JP2008311562A - Light receiving element - Google Patents

Abstract

In a light receiving element corresponding to light of a short wavelength, both high sensitivity and high speed response are achieved.
A light receiving element is formed on a semiconductor substrate, a light absorption layer that includes a low-concentration impurity layer and absorbs light of a predetermined wavelength band, and the light absorption layer. And a high concentration impurity layer 4 having an impurity concentration higher than that of the low concentration impurity layer. At least in the high-concentration impurity layer, a plurality of low-refractive index regions 6 having a light-related refractive index smaller than that of the high-concentration impurity layer are arranged at regular intervals, and a periodic refractive index distribution is formed in the main surface direction of the semiconductor substrate 1. By having it, the photonic crystal part 21 which transmits the light of a predetermined | prescribed wavelength band is comprised.
[Selection] Figure 1

Description

  The present invention relates to a light receiving element used in an optical pickup device or the like.

  At present, a light receiving element for an optical pickup used in an optical disk apparatus represented by a CD-R (Compact Disk-Recordable) drive, a DVD (Digital Versatile Disk) drive, or the like is mainly a laser that is reflected by an optical disk and returned. A photodiode for receiving light and a signal processing circuit region for processing an electric signal generated by a light receiving element such as a photodiode based on the received laser light are configured.

  In recent years, there has been a demand for high-speed operation of optical disk devices and an increase in storage capacity. For this reason, also in the optical pickup system for DVDs, the wavelength of the semiconductor laser serving as the light source has been shortened for the purpose of increasing the storage capacity of the optical disk. In other words, a red semiconductor laser that emits light having a wavelength of 650 nm is conventionally used, but a system using a blue semiconductor laser that emits light having a wavelength of 405 nm is changing.

  Along with the shortening of the wavelength of the light source, the light receiving element is required to have characteristics matching the blue wavelength. The shorter the wavelength of light to be received, the greater the light absorption coefficient by silicon. For this reason, the shorter the wavelength of light applied to the photodiode, the more light is absorbed in the vicinity of the surface of the semiconductor layer and light carriers are generated.

  The penetration depth of light into the semiconductor layer, for example, the distance from the semiconductor surface to the position where the light intensity of the laser light is attenuated by 60% by light absorption is about 4.0 μm in the case of conventional red light (wavelength 650 nm). On the other hand, in the case of blue light (wavelength 405 nm), it is about 0.3 μm. That is, most of the blue light is absorbed in shallower regions of the semiconductor.

  Here, in the impurity region of the semiconductor layer, the higher the impurity concentration, the shorter the lifetime of the photocarrier. That is, even if optical carriers are generated due to light absorption, they disappear due to recombination and are unlikely to contribute to the photocurrent extracted as an external current. Therefore, the sensitivity to incident light is reduced. As described above, the shorter the wavelength of incident light is, the more near the surface of the semiconductor substrate is absorbed, the lower the sensitivity due to the high impurity concentration in the vicinity of the surface.

  On the other hand, the parasitic resistance increases as the impurity concentration in the vicinity of the semiconductor substrate surface decreases. This is known to cause a decrease in the response speed of the light receiving element.

  As described above, the improvement in sensitivity and the response speed are contradictory to the requirements for realizing the impurity concentration in the semiconductor layer of the light receiving element.

As an example of a technique corresponding to this, a light receiving element or the like in which a low concentration region and a high concentration region are periodically formed in a lattice shape at regular intervals has been proposed (see, for example, Patent Document 1).
JP 2003-158251 A

  However, in the light receiving element of Patent Document 1, a part of the light enters the high concentration region, and such light is absorbed by the region having low light receiving sensitivity. For this reason, when it considers as the whole light receiving element, the fall of a sensitivity has generate | occur | produced still. On the contrary, the light irradiated to the low concentration region is absorbed in the region having high light receiving sensitivity, but since the low concentration region exists on the substrate surface, the parasitic resistance increases on the substrate surface, thereby Response speed is delayed. Thus, coexistence with high sensitivity and high-speed response is not fully realized.

  Accordingly, the present invention has been made to solve such a problem, and an object of the present invention is to provide a light receiving element that satisfies both the characteristics of high sensitivity and high speed response particularly to a blue laser.

  In order to achieve the above object, the inventors of the present application have a high concentration in which the impurity concentration is increased in order to reduce the parasitic resistance on the light absorption layer in which the impurity concentration is decreased in order to prevent the disappearance of the optical carriers due to recombination. The idea was to suppress the absorption of incident light in the high-concentration impurity layer by forming an impurity layer and forming a photonic crystal that transmits the incident light in the high-concentration impurity layer.

  Specifically, the light receiving element of the present invention is formed on a semiconductor substrate, a light absorption layer formed on the semiconductor substrate, including a low-concentration impurity layer and absorbing light in a predetermined wavelength band, and the light absorption layer. A plurality of low-refractive indexes having a lower refractive index for light in a predetermined wavelength band than that of the high-concentration impurity layer, at least in the high-concentration impurity layer. The regions are arranged at regular intervals, thereby forming a photonic crystal portion that transmits light of a predetermined wavelength band by having a periodic refractive index distribution in the main surface direction of the semiconductor substrate.

  According to the light receiving element of the present invention, the photonic crystal that transmits light of a predetermined wavelength band is formed in the high concentration impurity layer formed on the light absorption layer. For this reason, light of a predetermined wavelength incident on the light receiving element is subjected to Bragg reflection by the periodic refractive index distribution in the photonic crystal portion of the high concentration impurity layer and is not absorbed. That is, incident light is transmitted without being attenuated in the photonic crystal part, and as a result, more incident light reaches the light absorption layer.

