JP2010067655A - Semiconductor optical element, optical pickup, and optical-disk recording/reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor optical element that satisfies the desired optical characteristics in both cases of short-wavelength incident light and an intermediate wavelength incident light. <P>SOLUTION: The semiconductor optical element has a first-conductivity type semiconductor substrate 20; a first-conductivity type first semiconductor layer 23, formed on the semiconductor substrate; a plurality of second semiconductor layers 25, 26, formed on the surface of the first semiconductor layer so as to be separated from each other and constituting a plurality of photodiodes by combinations with the semiconductor substrate; and a second-conductivity type third semiconductor layer 27, located between the two second semiconductor layers, adjacent to each other in a prescribed direction, of the plurality of second semiconductor layers and formed inside the first semiconductor layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a semiconductor optical element, an optical pickup, and an optical disc recording / reproducing apparatus. Specifically, the present invention relates to a semiconductor optical element having a light receiving element as an optical element, and an optical pickup and an optical disc recording / reproducing apparatus using the same.

  An optical disc recording / reproducing apparatus records data using an optical disc such as a CD (compact disc: including CD-R, CD-RW), DVD (digital versatile disc), BD (Blu-ray disc) as a recording medium. -A device that performs playback. The optical disc recording / reproducing apparatus includes an optical pickup. The optical pickup has a light emitting element and a light receiving element inside the pickup. A PN junction or PIN junction photodiode is used for the light receiving element of the optical pickup.

  Photodiodes are mainly classified into RF photodiodes and FRONT photodiodes depending on applications. The RF photodiode mainly has a role of monitoring an RF signal and a tracking / focus servo, and the front photodiode has a role of monitoring laser power and performing APC (Auto Power Control). Usually, a photodiode divided into a plurality of regions is used as the RF photodiode.

  As described above, the photodiode used for the optical pickup is separated into a plurality of regions. In the method of arranging ordinary photodiodes side by side, it is necessary to form a plurality of photodiodes apart from each other. For this reason, the separation width of the photodiodes is widened, and light incident between the photodiodes is wasted. Therefore, at present, a separation structure using a diffusion layer is employed in order to narrow the separation width between the photodiodes.

  9A and 9B illustrate an example of a photodiode separation structure employed in a semiconductor optical element for an optical pickup. FIG. 9A is a plan view and FIG. 9B is a cross-sectional view. In FIG. 9, a P-type low concentration layer 41 is formed on a P-type semiconductor substrate 40. The semiconductor substrate 40 is configured using a P-type silicon substrate. The element isolation unit 42 has a local oxidation of silicon (LOCS) structure, and partitions on the semiconductor substrate 40 a light receiving element region including a photodiode to be described later so as to be separated from other element regions. Such a separation structure is disclosed in Patent Document 1 and Patent Document 2, for example.

  In the light receiving element region partitioned by the element isolation part 42, a PN junction first photodiode (PD) 43 and a PN junction second photodiode (PD) 44 are provided. The first photodiode 43 has an N-type semiconductor layer 45 formed on the surface portion of the low-concentration layer 41 as a cathode, and the second photodiode 44 is an N-type semiconductor formed on the surface portion of the low-concentration layer 41. Layer 46 is the cathode. A P-type semiconductor layer 47 is formed between the two N-type semiconductor layers 45 and 46. The P-type semiconductor layer 47 is formed on the surface portion of the low concentration layer 41 so as to be interposed between the N-type semiconductor layers 45 and 46. For this reason, the first photodiode 43 and the second photodiode 44 are separated using the P-type semiconductor layer 47 as a separation part.

  In the semiconductor optical element having the above configuration, depending on the conditions (concentration, width, depth, etc.) for forming the P-type semiconductor layer 47, the sensitivity characteristics at the separation part, the leakage between the cathodes, the PN junction leakage, the capacitance, The characteristic changes. For this reason, the formation conditions of the P-type semiconductor layer 47 are determined so as to satisfy the required specifications for each characteristic.

  10A and 10B illustrate another example of a photodiode separation structure employed in a semiconductor optical element for an optical pickup. FIG. 10A is a plan view and FIG. 10B is a cross-sectional view. In FIG. 10, a P-type low concentration layer 51 is formed on a P-type semiconductor substrate 50. The semiconductor substrate 50 is configured using a P-type silicon substrate. The element isolation part 52 has a LOCS structure and partitions a light receiving element region including a photodiode, which will be described later, on the semiconductor substrate 50 so as to be separated from other element regions.

  In the light receiving element region partitioned by the element isolation unit 52, a PN junction first photodiode 53, a PN junction second photodiode 54, and a PN junction dummy photodiode 55 are provided. The first photodiode 53 has an N-type semiconductor layer 56 formed on the surface portion of the low-concentration layer 51 as a cathode, and the second photodiode 54 is an N-type semiconductor formed on the surface portion of the low-concentration layer 51. Layer 57 is the cathode. The dummy photodiode 55 uses the N-type semiconductor layer 58 formed on the surface portion of the low concentration layer 51 as a cathode.

