JPH04259256A - Solid state image sensor - Google Patents

Abstract

PURPOSE:To provide a solid state image sensor which reduces a surface reflection of a microlens, has high reproducibility of a,contrast, and can prevent generation of ghost, a flare, etc. CONSTITUTION:A microlens array 24 formed of a transparent photosensitive resin is disposed on a main surface of an interline transfer CCD image sensor, and a reflection preventive film 25 made of magnesium fluoride having an intermediate refractive index of refractive indexes of the air and photosensitive resin for constituting the array 24, cryolite, etc., is formed on the array 24 by a vacuum deposition method, etc. Thus, its surface reflectivity can be reduced to about 1%.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device provided with a microlens array for improving sensitivity.

0002

[Prior Art] Recently, in order to improve the sensitivity of solid-state imaging devices, on-chip
Alternatively, microlenses are formed using bonding technology to improve the aperture ratio. Regarding such a technique, for example, Japanese Patent Laid-Open No. 60-38989 discloses one applied to an interline transfer CCD imaging device.

Next, the technical content disclosed in the above publication will be explained. First, Figure 2 shows the interline transfer CC
D is a conceptual plan view of an imaging device, where 11 is a photoelectric conversion element made of, for example, a photodiode, and 12 is a vertical CCD register for reading out the signal photoelectrically converted by the photoelectric conversion element 11. Although not shown, the photodiode and the vertical CCD register 12 A transfer gate region for controlling transfer of signal charges is arranged between them. Reference numeral 13 denotes a horizontal CCD register that reads out the signals of the vertical CCD register 12, which have been transferred in parallel, to the output section 14 line by line. FIG. 3 is an enlarged view of FIG. 2, where 11 is a photoelectric conversion element and 12 is a vertical CCD.
Register, 15 is transfer gate area, 16, 1
Reference numeral 7 denotes a transfer electrode of the vertical CCD register 12, and polycrystalline silicon is usually used. Transfer electrodes 16 and 17 are 1
A 1/2-stage CCD is formed corresponding to one photoelectric conversion element 11, and although not shown, each transfer electrode also has a vertical CCD.
The D register 12 has a two-layer gate structure or impurity control of the substrate semiconductor so that it has two different potentials. Further, the transfer electrodes 16 and 17 are connected to adjacent vertical CCDs through the vertical separation section 18 of the photoelectric conversion element 11.
Connected to a register. Further, the transfer gate region 15 and the vertical CCD register 12 are shielded from light by a layer 19 made of, for example, Al, which does not transmit light. In the CCD imaging device configured in this manner, the actual aperture ratio of the photoelectric conversion element 11 is limited to 20 to 40%.

[0004] Next, such a CC disclosed in the above publication
A method of forming a microlens provided to improve the aperture ratio in the D imaging device will be described. FIG. 4 schematically shows a cross section taken along line AA' in FIG. The interline transfer CCD imaging device includes a photoelectric conversion element 11 such as a photodiode having a conductivity type opposite to that of the substrate impurity, a transfer gate region 15 whose threshold voltage is controlled by the impurity, and a buried channel on the main surface of a semiconductor substrate 10. A vertical CCD register 12 is formed. Transfer electrodes 16 are arranged on the surface of the substrate with an insulating film 20 interposed therebetween. Further, a light shielding layer 19 made of aluminum is provided through the phosphor glass layer 21 to shield the vertical CCD register 12 and the transfer gate region 15 from light.
is located.

[0005] Interline transfer CC with such a configuration
To form a lens for improving the aperture ratio in the D imaging device, first, as shown in FIG. 5, a transparent and photosensitive first resin layer 22 is formed on the main surface of the CCD imaging device. The photosensitive resin layer 22 serves to eliminate unevenness on the main surface of the CCD image pickup device, and also serves to adjust the focal length of the lens to be formed later so that the focal point is on the photoelectric conversion element. The thickness of the transparent photosensitive resin layer 22 is determined by the curvature of the lens, the refractive index of the lens material, and the aperture ratio of the photoelectric conversion element 11. When the photosensitive resin layer 22 is used as a condensing lens as in this configuration example, the refractive index is 1.5, the radius of curvature of the lens is the pitch of the photoelectric conversion element 11, and the aperture ratio of the photoelectric conversion element 11 is 50%. The thickness of the photosensitive resin layer 22 is required to be at least 1/2 or more of the pitch of the photoelectric conversion elements 11.