  The light reaching the light absorption layer is absorbed and generates photocarriers (electrons and holes). At this time, since the impurity concentration in the low-concentration impurity layer is low, the disappearance of photocarriers due to recombination is small and the sensitivity is high (the impurity concentration of the low-concentration impurity layer is set so as to realize this). In addition, since the impurity concentration is high near the surface of the light receiving element, a high concentration impurity layer having a low parasitic resistance is provided, so that the response is fast (higher than the low concentration impurity layer to realize this). The impurity concentration of the high concentration impurity layer is set as the impurity concentration). Thus, the light receiving element of the present invention achieves both high sensitivity and high speed response.

  In addition, it is preferable that the photonic crystal part reaches the light absorption layer by forming the plurality of low refractive index regions so as to penetrate the high concentration impurity layer and reach the light absorption layer.

  If it does in this way, the light which injected into the light receiving element can reach | attain a light absorption layer, without passing through the high concentration impurity layer of the part in which the photonic crystal part is not comprised. Thereby, further improvement in response speed and light sensitivity is realized.

  First, further improvement in response speed will be described.

  When electrons and holes, which are photocarriers, are generated by the incidence of light, the electrons move to the cathode and the holes move to the anode, contributing to the photocurrent. When electrons and holes are generated in the light absorption layer, these electrons and holes are quickly carried out of the light absorption layer by electric field drift, and then move to the cathode and anode, respectively.

  On the other hand, when photocarriers are generated in the high-concentration impurity layer provided on the light absorption layer, either one of electrons and holes moves to the light absorption layer by diffusion, and then the cathode is formed in the same manner as described above. Or it is carried to the anode. In particular, the movement of optical carriers due to diffusion in the high-concentration impurity layer is significantly slower than the movement due to electric field drift in the light absorption layer. As a result, the time until both electrons and holes, which are photocarriers generated in pairs in the high-concentration impurity layer, reach the cathode and anode, is longer than that in the case of photocarriers generated in the light absorption layer. That is, the photocarrier generated in the high concentration impurity layer causes the response speed to decrease.

  Therefore, by providing the photonic crystal portion so as to reach the light absorption layer as described above, generation of photocarriers in the high concentration impurity layer can be prevented and the response speed can be improved.

  Next, the further improvement in photosensitivity is due to the fact that absorption in a high-concentration impurity layer, in which photocarriers tend to disappear due to recombination, can be avoided, thereby preventing a decrease in sensitivity. In this way, further improvement in response speed and photosensitivity is realized.

  In the light receiving element of the present invention, the plurality of low refractive index regions are preferably a plurality of cavities provided at least in the high concentration impurity layer.

  The refractive index of the cavity is smaller than that of the high concentration impurity layer formed of silicon or the like. Therefore, by arranging a plurality of cavities in the high concentration impurity layer, a periodic refractive index distribution can be realized and a photonic crystal part can be obtained.

  Further, the plurality of low refractive index regions may have a structure in which at least a plurality of concave portions provided in the high concentration impurity layer are embedded with a material having a lower refractive index with respect to light in a predetermined wavelength band than the high concentration impurity layer. preferable.

  In this way, a periodic refractive index distribution can be realized by the difference in refractive index between the material constituting the high concentration impurity layer and the material having a lower refractive index, and a photonic crystal portion can be obtained. At this time, an arbitrary refractive index difference can be generated by selecting a material having a desired refractive index and embedding the recess, thereby obtaining a photonic crystal portion that easily transmits light of a predetermined wavelength band. be able to.

  In such a structure, it is preferable that an antireflection film made of a material for embedding a plurality of recesses is formed on the high concentration impurity layer.

  In this way, in addition to the above-described effect of providing a low refractive index region having a structure in which the concave portion is embedded with a low refractive index material, reflection of light on the surface of the light receiving element is suppressed from the antireflection film, and incident light is increased. By doing so, the sensitivity of the light receiving element can be improved. In particular, it is possible to achieve both anti-reflection for long-wavelength light and light transmittance of the photonic crystal part for short-wavelength light at the same time, achieving both high sensitivity and high-speed response over a wide wavelength range. .

  The plurality of low refractive index regions are preferably regions having the same conductivity type as the high concentration region and having a lower impurity concentration than the high concentration region.

  That is, it is preferable to realize a periodic refractive index distribution by utilizing a difference in refractive index due to a difference in concentration of impurities of the same conductivity type, thereby forming a photonic crystal portion. Here, a difference in refractive index can be set by setting a difference in impurity concentration, and a photonic crystal part that transmits light in a desired wavelength band can be obtained.

  Each of the plurality of low refractive index regions preferably has a circular planar shape.

  When a circular low refractive index region is used, the reproducibility of uniform pattern formation is high and the symmetry is also high. This is desirable for realizing a photonic crystal part that transmits light in a desired wavelength band.

  The light absorption layer includes a first conductivity type low concentration impurity layer as a low concentration impurity layer and a second conductivity type low concentration impurity layer formed thereon, and the high concentration impurity layer is of the second conductivity type. It is preferable.

  Thus, light absorption can be performed in the depletion layer formed at the interface between the first conductivity type low concentration impurity layer and the second conductivity type low concentration impurity layer.

Moreover, it is preferable that the plurality of low refractive index regions have a planar shape having a dimension corresponding to the wavelength of light in a predetermined wavelength band. Further, the refractive index for light in a predetermined wavelength band of the high-concentration impurity layer is n ₁ , the refractive index for light in a predetermined wavelength band of a plurality of low refractive index regions is n ₂ , and the center wavelength of the predetermined wavelength band is λ, When the interval between the plurality of low refractive index regions is D, it is preferable that the following formula D = (λ / 2n ₁ ) + (λ / 2n ₂ ) holds.