  A P-type semiconductor layer 59 is formed between the semiconductor layer 56 of the first photodiode 53 and the semiconductor layer 58 of the dummy photodiode 55. The semiconductor layer 59 is formed on the surface portion of the low concentration layer 51 in a state of being interposed between the n-type semiconductor layers 56 and 58. On the other hand, a P-type semiconductor device 60 is formed between the semiconductor layer 57 of the second photodiode 54 and the semiconductor layer 58 of the dummy photodiode 55. The semiconductor layer 60 is formed on the surface portion of the low concentration layer 51 in a state of being interposed between the N-type semiconductor layers 57 and 58. Therefore, the first photodiode 53 and the second photodiode 54 are separated from each other by using the N-type semiconductor layer 58 and the P-type semiconductor layers 59 and 60 located on both sides thereof as a separation part. Such a separation structure is disclosed in Patent Document 3, for example.

  Normally, when the output between the adjacent photodiodes such as tracking and focus is calculated and used, the structure shown in FIG. 9 that can narrow the distance between the photodiodes is used. When the reduction of crosstalk between photodiodes is required, the structure shown in FIG. 10 is used.

  By the way, for recording / reproduction of an optical disk, light of different wavelengths is used depending on the type of the optical disk. Specifically, a short wavelength light of 405 nm is used for BD, a medium wavelength light of 650 nm is used for DVD, and a medium wavelength light of 780 nm is used for CD. For such short-wavelength light and medium-wavelength light used for optical discs, for example, optical characteristics as shown in FIG. 11 are required. There are two main characteristics of this optical characteristic.

  The first required characteristic is that the addition output (the sum of the outputs of the two photodiodes) is smaller than 1 when light is irradiated between the two photodiodes PD1 and PD2. The sensitivity smaller than 1 assumes a sensitivity in the range of 0.1 or more and 0.95 or less when the sensitivity when light is incident on a normal photodiode region is defined as 1. Furthermore, the addition output is almost flat (sensitivity fluctuation curve is gentle) no matter which position is irradiated with light in the separation region between the photodiodes PD1 and PD2. This optical characteristic can be obtained by irradiating light between the photodiodes so that some of the carriers recombine or flow into a power source or the like to be removed.

  The second required characteristic is that when the light irradiation position between the two photodiodes PD1 and PD2 is linearly changed from one photodiode end to the other photodiode end, it corresponds to the light irradiation position. Thus, the outputs of the photodiodes PD1 and PD2 change linearly. This optical characteristic is that the distance between the two photodiodes PD1 and PD2 is relatively wide (10 to 50 μm), and when light is incident on the region between the photodiodes, the portion from the portion where the light is actually irradiated to the photodiodes. It is obtained when carriers flow through the photodiodes PD1 and PD2 at a ratio corresponding to the distance.

  When the structure shown in FIG. 9 is adopted, the concentration of the P-type semiconductor layer 47 interposed between the photodiodes 43 and 44 is increased (for example, 1E + 19 [1 / cm 3]) and the depth is decreased (for example, 0.2 μm). Thus, the target characteristics as shown in FIG. 11 can be realized when short-wavelength light is incident. The reason for this will be described. Short wavelength light has a larger absorption coefficient than medium wavelength light, and 75% of carriers are generated in the region of 0.2 μm from the silicon surface. For this reason, some carriers are recombined inside the high-concentration P-type semiconductor layer 47. The remaining carriers flow into the photodiodes 43 and 44 according to the distance to the N-type semiconductor layers 45 and 46, respectively. Further, when the concentration of the P-type semiconductor layer 47 is high, the lifetime of carriers is shortened, and recombination is likely to occur. Therefore, the optical characteristics as shown in FIG. 11 are exhibited.

  On the other hand, when the structure shown in FIG. 10 is adopted, the target characteristics as shown in FIG. 11 can be realized when medium wavelength light is incident. The reason for this is that medium wavelength light has a smaller absorption coefficient than short wavelength light. For this reason, for example, assuming that carriers generated in a region within 1 μm from the silicon surface flow into the dummy photodiode 55, 24% of carriers generated near the silicon surface are attracted to the dummy photodiode 55 (650 nm). Assuming medium wavelength light). Further, the remaining 76% of carriers generated in a deeper region flow into the photodiodes 53, 54, and 55 according to the distances to the N-type semiconductor layers 56, 57, and 58, respectively. Therefore, the optical characteristics as shown in FIG. 11 are exhibited.

JP 2001-148503 A JP 2007-329512 A JP-A-7-183563

  However, when the structure shown in FIG. 9 is adopted, for example, when medium wavelength light of 650 nm is incident, the ratio of carriers generated in the region of 0.2 μm from the silicon surface is reduced to 5%. For this reason, the proportion of carriers recombined inside the high-concentration P-type semiconductor layer 47 is also very low, at 5% or less. Therefore, as the optical characteristics, the added output between the photodiodes 43 and 44 is approximately 1 as shown in FIG. 12, and the first required characteristic cannot be satisfied.

  When the structure shown in FIG. 10 is adopted, it is assumed that, when short wavelength light is incident, for example, carriers generated in a region within 1 μm from the silicon surface flow into the dummy photodiode 55 as described above. 99.9% of the carriers generated by the incident light are attracted to the dummy photodiode 55 and removed. For this reason, as the optical characteristics, the added output ≈ 0 as shown in FIG. 13, and the first required characteristic and the second required characteristic cannot be satisfied.

  An object of the present invention is to provide a semiconductor optical element that can satisfy desired optical characteristics (optical characteristics as shown in FIG. 11) regardless of whether incident light is short-wavelength light or medium-wavelength light. is there.

