Abstract:
An exposure method is disclosed. A wafer coated with a photoresist layer having an exposure threshold dose is provided. The wafer has at least a central region and a peripheral region. Then, a compensating light beam having a first dose directs on the photoresist layer within the peripheral region. Next, a patterned light beam having a second dose is then projected, in a step-and-scan manner, onto the photoresist layer, thereby exposing the photoresist layer. The total dose of the first energy and the second energy is above than the exposure threshold dose.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an exposure method used in the semiconductor process, more particularly to an exposure method which can correct the variation of the after-etch-inspection critical dimension (AEICD). 
     2. Description of the Prior Art 
     Lithography process is an important step in the transfer of the circuit pattern onto the substrate. After the photoresist is exposed to a patterned light beam and developed and after the substrate is etched, the substrate not covered by the photoresist is removed. In this way, the pattern can be transferred onto the substrate. 
     However, during the etching process, including wet etching and dry etching, due to the loading effect, the etching rate of the die region near the periphery of the wafer is different from the etching rate of the die region near the center of the wafer. Therefore, the after-etch-inspection critical dimension (AEICD) will vary in the die region located in different positions of the wafer. Accordingly, in the semi-conductor field, one of the challenges is to improve the AEICD uniformity. 
     SUMMARY OF THE INVENTION 
     It is therefore an objective of the present invention to provide an exposure method to correct the variation of the AEICD caused by the loading effect. 
     According to a preferred embodiment of the present invention, an exposure method includes: initially, a wafer covered by a photoresist layer having an exposure threshold dose is provided, and the wafer includes a center region and a peripheral region surrounding the center region, wherein the peripheral region is free of overlapping the center region. Next, a compensating light beam having a first dose is directed onto the photoresist layer within the peripheral region. Then, a die region positioned in both the center region and the peripheral region is provided. Finally, a patterned light beam having a second dose is projected, in a step-and-scan manner, onto the photoresist layer, whereby the photoresist layer in the die region is exposed, wherein both the compensating light beam and the patterned light beam are directed onto the photoresist layer within the die region. 
     According to another preferred embodiment of the present invention, an exposure method, includes: first, a wafer covered by a photoresist layer having an exposure threshold dose is provided, and the wafer comprises a center region and a peripheral region surrounding the center region, wherein the peripheral region is free of overlapping the center region. After that, a first stage radiation is processed by directing a compensating light beam having a first dose onto the photoresist layer within the peripheral region. Finally, a second stage radiation is processed by projecting a patterned light beam having a second dose onto the photoresist layer, wherein the total dose of the first dose and the second dose is above than the exposure threshold dose of the photoresist layer. 
     According to another preferred embodiment of the present invention, an exposure method, includes: initially, a wafer covered by a photoresist layer is provided, and the wafer comprises a die region, wherein the die region comprises a first area and a second area, and the first area is free of overlapping the second area. Then, a first stage radiation is processed by directing a compensating light beam having a first dose onto the photoresist layer within the first area and the second area. Finally, a second stage radiation is processed by projecting a patterned light beam having a second dose onto the photoresist layer within the first area and the second area. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a feedback controlling system in accordance with the first embodiment of the present invention. 
         FIG. 2   a  shows a first stage radiation process: directing a compensating light beam having a first dose onto the wafer according to the first embodiment of the present invention. 
         FIG. 2   b  shows a second stage radiation process: projecting a patterned light beam having a second dose onto the wafer according to the first embodiment of the present invention. 
         FIG. 3  depicts diagrams illustrating the relation between the dimension of the ADICD and the dose distribution of two-stage radiation according to the first embodiment of the present invention. 
         FIG. 4   a  shows a first stage radiation process: directing a compensating light beam having a first dose onto the wafer according to a second embodiment of the present invention. 
         FIG. 4   b  shows a second stage radiation process: projecting a patterned light beam having a second dose onto the wafer according to a second embodiment of the present invention. 
         FIG. 5  depicts diagrams illustrating the relation between the dimension of the ADICD and the dose distribution of two-stage radiation according to the second embodiment of the present invention. 
         FIG. 6  shows a side view of the wafer having a plurality of circular regions. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic drawing illustrating a top view of a wafer. As shown in  FIG. 1 , a wafer  10  covered by a photoresist layer  11  having an exposure threshold dose is provided. The wafer  10  is divided into a plurality of die regions each including a plurality of dies. For example, a first die region  12  is positioned at the periphery of the wafer  10  and a second die region  14  (surrounded by a bold line) is positioned in the center of the wafer  10 . The first die region  12  and the second die region  14  do not overlap with each other. Furthermore, the wafer  10  is divided into a peripheral region  13  (marked by dots) and a center region  15  (marked by oblique lines). The peripheral region  13  and the center region  15  do not overlap with each other and the peripheral region  13  surrounds the center region  15 . In addition, at least a part of the first die region  12  overlaps the peripheral region  13 . The peripheral region  13  is a region influenced by the loading effect. According to a preferred embodiment of the present invention, the peripheral region  13  is a circular region positioned at the periphery of the wafer. 
