JPH10144951A - Semiconductor photo-detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce effects of light interference by a protective film and to supply a correct detecting signal to respond to an incident light by unevenly forming a thickness of the protecting film on a light-receiving surface. SOLUTION: A thickness of a protective film 14 is unevenly formed, to reduce an interference of light at the inner part of the protective film 14 provided on a surface of a light-receiving surface. For example the protective film 14 is formed which is made of dioxide silicon having the film thickness with several step differences in the longitudinal direction of a light-receiving surface 12 of each photodiode 11 which constitutes a photodiode array 10. That is regions L1-L5 each having protecting film 14 with about the same film thickness is provided by crossing plural photodiodes 11. The maximum film thickness d2 is made to be about 2 times the minimum film thickness d1, and each step difference for each regions L2-L4 between two regions L1 and L5 having the film thickness is made to be almost equal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light receiving element, and more particularly to a single light receiving element or a light receiving element array used for detecting measurement light in a spectrophotometer or the like.

[0002]

2. Description of the Related Art For example, a configuration of a spectrophotometer for detecting components separated by liquid chromatography is as shown in FIG. Light from the light source 20 is absorbed at a wavelength corresponding to the components contained in the sample while passing through the flow cell 21 through which the sample separated by a column (not shown) flows. Light that has passed through the flow cell 21 is restricted by the slit 22, is split by a wavelength dispersion element 23 such as a diffraction grating, and is irradiated onto a photodiode array 24. The photodiode array 24 is formed by arranging a large number of photodiodes in the spectral direction, so that the intensity of each wavelength of the spectral spectrum can be measured at the same time.

FIG. 5 is a plan view showing an example of the structure of the photodiode array 24. About 30μm × 2000
Photodiode 2 having an elongate light receiving surface of μm 2
5 are arranged at a narrow pitch of about 20 μm (for example, 256 to 1024). Since the light receiving surface width of one photodiode is very narrow, in a spectrophotometer with the above configuration, light in a narrow wavelength range near a specific wavelength enters each photodiode.

[0004]

When light having a spectrum as shown in FIG. 6A is incident on the photodiode array 24 in the above arrangement of the spectrophotometer, the spectrum detected by the photodiode array 24 is as shown in FIG.
The result is as shown in FIG. That is, it has a shape in which a waveform having strong and weak waves in the wavelength direction is superimposed on the original spectrum shape. The cause of such a phenomenon will be described with reference to FIG. Photodiode light receiving part (p-type semiconductor) 3
A protective film 31 of silicon dioxide or the like is formed on the surface of No. 0 to prevent deterioration. The protective film 31 has a substantially uniform thickness d on the surface of the light receiving section 30 except for electrodes (bonding pads) and the like. When such a photodiode is irradiated with the monochromatic light substantially vertically, a part of the incident light is reflected between the surface of the light receiving unit 30 and the surface of the protective film 31,
The reflected light causes interference. If the thickness d of the protective film 31 is an even multiple of the wavelength of the incident light, the light is enhanced by the interference, and if the thickness d is an odd multiple, the light is weakened by the interference. For this reason, the spectral spectrum detected by the photodiode array 24 has a strong or weak wave at a wavelength corresponding to the thickness of the protective film (this wave in the spectrum is hereinafter referred to as “interference wave”).
Will have.

[0005] One type of noise due to such optical interference is:
In particular, it affects high-precision measurement. Furthermore, since the thickness d of the protective film of the photodiode changes with temperature, the shape of the interference wave also changes with temperature, making high-precision measurement more difficult.

The present invention has been made to solve such a problem, and an object of the present invention is to reduce the influence of light interference on a protective film and to accurately detect a detection signal with respect to incident light. It is an object of the present invention to provide a semiconductor light receiving element capable of outputting a light.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems. It is an object of the present invention to reduce the interference of light inside a protective film in a semiconductor light-receiving element having a protective film on the surface of a light-receiving surface. In addition, the thickness of the protective film is formed to be non-uniform.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the semiconductor light receiving device of the present invention, for example, by changing the thickness of the protective film on the surface of the light receiving surface of one light receiving element in a stepwise manner, it is possible to form an uneven protective film. Eggplant Further, a taper shape in which the thickness of the protective film continuously changes may be employed. When monochromatic light is substantially perpendicularly incident on the light receiving surface of the light receiving element, the wavelength of light intensity due to interference inside the protective film depends on the thickness of the protective film. That is, if the thickness of the protective film is different, the wavelength at which light is strengthened and the wavelength at which light is weakened are different, so that the intensity of light due to interference is canceled inside the protective film having an uneven thickness, thereby reducing the influence of interference. It is reduced.

Therefore, when a spectral spectrum is obtained by the light receiving element array using the semiconductor light receiving elements according to the present invention, emphasis or attenuation at a specific wavelength due to interference is eliminated or reduced even if not eliminated, and an accurate spectrum is obtained. be able to.

