JP2007329512A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problem: an element isolation structure is formed through complex formation processes in a four-partitioning photodetector. <P>SOLUTION: On a P-sub layer 80, which acts as a common anode of a PIN photodiode (PIN-PD) for each section 62, a high resistivity epitaxial layer 82 is grown, which acts as an i-layer of the PIN-PD. An isolation region 64 being a p+ region is formed by ion injection from a surface of a substrate on a boundary of the section 62. When reverse-biasing a cathode region 66 formed in each section 62 and the P-sub layer 80 to make the PIN-PD function, the isolation region 64 is made to be a ground potential along with the P-sub layer 80 to become an anode. As a result, a potential barrier against electrons is formed in an epitaxial layer 82 at a location sandwiched by the isolation region 64 and P-sub layer 80, thereby preventing electrons generated by absorbing light in each section 62 from moving to an adjacent section 62 and obtaining an element isolation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light-receiving unit composed of a PIN (p-intrinsic-n) photodiode, and the light-receiving unit is divided into a plurality of sections capable of separately outputting a light reception signal.

  In recent years, optical disks such as CD (Compact Disk) and DVD (Digital Versatile Disk) have come to occupy a large position as information recording media. These optical disk reproducing devices reproduce recorded data based on a change in reflected light intensity of laser light irradiated along a track of the optical disk.

  FIG. 5 is a schematic diagram of an optical pickup mechanism that performs irradiation of the laser light and detection of reflected light. A small and low power consumption semiconductor laser element 2 is used as the laser light source, and the laser light emitted from the semiconductor laser element 2 is focused on the surface of the optical disk 8 by the collimating lens 4 and the objective lens 6. The focused laser beam is irradiated along the track of the optical disc 8, and the optical disc 8 changes the amount of reflected light toward the optical pickup mechanism in accordance with the data recorded along the track.

  The polarization beam splitter 10 provided on the optical path transmits only the longitudinal polarization component (p wave) of the incident light. After the light reflected from the optical disk 8 is transmitted through the λ / 4 plate 12, the polarization plane is rotated by 90 ° together with the rotation of the λ / 4 plate 12 at the time of irradiation. Incident as (s wave). The polarization beam splitter 10 reflects the reflected light in a direction different from the irradiation light according to the rotated polarization plane. The reflected light separated from the irradiation light by the polarization beam splitter 10 enters the photodetector 18 via the focusing lens 14 and the cylindrical lens 16.

  The optical disk reproducing device detects data based on the reflected light, and servo-controls the positional relationship between the optical pickup mechanism and the optical disk 8. Specifically, tracking servo for irradiating the laser beam along the center line of the track and focus servo for keeping the distance between the optical disc 8 and the optical pickup mechanism constant are performed. In order to obtain such information for servo control, a photodetector 18 that receives a reflected light image divided into a plurality of sections is used. The cylindrical lens 16 is provided to perform focus servo control.

  Incidentally, in the focus servo control, the position of the optical pickup mechanism is variably controlled by an actuator based on the output signal of the photodetector 18 to keep the distance from the optical disk 8 constant. Thereby, the fluctuation | variation of the reflected light amount according to the shift | offset | difference of the focus of the irradiated light on the surface of the optical disk 8 is suppressed, and the noise superimposed on the received light signal according to data is suppressed.

  FIG. 6 is a schematic diagram illustrating a light receiving unit of the photodetector 18 and a reflected light image on the light receiving unit. According to the principle of the astigmatism method, the image of the reflected light that has passed through the cylindrical lens 16 is in two orthogonal directions according to the distance d between the optical disk 8 and the objective lens 6 (the vertical direction in FIG. 5 and the vertical direction in FIG. 5). The dimensional ratio of changes. Specifically, when the distance d is a target value, the reflected light image is set to be a perfect circle 30 as shown in FIG. For example, when the distance d is over, the reflected light image becomes a vertically long ellipse 32 as shown in FIG. 6 (a), while when it is under, as shown in FIG. 6 (c). The reflected light image becomes a horizontally long ellipse 34.

  The photodetector element 18 has a light receiving portion divided into four 2 × 2 sections 36, and each section constitutes a light receiving element that outputs a light reception signal. The photodetector 18 is arranged so that the diagonal direction of the 2 × 2 square array of light receiving elements coincides with the axes of the vertically long ellipse 32 and the horizontally long ellipse 34. With this arrangement, each reflection is based on the difference between the sum of the output signals of the two light receiving elements arranged on the diagonal line in the vertical direction and the sum of the output signals of the two light receiving elements arranged on the diagonal line in the horizontal direction in FIG. The shape of the optical image can be determined and used to control the distance d.

