Abstract:
A method for leveling a wafer in a photolithography apparatus is disclosed, including inputting a wafer into the photolithography apparatus to be supported by a chuck, using at least three image capture devices to capture images of corresponding alignment marks on the wafer; and leveling the wafer according to the clarity of the images of the corresponding alignment marks on the wafer captured by the image capture device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to a photolithography apparatus, and more particularly relates to a method for leveling a semiconductor wafer during the photolithography process. 
         [0003]    2. Description of the Related Art 
         [0004]    Various techniques have previously been used to manufacture integrated circuits on semiconductor wafers. Optical projection lithography using ultra-violet light is one of the more common techniques. Projection lithography techniques use a mask which is several times larger than the integrated circuit. The pattern or circuit is projected from a distance onto a photoresist on a semiconductor wafer. 
         [0005]    A photolithography apparatus operates by projecting an image containing a portion of an integrated circuit onto chips on a semiconductor wafer by using a mask or exposure field. Before exposure of the photolithography process, it is required that the wafer for the mask be leveled and the wafer be parallel. 
         [0006]      FIG. 1A˜FIG .  1 C show a leveling procedure of a conventional SUSS aligner tool. As shown in  FIG. 1A , the wafer  102  leveling method is accomplished by wedge error compensation (WEC), which includes small balls  106  substantially having diameters of about 2 mm, disposed on a chuck  108 . As shown in  FIG. 1B , after the wafer  102  is set on the chuck  108 , the chuck  108  rises till the balls  106  touch the mask  104  for leveling the wafer  102 , while assuming that the mask  104  and the wafer  102  are parallel with each other. Next, referring to  FIG. 1C , the chuck  108  moves down and then rises again to set up an exposure procedure. However, the wafer  102  leveling method has some drawbacks. Referring to  FIG. 1D , during exposure, the wafer  102  is coated with a photoresist, and when the photoresist is not coated uniformly and particles  110  are disposed thereon, the wafer  102  leveling method may cause particles  110  or photoresist to stick onto the mask  104 . The conventional photolithography apparatus cannot eliminate the preceding drawback. 
         [0007]    In addition, as the line width for integrated circuits used in semiconductor devices becomes smaller and smaller, accuracy of the leveling of the ball, which is at the mm level, cannot meet requirements of device processes requiring a minimum exposure gap of about 10 μm. Therefore, a novel method for leveling a wafer and photolithography with a leveling element are required. 
       BRIEF SUMMARY OF INVENTION 
       [0008]    According to the issues described, the invention provides a method for leveling a wafer in a photolithography apparatus, comprising inputting a wafer into the photolithography apparatus to be supported by a chuck, using at least three image capture devices to capture images of corresponding alignment marks on the wafer; and leveling the wafer according to the clarity of the images of the corresponding alignment marks on the wafer captured by the image capture device. 
         [0009]    The invention further provides a photolithography apparatus with a novel element or procedure for leveling a wafer, comprising a chuck for supporting a wafer; and at least three image capture devices for capturing images of corresponding alignment marks on the wafer arranged at three corners of the chuck in a triangular state. The three image capture devices are wafer leveling elements of the photolithography apparatus. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0011]      FIG. 1A˜FIG .  1 C show a leveling procedure of a conventional SUSS aligner tool. 
           [0012]      FIG. 1D  shows an issue of a conventional SUSS aligner tool. 
           [0013]      FIG. 2A˜FIG .  2 B show a method for leveling a semiconductor wafer during the photolithography process of an embodiment of the invention. 
           [0014]      FIG. 2C  show a schematic plan view of arrangement of cameras of an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0015]    The following description is of the contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense, not for limiting the invention. 
         [0016]      FIG. 2A˜FIG .  2 B show a method for leveling a semiconductor wafer  208  during the photolithography process of an embodiment of the invention. First, referring to  FIG. 2A  and  FIG. 2C , wherein  FIG. 2C  shows a schematic plan view of arrangement of cameras  202 , at least three cameras  202  are disposed over a mask  204  and a wafer  208  in the photolithography apparatus, and specifically the three cameras  202  are arranged at three corners of the chuck (not shown) in a triangular state. Referring to  FIG. 2A , before the exposure step, the mask  204  is inputted into the lithography apparatus and is aligned using the cameras  202  to find the positions of the alignment mark  206  on the mask  204 . Next, referring to  FIG. 2B , the mask  204  is removed and then the wafer  208  is inputted. The wafer  208  is aligned using the cameras  202  to find the positions of the alignment mark  206  on the wafer  208 , and the wafer  208  is substantially leveled according to focus of the alignment marks  210  on the wafer  208  captured by the cameras  202 . In an embodiment of the invention, the wafer  208  is aligned and leveled simultaneously using the cameras  202  capturing the images the alignment marks  210  on the wafer  208 . The detailed procedure for leveling the wafer  208  on the chuck will be discussed below. 
         [0017]    After the wafer  208  is inputted into the photolithography apparatus, the cameras  202  focus on the alignment marks  210  on the wafer  208  and the clarity of the picture of the alignment marks  210  captured by the cameras  202  are defined by degree. For example, the embodiment would be set if clarity of the picture of the alignment mark  210  captured by the cameras  202  is over 80 degrees. Following, the photolithography apparatus will receive a signal from a computer which represents that the alignment mark  210  on the wafer  208  is in the focus d range. Alternatively, if the clarity of the picture of the alignment mark  210  captured by the cameras  202  is not over 80 degrees, it represents that the alignment mark  210  is not in focus and the photolithography apparatus will receive a signal which represents that the alignment mark  210  on the wafer  208  is not in the focus d range. Therefore, the computer will inform the chuck to adjust the wafer  208 . Furthermore, when all of the three cameras  202  capture clear pictures of the three alignment marks  210  on three corners of the wafer  208 , which means that clarity of the three picture will all be over 80 degrees, the photolithography apparatus will receive a signal which represents that the wafer  208  is to be leveled. Meanwhile, when clarity of at least one or two of the three pictures is not over 80 degrees, it represents that the wafer  208  is still not leveled and the computer will inform the chuck to adjust the wafer  208 . It is noted that the focus range d of the camera  202  is about 20 μm which is much less than the diameters of the leveling balls. Hence, the precision of the leveling method of the embodiment can be greatly improved to meet requirements of devices. 
         [0018]    After leveling the wafer, the mask can be inputted into the photolithography apparatus, and the chuck would move down and then rises again to set up exposure. Next, an exposure step is performed to transfer pattern from the mask to the layers on the wafer. It is noted that the procedure in the paragraph is a standard photolithography process and is not described in further detail. 
         [0019]    The embodiment of the invention at least has the following advantages. The embodiment of the invention does not require balls to be mounted on the WEC component to touch the mask, such that when uniformity of the wafer or the layer on the wafer is not good, or some particles have fallen on the wafer, stick issues should not occur. Further, the embodiment uses focus of cameras to check and level the wafer. Since focus of cameras is μm level, the embodiment has better precision and sensitivity than the conventional art. 
         [0020]    While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.