JP2001352093A - Semiconductor light-receiving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the characteristics of a photodiode and a semiconductor light-receiving device, comprising a photodiode and a signal-processing circuit formed on the same semiconductor substrate. SOLUTION: The semiconductor light-receiving device comprises a first conductivity-type substrate (1) and second conductivity-type semiconductor epitaxial growth layers (2, 30) formed thereon. The second conductivity-type semiconductor epitaxial growth layers (2, 30) are isolated into a plurality of second conductivity-type islands (2) by first conductivity-type isolation regions (6, 7). A first conductivity-type silicon germanium mixed crystal layer (8) is formed on at least one second conductivity-type island and a photodiode is formed by the first conductivity-type silicon germanium mixed crystal layer (8) and the second conductivity-type island (2).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light receiving device, and more particularly to a light receiving device including a photodiode on a semiconductor substrate and a characteristic improvement in a light receiving device including a photodiode and a signal processing circuit on the same substrate. Things.

[0002]

2. Description of the Related Art A photodiode for converting an optical signal into an electric signal and a signal processing circuit for shaping and amplifying the waveform of the photoelectrically converted signal are formed on the same semiconductor substrate.
EICs (optoelectronic integrated circuits) are widely used, for example, in optical pickups of optical disk devices, and in light receiving devices and photocouplers in optical space transmission and optical fiber data links. Forming a photodiode and a signal processing circuit on the same substrate reduces malfunctions due to the effects of electromagnetic noise from element-to-element wiring, reduces the mounting area, and reduces circuit design compared to the case where each element is formed individually. There are various advantages such as simplification and cost reduction.

In FIG. 14, a typical example of a conventional light receiving device with a built-in signal processing circuit having such features is illustrated in a schematic cross-sectional view. In the drawings of the present application, the same reference numerals denote the same or corresponding parts, and dimensional relationships such as thickness and length of each part are appropriately changed for clarity and simplification of the drawings. Does not represent the dimensional relationship of

In the light receiving device with a built-in signal processing circuit shown in FIG. 14, an n-type silicon crystal growth layer 2 is formed on a p-type silicon substrate 1, and this n-type silicon crystal growth layer 2 , 7 into a plurality of islands. The island 100 is a photodiode unit, and the island 200 adjacent thereto is a signal processing circuit unit (npn transistor). The signal light enters from above the photodiode unit 100 and is photoelectrically converted by a photodiode including a pn junction by the p-type silicon substrate 1 and the n-type silicon crystal growth layer 2. In the circuit section 200 for processing the photoelectric conversion signal, a p-type base region 3 and an n-type emitter region 4 are formed on the surface of the n-type silicon crystal growth layer 2. n-type silicon crystal growth layer 2
A silicon oxide film 16 and a silicon nitride film 17 functioning as an anti-reflection layer and a protective layer are formed on the surface of the substrate.

In the photodiode section 100, n
Cathode electrode 21 is electrically connected to n-type silicon crystal growth layer 2 via type contact region 10, and anode electrode 22 is electrically connected to p-type silicon substrate 1 via p-type isolation regions 6 and 7. It is connected. Signal processing circuit 2
00, the base electrode 23 and the emitter electrode 24
Are connected to the p-type base region 3 and the n-type emitter region 4, respectively. An n-type buried diffusion layer 11 having a high impurity concentration is formed at the bottom of the n-type silicon crystal growth layer 2 serving as a collector. 25, which reduces the series resistance of the collector.

In recent years, the speed of optical disc devices such as CD-ROMs and DVDs has been rapidly increasing, and the demand for higher speed of optical pickup devices applied to moving images and the like has become extremely strong. . Furthermore, in optical communication modules and optical space transmission systems, it is necessary to process a large amount of data at a high speed.
There is an increasing demand for higher speed semiconductor light receiving devices. In response to such demands, the manufacturing technology of a semiconductor device using silicon as a material is highly established.
Since the light receiving device as shown in FIG. 4 can be manufactured very inexpensively, a high-speed light receiving device has been realized by devising its structure skillfully.

