The present invention relates to a method of manufacturing color filters, and more particularly, to a method of increasing the adhesion of color filters and preventing cross talk effects on a semiconductor wafer.
Charge-coupled device (CCDs) have been the mainstay of conventional imaging circuits for converting light into an electrical signal. The applications of CCDs include monitors, transcription machines and cameras. Although CCDs have many advantages, CCDs also suffer from high costs and the limitations imposed by its volume. To overcome the weakness of CCDs and reduce costs and dimensions, a CMOS photodiode device is developed. Since a CMOS photodiode device can be produced by using conventional techniques, both cost and the volume of the sensor can be reduced. The applications of CMOS photodiodes include PC cameras, digital cameras etc.
Whether the image sensor device is composed of CCD or CMOS photodiode, the incident light must be separated into a combination of light of different wave lengths, for example, red, blue and green light. Then, the light is received by corresponding sensor devices and is transformed into electrical signals so as to obtain the original color of incident light by return of the electrical signals. Therefore, a color filter array must be formed on each photosensor device. Currently, color filters are produced by either patterning photosensitive resins using a photo-etching process with the resultant patterns being dyed by a dyeing material, or a photoresist containing dyeing material is directly used to produce color filters.
Please refer to FIG. 1 to FIG. 6. FIG. 1 to FIG. 6 are cross-sectional diagrams of manufacturing a color filter array on a photosensor device according to the prior art method. As shown in FIG. 1, the semiconductor wafer 10 contains a silicon substrate 12 and a P-well 14 positioned on the silicon substrate 12. The photosensor device contains a plurality of CMOS photodiodes and each photodiode contains a metal-oxide semiconductor (MOS) transistor (not shown) positioned on the P-well 14. A photosensor area 18 is formed on the P-well 14 to electrically connect with the MOS transistor. The MOS transistor is a complementary metal-oxide semiconductor (CMOS) transistor composed of an NMOS transistor and a PMOS transistor and functions as a CMOS transistor sensor. The semiconductor wafer 10 also contains a plurality of field oxide layers or shallow trench isolation (STI) structures 16 positioned on the silicon substrate 12 that surrounds the photo sensor area 18. The STI structures 16 act as a dielectric insulating material to prevent short circuiting due to contact between the photosensor areas 18 and other units.
First, a passivation layer 20 is formed on the surface of the semiconductor wafer 10 that covers each photo sensor area 18. Next, as shown in FIG. 2, a red color filter layer (not shown) is formed on the surface of the semiconductor wafer 10. The color filter layer is composed of a positive type photoresist containing a red dye in a large amount (dry weight) of 10 to 50 wt %. A pattern-exposure process is used to form patterns of red color filters in the color filter layer, then the exposed portions of the filter layer is removed to form each red color filter 22. For increasing the effect and reliability of color filters, an ultraviolet (UV) light irradiation and heating process is performed after the formation of the red color filters 22. The UV light used has a wavelength of 320 nm or less at a quantity of 20 J/cm2 or less. The heating process is preferably performed in an inert atmosphere, for example, in nitrogen (N2) for suppressing the oxidation of the photoresist material. The starting temperature of the heating process is between a range of 60xc2x0 C. to 140xc2x0 C. Then, an average increasing temperature rate used in the heating process is 1.5xc2x0 C./sec. The end temperature of the heating process is between a range of 160xc2x0 C. to 220xc2x0 C.
Next, green and blue color filters are formed by repeating the above-mentioned processes. As shown in FIG. 3, a green color filter layer 24 is formed on the surface of the semiconductor wafer 10. The color filter layer 24 is composed of a positive type photoresist containing a green dye in a large amount (dry weight) of 10 to 50 wt %. As shown in FIG. 4, a pattern-exposure process is used to form patterns of green color filters in the color filter layer 24, then the exposed portions of the filter layer 24 is removed to form each green color filter 26. For increasing the effect and reliability of color filters, a UV light irradiation and heating process is also performed after the formation of green color filters 26. The UV light used has a wavelength of 320 nm or less at a quantity of 20 J/cm2 or less. The heating process is preferably performed in an inert atmosphere, for example, in nitrogen (N2) for suppressing the oxidation of the photoresist material. The starting temperature in heating process is between a range of 60xc2x0 C. to 140xc2x0 C. Then, an average increasing temperature rate used in the heating process is 1.5xc2x0 C./sec. The end temperature of the heating process is between a range of 160xc2x0 C. to 220xc2x0 C.
As shown in FIG. 5, a blue color filter layer 28 is formed on the surface of the semiconductor wafer 10. The color filter layer 28 is composed of a positive type photoresist containing a blue dye in a large amount (dry weight) of 10 to 50 wt %. As shown in FIG. 6, a pattern-exposure process is used to form patterns of blue color filters in the color filter layer 28, then the exposed portions of the filter layer 28 is removed to form each blue color filter 30. For increasing the effect and reliability of color filters, a UV light irradiation and heating process is also performed after the formation of the blue color filters 30. The UV light used for irradiation has a wavelength of 320 nm or less at a quantity of 20 J/cm2 or less. The heating process is preferably performed in an inert atmosphere, for example, in nitrogen (N2) for suppressing the oxidation of the photoresist material. The starting temperature of the heating process is between a range of 60xc2x0 C. to 140xc2x0 C. Then, an average increasing temperature rate used in the heating process is 1.5xc2x0 C./sec. The end temperature of the heating process is between a range of 160xc2x0 C. to 220xc2x0 C. The color filter array of a photosensor device produced by the prior art method is then completed.
Color filters produced by the prior art method have only the bottom surfaces contacting the passivation layer. Therefore, adhesion is weak and stripping of the color filters easily occurs. Also, a space exists between each color filter, so that scattered light easily penetrates through the space to enter the neighboring photosensor area and result in cross talk effects. The noise signals received by CMOS transistor sensors increase and the sensitivity is reduced.
It is therefore a primary objective of the present invention to provide a method of manufacturing color filters for increasing adhesion of color filters and preventing stripping of the color filters. A barrier layer is simultaneously formed to prevent incident light from penetrating the space between the color filters to cause cross talk effects.
The present invention provides a method for increasing both the adhesion of color filters and preventing cross talk effects on a semiconductor wafer. The semiconductor wafer comprises a substrate, a plurality of metal-oxide semiconductor (MOS) transistor sensors positioned on the substrate, and a plurality of insulators positioned on the substrate. Each insulator is positioned between two MOS transistor sensors. The method first involves forming a dielectric layer on the semiconductor wafer, which covers each MOS transistor sensor and insulators. Then, a plurality of metal layers are formed on the dielectric layer, each two metal layers positioned approximately above two ends of one MOS transistor sensor. Next, a passivation layer is formed, followed by the formation of a first color filter on the passivation layer and above one MOS transistor sensor. Two ends of the first color filter are aligned approximately above the two metal layers. Thereafter, a second color filter and a third color filter are sequentially formed on the passivation layer, and portions of both the second color filter and the third color filter cover one end of the first color filter. The portion of the second color filter covering the first color filter and the portion of the third color filter covering the first color filter are both used to enhance adhesion of the color filters, and simultaneously, the portion of the second color filter covering the first color filter and the portion of the third color filter covering the first color filter are both used as barriers to prevent cross talk effects.
The color filters produced by the present invention have portions covering one another so as to increase both the contact areas and the adhesion of the color filters. As well, the covered portions of each color filter are used as a barrier layer to prevent cross talk effects.
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.