JP3959710B2 - Method for manufacturing solid-state imaging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a solid-state imaging device, and more particularly to a method for manufacturing a solid-state imaging device having an on-chip microlens.
[0002]
[Prior art]
In a solid-state imaging device having an on-chip microlens, a wire is bonded to a bonding pad portion (hereinafter referred to as a “pad portion”) in the vicinity of a photoelectric conversion portion that is a sensor portion. A process for opening the pad window in the organic material film is required.
There are two prior art examples shown in FIGS. 3 and 4 as typical processing methods known in the art. 3 and 4 are partial cross-sectional views showing the progress of the manufacturing process of the solid-state imaging device.
[0003]
First, the manufacturing method in the prior art of FIG. 3 is demonstrated.
In FIG. 3A, a semiconductor substrate 32 is made of a silicon substrate or the like, and a pad portion 34 made of an aluminum electrode is formed at a predetermined position on the upper surface thereof.
Although not shown in the figure, in the photoelectric conversion region of the semiconductor substrate 32, a photodiode that receives light and converts it into charges, a charge transfer unit that transfers charges, and a polysilicon electrode that applies a transfer clock signal In addition, a light shielding film that shields the surface other than the insulating film and the photodiode is formed.
A planarizing film 36 made of an acrylic resin or the like is formed on the upper surface of the semiconductor substrate 32 including the photoelectric conversion region and the pad portion 34 in order to suppress unevenness of the surface. Further, a color filter film 38 is formed on the portion of the planarizing film 36 corresponding to the photoelectric conversion region of the semiconductor substrate 32 by a photolithography method, a staining method, or the like using a dye-containing photosensitive resin.
[0004]
Next, by coating a transparent photosensitive resin comprising a styrene-based resin on the upper surface of the planarization film 36, as shown in FIG. 3 (b), the transparent organic film 40 is formed. As will be described later, the transparent organic film 40 constitutes a lens material.
Simultaneously with the formation of the transparent organic film 40, a pad window opening 42 is formed at the position of the transparent organic film 40 corresponding to the pad section 34 by photolithography.
[0005]
Next, a photosensitive resin film is formed on the upper surface of the transparent organic film 40 corresponding to the opening 42 and the color filter 38, and as shown in FIG. 3C, a microlens shape is formed by a photolithography method and a thermal reflow method. The transparent resin film 44 is formed. In this case, the thermal reflow is performed at a temperature of 150 ° C. to 180 ° C. for 120 seconds to 240 seconds in order to form an optimum lens shape.
[0006]
Next, the microlens shape of the transparent resin film 44 is transferred to the transparent organic film 40 as a lens material by anisotropic plasma dry etching to form an on-chip microlens 46 as shown in FIG. At the same time, the transparent organic film 40 on the upper surface of the pad portion 34 is etched to form a pad window 48.
[0007]
Next, the manufacturing method in the prior art of FIG. 4 is demonstrated.
4A , the semiconductor substrate 32 is made of a silicon substrate or the like, and a pad portion 34 made of an aluminum electrode is formed at a predetermined position on the upper surface thereof. Although not shown in the drawing as in the case of the prior art described above, a photodiode, a charge transfer unit, a polysilicon electrode, an insulating film, a light shielding film, and the like are formed in the photoelectric conversion region of the semiconductor substrate 32. ing. Further, a planarizing film 36 made of acrylic resin or the like is formed on the upper surface of the semiconductor substrate 32 including the photoelectric conversion region and the pad portion 34 in order to suppress unevenness of the surface, and a predetermined surface on the upper surface of the planarizing film 36 is formed. A color filter film 38 is formed on the portion. Further, a planarizing film 50 made of an acrylic resin or the like is formed on the upper surface of the planarizing film 36 including the color filter film 38 in order to planarize the base for microlens formation.
[0008]
Next, as shown in FIG. 4B, a transparent microlens-shaped photosensitive resin 42 is applied as a lens material, and the photosensitive resin 42 and the planarizing film 50 are formed by photolithography and thermal reflow. And an on-chip microlens 46 is formed on the upper surface of the color filter film 38. Next, after applying a pad window resist, an opening 42 for the pad window is formed in a portion of the pad window resist 40 corresponding to the pad portion 34 by photolithography, as shown in FIG. Is done.