Conventionally, the protective film is formed so as to be uniform. However, in practice, there has been unintended non-uniformity due to manufacturing limitations and the like. Such non-uniformity differs depending on the method of forming the protective film and the conditions for forming the protective film, but is generally about 10% of the thickness of the protective film at most. On the other hand, in the semiconductor light receiving device of the present invention, sufficient nonuniformity is required to reduce the interference of light inside the protective film, and for this purpose, a method of intentionally forming the nonuniform protective film is used. Must be used. Further, as the preferable nonuniformity of the protective film, the difference between the minimum film thickness and the maximum film thickness is preferably about 1.5 to 2 times for the reason described below. And providing a plurality of steps of 4 to 5 or more between the maximum film thickness and the minimum film thickness,
Alternatively, a tapered shape whose thickness continuously changes may be used.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a semiconductor light receiving device according to the present invention will be described with reference to the drawings. FIG. 1 is a plan view (a) of a photodiode array according to this embodiment and a sectional view taken along line A1-A2 (b). In the photodiode array 10, a protective film 14 of silicon dioxide having several steps in the film thickness is formed in the longitudinal direction of the light receiving surface 12 of one photodiode 11. That is, regions L1 to L5 each having the protective film 14 having substantially the same thickness are provided across the plurality of photodiodes 11. In this embodiment, the maximum thickness d2 of the protective film 14 is set to be about twice as large as the minimum thickness d1, and the two regions L having that thickness are formed.
The steps of the respective regions L2 to L4 between 1 and L5 are made substantially equal.

In order to form the protective film 14 having such a shape, for example, the following method is used. First, the protective film 14 having the largest and uniform thickness d2 is formed on the surface of the light receiving section 13. As this forming method, a known thermal oxidation method, a CVD method, or the like can be used. Thereafter, a resist pattern corresponding to each of the regions L1 to L5 is prepared, the region L5 is masked, and the other regions L1 to L4 are etched to the thickness of the region L4. Next, the regions L4 and L5 are masked to form the other regions L1 to L5.
L3 is etched to the thickness of the region L3. This is repeated to finally set the thickness of the protective film 14 in the region L1 to d1.
Conversely, by performing masking when depositing the protective film 14 on the surface of the light receiving portion 13, protective films having different thicknesses can be sequentially formed.

When the photodiode array 10 having the above-described structure is irradiated with spectral light having a flat spectrum, each region L having a different thickness of the protective film 14 is obtained.
The spectral spectra detected at 1 to L5 are as shown in FIGS. That is, since the intensity wavelength of the interference wave depends on the thickness of the protective film 14, the intensity wavelength of the interference wave differs in each of the regions L1 to L5. As described above, when the film thickness of the protective film is an even multiple of the wavelength of light, the light is intensified. Therefore, as the film thickness increases, the wavelength interval of the interference wave increases, and when the film thickness increases, the interference wave increases. The wavelength at which the maximum becomes the same as the wavelength at which the original interference wave becomes the maximum. As described above, the spectrum of each of the regions L1 to L5 having the protective film 14 whose film thickness changes stepwise between d1 and d2 is gradually expanded in the wavelength direction. Is the sum of these waveforms. As a result, the interference waves cancel each other out, and the spectral spectrum of the spectrum is greatly reduced as shown in FIG.

FIG. 2 is a sectional view showing the structure of another embodiment of the semiconductor light receiving element according to the present invention. In this example, the thickness of the protective film 14 does not have a step but has a tapered shape that changes continuously. With such a shape, the effect of canceling the interference wave inside the protective film 14 is further enhanced,
Flatter characteristics can be obtained.

In the above embodiment, the present invention is applied to a photodiode array. However, it is apparent that the present invention is effective in applications in which monochromatic light is introduced even with a single photodiode. is there.

The above-described embodiment is merely an example, and it is apparent that modifications and modifications can be made as appropriate within the spirit and scope of the present invention. For example, there is no limitation on the type of semiconductor or the type of protective film of the light receiving unit in the semiconductor light receiving element.

[Brief description of the drawings]

FIG. 1A is a plan view of a photodiode array according to an embodiment of a semiconductor light receiving element of the present invention, and FIG. 1B is a cross-sectional view taken along line A1-A2.

FIG. 2 is a sectional view showing a configuration of another embodiment of the semiconductor light receiving element of the present invention.

FIG. 3 is a waveform chart for explaining the operation of the photodiode array according to the embodiment of FIG.

FIG. 4 is a schematic configuration diagram of a spectrophotometer for liquid chromatography to which the photodiode array of the present invention is applied.

FIG. 5 is a plan view showing an example of a configuration of a conventional photodiode array.

FIG. 6 is a view showing a spectrum detected by a conventional photodiode array.

FIG. 7 is a cross-sectional view illustrating a light interference phenomenon in a conventional photodiode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Photodiode array 11 ... Photodiode 13 ... Light receiving part 14 ... Protective film

Claims (1)

[Claims] 1. A semiconductor light receiving element having a protective film on the surface of a light receiving surface, wherein the thickness of the protective film is formed to be non-uniform in order to reduce interference of light inside the protective film. Semiconductor light receiving element.