JP3287982B2 - Optical waveguide type photodetector incorporating signal processing circuit and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide type light receiving element having an optical waveguide formed on the same substrate as a photoelectric conversion element incorporating a signal processing circuit used in an optical pickup or the like, and a method of manufacturing the same. In particular, the present invention relates to stabilizing element characteristics of a signal processing circuit portion.

[0002]

2. Description of the Related Art Optical pickups are widely used for compact discs (CD) and mini discs (MD). Recently, there has been an increasing demand for miniaturization of optical pickups, and as a measure therefor, attempts have been made to integrate optical components on a photodetector using an optical waveguide.
FIG. 10 shows an example of such an optical waveguide pickup.
The light emitted from the semiconductor laser 111 is
The optical integrated detection element 1
20 are provided. That is, the optical integrated detection element 1
Reference numeral 20 denotes a buffer layer 112 on the silicon substrate 1, for example.
, An optical waveguide layer 113 is formed. A photodetector 114 is connected to the optical waveguide layer 113.
This is usually divided into a plurality of photodiodes in order to use its output for each control. Further, a first gap layer 115 having a lower refractive index than the optical waveguide layer 113 is stacked on the optical waveguide layer 113. This first
On the gap layer 115, a second gap layer 116 having a lower refractive index than the optical waveguide layer 113 is laminated. The end face portion 116a of the second gap layer 116 includes
An opening 117 is formed. The second gap layer 1
An adhesive layer 118 having a higher refractive index than the optical waveguide layer 113 is provided in the 16 openings 117, and the adhesive layer 118 allows the first gap layer 115 and an upper portion of the adhesive layer 118 to be formed. A prism 119 made of a dielectric material having a higher refractive index than the optical waveguide layer 113 is bonded and fixed.

[0003] As the first gap layer 115 and the second gap layer 116, an SiO ₂ based film is used.
The refractive index of 18 is different from that of each of the gap layers 115 and 116 described above.
Is higher than the refractive index. The respective refractive indices of the first gap layer 115 and the second gap layer 116 have no particular magnitude relation. End face 116a of second gap layer 115
Is such that the guided light A travels through the optical waveguide layer 113,
Being on the slope. Note that no circuit element is provided in the device of FIG.

In such a configuration, the semiconductor laser 1
The light emitted from the light 11 is collimated by the collimating lens 102, and the prism 119 of the optical integrated detection element 120
, Part of the incident light is reflected by the bottom surface of the prism, and the other incident light is guided to the left in FIG. The guided light is radiated again by the prism 119. This is called so-called decoupling.
The light reflected by the bottom surface of the prism 119 and the light radiated by the decoupling are combined again to increase the light intensity, exit from the prism 119, and are condensed by the objective lens 115 to be condensed by the objective lens 115. Irradiated on the upper side, thereby recording and reading information.
The reflected light from the optical disk 101 again enters the prism 119 via the objective lens 115. Then, a part of the incident light is reflected by the bottom surface of the prism 119, and the other light is reflected by the adhesive layer 118 and the first gap layer 1.
The light is guided to the left of the optical waveguide layer 113 through the line 15.
The guided light A travels rightward in the optical waveguide layer 113 without being decoupled to the prism 119 again due to the presence of the second gap layer 116. In this case, the thickness of the first gap layer 115 is controlled so that a predetermined amount of light is guided into the optical waveguide layer 113. When the thickness of the second gap layer 116 is small, a part of the waveguide light A radiates to the prism 119. Therefore, the thickness of the second gap layer 116 is set so that the waveguide light A does not radiate. In this case, the thickness may be set to 1 μm or more.

[0005] A waveguide mirror (not shown) is formed on the optical integrated detection element 120 so as to converge the guided light toward the photodetector 114. By appropriately adjusting the output of each photodiode constituting the photodetector 114 by the operation, a focus error signal, a radial error signal, and a reproduction information signal required for controlling the optical pickup can be obtained.

In the above-described optical waveguide type photodetector, it is conceivable to form an IC for processing a photoelectrically converted signal on the same substrate together with a photodiode as a photodetector. FIG. 11 shows a schematic cross-sectional view of an example of such an optical waveguide type detection element.

FIG. 11 is an enlarged sectional view of a portion where the photodetector of the optical pickup as shown in FIG. 10 and a signal processing circuit are integrated together with the photodetector. A portion is a photodiode, B portion is a circuit supporting portion, and C portion is a coupling portion between the optical waveguide and the photodiode.