[0009]
Next, as shown in FIG. 4C , a planarization film corresponding to the upper surface of the pad portion 34 is formed by plasma dry etching using an etching gas of a fluorinated gas (CF ₄ ) and an oxygen gas (O ₂ ) . The pad window 52 is formed by removing portions 50 and the planarizing film 36. At this time, a cured film is formed on the upper surface of the pad window opening resist 40 by plasma. Therefore, since the resist peeling becomes difficult due to an organic solvent, the pad window resist 40 was separated and removed by the solubility and highly volatile solvent, to form a solid-state imaging device as shown in FIG. 4 (e).
[0010]
[Problems to be solved by the invention]
However, the conventional method for manufacturing a solid-state imaging device has various problems. First, in the manufacturing method shown in FIG. 3 , since the opening 42 for the pad window 48 is processed before the formation of the microlens shape, the photosensitive resin 44 shown in FIG. The coating unevenness occurs due to the step difference of the opening 42. As a result, there is a problem that non-uniformity occurs in the on-chip microlens 46 and causes imaging unevenness.
[0011]
Further, as shown in FIG. 3D, the step of transferring the microlens-shaped photosensitive resin 44 and the step of forming the pad window 48 are performed at the same time, so that the planarizing film 36, which is an organic material film, When the etching selectivity with the pad portion 34 made of an aluminum electrode is not sufficient, the film thickness of the pad portion 34 is reduced by plasma dry etching, and the mechanical strength of wire bonding is lowered, resulting in a bonding failure. there were.
[0012]
As a countermeasure against this, a proposal has been made to form an organic film for protecting the aluminum electrode on the upper surface of the pad portion 34 as disclosed in JP-A-11-145439. However, since the etching amount of plasma dry etching varies within and between the surfaces of the film, in order to completely remove the organic film for protecting the aluminum electrode from the upper surface of the pad portion 34, the etching amount is somewhat. It is necessary to provide a margin (strong etching), and it is inevitable that the pad portion 34 is reduced in film thickness. For this reason, guarantee of sufficient mechanical strength of wire bonding cannot be obtained.
[0013]
Since the pad portion 34 includes a film other than the aluminum electrode, the pad portion 34 originally has a considerable film thickness. For this reason, not only when the microlens-shaped photosensitive resin 44 is applied, but also when it is applied with a color filter film or a planarizing film, coating unevenness occurs due to the step difference of the pad portion 34. For this reason, non-uniformity occurs on the surface of the on-chip microlens 46 that causes imaging unevenness not only in the process of applying the microlens shape but also in other processes.
[0014]
Next, in the manufacturing method of the conventional example shown in FIG. 4 , when the microlens-shaped photosensitive resin 44 is applied, there is no level difference on the surface, so that application unevenness does not occur. In order to peel and remove the cured film having a considerable thickness formed on the upper surface of 40, it is necessary to use a solvent having high solubility and volatility. As a result, the formed on-chip microlens 46 has a nonuniformity on the surface due to a change in shape or damage to the surface, which causes a problem of imaging unevenness.
[0015]
As in the case of the manufacturing method of FIG. 3 , when the etching selectivity between the planarization film 36, which is an organic material film, and the pad portion 34 made of an aluminum electrode is not sufficient, the plasma dry process in FIG. The film thickness of the pad portion 34 is reduced by the etching, and there is a problem that the mechanical strength of wire bonding is lowered and bonding failure occurs.
[0016]
The present invention has been made to solve such problems, and it is easy to remove and remove the resist for opening the pad window without causing non-uniformity that causes imaging unevenness on the surface of the on-chip microlens. In addition, an object of the present invention is to provide a method for manufacturing a solid-state imaging device capable of preventing the film loss of the aluminum electrode in the pad portion and maintaining the mechanical strength of wire bonding.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, a method for manufacturing a solid-state imaging device according to the present invention includes a first step of forming a bonding pad portion on an upper surface of a semiconductor substrate on which a predetermined photoelectric conversion region is formed, and the bonding pad portion. A second step of forming an on-chip microlens on the upper side of the semiconductor substrate; and a third step of applying a resist to the upper surface of the on-chip microlens to form an opening in the resist corresponding to the bonding pad portion. And a fourth step of removing the portion of the on-chip microlens corresponding to the opening of the resist to expose the upper surface of the bonding pad portion.
