Abstract:
The present invention provides a method for detecting instantaneously a flare noise within patterns of a semiconductor device, including the steps of: A method for detecting a flare noise in a semiconductor device, comprising the steps of: preparing a mask having a plurality of expose-areas having different light energy-levels when photo exposing and a plurality of dummy patterns with different sizes for detecting flare noises in each expose-area; forming dummy patterns on a wafer through a photolithography process with the mask; and detecting the flare noise by comparing the dummy patterns in each expose-area with optical microscope.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a method for detecting a flare noise of a photo exposure equipment; and, more particularly, to a method for detecting a flare noise of a semiconductor device capable of an instantaneous detection through the use of the Kirk&#39;s method or modifications of a mask layout.  
         DESCRIPTION OF RELATED ARTS  
         [0002]    Generally, flare noise is a kind of light noise that wonders around a lens with regardless of a light passing through a mask pattern due to defects in a lens of a photo exposure equipment itself or scatterings at an incomplete anti-reflective coating (hereinafter referred as to ARC) or a mask and becomes an incident light to a wafer. Especially, an illumination optic mainly causes this flare noise since it is relatively not processed with a complete ARC process compared to a projection optic.  
           [0003]    Also, the flare noise is observed when the incident light gets scattered because of the above-described unstable lens elements. Moreover, the flare noise causes an increase in intensity of an overall light and an irregular distribution of light, which, in turn, result in a decrease in contrast of the Aerial image or an excessive photo exposure at an overly exposed open area of the mask. Therefore, there is ultimately observed decreases in uniformity of critical dimension (hereinafter referred as to CD) and a process margin.  
           [0004]    The flare noise at the photo exposure equipment has been a known problem; however, the flare noise is currently considered as a main cause of the decrease in the uniformity of the CD and the process margin since design rules for a semiconductor device have recently reached its limitation and uniformities of the CD and illumination recently are emphasized extensively in today.  
           [0005]    Meanwhile, among methods for detecting the flare noise, there has been commonly employed a method wherein a device is inspected with a predetermined period by using a specific function included in a photo exposure equipment or a test mask. The firefly method and the Kirk&#39;s method are the most well-known methods for detecting the flare noise.  
           [0006]    Unfortunately, since the above two representative methods are highly complex, the inspection period cannot be shortened into a preset extent of time. Also, even if the flare noise occurs, it is detected after damages of patterns are already taken place in a number of devices. Hence, it is required to develop a new innovative method for complementing the existing detection methods.  
         SUMMARY OF THE INVENTION  
         [0007]    It is, therefore, an object of the present invention to provide a method for detecting a flare noise of a semiconductor device capable of an instantaneous detection at a semiconductor pattern.  
           [0008]    In accordance with an aspect of the present invention, there is provided a method for detecting a flare noise in a semiconductor device, comprising the steps of: preparing a mask having a plurality of expose-areas having different light energy levels when photo exposing and a plurality of dummy patterns with different sizes for detecting flare noises in each expose-area; forming dummy patterns on a wafer through a photolithography process with the mask; and detecting the flare noise by comparing the dummy patterns in each expose-area with optical microscope.  
           [0009]    Preferably, at the step of duplicating the dummy pattern to the wafer, the light energy level of incident lights for each area vary in accordance with the number of superposed shots. Areas where the shots are superposed include scribe lanes, and the dummy pattern is formed in a shape of square. Also, the step of detecting the flare noise includes further steps of: preparing first relation among the flare noise, a variation of energy and a fitting coefficient from sample dummy patterns having same size, wherein the fitting coefficient denotes variations of the flare noise according the variation of the energy; preparing second relations among a specific energy, the fitting coefficient and the size of dummy patterns which are not formed or deformed at the specific energy; finding a specific fitting coefficient corresponding the specific energy and the size of dummy patterns which are not formed or deformed from the second relations by comparing the dummy patterns in each expose-area with optical microscope; and finding the flare noise corresponding the specific coefficient from the first relations.  
           [0010]    It is generally thought to observe continuously a critical dimension (CD) affected by the flare noise at a real pattern. However, use of this method that employs a precision CD measuring equipment causes a problem in decreasing overall yields of semiconductor devices. Accordingly, it is necessary to put efforts to develop the kirk&#39;s method on a mask of a semiconductor device, wherein a simple maneuvering of an optical microscope is applied for detecting the flare noise. In connection with this aim, the present invention provides a method for detecting the flare noise by using the mask layout and a characteristic of superposition of neighboring shots when photo-exposing through the use of a photo exposure equipment. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING(s)  
       [0011]    The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:  
         [0012]    [0012]FIG. 1 is a schematic diagram for describing a flare noise phenomenon that occurs due to stray lights at an image plane;  
         [0013]    [0013]FIG. 2 is a schematic diagram depicting block sizes of the kirk&#39;s split for describing the Kirk&#39;s method;  
         [0014]    [0014]FIG. 3 is a plane view illustrating a mask layout for embodying the Kirk&#39;s method at the mask in accordance with a preferred embodiment of the present invention; and  
         [0015]    [0015]FIG. 4 is a graph showing a relationship between block size and light exposure energy in accordance with the Kirk&#39;s method. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    Other objects and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter.  