  In this way, the photonic crystal part that transmits light of a predetermined wavelength band is reliably constituted by the high concentration impurity layer and the low refractive index region.

  As described above, according to the light receiving element of the present invention, the photonic crystal part that transmits light of a predetermined wavelength band is configured in the high concentration impurity layer formed in the vicinity of the surface of the light receiving element. The incident light reaches the light absorbing layer including the low concentration impurity layer thereunder without being absorbed in the high concentration impurity layer. Thereby, both the recombination of carriers in the high concentration impurity layer and the parasitic resistance in the vicinity of the surface of the light receiving element are suppressed, and the light receiving element achieves both high sensitivity and high speed response. In particular, it is possible to provide a high-performance light-receiving element suitable for short-wavelength light that is easily absorbed near the surface of the element, for example, a blue laser.

  Hereinafter, light receiving elements according to embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same component which appears over several drawings, and detailed description may be abbreviate | omitted by it.

(First embodiment)
FIGS. 1A and 1B are diagrams schematically illustrating a main part of the light receiving element according to the first embodiment, which are a plan view and a cross-sectional view in order. 1A is a cross section taken along line Ia-Ia ′ in FIG.

  As shown in FIG. 1A, the light receiving element 20 of the present embodiment is configured as a PIN photodiode. More specifically, the light receiving element 20 is formed using a high-concentration P + type silicon substrate 1, and on the high-concentration P + type silicon substrate 1, a low-concentration P-type silicon layer 2 (film thickness 15 μm) and a low concentration are formed. An N-type silicon layer 3 (film thickness 5 μm), a high concentration N + -type silicon layer 4 and a silicon oxide film 5 are laminated in this order from the bottom. Further, a cathode electrode wiring 7 is provided so as to penetrate the silicon oxide film 5 and reach the high concentration N + type silicon layer 4, and the back surface of the high concentration P + type silicon substrate 1 (a low concentration P type silicon layer 2 is formed). The anode electrode wiring 8 is provided on the surface opposite to the surface that is provided.

  Since the interface between the N-type layer and the P-type layer, that is, the interface between the low-concentration P-type silicon layer 2 and the low-concentration N-type silicon layer 3 forms a PN junction, a depletion layer is formed in this portion. The The depletion layer mainly functions as a light absorption layer.

  In addition, a plurality of cavities 6 that penetrate the high concentration N + type silicon layer 4 (and the silicon oxide film 5) and reach the low concentration N type silicon layer 3 are formed. The cavity 6 may be formed deeper than the lower surface of the high concentration N + type silicon layer. The light receiving element 20 in FIG. 1A is such an example, and the thickness of the cavity 6 is about 500 nm while the thickness of the silicon oxide film 5 is about 100 nm.

  As shown in FIG. 1B, the cavity 6 has a circular planar shape and is regularly provided at equal intervals. In FIG. 1B, the illustration of the silicon oxide film 5 is omitted.

  The refractive index (1.0) of the cavity 6 is lower than the refractive index (5.6) of the high-concentration N + type silicon layer 4, and a plurality of cavities 6 having the same diameter A1 are provided at equal intervals. ing. For this reason, the high-concentration N + type silicon layer 4 and the plurality of cavities 6 cause a periodic refractive index distribution in the main surface direction of the high-concentration P + type silicon substrate 1 to constitute the photonic crystal portion 21. .

  The light receiving element 20 of this embodiment is for receiving a blue laser (wavelength 405 nm). Therefore, the diameter A1 of the cavity 6 is set to 400 nm which is substantially the same as the wavelength of incident light (laser light). Moreover, the space | interval D1 between the cavity parts 6 is 240 nm, and is arranged independently, respectively. Thus, in order to function as a photonic crystal, a plurality of low refractive index cavities 6 are arranged as a pattern having the same size as the wavelength of incident light.

  In the light receiving element 20 of this embodiment having such a configuration, for example, when the surface of the light receiving element 20 is irradiated with laser light reflected by an optical disc, the photonic crystal portion 21 intersects the main surface direction (crossing the incident direction). Due to the periodic refractive index profile of (direction). As a result, the laser beam is not absorbed in the photonic crystal portion 21 having an optical band gap in the optical wavelength range of the laser beam, and the laser beam passes through the cavity 6 or the N + type silicon layer 4 constituting the photonic crystal. As a result, the laser light reaches the low-concentration N-type silicon layer 3 having a low impurity concentration formed in a region deeper than the high-concentration N + -type silicon layer 4 without being attenuated.

  Thereafter, blue light having a large light absorption coefficient is absorbed in the low-concentration N-type silicon layer 3 and the low-concentration P-type silicon layer 2 and converted into photocarriers (electrons and holes) in the depletion layer at the interface between them. . Electrons of the generated optical carriers are quickly sucked up to the high concentration N + type silicon layer 4 on the light receiving element surface side by electric field drift. As shown in FIG. 1B, since the plurality of cavities 6 are independent from each other (not connected), the high-concentration N + type silicon layer 4 is continuous in the main surface direction of the light receiving element 20 and sucked up. The generated electrons can easily reach the cathode electrode wiring 7 through the high-concentration N + type silicon layer 4. In addition, the hole of the generated photocarriers moves to the anode electrode wiring 8 side and contributes to the photocurrent.

