Abstract:
A method of removing non-polar colorants of a color filter array rapidly from a bottom layer starts by performing a cracking process to decompose cross-linked polymeric molecules of non-polar R/G/B colorants to smaller fragments. A plasma cleaning process is performed to oxidize the cracked non-polar R/G/B colorants. Then, a solvent cleaning process is performed by using a non-polar solvent to remove the non-polar R/G/B colorants from the bottom layer.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of rapidly reworking color filters, and more particularly, to a method of completely removing non-polar R/G/B colorants of a color filter array by utilizing a PAD-PI type negative photoresist, plasma clean process and solvent clean process. 
     2. Description of the Prior Art 
     A charge-coupled device (CCD) is an optical electronic device used to transform light into an electronic signal. Applications of the charge-coupled device include monitors, transcription machines and cameras etc. However, due to high cost and large dimensions of the charge-coupled device, there are limitations in applications of the charge-coupled device. To overcome the above mentioned drawbacks, a CMOS photodiode is therefore produced. Because the CMOS photodiode is produced by utilizing traditional semiconductor fabrication, the dimensions and production cost of the CMOS photodiode are reduced. Additionally, the CMOS photodiode can be applied in personal computer cameras and digital cameras. 
     Whether image sensing equipment is composed of a CCD or a CMOS photodiode, incident light must be divided into a combination of rays with different wavelengths, such as red light, blue light and green light. For example, yellow light can be divided into a combination of 50% blue light and 50% green light. As a result, an optical sensing device needs a filtering array to divide incident light. A color filter is made of a photosensitive resin and is patterned by utilizing a photolithography process and an etching process. Then, the color filter is colored by dyes. Directly utilizing a photoresist containing dyes may also serve as the color filter. 
     As errors occur in fabricating a color filter array, the color filter array needs to be removed completely. Usually, the color filter array is removed by utilizing a plasma cleaning process. However, after the color filter array is aligned in a photolithography process, molecules of dyes in the color filter array perpetrate a cross-linking reaction to form polymers with larger molecular weight. As a result, the color filter array cannot be removed completely by utilizing the plasma cleaning process. 
     In general, a positive photoresist is removed by utilizing solutions composed of N-methyl-2pyrrolidone (NMP) and acetone, or by utilizing the plasma cleaning process and a solvent cleaning process. Before the color filter array is aligned in a photolithographic process, the color filter array can be removed completely by a color filter array (CFA) development solution. However, after the color filter array is aligned in a photolithographic process, the color filter array cannot be removed completely by the CFA development solution. The color filter array is a negative photoresist, which contributes to a cross-linking reaction in an exposing process. The cross-linked color filter array cannot be removed completely by utilizing the NMP solution, the development solution and the plasma ash cleaning process. As a result, it is necessary to develop a method of completely removing the cross-linked color filter array. 
     SUMMARY OF THE INVENTION 
     It is therefore a primary objective of the present invention to provide a method of rapidly removing non-polar R/G/B colorants of a color filter array. 
     In a preferred embodiment, the present invention provides a method to remove a color filter array rapidly. The color filter array composed of non-polar colorants is formed on a silicon nitride layer. A cracking pre-treatment is performed to decompose cross-linked polymers in the non-polar R/G/B colorants into small molecules. A plasma ash cleaning process is performed subsequently in order to oxidize the non-polar R/G/B colorants. Then, a solvent cleaning process is performed. 
     It is an advantage of the present invention that a cracking pre-treatment is utilized to decompose the cross-linked polymers in the non-polar R/G/B colorants into small molecules. The cracking pre-treatment utilizes a PAD-PI development solution, which is a negative photoresist development solution comprising methoxy-2-propyl-acetate. The PAD-PI development solution can effectively decompose cross-linked polymers into small molecules, which can be removed by a plasma ash cleaning process and a solvent cleaning process. 