         [0017]    [0017]FIG. 1 is a schematic diagram for describing a flare noise phenomenon occurring due to stray lights at an image plane. Additionally, it should be noted that the flare noise occurs when a light reaches to undesignated areas in addition to an originally designated areas, and thus, is different from diffraction.  
         [0018]    With reference to FIG. 1, the vertical axis represents light energy (E) whereas the horizontal axis represents each designated area for the light energy (E). As shown in FIG. 1, such stray light denoted as ‘B’ causes the light energy (E) to be arrived at an area ‘D’, where it is to shied the arrival of E, instead of an area ‘C’ where E should be arrived. Hence, it is preferable that the light energy (E) should have a value of ‘0’ at the area ‘D’; however, the energy level graphed in FIG. 1 shows that there presents the light energy with a level of ‘A’ because of the stray light.  
         [0019]    [0019]FIG. 2 is a schematic diagram illustrating block sizes of the Kirk&#39;s split for describing the Kirk&#39;s method. Referring to FIG. 2, in the Kirk&#39;s method, a mask is formed by splitting each block with a predetermined size. In this case, sizes of the splitted blocks disappearing at a particular area with a specific light energy vary in accordance with amounts of the flare noise. At this time, the flare noise can be expressed in a relationship of the disappearing block size against a particular light energy level, and this relationship is expressed as the following equation.  
           F (Flare noise)[%] E 0 /Ex ×100   Eq. 1  
         [0020]    Herein, E0 represents a basic energy required for all photo registry patterns to be disappeared in a state of non-blocking while Ex represents an energy required for a block with a size ‘x’ to be disappeared by the flare noise when the block of which size is ‘x’ is in a blocking state. In addition, ‘x’ is a box size wherein the flare noise is saturated by being distinguished from diffraction, and a DRAM process commonly uses a value of the box size in a range from about 5 μm to about 1 μm.  
         [0021]    The most difficult problem in implementing the Kirk&#39;s method on the mask for developing an actual device is to set an appropriate light energy and attain a sufficient space for inserting the splitted blocks. The reason for this problem is because the light energy of the mask for use of the actual device is determined by the device pattern unlike from the Kirk&#39;s method wherein an arbitrary determination of the light energy is applied.  
         [0022]    However, it is still possible to obtain a minimum area and a necessary energy level through the appropriate use of a mask layout and an exposure mode of a photo exposure equipment. The present invention is to provide splits released by the Kirk&#39;s method, i.e., dummy patterns that can be established on an actual mask.  
         [0023]    To accomplish this establishment, there are used a light energy of incident lights having a plurality of different areas during photo exposure and a mask having a plurality of the dummy patterns with different sizes for detecting the flare noise at each designated area in accordance with the Kirk&#39;s method.  
         [0024]    Referring to FIG. 3, if it is assumed that reference numerals  30 A to  30 D represent areas of the patterns, each being duplicated by one application of a photo exposure, i.e., shots, the unit light energy ‘E’ attained by one application of the photo exposure in these areas will be investigated and a region including the areas, that is, the unit energy ‘E’ with respect to the photo exposure area X for one application of the photo exposure will also be investigated.  
         [0025]    Meanwhile, since there is an error within a blade of the photo exposure equipment itself, a region other than a main pattern for a device layout, e.g., a scribe lane is made to perform the photo exposure by superposing the neighbored shots  30 A to  30 D. In accordance with the preferred embodiment of the present invention, the reference numeral ‘Y’ in FIG. 3 is superposed and photo exposed when performing the photo exposure to the neighboring two shots  30 A and  30 B. Accordingly, ‘Y’ is doubly photo exposed, and thus, it becomes the photo exposure area of two applications wherein twice of the unit light energy ‘2E’ is inputted.  
         [0026]    Also, the reference numeral ‘Z’ in FIG. 3 is superposed and photo exposed when four neighboring shots  30 A to  30 D are photo exposed, and thus, the photo exposure on ‘Z’ occurs four times, resulting in the photo exposure area of four applications wherein four times of the unit light energy ‘4E’ is inputted.  
         [0027]    Hence, the above described light energy, i.e., ‘E’, ‘2E’ and ‘4E’ will be investigated at the region ‘X’, ‘Y’ and ‘Z’, respectively. In case that appropriate block sizes, that is, dummy patterns having various sizes are inserted into the regions ‘Y’ and ‘Z’, it is possible to detect the flare noise through combinations of the light energy ‘E’, ‘2E’ and ‘4E’ with each dummy patterns.  
         [0028]    Hereinafter, a method for calculating the block size of the dummy pattern mandated to be inserted into each light energy level and a method for calculating the flare noise through the above method will be described in more detail.  
         [0029]    [0029]FIG. 4 shows a relationship between the block size having a square shape and the light energy, and the following equation expresses this relationship. Also, the block size is expressed in a log scale.  