[0007]

However, a light-receiving device made of silicon can be manufactured at low cost, but there are various restrictions due to the physical properties of silicon. For example, photocouplers typically have 950
A light having a wavelength of nm is used, and the absorption coefficient of silicon for this light is about 400 cm ⁻¹ , and 90% of the incident light.
Requires a silicon thickness of less than 60 μm. However, in the light receiving device as shown in FIG. 14, the n-type silicon crystal growth layer 2 usually has a thickness of about several μm, that is, a pn junction exists at a depth of several μm from the surface. I do. In such a case, most of the signal light that has entered the inside of the substrate 1 generates carriers inside the substrate, and these carriers diffuse to the depletion layer end near the pn junction to become current components. Therefore, there is a problem that the transit time until the carriers diffuse from the inside of the substrate to the end of the depletion layer becomes longer, and the response speed of the photodiode becomes slower.

In addition, since a large amount of light is incident on the write-ready photodiode in an optical disk device such as a CD-R device, the absolute amount of light entering the substrate increases. As the writing speed increases, carriers that move with a delay from the inside of the substrate affect the response characteristics of the photodiode. Therefore, the development of a high-sensitivity and high-speed light-receiving device that is not affected by such carriers has been developed. Is desired.

On the other hand, III-V group compound semiconductors and the like are superior in speed in terms of physical properties as compared with silicon, and the use of such compound semiconductor materials makes it possible to realize desired device characteristics. However, compound semiconductor materials themselves are more expensive than silicon, and the cost of the manufacturing process is more expensive than silicon, so the resulting compound semiconductor devices are considerably more expensive than silicon devices. turn into.

In view of the above-mentioned problems in the prior art, an object of the present invention is to provide a high-sensitivity and high-speed semiconductor light-receiving device with almost no complicated process and no increase in cost. The purpose is to improve the characteristics of.

[0011]

A semiconductor light receiving device according to the present invention includes a first conductive type semiconductor substrate and a second conductive type semiconductor crystal growth layer thereon, wherein the second conductive type semiconductor crystal growth layer comprises a first conductive type semiconductor crystal growth layer. A first conductivity type silicon-germanium mixed crystal layer formed on at least one of the second conductivity type islands by a first conductivity type silicon germanium A photodiode including a semiconductor junction between the mixed crystal layer and the island of the second conductivity type is formed.

In such a semiconductor light receiving device, a signal processing circuit for processing a photoelectric conversion signal from the photodiode may be formed on at least one island different from the island on which the photodiode is formed. preferable.

A first conductivity type silicon-germanium mixed crystal layer is also formed on the second conductivity type island on which the signal processing circuit portion is formed, and can be used as a base of a transistor, and a photodiode is formed thereon. 2
The first conductive type silicon germanium mixed crystal layer on the conductive type island can be used as a light receiving layer of a photodiode.

In the first-conductivity-type silicon-germanium mixed crystal layer, the germanium concentration is preferably reduced from the interface side to the second-conductivity-type semiconductor crystal growth layer toward the surface side.

As the second conductive type semiconductor crystal growth layer,
A conductive silicon germanium mixed crystal layer can be preferably used. In the second conductivity type silicon-germanium mixed crystal layer, the germanium concentration is minimized at a predetermined position in the thickness direction, and the germanium concentration is increased as the distance from the minimum position of the germanium concentration in the thickness direction increases. Is preferred.

A second conductivity type buried layer having a high impurity concentration and acting as an extraction electrode of the diode may be formed at the bottom of the second semiconductor crystal growth layer constituting the diode.

As an antireflection film on the surface of the photodiode, a silicon oxide film, a silicon nitride film, or a laminated structure thereof can be used. Further, an amorphous carbon film may be used as the antireflection film.

At least one of the first-conductivity-type silicon-germanium mixed crystal layer and the second-conductivity-type silicon-germanium mixed crystal layer in the light receiving device may be formed to contain carbon.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Silicon germanium mixed crystal, which is a crystal of a mixture of germanium and silicon, has good compatibility with silicon because germanium is the same group IV semiconductor as silicon, and the silicon semiconductor manufacturing process can be applied. The feature is that the device manufacturing cost can be reduced as compared with the compound semiconductor manufacturing process.
In addition, since silicon-germanium mixed crystal has higher carrier mobility than silicon, a device manufactured using the same is excellent in high-speed operation. Further, the energy band gap of silicon-germanium mixed crystal can be freely controlled between the band gap of germanium (about 0.67 eV) and the band gap of silicon (about 1.11 eV).