For example, an N-type epitaxial layer 5 is formed on the surface of a P-type silicon substrate 1, and an N-type buried diffusion layer 2 is buried below a circuit element portion B on the right side. The P-type diffusion layer 6 on the surface of the N-type epitaxial layer 5 and the N-type diffusion layer 9 on the surface
A PN transistor is formed. On these surfaces, metal electrodes 10, 10,... Penetrating the SiO ₂ film 7 are provided.

Each circuit element is separated from an adjacent element by a P-type buried isolation / diffusion layer 3 and a P-type isolation / diffusion layer 4.

On the left, a photodiode is formed by the N-type epitaxial layer 5, the P-type diffusion layer 6 formed on the surface thereof, and the P-type substrate 1. This is divided into a plurality as necessary. As a cathode of the photodiode, an electrode 10 is provided in the N-type diffusion layer 9 provided in the N-type epitaxial layer 5 through the SiO ₂ film 7 on the surface. The surface of the left P-type diffusion layer 6 and the right SiO
The surface of the _second film 7 is covered with the SiN film 8. Si on the left
The surface of the N film 8 and the surface of the SiN film 8 near the right electrode portion are covered with an SiO ₂ film 121 serving as a buffer layer. SiO ₂ film 121 of the photodiode surface is the waveguide layer 12 is removed is such that the photodiode coupling, SiO ₂ film 12 of the other portion
1 is covered with a waveguide layer 12 made of, for example, glass. Furthermore, the upper portion is covered with a cladding layer 13 of, for example, SiO ₂ (corresponding to the first gap layer 115 in FIG. 10).

As is apparent from FIG. 11, the left SiO ₂
The thickness of the film 121 is almost equal to the thickness of the SiO ₂ film 121 on the right. Right electrode 10 and SiO ₂ film 7 and S
The SiO ₂ film 121 above the iN film 8 actually has irregularities, but is flattened in FIG. 11 for simplicity.

[0012]

SiO ₂ film 121 serving as the buffer layer of the waveguide The object of the invention is to solve the above-the role portions of the buffer layer of the waveguide to the left photodiode, the signal processing circuit of the right IC There is a portion that serves as a surface protection film for the portion, and is formed at the same time. In a relatively thin waveguide layer, such as a single mode waveguide,
The SiO ₂ film as the buffer layer of the waveguide needs to have a thickness of about 2 μm or more, and if it is thinner, the absorption of the guided light by the silicon substrate 1 cannot be ignored. However, the film thickness of SiO ₂ , which is usually used as a surface protection film for an IC portion, is about 1 μm. If the film thickness is further increased, the characteristics of electronic circuit elements will fluctuate due to the film stress of SiO ₂ . As described above, in the structure of FIG. 11, the optical waveguide cannot be formed on the same substrate as the IC without causing a change in the element characteristics of the IC part, which is a problem.

[0013]

In the present invention, in order to solve the problems] After forming the above thick SiO ₂ film 2μm on the substrate of the waveguide forming part and the IC forming portion, thinning or complete an SiO ₂ film of the IC portion The step of removing is added. Thereby, the film stress applied to the IC portion by the SiO ₂ film was reduced.

[0014]

FIG. 1 is a schematic sectional view of an embodiment of the present invention. It generally corresponds to FIG. 11, and the same reference numerals indicate the same parts. In the present invention, the SiO ₂ film 11-1 (hereinafter also referred to as a buffer layer), which is the buffer layer of the waveguide, has a different thickness from the protective film 11-2 (hereinafter also referred to as the protective film) in the IC portion. Partial protective film 11-
2 is thinner than the buffer layer 11-1. By setting the thickness of the protective film 11-2 in the IC portion to about 1 μm or less, it is possible to suppress the fluctuation of the electronic element characteristics due to the film stress.
FIG. 2 shows a graph serving as the basis. The horizontal axis of FIG. 2 is the thickness of the protective film 11-2, the vertical axis represents the relative value of the h _FE of the NPN transistor. According to this figure, when the thickness of the protective film 11-2 is equal to or greater than 1 [mu] m, the value of the h _FE is seen that begin to change. That is, when the thickness of the protective film 11-2 is 1 μm or less, the fluctuation in the characteristics of the NPN transistor can be suppressed.

