Abstract:
A positioning method in a microprocessing process of bulk silicon comprises the steps of: fabricating, on a first surface of a first substrate ( 10 ), a first pattern ( 100 ), a stepper photo-etching machine alignment mark ( 200 ) for positioning the first pattern, and a double-sided photo-etching machine first alignment mark ( 300 ) for positioning the stepper photo-etching machine alignment mark; fabricating, on a second surface, opposite to the first surface, of the first substrate, a double-sided photo-etching machine second alignment mark ( 400 ) corresponding to the double-sided photo-etching machine first alignment mark; bonding a second substrate ( 20 ) on the first surface of the first substrate; performing thinning on a first surface of the second substrate; fabricating, on the first surface of the second substrate, a double-sided photo-etching machine third alignment mark ( 500 ) corresponding to the double-sided photo-etching machine second alignment mark; and finding, on the first surface of the second substrate by using the double-sided photo-etching machine third alignment mark, a corresponding position of the stepper photo-etching machine alignment mark.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a technical field of semiconductors, and more particularly relates to a positioning method in micromachining process for a bulk silicon. 
       BACKGROUND OF THE INVENTION 
       [0002]    MEMS micromachining technology includes a micromachining process for a bulk silicon and a surface micromachining technology. A commonly used micromachining process for a bulk silicon is: first fabricating patterns (such as a deep channel) on one silicon wafer, and then bonding the silicon wafer to another one silicon wafer, performing a grinding to the bonded silicon wafer, and fabricating patterns on a surface of the bonded silicon wafer. The micromachining process for a bulk silicon can manufacture a monocrystalline silicon structure having a greater thickness, and is extensively applied to fields such as an acceleration sensor, a gyroscope, and a microscope. In order to guarantee an alignment between the patterns on surfaces of the upper silicon wafer and the lower silicon wafer, before bonding, it requires a double-sided lithography machine to fabricate pattern on the lower surface of the first silicon wafer, the pattern is aligned to the pattern on the upper surface. After being bonded to the second silicon wafer, it also requires the double-sided lithography machine to fabricate pattern on the upper surface on the second silicon wafer, the pattern is aligned to the pattern on the lower surface of the silicon wafer, such that the pattern on the upper surface of the second silicon wafer is indirectly aligned to the pattern on the upper surface of the first silicon wafer. The double-sided lithography machine adopts a proximity exposure and a contact exposure, i.e. adopts an optical system to project the pattern on the silicon wafer with the proportion of 1:1, it requires a mask having a dimension equal to that of the silicon wafer, the dimension and position of the pattern is required to be completely the same as that in practical situation. An alignment accuracy of the method is relative lower, the alignment accuracy generally is 2-3 micrometers. Because the double-sided lithography machine is adopted twice, the alignment accuracy between the patterns on the upper surface and the lower surface generally is 4-6 micrometers, the alignment accuracy is poor. 
       SUMMARY OF THE INVENTION 
       [0003]    Accordingly, it is necessary to provide positioning method in micromachining process for a bulk silicon which can effectively enhance an alignment accuracy. 
         [0004]    A positioning method in micromachining process for a bulk silicon includes: fabricating a first pattern, a stepper lithography machine alignment mark configured to position the first pattern, and a first alignment mark for a double-sided lithography machine configured to position the stepper lithography machine alignment mark on a first surface of a first substrate; fabricating a second alignment mark for a double-sided lithography machine corresponding to the first alignment mark for a double-sided lithography machine on a second surface of the first substrate opposite to the first surface; bonding a second substrate on the first surface of the first substrate; performing a grinding process to a first surface of the second substrate; fabricating a third alignment mark for a double-sided lithography machine corresponding to the second alignment mark for a double-sided lithography machine on the first surface of the second substrate; and finding a position corresponding to the stepper lithography machine alignment mark by the third alignment mark for a double-sided lithography machine on the first surface of the second substrate. 
