JP2008306055A - Optical semiconductor device, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical semiconductor device capable of receiving a plurality of light beams differing in wavelength from one another with good sensitivity. <P>SOLUTION: On a top surface of an epitaxial layer 2, N type impurities are ion-implanted to form N<SP>+</SP>semiconductor layers 5 and 6 as a photodetection portion. Then a silicon nitride film 7 is formed on a silicon oxide film 4, and only a region of the silicon nitride film 7 which corresponds to the N<SP>+</SP>semiconductor layer 5 is selectively etched to be removed. Then, a silicon nitride film 8 is formed on the silicon oxide film 4 and silicon nitride film 7. Thus, a plurality of photodiodes 15 and 16 are formed. An antireflective film covering each photodiode is suitably varied in film thickness, so reflection of light having a specified wavelength can effectively be reduced, so that a plurality of kinds of light differing in wavelength can be received with good sensitivity. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical semiconductor device in which a light receiving element is formed on a semiconductor substrate.

  Conventionally, a photodiode is known as an element for converting an optical signal into an electric signal by absorbing light. When a photodiode is formed on a semiconductor substrate, the surface (light incident surface) is covered with an insulating film such as a silicon oxide film or a silicon nitride film. Since the refractive index of light differs between the insulating film and the semiconductor substrate, the insulating film has a function as an antireflection film for preventing reflection of light on the incident surface. The sensitivity is improved by suppressing the loss, and the photocurrent conversion efficiency is improved.

Techniques related to the present invention are described in, for example, the following patent documents.
JP-A-9-153604

  In recent years, various optical disks have been developed. Laser light with a wavelength of about 780 nm is used for CD (Compact Disc), and laser light with a wavelength of about 650 nm is used for DVD (Digital Video Disc). A high-density DVD called (High Definition Digital Video Disc) uses laser light with a short wavelength of about 405 nm.

  However, for example, when trying to receive laser beams of the above-mentioned three types of wavelengths with a photodiode, the conventional antireflection film configuration has a problem that the sensitivity of the laser beam of any wavelength is lowered. For example, when an antireflection film is formed so as to correspond to a high-density DVD, the sensitivity of laser light related to CD or DVD is low, and conversely, when an antireflection film is formed so as to correspond to CD or DVD. The sensitivity of the laser beam related to the high-density DVD was low.

  Therefore, an object of the present invention is to provide a novel antireflection film structure and to provide an optical semiconductor device capable of improving the sensitivity of a plurality of lights having different wavelengths.

  The present invention has been made in view of the above problems, and its main features are as follows. That is, in the method for manufacturing an optical semiconductor device of the present invention, a first light receiving element and a second light receiving element for receiving light having a wavelength different from that of the first light receiving element are formed on a semiconductor substrate. And a step of forming an antireflection film that covers the first and second light receiving elements, and in the step of forming the antireflection film, the reflection of the region that covers the first light receiving element The antireflection film is formed so that a film thickness of the prevention film is different from a film thickness of a region covering the second light receiving element.

  The optical semiconductor device of the present invention includes a first light receiving element formed on a semiconductor substrate, a second light receiving element for receiving light having a wavelength different from that of the first light receiving element, and the first light receiving element. And an antireflection film that covers the first and second light receiving elements, wherein the antireflection film includes a film thickness in a region that covers the first light receiving element and a film in a region that covers the second light receiving element. It is characterized by a difference in thickness.

  In the present invention, a plurality of light receiving elements are formed, and the film thickness of the antireflection film covering the light receiving elements is changed in accordance with the wavelength of light to be received. This makes it possible to improve the sensitivity of a plurality of lights having different wavelengths.

  Next, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 to FIG. 3 are cross-sectional views shown in the order of manufacturing steps. The manufacturing process described below is performed using a wafer-like semiconductor substrate, and a large number of optical semiconductor devices are formed in a matrix with a predetermined dicing line as a boundary. Only the region in which two photodiodes are formed will be described. Moreover, the following manufacturing process is an example to the last, and it is also possible to employ | adopt another manufacturing process.