FIGS. 3 to 5 show steps for obtaining the structure of FIG. FIG. 3 shows a state in which an electronic element such as an NPN transistor and a photodiode are formed on a silicon substrate 1 and metal wiring is provided. This is formed as follows. An N-type diffusion layer serving as an N-type buried diffusion layer 2 and P-type diffusion layers serving as P-type buried isolation diffusion layers 3, 3,... Are formed in predetermined regions of circuit elements on the surface of the silicon substrate 1. Next, an N-type epitaxial layer 5 is formed on the entire surface. Next, the P-type diffusion layers 6, 6,... Are formed in the planned anode region of the photodiode and the P-type required portion of the circuit element portion, and at the same time, the P-type isolation diffusion layers 4, 4,. The N-type diffusion layers 9, 9,...
To form Next, a SiO ₂ film 7 is formed above the electrode take-out portion, and for example, 10 μm is formed so as to cover the entire surface of the electrode take-out portion and the lower portion of the photodiode and the waveguide.
After the formation of the SiN film 8 having a thickness of 0 μm, holes are formed in the portions where the electrodes are to be formed, and the electrodes 10, 10,...

Next, as shown in FIG. 4, an SiO ₂ film 11 serving as a buffer layer of a waveguide or a protective film for an IC portion is formed on the entire surface by a CVD method. As the SiO ₂ film 11, a PSG film doped with phosphorus may be used. The thickness of the SiO ₂ film 11 is 2 μm or more, which is a film thickness required to function as a buffer layer of the waveguide.

Next, as shown in FIG.
_{2 The} film 11-2 is thinned to a thickness of 1 μm or less by performing ordinary photoetching. The function as a surface protective film is made as thin as possible without impairing the function. The SiO ₂ film 11-1 serving as a buffer layer is an SiO ₂ film 11-2.
Thicker. Subsequently, although not shown, the SiO ₂ film of the optical waveguide and the coupling portion C of the photodiode is processed into a tapered shape, and a waveguide 12 made of # 7059 glass is formed thereon to a thickness of, for example, about 300 μm. An SiO ₂ film 13 (corresponding to the first gap layer 115 in FIG. 10) which is formed on the entire surface by a sputtering method and serves as a cladding layer
The structure shown in FIG. 1 is obtained by depositing about 00 μm by a sputtering method.

FIG. 6 shows another embodiment of the present invention.
The SiN film 8-1 is formed on the semi-finished SiN film 8 manufactured by the steps up to FIG.
By using the iN film 8-1 as an etching stopper, the SiO ₂ film 11-2 above the IC portion in FIG. 1 is completely removed, thereby relaxing the stress generated in the IC portion. FIG. 7 is a cross-sectional view of the intermediate process in this case.
-9.

FIG. 7 corresponds to FIG. 4, and shows a state in which an SiN film 8-1 as an interlayer insulating film is laminated instead of the SiO ₂ film 112 on the surface of the semi-finished product in which the metal wiring of FIG. is there.

Next, as shown in FIG.
SiO to be used as a protective layer for the upper layer or IC part_TwoMembrane 11
Is formed by CVD. After this, S on the surface of the IC
iO _TwoThe film 11 is removed by etching to obtain the state shown in FIG.
And coupling the optical waveguide with the photodiode
SiO of part C_TwoThe film 11 is processed into a tapered shape to form a waveguide 12.
And SiO of the cladding layer 13_TwoThe film is deposited and the structure of FIG.
Get the structure.

In the structure of FIG. 1, the SiO ₂ film 1 in the IC portion
In order to reduce the thickness of the SiO ₂ film 11 to about 1 μm, there is a possibility that a problem may occur that the thickness of the SiO ₂ film 11-2 remaining in the IC portion varies due to a variation in an etching rate when the SiO ₂ film 11 is etched. but according to the structure of FIG. 6, SiO during etching of the SiO ₂ film 11
By using an etchant having high etching selectivity between the _two films and the SiN film, the SiN film serves as an etching stopper, and such a problem does not occur. The SiN film 8-1 plays a role as a protective film of the IC portion.

[0022]

As described above, according to the present invention, since the stress applied to the element in the IC portion can be reduced, the optical element can be connected to the optical element using the optical waveguide without causing a change in the characteristics of the electronic circuit element. The diode and the IC can be integrated on the same substrate, which can contribute to miniaturization of the optical pickup.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an embodiment of the present invention.

FIG. 2 is a characteristic graph for explaining the effect of the present invention.

