JP2000174245A - Semiconductor device with built-in photo detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily form a high-reliability light shielding structure without great increase in the process by providing a diamond-like C film least above a light shield requiring region. SOLUTION: After forming photo diode elements and NPN transistor elements, a first silicon oxide insulating film 90 is formed on the entire surface, metal electrodes 100 of the photo diode elements and NPN transistor elements are made from a first metal layer, a diamond-like C film 140 of about 1 μm is formed on the entire wafer surface by the CVD, regions on photo detectors are removed by the RIE method, a wiring is formed from a second metal layer 120, and a silicon oxide protective film 130 is formed, thereby obtaining a desired structure. Since the diamond-like C film 140 serves also as a layer insulation film and a light shielding film, it has a high reliability light shielding structure allowing a double layer wiring to be laid, without augmenting the manufacturing process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device having a light receiving element.

[0002]

2. Description of the Related Art In a semiconductor device, an integrated circuit including a light receiving element such as a photodiode is incorporated in a package having a light transmitting window. After passing through the window, the incident light reaches a light receiving element such as a photodiode on a semiconductor substrate and is detected, and a detection signal generated at that time is processed by a circuit including transistors and resistors on the same substrate. Output.

At this time, when the incident light irradiates an active element or a passive element other than the light receiving element, a change in the carrier concentration due to the excitation of the light causes a change in the intrinsic characteristics of the element, for example, a hFE change or diffusion of the NPN transistor. The circuit may malfunction due to a change in the resistance value of the resistor. Also, if light other than the required incident light enters from the peripheral area of the light receiving element, it causes an increase in noise of the output signal,
Reliability decreases.

For this reason, it is necessary to provide a light-shielding layer all around the light-receiving element in the chip. Silicon oxide and silicon nitride, which are an interlayer insulating layer and a protective layer used in a normal semiconductor process, transmit visible light. Cannot be used for this purpose. Therefore, in general, in a semiconductor device equipped with a light receiving element, in order to protect the lower element from incident light, an A used for an electric wiring material is formed above a region other than the light receiving element.
A light shielding effect is provided by forming a metal film such as lSi.

An outline of the structure and manufacturing process of a semiconductor device incorporating a light receiving element, which is a general example of such a device, will be described below with reference to sectional views of a photodiode element and an NPN transistor element.

First, as shown in FIG. 6A, after patterning a P-type semiconductor substrate 10, an N-type buried layer 20 of antimony and a lower P-type of boron are formed by ion implantation or thermal diffusion. An element isolation layer 30 is formed.

As shown in FIG. 6B, an N-type epitaxial layer 40 is grown to a thickness of about 3 μm,
The collector compensation diffusion layer 50 of the transistor is phosphorus
The mold isolation layer 60 is formed of boron by an ion implantation method or a thermal diffusion method.

Further, as shown in FIG. 6C, the P-type diffusion layer 70 of the photodiode and the base diffusion layer 71 of the NPN transistor are formed of boron, and the NP
After forming the emitter diffusion layer 80 of the N transistor,
A first insulating layer 90 made of silicon oxide is formed on the entire surface.

Then, as shown in FIG. 6D, the photodiode element and the N-type are formed with a first metal layer having a thickness of about 1.1 μm.
Metal electrodes 100 of both elements of the PN transistor element are formed, and a second insulating layer 110 made of silicon nitride having a thickness of about 1 μm is deposited.

Finally, as shown in FIG. 6 (e), a light-shielding region 120 is formed in a region other than the upper portion of the light receiving element by using a second wiring layer having a thickness of about 0.9 μm. Then, a protective film 130 made of silicon oxide having a thickness of about 1.2 μm is deposited to form an element structure.

The points to be noted in the above conventional example are as follows.
This means that it is not possible to form a wiring using the second metal layer at the place where the light shielding layer is formed.

[0012]

Generally, in the element structure as described above, since the ratio of the light-shielding region to the light-receiving element area is large, the area of the light-shielding region becomes enormous, causing the following problems.

(1) The light-shielding metal film is formed also as the second wiring layer in order to prevent an increase in the number of manufacturing steps. However, since a region occupying a large area exists in the wiring layer, the degree of freedom in layout is low. This leads to an increase in the IC chip size, leading to an increase in cost. Of course, the layout problem can be avoided by adding a metal layer used for wiring, but the cost increase associated therewith is far greater than the effect due to the chip size.

(2) A thin-film metal layer having a large area causes a stress and may have an unexpected adverse effect on the characteristics of the device, so that the layout is limited.

(3) A commonly used as a wiring metal
When lSi is formed in a large area, when gas absorbed inside during heat treatment of a sinter or the like is generated, all of the gas cannot be exhausted from the pattern edge portion, and the gas accumulates and swells between the metal film and the lower insulating layer. If it ruptures or scatters, it may cause a serious problem in the reliability of the IC. Therefore, an extra optimal slit must be formed according to the shape.