After the photosensitive resin layer 22 is deposited, the photosensitive resin layer 22 on the bonding pad portion and the scribe line of the imaging device is removed using the photoresist action of the resin itself. After that, in order to harden the photosensitive resin layer 22, the resin layer 22
Heat treated above the conversion temperature of Next, the photosensitive resin layer 22
A second photosensitive resin layer 23 for forming a lens array is deposited thereon. After that, the second photosensitive resin layer 23 is
Through the photoresist process of exposure and development, a portion on the light shielding layer 19 and a portion on the vertical separation portion 18 that vertically separates the photoelectric conversion elements 11 are removed. FIG. 6 is a schematic plan view of the second photosensitive resin layer 23 after development, and the second photosensitive resin layer 23 is formed in a mosaic shape corresponding to the photoelectric conversion elements 11. Note that FIG. 7 is a diagram showing a cross section of FIG. 6.

Thereafter, the second photosensitive resin layer 23 is heat-treated at a temperature higher than the conversion temperature of the resin and lower than the temperature at which the first photosensitive resin layer 22 was heat-treated. The microlens array section 24 is formed by molding into a lens shape. FIG. 8 shows the second photosensitive resin layer 23
FIG. 2 is a cross-sectional view of after heat treatment.

In the CCD imaging device in which the microlens array section 24 is formed in this manner, the incident light passes through the lens array section 24 made of the lens-shaped second photosensitive resin layer 23.
Due to the radius of curvature and the thickness of the first photosensitive resin layer 22, the light irradiated onto the light shielding layer 19 and the vertical separation portion 18 of the photoelectric conversion element 11 can be completely focused into the photoelectric conversion element 11. can.

[0009]

[Problems to be Solved by the Invention] By the way, in a conventional solid-state imaging device provided with a microlens array section to improve the aperture ratio, as shown in FIG. Generally, air is in contact with the lens array section 24. As shown in the above-mentioned publication, a transparent photosensitive resin such as PMMA is used as the lens material, and the refractive index of this photosensitive resin is about 1.6. On the other hand, since the refractive index of air is 1.0, the reflectance R at the interface between the microlens array section 24 and air is calculated as follows: R=[(1.6-1.0)/(1.6+1. 0)]2
It reaches ≒5%. Due to this reflection, conventional solid-state imaging devices cannot capture images of objects with strong contrast.
There have been problems in that details in dark areas cannot be imaged well, and phenomena such as ghosts and flares appear when the light intensity is strong.

The present invention has been made to solve the above-mentioned problems in conventional solid-state imaging devices equipped with microlens arrays.It reduces reflection at the interface between microlenses and air, provides good contrast reproducibility, An object of the present invention is to provide a solid-state imaging device equipped with a microlens that prevents ghosts, flares, etc. from occurring.

[0011]

[Means and operations for solving the problems] In order to solve the above-mentioned problems, the present invention provides a group of photoelectric conversion elements arranged on the same semiconductor substrate, and a light-concentrating effect on the upper part of the light-receiving photodiode in the photoelectric conversion elements. In the solid-state imaging device provided with a microlens array, at least one type of antireflection film is formed on the top of the microlens array.

[0012] By providing an antireflection film on the top of the microlens array in this way, reflection on the lens surface can be reduced to about 1/5 of the conventional level. This makes it possible to accurately capture a high-contrast image, and also to realize a solid-state imaging device that does not generate ghosts or flares even when capturing an image of a subject with high illuminance.

[0013]

[Example] Next, an example will be explained. FIG. 1 is a cross-sectional view showing an embodiment of a solid-state imaging device according to the present invention, and members that are the same or equivalent to those of the conventional device shown in FIG. In the conventional example, as shown in FIG. 8, the microlens array section 2 made of the second photosensitive resin
However, in the present invention, after forming the microlens array section 24, as shown in FIG. Magnesium fluoride (refractive index n = 1.38) or cryolite (refractive index n = 1.38) has an intermediate refractive index.
An antireflection film 25 made of a material such as n=1.35) is formed on the top of the wafer surface.

For forming the antireflection film 25, a vacuum evaporation method or a sputtering method is used.
The lens portion 24 is formed under low temperature and low damage conditions that do not denature the material of the lens portion 24. Thereafter, using a photolithography method, the antireflection film only on the pad portion is removed by a wet method or dry etching method, and then the resist is removed to complete the process.

The thickness d of the antireflection film 25 is preferably given by the following equation (1). d=λ/4n·(2k−1) (1) Here, λ is the wavelength of the incident light, and k is a natural number. For example, when k=1, λ=550nm, n=1.3
If the thickness d is calculated as 8, it will be approximately 100 nm. When such an anti-reflection film is provided, the
It was confirmed by calculations and experiments that the reflectance of 5% was reduced to ~1%.