As described above, the silicon-germanium mixed crystal can reduce the forbidden band width as compared with silicon, and can have high sensitivity to long-wavelength light. Therefore, for example, the wavelength 1.3 generally used for optical fibers
Silicon has no sensitivity to light of μm, but silicon germanium mixed crystal can have sensitivity,
An optical fiber light receiving device can be provided at a lower cost than when a conventional compound semiconductor is used. In addition to these features, the silicon germanium semiconductor device has an advantage that power consumption can be reduced as compared with a silicon semiconductor device. Therefore, in the semiconductor light receiving device according to the embodiment of the present invention described below, various advantages of the silicon-germanium mixed crystal are utilized.

(Embodiment 1) In FIG. 1, the structure of a light receiving device with a built-in circuit according to Embodiment 1 of the present invention is illustrated in a schematic sectional view. This light receiving device with a built-in circuit includes a light receiving element unit 100 and a signal processing circuit unit 200 formed adjacent to each other. Note that, for example, a multilayer wiring and a protective film formed after the metal wiring processing step are shown in FIG.
Are omitted and not shown.

In the light receiving device with a built-in circuit of FIG. 1, an n-type silicon crystal growth layer 2 is formed on a p-type silicon substrate 1. The n-type silicon crystal growth layer 2 is separated into a plurality of islands by p-type separation regions 6 and 7 formed so as to reach the surface of the p-type silicon substrate 1 from the surface. In the photodiode portion 100 of the plurality of islands, the p-type silicon germanium mixed crystal layer 8 is grown on the n-type silicon crystal growth layer 2. The surface of the n-type silicon crystal growth layer 2 is covered with an insulator layer 15 such as a silicon oxide film 16, a silicon nitride film 17, and a silicon oxide film which are sequentially stacked. p-type silicon germanium mixed crystal layer 8
A p-type contact region 9 is formed on the surface of the substrate, and is connected to the anode electrode 22. The anode electrode 22 may be connected to the p-type isolation regions 6 and 7 in a region other than the cross section of FIG. In that case, the p-type isolation regions 6 and 7 also function as the anode of the photodiode including the junction between the n-type silicon crystal growth layer 2 and the p-type silicon substrate 1. An n-type contact region 10 is formed on the surface of the n-type silicon crystal growth layer 2, and is connected to a cathode electrode 21.

The island adjacent to the photodiode section 100 as described above is the signal processing circuit section 200.
In the signal processing circuit section 200, a high impurity concentration n-type buried region 11, an n-type compensation diffusion region 12, and an n-type silicon crystal growth layer 2 acting as a collector provided to reduce the collector resistance. a p-type base region 13,
And n-type emitter region 14 constitute an npn transistor. Base region 13 is connected to metal base electrode 23 via polysilicon base electrode 20. Emitter region 14 is connected to metal emitter electrode 24 via polysilicon emitter electrode 19. The n-type buried region 11 acting as a low-resistance collector region is connected to the metal collector electrode 25 via the n-type compensation region 12.

The most important feature of the light receiving device with a built-in circuit of FIG. 2 configured as described above is that the p-type silicon germanium mixed crystal layer 8 is formed on the n-type silicon crystal growth layer 2 of the photodiode section 100. That is.

FIG. 2 shows silicon (Si) and germanium.
Graph showing the wavelength dependence of the light absorption coefficient in (Ge)
It is. That is, in this graph, the horizontal axis is the wavelength of light
(Μm), and the vertical axis indicates the absorption coefficient (cm^-1)
ing. The dashed curve represents silicon and the solid curve
The curve represents germanium. You can see from Figure 2
The light absorption coefficient of germanium is larger than that of silicon.
The mixed crystal silicon-germanium mixed crystal
The light absorption coefficient is between that of silicon and germanium
Can be controlled by In other words, silicon-germanium mixed crystal
Light absorption coefficient α _SiGeIs always the light absorption coefficient α of silicon_Si
Greater (α_SiGe> Α_Si)Become.

