JPH0330374A - Semiconductor photosensor - Google Patents

Abstract

PURPOSE:To enhance the contrast between photodiodes while reducing the dispersion in sensitivity by a method wherein the first conductivity type high concentration carrier distribution region is provided inside a substrate beneath a multitude of pn junction photodiodes. CONSTITUTION:The first conductivity type high concentration carrier distribution region 5 is provided inside a substrate 1 beneath a multitude of pn junction photodiodes. The carriers generated on the surface side are attracted to the photodiode side by the potential running from the carrier distribution region 5 to the photodiodes to increase the collecting efficiency of the carriers for augmenting the contribution to the photoelectric current. On the other hand, the carriers generated inside the substrate beneath the carrier distribution region 5 are obstructed by the potential barrier of the carrier distribution region 5 not to contribute to the photoelectric current of any photodiodes at all. Through these procedures, the carrier generated only on the parts near the photodiodes can effectively contribute to the photoelectric current so that the sensitivity of respective photodiodes may be augmented to enhance the contrast between the photodiodes while reducing the dispersion in the sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor optical sensor used in cameras and the like, and particularly relates to a semiconductor optical sensor including a plurality of pn junction photodiodes.

[Conventional technology]

Conventionally, the structure of a semiconductor optical sensor equipped with a plurality of pn junction photodiodes is as shown in FIGS. 1 and 3, as shown in FIG. The p-n junction between the p-type head region 2 of this isolation island and the n-type semiconductor substrate l is one p-type head region 2.
It functions as an n-junction photodiode. Furthermore, as shown in FIG. 4, a device in which a p-type head t*2 is embedded in an n-type semiconductor substrate l is also known.

When each pn junction diode is electrically energized as shown, depletion layers 1a and 2a are formed on both sides from the junction surface,
When light enters, an electron/genuine bill pair is generated, and a photocurrent flows with an intensity proportional to the intensity of the light. Almost 100% of carriers generated in the depletion layers 1a and 2a flow as current due to the depletion electric field in the depletion layers 1a and 2a, but carriers generated in the non-depletion layers of the n-type semiconductor substrate 1 and the p-type head region 2 Killaa diffuses during the carrier lifetime and forms the depletion layer 1a2.
Only those that reach a contribute as photocurrent, and the others recombine and are lost in the form of thermal energy.

[Problem to be solved by the invention]

In the structure of the conventional semiconductor optical sensor described above, carriers generated in the non-depletion layer of the n-type semiconductor substrate 2 shown in FIG. Spread with probability. Therefore, what effectively contributes to photocurrent is approximately 1/2 of the generated carriers.
and remained at a low level. Carriers 3 generated near each photodiode have a high probability of reaching the depletion layers 1a and 2a of the nearby photodiodes and contributing as photocurrent, but in the case of carriers 4 generated far away from the photodiode, , the probability of reaching multiple photodiodes is approximately the same. For this reason, carriers generated directly under one photodiode also reach other photodiodes, and carriers are exchanged between photodiodes, resulting in strong interaction (crosstalk) between photodiodes. ,
This may worsen the contrast between photodiodes or cause variations in sensitivity.

An object of the present invention is to improve contrast between photodiodes and reduce sensitivity variations by converging carriers generated in a non-depletion layer, thereby providing a semiconductor optical sensor with higher precision.

[Means to solve the problem]

In order to solve the above problems, the means taken by the present invention is to provide a structure in which a high concentration first iJ type carrier collection region is provided inside the substrate under a plurality of pn junction photodiodes.

[Effect]

According to this means, carriers generated on the surface side of the highly concentrated first conductivity type carrier collection region inside the substrate are pulled toward the photodiode by the potential flowing from the carrier collection region toward the photodiode.
The carrier collection efficiency increases and the contribution to photocurrent increases. In addition, carriers generated inside the substrate below the carrier-concentration region are generated at the potential lII” of the carrier-concentration region.
1 and does not contribute to any photodiode photocurrent. In this way, only the carriers generated in the vicinity of the photodiodes effectively contribute, so that the sensitivity of each photodiode increases, the contrast between the photodiodes improves, and sensitivity variations are reduced.

〔Example〕

Next, embodiments of the present invention will be described based on the accompanying drawings.