FIG. 3 is a schematic cross-sectional view of an intermediate step for obtaining the structure of FIG. 1;

FIG. 4 is a schematic sectional view showing an intermediate step for obtaining the structure of FIG. 1;

FIG. 5 is a schematic sectional view showing an intermediate step for obtaining the structure of FIG. 1;

FIG. 6 is a schematic sectional view of another embodiment of the present invention.

FIG. 7 is a schematic sectional view showing an intermediate step for obtaining the structure of FIG. 6;

FIG. 8 is a schematic sectional view showing an intermediate step for obtaining the structure of FIG. 6;

FIG. 9 is a schematic sectional view showing an intermediate step for obtaining the structure of FIG. 6;

FIG. 10 is a schematic sectional view of a conventional optical pickup.

FIG. 11 is a schematic sectional view of a conventional optical waveguide type photodetector.

[Explanation of symbols]

Reference Signs List 1 silicon substrate 2 N-type buried diffusion layer 3 P-type buried separation diffusion layer 4 P-type separation diffusion layer 5 N-type epitaxial layer 6 P-type diffusion layer 7 SiO ₂ film 8 SiN film 9 N-type diffusion layer 10 electrode 11 SiO ₂ film 12 waveguide 13 cladding layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-170958 (JP, A) JP-A-61-222165 (JP, A) JP-A-62-81758 (JP, A) JP-A-63-81758 116458 (JP, A) JP-A-64-14955 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 27/14 G02B 6/122 H01L 27/15

Claims (6)

(57) [Claims] 1. An optical waveguide type photodetector having a built-in signal processing circuit, comprising a semiconductor substrate, a photodetector formed on a surface of the semiconductor substrate, a signal processing circuit, and a light guide to the photodetector. in, characterized in that the SiO ₂ film is provided, said thin SiO ₂ film from an SiO ₂ film as a surface protective film on the surface of the signal processing circuit is provided as a buffer layer between the waveguide and the semiconductor substrate An optical waveguide type photodetector having a built-in signal processing circuit. 2. A method for manufacturing an optical waveguide type photodetector including a signal processing circuit formed on a surface of a semiconductor substrate, wherein an SiO ₂ film used as a buffer layer between the waveguide and the semiconductor substrate and the signal processing circuit are provided. S which is the surface protection film of the part
An optical waveguide type photodetector incorporating a signal processing circuit, wherein an iO ₂ film is formed at the same time, and the thickness of the SiO ₂ film as a surface protective film is made smaller than the thickness of the SiO ₂ film as a buffer layer. Manufacturing method. 3. A SiO film for a surface protection film in a signal processing circuit portion.
_{2. The} method for manufacturing an optical waveguide type photodetector incorporating a signal processing circuit according to claim 1, wherein the thickness of the _two films is 0.1 μm or more and 1 μm or less. 4. An optical waveguide type photodetector having a built-in signal processing circuit, comprising a semiconductor substrate, a photodetector and a signal processing circuit formed on the surface of the semiconductor substrate, and a light waveguide to the photodetector. In the output device, a buffer layer is formed between the waveguide and the semiconductor substrate.
_Two films are provided. A SiN film is provided as a surface protection film on the surface of the signal processing circuit. In the signal processing circuit, the SiN film and the optical waveguide are directly connected to each other.
An optical waveguide type photodetector having a built-in signal processing circuit, which is in contact with the optical waveguide. 5. A semiconductor substrate and formed on a surface of the semiconductor substrate.
Photodetector and signal processing circuit, and guide light to the photodetector
Optical waveguide type photodetector with built-in signal processing circuit having waveguide
In the output device, a buffer layer is formed between the waveguide and the semiconductor substrate as SiO.
_Two films are provided, and a SiN film is provided as a surface protection film on the surface of the signal processing circuit.
In the signal processing circuit portion, SiO ₂ as a buffer layer is used.
The film has been etched away using the SiN film as a stopper.
Waveguide type with built-in signal processing circuit
Light detector. 6. A signal processing formed on a surface of a semiconductor substrate.
In manufacturing method of optical waveguide type photodetector with built-in circuit
To form a SiN film on the surface of the signal processing circuit.
As a buffer layer between the waveguide and the semiconductor substrate on the surface of
SiO ₂ film of SiO ₂ film and the signal processing circuit portion of the surface to be used
And SiO _{2 on} the surface of the signal processing circuit portion at the same time.
The film is removed by etching using the SiN film as a stopper.
Waveguide type with built-in signal processing circuit
Manufacturing method of photodetector.