JP3035955B2 - Method for manufacturing solid-state imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid-state imaging device, and more particularly to a method for forming a convex condensing lens corresponding to each pixel of a light receiving section.

2. Description of the Related Art Conventionally, various types of solid-state imaging devices, color and monochrome, for example, interline transfer CCD type and MOS type have been developed and commercialized, and the performance of each has been improved.

Generally, in this type of solid-state imaging device, the optical input signal is determined by (quantum efficiency) × (aperture ratio) × (subject illuminance). As a result of various improvements, the quantum efficiency has almost reached the theoretical value at present. Therefore, increasing the aperture ratio, that is, increasing the ratio of the area of the light receiving portion to the entire surface of the element is an important theme for increasing the utilization factor, that is, the sensitivity, of incident light.

[Problems to be Solved by the Invention] However, the above-described conventional solid-state imaging device needs to provide a signal charge transfer path or a signal line adjacent to the light receiving unit structurally, and the aperture ratio of the light receiving unit is increased. There is a limit to The limit is set at 50 to 60% even for a MOS solid-state imaging device that can have a relatively large aperture ratio, and 30 to 40% for a CCD solid-state imaging device. Further, in consideration of the miniaturization of the solid-state imaging device itself or the increase in the density of pixels, it is impossible to further increase the aperture ratio, but rather, it is considered that the aperture ratio decreases as the number of pixels increases. As a means for solving this problem, a uniform solid-state imaging device in which a uniform photoconductive film used as a target material of an imaging tube is stacked over the entire light-receiving region of the solid-state imaging device and receives light of approximately 100% of the area of the light-receiving region. Has been proposed. However, this structure has many problems such as being incompatible with a normal VLSI process and having an afterimage and image sticking peculiar to a photoconductive film.

From such a situation, recently corresponding to each pixel of the light receiving unit,
A method has been proposed in which a convex lens is formed, the incident light is condensed, the light receiving area is effectively enlarged, and the utilization rate (sensitivity) of the incident light is improved. The rate can be improved to 70-80%.

Various methods have been proposed as a method of manufacturing this convex lens, but the basic idea is to use visible light (wavelength 400 nm to 7 nm).
Using a material having a high transmittance to (00 nm), for example, a novolak resin-based resist, an organic PMMA (polymethyl methacrylate), or the like, and selectively patterning corresponding to each pixel by a lithography technique, and performing an appropriate heat treatment. It liquefies and sways into a convex lens shape. However, in this type of manufacturing method, the conditions of the heat treatment are considerably narrow in terms of conditions, for example, the underlying color filter layer is easily damaged by heat and easily deteriorates, and the heat history of the assembly process of incorporating the element into a package must be considered. Since it is limited to the range (for example, 150 ° C. to 170 ° C.), there is a disadvantage that the material for liquefying under the condition and obtaining a lens having a desired curvature is limited. Further, there is a disadvantage that extremely strict manufacturing conditions and management are required, such as a change in the shape and curvature of the lens due to a slight change in the heat treatment conditions.

[Means for Solving the Problems] The present invention provides a new method of manufacturing a convex condensing lens in view of such a conventional situation. The manufacturing method according to the present invention includes a step of flattening by providing a flattening layer on the surface of the light receiving section, a step of applying a lens material on the flattening layer, and a step of receiving light corresponding to each pixel of the light receiving section. A step of selectively forming a photoresist pattern of a lens material between the portions, and a step of expanding the volume of the lens material to give a spherical curvature to form a convex lens having a desired curvature. I do.

Example Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a unit cell of a light receiving section according to one embodiment of the present invention. FIG. 1 (a) is a plan view, and FIG.
FIG. 2 is a longitudinal sectional view cut along AA ′ in FIG. FIG. 1 shows an example in which the present invention is applied to an interline CCD type solid-state imaging device, wherein 1 is a convex condensing lens formed by the manufacturing method of the present invention, 2 is a color filter layer as a flattening layer, and 3 is The signal charge transfer electrode portion, 4 is a light shielding film, 5 is a light receiving pixel, and 6 is a semiconductor substrate. The details of the diffusion layer region and the like in the semiconductor substrate 6 are not particularly important in discussing the relationship with the present invention, and are not shown.