Therefore, in the photodiode 100 according to the first embodiment shown in FIG. 1, the light by the p-type silicon germanium mixed crystal layer 8 as the surface layer is different from that of the conventional example of FIG. 14 in which the surface layer is silicon. An increase in absorption occurs. That is, since the generation of carriers in the surface layer can be increased to suppress the generation of carriers inside the substrate, even when long-wavelength light or a large amount of light is incident, the light diffuses from the inside of the substrate with a delay. Coming carriers can be reduced. As a result, the photodiode 100 included in the light receiving device of FIG.
Can be speeded up. For example, if a p-type silicon germanium mixed crystal layer 8 having an absorption coefficient α _SiGe of about 4000 cm ⁻¹ and a thickness of about 1 μm is formed for light of wavelength λ = 950 nm generally used for a photocoupler,
The distance from the surface required to absorb 0% of light is from about 58 μm to about 48 μm, which can be reduced by about 10 μm.

As described above, in the light receiving device with a built-in circuit as shown in FIG. 1, by setting the germanium concentration and the film thickness of the p-type silicon-germanium mixed crystal layer 8 appropriately, a desired high sensitivity and high sensitivity can be obtained. A light receiving device with a built-in circuit that satisfies high-speed response can be obtained.

The cross-sectional views of FIGS. 3 and 4 illustrate an example of a method of manufacturing the photodetector with a built-in circuit as shown in FIG.

First, as shown in FIG.
On the surface of p-type semiconductor substrate 1, p-type isolation diffusion region 6 and n-type buried diffusion layer 11 are formed at predetermined positions.

In FIG. 3B, the p-type semiconductor substrate 1
An n-type semiconductor crystal growth layer 2 is formed thereon. A p-type isolation diffusion region 7 is formed so as to connect from the surface of the n-type semiconductor crystal growth device 2 to the p-type isolation region 6, whereby the n-type semiconductor crystal growth layer 2 is separated into a plurality of islands. An n-type compensation diffusion region 12 is formed from the surface of n-type semiconductor crystal growth layer 2 to n-type buried layer 11.

In FIG. 3C, a silicon oxide film 16 is formed so as to cover the entire surface of the semiconductor crystal growth layer 2, and the silicon oxide film 16 is partially removed in a region where the base of the pnp transistor is formed. Thus, p-type base diffusion region 13 is formed. Thereafter, a part of the silicon oxide film 16 in the photodiode portion is removed, and a p-type silicon germanium mixed crystal layer 8 is formed in the removed region. A p-type contact region 9 is formed on a part of the surface of the p-type silicon-germanium mixed crystal layer 8, and an n-type contact region 10 is formed on a part of the surface of the n-type semiconductor crystal growth layer 2. .

In FIG. 4A, a polysilicon base electrode 20 and a silicon nitride film 17 are sequentially formed, and a sidewall 18 for electrically insulating the base electrode and the emitter electrode is formed.

In FIG. 4B, the side wall 18
An n-type polysilicon emitter electrode 19 is formed so as to cover the region surrounded by and the sidewalls thereof, and an n-type emitter diffusion region 14 is formed by diffusion of impurities from the polysilicon emitter electrode.

In FIG. 4C, an insulating layer 15 made of a silicon oxide film or the like is formed so as to cover the entire surface of the substrate, a contact hole is formed at a predetermined position, and a silicon germanium mixed crystal layer is formed. 8 are exposed. And a metal cathode electrode 21 connected to the n-type contact region 10 of the photodiode;
Anode electrode 22 connected to mold contact region 9
Is formed using, for example, an aluminum alloy containing silicon. At this time, although not shown in the cross section of FIG. 4C, the metal anode electrode 22 may be connected to the p-type isolation region 7 in another region. In the signal processing circuit section, a metal base electrode 23, a metal emitter electrode 24, and a metal collector electrode 25 are formed using aluminum through predetermined contact holes for electrical connection to the formed npn transistor. Is done. Thereafter, as described above, a step of forming a multilayer wiring and a protective film (not shown) is performed by appropriately employing a process generally performed in the field of semiconductor technology, thereby completing the photodetector with a built-in circuit. I do.

