JP4338542B2 - Light receiving element - Google Patents

Description

  The present invention relates to a light receiving element that can receive visible light from infrared, and more particularly to a light receiving element suitable for use in monitoring light having a short wavelength.

  A light receiving element that monitors the output of a laser beam having a wavelength from infrared to red is used as a light receiving element having a PIN structure by diffusing P and N type impurities into a semiconductor substrate made of silicon (for example, Patent Document 1). 1). As shown in FIG. 10, such a light receiving element has a P-type impurity such as B (boron) diffused at a high concentration on the surface of a semiconductor substrate 100 made of silicon containing a low-concentration N-type impurity. A high-concentration impurity layer 101 and an insulating film 102 covering them are formed, a contact hole 103 is formed in a part of the insulating film 102, and a P-type electrode 104 is connected through the contact hole 103 to form a light-receiving region having a constant area. Form. An N-type impurity layer 105 is formed by diffusing N-type impurities such as P (phosphorus) at a high concentration on the back side of the semiconductor substrate 100, and an N-type electrode 106 is connected to the N-type impurity layer 105 to constitute a light receiving element. .

When such a light receiving element is used for monitoring a blue or blue-violet LED or laser diode having a short wavelength, the light absorption at the surface of the light receiving element, particularly the high-concentration impurity layer 101, is large. In comparison with this, only a sensitivity of about 1/5 can be obtained.
Japanese Patent Laid-Open No. 4-76964

  Therefore, an object of the present invention is to increase the sensitivity of a light receiving element, efficiently receive light of blue or blue-violet short wavelength light, increase the sensitivity, and provide a structure suitable for it.

As described in claim 1, the light receiving element of the present invention has a high concentration of one conductivity type formed by forming a high concentration one conductivity type impurity layer and a reverse conductivity type impurity layer on a semiconductor substrate having a low impurity concentration and connecting to the electrode. In a PN-type or PIN-type light-receiving element in which a light-receiving region having a certain area is formed by arranging an impurity layer on the substrate surface, a low-concentration layer in which the low-concentration impurity layer of the semiconductor substrate is exposed on the substrate surface in the light-receiving region A plurality of exposed regions are formed, and these low-concentration layer exposed regions are arranged in a dispersed manner in the light-receiving region, and a high-concentration impurity layer connected to the electrode is radiated over the light-receiving region around the electrode. The electrode is arranged in the center of the light receiving region, and the low concentration layer exposed regions are distributed and arranged so as to surround the electrode .

According to the present invention, since light absorption on the surface of the light receiving element is suppressed even for light with a short wavelength, sensitivity can be increased. An electrode is arranged in the center of the light receiving region, the low-concentration layer exposed region is dispersed and arranged so as to surround the electrode, and the arrangement of the exposed region and the high-concentration layer is optimized, so that it is suitable for increasing sensitivity. Structure can be provided. In particular, since the high-concentration impurity layer is disposed so as to extend radially over the entire light receiving region with the electrode as the center, the photocurrent can be efficiently collected on the electrode by the high-concentration impurity layer.

  Embodiments of the present invention will be described below with reference to the drawings. 1 is a plan view showing an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line AA in FIG. 1, and FIG. 3 is a cross-sectional view taken along line BB in FIG. In these figures, the light receiving element 1 is a PN type or PIN type light receiving element by diffusing P-type and N-type impurities into a silicon semiconductor substrate 2 containing low-concentration impurities.

The semiconductor substrate 2 is made of single crystal silicon containing low-concentration impurities necessary to function as an I layer. The semiconductor substrate 2 is N-type, and its impurity concentration is, for example, 4 × 10 ¹² cm ⁻³ or less.