       FIG. 2   a  shows a first stage radiation process: directing a compensating light beam having a first dose onto the wafer according to the first embodiment of the present invention.  FIG. 2   b  shows a second stage radiation process: projecting a patterned light beam having a second dose onto the wafer according to the first embodiment of the present invention. 
     Please refer to  FIG. 1 ,  FIG. 2   a  and  FIG. 2   b  together. As shown in  FIG. 2   a , the exposure method according to the first embodiment of the present invention has the steps as follows: initially, the wafer  10  is performed a first-stage radiation. During the first-stage radiation, a compensating light beam  16  having a first dose is directed onto the photoresist layer  11  within the peripheral region  13  and the center region  15 . The main purpose of the compensating light beam  16  is not for exposure. In other word, the compensating light beam directs onto the photoresist layer  11  without blocking. 
     The feature of the first embodiment of the present invention is that the first dose of the compensating light beam  16  in the center region  15  is uniform. The first dose of the compensating light beam  16  in the peripheral region having a distribution that gradually decreases from point B which is near the center of the wafer  10  along the direction of a radius of the wafer  10  to the point A which is near the edge of the wafer  10 . Furthermore, a part of the first die region  12  overlaps with the center region  15  and the peripheral region  13 , such as an overlapping region  20  (marked by a circle) which represents a die. A first area  21  in the overlapping region  20  is the overlapping part of the first die region  12  and of the peripheral region  13 . A second area  23  in the overlapping region  20  is the overlapping part of the first die region  12  and of the center region  15 . The first dose is uniform in the second area  23  and the first dose in the second area  23  is the same as that in the center region  15 . However, the first dose varies with the position of the first area  21  on the wafer  10 . Furthermore, the first dose of the compensating light beam  16  is less than the exposure threshold dose of the photoresist layer  11 . 
     Then, as shown in  FIG. 2   b , the wafer  10  undergoes a second-stage radiation. During the second-stage radiation, a light beam  18  having a second dose projects onto the photoresist layer  11  within the first die region  12  and the second die region  14  in a step-and-scan manner. The purpose of the light beam  18  is for patterning. That is to say, the light beam  18  passes though a photomask (not shown) to pattern the photoresist layer  11 . In addition, the second dose of the light beam  18  is uniform in the peripheral region  13  and the center region  15 . The second-stage radiation is preferably performed in a scanning machine. The first-stage radiation can be performed in a scanning machine or in other exposure machines. 
       FIG. 3  depicts diagrams illustrating the relation between the dimension of the ADICD and the dose distribution of two-stage radiation according to the first embodiment of the present invention. 
     As shown in  FIG. 3 , after the first stage radiation and the second stage radiation, the total dose of the first dose and the second dose in the center region  15  is uniform, and the total dose of the first dose and the second dose in the peripheral region  13  has a distribution that gradually decreases from point B to point A. Therefore, after the photoresist is developed, the after development inspect critical dimension (ADICD) in the peripheral region  13  has a distribution that will gradually increase from a region near the center of the wafer along the direction of a radius of the wafer. That is to say, the ADICD distribution will gradually increase from point B to point A. In this way, the variation of AEICD in the peripheral region  13  and the center region  15  due to loading effect can be compensated before the etching process. Accordingly, the AEICD will be uniform in the peripheral region  13  and the center region  15 . 
     Moreover, the compensating light beam  16  and the light beam  18  have the same wave length. The second dose can be more or less than the threshold dose of the photoresist layer  11 . As long as the total dose of the first dose and the second dose is above than the exposure threshold dose of the photoresist layer  11 . 
     According to a variation of the first embodiment, the first-stage radiation can be performed by projecting the light beam  18  onto the first die region  12  and the second die region  14  of the wafer  10  in a step-and-scan manner. The second-stage radiation can be performed by directing the compensating light beam  16  onto the photoresist layer  11  of the wafer  10 . 
     According to the second embodiment of the present invention, another exposure method is provided in the present invention. Unlike the first embodiment, the compensating light beam in the peripheral region has a distribution that gradually increases from a region near the center of the wafer along the direction of a radius of the wafer in the second embodiment. The elements with the same function in the second embodiment will use the same numeral as that in the first embodiment. 
       FIG. 4   a  shows a first stage radiation process: directing a compensating light beam having a first dose onto the wafer according to the second embodiment of the present invention.  FIG. 4   b  shows a second stage radiation process: projecting a patterned light beam having a second dose onto the wafer according to the second embodiment of the present invention. 