First, as shown in FIG. 1, a non-doped epitaxial layer 2 and a P ⁺ isolation layer 3 for separating the epitaxial layer 2 into a plurality of island-like regions are formed on a P-type semiconductor substrate 1. The epitaxial layer 2 can be formed by a known epitaxial crystal growth method. The P ⁺ isolation layer 3 has a configuration in which an upper isolation layer 3 a and a lower isolation layer 3 b made of P-type impurities are overlapped and integrated in the epitaxial layer 2. Upper isolation layer 3 a is formed by downwardly diffusing P-type impurities such as boron (B) from the upper surface of epitaxial layer 2. On the other hand, the lower separation layer 3 b is formed by upwardly diffusing P-type impurities such as boron (B) from the bottom side of the semiconductor substrate 1. Adjacent regions are electrically separated by the P ⁺ separation layer 3.

  Next, a silicon oxide film 4 is formed on the entire surface of the epitaxial layer 2 by, for example, a thermal oxidation method. The thickness of the silicon oxide film 4 is about 150 mm, for example. The silicon oxide film 4 becomes a part of an antireflection film (a film for preventing reflection of light on the incident surface and suppressing loss of light reaching the incident surface) in the light receiving portion of the photodiode.

Next, a resist layer (not shown) having an opening is formed on a predetermined region of the epitaxial layer 2, and N-type impurities such as arsenic (As) are ion-implanted using the resist layer as a mask, thereby receiving light from the photodiode. N ⁺ semiconductor layers 5 and 6 to be a part are formed.

Next, as shown in FIG. 2, a silicon nitride film 7 is formed on the silicon oxide film 4 by, for example, a CVD method. The thickness of the silicon nitride film 7 is about 380 mm. Next, a region corresponding to the N ⁺ semiconductor layer 5 in the silicon nitride film 7 is selectively etched and removed to expose the underlying silicon oxide film 4. Next, a silicon nitride film 8 is formed on the silicon oxide film 4 and the silicon nitride film 7 by, for example, a CVD method. The film thickness of the silicon nitride film 8 is, for example, about 320 mm, and the film thickness is changed according to light having a wavelength desired to be received with high sensitivity by the photodiode 15.

Thus, the silicon nitride film in the region corresponding to the N ⁺ semiconductor layer 5 has a single-layer structure of the silicon nitride film 8 and has a thickness of about 320 mm. The silicon nitride film in the region corresponding to the N ⁺ semiconductor layer 6 The nitride film has a two-layer structure of silicon nitride films 7 and 8 and has a thickness of about 700 mm. It is also possible to form a multilayer silicon nitride film to control the film thickness. The silicon nitride films 7 and 8 become part of the antireflection film in the light receiving portion of the photodiode.

  If only the silicon nitride films 7 and 8 are formed directly on the epitaxial layer 2 without forming the silicon oxide film 4, the surface of the epitaxial layer 2 becomes unstable and the dark current of the photodiode increases. To do. Therefore, it is preferable to form the silicon nitride films 7 and 8 through the silicon oxide film 4 (preferably a silicon oxide film formed by a thermal oxidation method).

Next, as shown in FIG. 3, a BPSG (Boron Phospho Silicate Glass) film or SOG (Spin On Glass) film is deposited as an insulating film 9 on the entire surface, and the insulating film 9 is selectively formed using a known photolithography technique. Then, contact holes reaching the N ⁺ semiconductor layer 5 and the N ⁺ semiconductor layer 6 are formed. Next, cathode electrodes 10 and 11 made of aluminum, titanium, or the like are formed in each contact hole by sputtering or the like. Although not shown in the drawing, an anode electrode is similarly formed on a predetermined region of the P ⁺ isolation layer 3, and the semiconductor substrate 1 and the P ⁺ isolation layer 3 are used as an anode region.

  Next, the semiconductor substrate 1 is cut along predetermined dicing lines and divided into individual semiconductor chips. Through the above steps, an optical semiconductor device in which at least two photodiodes (photodiode 15 and photodiode 16) are formed on the semiconductor substrate 1 is completed.

  The photodiodes 15 and 16 are operated in a reverse bias state by applying a predetermined potential to the cathode electrodes 10 and 11 and the anode electrode (not shown). In the photodiodes 15 and 16, since the epitaxial layer 2 is formed by non-doping and has a high specific resistance, a wider depletion layer region can be ensured when a reverse bias is applied. That is, by making the entire epitaxial layer 2 a depletion layer region, the moving speed of carriers generated by the incidence of light can be improved, and a high-speed response can be realized.

