Phase shift mask for double patterning and method for exposing wafer using the same

A phase shift mask includes a substrate; a first phase shift pattern formed in a groove shape having a first depth within the substrate so that when a first light with a first wave length is incident, the first light transmitted through a surface of the substrate and the first light transmitted through the groove are destructively interfered and when a second light with a second wave length is incident, the second light transmitted through the surface of the substrate and the second light transmitted through the groove have a phase difference of 180 degrees; and a second phase shift pattern formed in a groove shape having a second depth within the substrate so that when the first light with the first wave length is incident, the first light transmitted through the surface of the substrate and the first light transmitted through the groove have a phase difference of 180 degrees and when the second light with the second wave length is incident, the second light transmitted through the surface of the substrate and the second light transmitted through the groove are destructively interfered.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Korean patent application number 10-2008-0038912, filed on Apr. 25, 2008, which is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a photolithography, and more particularly, to a phase shift mask for double patterning and a method for exposing a wafer using the same.

As semiconductor devices are highly integrated, it is more and more difficult to form a fine pattern due to a resolution limit in a photolithography process. That is to say, although a size of the pattern required in the semiconductor device becomes finer and finer, a photolithography technology cannot keep up with the trend that the size of the pattern becomes finer.

In order to overcome such resolution limit in the exposure, there has been suggested Double Patterning Technology (DPT) using two masks. The DPT is a method that divides the entire pattern which should be included in one mask into two masks and transfers the entire pattern through two-time photolithography process using respective masks. Since this exposure using the DPT performs two-time photolithography process using two masks, registration of the mask in an exposure apparatus is a very important factor. In other words, the patterns respectively disposed in the two masks can be transferred onto a wafer with accurate distance only when the two masks in which the pattern is divisionally disposed are registered at exactly the same position in the exposure apparatus. However, it is not easy to perform accurately such mask registration. Also, when the registration error is more than a certain level, a distance between the pattern transferred through a first mask and the pattern transferred through a second mask is excessively narrowed or broaden, which may result in pattern defects.

SUMMARY OF THE INVENTION

In one embodiment, a phase shift mask includes a substrate; a first phase shift pattern formed in a groove shape having a first depth within the substrate so that when a first light with a first wave length is incident, the first light transmitted through a surface of the substrate and the first light transmitted through the groove are destructively interfered and when a second light with a second wave length is incident, the second light transmitted through the surface of the substrate and the second light transmitted through the groove have a phase difference of 180 degrees; and a second phase shift pattern formed in a groove shape having a second depth within the substrate so that when the first light with the first wave length is incident, the first light transmitted through the surface of the substrate and the first light transmitted through the groove have a phase difference of 180 degrees and when the second light with the second wave length is incident, the second light transmitted through the surface of the substrate and the second light transmitted through the groove are destructively interfered.

In another embodiment, a method for exposing a wafer using a double patterning technology includes disposing a phase shift mask over a wafer within an exposure apparatus, the phase shift mask having a first phase shift pattern within a substrate formed in a groove having a first depth in which a destructive interference is generated with respect to a first light with a first wave length and a second phase shift pattern within the substrate formed in a groove having a second depth in which a destructive interference is generated with respect to a second light with a second wave length which differs from the first wave length; transferring the second phase shift pattern onto the wafer by exposing the first light with the first wave length to be incident to the phase shift mask; and transferring the first phase shift pattern onto the wafer by exposing the second light with the second wave length to be incident to the phase shift mask.

DESCRIPTION OF SPECIFIC EMBODIMENTS

FIGS. 1A and 1Billustrate respectively a cross-sectional view and a plan view of a phase shift mask for double patterning according to an embodiment of the present invention, and a cross-sectional structure taken along line A-A′ inFIG. 1Bis shown inFIG. 1A. Referring toFIGS. 1A and 1B, the phase shift mask includes a substrate100and a first phase shift pattern121and a second phase shift pattern122disposed within the substrate100. The first phase shift pattern121and the second phase shift pattern122are preferably disposed so as to be adjacent to each other. The substrate100is a transparent substrate such as quartz. The first phase shift pattern121is formed in a groove shape having a first depth h1from a surface of the substrate100, and the second phase shift pattern122is formed in a groove shape having a second depth h2from the surface of the substrate100. As such, as the first phase shift pattern121and the second phase shift pattern122are formed in the groove shape, there occurs a phase difference of a predetermined angle, e.g. 180 degree between a light transmitted through the surface of the substrate100and a light transmitted through the first phase shift pattern121and the second phase shift pattern122. A mask pattern110is disposed over the surface of the substrate100and this mask pattern110exposes, by a predetermined area, the surface of the substrate100in the vicinity of the first phase shift pattern121and the second phase shift pattern122. The area of the exposed surface of the substrate100is determined by the mask pattern110, and proper control of this area can increase contrast in the exposure process using the phase shift mask. A mask pattern110is formed of a chrome layer or a molybdenum silicon layer.

