JP2005158834A - Optical semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical semiconductor device where detection efficiency and a high frequency response characteristic of light energy are improved. <P>SOLUTION: The optical semiconductor device is provided with a p-type semiconductor substrate 10, a photodiode 20 formed on the surface of the p-type semiconductor substrate 10, and a peripheral circuit 30 formed at a position adjacent to the photodiode 20 on the surface of the p-type semiconductor substrate 10. A plurality of trenches Tp and Tn extended deeper than the peripheral circuit 30 are formed on the surface of the photodiode 20. A p<SP>+</SP>-type diffusion layer 21p and an n<SP>+</SP>-type diffusion layer 21n are formed in the trenches Tp and Tn. The p<SP>+</SP>-type diffusion layer 21p and the n<SP>+</SP>-type diffusion layer 21n in the adjacent trenches Tp and Tn are formed so that the diffusion layers different in conduction types are made adjacent. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical semiconductor device having a light receiving element, and more particularly to an optical semiconductor device in which a light receiving element and a CMOS are formed on the same substrate.

  2. Description of the Related Art In recent years, an optical semiconductor device in which a light receiving element (for example, photodiode) and its peripheral circuit are formed on the same substrate has attracted attention as a light detecting element used for light detection such as a DVD (Digital Video Disk) or infrared communication. According to the above optical semiconductor device, it is not necessary to separately form the light receiving element and its peripheral circuit, so that the manufacturing cost of the optical semiconductor device can be reduced as much as possible. In addition, electromagnetic interference from the outside of the optical semiconductor device can be suppressed as low as possible.

  Next, an optical semiconductor device according to a conventional example will be described with reference to the drawings. FIG. 5 is a schematic cross-sectional view of an optical semiconductor device according to a conventional example. As shown in FIG. 5, a photodiode portion 20 s is formed on the surface of the p-type semiconductor substrate 10. A peripheral circuit portion 30 is formed at a position adjacent to the photodiode portion 20s.

  Here, in the photodiode portion 20 s, a p + -type diffusion layer 21 ps connected to the terminal a is formed on the surface of the p-type semiconductor substrate 10. The terminal a is grounded via a resistor R (not shown). A second n-type well 22s is formed on the surface of the p-type semiconductor substrate 10 at a position adjacent to the p + -type diffusion layer 21ps. On the surface of the second n-type well 22s, an n + -type diffusion layer 21ns connected to the terminal b is formed. A power supply voltage Vdd is supplied to the terminal b.

  Further, in the peripheral circuit portion 30, the second n-type well 31 has the same depth as the second n-type well 22s formed in the photodiode portion 20s (the depth from the surface of the p-type semiconductor substrate 10). ). Further, in the second n-type well 31, a p-type well 32p and a first n-type well 32n are formed adjacent to each other. In the p-type well 32p, an n-channel MOS transistor NMOS having a source and drain made of n + -type diffusion layers 33n and 34n and a gate electrode 35n formed through an insulating film is formed. In the first n-type well 32n, a p-channel MOS transistor PMOS having a source and drain composed of p + type diffusion layers 33p and 34p and a gate electrode 35p formed through an insulating film is formed. Yes. That is, the peripheral circuit unit 30 is configured by a CMOS transistor including an n-channel MOS transistor NMOS and a p-channel MOS transistor PMOS.

  Next, the operation of the optical semiconductor device according to the conventional example will be described with reference to FIG. 5 and the equivalent circuit diagram of the photodiode portion 20s shown in FIG. Here, it is assumed that the light to be detected is infrared light. When light to be detected is incident on the photodiode portion 20s, the incident light is incident on the depletion layer 23s present at the boundary between the second n-type well 22s, the second n-type well 22s and the p-type semiconductor substrate 10, And reaches the p-type semiconductor substrate outside the depletion layer 23s. In this case, pairs of free electrons and holes (hereinafter abbreviated as “electron-hole pairs”) are generated in the second n-type well 22 s, the depletion layer 23 s, and the p-type semiconductor substrate 10.