  The present invention includes a first conductivity type semiconductor substrate, a first conductivity type first semiconductor layer formed on the semiconductor substrate, and a surface portion of the first semiconductor layer formed in a state of being separated from each other, A plurality of second conductivity type second semiconductor layers constituting a plurality of photodiodes in combination with a semiconductor substrate, and two second semiconductor layers adjacent to each other in the substrate surface direction of the semiconductor substrate among the plurality of second semiconductor layers. The present invention relates to a semiconductor optical element having a second conductivity type third semiconductor layer formed between the semiconductor layers and formed inside the first semiconductor layer.

  In the semiconductor optical element according to the present invention, of the second semiconductor layers adjacent to each other in the substrate surface direction among the plurality of second conductivity type second semiconductor layers constituting the plurality of photodiodes in combination with the semiconductor substrate. By providing a third semiconductor layer of the second conductivity type between and inside the first semiconductor layer, the carrier generated by light energy can be used regardless of whether the incident light is short wavelength light or medium wavelength light. A part is attracted to the third semiconductor layer, and the remaining carriers flow into the photodiodes according to the distances to the respective second semiconductor layers.

  ADVANTAGE OF THE INVENTION According to this invention, even if incident light is any of short wavelength light and medium wavelength light, the semiconductor optical element which can satisfy | fill a desired optical characteristic can be provided.

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the technical scope of the present invention is not limited to the embodiments described below, and various modifications and improvements have been made within the scope of deriving specific effects obtained by the constituent requirements of the invention and combinations thereof. Including form.

  FIG. 1 is a schematic diagram showing a configuration example of an optical disc recording / reproducing apparatus to which the present invention is applied. The optical disk recording / reproducing apparatus 1 handles, for example, an optical disk such as a CD, DVD, or BD as a recording medium.

  The optical disk recording / reproducing apparatus 1 includes an optical pickup 3, a disk rotation driving mechanism 4, a feeding mechanism 5, and a control unit 6. The optical pickup 3 performs recording and / or reproduction of information (data) on the optical disk 2. The disk rotation drive mechanism 4 drives the optical disk 2 to rotate. The feed mechanism 5 moves the optical pickup 3 in the radial direction of the optical disk 2. Although not shown, the feed mechanism 5 includes a support base that supports the optical pickup 3, a main shaft and a sub shaft that movably support the support base, and a sled motor that moves the support base. The control unit 6 controls the optical pickup 3, the disk rotation drive mechanism 4 and the feed mechanism 5.

  The disk rotation drive mechanism 4 has a disk table 7 and a spindle motor 8. The optical disk 2 is placed on the disk table 7. The spindle motor 8 serves as a drive source for rotationally driving the disk table 7.

  The control unit 6 includes an access control circuit 9, a servo circuit 10, a drive controller 11, a signal demodulator 12, an error correction circuit 13, and an interface 14. The access control circuit 9 controls the position of the optical pickup 3 with respect to the radial direction of the optical disk 2 by drivingly controlling the feeding mechanism 5. The servo circuit 10 drives and controls the biaxial actuator of the optical pickup 3. The drive controller 11 controls the access control circuit 9 and the servo circuit 10. The signal demodulator 12 demodulates the signal from the optical pickup 3. The error correction circuit 13 corrects an error of the signal demodulated by the signal demodulator 12. The interface 14 is for outputting the signal error-corrected by the error correction circuit 13 to an electronic device such as an external computer.

  In the optical disk recording / reproducing apparatus 1 configured as described above, the disk table 7 on which the optical disk 2 is mounted is rotated by the spindle motor 8 of the disk rotation drive mechanism 4. At that time, the optical pickup 3 is moved to a position corresponding to a desired recording track of the optical disk 2 by controlling the driving of the feeding mechanism 5 in accordance with a control signal from the access control circuit 9 of the control unit 6. Information is recorded on and reproduced from the disc 2.

  Although not shown, the optical pickup 3 has an optical system for reproducing information from the optical disk 2 and a lens driving mechanism for driving and displacing an objective lens included in the optical system. Among these, the optical pickup 3 is configured using at least a light emitting element and a light receiving element. The light emitting element emits laser light having a predetermined wavelength toward the optical disk 2. The light receiving element receives the return light from the optical disk 2. The semiconductor optical element according to the present invention may have only a light receiving element, or may have a light emitting element and a light receiving element integrally.

  For example, if the optical disk 2 is a CD, the light emitting element emits a laser beam having a wavelength of 780 nm, if the optical disk 2 is a DVD, emits a laser beam having a wavelength of 650 nm, and if the optical disk 2 is a BD, the wavelength is 405 nm. The laser beam is emitted.

  By the way, the absorption length of the short wavelength light of 405 nm applied to the BD is 0.14 nm, the absorption length of the medium wavelength light of 650 nm applied to the DVD is 3.7 μm, and the absorption length of 780 nm applied to the CD. The absorption length of medium wavelength light is 8.7 μm. In the short wavelength light and the medium wavelength light, 63% of the light is absorbed in a shallow region above the corresponding absorption length, and carriers are generated at a ratio corresponding thereto.

  Next, the structure of the semiconductor optical element according to the embodiment of the present invention will be described. In the embodiment of the present invention, a case where the first conductivity type is P-type and the second conductivity type is N-type will be described as an example.