         Log(block size)= A *Exp( B *Energy)   Eq. 2  
         [0030]    Herein, ‘A’ and ‘B’ express fitting coefficients. As an example, the light energy in the preferred embodiment of the present invention is fixed with a level of ‘E’, ‘2E’ and ‘4E’. According to experimental data, it is analyzed that the fitting coefficient ‘A’ nearly does not affect changes of other variables and is possible to become a constant as in an average value. In this case, it is also possible to set a relationship between the size of the disappearing dummy pattern and the fitting coefficient ‘B’. For instance, if the dummy pattern size is fixed in a size of about 5 μm, the light energy with respect to the fitting coefficient ‘B’ can be calculated and this value is related to a value for the flare noise.  
         [0031]    The following Table 1 shows a relationship between the fitting coefficient ‘A’ or ‘B’ and the flare noise F while Table 2 shows a relationship between the fitting coefficient and the fixed light energy. Herein, the unit light energy E is set with a value of 50.  
                                                     TABLE 1                       A   B   Size (μm)   E   F                                0.035   0.01   5   299.43   3.67       0.035   0.012   5   249.52   4.41       0.035   0.014   5   213.88   5.14       0.035   0.016   5   187.44   5.88       0.035   0.018   5   166.35   6.62       0.035   0.02   5   149.71   7.35       0.035   0.022   5   136.10   8.08       0.035   0.024   5   124.76   8.82       0.035   0.026   5   115.16   9.55       0.035   0.028   5   106.94   10.29       0.035   0.03   5   99.81   11.02       0.035   0.032   5   93.57   11.76                  
 
         [0032]    [0032]                                     TABLE 2                       E   Size (μm)   B                                200   1.2   0.0041       200   1.5   0.0081       200   2   0.0108       200   3   0.0131       200   4   0.0142       200   5   0.0150       200   6   0.0155       200   7   0.0159       200   8   0.0163       100   1.2   0.0082       100   1.5   0.0162       100   2   0.0215       100   3   0.0261       100   4   0.0285       100   5   0.0299       100   6   0.0310       100   7   0.0318       100   8   0.0325       50   1.2   0.0163       50   1.5   0.0323       50   2   0.0430       50   3   0.0522       50   4   0.0569       50   5   0.0599       50   6   0.0620       50   7   0.0637       50   8   0.0650                    
         [0033]    For example, if the dummy patterns with a size of about 7 μm disappeared or about to be disappeared in the light energy of ‘4E’, that is, in a value of 200, Table 2 is referred to determine a value of the fitting coefficient ‘B’ with inputted values of 200 for the light energy ‘4E’ and 7 μm for the dummy pattern size.  
         [0034]    At this time, Table 2 provides the value of 0.0159 for the fitting coefficient ‘B’, and then, the closest value to this determined fitting coefficient ‘B’ is retrieved in Table 1. Since the closet value of the fitting coefficient ‘B’ in Table 1 is 0.016, a value for the flare noise is determined to be 5.88%. In Table 1, 5 μm is set to be a referential dummy pattern size.  
         [0035]    As another example for determining the fitting coefficient and the flare noise, if the dummy patterns with a size of about 8 μm are all disappeared in the light energy of ‘4E’ that is, in a value of 200, then values of the fitting coefficient ‘B’ with respect to each dummy pattern size are retrieved from a next light energy level ‘2E’, i.e., a value of 100 in Table 2. At this time, in case that the dummy pattern of which size is about 5 μm disappears in the light energy level ‘100’, the fitting coefficient ‘B’ has a value of 0.0299. With reference to this obtained fitting coefficient value, the flare noise is determined to be 10.29% in Table 1. Also, if the flare noise becomes greater than about 10%, a photo exposure equipment is required to be compensated.  
         [0036]    In other words, when detecting the flare noise, a closest fitting coefficient ‘B’ is firstly retrieved among the areas in a sequential order from the area having the highest light energy level according to the dummy pattern size and the light energy by referring to Table 2 including the fitting coefficient with respect to the dummy pattern size and the light energy. Then, with use of the retrieved fitting coefficient ‘B’ and the dummy pattern size, values for the fitting coefficient and the flare noise are retrieved again from Table 1.  
         [0037]    This procedure can be operated with a simple real time scheme through the use of an optical microscope without employing a scanning electron microscope (SEM).  
         [0038]    In summary, the preferred embodiment of the present invention uses a characteristic of the superposition between neighboring shots when photo exposing a mask layout of a device and a photo exposure equipment. At these superposed areas, e.g., scribe lanes, dummy patterns corresponding to split blocks having different sizes are formed in accordance with the Kirk&#39;s method. It is also possible to check instantaneously disappearances of the dummy patterns allocated at each different area, which result in subsequent disappearances of light energy, through the use of an optical microscope when photo exposing. Therefore, it is not required to put additional efforts for equipment maintenance and equipment inspection time, and a flare noise effect can also be minimized.  
         [0039]    In other words, by following the preferred embodiment of the present invention, it is possible to detect instantaneously the flare noise of the photo exposure equipment from a wafer of a semiconductor device. Because of this ability in the instantaneous detection, such additional efforts for equipment maintenance and equipment inspection time are not required and it is also possible to minimize the flare noise effect of the semiconductor device.  
         [0040]    While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.