  Among the electron-hole pairs, electrons and holes generated in the depletion layer 23 s are accelerated by an electric field in the vicinity of the boundary between the second n-type well 22 s and the p-type semiconductor substrate 10. , Respectively, move to the terminal a side of the p + -type diffusion layer 21ps and to the terminal b of the n + -type diffusion layer 21ns, and as a result, a current flows between the terminal a and the terminal b. This current is called a drift current. On the other hand, the electrons and holes of the electron-hole pair generated in the second n-type well 22s and the p-type semiconductor substrate 10 move to the terminals a and b, respectively, by diffusion according to their distribution density gradients. As a result, current flows. This current is called a diffusion current.

  These drift current and diffusion current are the reverse current I in the photodiode portion 20s (see arrows in FIG. 6). These reverse currents I flow through the grounded resistor R. The voltage generated by the voltage drop due to the resistor R is amplified by the amplifier AMP and output as a light detection signal (see FIG. 6).

In addition, the following patent documents are mentioned as related technical documents.
JP 09-148617 A

  However, in the optical semiconductor device according to the conventional example, there has been a problem that the light energy cannot be sufficiently detected depending on the wavelength of light to be detected.

  That is, for example, when detecting infrared rays, the light energy of incident infrared rays penetrates to the deep part (for example, 20 μm) of the silicon substrate. However, in the optical semiconductor device according to the conventional example, the depth of the well, that is, the depth of the second n-type well 22s is about 5 μm at most. Therefore, the depletion layer 23s is also present at the above depth. Therefore, most of the light energy of the incident light does not contribute to the generation of electron-hole pairs in the depletion layer 23 s with high light detection efficiency, and the electrons in the p-type semiconductor substrate 10 deeper than the depletion layer 23 s. -Contributes to the generation of hole pairs. That is, the light detection is performed mainly by the diffusion current regardless of the drift current, so that the efficiency in detecting the light is lowered.

  In addition, since the resistance between the p + type diffusion layer 21 ps and the n + type diffusion layer 21 ns in the p-type semiconductor substrate 10 is high, and the movement distance of the electron-hole pair is long, the light energy is reduced. The high frequency response characteristics at the time of detection were deteriorated.

  Accordingly, the present invention provides an optical semiconductor device with improved light energy detection efficiency and high frequency response characteristics.

  The optical semiconductor device of the present invention has been made in view of the above-described problems, and includes a first conductivity type (p-type) semiconductor substrate, a light receiving portion formed on the surface of the first conductivity type semiconductor substrate, A peripheral circuit portion formed at a position adjacent to the light receiving portion on the surface of the first conductivity type semiconductor substrate, and the light receiving portion includes a plurality of diffusion regions (diffusion layers) formed deeper than the peripheral circuit portion. ).

  The optical semiconductor device according to the present invention includes a first conductivity type diffusion region (p + type diffusion layer) in which a plurality of diffusion regions having the above-described configuration are embedded in a groove formed on the surface of the first conductivity type semiconductor substrate. It consists of a second conductivity type diffusion region (n + type diffusion layer), and the first conductivity type diffusion region and the second conductivity type diffusion region are formed so that different conductivity type diffusion regions are adjacent to each other, and constitute a photodiode. It is characterized by.

  In the optical semiconductor device of the present invention, the plurality of diffusion regions having the above-described configuration includes a plurality of second conductivity type diffusion regions embedded in grooves formed on the surface of the first conductivity type semiconductor substrate, The second conductivity type diffusion regions are formed adjacent to each other and constitute a phototransistor.

  The optical semiconductor device of the present invention is characterized in that the peripheral circuit portion having the above-described configuration is formed of a CMOS transistor.