<First Embodiment>
2A and 2B illustrate the structure of the semiconductor optical element according to the first embodiment of the present invention. FIG. 2A is a plan view and FIG. 2B is a cross-sectional view. In FIG. 2, two photodiodes (PD) 21 and 22 are formed using a P-type semiconductor substrate 20. The two photodiodes 21 and 22 are arranged adjacent to each other in the substrate surface direction of the semiconductor substrate 20. The P-type semiconductor substrate 20 serves as a common anode for the two photodiodes 21 and 22, and is configured using, for example, a P-type silicon substrate. A P-type and low impurity concentration epitaxial layer 23 is formed on the semiconductor substrate 20. The P type epitaxial layer 23 corresponds to a first semiconductor layer of the first conductivity type. The element isolation unit 24 has a LOCS structure and partitions the light receiving element region including the photodiodes 21 and 22 on the semiconductor substrate 20 so as to be separated from other element regions.

  The two photodiodes 21 and 22 described above are provided in the light receiving element region partitioned by the element separation unit 24. Each of the photodiodes 21 and 22 is formed in a rectangular shape in plan view. The “rectangular shape” described here is a term having both the meanings of a rectangle and a square. However, the planar shape of the photodiodes 21 and 22 is not limited to a rectangle, and may be a rhombus, for example. One photodiode (hereinafter also referred to as “first photodiode”) 21 is a PN junction photodiode, and the other photodiode (hereinafter also referred to as “second photodiode”) 22 is also a PN junction photodiode. It is a diode.

  The first photodiode 21 has an N-type semiconductor layer 25 formed on the surface portion of the epitaxial layer 23 as a cathode, and the second photodiode 22 has an N-type semiconductor layer 26 formed on the surface portion of the epitaxial layer 23. Is the cathode. The N-type semiconductor layers 25 and 26 correspond to second-conductivity-type second semiconductor layers, respectively. Note that “formed on the surface portion” described here means forming from the upper surface of the epitaxial layer 23 with a predetermined thickness in the depth direction of the epitaxial layer 23 (the thickness direction of the semiconductor substrate 20). For this reason, the upper surface of the layer formed on the surface portion of the epitaxial layer 23 is arranged flush with the upper surface of the epitaxial layer 23. In other words, any layer having an upper surface flush with the upper surface of the epitaxial layer 23 is formed on the surface portion of the epitaxial layer 23.

  An N-type semiconductor layer 27 is embedded in the epitaxial layer 23. The N-type semiconductor layer 27 corresponds to a second conductivity-type third semiconductor layer. The semiconductor layer 27 is formed in an island shape inside the epitaxial layer 23 in a rectangular shape in plan view. The semiconductor layer 27 is arranged in a state of being interposed between the two semiconductor layers 25 and 26 in a plan view. In the direction in which the two semiconductor layers 25 and 26 are aligned (the left-right direction in the figure), the epitaxial layer 23 is interposed between the one semiconductor layer 25 and the semiconductor layer 27, and the other semiconductor layer 26 and the semiconductor layer 27 are interposed. Between these, the epitaxial layer 23 is interposed in a slit shape.

  In addition, the semiconductor layer 27 is disposed at a position (downward) deeper than the two semiconductor layers 25 and 26 when viewed in cross section. The semiconductor layer 27 is electrically connected to, for example, a power source (not shown) so that carriers generated by light irradiation can be absorbed. The depth dimension D from the surface of the epitaxial layer 23 to the semiconductor layer 27 is set according to the optical characteristics required for the semiconductor optical element.

  When manufacturing the semiconductor optical element having the above-described configuration, first, a P-type epitaxial layer 23 having a low impurity concentration is formed on the surface (upper surface) of the P-type semiconductor substrate 20 by crystal growth of silicon.

  Next, an N-type semiconductor layer 27 is formed in a region corresponding to the two photodiodes 21 and 22 by an ion implantation method. In the case where the N-type semiconductor layer 27 is formed inside the epitaxial layer 23, ion implantation at high energy, for example, phosphorus (P) ions that become impurities, 3 [MeV] energy, 5E + 12 [1 / cm <2>] Ion implantation is performed under the condition of the dose amount.

  Note that the process of forming the N-type semiconductor layer 27 can be combined with the process of forming a deep N well layer for a substrate isolation type MOS transistor, the process of forming an N-type island of a VPNP transistor, and the like.

  The N-type semiconductor layer 27 is, for example, an N-type well so as to surround the light-receiving element region partitioned by the element isolation part 24 as shown in the plan view of FIG. 3A and the cross-sectional view of FIG. A layer 28 is formed, and the both end portions of the semiconductor layer 27 are connected to the well layer 28. An electrode 29 is taken out from the well layer 28 and connected to a power source or the like.

  Next, N-type semiconductor layers 25 and 26 are formed by introducing impurities into portions to be the photodiodes 21 and 22. Thus, two photodiodes 21 and 22 are formed in the light receiving element region with the P-type semiconductor substrate 20 as a common anode and the N-type semiconductor layers 25 and 26 as individual cathodes.

  When operating the semiconductor optical element thus obtained, a reverse bias voltage is applied between the anode and cathode of each of the photodiodes 21 and 22. During this operation, the optical characteristics when the short wavelength light is irradiated to the region between the photodiodes 21 and 22 and the optical characteristics when the medium wavelength light is irradiated are as follows.

  First, when short wavelength light is irradiated to the region between the photodiodes 21 and 22, 75% of carriers are generated in the region of 0.2 μm from the silicon surface as described above. Further, when the region between the photodiodes 21 and 22 is irradiated with, for example, medium wavelength light of 650 nm, the ratio of carriers generated in the region of 0.2 μm from the silicon surface is 5% as described above. In other words, when the incident light is short wavelength light, relatively many carriers are generated in a shallow region of the silicon surface, and when the incident light is medium wavelength light, relatively many carriers are generated in a deep region inside the silicon. Will occur.