[0018]
According to the present invention, after the on-chip microlens is formed by the above configuration, the on-chip microlens corresponding to the bonding pad portion is removed to form an opening, and the upper surface of the bonding pad portion is exposed, thereby enabling the on-chip microlens. Since the coating unevenness of the photosensitive resin film does not occur in the formation process of the chip microlens, it is easy to remove and remove the resist for opening the pad window without causing non-uniformity that causes imaging unevenness on the surface of the on-chip microlens. To. In addition, since the upper surface of the bonding pad portion is exposed by plasma dry etching using only oxygen gas, the film thickness of the aluminum electrode in the bonding pad portion can be prevented and the mechanical strength of wire bonding can be maintained.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Next, will be described with reference to the drawings implementation form in a method for manufacturing a solid-state imaging device according to the present invention.
It will be described first implementation mode in the method for manufacturing a solid-state imaging device of the present invention. Figure 1 is a partial sectional view showing the progress of the manufacturing process of the solid-state imaging device in the form of implementation.
In FIG. 1A, a semiconductor substrate 12 is made of a silicon substrate or the like, an aluminum film is formed at a predetermined position on the upper surface thereof by sputtering or the like, and then an aluminum electrode bonding pad portion (hereinafter referred to as “pad portion”) is formed by photolithography. 14) is formed. Although not shown in the drawing, in the photoelectric conversion region of the semiconductor substrate 12, a photodiode that receives light and converts it into charges, a charge transfer unit that transfers charges, and a polysilicon electrode that applies a transfer clock signal In addition, a light shielding film that shields the surface other than the insulating film and the photodiode is formed.
[0020]
On the upper surface of the semiconductor substrate 12 including the photoelectric conversion region and the pad portion 14, a planarizing film 16 made of an acrylic resin such as an acrylic resin, a polyimide resin, an isocyanate resin, or a urethane resin is used in order to suppress unevenness of the surface. Is formed by spin coating or the like. Although not shown in the drawing, a color filter film is formed on the upper surface of the planarizing film 16 corresponding to the photoelectric conversion region of the semiconductor substrate 12 by a photolithography method or a staining method using a dye-containing photosensitive resin. ing.
[0021]
Next, as shown in FIG. 1B, a photosensitive resin made of a transparent lens material made of styrene resin or the like is applied to the upper surface of the flattening film 16 by spin coating or the like to have a very flat surface. A transparent organic film 18 is formed. Next, a photosensitive resin film is applied to the upper surface of the transparent organic film 18 by spin coating or the like. In this case, since the surface of the transparent organic film 18 is extremely flat, there is no uneven coating of the photosensitive resin film. In this case, the photosensitive resin includes a positive type such as a novolac type and a negative type such as a polystyrene type.
[0022]
Thereafter, a microlens-shaped photosensitive resin film 20 is formed by photolithography and thermal reflow as shown in FIG. Specifically, the photosensitive resin film is exposed and developed with ultraviolet rays and patterned to form a microlens-shaped mask. In this case, the thermal reflow is performed at a temperature of 150 ° C. to 180 ° C. for 120 seconds to 240 seconds in order to form an optimum microlens shape.
[0023]
Next, the microlens-shaped photosensitive resin film 20 is transferred to the transparent organic film 18 that is a lens material by anisotropic plasma dry etching, and as shown in FIG. 22 is formed. That is, the microlens shape is transferred to the transparent organic film 18 using the patterned photosensitive resin film 20 as a mask to form the on-chip microlens 22. Next, a pad window opening resist is applied to the upper surface of the on-chip microlens 22, and an opening 26 is formed in the pad window opening resist 24 by photolithography as shown in FIG. That is, after the on-chip microlens 22 is formed, the opening 26 is formed in the pad window opening resist 24.
[0024]
Next, the part of the on-chip microlens 22 located immediately below the opening 26 of the pad window opening resist 24 and the planarizing film 16 thereunder are removed by plasma dry etching, and the structure shown in FIG. Thus, the pad window 28 is formed to expose the pad portion 14. In this plasma dry etching process, by using only oxygen gas as an etching gas, the film loss of the aluminum electrode of the pad portion 14 is prevented, the plasma power is set to zero, and the chamber temperature is set to 100 ° C. or less. Generation of a cured film on the surface of the pad window opening resist 24 is reduced.
[0025]
Next, the cured film formed on the surface of the pad window opening resist 24 is removed by ashing. As described above, the cured film is very thin and can be easily removed by ashing. No damage to on-chip microlenses. Also in this case, only oxygen gas is used, the plasma power is set to zero, and the chamber temperature is set to 100 ° C. or lower. Next, as shown in FIG. 2G, an on-chip microlens is obtained by peeling and removing the pad window opening resist 24 using an organic solvent having low solubility and volatility such as MMP and EL. The surface of 22 is not changed in shape and damaged.
