Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 094105479 filed in Taiwan, R.O.C. on Feb. 23, 2005, the entire contents of which are hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of Invention  
         [0003]     The present invention relates to a method for utilizing a dry film, and particularly, to an application method for pressing a dry film onto a substrate, such as a wafer, during a wafer level packaging process.  
         [0004]     2. Related Art  
         [0005]     In the domain of the wafer level packaging, an image transfer is usually performed through photoresist materials for forming bumps or circuits on a wafer by depositing or etching. In order to achieve a suitable thickness and a favorable image effect, the currently employed photoresist material is dry films. The conventional dry film has a three-layer structure, comprising a carrier film with light transmission, at least one photoresist layer, and a passivation layer, wherein the photoresist layer is sandwiched between the carrier film and the passivation layer. After the passivation layer is peeled off, the photoresist layer of the dry film is pressed onto a substrate, such as a wafer, to be exposed and developed, thereby forming patterned images. However, when the dry film is pressed onto the wafer, the contaminant produced during the process may cause the inaccurate exposure and degrade the production yield.  
         [0006]     With reference to  FIG. 1 , in the wafer level packaging process, when a dry film  10  is pressed onto a wafer  20  or a packaged substrate, a photoresist layer  11 , such as the acrylic photosensitive resin, in the dry film  10  is attached to an active area  21  of the wafer  20 , and a carrier film  12  with light transmission of the dry film  10  is covered on the photoresist layer  11 . In the step of exposure, a mask  30  is disposed above the wafer  20  and the dry film  10 , and an exposure beam  31 , such as ultraviolet light, passes through the mask  30  and then the carrier film  12 , and finally reaches the photoresist layer  11 , such that a photochemical reaction occurs on the irradiated part of the photoresist layer  11 . When the photoresist layer  11  is a positive photoresist, the irradiated part will be removed after development. When the photoresist layer  11  is a negative photoresist, the irradiated part will be remained after development. Therefore, the sequent production yield depends on the quality of the exposure. However, before the exposure, contaminant, such as residual photoresist  13  and particles  14 , may be remained on the carrier film  12  of the dry film  10 . Due to the residual photoresist  13  and the particles  14 , the exposure beam  31  may be refracted or scattered, leading to inaccurate exposure. Furthermore, dry film burrs  15  appear around the dry film  10  after the dry film  10  has been pressed and cut, which also influences the quality of exposure.  
       SUMMARY OF THE INVENTION  
       [0007]     One object of the present invention is to provide a method for utilizing a dry film. After a dry film is pressed onto a substrate and before the exposure, a carrier film with light transmission of the dry film is cleaned in a darkroom for removing the contaminant, such as residual photoresist and particles, on the carrier film. At the same time, the dry film burrs around the dry film may be removed. Thereby, an accurate exposure and an excellent sequent production yield are achieved.  
         [0008]     Another object of the present invention is to provide a method for forming a photoresist on a wafer. In the method, a carrier film with light transmission is formed on a photoresist layer on an active area of a wafer, and thus the photoresist layer is protected from being removed when the carrier film and the wafer are cleaned.  
         [0009]     A further object of the present invention is to provide a flow process for cleaning a dry film pressed on a wafer. The flow process comprises performing a step of chemical spraying for removing the residual photoresist and particles on the carrier film; performing a step of rinsing through de-ionized (DI) water for removing chemical solution; and performing a step of drying for removing the DI water, thereby achieving a sufficient cleaning.  
         [0010]     According to the method for utilizing a dry film provided by the present invention, it comprises providing a dry film at least comprising a carrier film with light transmission and a photoresist layer. The film is pressed onto a substrate, such as a wafer, such that the photoresist layer is attached to the substrate. The carrier film of the dry film is cleaned in a darkroom for facilitating the sequent exposure and development. Generally, before the carrier film is cleaned, the dry film is firstly cut to a size corresponding to that of the substrate. The carrier film is cleaned for removing the contaminant, such as residual photoresist and particles, on the carrier film, and the dry film burrs on the edge of the dry film is removed simultaneously. Furthermore, in an embodiment, the step of cleaning the carrier film further includes chemical spraying, water rinsing, drying, and the like. And after the step of cleaning the carrier film, the edge of the photoresist layer of the dry film will shrink.  
         [0011]     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the present invention, and wherein:  
         [0013]      FIG. 1  is a sectional schematic view of a conventional wafer during the exposure after a dry film is pressed on and the wafer is cut.  
         [0014]      FIGS. 2A  to  2 H are sectional schematic views of the process of utilizing a dry film on a substrate according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     The method for utilizing a dry film provided by the present invention is applicable to a wafer level packaging process, and an embodiment is described below.  
         [0016]     Firstly, with reference to  FIG. 2A , a dry film  100  is provided. The dry film  100  comprises at least three layers, namely at least one photoresist layer  111 , a carrier film  112  with light transmission, and a passivation film  113 . The photoresist layer  111  is a kind of photosensitive resin and may be a positive photoresist or a negative photoresist. The photoresist layer  111  is formed on the carrier film  112  and covered by the passivation film  113 . In the present embodiment, the photoresist layer  111  is a negative photoresist as a plating bump. Generally, the material of the carrier film  112  is PET, i.e., polyester, which is also referred to as Mylar film and the material of the passivation film  113  is PE, i.e., polyethylene.  