  In this embodiment, a plurality of photodiodes are formed, and the thickness of the silicon nitride film covering each photodiode is changed, that is, the thickness of the antireflection film is changed. Therefore, according to the present embodiment, an antireflection film having an optimum film thickness can be formed for each photodiode according to the wavelength, and the sensitivity of a plurality of lights having different wavelengths can be improved in one optical semiconductor device.

  4A to 4C show the relationship between the reflectance of light in the air and the film thickness of the silicon nitride film in the optical semiconductor device of this embodiment. 4A to 4C, when the thickness of the silicon oxide film 4 is 150 mm, 100 mm, and 200 mm, respectively, the reflectivity when light of each wavelength (λ) of 405 nm, 650 nm, and 780 nm is incident ( The relationship between (Reflectivity) and the thickness of the silicon nitride film (SiN Thickness) is shown.

  As shown in FIG. 4A, the reflectance of light having a wavelength of 405 nm was the lowest when the thickness of the silicon nitride film was about 320 mm, and was 5% or less. Further, the reflectance of light having a wavelength of 650 nm was lowest when the wavelength was about 600 mm, and the reflectance of light having a wavelength of 780 nm was lowest when the wavelength was about 800 mm. From this result, the film thickness of the silicon nitride film in the photodiode 15 (the film thickness of the silicon nitride film 8) is about 320 mm, and the film thickness of the silicon nitride film in the photodiode 16 (the total film thickness of the silicon nitride films 7 and 8). By setting it to about 700 mm, it is possible to receive light of three wavelengths (405 nm, 650 nm, and 780 nm) with high sensitivity. Further, when the thickness of the silicon oxide film 4 is changed to 100 mm or 200 mm, the film thickness of the silicon nitride film may be set based on the results of FIGS. 4B and 4C. As will be described later, when the silicon nitride films 7 and 8 are used for purposes other than antireflection, such as the dielectric 25 of the capacitor 20, the silicon nitride films 7 and 8 according to the characteristics required for the capacitor 20, etc. The film thickness of 8 is also adjusted. For example, when the capacitor 20 described later is provided, the film thickness of the silicon nitride film 7 is set to 195 mm, and the film thickness of the silicon nitride film 8 is set to 320 mm, so that the film thickness of the dielectric 25 is set to 515 mm.

  As described above, a photodiode having an antireflection film having an optimum film thickness for suppressing reflection of light of a certain wavelength and an antireflection film having an optimum film thickness for suppressing reflection of light of another wavelength are provided. By providing both photodiodes, each light can be received with high sensitivity by one optical semiconductor device. Therefore, the photodiode 15 is formed as a light receiving element for receiving light having a short wavelength (wavelength of 500 nm or less) for high density DVD such as Blu-ray or HD-DVD, and the photodiode 16 is used for CD / DVD (CD and DVD). Or a light receiving element for receiving light having a wavelength of 600 to 800 nm. In order to further improve the sensitivity of light reception, for example, a photodiode having an antireflection film with an optimum film thickness for each of the three wavelengths (405 nm, 650 nm, and 780 nm) may be formed individually.

  Next, a second embodiment of the present invention will be described with reference to the drawings. In addition, about the structure similar to 1st Embodiment, the same code | symbol is shown and the description is abbreviate | omitted. FIG. 5 is a sectional view showing an optical semiconductor device in which the photodiodes 15 and 16, the capacitor 20, and the NPN transistor 30 described in the first embodiment are formed on the same semiconductor substrate.

P ⁺ isolation layers 3 and 21 for isolating the epitaxial layer 2 into a plurality of islands are formed. An element isolation insulating film 22 is formed on the P ⁺ isolation layer 21 by, for example, the LOCOS method.

  A lower electrode 23 made of, for example, a polysilicon layer is formed on the element isolation insulating film 22. A part of the lower electrode 23 is covered with, for example, a silicon oxide film 24 formed by the CVD method, but most of the lower electrode 23 is covered with the above-described laminated film of the silicon nitride film 7 and the silicon nitride film 8. The film is a dielectric 25 of the capacitor 20. That is, after the silicon oxide film 24 is formed, the silicon oxide film 24 on the lower electrode 23 is selectively removed, and then the silicon nitride films 7 and 8 are formed.

