Exposure mask and method of forming a contact hole of a semiconductor device employing the same

An exposure mask and a method of forming a contact hole of a semiconductor device using the same, in which micro patterns can be formed are disclosed herein. In an aspect, an exposure mask method includes a mask substrate, a light-shield pattern formed on the mask substrate, and a transparent pattern in which a plurality of patterns, which are limited to the light-shield pattern and have different short-direction widths and long-direction widths, form a group which is repeatedly arranged. Accordingly, micro photoresist patterns can be formed uniformly.

CROSS-REFERENCE TO RELATED APPLICATION

The priority of Korean patent application number 10-2007-44116, filed on May 7, 2007, the disclosure of which is incorporated by reference in its entirety, is claimed.

BACKGROUND OF THE INVENTION

The invention relates, in general, to semiconductor devices and, more particularly, to an exposure mask and a method of forming a contact hole of a semiconductor device using the same, in which micro patterns can be formed.

In processes for manufacturing semiconductor devices, a variety of patterns for forming a bit line contact holes, drain contact holes, and so forth are formed by photolithography processes. In such a photolithography process, a photoresist pattern is formed on a wafer by coating a photoresist layer and exposing and developing the photoresist layer employing an exposure mask reticle. Desired patterns are formed by an etch process using the photoresist pattern as a mask. The exposure mask is fabricated by forming a nontransparent chrome pattern on a transparent substrate, such as a quartz substrate. In order to form contact holes having a cross section of the same size and shape, transparent patterns that are opened only in the nontransparent chrome pattern must have the same size and shape.

However, the photoresist pattern formed on the wafer through the photolithography process is greatly distorted compared with a pattern formed in the exposure mask. Distortion is generated by an optical proximity effect in which light passing through the exposure mask pattern generates interference between neighboring patterns in the photolithography process. The optical proximity effect becomes profound when the size of a pattern to be resolved is smaller than that of the wavelength of a light source. Accordingly, there is a problem when the critical dimension of the contact hole pattern formed in the semiconductor substrate is smaller than that of a desired pattern.

FIG. 1is a scanning electron microscope (SEM) photograph of photoresist patterns of 60 nm in size, which are formed by using an exposure mask having transparent patterns with the same shape and size.

As shown inFIG. 1, even though photoresist patterns having the transparent patterns with the same shape and size have been used, they are distorted and very irregular. The irregular photoresist patterns are further distorted as the size decreases. This problem must be solved in order to fabricate high-integrated semiconductor devices.

SUMMARY OF THE INVENTION

Accordingly, the invention provides an exposure mask and a method wherein uniform and micro photoresist patterns can be formed by performing a photolithography process on a photoresist by using an exposure mask including transparent patterns in which a group, formed by a plurality of patterns having the same cross-sectional area but different widths or lengths, is repeatedly arranged.

One aspect of the invention provides an exposure mask including a mask substrate, a light-shield pattern formed on the mask substrate, and a transparent pattern in which a plurality of patterns, which are limited to the light-shield pattern and have different short-direction widths and long-direction widths, form a group, which is repeatedly arranged. Accordingly, micro photoresist patterns can be formed more uniformly.

In another aspect, the invention, provides a method of forming a contact hole of a semiconductor device, including the steps of forming an etch-stop layer, an insulating layer, a hard mask, and a photoresist over a semiconductor substrate, patterning the photoresist by employing an exposure mask including a transparent pattern in which a plurality of patterns having different short-direction widths and long-direction widths form a group which is repeatedly arranged, patterning the hard mask by employing the photoresist, etching the insulating layer and the etch-stop layer by employing the hard mask, and forming a contact hole through the exposed semiconductor substrate.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Specific embodiments according to the invention are described below with reference to the accompanying drawings.

FIG. 2Ais a plan view of an exposure mask for illustrating an embodiment of patterns of an exposure mask, which are formed according to an embodiment of the invention.

Referring toFIG. 2A, an exposure mask312can be formed by forming a light-shield pattern316made of nontransparent material through which an exposure light source used in a photolithography process cannot transmit, such as chromium, on the surface of a mask substrate314made of a transparent material through which an exposure light source cannot transmit, such as SiO2. A plurality of regions where the light-shield pattern316is not formed in the mask substrate314become a plurality of first transparent patterns318aand second transparent patterns318b.

The centers of the first transparent pattern318aand the second transparent pattern318bare formed to match to (e.g., coincide with) the centers of regions where drain contact holes are formed in a subsequent process. The first transparent pattern318aand the second transparent pattern318bhave different widths and lengths. A pair of the first transparent pattern318aand the second transparent pattern318bform a group.