  Thus, according to the light receiving element 20 of the present embodiment, the photonic crystal portion 21 is configured so that light having a wavelength corresponding to the optical band gap is absorbed in the high-concentration N + type silicon layer 4. Instead, it reaches the low concentration N-type silicon layer 3 and the low concentration P-type silicon layer 2 below. In other words, light can be absorbed in the low-concentration impurity layer while avoiding light absorption in the high-concentration impurity layer, which causes significant recombination and causes a decrease in sensitivity.

  Further, a high-concentration N + type silicon layer 4 having a small parasitic resistance is provided in the vicinity of the surface of the light receiving element 20, and the generated optical carriers diffuse through the high-concentration N + type silicon layer 4, so that the response speed is improved. Yes.

  Therefore, the light receiving element 20 of the present embodiment realizes both high sensitivity and high speed response, and is a light receiving element suitable for a blue laser (wavelength 405 nm) which is a short wavelength light with a large absorption coefficient for silicon. .

  As a specific example, the light receiving element 20 having a sensitivity of 0.3 A / W and a frequency of −1 dB and a characteristic of 220 MHz with respect to the wavelength λ = 405 nm of the incident light was obtained. In the case of the conventional light receiving element, for example, the sensitivity is 0.26 A / W and the frequency characteristic is −1 dB at 200 MHz with respect to the wavelength λ = 405 nm of the same incident light. Thus, the light receiving element 20 of the present embodiment surely achieves both high sensitivity and high speed response.

  In addition, as an example of the pattern size of the low refractive index region, an example of this embodiment in which the diameter A1 of the cavity 6 is 400 nm, which is equivalent to the wavelength of the incident light (laser light wavelength, 405 nm), is a desirable configuration. However, in consideration of the presence of wavelength distribution in the laser light, it is preferable to set the diameter of the cavity 6 to a size of about ± 50 nm with respect to the center wavelength of the incident light. In this way, the present invention is not limited to the case of incident light having a single wavelength such as a wavelength of 405 nm, and a configuration suitable for light of various wavelengths taking into account variations in consideration of the wavelength distribution of the incident light can also be employed.

  In the present embodiment, an example in which the high-concentration P + type silicon substrate 1 is used has been described. However, the present invention is not limited to this, and each component may have a reverse conductivity type. Furthermore, although the example in which the anode electrode wiring 8 is formed on the back surface of the high concentration P + type silicon substrate 1 has been described, the present invention is not limited to this. For example, an insulating separation layer is provided between the anode and the cathode, and a contact layer connected to the high-concentration P + type silicon substrate 1 is formed from the surface (the side where the silicon oxide film 5 of the light receiving element 20 is formed). It is also possible to draw out the anode electrode.

  Next, a method for manufacturing the light receiving element 20 of the present embodiment will be described with reference to the drawings. 2A to 2F are cross-sectional views for explaining a method of manufacturing the light receiving element 20, particularly a step of forming a light receiving region.

First, as shown in FIG. 2A, a low concentration having a specific resistance of about 100 Ωcm and a thickness of about 20 μm is formed on a high concentration P + type silicon substrate 1 having an impurity concentration of about 1 × 10 ¹⁹ / cm ³ by epitaxial growth. A P-type silicon layer 2 is formed. Subsequently, the low-concentration N-type silicon layer 3 having a specific resistance of about 100 Ωcm and a film thickness of about 10 μm is formed on the low-concentration P-type silicon layer 2 by the same epitaxial growth method. Note that the impurity concentrations of the low-concentration P-type silicon layer 2 and the low-concentration N-type silicon layer 3 are set so as to avoid the disappearance of photocarriers generated by depletion of both due to recombination.

  Next, as shown in FIG. 2B, a silicon oxide film 5 (for example, a thermal oxide film) is formed on the low concentration N-type silicon layer 3.

Thereafter, as shown in FIG. 2C, impurity implantation is performed on the low-concentration N-type silicon layer 3 in a necessary range using a masking process. Thereby, the high concentration N + type silicon layer 4 is formed on the low concentration N type silicon layer 3. At this time, for example, As (arsenic) is used as the impurity, and the ion implantation energy is 20 keV and the ion implantation amount is 5 × 10 ¹⁴ / cm ² . Such doping conditions (impurity concentration of the high-concentration N + type silicon layer 4) are set so that the parasitic resistance of the high-concentration N + type silicon layer 4 becomes sufficiently small in order to realize a high-speed response of the light receiving element.

  Next, as shown in FIG. 2D, contact holes are provided in the silicon oxide film 5 formed on the high concentration N + type silicon layer 4. A cathode electrode wiring 7 is formed so as to be connected to the high concentration N + type silicon layer 4 through the contact hole.

  Further, as shown in FIG. 2E, the anode electrode wiring 8 is formed on the back surface of the high-concentration P + type silicon substrate 1.

  Next, the process shown in FIG. That is, after the anode electrode wiring 8 and the cathode electrode wiring 7 are formed, a mask having a predetermined pattern is formed by using a lithography technique, and the high concentration N + type silicon layer 4 is penetrated by anisotropic dry etching. A plurality of cavities 6 are formed.

  Here, as shown in FIG. 1B, the plurality of cavities 6 are arranged in the high-concentration N + type silicon layer 4 without contacting each other. Each cavity 6 has a circular planar shape having a diameter A1 of 400 nm which is substantially the same as the wavelength of incident light. The distance D1 between the cavities 6 is 240 nm.

  The depth of the cavity 6 is about 500 nm from the surface of the silicon oxide film 5. This is because the depth of the high-concentration N + type silicon layer 4 is about 400 nm, so that the cavity 6 is formed deeper than this as shown in FIG. As will be described later, it is desirable that the photonic crystal portion 21 reaches the low-concentration N-type silicon layer 3, and that the cavity 6 is formed deeper than the upper surface of the low-concentration N-type silicon layer 3. There is no big problem. For this reason, the cavity 6 is preferably formed deeper than the upper surface of the low-concentration N-type silicon layer 3 from the viewpoint of processing accuracy and the like.