  The present invention forms a plurality of trenches (narrow grooves) extending deeper than the peripheral circuit portion on the surface of the light receiving portion (photodiode portion or phototransistor portion) where the light receiving element of the optical semiconductor device is formed, A p + type diffusion layer or an n + type diffusion layer was formed in the trench. As a result, the depletion layer is widely formed from the shallow region to the deep region of the p-type semiconductor substrate, so that most of the incident light can be detected as a drift current. Further, since the distance between the p + type diffusion layer and the n + type diffusion layer is shortened, the resistance in the p type semiconductor substrate becomes low. Accordingly, it is possible to improve the detection efficiency and high frequency response characteristics of light energy.

  In addition, since the p + -type diffusion layer and the n + -type diffusion layer are formed in the trench, it is possible to make the formation region of the photodiode portion and the phototransistor portion as small as possible. Therefore, it is possible to reduce the size of the optical semiconductor device.

  Next, an optical semiconductor device according to a first embodiment of the present invention will be described with reference to the drawings. The same components as those of the optical semiconductor device according to the conventional example shown in FIG.

  The optical semiconductor device according to the present embodiment is used for, for example, an infrared communication device of IrDA (Infrared Data Association) standard, but is used by being incorporated in other devices or systems, or used alone. It may be.

  FIG. 1 is a schematic cross-sectional view of an optical semiconductor device according to the first embodiment of the present invention. As shown in FIG. 1, a photodiode portion 20 as a light receiving element is formed on the surface of a p-type semiconductor substrate 10 such as a p-type silicon substrate. A peripheral circuit section 30 is formed at a position adjacent to the photodiode section 20.

  Here, the peripheral circuit section 30 has the same configuration as the peripheral circuit section of the optical semiconductor device according to the conventional example shown in FIG. That is, the peripheral circuit unit 30 is composed of a CMOS transistor.

  On the other hand, in the photodiode portion 20, a plurality of p + type diffusion layers 21p and n + type diffusion layers 21n extending deeper than the peripheral circuit portion 30 adjacent thereto are formed. That is, trenches (narrow grooves) Tp and Tn extending deeper than the second n-type well 31 of the peripheral circuit unit 30 are formed adjacent to each other at a predetermined interval on the surface of the p-type semiconductor device 10. Yes. The trenches Tp and the trenches Tn are formed adjacent to each other alternately.

  In these trenches Tp and Tn, a p + type diffusion layer 21p connected to the terminal a and an n + type diffusion layer 21n connected to the terminal b are respectively buried. That is, the p + -type diffusion layer 21p formed in the trench Tp and the n + -type diffusion layer 21n formed in the trench Tn are formed on the p-type semiconductor substrate 10 so that diffusion layers having different conductivity types are adjacent to each other. ing. The terminal a is grounded via a resistor R (not shown), and the terminal b is connected to a power source (not shown) that supplies a power supply voltage Vdd.

  Next, the detailed structure of the photodiode portion 20 will be described with reference to the drawings. FIG. 2 is a cross-sectional view of the vicinity of the trenches Tp and Tn in the photodiode unit 20. As shown in FIG. 2, a silicon oxide film 11 is formed on the surface of the p-type semiconductor substrate 10. A plurality of trenches Tp and Tn are formed in the silicon oxide film 11 and the p-type semiconductor substrate 10 so as to extend in the vertical direction of the p-type semiconductor substrate 10 by, for example, a trench etcher. These trenches Tp and Tn are formed adjacent to each other at a predetermined interval.

  A p + type polysilicon layer 21 psi and an n + type polysilicon layer 21 nsi are formed in each of the trenches Tp and Tn. A p + type diffusion layer 21p and an n + type diffusion layer 21n are formed outside the p + type polysilicon layer 21psi and the n + type polysilicon layer 21nsi, respectively. A tungsten silicide (WSi) 21 w is formed on the p + type polysilicon layer 21 psi and the n + type polysilicon layer 21 nsi. Here, the WSi 21w may be formed so as to fill the hollow portions of the trenches Tp and Tn. Alternatively, for example, a metal such as tungsten (W) or aluminum (Al) may be formed so as to be embedded in the cavity of each of the trenches Tp and Tn in which the tungsten silicide 21w is formed.