A P-type high-concentration impurity layer 3 is formed on most of the surface of the semiconductor substrate 2 by diffusing P-type impurities such as B (boron) at a high concentration using a diffusion mask having a predetermined shape. The thickness of the P-type high concentration impurity layer 3 is 1 to 2 μm, and the impurity concentration is, for example, about 1 × 10 ²⁰ cm ⁻³ . The P-type high concentration impurity layer 3 forms a light receiving region 4 having a certain area on the surface of the semiconductor substrate 2. An insulating film 5 made of silicon nitride, silicon oxide or the like is formed so as to cover the surface of the semiconductor substrate 2 on which the P-type high concentration impurity layer 3 is formed. A contact hole 6 is formed in a part of the insulating film 5 on the light receiving region 4, and the P-type electrode 7 is ohmically connected to the P-type high concentration impurity layer 3 through the contact hole 6. N-type impurities such as P (phosphorus) are diffused at a high concentration on the back side of the semiconductor substrate 2 to form an N-type high-concentration impurity layer 8, and an N-type electrode 9 is ohmically connected thereto. The thickness of the N-type high concentration impurity layer 8 is 20 to 50 μm, and the impurity concentration is, for example, about 1 × 10 ²⁰ cm ⁻³ .

  In a normal case, the light receiving region 4 is filled with an impurity layer of one conductivity type (P type in this example), but this impurity layer acts as an absorption layer for light (especially near a wavelength of blue to blue-violet). Therefore, in the present invention, a plurality of low concentration layer exposed regions 10 for suppressing the light absorption are formed in the light receiving region 4. The low concentration layer exposed region 10 is formed by exposing a low concentration impurity layer constituting the semiconductor substrate 2 to the substrate surface. The low-concentration layer exposed region 10 is formed by changing the shape of the mask pattern when the high-concentration impurity layer 3 is formed by selective diffusion. In this embodiment, the low-concentration layer exposed region 10 is formed into a minute square shape or rectangular shape, and these are dispersed and arranged in a two-dimensional matrix shape over substantially the entire light receiving region 4. Therefore, part of the light incident on the light receiving region is incident through the low concentration layer exposed region 10, so that light absorption in the high concentration impurity layer 3 is suppressed.

  When a constant reverse bias is applied between the electrodes, positive and negative carriers are generated by the energy of incident light in the low-concentration layer portion functioning as the I layer of the semiconductor substrate. A photocurrent is generated by moving to one of the N high-concentration impurity layers. Incident light is converted into electricity by such photoelectric conversion.

  4 and 5 show another embodiment in which the shape of the low-concentration layer exposed region 10 is changed. Since other configurations are the same as those of the previous embodiment, the differences will be mainly described. The embodiment shown in FIG. 4 is characterized in that the low-concentration layer exposed region 10 has a strip shape and is distributed in the light receiving region 4 in a certain direction. By disposing the low-concentration layer exposed region 10 in the light receiving region 4, the light conversion efficiency can be enhanced over the entire light receiving region.

  The embodiment shown in FIG. 5 is characterized in that the low-concentration layer exposed region 10 is arranged in a strip shape and dispersed in a plurality of directions in the light receiving region. That is, it is characterized in that the vertically and horizontally long low-concentration layer exposed regions 10 are arranged by dividing one of the diagonal lines of the light receiving region 4 as a boundary. By disposing the low-concentration layer exposed region 10 in the light receiving region 4, the light conversion efficiency can be improved over the entire light receiving region 4.

  The embodiment shown in FIGS. 1 and 5 is common in that the high-concentration impurity layer 3 (located between the low-concentration layer exposed regions 10 and 10) extends radially around the electrode 7. Thus, since the high concentration impurity layer 3 extends radially over the entire light receiving region 4 with the electrode 7 as the center, the photocurrent can be efficiently collected on the electrode 7 by the high concentration impurity layer 3.