     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 which is illustrated in the various figures and drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a flow chart of removing non-polar R/G/B colorants of a color filter array according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     Please refer to FIG.  1 . FIG. 1 is a flow chart  10  of a method of removing non-polar R/G/B colorants of a color filter array according to the present invention. The color filter array composed of non-polar R/G/B colorants is formed on a silicon nitride (SiN) layer of a filter. As shown in FIG. 1, a CFA optical alignment  12  of the color filter array is performed. Then, a cracking pre-treatment  14  is performed on the color filter array, which fails in the CFA optical alignment  12 . The cracking pre-treatment  14  is utilized in order to decompose cross-linked polymers in the non-polar R/G/B colorants of the color filter array into small molecules. The cracking pre-treatment  14  rinses the color filter array in a non-polar development solution, using a time for rinsing of tens of seconds. A plasma ash cleaning process  16  is performed to oxidize the non-polar R/G/B colorants. Then, a solvent cleaning process  18  is performed to complete the method of removing non-polar R/G/B colorants of a color filter array. 
     In the present invention, a positive photoresist development solution, a PAD-PI development solution containing methoxy-2-propyl-acetate, and an NMP solution are utilized in the cracking pre-treatment  14 . According to experimental results, when utilizing the positive photoresist development solution and the NMP solution, there still exists residue of the color filter array after performing the plasma ash cleaning process  16  and the solvent cleaning process  18 . However, when utilizing the PAD-PI development solution, there exists no residue of the color filter array after performing the plasma ash cleaning process  16  and the solvent cleaning process  18 . 
     Because the PAD-PI development solution is a non-polar solution, it can decompose the cross-linked polymers in the R/G/B colorants of the color filter array into small molecules. However, positive photoresist development solution is a polar solution and the NMP solution is between a polar and a non-polar solution and both of them cannot decompose the cross-linked polymers in the R/G/B colorants of the color filter array into small molecules. 
     As a result, the cracking pre-treatment  14  is the most important step in removing the color filter array. The cracking pre-treatment  14  rinses the color filter array in the PAD-PI development solution. When rinsing time is longer, decomposition of the cross-linked polymers is more complete and it is easier to remove the color filter array. Rinsing time typically ranges between 45 and 100 seconds, optimally 90 seconds. After performing the plasma ash cleaning process  16  utilizing oxygen-containing plasma and the solvent cleaning process  18  utilizing a non-polar solvent of ST26S, the color filter array can be removed completely in a short time. Additionally, the solvent cleaning process  18  can utilize commercial ACT935 or EKC270 cleaning solvent. 
     The above mentioned color filter array is not covered by a planar layer. Therefore, the cracking pre-treatment  14  and the plasma ash cleaning process  16  only need be performed one time to remove the color filter array completely. However, as the planar layer is coated on the color filter array, the color filter array cannot be completely removed by utilizing the cracking pre-treatment  14  and the plasma ash cleaning process  16  only one time. As a result, the cracking pre-treatment  14  and the plasma ash cleaning process  16  have to be performed more than one time. 
     A color filter array covered by a planar layer comprises a silicon nitride layer, a color filter array composed of non-polar R/G/B colorants formed on the silicon nitride layer, a planar layer composed of borophosphoslicate glass (BPSG) formed on the color filter array and a micro-lens layer formed on the planar layer. The non-polar R/G/B colorants comprise negative photoresist containing acetate resin. 
     In the present invention, when the color filter array is covered by the planar layer and the micro-lens layer, the cracking pre-treatment  14  and the plasma ash cleaning process  16  have to be performed more than one time to remove the color filter array completely. First, the cracking pre-treatment  14  is performed. The plasma ash cleaning process  16  utilizing oxygen plasma is performed for about 50 seconds. Then, the cracking pre-treatment  14  and the plasma ash cleaning process  16  are repeated at least one time. Then, the solvent cleaning process  18  utilizing non-polar ST26S solvent is performed. At this point, removal of the non-polar R/G/B colorants, the planar layer and the micro-lens layer is completed. The cracking pre-treatment  14  rinses the color filter array in the PAD-PI development solution containing methoxy-2-propyl-acetate. Rinsing time is between 45 and 100 seconds. As a result, the non-polar R/G/B colorants, the planar layer and the micro-lens layer can be removed in 2.5 hours. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.