  Here, the p + type diffusion layer 21p and the n + type diffusion layer 21n are preferably formed as follows, for example. That is, a polysilicon layer is first formed. Next, using the mask, the polysilicon layer in the trench Tp is doped with p + impurities, and the polysilicon layer in the trench Tn is doped with n + impurities. As a result, a p + type polysilicon layer 21 psi is formed in the trench Tp, and a p + type diffusion layer 21 p is formed outside the p + type polysilicon layer 21 psi due to leaching of the doped p + type impurity. Similarly, an n + type polysilicon layer 21 nsi is formed in the trench Tn, and an n + type diffusion layer 21 n is formed outside the n + type polysilicon layer 21 nsi by oozing out of the doped n + type impurity.

  In the optical semiconductor device of this embodiment shown in FIG. 1, a plurality of p + type diffusion layers 21p and n + type diffusion layers 21n are alternately formed adjacent to the photodiode portion 20, but the present invention is It is not limited to this. That is, the optical semiconductor device of this embodiment may be one in which a pair of p + type diffusion layer 21p and n + type diffusion layer 21n is formed in the photodiode portion 20.

  In the present embodiment, a trench is formed in the photodiode portion 20, and the trench is embedded with the p + type diffusion layer 21p and the n + type diffusion layer 21n. However, the present invention is not limited to this. That is, as long as it extends in the vertical direction of the p-type semiconductor substrate 10 and is formed deeper than the peripheral circuit portion 30, other shapes of grooves or holes may be formed instead of the trenches Tp and Tn. .

  Next, the operation of the above-described optical semiconductor device according to the present embodiment will be described with reference to FIGS. 1 and 2 and the equivalent circuit diagram of the photodiode section shown in FIG. Here, it is assumed that the light to be detected is infrared light. When infrared light enters the photodiode portion 20, the light reaches a depth near the bottom of the trenches Tp and Tn. That is, light is incident so as to traverse the p + type diffusion layer 21p and the n + type diffusion layer 21n formed in the trenches Tp and Tn.

  When light enters the n + -type diffusion layer 21 n, electron-hole pairs are generated in the depletion layer 40 existing at the boundary between the n + -type diffusion layer 21 n and the p-type semiconductor substrate 10. The electrons of the electron-hole pair generated in the depletion layer 40 are accelerated by the electric field at the boundary between the n + type diffusion layer 21n and the p type semiconductor substrate 10 and move to the terminal a of the p + type diffusion layer 21p. Further, the holes move to the terminal b of the n + type diffusion layer 21n. As a result, a drift current (current generated when an electron-hole pair is accelerated by an electric field in the vicinity of the pn junction) according to the detected light intensity flows between the terminal a and the terminal b.

  This drift current is amplified and output by an amplifier AMP, as shown in the equivalent circuit diagram of the photodiode section 20s in FIG. 6, similarly to the current output from the photodiode section 20s of the optical semiconductor device according to the conventional example. The

  As described above, since most of the incident light can be detected by the drift current flowing through the photodiode portion 20, the light detection efficiency can be improved as compared with the conventional example. Further, by forming the p + type diffusion layer 21 p and the n + type diffusion layer 21 n in the trenches Tp and Tn extending in the vertical direction of the p type semiconductor substrate 10, the electron-hole pair in the p type semiconductor substrate 10 is formed. The moving distance becomes shorter than that of the conventional example, and the resistance of the moving path becomes low. Therefore, it is possible to increase the high-frequency response characteristics at the time of light detection as compared with the conventional example.

  Further, since the p + -type diffusion layer 21p and the n + -type diffusion layer 21n are formed in the trenches Tp and Tn, it is possible to make the photodiode portion 20 formation region as small as possible. Therefore, it is possible to reduce the size of the optical semiconductor device.