  By adopting such a structure for the capacitor 20, it is possible to suppress a variation in the capacitance value due to a variation in the film thickness of the silicon oxide film 24 and obtain a desired capacitance value with high accuracy. Further, since the dielectric 25 is formed in the same process as the process of forming the antireflection film of the photodiodes 15 and 16, the number of manufacturing processes is reduced. Further, by using a silicon nitride film having a dielectric constant larger than that of the silicon oxide film as the dielectric 25, the capacitance value can be increased. An upper electrode 26 is formed on the lower electrode 23 with a dielectric 25 interposed therebetween.

Next, the formation region of the NPN transistor 30 will be described. Near the interface between the bottom of the semiconductor substrate 1 and the epitaxial layer 2, an N ⁺ type buried layer 31 is formed. The buried layer 31 is formed by implanting N-type impurities (for example, phosphorus ions) into the semiconductor substrate 1 at a high concentration and performing epitaxial growth. An N ⁻ semiconductor layer 32 is formed on the surface of the epitaxial layer 2 by a known epitaxial crystal growth method.

Element isolation insulating films 33 and 34 similar to the element isolation insulating film 22 are formed on the surface of the epitaxial layer 2, and a base region is formed on the surface of the N ⁻ semiconductor layer 32 surrounded by the element isolation insulating films 22 and 33. As a result, a P ⁻ well layer 35 is formed. In the P ⁻ well layer 35, a P ⁺ impurity layer 36 as a base lead-out region and an N ⁺ impurity layer 37 as an emitter region are formed with a predetermined distance apart.

The P ⁺ impurity layer 36 is formed by the following process, for example. After the insulating film 9 is formed, the insulating film 9, the underlying silicon nitride films 7 and 8, and the silicon oxide film 4 are selectively removed to form a contact hole that reaches the region where the P ⁺ impurity layer 36 is to be formed. . Next, P ⁺ impurity layers 36 are formed by implanting and diffusing P-type impurity ions such as boron difluoride (BF ₂ ) into the P ⁻ well layer 35 through the contact holes.

Further, the N ⁺ impurity layer 37 is formed by the following process, for example. After the silicon oxide film 4 and the silicon nitride films 7 and 8 are formed on the entire surface, these are selectively etched to form the N ⁺ impurity layer 37 through the silicon nitride films 7 and 8 and the silicon oxide film 4. A contact hole reaching the region is formed. Next, a wiring layer 38 made of, for example, polysilicon is formed in the contact hole. Next, N-type impurities such as arsenic (As) are added to the wiring layer 38 and subjected to thermal diffusion treatment. Thus, the N ⁺ impurity layer 37 is formed by diffusing the N-type impurity on the surface of the P ⁻ well layer 35 via the wiring layer 38. Note that the silicon oxide film 4 is etched through the contact hole reaching the region where the N ⁺ impurity layer 37 is to be formed, that is, using the silicon nitride films 7 and 8 as a mask, and then using the silicon nitride films 7 and 8 as a mask. The N ⁺ impurity layer 37 can also be formed by performing ion implantation and diffusing. As shown in these figures, by using the silicon nitride films 7 and 8 as a mask when forming the N ⁺ impurity layer 37, the mask forming process can be reduced and the manufacturing process can be simplified.

An N ⁺ impurity layer 39 is formed on the surface of the N ⁻ semiconductor layer 32 so as to be in contact with the buried layer 31 at the bottom as a collector region.

An insulating film 9 is formed on the entire surface of the semiconductor substrate 1, and contact holes reaching the upper electrode 26, the wiring layer 38, the N ⁺ impurity layer 39, the P ⁺ impurity layer 36, and the lower electrode 23 are formed in the insulating film 9. In each contact hole, electrodes for connection to the outside, such as the extraction electrode 40, the emitter electrode 41, the collector electrode 42, and the base electrode 43, are formed. Note that illustration of a contact hole reaching the lower electrode 23 and an electrode connected to the lower electrode 23 is omitted.

  As described above, in the optical semiconductor device according to the second embodiment, the thickness of the silicon nitride film (the thickness of the antireflection film) covering each photodiode (photodiodes 15 and 16) is also the same as in the first embodiment. It is changing. As a result, by forming an antireflection film having an optimum film thickness for each photodiode, it becomes possible to receive light having different wavelengths with high sensitivity.

  Further, by using the silicon nitride films 7 and 8 as antireflection films as the dielectric 25 of the capacitor 20, the manufacturing process can be simplified and the manufacturing cost can be suppressed. Further, by using the silicon nitride films 7 and 8 as a mask when forming the impurity layer of the NPN transistor 30, the manufacturing process can be similarly simplified and the manufacturing cost can be suppressed.