  Therefore, considering the difference in absorption length between short-wavelength light and medium-wavelength light, the embedding depth of the N-type semiconductor layer 27 relative to the upper surface of the epitaxial layer 23 serving as the silicon surface, and the plane of the semiconductor layer 27 The general size (rectangular size), thickness, etc. are set. For example, when 405 nm laser light corresponding to BD is used as short wavelength light and 650 nm laser light corresponding to DVD is used as medium wavelength light, the absorption length (0.14 μm, 3.. In consideration of the difference of 7 μm), the N-type semiconductor layer 27 is formed in a range of a depth of 1 to 2 μm from the silicon surface.

  Thereby, when the laser light irradiated to the area | region between photodiodes 21 and 22 is short wavelength light, many carriers generate | occur | produce in the shallow area | region of a silicon surface. In such a case, a part of the relationship between the positions of the N-type semiconductor layers 25 and 26 serving as the cathodes of the photodiodes 21 and 22, the position of the N-type semiconductor layer 27 interposed therebetween, and the position at which carriers are generated. The carriers are absorbed by the N-type semiconductor layer 27 and flow into the power source. The remaining carriers flow into the photodiodes 21 and 22 according to the distance to the N-type semiconductor layers 25 and 26, respectively.

  On the other hand, even when the laser light applied to the region between the photodiodes 21 and 22 is medium wavelength light, due to the above positional relationship, some carriers are absorbed by the N-type semiconductor layer 27 and flow into the power source. The remaining carriers flow into the photodiodes 21 and 22 according to the distance to the N-type semiconductor layers 25 and 26, respectively. Carriers absorbed by the N-type semiconductor layer 27 are removed by flowing into the power source. For this reason, it is not reflected in the addition output. Therefore, the optical characteristics as shown in FIG. 11 can be satisfied regardless of whether the wavelength of the laser light applied to the region between the photodiodes 21 and 22 is a short wavelength or a medium wavelength.

  Here, the N-type semiconductor layer 27 is formed in a single island shape, but the present invention is not limited to this. For example, as shown in FIG. A slit-like structure in which the layer 27 is separated into a plurality (four in the illustrated example) of semiconductor layers 27a to 27d may be employed. When such an element structure is adopted, the ratio of the carriers generated on the silicon surface or inside the silicon is changed by separating the N-type semiconductor layer 27 into a plurality of semiconductor layers 27a to 27d. For this reason, the crosstalk characteristic in a separation part can be changed.

<Second Embodiment>
5A and 5B illustrate the structure of a semiconductor optical element according to the second embodiment of the present invention. FIG. 5A is a plan view and FIG. 5B is a cross-sectional view. The semiconductor optical element according to the second embodiment is different from the element structure of the first embodiment in that a P-type semiconductor layer 30 is added. The P-type semiconductor layer 30 corresponds to a first conductivity-type fourth semiconductor layer. The semiconductor layer 30 is a layer having a higher impurity concentration than the epitaxial layer 23.

  The P-type semiconductor layer 30 is arranged in a state of being interposed between the two N-type semiconductor layers 25 and 26 in a plan view. The semiconductor layer 30 is formed in a rectangular shape in plan view on the surface portion of the epitaxial layer 23. In the arrangement direction of the two semiconductor layers 25, 26 (left-right direction in the figure), the epitaxial layer 23 is interposed in a slit shape between one semiconductor layer 25 and the semiconductor layer 30, and the other semiconductor layer 26 and the semiconductor layer 30. Between these, the epitaxial layer 23 is interposed in a slit shape. However, there may be no space between the semiconductor layer 25 and the semiconductor layer 30 and between the semiconductor layer 26 and the semiconductor layer 30.

  In addition, the P-type semiconductor layer 30 is formed thinner than the two semiconductor layers 25 and 26 in a cross-sectional view. However, the semiconductor layer 30 may be thicker than the semiconductor layers 25 and 26. The P-type semiconductor layer 30 is disposed so as to face the above-described N-type semiconductor layer 27 via the epitaxial layer 23 (in an overlapping state when viewed in plan).

  When manufacturing the semiconductor optical element having the above-described configuration, first, a P-type epitaxial layer 23 having a low impurity concentration is formed on the surface (upper surface) of the P-type semiconductor substrate 20 by crystal growth of silicon.

  Next, an N-type semiconductor layer 27 is formed in a region corresponding to the two photodiodes 21 and 22 by an ion implantation method. In the case where the N-type semiconductor layer 27 is formed inside the epitaxial layer 23, ion implantation at high energy, for example, phosphorus (P) ions that become impurities, 3 [MeV] energy, 5E + 12 [1 / cm <2>] Ion implantation is performed under the condition of the dose amount.

  Note that the process of forming the N-type semiconductor layer 27 can be combined with the process of forming a deep N well layer for a substrate isolation type MOS transistor, the process of forming an N-type island of a VPNP transistor, and the like.

  In addition, the N-type semiconductor layer 27 is formed so as to surround the light-receiving element region partitioned by the element isolation portion 24 as shown in the plan view of FIG. 3A and the cross-sectional view of FIG. A well layer 28 is formed, and both end portions of the semiconductor layer 27 are connected to the well layer 28. An electrode 29 is taken out from the well layer 28 and connected to a power source or the like.

