JPH02291180A - Photodiode - Google Patents

Abstract

PURPOSE:To restrain a dark current from increasing without decreasing the detecting efficiency by a method wherein, within the title photodiode used as a photodetector in an ultraviolet ray region, high impurity layers in higher concentration than that of any other parts of a semiconductor substrate are formed on the surface layer of the semiconductor substrate. CONSTITUTION:A PN junction part is formed in the part near the surface on an N type semiconductor substrate 1 wherein a P<+> type region 2 is formed while a protective film 3 is formed on the surface of the substrate 1. After forming high concentration regions 4 on the surface layer of the semiconductor substrate 1 by diffusing an impurity in the same conductivity type as that of the substrate 1 such as As etc., B<+> is implanted. Since a depletion layer (a) formed by impressing the same PN junction part with voltage is prevented from diffusing up to the surface of the substrate 1 by the high concentration regions 4 formed near the surface of the substrate 1, the charge generated from the damaged part in the boundary between the substrate 1 and the protective film 3 can not transfer to the depletion layer (a) so that a dark current may be prevented from increasing as well as the whole ultraviolet rays to be detected may enter into the title photodiode not to decrease the detecting efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a photodiode, and more particularly to a photodiode used as a light receiving element for light in the ultraviolet region.

<Prior Art> For example, as shown in FIG. 6, the photodiode has a so-called junction type structure in which a P'' region 62 is formed in an N-type semiconductor substrate 61. 1・
A voltage is applied to the diode 110PN junction, and light incident on the depletion layer generated in the semiconductor thereby generates a current corresponding to the incident energy, and this current is taken out to the outside.

When the photo-I tie-out with the above structure receives ultraviolet light, high-energy ultraviolet light is transmitted to the substrate 61 and the protective film 6.
Because it is absorbed at the boundary with 3, that part is damaged. This caused a problem in that the current in the PN junction increased and the characteristics deteriorated.

Therefore, conventionally, as shown in FIG. 7, a repellent film 64 such as A1 is formed on the surface of the protective film 63, and the substrate 61 and the protective film 64 are
This prevents ultraviolet light from entering the boundary with 2.

<Problems to be Solved by the Invention> By the way, according to the method of preventing damage to the surface of the substrate 61 using the reflective film described above, a part of the ultraviolet light to be received is reflected by the reflective film, so that the PN of the ultraviolet light is The problem remained that the amount of light incident on the junction was reduced and the detection efficiency was lowered.

An object of the present invention is to provide a PHO1 diode having a structure that can suppress an increase in dark current without reducing detection efficiency.

<Means for Solving the Problems> A configuration for achieving the above object will be described with reference to FIG. 1 corresponding to an embodiment. The photodiode is characterized in that an impurity layer 4 having a higher concentration than other parts of the semiconductor substrate 1 is formed at least around the PN junction in the surface layer of the semiconductor substrate 1.

<Function> The depletion layer created in the semiconductor substrate 1 by the impurity layer 4 is
As a result, even if the boundary between the surface of the substrate 1 and the protective film 3 is damaged by ultraviolet light, the charge will not move from the damaged area to the depletion layer, thereby reducing the increase in dark current. It can be suppressed.

<Embodiment> FIG. 1 is a longitudinal sectional view showing the structure of an embodiment of the present invention, and FIG. 2 is a horizontal sectional view thereof.

In this embodiment, a P+/I region 2 is formed in an N-type semiconductor substrate 1.
A PN junction type photodiode in which
For example, As is present around the PN junction near the surface of the substrate 1.
A high concentration region 4 is formed with impurities such as ``.'' A protective film 3 is formed on the surface of the substrate 1.

In the above structure, A
It can be obtained by diffusing s'' to form a high concentration region 4 and then implanting B. The impurity forming the high concentration region 4 is not limited to As'', for example, P. ” (phosphorus), etc., N-type semiconductor substrate 1
It suffices if the impurity is of the same conductivity type as .

Next, the effect will be explained. When voltage is applied to the PN junction,
Although a depletion layer is formed in the substrate 1, this depletion layer does not extend to the surface of the substrate 1 due to the high concentration region 4 formed near the surface of the substrate 1. As a result, even if the boundary between the substrate 1 and the protective film 3 is damaged by the incidence of ultraviolet light, the charges generated from the damaged area will not move to the depletion layer (and an increase in dark current can be prevented). can. Moreover, since all of the ultraviolet light that should be received enters the photodiode, detection efficiency does not decrease.

Here, the distance d between the high concentration region 4 and the PN junction surface is set so that a sufficient breakdown voltage can be obtained between the two.
It is appropriately selected based on the concentration of the substrate 1, the concentration of the high concentration region 4, the level of the voltage applied to the PN junction, etc. Note that when the level of the voltage applied to the PN junction is low, the interval d is not necessarily necessary, and furthermore, as shown in FIG. 3, the high concentration region 4 may be formed over the entire surface layer of the substrate 1. It's okay.

In addition, the width W of the high concentration region 4 is determined based on the concentration of the substrate 1, the concentration of the high concentration region 4, and the voltage applied to the PN junction so that the depletion layer generated in the substrate 1 can be prevented from spreading to the surface of the substrate 1. Select as appropriate based on level etc.

In the above embodiment, a photodiode in which one PN junction was provided on one substrate was explained, but the present invention is not limited to this, and as shown in FIG. A plurality of P' regions 42...42 are formed on a semiconductor substrate 41 of the type
It can be applied to photodiode arrays with

Also in this example, the high concentration regions 44 . . . 44 can be formed by the same manufacturing procedure as in the previous example.

Note that, as shown in FIG. 5, if the voltage is applied to the high concentration region 44 and the substrate 41, the potential of the substrate 41 is fixed;
The stabilization of the characteristics of the Fol diode can be further improved.

The above is a photo 1 in which a P'' region is formed on an N-type semiconductor substrate.
- Although an example in which the present invention is applied to a diode has been described, it is of course applicable to a photodiode in which an N' region is formed on a P-type semiconductor substrate.

<Effects of the Invention> According to the present invention, in a PN junction type photo diode, an impurity layer having a higher concentration than other parts of the semiconductor substrate is formed at least around the PN junction in the surface layer of the semiconductor substrate. Therefore, even if the light to be detected is ultraviolet light, an increase in supply current can be prevented without reducing detection efficiency.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing the structure of an embodiment of the present invention, and FIG. 2 is a horizontal sectional view thereof. FIG. 3 is a longitudinal sectional view showing the structure of a modification of the embodiment shown in FIG. 4 and 5 are longitudinal sectional views showing the structure of another embodiment of the present invention. FIG. 6 is a longitudinal cross-sectional view showing a general structural example of a PN junction type Fol-1 diode, and FIG. 7 is a dark cross-sectional view not showing a conventional structural example of a Fol-diode for ultraviolet light. 1... N-type semiconductor substrate 2... P'' region 3... Protective film 4... High concentration region (impurity layer)

Claims (1)

[Claims] In a photodiode in which a PN junction is formed on a semiconductor substrate, an impurity layer having a higher concentration than other parts of the semiconductor substrate is formed at least around the PN junction in the surface layer of the semiconductor substrate. Characterized by
Photodiode.