  Since the data rate read from the optical disk is very high, the photodetector 18 is composed of a semiconductor element using a PIN photodiode having a high response speed. FIG. 7 is a schematic cross-sectional view of a conventional photodetector 18. This figure shows a sectional view perpendicular to the semiconductor substrate through two adjacent light receiving elements. In this semiconductor element, a p + region serving as an anode region 42 is formed on the surface of a p-type semiconductor substrate 40, and an i layer 44 having a low impurity concentration and a high specific resistance is formed thereon by epitaxial growth. In the i layer 44, a separation region 46 that is formed of a p + region at a position corresponding to the boundary of the light receiving element and continues to the anode region 42 is formed. Further, an n + region that becomes the cathode region 48 is formed on the surface of the i layer 44.

  The anode region 42, the i layer 44, and the cathode region 48 constitute a PIN photodiode that serves as a light receiving element of the photodetector 18. In this PIN photodiode, an anode region 42 and a cathode region 48 are connected to voltage terminals, respectively, and a reverse bias voltage is applied between them. A depletion layer is formed in the i layer 44 in the reverse bias state, and electrons generated by absorption of incident light in the depletion layer move to the cathode region 48 by an electric field in the depletion layer, and are output as a light reception signal. . Here, the separation region 46 reaches the anode region 42 from the surface of the i layer 44 as described above. Thereby, i layer 44 is divided for every light receiving element, and crosstalk between light receiving elements is prevented.

The thickness of the i layer 44 is set to be equal to or greater than the absorption length of the light to be detected in the semiconductor. For example, the absorption length of silicon for light in the 780 nm band and 650 nm band used for CDs and DVDs is about 10 to 20 μm. Here, the p + layer in the isolation region 46 is formed by being pushed in in the depth direction by thermal diffusion after ion implantation. However, in thermal diffusion, the region expands in the horizontal direction as well as in the depth direction. Therefore, when the i layer 44 is relatively thick, in order to form the isolation region 46 whose width is suppressed, the i layer 44 is divided into a plurality of times of epitaxial growth, and each time the epitaxial layer 48 is formed. The isolation region 52 reaching the lower surface of the epitaxial layer 48 is formed by performing ion implantation and thermal diffusion from the surface. By stacking the isolation region 52 together with the epitaxial layer 48 in this manner, the isolation region 46 extending in the depth direction while suppressing the width is formed.
JP-A-10-107243 JP 2001-60713 A

  In the semiconductor element constituting the conventional photodetector 18, when a relatively thick i layer of 10 to 20 μm is formed, the formation of the epitaxial layer 50 and the isolation region 52 is repeated a plurality of times. Therefore, there has been a problem that the manufacturing cost becomes high. Further, there is a problem that the inter-terminal capacitance between the anode and the cathode is increased by the junction area between the isolation region 46 and the i layer 44, and the high-speed response characteristic of the PIN photodiode is impaired.

  The present invention has been made to solve the above-described problems, and can reduce the manufacturing cost. The semiconductor device has suitable performance as a split photodetector that detects an optical signal from an optical disk or the like. The purpose is to provide.

  A semiconductor device according to the present invention is a semiconductor device in which a light receiving portion divided into a plurality of sections is formed on a surface of a semiconductor substrate, and a low impurity concentration intermediate semiconductor region provided on the surface, and a lower surface of the intermediate semiconductor region A first conductivity type lower semiconductor region having a higher impurity concentration than the intermediate semiconductor region, which is disposed in contact with the first voltage, and is formed on a surface of the intermediate semiconductor region along a boundary between partitions; The first conductivity type boundary semiconductor region having a higher impurity concentration than the intermediate semiconductor region, to which one voltage is applied, and the respective regions on the surface of the intermediate semiconductor region are formed, and the second voltage is applied. A plurality of upper semiconductor regions of the second conductivity type having a higher impurity concentration than the intermediate semiconductor region, and having an intermediate semiconductor region between the boundary semiconductor region and the lower semiconductor region, the first voltage being the lower semiconductor From the area side The second voltage is applied from the upper semiconductor region side, and each upper semiconductor region and the lower semiconductor region are reversely biased by the first voltage and the second voltage, and a depletion layer is formed in the intermediate semiconductor region. The boundary semiconductor region is formed with a potential barrier against movement of the signal charge between the compartments with the lower semiconductor region according to the first voltage.

  In another semiconductor device according to the present invention, the lower semiconductor region has a convex portion protruding upward at a position facing the boundary semiconductor region.