         [0005]    In aforementioned positioning method in micromachining process for a bulk silicon, a method combining the double-sided lithography to the stepper lithography is adopted, the stepper lithography machine alignment mark for the stepper lithography machine on the first substrate is found by the double-sided lithography machine, and then the second substrate is directly aligned by the stepper lithography machine. The alignment accuracy of the stepper lithography machine is equivalent to an alignment accuracy of the patterns on surfaces of the upper/lower substrate, such that the alignment accuracy of the micromachining process for a bulk silicon is improved greatly. The stepper lithography machine is an integrated optic-mechanical-electron system which gathers precision optics, precision mechanics and automatic controls, the alignment accuracy can be less than 0.5 micrometers, therefore, the alignment accuracy of the micromachining process for a bulk silicon can be less than 0.5 micrometers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    In order to illustrate the technical solution of the invention or prior art more clearly, hereinafter, a brief introduction of accompanying drawings employed in the description of the embodiments or the prior art is provided. It is apparent that accompanying drawings described hereinafter merely are several embodiments of the invention. For one skilled in the art, other drawings can be obtained according to the accompanying drawings, without a creative work 
           [0007]      FIG. 1  is a flow chart of a position method in micromachining process for a bulk silicon according to an embodiment; 
           [0008]      FIG. 2  is a perspective view of a first substrate after a second alignment mark for a double-sided lithography machine is fabricated; 
           [0009]      FIG. 3  is a perspective view of a second substrate after a third alignment mark for a double-sided lithography machine is fabricated; 
           [0010]      FIG. 4  is a perspective view of a second substrate after a recess and a first pattern are fabricated; and 
           [0011]      FIG. 5  is a flow chart of a position method in micromachining process for a bulk silicon according to another embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0012]    Embodiments of the invention are described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. The various embodiments of the invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
         [0013]    Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms in the description of the invention are for the purpose of describing specific embodiments, and are not intend to limit the invention. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
         [0014]      FIG. 1  is a flow chart of a position method in micromachining process for a bulk silicon according to an embodiment. 
         [0015]    Referring to  FIG. 2  and  FIG. 3 , a positioning method in micromachining process for a bulk silicon includes steps as follows: 
         [0016]    In step S 100 , a first pattern  100 , a stepper lithography machine alignment mark  200  configured to position the first pattern  100 , and a first alignment mark for a double-sided lithography machine  300  configured to position the stepper lithography machine alignment mark  200  are fabricated on a front surface of a first substrate  10 . The first substrate  10  can be a silicon wafer. The first pattern  100  is fabricated, the stepper lithography machine alignment mark  200  which can position the first pattern  100  is fabricated, and the first alignment mark for a double-sided lithography machine  300  which can position the stepper lithography machine alignment mark  200  is fabricated, i.e. a position of the first pattern  100  can be determined by the stepper lithography machine alignment mark  200 , a position of the stepper lithography machine alignment mark  200  can be determined by the first alignment mark for a double-sided lithography machine  300 . The number of the stepper lithography machine alignment mark  200  should be multiple, and preferably, it is at least 5 to guarantee relative high alignment accuracy. The number of the first alignment marks for a double-sided lithography machine  300  is at least 2 to guarantee relative high alignment accuracy. 
         [0017]    In step S 200 , a second alignment mark for a double-sided lithography machine  400  corresponding to the first alignment mark for a double-sided lithography machine  300  is fabricated on a rear surface of the first substrate  10 . The “corresponding to” herein is “having a position corresponding to”, i.e. a position of the first alignment mark for a double-sided lithography machine  300  on the front surface of the first substrate  10  is corresponding to a position of the second alignment mark for a double-sided lithography machine  400  on the rear surface.  FIG. 2  is a perspective view of a first substrate after a second alignment mark for a double-sided lithography machine is fabricated. 
         [0018]    In step S 300 , a second substrate  20  is bonded on the front surface of the first substrate  10 . The second substrate  20  is made of material which is same as that of the first substrate  10 , and the second substrate  20  is a silicon wafer. 
         [0019]    In step S 400 , a grinding process is performed to the front surface of the second substrate  20 . The grinding process is applied to the front surface to reach a required thickness of the device. 