The thickness of the anti-reflection film mentioned above was calculated assuming k=1, but of course the value of k may be any natural number, and in particular, if k is sufficiently large, the entire visible light range An antireflection film that is flat and has a low reflectance can be obtained.

[0017] Also, B. G. In the case of a three-chip color solid-state imaging device using each sensor for R, each sensor has a λ1
=450nm, λ2 =550nm, λ3
In the case of receiving light centered at =650nm,
If k=1, on each sensor, d1 =45
0/4×1.38=82nm, d2=100nm
, d3 = 118 nm. By forming antireflection films of different thicknesses, it is possible to reduce the chip surface reflection at each sensor to the maximum.

[0018] Also, in a single-chip color solid-state imaging device,
By forming optimal anti-reflection films with different thicknesses on the photodiodes of each color, it is possible to suppress surface reflection and increase the amount of light incident on the photodiodes compared to conventional methods. .

Further, in the above embodiment, a single-layer anti-reflection film was formed, but since it is sufficient to suppress surface reflection, it is of course possible to use a multi-layer anti-reflection film structure having two or more layers.

Furthermore, although the above embodiments have been applied to a solid-state imaging device equipped with an on-chip type microlens array, the present invention can also be applied to a solid-state imaging device equipped with an attached-type microlens array. can be applied and similar effects can be obtained.

Further, in the above embodiment, the microlens array was constructed using an organic material, but an inorganic material may also be used as the lens material. For example, when a Si3 N4 film (n=2.0) is used as the lens material, an SiO2 film (n=1.4) is used as the antireflection film.
5) is preferable, or by further forming a thin film of magnesium fluoride or cryolite used in the above embodiments on this SiO2 film, the antireflection effect can be further improved.

Furthermore, although the above embodiments show the application of the present invention to a CCD imaging device, it is also possible to apply the present invention to a MOS type or CMD image pickup device.
(Charge Modulation Device
It is of course applicable to solid-state imaging devices using amplification type light receiving elements such as ).

[0023]

[Effect of the invention] As explained above based on the embodiments,
According to the present invention, it is possible to significantly reduce reflection on the lens surface to about 1/5 of the conventional level, and it is possible to accurately capture a high contrast image, and when capturing an image of a subject with high illuminance. Also, a solid-state imaging device that does not cause ghosts or flares can be obtained. Further, as reflection on the lens surface is reduced, the amount of incident light increases, resulting in an advantage of improved sensitivity.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of a solid-state imaging device according to the present invention.

FIG. 2 is a schematic plan view showing a configuration example of a conventional interline transfer CCD imaging device.

FIG. 3 is a partially enlarged view of FIG. 2;

FIG. 4 is a diagram showing a cross section taken along line AA' in FIG. 3;

[Figure 5] CCD with conventional microlens array section
FIG. 3 is a cross-sectional view showing the manufacturing process of the solid-state imaging device.

6 is a plan view showing a manufacturing process following the manufacturing process shown in FIG. 5. FIG.

FIG. 7 is a diagram showing a cross section of FIG. 6;

FIG. 8 is a diagram showing a cross section of a CCD solid-state imaging device in which a microlens array section is formed.

[Explanation of symbols]

10 Semiconductor substrate 11 Photoelectric conversion element 12 Vertical CCD register 13 Horizontal CCD register 14 Output section 15 Transfer gate area 16 Transfer electrode 17 Transfer electrode 18 Vertical separation section 19 Light shielding layer 20 Insulating film 21 Phosphorus glass layer 22 First photosensitive resin layer 23 Second photosensitive resin layer 24 Microlens array section 25 Anti-reflection film

Claims (3)

[Claims] 1. A solid-state imaging device in which a group of photoelectric conversion elements are arranged on the same semiconductor substrate, and a microlens array having a light-concentrating function is provided above a light-receiving photodiode in the photoelectric conversion elements, wherein the microlens array is arranged above the microlens array. A solid-state imaging device characterized in that at least one type of anti-reflection film is formed on the solid-state imaging device. 2. The solid-state imaging device according to claim 1, wherein the microlens array is made of a resin transparent to visible light, and the antireflection film is made of magnesium fluoride or cryolite. 3. The antireflection film is a film given by d=λ/4n·(2k−1) (where λ is the peak wavelength of incident light and k is a natural number), where n is the refractive index of the antireflection film. 3. The solid-state imaging device according to claim 1, wherein the solid-state imaging device has a thickness d.