Semiconductor device manufacturing: process – Chemical etching – Combined with coating step
Reexamination Certificate
2000-06-01
2002-12-24
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Chemical etching
Combined with coating step
C438S702000, C438S703000, C438S717000, C438S724000, C438S725000, C438S754000, C438S757000
Reexamination Certificate
active
06498105
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of fabricating semiconductor devices and, more particularly, to a method of forming fine patterns of semiconductor devices.
2. Description of the Related Art
There is currently a great amount of research in methods for forming fine patterns of semiconductor devices and photomasks necessary therefore because semiconductor devices are becoming more highly integrated. Presently, a phase shift mask process is widely used to form fine patterns of semiconductor devices because it is highly effective in forming periodic patterns. However, elaborate techniques are required to form a phase shift mask, and it is expensive to fabricate the phase shift mask, moreover, phase shift mask processes do not effectively form aperiodic patterns. Thus, processes using a phase shift mask are inappropriate for forming fine aperiodic or abnormal patterns at low cost. Since, pattern density increases as integration increases and pattern abnormalities increase as pattern density increases, pattern abnormalities in semiconductor devices increase with the increased integration thereof.
FIG. 1
is a plan view partially showing a conventional photomask
1
. Here, reference numerals
5
and
7
denote a cell array region having high pattern density and a peripheral circuit region having low pattern density, respectively.
Referring to
FIG. 1
, adjacent contact hole patterns
3
are two-dimensionally separated by a predetermined distance d in the cell array region
5
. On the other hand, contact hole patterns
3
in the peripheral circuit region
7
are two-dimensionally separated by a distance which is wider than the predetermined distance d.
FIG. 2A
is a cross-sectional view of the photomask
1
shown in
FIG. 1
taken along line A-A′.
FIG. 2B
is a graph of the light intensity of light beams passing through the contact hole patterns
3
of the photomask
1
shown in FIG.
2
A.
FIG. 2C
is a cross-sectional view of a profile of a photoresist pattern
26
formed in accordance with the light intensity of the graph shown in FIG.
2
B. Here, reference characters
5
and
7
denote the cell array region
5
and the peripheral circuit region
7
of
FIG. 1
, respectively.
Referring to
FIGS. 2A
,
2
B and
2
C, an interdielectric layer
23
is formed on a semiconductor substrate
21
, and an etch mask layer
25
having a high selectivity with respect to the interdielectric layer
23
is formed on the interdielectric layer
23
. A photoresist layer
26
is formed on the etch mask layer
25
, and the photoresist layer
26
is exposed to ultraviolet light using the photomask
1
and light
20
shown in FIG.
2
A. The photomask
1
is composed of a transparent substrate
22
and an opaque material pattern
24
formed in a predetermined region on one side of the transparent substrate
22
. The opaque material pattern is made of a chrome pattern. The opaque material pattern
24
is formed in the regions between the plurality of contact hole patterns
3
shown in FIG.
1
. That is, the opaque material pattern
24
is formed by removing material or preventing the formation of material where the contact hole patterns
3
are transcribed thereon, thereby defining holes where the contact hole patterns are transcribed.
As described above, light
20
passes through the transparent substrate
22
and through the contact hole patterns
3
of the opaque material pattern
24
when the light
20
radiates the photomask
1
. The light which passes through the transparent substrate
22
and the contact hole patterns
3
exposes a predetermined region of the photoresist layer
26
formed on the semiconductor substrate
21
. The diffraction or interference effect on the light beams passing through the transparent substrate
22
and contact hole patterns
3
is more severe as the distance d between adjacent holes in the contact hole pattern
3
decreases. The etch mask layer
25
is formed on the interdielectric layer
23
and acts as an antireflection layer, but the diffraction and interference effects cannot be overcome.
Thus, as shown in
FIG. 2B
, light beams irradiate some of the region under the opaque material pattern
24
. As a result, the portion of the photoresist pattern
26
corresponding to the contact hole patterns
3
formed in the cell array region
5
are inaccurately formed. Thus, when the etch mask layer
25
and the interdielectric layer
23
are etched using the photoresist pattern
26
as a mask, contact holes having an inaccurate profile are formed in the cell array region
5
.
In the conventional art, when the sizes or shapes of patterns of the photomask
1
are different, it is difficult to optimize profiles of all patterns formed on the semiconductor substrate. For example, when patterns having various sizes or shapes are mixed in the photomask
1
, it is difficult to optimize profiles of all patterns. This is because conditions of the photo process, for example, conditions of exposure and development, must be changed in accordance with the size or the shape of the pattern.
The present invention is directed to overcoming or at least reducing the effects of one or more of the problems set forth above.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention there is provided a photomask for forming fine patterns capable of optimizing the profiles of all patterns formed in a high pattern density region. More specifically, there is provided a photomask for forming fine patterns by etching one material layer formed on a semiconductor substrate. The photomask for forming fine patterns includes at least two sub-photomasks. Each of the sub-photomasks is composed of one transparent substrate and patterns on one side of the transparent substrate. All of the patterns to be formed can be thought of as an entire set of patterns which are split into subsets of patterns. The union of the subset of patterns is the entire set of patterns. Each sub-photomask is transcribed with a corresponding subset of patterns. The patterns of one sub-photomask correspond to one of the groups obtained by classifying a group of patterns finally formed on the semiconductor substrate. For instance, when the photomask is composed of two sub-photomasks, patterns on a substrate of the first sub-photomask (i.e., patterns of a first group) are patterns obtained by transcribing some of the entire set of patterns. The patterns on a substrate of the second sub-photomask (i.e., patterns of the second group) are patterns obtained by transcribing the entire set of patterns with the exception of the patterns of the first group.
In accordance with another aspect of the present invention, at least one of the patterns on one sub-photomask may overlap with at least one of the patterns on another sub-photomask. The overlapped pattern may correspond to a pattern such as an alignment key, which is difficult to completely pattern with one photo process.
In a further aspect of the present invention, when the sizes of the patterns in the entire set of patterns are the same, the minimum distance between patterns on the substrate of each of the sub-photomasks is wider than the minimum distance among the entire set of patterns. Thus, when the photo process is performed using each of the sub-photomasks, the distance between patterns is increased, so that the interference and/or diffraction effect of light beams can be remarkably suppressed.
In accordance with yet another aspect of the present invention, when there are two different shapes of patterns in the entire set of patterns, patterns of the same shape are transcribed on a substrate of one sub-photomask. For instance, when the entire set of patterns are classified into two kinds of shapes, i.e., rectangular patterns and regular square patterns, the rectangular patterns are transcribed on the substrate of one sub-photomask and regular square patterns are transcribed on the substrate of another sub-photomask. Here, the rectangular pattern may be a pattern for forming an interconnection of
Keshavan Belur
Smith Matthew
LandOfFree
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