Abstract:
Disclosed is an apparatus and method for yield enhancement of making a semiconductor device. The apparatus for yield enhancement of making a semiconductor device comprises: a semiconductor device comprising an epitaxial layer in which a defect is included, and a photo-resistor on the epitaxial layer and covering the defect; an image recognition system to detect and identify a location of the defect; and an exposing module comprising a first light source to expose a part of the photo-resistor substantially corresponding to the detected defect identified by the image recognition system.

Description:
TECHNICAL FIELD 
     The application relates to an apparatus and method for making a semiconductor device, and more particular to an apparatus and method for yield enhancement of making a semiconductor device by detecting a defect included in an epitaxial layer of the semiconductor device and forming a photo-resist comprising a region substantially corresponding to the detected defect. 
     DESCRIPTION OF BACKGROUND ART 
     Because the petroleum source is limited, various kinds of substitutive energy are developed extensively and turned into products. Among those, the solar cell has become the commercial products for either the industrial or the residential use, and the III-V group material solar cell is mainly applied to the space industry and the industrial field because of its high conversion efficiency. 
     However, there are many kinds of defects existing in/on the epitaxial layer of III-V group material. For example, as shown in  FIG. 1 , a pinhole defect  101  which is usually caused by a dislocation under stress occurs during the epitaxial growth of the III-V group material, and cracks  102  along the lattices also happen, especially in the wafer bonding process or the substrate transferring process. There are other kinds of defects, such as particles on the epitaxial layer or hilllocks which are particles covered by the epitaxial layer and exists in the epitaxial layer. These defects in/on the epitaxial layer result in device problems such as current leakage, and make the photovoltaic device operate abnormally. As the demand for a larger size photovoltaic device increases, the yield loss due to the defect becomes higher. For example, a 4-inch wafer produces only two photovoltaic devices used in aerospace industry, and the defect in/on the epitaxial layer results in 50% yield loss accordingly. In some prior art, a laser is used to burn and remove the defects. However, it is difficult to remove the residual material produced in the laser treatment, and the residual material may also lead to a current leakage. 
     SUMMARY OF THE DISCLOSURE 
     Disclosed is an apparatus and method for yield enhancement of making a semiconductor device. The apparatus for yield enhancement of making a semiconductor device comprises: a semiconductor device comprising an epitaxial layer in which a defect is included, and a photo-resist on the epitaxial layer and covering the defect; an image recognition system to detect and identify a location of the defect; and an exposing module comprising a first light source to expose a part of the photo-resist substantially corresponding to the detected defect identified by the image recognition system. The method for yield enhancement of making a semiconductor device, comprises the steps of: providing a semiconductor device comprising an epitaxial layer in which a defect is included; coating a photo-resist on the epitaxial layer; providing an image recognition system to detect and identify a location of the defect; exposing a part of the photo-resist substantially corresponding to the detected defect identified by the image recognition system; developing to remove the exposed part of the photo-resist; and removing a part of the epitaxial layer where the photo-resist is removed. Also disclosed is a method for yield enhancement of making a semiconductor device, comprising the steps of providing a semiconductor device comprising an epitaxial layer in which a defect is included; providing an image recognition system to detect and identify a location of the defect; forming a photo-resist on the epitaxial layer, wherein a part of the photo-resist is removed to substantially correspond to the detected defect identified by the image recognition system; and removing a part of the epitaxial layer with the photo-resist. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates defects existing in/on the epitaxial layer of III-V group material of a photovoltaic device known in the prior art. 
         FIG. 2A  illustrates the function block diagram of the apparatus in accordance with one embodiment of the present application. 
         FIG. 2B  illustrates the details of a part of the apparatus in  FIG. 2A . 
         FIGS. 3A to 3L  illustrate a method in accordance with one embodiment of the present application. 
         FIG. 4  illustrates the process of the exposing step related to the method in  FIGS. 3A to 3L . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 2A  and  FIG. 2B  illustrate an apparatus in accordance with one embodiment of the present application.  FIG. 2A  shows the function block diagram of the apparatus, and  FIG. 2B  illustrates the details of a part of the apparatus. Please refer to  FIG. 2A . The apparatus  200  is used for detecting a defect included in an epitaxial layer on a substrate of a wafer and forming a photo-resist comprising a region substantially corresponding to the detected defect. The apparatus  200  comprises a coating module  210 , an exposing module  220 , a developing module  230 , and an image recognition system  240 . The apparatus  200  may further comprise a mask-used exposing module  250  to transfer a pattern on a mask, such as cutting lines, to the photo-resist for use in other process. It is noted that the mask-used exposing “module” can also be in the form of an “apparatus” which is associated with the apparatus  200 . Here a “module” means a part of an “apparatus” and provides a specific function in the apparatus when assembled to the apparatus. A module cannot function independently. In contrast, an apparatus can function independently, and can be optionally associated with another apparatus to perform its function. And “associated with” means the electrical signals are exchanged, and sometimes may also mean mechanical connection if necessary. 