  According to the present invention, since the boundary semiconductor region provided at the boundary between the sections to be the light receiving elements is formed after the intermediate semiconductor region to be the i layer is completed, the manufacturing cost is suppressed. The The boundary semiconductor region reaches only a part of the depth from the surface of the intermediate semiconductor region, and the intermediate semiconductor region exists between the boundary semiconductor region and the lower semiconductor region in the boundary portion of the partition. The intermediate semiconductor region in the boundary portion serves as a potential barrier against signal charges collected in the upper semiconductor region by applying a voltage that is reverse biased to the upper semiconductor region in both the boundary semiconductor region and the lower semiconductor region. Thereby, crosstalk between the sections is suppressed. Further, by forming the boundary semiconductor region only to a part of the depth of the intermediate semiconductor region, the inter-terminal capacitance between the boundary semiconductor region and the lower semiconductor region and the upper semiconductor region is suppressed, and the response speed is increased. . Furthermore, since the intermediate semiconductor region at the boundary is also subjected to photoelectric conversion, the conversion efficiency is improved. Further, in the case where light can be incident on the surface of the boundary semiconductor region, the light can pass through the boundary semiconductor region, enter the intermediate semiconductor region of the boundary portion, and be photoelectrically converted. That is, the semiconductor device according to the present invention is sensitive to light incident on the boundary portion of the section, and detection loss at the boundary portion is suppressed, so that an optical image extending over a plurality of sections is provided for each section. It can be divided and detected with high accuracy.

Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.
[Embodiment 1]
FIG. 1 is a schematic plan view of a photodetector which is a semiconductor element of the embodiment. The photodetector 60 is formed on a semiconductor substrate made of silicon, and a light receiving portion is disposed in an opening (not shown) provided in a protective film laminated on the surface of the semiconductor substrate. The light receiving unit divides the light incident on the substrate surface into 2 × 2 four sections 62 and receives the light.

Each partition 62 is delimited by an isolation region 64 (boundary semiconductor region) formed on the surface of the surrounding semiconductor substrate. The isolation region 64 is formed, for example, as a p + region in which a high concentration p-type impurity is diffused. In the portion corresponding to the light receiving portion of the silicon substrate, electrons and holes are generated by absorption of light. In each section 62, a cathode region 66 (upper semiconductor region) that collects electrons among the generated charges is arranged as a cathode of the PIN photodiode. The cathode region 66 is formed, for example, as an n + region in which a high concentration n-type impurity is diffused.

  The isolation region 64 and each cathode region 66 are connected to wirings formed of, for example, an aluminum (Al) layer or the like through contacts. For example, a ground potential is applied to the isolation region 64 by the wiring 68. Further, the signal charge collected in each cathode region 66 is read out via the wiring 70.

  FIG. 2 is a schematic cross-sectional view showing the structure of the light receiving section in a cross section passing through the straight line A-A ′ shown in FIG. 1 and perpendicular to the semiconductor substrate. This photodetector 60 has a lower specific impurity concentration and a higher specific resistance than the P-sub layer 80 on one main surface of the P-sub layer 80 (lower semiconductor region) which is a p-type silicon substrate into which a p-type impurity has been introduced. The semiconductor substrate is formed using a semiconductor substrate on which a semiconductor layer is stacked. The P-sub layer 80 becomes the anode of the PIN photodiode. The high resistivity semiconductor layer stacked thereon is formed by, for example, epitaxial growth. The epitaxial layer 82 constitutes an i layer (intermediate semiconductor region) of the PIN photodiode. The low concentration impurity introduced into the epitaxial layer 82 is, for example, a p-type impurity. The isolation region 64 and the cathode region 66 described above are formed on the surface of the epitaxial layer 82.

  Here, the silicon substrate on which the epitaxial layer 82 is laminated is provided by a semiconductor substrate maker, and the photodetector 60 can be manufactured using the silicon substrate. Impurities are introduced into the isolation region 64 and the cathode region 66 by forming a mask formed by a photolithographic technique on the surface of the silicon substrate on which the epitaxial layer 82 is formed, and ion implantation is performed using the mask. This is realized by selectively performing.

  Impurities introduced by ion implantation at positions where the separation region 64 and the cathode region 66 of the substrate are respectively formed are further pushed into the substrate depth direction by performing a thermal diffusion process as necessary. The pushing amount can be controlled separately for each of the separation region 64 and the cathode region 66. For example, the separation region 64 has a function of suppressing crosstalk between the compartments 62 of the signal charge collected in each cathode region 66, as will be described later. Therefore, the depth of the separation region 64 can be set deeper than that of the cathode region 66, for example. On the other hand, by reducing the depth of the cathode region 66, the depletion layer formed in the i layer therebelow spreads from near the substrate surface, and an improvement in photoelectric conversion efficiency can be expected. When the cathode region 66 is formed to be shallower than the separation region 64 as described above, it is preferable to perform ion implantation and thermal diffusion of impurities into the separation region 64 prior to ion implantation into the cathode region 66.