The first depth h1of the first phase shift pattern121is set so that when a first light with a first wave length is incident, the first light transmitted through the surface of the substrate100and the first light transmitted through the first phase shift pattern121are destructively interfered. Specifically, the first depth h1of the first phase shift pattern121is determined by an equation h1=A×(λ1/2(n−1)), wherein in this equation, A is an odd number for inducing the destructive interference, λ1is the first wave length and n is a refractive index of the substrate100. The second depth h2of the second phase shift pattern122is set so that when a second light with a second wave length is incident, the second light transmitted through the surface of the substrate100and the second light transmitted through the second phase shift pattern122are destructively interfered. Specifically, the second depth h2of the second phase shift pattern122is determined by an equation h2=A×(λ2/2(n−1)), wherein in this equation, A is an odd number for inducing the destructive interference, λ2is the second wave length and n is a refractive index of the substrate100. Preferably, the first depth h1of the first phase shift pattern121is set so that when the second light with the second wave length is incident, the second light transmitted through the surface of the substrate100and the first light transmitted through the first phase shift pattern121are constructively interfered. The second depth h2of the second phase shift pattern122is set so that when the first light with the first wave length is incident, the first light transmitted through the surface of the substrate100and the second light transmitted through the second phase shift pattern122are constructively interfered. In this case, when the first light with the first wave length is incident to the phase shift mask, the first light passing through the first phase shift pattern121is destructively interfered with the first light transmitted through the surface of the substrate100, but the first light passing through the second phase shift pattern122is constructively interfered with the first light transmitted through the surface of the substrate100. Therefore, the second phase shift pattern122alone is transferred onto the wafer. When the second light with the second wave length is incident to the phase shift mask, the second light passing through the first phase shift pattern121is constructively interfered with the second light transmitted through the surface of the substrate100, but the second light passing through the second phase shift pattern122is destructively interfered with the second light transmitted through the surface of the substrate100. Therefore, the first phase shift pattern121alone is transferred onto the wafer.

The phase shift mask of such structure can perform the exposure with application of the double patterning without mask replacement, which will be described in more detail with reference toFIGS. 2A to 3B.

Referring first toFIG. 2A, a phase shift mask1000is disposed over a wafer2000within an exposure apparatus. The phase shift mask1000may have the same structure as described with reference toFIGS. 1A and 1B, and therefore duplicate description will not be made. The wafer2000has a structure in which a pattern target layer210is disposed over a substrate200and a photoresist layer220to be exposed is coated over the pattern target layer210, but not particularly limited thereto.

A first exposure uses a first light with a first wave length λ1. To this end, the first light130with the first wave length λ1is incident to the phase shift mask1000. The first light130with the first wave length λ1may be divided into a first light131passing through where a surface of a substrate100, a first light132passing through the first phase shift pattern121and a first light133passing through the second phase shift pattern122. When the first light130passes through the mask1000, as indicated by a reference symbol “3000” in the figure, an intensity of the first light132transmitted through the first phase shift pattern121becomes close to 0, but the intensity of the first light133transmitted through the second phase shift pattern122is amplified. Therefore, the second phase shift pattern122alone is transferred onto the photoresist layer220.

More specifically, since the first light130has the first wave length λ1, the first light131transmitted through the surface of the substrate100adjacent to the first phase shift pattern121and the first light132transmitted through the first phase shift pattern121are destructively interfered. Therefore, the first phase shift pattern121is not transferred onto the photoresist layer220. On the contrary, the first light131transmitted through the surface of the substrate100adjacent to the second phase shift pattern122and the first light133transmitted through the second phase shift pattern122show the phase difference of 180° without the destructive interference and the second phase shift pattern122is thus transferred onto the resist layer220. As the result of performing such first exposure, as shown inFIG. 2B, a second exposed region222corresponding to the second phase shift pattern122is formed over the photoresist layer220.

Next, referring toFIG. 3A, a second exposure uses a second light with a second wave length λ2. To this end, the second light140with the second wave length λ2is incident to the phase shift mask1000. The second light140with the second wave length λ2may be divided into a second light141passing through where a surface of a substrate100, a second light142passing through the first phase shift pattern121and a second light143passing through the second phase shift pattern122. When the second light140passes through the mask1000, as indicated by a reference symbol “4000” in the figure, an intensity of the second light142transmitted through the first phase shift pattern121is amplified, but the intensity of the second light143transmitted through the second phase shift pattern122becomes close to 0. Therefore, the first phase shift pattern121alone is transferred onto the photoresist layer220.

More specifically, since the second light140has the second wave length λ2, the second light141transmitted through the surface of the substrate100adjacent to the second phase shift pattern122and the second light142transmitted through the second phase shift pattern122are destructively interfered. Therefore, the second phase shift pattern122is not transferred onto the photoresist layer220by the second exposure using the second light140with the second wave length λ2. On the contrary, the second light141transmitted through the surface of the substrate100adjacent to the first phase shift pattern121and the second light143transmitted through the first phase shift pattern121show the phase difference of 180° without the destructive interference and the first phase shift pattern121is thus transferred onto the resist layer220. As the result of performing such second exposure, as shown inFIG. 3B, a first exposed region221corresponding to the first phase shift pattern121is formed over the photoresist layer220in a region adjacent to the second exposed region222formed by the first exposure.

Although a distance between the first exposed region221and the second exposed region222is such a fine distance that cannot be accurately realized using standard photolithography due to its resolution limit, the first exposed region221and the second exposed region222of the fine distance can be formed by forming the exposed region221and the second exposed region222separately through the first exposure using the first light with the first wave length λ1and the second exposure using the second light with the second wave length λ2. In addition, by performing the first exposure and the second exposure using a single mask, the problem of registration error between masks generated when using two masks can be prevented from the beginning.

FIG. 4illustrates a cross-sectional view of patterns formed using the wafer exposure method according to an embodiment of the present invention. Referring toFIG. 4, a development process is performed on the photoresist layer220, in which the first exposed region221and the second exposed region222are formed by the first exposure and the second exposure, to form a first photoresist layer pattern223and a second photoresist layer pattern224respectively corresponding to the first exposed region221and the second exposed region222. Subsequently, by etching the exposed portion of the pattern target layer210using the first photoresist layer pattern223and the second photoresist layer pattern224as an etching mask, the first pattern211and the second pattern212having fine distance are formed over the substrate200.