     The coating module  210  is used to coat a photo-resist on the epitaxial layer. The exposing module  220  comprising a first light source (not shown) is used to expose a part of the photo-resist. The image recognition system  240  is used to detect the defect and comprises a second light source  241 , an image sensor  242 , and a comparison unit  243 . It is noted that the image recognition system  240  can be set inside the exposing module  220  or a different module separated from the exposing module  220 . In another embodiment, only some elements of the image recognition system  240  such as the second light source  241  and the image sensor  242  are inside the exposing module  220 , and the electrical signals can be exchanged between the image recognition system  240  and the exposing module  220 . In the case that the whole image recognition system  240  is set inside the exposing module  220  or in the case that some elements of the image recognition system  240  are set inside the exposing module  220 , the defect detecting and the exposing step can be performed substantially at the same time. That is, the defect is detected by the image recognition system  240  and the part of the photo-resist substantially corresponding to the defect detected is exposed by the exposing module  220  immediately. When the image recognition system  240  is not in a module separated from the exposing module  220 , the time interval between the finish of defect detecting and the actuation of the exposing step is very short because there is not time spent on wafer transferring between two separated modules. If the image recognition system  240  is set inside a module separated from the exposing module  220 , the wafer may be first loaded into the module where the image recognition system  240  is set inside to detect the defect, and then the information of the location of the defect detected is sent to the exposing module  220  to which the wafer is then transferred, and the part of the photo-resist substantially corresponding to the defect detected is exposed accordingly. 
     As mentioned above, the apparatus  200  may further comprise a mask-used exposing module  250  or be associated with a mask-used exposing apparatus  250  to transfer a pattern on a mask to the photo-resist. A part of the photo-resist corresponding to the pattern in the mask may be optionally exposed by the mask-used exposing module (or apparatus)  250  before the detecting step or after the exposing step. The part of the photo-resist corresponding to the pattern in the mask together with the exposed part of the photo-resist substantially corresponding to the defect detected may be removed later in a developing step. The developing module  230  is used to develop the exposed photo-resist so the part of the photo-resist exposed by the first light source in the exposing module  220  and the part exposed by the mask-used exposing module (or apparatus)  250  are removed after the developing. 
     Please refer to  FIG. 2B . The left part of the figure illustrates the details of the image recognition system  240  and some parts of the exposing module  220 . The right part of the figure illustrates the mask-used exposing module (or apparatus)  250 . The image recognition system  240  comprises elements enclosed by the broken line, i.e. the second light source  241 , the image sensor  242 , and the comparison unit  243 , and the exposing module  220  comprises a first light source  221  and a platform  222 . As mentioned above, the figure shows the case which the whole image recognition system  240  is set inside the exposing module  220  and the electrical signals of the image recognition system  240  and the exposing module  220  are exchanged so that the detecting of the defect and the exposing step are performed substantially at the same time. A wafer  201  is loaded into the exposing module  220  and disposed on a platform  222  of the exposing module  220 . The platform  222  carries the wafer  201  and moves under the first light source  221  of the exposing module  220  and the second light source  241  and the image sensor  242  of the image recognition system  240 . The second light source  241  provides illumination for image recognition and is different from the first light source  221  used for exposing. For example, when the photo-resist is a positive type photo-resist, the first light source is UV light which causes the positive type photo-resist to have a chemical reaction, and the second light source is non-UV light which provides illumination for image recognition and does not cause the positive type photo-resist to have a chemical reaction. The image sensor  242  is used to capture an image of a pattern on the epitaxial layer on the wafer  201 . The image sensor  242  comprises, for example, a CCD (Charge-coupled Device) or a CMOS image sensor. The comparison unit  243  is used to compare the image of the pattern captured by the image sensor  242  with a pre-determined pattern stored in the comparison unit  243  for determining whether the pattern is a defect or not. The whole image recognition system  240  is set inside the exposing module  220  and the electrical signals of the image recognition system  240  and associated with the exposing module  220  are exchanged so that the detecting of the defect and the exposing step are performed substantially at the same time. That is, the wafer  201  is moved to be scanned by the image sensor  242 , and when a defect is determined by the comparison unit  243 , a signal from the comparison unit  243  is transferred to the exposing module  220  so that the first light source  221  is actuated to expose the part of the photo-resist substantially corresponding to the defect detected. 
     In addition, as mentioned in  FIG. 2A , the wafer  201  may be optionally transferred to the mask-used exposing module (or apparatus)  250  before the detecting step or after the exposing step. It is noted that when the wafer  201  is transferred to the mask-used exposing module (or apparatus)  250  before the detecting step, the wafer  201  is transferred directly from the coating module  210  after the aforementioned coating step. 