[0026]
As described above, according to the manufacturing method of the solid-state imaging device according to the above implementation, after forming the on-chip microlens 22, the pad window by removing a portion of the on-chip microlens 22 corresponding to the pad portion 14 By forming 28 and exposing the upper surface of the pad portion 14, uneven coating of the photosensitive resin film 20 does not occur in the formation process of the on-chip microlens 22, and thus causes uneven imaging on the surface of the on-chip microlens 22. Non-uniformity is not generated. Further, since the generation of the cured film of the pad window opening resist 24 can be reduced by the plasma dry etching process using only oxygen gas, the removal and removal of the pad window opening resist 24 is facilitated. Furthermore, the film strength of the aluminum electrode of the pad part 14 can be prevented and the mechanical strength of wire bonding can be maintained.
[0027]
【The invention's effect】
According to the present invention, it is possible to easily remove and remove the resist for opening the pad window and to reduce the film thickness of the aluminum electrode in the pad portion without causing non-uniformity that causes imaging unevenness on the surface of the on-chip microlens. Can prevent and maintain the mechanical strength of wire bonding.
[Brief description of the drawings]
Partial cross-sectional view showing the progress of the manufacturing process of the solid-state imaging device according to the implementation of the present invention; FIG.
FIG. 2 is a partial cross-sectional view of the manufacturing process following FIG. 1;
FIG. 3 is a partial cross-sectional view showing a progress of a manufacturing process of a solid-state imaging device in a conventional example.
FIG. 4 is a partial cross-sectional view showing the progress of a manufacturing process of a solid-state imaging device in another conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 12 ... Semiconductor substrate, 14 ... Bonding pad part, 16 ... Planarization film, 18 ... Transparent organic film, 20 ... Photosensitive resin film, 22 ... On-chip micro lens, 24 ... Pad window opening Resist, 26 ... opening, 28 ... pad window.

Claims (10)

A first step of forming a bonding pad portion on the upper surface of the semiconductor substrate on which the photoelectric conversion region is formed;
A second step of forming an on-chip microlens on the upper side of the semiconductor substrate including the bonding pad portion;
A third step of applying a resist on the upper surface of the on-chip microlens to form an opening in the resist corresponding to the bonding pad portion;
A fourth step of removing a portion of the on-chip microlens located immediately below the opening of the resist to expose the upper surface of the bonding pad portion;
A method for manufacturing a solid-state imaging device.   2. The second step is characterized in that after the planarization film is formed on the upper surface of the semiconductor substrate including the bonding pad portion, the on-chip microlens is formed on the upper surface of the planarization film. The manufacturing method of the solid-state imaging device as described in 2.   In the second step, an organic film made of a transparent lens material is formed on the upper surface of the planarizing film, a microlens-shaped photosensitive resin film is formed on the upper surface of the organic film, and the organic film 3. The method of manufacturing a solid-state imaging device according to claim 2, wherein the on-chip microlens is formed by transferring the shape of the microlens.   4. The method of manufacturing a solid-state imaging device according to claim 3, wherein in the second step, the shape of the microlens is transferred to the organic film by anisotropic plasma dry etching.   The fourth step is characterized in that a portion of the on-chip microlens corresponding to the opening of the resist is removed by a plasma dry etching process using only oxygen gas to expose the upper surface of the bonding pad portion. A method for manufacturing a solid-state imaging device according to claim 1.   6. The method of manufacturing a solid-state imaging device according to claim 5, wherein in the fourth step, the plasma dry etching process is performed under the conditions that the plasma power is zero and the chamber temperature is 100 ° C. or less.   6. The method of manufacturing a solid-state imaging device according to claim 5, further comprising a fifth step of removing the cured film formed on the upper surface of the resist by the plasma dry etching process by an ashing process.   8. The method according to claim 7, further comprising a sixth step of exposing the on-chip microlens by removing the resist with an organic solvent having low solubility and low volatility after the ashing process in the fifth step. The manufacturing method of the solid-state imaging device as described in 2.   8. The method of manufacturing a solid-state imaging device according to claim 7, wherein in the fifth step, the ashing process is performed using only oxygen gas under a chamber temperature of 100 [deg.] C. or less.   The method for manufacturing a solid-state imaging device according to claim 1, further comprising a step of forming a color filter film between the first step and the second step.

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