin developing or spin rinsing, which involves rapidly revolving a wafer while depositing a solution on the wafer near the axis of revolution so the solution is distributed over the wafer by centrifugal force. Thus, the prior art methods of photolithography cannot form structures below a critical inter-lines dimension which is limited by the mechanical strength of the photoresist.
BRIEF SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided a method of forming a photoresist layer, comprising providing a surface, depositing a photoresist layer on the surface, the photoresist layer having material properties, exposing the photoresist layer through a mask, developing the photoresist layer, and treating the photoresist layer while the photoresist layer is immersed in a liquid to change the photoresist layer's material properties.
According to another aspect of the present invention, there is provided a method of making a semiconductor device, comprising forming at least one semiconductor device on a substrate, forming an insulating layer over the semiconductor device, forming a photoresist layer over the insulating layer, the photoresist layer having material properties, exposing the photoresist layer through a mask, developing the photoresist layer to form an opening in the photoresist layer, treating the photoresist layer while the photoresist material is immersed in a liquid to change the photoresists layer's material properties, forming a narrow line in the insulating layer, and forming a conductive layer in the narrow line.
According to another aspect of the present invention, there is provided a semiconductor device made by using the methods described herein.
According to another aspect of the present invention, there is provided a composition for a photoresist consisting essentially of a matrix material, a sensitizer material, a solv
Bell Scott A.
Lukanc Todd
Lyons Christopher F.
Plat Marina V.
Advanced Micro Devices , Inc.
Barreca Nicole
Foley & Lardner
Huff Mark F.
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