     The mask-used exposing module (or apparatus)  250  comprises a mask table  253  on which a mask  202  is disposed, a platform  252  on which the wafer  201  is disposed on, and a light source  251 . A part of the photo-resist corresponding to a pattern in the mask  202  may be optionally exposed by the mask-used exposing module (or apparatus)  250  with the light source  251  before the detecting step or after the exposing step. The light source  251  may be the same as the first light source  221 , i.e. UV light. The pattern in the mask  202  comprises, for example, cutting lines around a solar cell chip. 
       FIGS. 3A to 3L  illustrate a method in accordance with one embodiment of the present application. The method is used for removing a defect from an epitaxial layer on a substrate of a wafer and can be further used for forming a photovoltaic device. The method may be carried out with the utilization of the apparatus as previously illustrated in  FIGS. 2A and 2B . 
     As shown in  FIG. 3A , the method comprises providing a wafer comprising a substrate  301  on which an epitaxial stack  302  is formed first. The epitaxial stack  302  comprises a plurality of layers of III-V group material to form at least one p-n junction of a solar cell. The epitaxial stack  302  comprises a defect  302   d . The defect  302   d  may be any one of those illustrated in  FIG. 1 . In  FIG. 3B , a photo-resist  300   r  is coated on the epitaxial stack  302  by the aforementioned coating module  210 . The wafer is then transferred to the aforementioned mask-used exposing module (or apparatus)  250  directly from the coating module  210  after the coating step. As mentioned above, this embodiment illustrates a case which a mask-used exposing is performed before a defect detecting step. The defect detecting step will be illustrated later in  FIG. 3C . In the embodiment, a mask  300 M is used, and the pattern in the mask  300 M, which is a pattern for cutting lines  300 MC around a solar cell chip, is transferred to the photo-resist  300   r  with an exposing by light (as the arrows shows) from the light source  251  of the mask-used exposing module (or apparatus)  250  shown in  FIG. 2B . The exposed pattern  300   rc  in the photo-resist  300   r  is used for forming the cutting lines in the wafer as will be illustrated later in  FIG. 3E . 
     As shown in  FIG. 3C , this embodiment illustrates a case which the detecting of the defect and an exposing step are performed substantially at the same time by using the apparatus shown in  FIG. 2B , and the wafer is transferred to the aforementioned exposing module  220  and a defect detecting step is performed. The wafer is scanned by the aforementioned image sensor  242  with the illumination provided by light from the second light source  241 . And once a defect, for example, the defect  302   d  is detected, the first light source  221  is actuated to expose the part of the photo-resist  300   rd  which is substantially corresponding to the defect detected. The first light source  221  used for exposing is different from the second light source  241  for image recognition. For example, the photo-resist  300   r  in this embodiment is a positive type photo-resist, and the first light source  221  is UV light which causes the positive type photo-resist  300   r  to have a chemical reaction, and the second light source  241  is non-UV light which provides illumination for image recognition and does not cause the positive type photo-resist to have a chemical reaction. The process of the exposing step is illustrated in  FIG. 4 . In  FIG. 4 , the light from the first light source  221  is projected onto the defect and forms a spot as denoted as a circle. The wafer is moved as the aforementioned platform  222  carrying the wafer moves, and spots are formed upon the wafer. In this example, as mentioned previously in  FIG. 1 , two kinds of defects, i.e., a pinhole defect  101  and cracks  102  are shown, and the area of these defects forms a defect area. The spots as denoted are formed substantially along the contour of the defect area and cover the whole defect area. Finally, the collection of these circles forms the exposed part as denoted by the solid line in the figure to cover the defect area. The area of the exposed part is substantial the same as or a little larger than the defect area. It is noted that the information of the location of the defect detected may be stored in the same apparatus or sent to another apparatus for a later use. 