  By forming the cavity 6, the cavity 6 having a relatively low refractive index is regularly arranged in a pattern having the same size as the wavelength of the incident light in the high-concentration N + type silicon layer 4 having a relatively high refractive index. It will be. As a result, the photonic crystal portion 21 is formed, and as described above, the laser light passes through the photonic crystal portion 21 without being absorbed and reaches the low-concentration N-type silicon layer 3 having a low impurity concentration. Absorbed. In this manner, the light receiving element 20 that achieves both high sensitivity and high speed response with respect to the reception of the blue laser can be manufactured.

  Here, the cavity 6 is formed in a state where the silicon oxide film 5 is formed on the high-concentration N + type silicon layer 4. However, another film laminated on the silicon oxide film 5, such as a SiN film, may be formed, or another film may be formed.

  Further, in this embodiment, all the cavity portions 6 penetrate the high concentration N + type silicon layer 4 and reach the low concentration N type silicon layer 3, and thus the photonic crystal portion 21 also has the low concentration N type silicon layer. 3 has been reached. This is a desirable configuration for improving the sensitivity and response speed of the light receiving element. However, it is also possible to adopt a configuration in which the cavity 6 does not penetrate the high concentration N + type silicon layer 4, that is, is formed so as to be accommodated in the high concentration N + type silicon layer 4.

  In this case, the photonic crystal part is formed in the range where the cavity 6 is formed, and absorption of incident light is prevented in the range of the photonic crystal part. In the high-concentration N + type silicon layer 4 outside the range of the photonic crystal part, photocarriers are reduced by recombination. In addition, photocarriers that do not disappear due to recombination and contribute to the photocurrent also cause a reduction in response speed.

  As described above, the optical carriers generated in the depletion layer generated at the interface between the low concentration N-type silicon layer 3 and the low concentration P-type silicon layer 2 move quickly due to the electric field drift. At this time, holes in the photocarrier move to the anode electrode wiring 8 side. On the other hand, when photocarriers are generated in the high-concentration N + type silicon layer 4 outside the range of the photonic crystal portion 21, the holes need to move to the depletion layer by diffusion. The moving speed at this time is significantly slower than that due to electric field drift. For this reason, the time to reach the anode electrode wiring 8 is slower than the holes generated in the depletion layer, which causes the response speed to decrease.

  For this reason, even if the cavity 6 does not reach the low-concentration N-type silicon layer 3, the effect of improving the sensitivity is exhibited, but more desirably, as shown in FIG. A structure in which the cavity 6 reaches the low-concentration N-type silicon layer 3 is preferable.

(Second Embodiment)
Next, a light receiving element 20a according to a second embodiment of the present invention will be described with reference to the drawings. 3A to 3F are cross-sectional views showing a process for manufacturing the light receiving element 20a, particularly the light receiving region thereof.

  A cross section of the light receiving element 20a of this embodiment is shown in FIG. This is a plurality of low refractive index portions 9a in which the cavity 6 is embedded with a low refractive index material such as SOG (Spin on Glass) in the light receiving element 20 of the first embodiment shown in FIG. You can think of it as a configuration. Accordingly, the low refractive index portions 9a have a circular planar shape as shown in FIG. 1B and are arranged at equal intervals independently of each other. The low refractive index material is a material having a lower refractive index with respect to incident light than the high-concentration N + type silicon layer 4.

  However, the diameter A2 of the pattern of the low refractive index portion 9a is 400 nm which is the same as the cavity 6 of the light receiving element 20 (equivalent to the assumed wavelength of incident light 405 nm), but the interval D1 of the cavity 6 of the light receiving element 20 is 240 nm. On the other hand, the interval D2 of the low refractive index portion 9a is 180 nm.

  Also in the light receiving element 20a, the high-concentration N + type silicon layer 4 and the low-refractive index portions 9a regularly arranged therein generate a periodic refractive index distribution in a direction intersecting the laser light incident direction. Part 21 is configured. For this reason, as in the case of the first embodiment, the incident light is subjected to Bragg reflection in the photonic crystal part 21 having an optical band gap in the light wavelength range of the incident light, and is transmitted without being absorbed and reduced. The concentration N-type silicon layer 3 is reached. Thereafter, incident light is absorbed in the depletion layer formed by the interface between the low concentration N-type silicon layer 3 and the low concentration P-type silicon layer 2 to generate optical carriers.

  As a result, the sensitivity of the light receiving element 20a is improved and the response speed is improved as a result of the reduced parasitic resistance due to the high concentration N + type silicon layer 4 formed on the low concentration N type silicon layer 3. This is the same as in the case of the first embodiment.

  The low refractive index material filled in the cavity 6 is not limited to SOG, and may be selected according to the wavelength of the incident light and the interval of the periodic pattern. On the contrary, the pattern interval of the photonic crystal part 21 can be set by using a material with a fixed refractive index. For example, any material may be used as long as it has a refractive index smaller than the refractive index n = 5.42 of the high-concentration N + type silicon layer 4 with respect to light having a wavelength of 405 nm and transmits light having a wavelength of 405 nm. When such a material is used, the photonic crystal portion 21 can be configured to generate an optical band gap.