  In the optical semiconductor device of the first embodiment described above, the photodiode unit 20 is provided as the light receiving unit, but the present invention is not limited to this. That is, according to the present invention, a phototransistor portion 20t may be provided instead of the photodiode portion 20 as in the second embodiment described below.

  Next, a second embodiment of the present invention will be described with reference to the drawings. Components similar to those of the optical semiconductor device according to the first embodiment illustrated in FIGS. 1 and 2 are denoted by the same reference numerals, and description thereof is omitted. Note that the optical semiconductor device according to the present embodiment is used in, for example, an infrared communication device conforming to the IrDA (Infrared Data Association) standard, as in the first embodiment, but is incorporated in other devices and systems. Or may be used alone.

  Although not shown, the phototransistor portion 20t that is the light receiving portion of the optical semiconductor device of the present embodiment is formed at the same position as the photodiode portion 20 on the p-type semiconductor substrate 10 of the first embodiment shown in FIG. ing. The peripheral circuit portion adjacent to the phototransistor portion 20t has the same configuration as the peripheral circuit portion 30 of the first embodiment shown in FIG. 1 and is formed on the p-type semiconductor substrate 10.

  In the phototransistor portion 20t, although not shown, a plurality of trenches (narrow grooves) Tnt extending in the vertical direction of the p-type semiconductor substrate 10 are formed adjacent to each other at a predetermined interval. The shapes of the trenches Tnt have the same shapes as the trenches Tp and Tn formed in the photodiode portion 20 of the first embodiment shown in FIG. Then, n + -type diffusion layers 21n are buried in these trenches Tnt.

  Although not shown, two different terminals a and terminals b are alternately connected to the trenches Tnt in the order of the trenches Tnt adjacent to each other in the n + type diffusion layer 21n of the trenches Tnt. That is, different terminals of the terminal a and the terminal b are connected to the n + type diffusion layer 21n of the adjacent trench Tnt. Here, the terminal a and the terminal b are the same as the terminal a and the terminal b in the first embodiment.

  Next, the detailed structure of the phototransistor portion 20t will be described with reference to the drawings. FIG. 3 is a cross-sectional view of the vicinity of the trench Tnt formed in the phototransistor portion 20t. As shown in FIG. 3, a silicon oxide film 11 is formed on the surface of the p-type semiconductor substrate 10. A plurality of trenches Tnt are formed in the silicon oxide film 11 and the p-type semiconductor substrate 10 so as to extend in the vertical direction of the p-type semiconductor substrate 10 by, for example, a trench etcher. These trenches Tnt are formed adjacent to each other at a predetermined interval.

  In each trench Tnt, as in the trench Tn of the first embodiment shown in FIG. 2, an n + type polysilicon layer 21nsi, an n + type diffusion layer 21n, and a tungsten silicide (WSi) 21w are formed. Here, the tungsten silicide 21w may be formed so as to fill the cavity of each trench Tnt. Alternatively, for example, a metal such as tungsten (W) or aluminum (Al) may be formed so as to be embedded in the cavity of each trench Tnt in which the tungsten silicide 21w is formed.

  In the phototransistor portion 20t of the optical semiconductor device of this embodiment, three or more n + type diffusion layers 21n may be formed, or only a pair of n + type diffusion layers 21n may be formed. Good.

  In this embodiment, the trench Tnt is formed in the phototransistor portion 20t, and the n + type diffusion layer 21n is embedded in the trench Tnt. However, the present invention is not limited to this. That is, as long as it extends in the vertical direction of the p-type semiconductor substrate 10 and is formed deeper than the peripheral circuit portion 30, other shapes of grooves or holes may be formed instead of the trench Tnt.

  Next, the operation of the optical semiconductor device according to the present embodiment will be described with reference to FIG. 3 and the equivalent circuit diagram of the phototransistor portion 20t shown in FIG. Here, it is assumed that the light to be detected is infrared light.