Alternatively, the first transparent pattern318aand the second transparent pattern318bcan have the same width. A short-direction width of the first transparent pattern318ais preferably 1 to 20% shorter than half the pitch between the first transparent pattern318aand the second transparent pattern318b, whereas a short-direction width of the second transparent pattern318bis preferably 1 to 20% longer than half the pitch between the first transparent pattern318aand the second transparent pattern318b. Further, a long-direction width of the first transparent pattern318aand a long-direction width of the second transparent pattern318bare preferably are formed such that the first transparent pattern318aand the second transparent pattern318bhave the same measure of cross-sectional area. Thus, the long-direction width of the first transparent pattern318ais further longer than that of the second transparent pattern318b. The short-direction width and the long-direction width of the first transparent pattern318aconstructed above can have a difference of 2 nm or more. Furthermore, the short-direction width and the long-direction width of the second transparent pattern318bpreferably have a difference of 2 nm or more.

The first transparent pattern318aand the second transparent pattern318b, forming one group, are preferably spaced apart from an adjacent group by a distance L, which is twice the pitch1between the first transparent pattern318aand the second transparent pattern318b. A plurality of groups formed by the first transparent pattern318aand the second transparent pattern318bare repeatedly arranged to form one row. Furthermore, columns in which the plurality of first transparent patterns318aand second transparent patterns318bare alternately formed are arranged on and below the row in which the plurality of first transparent patterns318aand second transparent patterns318bare alternately formed, thus forming the transparent pattern of the exposure mask312.

FIG. 2Bis a plan view of an exposure mask for illustrating another embodiment of patterns of an exposure mask, which are formed according to another embodiment of the invention.

Referring toFIG. 2B, in an exposure mask312, a plurality of regions where a light-shield pattern316is not formed in a mask substrate314become a plurality of first transparent patterns318aand second transparent patterns318b. The first transparent pattern318aand the second transparent pattern318bhave different widths and lengths. A pair of the first transparent pattern318aand the second transparent pattern318bforms a group.

Alternatively, the first transparent pattern318aand the second transparent pattern318bcan have the same width. A short-direction width of the first transparent pattern318ais preferably 1 to 20% shorter than half the pitch between the first transparent pattern318aand the second transparent pattern318b, whereas a short-direction width of the second transparent pattern318bis preferably 1 to 20% longer than half the pitch between the first transparent pattern318aand the second transparent pattern318b. Further, a long-direction width of the first transparent pattern318aand a long-direction width of the second transparent pattern318bare preferably formed such that the first transparent pattern318aand the second transparent pattern318bhave the same area. Thus, the long-direction width of the first transparent pattern318ais further longer than that of the second transparent pattern318b. The short-direction width and the long-direction width of the first transparent pattern318aconstructed above preferably have a difference of 2 nm or more. Furthermore, the short-direction width and the long-direction width of the second transparent pattern318bpreferably have a difference of 2 nm or more.

The first transparent pattern318aand the second transparent pattern318b, forming one group, are preferably spaced apart from each other by a distance L, which is twice the pitch1between the first transparent pattern318aand the second transparent pattern318b. A plurality of groups of first transparent patterns318aand second transparent patterns318bare repeatedly arranged to form one row. Furthermore, columns of transparent patterns in each of which one of the first transparent pattern318aand the second transparent pattern318bis deviated is arranged in plural numbers on and below the row in which the plurality of first transparent patterns318aand second transparent patterns318bare alternately formed, thus forming the transparent pattern of the exposure mask312.

Although a pair of two transparent patterns with different sizes may form one group, three or more transparent patterns can form one group. In this type of embodiment, the transparent patterns forming one group can have the same cross-sectional area, and a long-direction width and a short-direction width of each of the transparent patterns can have a gradually increasing or decreasing size, for example.

FIG. 3is a layout diagram for illustrating a method of forming a contact hole of a semiconductor device using the exposure mask according to an embodiment of the invention.

Referring toFIG. 3, a plurality of isolation regions101and active regions102are alternately formed on a specific region of a semiconductor substrate. In this case, the isolation regions101and the active regions102are parallel to each other. An isolation layer (not shown) is formed in the isolation region101, and a structure, such as a junction region (not shown) including a drain/source region and a gate (not shown), is formed in the active region102.

An insulating layer (not shown) is formed on the structure formed in the active region102. Part of the insulating layer is etched to form a drain contact hole through which the underlying drain region is exposed. A conductive material is formed in the drain contact hole, forming a drain contact plug103so that the bottom is connected to the drain region. A metal line is formed on the drain contact plug103to connect the drain region and the metal line.

An embodiment of the foregoing process of forming the drain contact hole103is described in more detail below.

FIGS. 4A and 4Bare cross-sectional views illustrating a method of forming a contact hole of a semiconductor device using an exposure mask according to an embodiment of the invention. In particular,FIG. 4illustrates a cross-sectional view of the semiconductor device taken along line A-A′ ofFIG. 3.FIG. 5is a plan view of a photoresist pattern patterned by a photolithography process employing the exposure mask of the invention.

Referring toFIG. 4A, a plurality of isolation layers302parallel to each other are formed in specific regions of a semiconductor substrate300including a cell region and a peri region, thus defining active regions. The cell region includes a plurality of strings. Each string includes a source select transistor (not shown), a plurality of memory cells (not shown) and a drain select transistor (not shown), which are connected in series. A peri transistor is formed in the peri region.