     And then as shown in  FIG. 3D , the wafer is transferred to the aforementioned developing module  230 , and the photo-resist  300   r  is developed to remove the exposed part of the photo-resist  300   r  so that a subsequent etch process is performed with the developed photo-resist  300   r  as a mask to remove the part of the epitaxial layer where the photo-resist is removed. The result after the etch process is shown in  FIG. 3E  where an empty part  302   d ′ substantially corresponding to the defect  302   d  detected and an empty part  302   c  corresponding to a cutting line are formed in the epitaxial stack. The etch process may be a dry etch or a wet etch, and the photo-resist  300   r  is removed after the etch process. Then as shown in  FIGS. 3F to 3J , a dielectric material is formed substantially in the region where the epitaxial stack  302  is removed; in other words, a dielectric material is formed in the empty part  302   d ′ and the empty part  302   c  shown in  FIG. 3E . As shown in  FIG. 3F , a dielectric layer  303  is formed. The dielectric layer  303  may be, for example, alumina, titanium dioxide, silicon nitride (SiN x ) or silicon oxide (SiO x ). In  FIG. 3G , a negative photo-resist  300 R is coated on the dielectric layer  303 , and an exposing is performed on the photo-resist  300 R with a mask  300 M 2 . The area of the pattern  300 M 2 C may be a little larger than the area of the pattern  300 MC in  FIG. 3B . The exposing can be performed by the mask-used exposing module (or apparatus)  250 . Since the photo-resist  300 R is a negative type, as will be illustrated in  FIG. 3I , the exposed part is left as a remaining part after developing. And then in  FIG. 3H , the information of the location of the defect detected stored as previously mentioned in  FIG. 3C  is used so that an exposing step may be carried out accordingly. The area of the exposed part can be substantial the same as or a little larger than the area of the empty part  302   d ′ shown in  FIG. 3E . As a result, as shown in  FIG. 3I , after a developing step, a first remaining part  300 RD substantially corresponding to the area of the defect  302   d  detected and a second remaining part  300 RC corresponding to cutting lines of the negative photo-resist  300 R are formed on the dielectric layer  303 . And then in  FIG. 3J , an etch process is performed to remove the part of the dielectric layer  303  uncovered by the first remaining part  300 RD and the second remaining part  300 RC of the photo-resist  300 R, and dielectric material  303 D and  303 C is formed substantially in the region where the epitaxial layer is removed. The etch process may be a dry etch or a wet etch, and first and second remaining parts  300 RD and  300 RC of the photo-resist are removed after the etch process. The dielectric material  303 D is formed in the region corresponding to the empty part  302   d ′ in  FIG. 3E  which is removed for the defect  302   d , and the dielectric material  303 C is formed in the region corresponding to empty part  302   c  in  FIG. 3E  which is removed for the cutting lines  303   c . The dielectric material  303 D provides an electrical isolation to the sidewalls of the empty part  302   d ′, and therefore avoids forming a current leakage path or the failure of the p-n junction in the epitaxial stack  302 . In addition, when an electrode passes or is located on the empty part  302   d ′, the dielectric material  303 D provides an electrical isolation between the electrode and the junction to avoids a shortage. 
     As shown in  FIG. 3K , an anti-reflective layer  304 , the first electrode  305 , and the second electrode  306  are subsequently formed. The main portion of the anti-reflective layer  304  is formed on the epitaxial stack  302  while a portion of the anti-reflective layer  304  is formed on the dielectric material  303 D to fill the concave part caused by the empty part  302   d ′ in  FIG. 3E  with the dielectric material  303 D formed thereon. The first electrode  305  is formed in the anti-reflective layer  304  and on the epitaxial stack  302 . The second electrode  306  is formed on the surface of substrate  301  opposite to the surface on which the epitaxial stack  302  is disposed. And in  FIG. 3L , as mentioned above, the cutting lines are formed around a solar cell chip, and the substrate  301  is cut along the cutting lines as indicated by the line LL′ to form the solar cell chips. 
     It is noted that the process flow shown in this embodiment may be adjusted by the person of the skill in the art. For example, though the cutting line pattern, i.e. the mask-used exposing, is performed before the detecting step in this embodiment, it is apparent that the mask-used exposing may be performed after the detecting step. Besides, the coating step may be performed after the detecting step. For example, the wafer may be first loaded to an separated module where the image recognition system  240  is set inside (or the exposing module  220  comprising an image recognition system set inside it) to have the detecting step performed, and then the wafer is transferred to the coating module  210  to have the coating step performed. And finally the stored information of the location of the detected defect is used in the exposing module  220  to have the exposing step performed accordingly after the coating step. Similarly, the order for the wafer to be transferred between different modules in the apparatus may be designed by the person of the skill in the art accordingly as the above illustration. In addition, though the four modules are integrated in one apparatus as shown in  FIG. 2A , one or more modules may be separated and formed as an independent apparatus by the person of the skill in the art. It is also noted that application of the apparatus and the method illustrated in the present application is not limited to a photovoltaic device, and can be commonly used for a semiconductor device, such as an LED. The yield of the semiconductor device is enhanced by detecting and removing the defect included in an epitaxial layer of the semiconductor device and forming a dielectric material in the region where the epitaxial layer is removed to provide an electrical isolation and avoid problems such as current leakage. 
     The above-mentioned embodiments are only examples to illustrate the principle of the present invention and its effect, rather than be used to limit the present invention. Other alternatives and modifications may be made by a person of ordinary skill in the art of the present application without escaping the spirit and scope of the application, and are within the scope of the present application.