         [0017]     Subsequently, with reference to  FIG. 2 , the dry film  100  is pressed onto a substrate. In the present embodiment, the substrate which the dry film  100  is pressed onto is a wafer  120 . However, the substrate can also be an IC carrier, a printed circuit board (PCB), a ceramic circuit board, and the like. During the process of pressing the dry film, the passivation film  113  is peeled off firstly, and then the photoresist layer  111  of the dry film  100  is attached to an active area  121  of the wafer  120 , wherein the dry film  100  may be rolled and attached to the active area  121  through a rolling device (not shown). The carrier film  112  of the dry film  100  is exposed, thereby covering and protecting the photoresist layer  111 . In the present embodiment, the wafer  120  is a semiconductor substrate on which an integrated circuit is formed. The wafer  120  has a passivation layer  122  or a molding layer. Alternatively, a redistribution wiring layer (RDL) is formed on the active area  121 . Generally, a priming coat (not shown), such as Hexamethyldisilizane (HMDS), is formed on the active area  121  of the wafer  120  in advance for increasing the adhesive force applied to the wafer  120  by the photoresist layer  111 .  
         [0018]     With reference to  FIG. 2C , with a cutting device  130 , the dry film  100  is cut to a size corresponding to that of the wafer  120 . Generally, after the dry film  100  has been cut, contaminant, such as the residual photoresist  114  or the particles  115 , is remained on the exposed surface of the carrier film  112 . Furthermore, dry film burrs  116  are also remained on the lateral margin of the photoresist layer  111 . The residual photoresist  114 , the particles  115 , or the dry film burrs  116  all influence the accuracy and quality of the exposure. However, the present invention is not limited to perform the cutting step of the dry film  100 . In another embodiment, the dry film  100  may be cut in advance, and then pressed and attached to the wafer  120 .  
         [0019]     Next, with reference to  FIGS. 2D, 2E , and  2 F, a cleaning step is performed to remove the residual photoresist  114  or the particles  115  remained after the step of cutting the dry film  100 , as well as the dry film burrs  116 . The cleaning step is mainly used to clean the carrier film  112 , as well as the wafer  120 . The cleaning step is performed in a darkroom. That is, the wafer  120  is placed in a darkroom or a yellow room to ensure the optical activity of the photoresist layer  111 , such that the inappropriate photochemical reaction of photoresist layer  111  is prevented from occurring. The cleaning step comprises a step of chemical spraying and a step of rinsing through DI water. Preferably, the cleaning step further comprises a step of drying to enhance the effect of cleaning. With reference to  FIG. 2D , in the step of chemical spraying, the chemical spraying solution  140  is used to spray the exposed surface of the carrier film  112 , wherein the chemical spraying solution  140  comprises the material of conventional negative photoresist developer or positive photoresist cleaning liquid with a thinner concentration, such as asxylene, PGME, or DI water. Thereby, the particles  115  come from the outside during the process, the particles  115  and the residual photoresist  114  stuck on the carrier film  112 , as well as the dry film burrs  116  on the lateral margin of the photoresist layer  111  are all removed through the cleaning step. Furthermore, under the protection of the carrier film  112 , the photoresist layer  111  is not removed excessively. Subsequently, with reference to  FIG. 2E , in the step of rinsing through the DI water, a DI water  150  is used to spray the exposed surface of the carrier film  112 , thereby continuously removing the particles  115 , the residual chemical spraying solution  140 , and the dissolved or loosened residual photoresist  114 . When the chemical spraying solution  140  is a DI water, i.e., it may dissolve the residual photoresist  114 , the step of chemical spraying and the step of rinsing may be integrated into one single step. Then, with reference to  FIG. 2F , in the step of drying, a dry gas  160 , such as nitrogen gas, is provided to remove the DI water  150  and continuously remove the particles  115 , thereby greatly enhancing the cleanliness of the exposed surface of the carrier film  112 . Furthermore, after the step of the whole cleaning, a lateral shrinkage  111   a  is formed in the photoresist layer  111  and used to determine whether or not the photoresist layer  111  has been cleaned and the cleaning effect.  
         [0020]     Next, with reference to  FIG. 2G , a step of exposing is performed. Generally, the cleaned wafer  120 , the photoresist layer  111  of the dry film  100 , and the carrier film  112  with light transmission are placed in a yellow room to be exposed. A mask  170  is disposed above the carrier film  112 , an exposure beam  171  passes through the mask  170  and then the carrier film  112 , and finally irradiates and patterns the photoresist layer  111 , such that the photoresist layer  111  has appropriate exposed zones  111 B and unexposed zones  111 C of an appropriate image. The exposed zones  111 B represent the photochemical reaction has occurred on the photoresist layer  111 . Preferably, the yellow room in the step of exposing is the same with the darkroom for cleaning the carrier film  112 , thereby facilitating the continuity of the operation.  
         [0021]     Subsequently, with reference to  FIG. 2H , the carrier film  112  is removed and the photoresist layer  111  is developed, thereby forming a pattern. Since the photoresist layer  111  is the negative photoresist, the photoresist in the unexposed zones  111 C is removed to form patterned recess regions  111 D, thereby forming or etching sequent bumps and circuits. Therefore, with the method for utilizing a dry film provided by the present invention, the carrier film  112  of the dry film  100  and the wafer  120  are cleaned sufficiently for achieving the accurate exposure, thereby forming correct patterned recess regions  111 D. When the exposure tests of dry films are performed on the same batch of wafers, the low yield of the conventional operation flow is 0.58%, and with the method for utilizing a dry film provided by the present invention, the low yield of the processed wafers is effectively reduced to 0.01%. Thus, the process is improved significantly. The method for utilizing a dry film provided by the present invention is used to manufacture bumps during a wafer level packaging process, such that the formed bumps in sequent have the same shape and size.  
         [0022]     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Technology Category: 3