  As shown in the equivalent circuit diagram of FIG. 4, a pair of adjacent n + -type diffusion layers 21 n together with the p-type semiconductor substrate 10 constitute a bipolar transistor Tb. That is, the phototransistor portion 20t is composed of one or a plurality of bipolar transistors Tb that are formed of pairs of n + type diffusion layers 21n. Here, each of a pair of n + type diffusion layers 21n corresponds to the collector and emitter of the bipolar transistor Tb, and the p type semiconductor substrate 10 corresponds to the base thereof.

  When light enters the phototransistor portion 20t, electron-hole pairs are generated in the n + -type diffusion layer 21n of the trench Tnt, the p-type semiconductor substrate 10 and the depletion layer 40t existing at the boundary. The generated holes stay in the base layer and raise the base potential. As a result, a forward current flows between the emitter and the base, the bipolar transistor Tb is turned on, and a collector current Ic flows. This collector current Ic flows through a resistor R connected to the collector. The voltage generated by the voltage drop due to the resistor R is amplified by the amplifier AMP and output.

  As described above, in this embodiment, unlike the photodiode portion 20 of the optical semiconductor device according to the first embodiment, only the trench Tnt for the n + -type diffusion layer 21n may be formed. Therefore, the manufacturing process of the optical semiconductor device can be simplified and the manufacturing cost can be reduced as compared with the case where the photodiode portion 20 is formed.

  In any of the above embodiments, the light to be detected is infrared light. However, the present invention is not limited to this, and may be light in a wavelength band other than infrared light. In this case, since the light incident on the optical semiconductor device may not reach the bottoms of the trenches Tp and Tn, the light detection efficiency is not always significantly improved as compared with the conventional optical semiconductor device.

  However, since the p + -type diffusion layer 21p and the n + -type diffusion layer 21n are formed in the trenches Tp and Tn, the movement distance of the electron-hole pair is shortened and the movement path becomes low resistance. High frequency response characteristics are improved. Further, since the p + -type diffusion layer 21p and the n + -type diffusion layer 21n are formed with a narrow width, the formation region of the photodiode portion 20 or the phototransistor portion 20t can be made as small as possible. Therefore, a smaller optical semiconductor device can be realized as compared with the conventional optical semiconductor device.

1 is a schematic cross-sectional view of an optical semiconductor device according to a first embodiment of the present invention. It is sectional drawing of the photodiode part which concerns on the 1st Embodiment of this invention. It is sectional drawing of the phototransistor part which concerns on the 2nd Embodiment of this invention. FIG. 6 is an equivalent circuit diagram of a phototransistor section according to a second embodiment of the present invention. It is a schematic sectional drawing of the optical semiconductor device which concerns on a prior art example. It is the equivalent circuit schematic of the photodiode part which concerns on the 1st Embodiment of this invention, and a prior art example.

Claims (4)

A first conductivity type semiconductor substrate; a light receiving portion formed on the surface of the first conductivity type semiconductor substrate; and a peripheral circuit portion formed at a position adjacent to the light reception portion on the surface of the first conductivity type semiconductor substrate. Have
2. The optical semiconductor device according to claim 1, wherein the light receiving part is composed of a plurality of diffusion regions formed deeper than the peripheral circuit part. The plurality of diffusion regions are composed of a first conductivity type diffusion region and a second conductivity type diffusion region embedded in a groove formed on a surface of the first conductivity type semiconductor substrate,
2. The photodiode according to claim 1, wherein the first conductivity type diffusion region and the second conductivity type diffusion region are formed so that diffusion regions of different conductivity types are adjacent to each other, and constitute a photodiode. Optical semiconductor device. The plurality of diffusion regions include a plurality of second conductivity type diffusion regions embedded in grooves formed on the surface of the first conductivity type semiconductor substrate,
The optical semiconductor device according to claim 1, wherein the plurality of second conductivity type diffusion regions are formed adjacent to each other to constitute a phototransistor. The optical semiconductor device according to claim 1, wherein the peripheral circuit unit is formed of a CMOS transistor.

Images