An ion implantation process is then performed on the entire surface including the transistors and the memory cells, so that a source region (not shown) is formed in the semiconductor substrate300at one side of the source select transistor and a drain region304in the semiconductor substrate300at one side of the drain select transistor. A junction region (not shown) is also formed between the memory cells.

Drain contact holes that are formed with different widths in a subsequent process form a pair, and the pair is repeatedly formed. Thus, the width of the drain region304can be preferably formed to correspond to the drain contact holes formed on the drain region304.

An etch-stop layer305and a first insulating layer306aare formed over the entire surface including the semiconductor substrate300. The first insulating layer306ais etched to form the source contact hole (not shown). The first insulating layer306acan be formed of an oxide layer. After a conductive material is formed in the source contact hole, and a polishing process, such as chemical mechanical polishing (CMP), is performed to form the source contact plug (not shown).

A second insulating layer306bis formed on the first insulating layer306aincluding the source contact plug. A hard mask308is formed on the second insulating layer306b. In this case, an etch-stop layer (not shown) can be further formed below the hard mask308. A photoresist layer is then formed on the hard mask308.

Thereafter, the exposure mask312formed as described above is disposed over the photoresist layer, which is then patterned by a photolithography process. In this case, the exposure mask312can be disposed between an exposure light source and the photoresist layer when the photolithography process is performing in order to selectively expose the surface of the photoresist layer. A development process is then performed on the exposed photoresist layer, forming a photoresist pattern310.

As shown inFIGS. 4A,4B, and5, the transparent patterns318aand318bhave a square or other rectangular shape, but the photoresist pattern310has an oval or circular shape due to interference and diffraction phenomena. Furthermore, the photoresist pattern310includes a plurality of pairs of open regions, each having a different short-direction width and long-direction width by means of the transparent patterns318aand318b. That is, the open region of the photoresist pattern310formed by the first transparent pattern (refer to318aofFIG. 2B) has a narrow transverse width and a wide longitudinal width, whereas the open region of the photoresist pattern310formed by the second transparent pattern (refer to318bofFIG. 2B) has a wide transverse width and a narrow longitudinal width compared with the open region of the photoresist pattern310formed by the first transparent pattern (refer to318aofFIG. 2B). This is because the first transparent pattern318aand the second transparent pattern318bhaving different transverse widths have effects on each other, such as assist hole effects, and pattern the photoresist. However, since the first transparent pattern (refer to318aofFIG. 2B) and the second transparent pattern (refer to318bofFIG. 2B), which form one group, have the same cross-sectional area, the open region of the photoresist pattern310forming one group has the same cross-sectional area.

Referring toFIG. 4B, the hard mask308is etched by an etch process employing the photoresist pattern (refer to310ofFIG. 4A), thus forming a hard mask pattern308a. An open region having a different short-direction width and long-direction width is also formed in each hard mask pattern308adue to the open region of the photoresist pattern310having a different short-direction width and long-direction width. The photoresist pattern310is then removed. The second insulating layer306b, the first insulating layer306aand part of the etch-stop layer305are etched by an etch process employing the hard mask pattern308a, thus forming drain contact holes320aand320bthrough which the drain region304formed in the semiconductor substrate302is exposed. In this case, the first drain contact hole320ahaving a narrow short-direction width and the second drain contact hole320bhaving a wide short-direction width due to the hard mask pattern308aare consecutively formed while forming one group. However, since the patterns forming one group have the same cross-sectional area in the above patterning process, the entire drain contact holes including the first drain contact hole320aand the second drain contact hole320bhave the same cross-sectional area.

In the etch process performed to form the first drain contact hole320aand the second drain contact hole320b, the etch process is performed on the basis of the first drain contact hole320aon which the etch process is performed slowly compared with the second drain contact hole320bdue to the narrow short-direction width. At this time, the second drain contact hole320bcan be prevented from being over-etched by forming the etch-stop layer305thicker.

Thereafter, though not shown in the drawings, conductive material is formed in the first drain contact hole320aand the second drain contact hole320bto form contact plugs electrically connected to the underlying drain region304. In this case, since the first drain contact hole320aand the second drain contact hole320bformed by the above process have the same cross-sectional area, the entire contact plugs are formed to have the same cross-sectional area. Thus, since the contact plugs have different sectional shapes, but have the same contact resistance Rs, semiconductor device characteristics may not be degraded. However, contact plugs forming a part can have different cross-sectional areas to the extent that the operating characteristics of the semiconductor device are not degraded.

Meanwhile, an example in which the drain contact holes are formed has been described above. However, the invention is not limited to the example, but can be applied to all processes of forming contact holes of semiconductor devices, such as bit line contact holes.

As described above, according to the invention, a photolithography process is performed on a photoresist by using an exposure mask including a transparent pattern in which a plurality of patterns having the same cross-sectional areas, but different long-direction widths and short-direction widths form a group and the group is repeatedly arranged. Accordingly, micro photoresist patterns can be formed uniformly.

Although the foregoing description has been made with reference to the specific embodiments, changes and modifications of the invention may be made without departing from the spirit and scope of the invention.