In the photonic crystal, the refractive index of the material and the pattern interval have the following relationship. That is, the wavelength of the incident light (center wavelength if the wavelength distribution of the incident light is considered) is λ, the refractive indexes of the high refractive index material and the low refractive index material for the incident light are sequentially n ₁ and n ₂ , and the periodic interval. When (here, the interval between the low refractive index portions 9a) is D, the following formula (1)
D = (λ / 2n ₁ ) + (λ / 2n ₂ ) (n ₁ > n ₂ ) (1)
If the above relationship is satisfied, a photonic crystal can be realized and an optical band gap can be generated. In the case of this embodiment, the refractive index of SOG is about 1.42, and the distance D2 is set to 180 nm as shown above from the equation (1).

  From the relationship of the formula (1), the periodic interval D can be increased as the material having a lower refractive index is used. Since the pattern formation is easier when the period interval D is larger, it is desirable to use a material having a lower refractive index.

  The light receiving element 20a of the present embodiment can be manufactured as follows, for example. First, the structure shown in FIG. 3A is the same as the structure shown in FIG. 2C in the first embodiment, and is formed by the steps shown in FIGS. 2A and 2B.

  Next, as shown in FIG. 3B, a plurality of cavities 6 penetrating the low-concentration N-type silicon layer 3 are formed. For this purpose, masking was performed by lithography and anisotropic dry etching was performed. The planar shape and arrangement are the same as in FIG. 1B, except that the diameter A2 of the cavity 6 is 400 nm and the interval D2 is 180 nm as described above.

  Next, as shown in FIG. 3C, an SOG layer 9 that fills the cavity 6 and covers the silicon oxide film 5 is formed by spin coating.

  Next, as shown in FIG. 3D, the SOG in the portion protruding from the cavity 6 is removed using a CMP (Chemical Mechanical Polishing) method. Thereby, the low refractive index portion 9a in which the cavity 6 is filled with SOG is formed.

  Next, as shown in FIG. 3E, a contact hole penetrating the silicon oxide film 5 is formed, and a cathode electrode wiring 7 connected to the high-concentration N + type silicon layer 4 is formed through the contact hole. Thereafter, as shown in FIG. 3F, the anode electrode wiring 8 is formed on the back surface of the high-concentration P + type silicon substrate 1.

(Third embodiment)
The light receiving element 20b according to the third embodiment of the present invention will be described below with reference to the drawings. 4A to 4F are cross-sectional views showing a process for manufacturing the light receiving element 20b, particularly the light receiving region thereof.

  The cross section of the light receiving element 20b of this embodiment is shown in FIG. This is because, in the light receiving element 20 of the first embodiment shown in FIG. 1A, the cavity 6 is buried with SiN to form the low refractive index portion 10a, and the SiN film 10b is formed with the same SiN. Can be thought of as a structure. However, assuming that light having a wavelength of 405 nm is also received here, the diameter A3 of the pattern of the low refractive index portion 10a is 400 nm, which is the same as that of the light receiving element 20, but the interval D3 between the low refractive index portions 10a is 140 nm. . Such a value of the distance D3 is determined by using the formula (1) because the refractive index of SiN is 2.00.

  Since SiN has a lower refractive index than that of the high-concentration N + type silicon layer 4, the low refractive index portion 10 a having a configuration in which the cavity 6 is filled with SiN is regularly arranged in a pattern having the same size as the wavelength of incident light. As a result, a periodic refractive index distribution is generated in the direction intersecting with the incident light. As a result, a photonic crystal portion 21 having an optical band gap in the light wavelength region of the incident light is formed, and the incident light is transmitted without being absorbed to receive the Bragg reflection, and enters the low-concentration N-type silicon layer 3. To reach. Thereafter, as described in the previous embodiment, generation and movement of optical carriers occur, and the light receiving element 20b is realized in which both improvement in sensitivity and improvement in response speed are realized.

  Further, in the light receiving element 20b of the present embodiment, the SiN film 10b is formed of the same SiN as the low refractive index portion 10a so as to cover the silicon oxide film 5 and the low refractive index portion 10a. The laminated film of the SiN film 10b and the silicon oxide film 5 functions as an antireflection film for red to infrared light. For this reason, the light receiving element 20b is excellent in transparency with respect to short wavelength light because of the photonic crystal portion 21, and is excellent in antireflection property with respect to long wavelength light.

  Therefore, the light receiving element 20b can efficiently receive a wide range of wavelengths from a short wavelength such as blue light to a long wavelength such as infrared light, and has high performance characteristics that achieve both high sensitivity and high speed response. It is to show.

  Since the low refractive index portions 10a formed in the high concentration N + type silicon layer 4 are independent from each other, the high concentration N + type silicon layer 4 is continuous in the main surface direction of the light receiving element. Therefore, it can be considered that the low refractive index portions 10a are connected to each other through the SiN film 10b formed of the same material. Regardless of this, the carrier passes through the high concentration N + type silicon layer 4 in the main surface. A route to move in the direction is secured.

  The light receiving element 20a of the present embodiment can be manufactured as follows, for example. First, the structure shown in FIG. 4A is the same as the structure shown in FIG. 2C in the first embodiment, and is formed by the steps shown in FIGS. 2A and 2B.

  Next, as shown in FIG. 4B, a plurality of cavities 6 penetrating the low-concentration N-type silicon layer 3 are formed. For this purpose, masking was performed by lithography and anisotropic dry etching was performed. The planar shape and arrangement are the same as in FIG. 1B, except that the diameter A3 of the cavity 6 is 400 nm and the distance D3 is 140 nm as described above.

  Next, as shown in FIG. 4C, a SiN film 10 that fills the cavity 6 and covers the silicon oxide film 5 is formed by a plasma CVD method or the like. Thereby, the low refractive index portion 10a in which the cavity 6 is filled with SiN is formed. Thereafter, as shown in FIG. 4D, the SiN film 10 is polished by the CMP method to leave the SiN film 10b with a desired thickness. Thereby, the laminated film of the SiN film 10b and the silicon oxide film 5 functions as an antireflection film.