         [0020]    In step S 500 , a third alignment mark for a double-sided lithography machine  500  corresponding to the second alignment mark for a double-sided lithography machine  400  is fabricated on the front surface of the second substrate  20 . The double-sided lithography machine is adopted to fabricate the third alignment mark for a double-sided lithography machine  500  corresponding to the second alignment mark for a double-sided lithography machine  400  on the front surface of the second substrate  20  by the second alignment mark for a double-sided lithography machine  400  on the rear surface of the first substrate  10 . The “corresponding to” herein is “having a position corresponding to”, i.e. the third alignment mark for a double-sided lithography machine  500  on the front surface of the second substrate  20  has a position corresponding to that of the second alignment mark for a double-sided lithography machine  400  on the rear surface of the first substrate  10 .  FIG. 3  is a perspective view of a second substrate after a third alignment mark for a double-sided lithography machine is fabricated. 
         [0021]    In step S 600 , a position corresponding to the stepper lithography machine alignment mark  200  is found on a front surface of the second substrate  20  by the third alignment mark for a double-sided lithography machine  500 . The specific principle is that, the position of the second alignment mark for a double-sided lithography machine  400  can be determined according to the third alignment mark for a double-sided lithography machine  500 , and then the first alignment mark for a double-sided lithography machine  300  can be determined according to the second alignment mark for a double-sided lithography machine  400 , and then the position of the stepper lithography machine alignment mark  200  can be determined according to the first alignment mark for a double-sided lithography machine  300 . 
         [0022]    The advantageous effect of the determination of the stepper lithography machine alignment mark  200  is that, the position of the first pattern  100  can be determined by the stepper lithography machine alignment mark  200  again in the following steps, such that a second pattern  700  corresponding to the position of the first pattern  100  can be fabricated. A method combining the double-sided lithography to the stepper lithography is adopted, the position of the stepper lithography machine alignment mark  200  of the stepper lithography machine on the first substrate is found by the double-sided lithography machine, and then an alignment is performed to the second substrate  20  directly by the stepper lithography machine. The alignment accuracy of the stepper lithography machine is equivalent to an alignment accuracy of the patterns (the first pattern  100  and the second pattern  700 ) on surfaces of the upper/lower substrate (the first substrate  10  and the second substrate  20 ), such that the alignment accuracy of the micromachining process for a bulk silicon is improved greatly. It is specifically illustrated with reference to the following embodiments. 
         [0023]      FIG. 5  is a flow chart of a position method in micromachining process for a bulk silicon according to another embodiment. 
         [0024]    A positioning method in micromachining process for a bulk silicon includes steps as follows: 
         [0025]    In step S 110 , a first pattern  100 , a stepper lithography machine alignment mark  200  configured to position the first pattern  100 , and a first alignment mark for a double-sided lithography machine  300  configured to position the stepper lithography machine alignment mark  200  are fabricated on a first surface (the front surface in the embodiment) of a first substrate  10 . The first substrate  10  can be a silicon wafer. The first pattern  100  is fabricated, the stepper lithography machine alignment mark  200  which can position the first pattern  100  is fabricated, and the first alignment mark for a double-sided lithography machine  300  which can position the stepper lithography machine alignment mark  200  is fabricated, i.e. a position of the first pattern  100  can be determined merely by the stepper lithography machine alignment mark  200 , a position of the stepper lithography machine alignment mark  200  can be determined by the first alignment mark for a double-sided lithography machine  300 . The number of the stepper lithography machine alignment marks  200  should be multiple, and preferably, it is at least 5 to guarantee relative high alignment accuracy. The number of the first alignment mark for a double-sided lithography machine  300  is at least 2 to guarantee relative high alignment accuracy. 
         [0026]    In step S 120 , a second alignment mark for a double-sided lithography machine  400  corresponding to the first alignment mark for a double-sided lithography machine  300  is fabricated on a second surface (the rear surface in the embodiment) of the first substrate  10 . The “corresponding to” herein is “having a position corresponding to”, i.e. a position of the first alignment mark for a double-sided lithography machine  300  on the front surface of the substrate  10  is corresponding to a position of the second alignment mark for a double-sided lithography machine  400  on the rear surface, as shown in  FIG. 2 . 