  As already described, the thickness of the epitaxial layer 82 constituting the i layer is set to be equal to or greater than the absorption length of light to be detected in the semiconductor. For example, the absorption length of silicon for light in the 780 nm band and 650 nm band used for CDs and DVDs is about 10 to 20 μm. This thickness is greater than the depth of the isolation region 64. That is, in the configuration of the photodetector 60, the isolation region 64 does not reach the P-sub layer 80, and the high resistivity epitaxial layer 82 is formed between the isolation region 64 and the P-sub layer 80. Present as a layer.

  As described above, the P-sub layer 80 is used as the anode of the PIN photodiode. That is, the P-sub layer 80 is applied with a ground potential from the back surface of the substrate, for example, and functions as an anode. Here, the isolation region 64 is applied with a ground potential by the wiring 68 provided on the substrate surface side as described above, and constitutes an anode together with the P-sub layer 80.

Next, the operation of the photodetector 60 will be described. FIG. 3 is a schematic diagram showing a circuit configuration during the operation of the photodetector 60 and a potential distribution in the element cross section corresponding to FIG. The cathode region 66 is brought into a reverse bias state by the voltage source 90 with respect to the isolation region 64 and the P-sub layer 80 which are set to the ground potential. Specifically, the wiring from each cathode region 66 (wiring 70 in FIG. 1) is connected to one input terminal of the operational amplifier 92, and the positive voltage Vb from the voltage source 90 is input to the other terminal of the operational amplifier 92. . The operational amplifier 92 has an output terminal connected to the cathode region 66 through a resistor, and constitutes a current detector. With this configuration, Vb is applied to the cathode region 66 and a voltage corresponding to the cathode current is taken out to the output terminal of the operational amplifier 92.

  In the sectional view, several equipotential lines are indicated by dotted lines. This sectional view shows that a depletion layer spreads in the epitaxial layer 82 constituting the i layer by applying a reverse bias voltage to the anode and the cathode of the PIN photodiode. The closer to the cathode region 66, the deeper, that is, the potential potential becomes, and a potential well for electrons is formed around each cathode region 66. By applying a ground potential that is a reverse bias to the cathode region 66 using the isolation region 64 and the P-sub layer 80 as an anode, the boundary region 94 between the isolation region 64 of the epitaxial layer 82 and the P-sub layer 80 is applied. The potential potential becomes shallower. That is, by setting the separation region 64 as an anode in addition to the P-sub layer 80 to the ground potential, the potential potential of the boundary region 94 under the separation region 64 is pulled in a direction of decreasing. Thereby, a potential barrier against the movement of electrons is formed between the potential wells corresponding to the sections 62 adjacent to each other with the isolation region 64 interposed therebetween.

  For example, in FIG. 2 or FIG. 3, the electrons generated in the i layer under the cathode region 66-1 on the left side by the incident light to the left section 62 cause the cathode region 66− along the electric field of the left potential well. 1 is easily movable, but it is difficult to move to the cathode region 66-2 on the right side because a potential barrier exists in the region 94. Therefore, the signal charges corresponding to the incident light on the left compartment 62 are collected exclusively in the cathode region 66-1. Similarly, the signal charges corresponding to the light incident on the right section 62 are less likely to move to the cathode region 66-1 due to the presence of the potential barrier, and are collected exclusively in the cathode region 66-2. The amount of electrons collected in each cathode region 66 is detected via the operational amplifier 92 as a cathode current.

  In the configuration of the photodetector 60, although the separation region 64 is an anode in addition to the P-sub layer 80 as described above, the i layer of the adjacent section 62 is connected under the separation region 64. First, element isolation between PIN photodiodes in each section 62 is realized, and a light reception signal in which crosstalk is suppressed is obtained for each section 62.

  A LOCOS (local oxidation of silicon) method is known as one conventional technique for element isolation. According to that technique, for example, a thick oxide film that grows into the substrate is grown selectively in the p + region as formed in the isolation region 64. Although the technology can be applied to the photodetector 60 as well, the technology is not adopted in the present embodiment.