  Thus, the manufacturing process of the light receiving element 20b can be simplified by forming the low refractive index portion 10a and the SiN film 10b for obtaining the antireflection film with the same material.

  Thereafter, as shown in FIG. 4E, a cathode electrode wiring 7 is formed through the SiN film 10b and the silicon oxide film 5 and connected to the high-concentration N + type silicon layer 4. Further, as shown in FIG. 4F, an anode electrode wiring 8 is formed on the back surface of the high concentration P + type silicon substrate 1.

  Thus, the light receiving element 20b of the present embodiment is manufactured. In addition, although the low refractive index part 10a was comprised using SiN as a material and the SiN film 10b used as a part of antireflection film was formed, it is not necessarily limited to this.

(Fourth embodiment)
Next, a light receiving element 20c according to a fourth embodiment of the present invention will be described with reference to the drawings. 5A and 5B are cross-sectional views showing a process for manufacturing the light receiving element 20c, particularly the light receiving region thereof. FIG. 5C is a plan view of the light receiving element 20c.

  A cross section of the light receiving element 20c of the present embodiment is shown in FIG. Here, the high concentration P + type silicon substrate 1, the low concentration P type silicon layer 2, the low concentration N type silicon layer 3, the silicon oxide film 5, the cathode electrode wiring 7 and the anode electrode wiring 8 are the same as those in the first embodiment. The same as the light receiving element 20. In the low-concentration N-type silicon layer 3, a high-concentration N + -type silicon layer 4a having a higher impurity concentration is formed as a pattern shown in FIG.

  In the light receiving element 20c, the photonic crystal portion 21 is configured by utilizing the fact that the low-concentration N-type silicon layer 3 and the high-concentration N + -type silicon layer 4a have different refractive indexes depending on the impurity concentration. That is, as shown in FIGS. 4B and 4C, the high concentration N + type silicon layer 4a is formed so as to leave the low concentration N type silicon layer 3 as a pattern having a circular plane shape and regularly arranged. The portion of the low-concentration N-type silicon layer 3 left between the high-concentration N + -type silicon layers 4a is the low refractive index portion 3a. Thereby, a periodic refractive index distribution is generated in a direction intersecting with the incident direction of light, and functions as a photonic crystal. Specific examples of the refractive index are 5.6 for the high concentration N + type silicon layer 4a and 5.42 for the low concentration N type silicon layer 3 (low refractive index portion 3a).

  In addition, the diameter A4 of the low refractive index portion 3a is 400 nm, which is equivalent to the assumption that light having a wavelength of 405 nm is assumed as incident light in this embodiment. Further, the distance D4 between the low refractive index portions 3a is set to 73.5 nm from the refractive index and the formula (1).

  Also in the light receiving element 20c, the incident light passes through the photonic crystal part 21 without being absorbed in order to receive Bragg reflection. That is, the high concentration N + type silicon layer 4a and the low refractive index portion 3a which is a part of the low concentration N type silicon layer 3 are disposed in the vicinity of the surface of the light receiving element 20c (the portion in contact with the silicon oxide film 5). However, the incident light is not absorbed in this portion, and therefore no optical carrier is generated.

  The light that has passed through the photonic crystal part 21 without being attenuated because it is not absorbed is then absorbed in the light absorption layer formed below the photonic crystal part 21 to generate optical carriers. What functions as a light absorption layer is mainly a depletion layer formed at the interface between the low-concentration N-type silicon layer 3 and the low-concentration P-type silicon layer 2.

  From the above, as described in the first to third embodiments of the present invention, the light receiving element 20c has both high sensitivity and high speed response. In particular, it is a light receiving element suitable for a blue laser.

  The light receiving element 20c can be manufactured, for example, as follows.

  First, the steps of FIGS. 2A and 2B described in the first embodiment are performed. Thereby, a structure in which the high concentration P + type silicon substrate 1, the low concentration P type silicon layer 2, the low concentration N type silicon layer 3 and the silicon oxide film 5 are laminated is obtained.

Next, as shown in FIG. 5A, after the photoresist 11 is provided as a mask, impurities are implanted to form a high-concentration N + type silicon layer 4a. At this time, the photoresist 11 is formed so as to cover the portion left as the low-concentration N-type silicon layer 3 as the low refractive index portion 3a. Further, for example, As (arsenic) is used as the impurity, the ion implantation energy is set to 20 keV, and the ion implantation amount is set to 5 × 10 ¹⁴ / cm ² . Thereby, as shown in FIG. 5B, a high concentration N + type silicon layer 4a having a refractive index higher than that of the low concentration N type silicon layer 3 is formed.

  Thereafter, when the cathode electrode wiring 7 and the anode electrode wiring 8 are formed in the same manner as in the other embodiments, the light receiving element 20c of this embodiment is formed.

(Fifth embodiment)
The light receiving element 20d according to the fifth embodiment of the present invention will be described below with reference to the drawings. FIGS. 6A and 6B are diagrams schematically showing a main part of the light receiving element according to the first embodiment, and are a plan view and a cross-sectional view in order. FIG. 6A is a cross section taken along line VIa-VIa ′ in FIG.

  The light receiving element 20d has a structure in which the cavity 6 of the light receiving element 20 according to the first embodiment has a circular planar shape, whereas the cavity 6b has a square planar shape. The dimension A5 of the side of the square is 400 nm which is equivalent to the wavelength 405 nm of the incident light assumed here, and the interval D5 between the cavity portions 6b is set to 240 nm using the above equation (1).