In view of such a situation, in order to provide a semiconductor device having a light-receiving element at a lower cost, a technique of using a thin light-shielding metal film is disclosed in, for example, Japanese Patent Application Laid-Open No.
No. 3,310,053. In this conventional example, it seems that there is a slight effect because three-layer wiring is assumed. However, due to cost considerations, it is actually necessary to manufacture using two-layer wiring. hard.

Therefore, a large increase in the number of steps is not required,
There is a demand for a semiconductor device having a built-in light receiving element and a method of manufacturing the same, which can easily manufacture a highly reliable light shielding structure.

[0018]

In order to achieve the above object, a semiconductor device incorporating a light receiving element according to the present invention is characterized in that a diamond-like carbon film is provided at least above a light-shielding required area.

Further, the diamond-like carbon film is characterized in that it also serves as an interlayer insulating film or a protective film.

Further, a diamond-like carbon film which is sufficiently thinner than the diamond-like carbon film above the light-shielding necessary area,
It is characterized in that it is provided above the light receiving element region.

Furthermore, the thickness of the diamond-like carbon film above the light-receiving element region is approximately の of the wavelength of the incident light, and the refractive index of the diamond-like carbon film is the square root of the refractive index of the lower silicon layer. It is characterized by being substantially equal to

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1, 2, 4, 5, and 6
In the above, 10 is a semiconductor substrate, 20 is an N-type buried layer, 30 is a lower P-type element isolation layer, 40 is an N-type epitaxial layer, 50 is a collector compensation diffusion layer, and 60 is an upper part. A P-type element isolation layer, 70 is a P-type diffusion layer of the photodiode, 71 is a base diffusion layer of the NPN transistor, and 80 is an emitter diffusion layer of the NPN transistor. Further, 90 is a first insulating layer, 100 is a first metal layer, and 110 is a second metal layer.
120 is a second metal layer, and 13 is a second metal layer.
0 is a protective film, and 140 is a diamond-like carbon film.

(First Embodiment) A first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a second embodiment of the present invention.
FIG. 2 is a cross-sectional view of a semiconductor device having a built-in light receiving element according to the first embodiment, and FIG. 2 is a diagram illustrating an example of a manufacturing process thereof.
In this embodiment, the present patent structure is realized by using a diamond-like carbon film instead of the second insulating film of the conventional example shown in FIG.

Hereinafter, the manufacturing process will be described in detail with reference to FIG. The structure up to the structure shown in FIG. 6C is the same as that of the conventional example. After forming both the photodiode element and the NPN transistor element, the conventional method until the first insulating layer 90 made of silicon oxide is formed on the entire surface. Create it as in the example. Thereafter, as shown in FIG. 2A, metal electrodes 100 of both the photodiode element and the NPN transistor element are formed on the first metal layer.

Further, as shown in FIG. 2B, after a diamond-like carbon film 140 is formed to a thickness of about 1 μm on the entire surface of the wafer by CVD, the region on the light receiving element is removed by RIE.

Finally, as shown in FIG. 2C, after forming a wiring with the second metal layer 120, a silicon oxide film 130 serving as a protective layer is formed to obtain a desired structure.

The diamond-like carbon film 140 used in this embodiment mainly contains carbon as a main component, contains a large amount of hydrogen,
It is a high hardness substance having P2 and SP3 bonds. Its electrical properties are an insulator, its dielectric constant is as low as silicon oxide and silicon nitride, and it has very good protection against chemical erosion. It has good adhesion to Si-based materials,
A film can be uniformly formed on a wafer surface to a thickness on the order of nm to μm by the CVD method, and can be processed by RIE technology. The physical properties can be controlled by changing the hydrogen content, the film formation temperature, the gas pressure, the applied voltage during the film formation, and the like.

The diamond-like carbon film has a good transmittance for far-infrared light, but has a large absorption from ultraviolet to visible light and has a light shielding effect. As shown in FIG. 3, by controlling the film forming conditions, the absorption coefficient in the visible light region can be increased to 10000 cm −1 or more, and the transmittance is 3 μm at a film thickness of about 1 μm generally used as an insulating film. % Or less. Also, the refractive index can be controlled in the range of 1.5 to 2.5.

In this embodiment, since the diamond-like carbon film 140 does not exist on the light receiving element, visible light can reach the light receiving element from the surface and can be detected. Visible light cannot reach an element such as a transistor because of being blocked by the carbon-like carbon film 140. Further, in this embodiment, since the diamond-like carbon film 140 also serves as an interlayer insulating film and a light-shielding film, a two-layer wiring can be realized without increasing the number of manufacturing steps.

(Second Embodiment) FIG. 4 shows a second embodiment of the present invention. Up to FIG. 6D, it is created in the same manner as in the conventional method. Next, as shown in FIG. 4, a diamond-like carbon film 140 is formed on the entire surface of the wafer by CVD to form a 1 μm
After forming about m, the region on the light receiving element is removed by RIE to obtain a desired structure.