FIG. 1 is a longitudinal sectional view showing the structure of a semiconductor optical sensor according to a first embodiment of the present invention. In FIG. 1, the same parts as those shown in FIG. 3 are given the same reference numerals, and their explanations will be omitted. In the figure, island-shaped p-wall regions 2 formed on the surface side of an n-type semiconductor substrate 1 are separated from each other by the number of photodiodes, and at a depth of about 10 μm from the surface, there is a highly concentrated n-type layer with carrier concentration. Region 5 is formed. Therefore, there are n-type regions 10.20 above and below the carrier concentration region 5.
are being distributed.

To explain the method for forming this highly concentrated n-type carrier collection region 5, first, a photoresistor is formed by opening a window in an n-type semiconductor substrate with a specific resistance of 2 to 3 Ω·cm using ordinary photolithography technology in the same way as in the case of forming a p-type region. After depositing the
Insert about X10"am-2. Then, in nitrogen gas
00℃, 30m1n, 1100℃ in oxygen gas, 2
When heat treatment is applied to 0m1n, the diffusion depth is only within the substrate ~
A high concentration n-type carrier collection region 5 of 1.5 pm and 8 degrees 5 Then, a p-wall region 2 is formed thereon by thermal diffusion.As a result, a highly concentrated n-type carrier accumulation region 5 is embedded in the n-type semiconductor substrate.

In the structure in which the carrier accumulation region 5 is embedded in this way, the carriers 3 generated in the n-type region 10 on the substrate surface side are pushed toward the photodiode by the potential of the carrier accumulation region 5, which is a highly concentrated n-type region. Therefore, carrier collection efficiency increases, and carriers generated near a certain photodiode reliably reach its depletion layer 1a, 2a. On the other hand, carriers 4 generated in the n-type region 20 under the carrier-concentration region 5 are blocked by the potential barrier of the carrier-concentration region 5, so they do not reach the depletion layers 1a and 2a of any photodiode and are converted into photocurrent. Does not contribute. In other words, only carriers generated in the vicinity of a certain photodiode contribute to the photocurrent of that photodiode, improving sensor sensitivity and reducing carrier exchange between photodiodes, improving contrast. Furthermore, since the influence of carriers from a distance is eliminated, variations in sensitivity are also reduced.

FIG. 2 is a longitudinal sectional view showing the structure of a semiconductor optical sensor according to a second embodiment of the present invention. This embodiment is applied to a semiconductor optical sensor having a buried p-type head region 2 shown in FIG.
is formed, and has the same effect as the first embodiment.

〔Effect of the invention〕

As described above, the present invention is characterized in that a highly concentrated carrier collection region of the first conductivity type is buried inside the substrate, and therefore has the following effects.

In other words, since the inside of the substrate is divided into two by a potential barrier in the highly concentrated carrier-concentration region, carriers generated in the non-depleted layer above the carrier-concentration region are quickly attracted to the nearby photodiode and contribute as a photocurrent. , carriers generated within the substrate below the carrier collection region do not stray into any of the photodiodes and do not contribute to photocurrent. Therefore, sensor sensitivity is improved, interaction between photodiodes is reduced, and contrast is improved. Furthermore, since the influence of carriers from a distance is eliminated, variations in sensitivity are also reduced.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing the structure of a semiconductor optical sensor according to a first embodiment of the present invention. FIG. 2 is a longitudinal sectional view showing the structure of a semiconductor optical sensor according to a second embodiment of the present invention. FIG. 3 is a longitudinal sectional view showing the structure of a conventional semiconductor optical sensor. FIG. 4 is a longitudinal sectional view showing the structure of another conventional semiconductor optical sensor. 1 n-type semiconductor substrate, 2 p-wall region of photodiode, la, 2a depletion layer, 3, 4 generated carriers,
5 High concentration n-type carrier collection region, 10 N-type region above the carrier collection region, 201 - Pull conductor substrate 5... High concentration ML carrier collection region 1st section 2 Σ

Claims (1)

[Claims] 1) A semiconductor optical sensor comprising a plurality of pn junction photodiodes each including a first conductivity type region and a plurality of island-shaped second conductivity type regions separated from each other, the plurality of semiconductor optical sensors comprising: A semiconductor optical sensor comprising a highly concentrated first conductivity type carrier collection region inside a substrate below a pn junction photodiode.