  In addition, this invention is not limited to the said embodiment, A change is possible in the range which does not deviate from the summary. For example, although the P-type semiconductor substrate 1 is used in the above-described embodiment, peripheral circuits such as photodiodes, capacitors, transistors, and the like similar to those in the above-described embodiment can be formed on an N-type semiconductor substrate. In the above embodiment, the silicon oxide film and the silicon nitride film are used as the antireflection film. However, it is possible to use a film made of other materials, and it is also possible to form an antireflection film having a multilayer structure. is there. Although the photodiodes for CD, DVD and high density DVD have been described above, the application of the present invention is not limited to this, and can be widely applied as a technique for forming a highly sensitive light receiving element.

It is sectional drawing which shows the manufacturing process of the optical semiconductor device which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the manufacturing process of the optical semiconductor device which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the optical semiconductor device which concerns on the 1st Embodiment of this invention, and its manufacturing process. It is a graph which shows the relationship between the silicon nitride film and the reflectance of the optical semiconductor device which concerns on the 1st and 2nd embodiment of this invention. It is sectional drawing which shows the optical semiconductor device which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Epitaxial layer 3 P ⁺ Separation layer 3a Upper separation layer 3b Lower separation layer 4 Silicon oxide film 5 N ⁺ Semiconductor layer 6 N ⁺ Semiconductor layer 7 Silicon nitride film 8 Silicon nitride film 9 Insulating film 10 Cathode electrode 11 Cathode electrode 15 Photodiode 16 Photodiode
20 Capacitance 21 P ⁺ Separation Layer 22 Element Isolation Insulating Film 23 Lower Electrode 24 Silicon Oxide Film 25 Dielectric 26 Upper Electrode
30 NPN transistor 31 Buried layer 32 N ⁻ Semiconductor layer 33 Element isolation insulating film 34 Element isolation insulating film 35 P ⁻ Well layer 36 P ⁺ Impurity layer 37 N ⁺ Impurity layer 38 Wiring layer
39 N ⁺ impurity layer
40 Extraction electrode 41 Emitter electrode 42 Collector electrode 43 Base electrode

Claims (6)

Forming on a semiconductor substrate a first light receiving element and a second light receiving element for receiving light having a wavelength different from that of the first light receiving element;
Forming an antireflection film covering the first and second light receiving elements,
In the step of forming the antireflection film, the thickness of the antireflection film in the region covering the first light receiving element and the thickness of the region covering the second light receiving element are different. A method of manufacturing an optical semiconductor device, comprising forming a prevention film. Forming a transistor on the semiconductor substrate;
Forming the transistor comprises forming an opening in the antireflection film;
The method of manufacturing an optical semiconductor device according to claim 1, further comprising: forming an impurity layer constituting the transistor on a surface of the semiconductor substrate using the opening as a mask. The first light receiving element is for a high density DVD and receives light having a wavelength of 500 nm or less, and the second light receiving element is for CD and DVD, or for CD or DVD. A light receiving element for receiving light having a wavelength of 600 to 800 nm,
2. The film thickness of the antireflection film in a region covering the first light receiving element is smaller than a film thickness of the antireflection film in a region covering the second light receiving element. A method for manufacturing an optical semiconductor device according to claim 2. A first light receiving element formed on a semiconductor substrate, and a second light receiving element for receiving light having a wavelength different from that of the first light receiving element;
An antireflection film covering the first and second light receiving elements,
In the optical semiconductor device, the antireflection film has a film thickness in a region covering the first light receiving element and a film thickness in a region covering the second light receiving element. 5. The capacitor according to claim 4, further comprising: a capacitive element including a first conductive layer, a dielectric, and a second conductive layer on the semiconductor substrate, wherein the antireflection film is used as the dielectric. Optical semiconductor device. The first light receiving element is for a high density DVD and receives light having a wavelength of 500 nm or less, and the second light receiving element is for CD and DVD, or for CD or DVD. A light receiving element for receiving light having a wavelength of 600 to 800 nm,
5. The film thickness of the antireflection film in the region covering the first light receiving element is smaller than the film thickness of the antireflection film in the region covering the second light receiving element. The optical semiconductor device according to claim 5.

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