         [0027]    In step S 130 , a second substrate  20  is bonded on the front surface of the first substrate  10 . The second substrate  20  is made of material which is same as that of the first substrate  10 , and the second substrate  20  is a silicon wafer. 
         [0028]    In step S 140 , a grinding process is performed to a first surface (the front surface in the embodiment) of the second substrate  20 . 
         [0029]    In step S 150 , a third alignment mark for a double-sided lithography machine  500  corresponding to the second alignment mark for a double-sided lithography machine  400  is fabricated on the front surface of the second substrate  20 . The double-sided lithography machine is adopted to fabricate the third alignment mark for a double-sided lithography machine  500  corresponding to the second alignment mark for a double-sided lithography machine  400  on the front surface of the second substrate  20  by virtue of the second alignment mark for a double-sided lithography machine  400  on the rear surface of the first substrate  10 . The “corresponding to” herein is “having a position corresponding to”, i.e. the third alignment mark for a double-sided lithography machine  500  on the front surface of the second substrate  20  has a position corresponding to that of the second alignment mark for a double-sided lithography machine  400  on the rear surface of the first substrate  10 , as shown in  FIG. 3 . 
         [0030]    In step S 160 , a position corresponding to the stepper lithography machine alignment mark  200  is found on the front surface of the second substrate  20  by the third alignment mark for a double-sided lithography machine  500 . The specific principle is that, the position of the second alignment mark for a double-sided lithography machine  400  can be determined according to the third alignment mark for a double-sided lithography machine  500 , and then the first alignment mark for a double-sided lithography machine  300  can be determined according to the second alignment mark for a double-sided lithography machine  400 , and then the position of the stepper lithography machine alignment mark  200  can be determined according to the first alignment mark for a double-sided lithography machine  300   
         [0031]    In step S 170 , a recess  600  is fabricated on the position corresponding to the stepper lithography machine alignment mark  200  on the front surface of the second substrate  20 , to expose the stepper lithography machine alignment mark  200  on the front surface of the first substrate  10 . A part of the substrate corresponding to stepper lithography machine alignment mark  200  on the front surface of the second substrate  20  is removed, the stepper lithography machine alignment mark  200  below the second substrate  20  is exposed. The removing method can be performed by using stepper lithography machine through etching technology, such as dry etching or wet etching. 
         [0032]    In step S 180 , a position corresponding to the first pattern  100  on the front surface of the second substrate  20  is found by the stepper lithography machine alignment mark  200 , and a second pattern  700  is fabricated on the position corresponding to the first pattern  100 . Because the position of the first pattern  100  can be determined by the stepper lithography machine alignment mark  200 , therefore, the second pattern  700  fabricated on the second substrate  20  by the stepper lithography machine alignment mark  200  has a position corresponding to the first pattern  100  on the first substrate  10 , an accurate alignment can be achieved.  FIG. 4  is a perspective view of a second substrate after a recess and a first pattern is fabricated, referring to  FIG. 4 . 
         [0033]    In aforementioned positioning method in micromachining process for a bulk silicon, a method combining the double-sided lithography to the stepper lithography is adopted, the stepper lithography machine alignment mark of the stepper lithography machine on the first substrate is found by the double-sided lithography machine, and then the second substrate is directly aligned by the stepper lithography machine. The alignment accuracy of the stepper lithography machine is equivalent to an alignment accuracy of the patterns on surfaces of the upper/lower substrate, such that the alignment accuracy of the micromachining process for a bulk silicon is improved greatly. The stepper lithography machine is an integrated optic-mechanical-electron system which gathers precision optics, precision mechanics and automatic controls, the alignment accuracy can be less than 0.5 micrometers, therefore, the alignment accuracy of the micromachining process for a bulk silicon can be less than 0.5 micrometers. 
         [0034]    The above are several embodiments of the present invention described in detail, and should not be deemed as limitations to the scope of the present invention. It should be noted that variations and improvements will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Therefore, the scope of the present invention is defined by the appended claims.