  Similarly to the light receiving element 20 of the first embodiment, the light receiving element 20d of the present embodiment is also a light receiving element that achieves both high sensitivity and high speed response. That is, a periodic refractive index distribution is generated by the cavity 6b and the high-concentration N + type silicon layer 4, and the photonic crystal part 21 having an optical band gap corresponding to the light wavelength region of the incident light is configured. Passes through the photonic crystal portion 21 without being absorbed. Light absorption is performed by a layer having a low impurity concentration below the photonic crystal portion 21, so that the photosensitivity is high, and the high-concentration N + type silicon layer 4 is disposed in the vicinity of the surface of the light receiving element 20d. High-speed response is realized.

  In the present embodiment, a square shape is used as an example of the planar shape of the hollow portion 6b instead of the circular shape, but the present invention is not limited to this. As another example of the circular shape, a polygonal shape is desirable in order to obtain a function as a photonic crystal. However, from the viewpoint of reproducibility and symmetry during uniform pattern formation and processing, a circular shape is desirable.

  Further, not only in the first embodiment, but also in each of the light receiving elements according to the second to fourth embodiments, it is naturally possible to make the planar shape of the low refractive index portion other than a circular shape.

  In the first to fifth embodiments described above, only the light receiving element has been described. In addition to this, it is applied to an optoelectronic integrated circuit in which transistors and the like are monolithically integrated on the same substrate, so-called OEIC. You can also

  Further, although a silicon-based photodiode has been described, it can also be applied to a compound semiconductor material. Further, the present invention is not limited to the PIN type light receiving element, and can be used for other light receiving elements such as an avalanche photodiode.

  The light-receiving element of the present invention has both high sensitivity and high-speed response and is compatible with incident light having a short wavelength, and is useful as a light-receiving element used in an optical pickup device, a light-receiving element used in an optical communication element, and the like.

1A and 1B are a sectional view and a plan view of a light receiving element 20 according to the first embodiment of the present invention. 2A to 2F are cross-sectional views illustrating the manufacturing process of the light receiving element 20. FIGS. 3A to 3F are views for explaining the light receiving element 20a according to the second embodiment of the present invention and the manufacturing process thereof. 4A to 4F are views for explaining a light receiving element 20b according to a third embodiment of the present invention and a manufacturing process thereof. FIGS. 5A to 5C are views for explaining a light receiving element 20c according to the third embodiment of the present invention and a manufacturing process thereof. 6A and 6B are a cross-sectional view and a plan view of a light receiving element 20d according to a fifth embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 High concentration P + type silicon substrate 2 Low concentration P type silicon layer 3 Low concentration N type silicon layer 3a Low refractive index part 4 High concentration N + type silicon layer 4a Type silicon layer 5 Silicon oxide film 6, 6a Cavity part 7 Cathode electrode wiring 8 Anode electrode wiring 9 SOG layer 9a Low refractive index portion 10 SiN film 10a Low refractive index portion 10b SiN film 11 Photoresist 20 Light receiving element 20a Light receiving element 20b Light receiving element 20c Light receiving element 20d Light receiving element 21 Photonic crystal part

Claims (10)

A semiconductor substrate;
A light absorption layer formed on the semiconductor substrate and including a low-concentration impurity layer and absorbing light of a predetermined wavelength band;
A high concentration impurity layer formed on the light absorption layer and having an impurity concentration higher than that of the low concentration impurity layer;
At least in the high concentration impurity layer, a plurality of low refractive index regions having a smaller refractive index with respect to light in the predetermined wavelength band than the high concentration impurity layer are arranged at regular intervals, whereby the main substrate of the semiconductor substrate is arranged. A light-receiving element comprising a photonic crystal portion that transmits light of the predetermined wavelength band by having a periodic refractive index distribution in a plane direction. In claim 1,
The plurality of low refractive index regions are formed so as to penetrate the high-concentration impurity layer and reach the light absorption layer, so that the photonic crystal portion reaches the light absorption layer. Light receiving element. In claim 1 or 2,
The plurality of low refractive index regions are a plurality of cavities provided in at least the high concentration impurity layer. In claim 1 or 2,
The plurality of low-refractive index regions have a structure in which at least a plurality of recesses provided in the high-concentration impurity layer are embedded with a material having a lower refractive index with respect to light in the predetermined wavelength band than the high-concentration impurity layer. A light receiving element characterized by that. In claim 4,
An antireflection film made of the material for embedding the plurality of recesses is formed on the high concentration impurity layer. In claim 1 or 2,
The plurality of low refractive index regions are regions having the same conductivity type as the high concentration region and having a lower impurity concentration than the high concentration region. In any one of Claims 1-6,
Each of the plurality of low refractive index regions has a circular planar shape. In any one of Claims 1-7,
The light absorption layer includes a first conductivity type low concentration impurity layer as the low concentration impurity layer and a second conductivity type low concentration impurity layer formed thereon,
The light-receiving element, wherein the high-concentration impurity layer is of a second conductivity type. In any one of Claims 1-8,
The plurality of low refractive index regions have a planar shape having a dimension corresponding to the wavelength of light in the predetermined wavelength band. In any one of Claims 1-9,
A refractive index of the high-concentration impurity layer with respect to light in the predetermined wavelength band is n ₁ ,
N ₂ , a refractive index of the plurality of low refractive index regions with respect to light in the predetermined wavelength band,
A center wavelength of the predetermined wavelength band is λ,
When the interval between the plurality of low refractive index regions is D, the following formula D = (λ / 2n ₁ ) + (λ / 2n ₂ )
The light receiving element characterized by that.

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