  By not forming the LOCOS oxide film on the isolation region 64 in this way, incident light from above the isolation region 64 is not attenuated by the LOCOS oxide film. Here, in this photodetector 60, the isolation region 64 is an i layer and can be depleted. Therefore, the light that has been suppressed from being attenuated and has entered from above the separation region 64 can reach the i layer below the separation region 64 to generate a signal charge, thereby improving the detection efficiency for the light incident on the light receiving unit. To do.

In addition, the separation region 64 can be an insensitive region for incident light detection. Here, by not forming the LOCOS oxide film, the lateral diffusion of the isolation region 64 in the formation process is avoided. As a result, since the ratio of the separation region 64 occupying the light receiving unit is suppressed, the detection efficiency for the light incident on the light receiving unit can be improved also in this respect.
[Embodiment 2]
The photodetector 60 according to the second embodiment is characterized by a cross-sectional structure in the direction perpendicular to the substrate. The planar structure can be the same as that of the first embodiment, for example, and FIG. 1 is used here. To do.
FIG. 4 is a schematic cross-sectional view showing the structure of the light receiving portion of the second embodiment in a cross section passing through the straight line AA ′ shown in FIG. 1 and perpendicular to the semiconductor substrate. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description is simplified. The photodetector 60 has a lower separation region 100 that is a p + region protruding from the P-sub layer 80 at a position facing the separation region 64.

  The lower isolation region 100 receives a voltage applied to the P-sub layer 80 and functions as an anode on the substrate side together with the P-sub layer 80. With the lower isolation region 100, the distance between the anode formed by the isolation region 64 and the anode on the substrate side is narrowed at the boundary of the section 62, and the potential barrier against electrons is formed in the epitaxial layer 82 between them. It can form more suitably. Therefore, the element isolation performance between the sections 62 is improved.

  For example, in the lower isolation region 100, the p-type impurity is formed by ion implantation or the like at a position corresponding to the boundary of the partition 62 of the epitaxial layer 82 at the stage where the epitaxial layer 82 is partially stacked on the P-sub layer 80. It is formed by introducing. After forming the lower isolation region 100 in this manner, the remaining thickness of the epitaxial layer 82 is grown, and the structure of the substrate surface such as the isolation region 64 and the cathode region 66 is formed in the same manner as in the first embodiment.

It is a schematic plan view of a photodetector which is a semiconductor element of an embodiment. It is a typical vertical sectional view showing the structure of the light receiving unit according to the first embodiment. It is a schematic diagram which shows the circuit structure at the time of operation | movement of a photodetector, and the potential distribution in a vertical cross section. It is a typical vertical sectional view which shows the structure of the light-receiving part which concerns on 2nd Embodiment. It is a schematic diagram of the optical pick-up mechanism which performs irradiation of a laser beam, and detection of reflected light. It is a schematic diagram which shows the light-receiving part of a photodetector, and the reflected light image on the said light-receiving part. It is a typical vertical sectional view of a conventional photodetector.

Explanation of symbols

  2 semiconductor laser elements, 8 optical disks, 10 polarizing beam splitters, 16 cylindrical lenses, 18, 60 photodetectors, 62 sections, 64 separation areas, 66 cathode areas, 68, 70 wiring, 80 P-sub layers, 82 epitaxial layers, 100 Lower separation region.

Claims (2)

A semiconductor device in which a light receiving portion divided into a plurality of sections is formed on the surface of a semiconductor substrate,
A low impurity concentration intermediate semiconductor region provided on the surface;
A lower semiconductor region of a first conductivity type having a higher impurity concentration than the intermediate semiconductor region, which is disposed in contact with the lower surface of the intermediate semiconductor region and to which a first voltage is applied;
A boundary semiconductor region of the first conductivity type having a higher impurity concentration than the intermediate semiconductor region, which is formed on a surface of the intermediate semiconductor region along a boundary between the partitions and to which a first voltage is applied;
A plurality of upper semiconductor regions of a second conductivity type having a higher impurity concentration than the intermediate semiconductor region, each of which is formed at a position corresponding to each section of the surface of the intermediate semiconductor region and to which a second voltage is applied;
Have
Having the intermediate semiconductor region between the boundary semiconductor region and the lower semiconductor region;
The first voltage is applied from the lower semiconductor region side, and the second voltage is applied from the upper semiconductor region side,
Each of the upper semiconductor region and the lower semiconductor region is reverse biased by the first voltage and the second voltage to form a depletion layer in the intermediate semiconductor region,
The boundary semiconductor region forms a potential barrier against movement of the signal charge between the compartments with the lower semiconductor region according to the first voltage;
A semiconductor device characterized by the above. The semiconductor device according to claim 1,
The lower semiconductor region has a convex portion protruding upward at a position facing the boundary semiconductor region.

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