     Please refer to  FIG. 1 ,  FIG. 4   a  and  FIG. 4   b  together. As shown in  FIG. 4   a , the exposure method according to the second embodiment of the present invention has the steps as follows: initially, the wafer  10  undergoes a first-stage radiation. During the first-stage radiation, a compensating light beam  16  having a first dose is directed onto the photoresist layer  11  within the first die region  12  in the peripheral region  13 . The photoresist layer  11  has a threshold dose for exposure. The main purpose of the compensating light beam  16  is not for patterning used in photoresist layer  11 . In addition, the first dose is zero in the center region  15 . However, in the peripheral region  13 , the first dose distribution of the compensating light beam  16  is gradually increased from point B which is near the center of the wafer along the direction of a radius of the wafer  10  to the point A. (please refer to the Roman numeral (i) in  FIG. 4   a ) In addition, the first dose is less than the threshold dose of the photoresist layer  11 . The first dose is zero in the center region  15 , which means the compensating light beam  16  does not direct onto the center region  15 . However, according to different requirements, the compensating light beam  16  can direct onto the center region  15  uniformly. (please refer to Roman numeral (ii) in  FIG. 4   a ) An overlapping region  20  includes a first area  21  and a second area  23 . During the first-stage radiation, the first dose is uniform in the second area  23  and the first dose in the second area  23  is the same as that in the center region  15 . However, in the first area  21 , the first dose varies with the position of the first area  21  on the wafer  10 . 
     Then, as shown in  FIG. 4   b , the wafer  10  undergoes a second-stage radiation. During the second-stage radiation, a light beam  18  having a second dose projects onto the photoresist layer  11  within the first die region  12  and the second die region  14  in a step-and-scan manner. The light beam  18  is for exposure. In addition, the second dose of the light beam  18  is uniform in the peripheral region  13  and the center region  15 . 
       FIG. 5  depicts diagrams illustrating the relation between the dimension of the ADICD and the dose distribution of two-stage radiation according to the second embodiment of the present invention. 
     As shown in  FIG. 5 , the total dose of the first dose and the second dose in the center region  15  is uniform. On the contrary, the total dose distribution of the first dose and the second dose in the peripheral region  13  is increased from point B to point A. Therefore, after the photoresist is developed, the after development inspect critical dimension (ADICD) distribution in the peripheral region  13  will gradually decrease from a region near the center of the wafer along the direction of a radius of the wafer. That is to say, the ADICD will decrease from point B to point A. Since the ADICD is adjusted before the etching process, the AEICD will be uniform in the peripheral region  13  and the center region  15 . 
     Moreover, the compensating light beam  16  and the light beam  18  have the same wave length. The second dose can be more or less than the threshold dose of the photoresist layer  11 , as long as the total dose of the first dose and the second dose are above than the exposure threshold dose of the photoresist layer  11 . 
     According to a variation of the second embodiment, the first-stage radiation can be performed by projecting the light beam  18  on the first die region  12  and the second die region  14  of the wafer  10  in a step-and-scan manner. The second-stage radiation can be performed by directing the compensating light beam  16  onto the photoresist layer  11  of the wafer  10 . That is to say, as long as the compensating light beam  16  is directing onto the photoresist layer  11  before the wafer is developed, the variation of the AEICD can be corrected. 
       FIG. 6  show a side view of the wafer  10  having a plurality of circular regions. To simplify the illustration, the first die region and the second die region are omitted. 
     The first embodiment and the second embodiment illustrate that the first dose in the peripheral region has dose distribution that gradually decreases or increases from a region near the center of the wafer along the direction of a radius of the wafer. The projecting route of the first dose is illustrated as follows for example. 
     As shown in  FIG. 6 , the peripheral region  13  is divided into a plurality of circular regions, such as circular regions  30 ,  32 ,  34 ,  36 . The compensating light beam  16  of different dose respectively encircles directing on each one of the circular regions  30 ,  32 ,  34 ,  36  when the wafer is rotating. The first dose in the same circular region is uniform. In addition, please refer to  FIGS. 2   a ,  4   a  and  6 . The dose is not uniform in a die which is part of the peripheral region  13  and part of the center region  14 . For example, the dose received by the photoresist layer  11  in the first area  21  and the second area  23  is different. 
     According to the present invention, the ADICD is adjusted by directing a compensating light beam  16  onto the region on the wafer which is affected by the loading effect. Therefore, the variation of the AEICD in the peripheral region and the center region can be corrected, and the AEICD in the peripheral region and the center region can be uniform. In addition, the dose received by each die region is identical when running the step-and-scan exposure process. Therefore, the cost for running the step-and-scan exposure process can be decreased. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.