  Next, a P-type semiconductor layer 30 is formed above the N-type semiconductor layer 27. When the P-type semiconductor layer 30 is formed on the surface portion of the epitaxial layer 23, for example, boron (B) ions serving as impurities are 50 [keV] so that the formation position is above the semiconductor layer 27. Ion implantation is performed under the condition of the energy of 7E + 12 [1 / cm 2].

  Next, N-type semiconductor layers 25 and 26 are formed by introducing impurities into portions to be the photodiodes 21 and 22. Thus, as in the first embodiment, the P-type semiconductor substrate 20 is used as a common anode, the N-type semiconductor layers 25 and 26 are used as individual cathodes, and the two photodiodes 21 and 22 are light-receiving elements. It will be formed in the region.

  In the semiconductor optical element thus obtained, the optical characteristics when the short wavelength light is irradiated to the region between the photodiodes 21 and 22 during operation and the optical characteristics when the medium wavelength light is irradiated are as follows. Become.

  First, when short wavelength light is irradiated to the region between the photodiodes 21 and 22, 75% of carriers are generated in the region of 0.2 μm from the silicon surface as described above. Therefore, some carriers are recombined inside the high-concentration P-type semiconductor layer 30, and the remaining carriers are supplied from the power source according to the distance to the N-type semiconductor layer 27 and the semiconductor layers 25 and 26. And into the photodiodes 21 and 22.

  On the other hand, when the intermediate wavelength light is irradiated to the region between the photodiodes 21 and 22, the ratio of carriers generated in the region of 0.2 μm from the silicon surface is 5% as described above, and most of the carriers are larger than that. Occurs in deep areas. In such a case, some of the carriers are absorbed by the N-type semiconductor layer 27 and flow into the power supply, and the remaining carriers are supplied to the photodiodes 21 and 22 according to the distance to the N-type semiconductor layers 25 and 26, respectively. Flows in.

  As a result, the optical characteristics as shown in FIG. 11 can be satisfied regardless of whether the wavelength of the laser light applied to the region between the photodiodes 21 and 22 is a short wavelength or a medium wavelength. Further, compared with the first embodiment, carriers generated when short-wavelength light is incident are recombined in the P-type semiconductor layer 30 to reduce the added output when short-wavelength light is incident. To do. For this reason, it becomes possible to make the crosstalk characteristic (change of the addition output at the photodiode end) relatively steep. Further, when the region between the photodiodes 21 and 22 is irradiated with light by changing the presence / absence of the P-type semiconductor layer 30 and the width / thickness / depth of the N-type semiconductor layer 27 from the silicon surface. It is possible to vary the magnitude of the added output. In addition, by forming the P-type semiconductor layer 30, an effect of reducing a leakage current generated between the two photodiodes 21 and 22 can be obtained.

  Also in the second embodiment, regarding the N-type semiconductor layer 27, as shown in FIG. 4, the N-type semiconductor layer 27 is replaced with a plurality of semiconductor layers 27a in the direction in which the two photodiodes 21 and 22 are arranged. You may employ | adopt the structure isolate | separated to -27d. Further, the N-type semiconductor layer 27 may be formed narrower than the N-type semiconductor layers 25 and 26 serving as cathodes of the photodiodes 21 and 22, for example, in order to change the crosstalk characteristics.

<Third Embodiment>
6A and 6B illustrate the structure of a semiconductor optical element according to the third embodiment of the present invention. FIG. 6A is a plan view and FIG. 6B is a cross-sectional view. In the semiconductor optical device according to the third embodiment, the cathodes of the photodiodes 21 and 22 are respectively formed by N-type epitaxial layers 31 and 32 as compared with the device structure of the second embodiment. The difference is that the P-type semiconductor layer 33 is added. The N type epitaxial layers 31 and 32 correspond to second conductive type second semiconductor layers, respectively. The P-type semiconductor layer 33 is a layer having a higher impurity concentration than the epitaxial layer 23. The P-type semiconductor layer 30 is a layer having a higher impurity concentration than the semiconductor layer 33.

  The P-type semiconductor layer 33 is arranged in a state of being interposed between the two N-type epitaxial layers 31 and 32 together with the P-type semiconductor layer 30 in a plan view. The semiconductor layer 33 is formed in a rectangular shape in plan view on the surface portion of the epitaxial layer 23 together with the P-type semiconductor layer 30 and the N-type epitaxial layers 31 and 32. The semiconductor layer 33 is formed in a rectangular shape that is slightly larger than the semiconductor layer 30. For this reason, when viewed in plan, the semiconductor layer 30 is disposed in the formation region of the semiconductor layer 33. However, the semiconductor layer 30 may be larger than the semiconductor layer 33. One side of the semiconductor layer 33 is disposed adjacent to one side of the epitaxial layer 31 that is the end side of the first photodiode 21, and the other side of the semiconductor layer 33 is the epitaxial layer 32 that is the end side of the second photodiode 22. It is arranged adjacent to one side. (

  Further, when the structure of the semiconductor optical element is viewed in cross section, the semiconductor layer 30 is formed thinner than the N-type epitaxial layers 31 and 32, and the semiconductor layer 33 is formed thicker than the N-type epitaxial layers 31 and 32. Has been. The upper surface of the semiconductor layer 33 is disposed flush with the upper surface of the epitaxial layer 23. The lowermost part of the semiconductor layer 33 is disposed in contact with the N-type semiconductor layer 27. However, the semiconductor layer 33 and the semiconductor layer 27 may not be in contact with each other as long as the positional relationship is up and down. The semiconductor layer 27 is formed in a rectangular shape with the same size as the semiconductor layer 30, and is disposed in a state facing the semiconductor layer 30.