In this embodiment, as in the first embodiment, since the diamond-like carbon film 140 does not exist on the light receiving element, visible light can reach the light receiving element from the surface and be detected. However, in other regions, the visible light cannot reach elements such as transistors due to being blocked by the thick diamond-like carbon film 140. In the present embodiment,
Since the diamond-like carbon film 140 also serves as a protective film and a light-shielding film, a two-layer wiring can be realized without increasing the number of manufacturing steps.

(Third Embodiment) FIG. 5 shows a third embodiment of the present invention. Up to FIG. 6D, it is created in the same manner as in the conventional method. Next, as shown in FIG.
The insulating layer 90 and the second insulating layer 110 are removed by an etching method.

Next, as shown in FIG. 5B, after a diamond-like carbon film 140 is formed on the entire surface of the wafer by a CVD method to a thickness of about 2 μm as a protective film, the first insulating layer 90 and the first insulating layer 90 on the light receiving element are formed. The diamond-like carbon film 140 on the light-receiving element region is etched with the same mask pattern as that used when the second insulating layer 110 was removed so that the film thickness becomes sufficient to transmit desired incident light.

According to the present embodiment, since the diamond-like carbon film 140 in the region other than the light receiving element is sufficiently thick, visible light is blocked so that it cannot reach a device such as a transistor. Since the carbon-like carbon film 140 is sufficiently thin, visible light can reach the light receiving element and be detected. Further, there is an advantage that scattered light of light incident on the light receiving element is also absorbed by the diamond-like carbon film 140 and cannot travel in the lateral direction. Further, in this embodiment, since the thin diamond-like carbon film 140 also functions as a protective film of the light receiving element, an improvement in reliability can be expected.

Further, in the present embodiment, the thickness of the diamond-like carbon film 140 on the light receiving element is set to be approximately の of the wavelength of the desired incident light in the diamond-like carbon film 140, and By controlling the film-forming conditions of the carbon film 140 so that the refractive index of the diamond-like carbon film 140 is substantially equal to the square root of the refractive index of the semiconductor substrate 10, the diamond-like carbon film 14 on the light receiving element is formed.
0 can be provided with the function of an antireflection film, and the light incident on the light receiving element can be effectively used.

For example, when silicon is used as the semiconductor substrate 10, its refractive index is about 3.42, so that the film is formed under the condition that the refractive index of the diamond-like carbon film 140 is about 1.85, If etching is performed to leave about 100 nm, which is a quarter of the wavelength in the diamond-like carbon film 140 with respect to the visible light wavelength of 780 nm,
Nearly 90% of the incident light can be used effectively.

[0037]

As described above, by using the structure of the present invention, it is possible to easily realize a semiconductor device incorporating a light receiving element having a highly reliable light-shielding structure without a significant increase in the number of steps. Becomes Furthermore, by making the diamond-like carbon film on the light receiving element a predetermined thickness, incident light can be used effectively.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a semiconductor device having a built-in light receiving element according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a manufacturing process according to the first embodiment of the present invention.

FIG. 3 is a diagram showing an example of a light absorption coefficient of a diamond-like carbon film.

FIG. 4 is a sectional view of a semiconductor device having a built-in light receiving element according to a second embodiment of the present invention.

FIG. 5 is a diagram illustrating an example of a manufacturing process of a semiconductor device having a built-in light receiving element according to a third embodiment of the present invention.

FIG. 6 is a diagram illustrating an example of a manufacturing process of a conventional semiconductor device having a built-in light receiving element.

[Explanation of symbols]

 Reference Signs List 10 semiconductor substrate 20 N-type buried layer 30 Lower P-type element isolation layer 40 N-type epitaxial layer 50 Collector compensation diffusion layer 60 Upper P-type element isolation layer 70 P-type diffusion layer of photodiode 71 Base diffusion layer of NPN transistor 80 NPN transistor Emitter diffusion layer 90 First insulating layer 100 First metal layer 110 Second insulating layer 120 Second metal layer 130 Protective film 140 Diamond-like carbon film

Claims (4)

[Claims] 1. A semiconductor device having a built-in light receiving element, wherein a diamond-like carbon film is provided at least above a light-shielding required area. 2. The semiconductor device according to claim 1, wherein the diamond-like carbon film also functions as an interlayer insulating film or a protective film. 3. A semiconductor device incorporating the light receiving element according to claim 1 or 2, wherein a diamond-like carbon film, which is sufficiently thinner than the diamond-like carbon film above the light-shielding necessary area, is provided above the light-receiving element area. A semiconductor device having a light receiving element built therein. 4. The semiconductor device according to claim 3, wherein the diamond-like carbon film on the light-receiving element region has a thickness of about １ ／ of the wavelength of incident light, and A semiconductor device having a built-in light receiving element, wherein the refractive index of the carbon film is substantially equal to the square root of the refractive index of the lower silicon layer.