A manufacturing method for obtaining a solid-state imaging device having a convex condensing lens having the structure shown in FIG. 1 will be described with reference to FIG. First, as shown in FIG. 2A, a base body of an interline CCD solid-state imaging device is formed by a known method. A color filter layer 2 is formed by laminating the layer as shown in FIG. Since the details of the structure of the color filter layer are not particularly important for explaining the present invention, they are simplified. still,
In the case of a monochrome solid-state imaging device, a color filter layer is not necessary, and it is simply a planarization layer using an organic PMMA or the like. Next, as shown in FIG.
Material to be dyed 7 same as the color filter forming material
(Eg gelatin, casein, etc.)
Apply with. Next, as shown in FIG. 3, a resist pattern 8 as shown in FIG. 2D is formed on the film 7 by photolithography using a mask pattern 10 corresponding to the pixel pattern of the light receiving section. In this state, the material 7 to be dyed is dyed using a dye for infrared rays (a dye material sensitive to infrared rays). The dyeing method is performed by immersing a solution in which the concentration of the infrared dye material is, for example, 0.1 to 0.1% at 45 to 50 ° C. for 10 to 15 minutes. In general, gelatin or casein, which is the material to be dyed as described above, is dyed at an appropriate temperature.
When immersed for a certain period of time, the material to be dyed is dyed and swells at the same time. That is, the volume expands due to staining.
Under the staining conditions as in this example, the increase in volume is about 50
%. Therefore, as shown in FIG. 2 (d) of the present embodiment, a resist pattern 8 covering the material to be dyed 7 is formed so as to surround the light receiving portion 5 at a portion corresponding to the light shielding film 4 and is selected. When dyed and swollen, the swollen region becomes a shape having the minimum surface free energy, that is, a spherical shape. FIG. 2 (e) shows this state, and the material 7 to be dyed swells to obtain the convex lens-shaped layer 1 as shown. The lens shape (curvature) depends on the dyeing conditions, such as solution concentration, temperature, immersion time, and
And the thickness of the color filter layer 2 is taken into consideration, and conditions for obtaining an optimum curvature for focusing at the light receiving section 5 are selected. After forming the desired convex lens-shaped layer 1 as described above, the unnecessary resist pattern 8 is removed with a ketone-based solvent, and finally the solid-state imaging device having the structure shown in FIG. Is obtained. Since the dye used for dyeing is made of a material having sensitivity to infrared rays, the convex lens layer 1 does not absorb light in the visible light region of 400 to 700 nm, and is used as a solid-state imaging device for visible light. It does not affect the optical characteristics at all.

FIG. 4 is a process chart showing a manufacturing method according to another embodiment of the present invention. The principle of the formation of the convex lens is exactly the same as that of the above-described embodiment, but the feature of this embodiment is that the material to be dyed 7 is, for example, a mask pattern as shown in FIG. A pattern 9 is used to remove a part of the material to be dyed 7 to form a groove 9 surrounding a light receiving portion at a portion corresponding to the light shielding film 4. Thereafter, similarly to the above-described embodiment, a resist pattern 8 is formed as shown in FIG. 4 (e), and the resist pattern 8 is immersed in a dye solution and dyed.
A solid-state imaging device having a convex lens as described above is obtained. The advantage of this embodiment is that when the material to be dyed 7 before patterning is separated from adjacent pixels by dyeing and swelling, there is no stress between the adjacent materials to be dyed and a convex with a large curvature. The mold lens 1 is easily obtained. This is because the thickness of the color filter layer 2 is small and the convex lens 1
This is advantageous when, for example, it is desired to set a short focal length, or when it is desired to further increase the light collection rate of incident light.

The present invention is not limited to the method of manufacturing the convex lens shown in the above-described two embodiments. It goes without saying that the present invention can be applied to the manufacture of a mold lens. Further, in this embodiment, the description has been given of the case where the base body of the solid-state imaging device is applied to an interline CCD type device, but a MOS type imaging device can be manufactured in exactly the same manner. Further, the present invention is not limited to the solid-state imaging device, and can be applied to various photo sensors.

[Effects of the Invention] As described above, according to the present invention, a convex condensing lens for improving the sensitivity of a solid-state imaging device can be formed without heat treatment by immersing the lens in an infrared dye and expanding the volume. Since the manufacturing method and the manufacturing technology are extensions of the technology of forming the color filter layer as the base, there is an effect that the manufacturing can be easily and simply performed with existing equipment and technology.

[Brief description of the drawings]

FIG. 1 (a) is a plan view of a unit cell of a light receiving section according to one embodiment of the present invention, FIG. 1 (b) is a longitudinal sectional view cut along AA 'of FIG. 1 (a), and FIG. 2 (a) to 2 (f) are process diagrams showing a manufacturing method according to an embodiment of the present invention, FIG. 3 is a plan view showing an example of a mask pattern used in the embodiment, and FIG. 4 (a).
(G) is a process drawing showing a manufacturing method of another embodiment of the present invention. Reference numeral 1 denotes a convex condensing lens, 2 denotes a color filter layer (lower flat layer), 3 denotes a signal charge transfer electrode portion, 4 denotes a light-shielding film, 5 denotes a light-receiving pixel, 6 denotes a semiconductor substrate, and 7 denotes a semiconductor substrate. Material to be dyed, 8: Photoresist, 9: Groove pattern groove for material to be dyed, 10: Mask pattern.

Claims (2)

(57) [Claims] A step of providing a flattening layer on the surface of the light receiving section for flattening; a step of applying a lens material on the flattening layer; A solid-state imaging method comprising the steps of: selectively forming a photoresist pattern of a lens material; and expanding the lens material by volume to give a spherical curvature to form a convex lens having a desired curvature. Device manufacturing method. 2. The solid-state imaging device according to claim 1, further comprising a step of selectively leaving said lens material on individual pixels of a light receiving section after being applied with said lens material. Manufacturing method.