  When manufacturing the semiconductor optical element having the above-described configuration, first, a P-type epitaxial layer 23 having a low impurity concentration is formed on the surface (upper surface) of the P-type semiconductor substrate 20 by crystal growth of silicon.

  Next, an N-type semiconductor layer 27 is formed in a region corresponding to the two photodiodes 21 and 22 by an ion implantation method. In the case where the N-type semiconductor layer 27 is formed inside the epitaxial layer 23, ion implantation at high energy, for example, phosphorus (P) ions that become impurities, 3 [MeV] energy, 5E + 12 [1 / cm <2>] Ion implantation is performed under the condition of the dose amount.

  Note that the process of forming the N-type semiconductor layer 27 can be combined with the process of forming a deep N well layer for a substrate isolation type MOS transistor, the process of forming an N-type island of a VPNP transistor, and the like.

  In addition, the N-type semiconductor layer 27 is formed so as to surround the light-receiving element region partitioned by the element isolation portion 24 as shown in the plan view of FIG. 3A and the cross-sectional view of FIG. A well layer 28 is formed, and both end portions of the semiconductor layer 27 are connected to the well layer 28. An electrode 29 is taken out from the well layer 28 and connected to a power source or the like.

  Next, N-type epitaxial layers (31, 32) are formed by crystal growth on the entire surface of the substrate including the portions to be the photodiodes 21, 22.

  Next, a P-type semiconductor layer 33 is formed by ion implantation in a region corresponding to between the two photodiodes 21 and 22. The impurity concentration of the semiconductor layer 33 needs to be higher than the impurity concentration of the N-type epitaxial layers 31 and 32. Therefore, assuming that the impurity concentration of the N type epitaxial layers 31 and 32 is 5E + 15 [1 / cm 3] and the thickness is 1 μm, when the P type semiconductor layer 33 is formed, for example, it becomes an impurity. Boron (B) ions are implanted under the conditions of an energy of 450 [keV] and a dose of 3E + 13 [1 / cm <2>].

  Next, a P-type semiconductor layer 30 having an impurity concentration higher than that of the semiconductor layer 33 is formed on the surface portion of the P-type semiconductor layer 33. When the P-type semiconductor layer 30 is formed, for example, boron (B) ions serving as impurities are ion-implanted under the conditions of an energy of 50 [keV] and a dose amount of 7E + 12 [1 / cm <2>].

  When operating the semiconductor optical element thus obtained, a reverse bias voltage is applied between the anode and cathode of each of the photodiodes 21 and 22. During this operation, the optical characteristics when the short wavelength light is irradiated to the region between the photodiodes 21 and 22 and the optical characteristics when the medium wavelength light is irradiated are as follows.

  First, when short wavelength light is irradiated to the region between the photodiodes 21 and 22, 75% of carriers are generated in the region of 0.2 μm from the silicon surface as described above. Therefore, some carriers are recombined inside the high-concentration P-type semiconductor layer 30, and the remaining carriers are supplied from the power source according to the distance to the N-type semiconductor layer 27 and the epitaxial layers 31 and 32. And into the photodiodes 21 and 22.

  On the other hand, when the intermediate wavelength light is irradiated to the region between the photodiodes 21 and 22, the ratio of carriers generated in the region of 0.2 μm from the silicon surface is 5% as described above, and most of the carriers are larger than that. Occurs in deep areas. In such a case, some of the carriers are absorbed by the N-type semiconductor layer 27 and flow into the power source, and the remaining carriers are supplied to the photodiodes 21 and 22 according to the distance to the N-type epitaxial layers 31 and 32, respectively. Flows in.

  As a result, the optical characteristics as shown in FIG. 11 can be satisfied regardless of whether the wavelength of the laser light applied to the region between the photodiodes 21 and 22 is a short wavelength or a medium wavelength. Further, compared with the first embodiment, carriers generated when short-wavelength light is incident are recombined in the P-type semiconductor layer 30 to reduce the added output when short-wavelength light is incident. To do. For this reason, it becomes possible to make the crosstalk characteristic (change of the addition output at the photodiode end) relatively steep.

  Also in the third embodiment, with respect to the N-type semiconductor layer 27, as shown in FIG. 4, the N-type semiconductor layer 27 is replaced with a plurality of semiconductor layers 27a in the direction in which the two photodiodes 21 and 22 are arranged. You may employ | adopt the structure isolate | separated to -27d. Further, the N-type semiconductor layer 27 may be formed narrower than the P-type semiconductor layer 30, for example, in order to change the crosstalk characteristics.

  Further, in each of the above embodiments, the case where two photodiodes are formed side by side in the light receiving element region of the semiconductor substrate 20 has been described as an example. However, the present invention is not limited to this, for example, the light receiving of the semiconductor substrate 20. When four photodiodes are formed side by side in the element region, the same configuration as described above may be adopted for two photodiodes adjacent to each other.