  6 and 7 show still another embodiment in which the shape of the low-concentration layer exposed region 10 and the arrangement of the electrodes 7 are changed. Here, FIG. 7 is a cross-sectional view taken along the line CC of FIG. Since other configurations are the same as those of the previous embodiment, the differences will be mainly described. The embodiment shown in FIGS. 6 and 7 is characterized in that the electrode 7 is disposed at the center of the light receiving region 4 and the low-concentration layer exposed regions 10 are annularly distributed so as to surround the electrode 7. By disposing the low-concentration layer exposed region 10 in the light receiving region 4, the light conversion efficiency can be enhanced over the entire light receiving region. The low-concentration layer exposed region 10 arranged so as to surround the electrode 7 is not a complete ring, but a part thereof is divided by the high-concentration impurity layer 3, so that the configuration shown in FIGS. Since the high-concentration impurity layer 3 can be configured to extend radially over the entire light receiving region 4 around the electrode 7, the photocurrent can be efficiently collected on the electrode 7 by the high-concentration impurity layer 3. .

  8 and 9 show still another embodiment in which the shape and arrangement of the high concentration impurity layer 8 and the electrode 9 are changed. Here, FIG. 9 is a cross-sectional view taken along the line DD of FIG. Since other configurations are the same as those of the previous embodiment, the differences will be mainly described. The embodiment shown in FIGS. 8 and 9 is characterized in that the high concentration impurity layer 8 and the electrode 9 arranged on the back side of the semiconductor substrate 2 are arranged on the front side of the semiconductor substrate 2 together with the electrode 7. The high-concentration impurity layer 8 is annularly arranged outside the light receiving region 4 with a certain interval. The electrode 9 is ohmically connected to the high concentration impurity layer 8 through a contact hole formed in the insulating film. By arranging the electrodes 7 and 9 on the same plane, the degree of freedom of electrode arrangement can be increased. In addition, since the arrangement of the PN layer is in the thickness direction of the substrate in the embodiments shown in FIGS. 1 to 7, the PN junction is in the same direction as the surface of the substrate in the embodiments shown in FIGS. The degree of freedom of arrangement can be increased.

In the above embodiment, since the low-concentration layer exposed region 10 is selectively formed by changing the diffusion mask, the surface of the semiconductor substrate 2 becomes flat.
The low-concentration layer exposed region 10 can also be formed by forming a high-concentration impurity layer on the front surface of the light-receiving region 4 and then selectively removing this layer to form irregularities on the substrate surface. In the above embodiment, the case where a silicon semiconductor is used has been exemplified. However, the present invention can also be applied to the case where a light receiving element is formed using another semiconductor. Further, the polarities of P and N of the impurities can be changed to opposite polarities.

  It can be used for a light receiving element having light receiving sensitivity from infrared to visible light. It can be used as a light-receiving element for monitoring LEDs or laser diodes having a wavelength from blue to blue-violet.

It is a top view which shows one Embodiment of this invention. FIG. 2 is a cross-sectional view taken along AA in FIG. 1. It is sectional drawing along BB of FIG. It is a top view which shows another embodiment of this invention. It is a top view which shows another embodiment of this invention. It is a top view which shows another embodiment of this invention. It is sectional drawing along CC of FIG. It is a top view which shows another embodiment of this invention. It is sectional drawing along DD of FIG. It is sectional drawing which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light receiving element 2 Semiconductor substrate 3 One conductivity type high concentration impurity layer 4 Light receiving region 5 Insulating film 6 Contact hole 7 Electrode 8 Reverse conductivity type high concentration impurity layer 9 Electrode 10 Low concentration layer exposure region

Claims (1)

A high-concentration one-conductivity-type impurity layer and a reverse-conductivity-type impurity layer are formed on a low-impurity concentration semiconductor substrate, and the one-conductivity-type high-concentration impurity layer connected to the electrode is disposed on the substrate surface to form a light-receiving region having a certain area. In the formed PN-type or PIN-type light-receiving element, a plurality of low-concentration layer exposed regions in which the low-concentration impurity layer of the semiconductor substrate is exposed on the substrate surface are formed in the light-receiving region. Dispersed and arranged in the light receiving region, a high-concentration impurity layer connected to the electrode is arranged so as to extend radially over the entire light receiving region around the electrode, and the electrode is arranged in the center of the light receiving region The light-receiving element is characterized in that the low-concentration layer exposed region is dispersed and arranged so as to surround the electrode .

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