  Further, in the semiconductor optical element satisfying the optical characteristics as shown in FIG. 11, the following effects can be obtained. That is, in the case of the semiconductor optical element shown in FIG. 9, when medium wavelength light is incident, the addition output at the center of the separation portion due to the P-type semiconductor layer 47 is not reduced. On the other hand, in the structure of the semiconductor light emitting device according to the present invention, regardless of whether the incident light is short-wavelength light or medium-wavelength light, the output of the added output is obtained at a certain distance (referred to as “L”) in the region between the photodiodes. A drop occurs. Using this characteristic, it is possible to perform focus servo and tracking servo simultaneously.

  That is, when the subject is in focus, as shown in FIG. 7A, the spot diameter is smaller than the distance L, and light is irradiated only to the region where the added output of the two photodiodes PD1 and PD2 is low. On the other hand, when the focus is shifted, the spot diameter is larger than the distance L as shown in FIG. 7B, and light is irradiated to the region where the added output of the two photodiodes PD1 and PD2 is high. . For this reason, the sum of the outputs of the two photodiodes PD1 and PD2 is higher in the state of FIG. 7B than in the state of FIG. 7A. Therefore, the focus servo can be performed by monitoring the total output of the two photodiodes PD1 and PD2.

  Further, as shown in FIG. 8A, if the light irradiation position is the center between the photodiodes PD1 and PD2, the outputs of the two photodiodes PD1 and PD2 are the same. On the other hand, as shown in FIG. 8B, when the light irradiation position is shifted from the center toward one photodiode PD1, the output of the one photodiode PD1 becomes high. Further, as shown in FIG. 8C, when the light irradiation position is shifted from the center toward the other photodiode PD2, the output of the other photodiode PD2 becomes high. Therefore, tracking servo can be performed by monitoring the outputs of the photodiodes PD1 and PD2.

It is the schematic which shows the structural example of the optical disk recording / reproducing apparatus with which this invention is applied. It is a figure explaining the structure of the semiconductor optical element which concerns on the 1st Embodiment of this invention. It is a figure explaining the electrode extraction structure of the semiconductor optical element which concerns on the 1st Embodiment of this invention. It is a figure explaining the modification of the semiconductor optical element which concerns on the 1st Embodiment of this invention. It is a figure explaining the structure of the semiconductor optical element concerning the 2nd Embodiment of this invention. It is a figure explaining the structure of the semiconductor optical element which concerns on the 3rd Embodiment of this invention. It is FIG. (1) explaining the effect acquired by the semiconductor optical element which concerns on this invention. It is FIG. (2) explaining the effect acquired by the semiconductor optical element which concerns on this invention. It is a figure explaining an example of the isolation structure of the photodiode employ | adopted as the semiconductor optical element for optical pick-ups. It is a figure explaining the other example of the isolation structure of the photodiode employ | adopted as the semiconductor optical element for optical pick-ups. It is a figure which shows an example of the optical characteristic requested | required of the semiconductor optical element for optical pick-ups. It is a figure which shows the optical characteristic corresponding to the element structure of FIG. It is a figure which shows the optical characteristic corresponding to the element structure of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Optical disc recording / reproducing apparatus, 2 ... Optical disc, 3 ... Optical pick-up, 20 ... Semiconductor substrate, 21, 22 ... Photodiode, 23, 31, 32 ... Epitaxial layer, 24 ... Element isolation part, 25, 26, 27 , 30, 33 ... Semiconductor layer

Claims (5)

A first conductivity type semiconductor substrate;
A first conductivity type first semiconductor layer formed on the semiconductor substrate;
A plurality of second semiconductor layers of a second conductivity type formed on the surface portion of the first semiconductor layer so as to be separated from each other and constituting a plurality of photodiodes in combination with the semiconductor substrate;
Of the plurality of second semiconductor layers, a second conductivity type second layer formed between the two second semiconductor layers adjacent to each other in the substrate surface direction of the semiconductor substrate and formed inside the first semiconductor layer. A semiconductor optical element having three semiconductor layers. The semiconductor optical element according to claim 1, wherein the third semiconductor layer is separated into a plurality of semiconductor layers in a direction in which the second semiconductor layers are adjacent to each other. A first conductivity type located between the adjacent second semiconductor layers and above the third semiconductor layer and formed at a surface portion of the first semiconductor layer with an impurity concentration higher than that of the first semiconductor layer. The semiconductor optical element according to claim 1, comprising the fourth semiconductor layer. A first conductivity type semiconductor substrate;
A first conductivity type first semiconductor layer formed on the semiconductor substrate;
A plurality of second semiconductor layers of a second conductivity type formed on the surface portion of the first semiconductor layer so as to be separated from each other and constituting a plurality of photodiodes in combination with the semiconductor substrate;
Of the plurality of second semiconductor layers, a second conductivity type second layer formed between the two second semiconductor layers adjacent to each other in the substrate surface direction of the semiconductor substrate and formed inside the first semiconductor layer. An optical pickup comprising a semiconductor optical element having three semiconductor layers. An optical pickup for recording and / or reproducing information on an optical disk;
The optical pickup is
A first conductivity type semiconductor substrate;
A first conductivity type first semiconductor layer formed on the semiconductor substrate;
A plurality of second semiconductor layers of a second conductivity type formed on the surface portion of the first semiconductor layer so as to be separated from each other and constituting a plurality of photodiodes in combination with the semiconductor substrate;
Of the plurality of second semiconductor layers, a second conductivity type second layer formed between the two second semiconductor layers adjacent to each other in the substrate surface direction of the semiconductor substrate and formed inside the first semiconductor layer. An optical disc recording / reproducing apparatus comprising a semiconductor optical element having three semiconductor layers.

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