(Embodiment 2) In FIG. 5, the structure of a light receiving device with a built-in circuit according to Embodiment 2 of the present invention is illustrated in a schematic sectional view. The light receiving device with a built-in circuit in FIG. 5 is similar to that in FIG. 1 except that the p-type base region 26 is formed of a p-type silicon germanium mixed crystal layer. The p-type silicon germanium mixed crystal layer 26 is formed simultaneously with the p-type silicon germanium mixed crystal layer 8 in the photodiode unit 100. On the p-type base layer 26, an n-type polysilicon emitter electrode 19 is formed.
The emitter region 27 integrated with the bottom layer of
A hetero junction is formed very close to the pn junction between the base and the emitter. That is, in the signal processing circuit unit 200, the npn heterojunction bipolar transistor (HB
T) is formed. Also, the photodiode section 10
0 is connected to the p-type contact region 9 via the polysilicon electrode 28, and the metal base electrode 23 in the HBT section 200 is connected to the p-type base region 26 via the polysilicon base electrode 29. It is connected to the.

In an HBT as shown in FIG. 5, carriers from the base to the emitter when a forward bias is applied between the emitter and the base due to a potential barrier due to a heterojunction near the pn junction between the emitter and the base. Since the injection of holes is prevented, the emitter injection efficiency is increased, and the current amplification factor (h _FE ) can be increased. In addition, since such an effect of preventing injection of carriers (holes) is obtained, even if the base width is reduced to reduce the base transit time of the carrier or the base impurity concentration is increased to reduce the base resistance. In addition, deterioration of device characteristics such as reduction in breakdown voltage and _hFE as seen in a homojunction transistor is not observed, and characteristics such as speeding up of the transistor can be improved.

As described above, in the photodetector with a built-in circuit as shown in FIG.
Silicon germanium mixed crystal layer 8 and transistor section 20
Since the zero-silicon-germanium mixed crystal layer 26 is formed at the same time, the device characteristics of both the photodiode and the transistor can be improved without substantially complicating the device manufacturing process. For example, λ = 950
The p-type silicon-germanium mixed crystal layers 8 and 26 having an absorption coefficient of α = 10 ⁴ cm ⁻¹ for light of nm
m, the photodiode section has λ = 9
The distance from the surface required to absorb 90% of the light when 50 nm signal light is incident is about 58 μm to about 4 μm.
The speed can be reduced to 6 μm, that is, the speed of the photodiode 100 can be increased by shortening the traveling distance of the carrier. In the transistor section 200, if the p-type silicon germanium mixed crystal layer 26 (similarly for 8) is set to a high impurity concentration, the base width becomes 100 n.
m, and the speed of the transistor can be increased.

As described above, the germanium concentration, the impurity concentration, and the p-type silicon germanium mixed crystal layers 8 and 26
By appropriately setting the thickness and the thickness, it is possible to obtain a light receiving device with a built-in circuit in which the speed of both the photodiode 100 and the transistor 200 is increased. Furthermore, a transistor using a silicon-germanium mixed crystal in the base region operates even at a low V _BE (base-emitter forward voltage) and has excellent frequency characteristics in a low current region, so that a low power consumption circuit is used. It is possible to obtain a built-in light receiving device.

The photodiode 100 and the HBT 2
00, p-type silicon germanium mixed crystal layer 8, 26
Can be grown with decreasing germanium concentration. Here, FIGS. 6A and 6B are graphs showing an energy band structure and a germanium concentration gradient in the photodiode unit 100 and the transistor unit 200, respectively. In this graph, x represents the depth direction of the semiconductor layer, and Ec and Ev represent the lower limit of the conduction band and the upper limit of the valence band, respectively. As shown in FIG. 6, in the silicon-germanium mixed crystal layers 8 and 26, the band gap can be widened toward the surface side by the germanium concentration gradient, whereby a potential gradient can be generated. Due to such a potential gradient in the silicon-germanium mixed crystal layer, electrons traveling in the photodiode and in the base of the transistor are further accelerated by the drift, so that both the photodiode and the transistor can be operated at high speed.

In the photodiode section 100, as shown in FIG. 7, the germanium concentration of the germanium mixed crystal layer 8 is set so that the surface layer has no sensitivity when a long wavelength signal light is used. Thereby, the signal light is photoelectrically converted inside the element where the energy band gap is smaller than the light energy. In this case, minority carriers (electrons) generated in the p-type silicon-germanium mixed crystal layer 8 having a germanium concentration gradient are accelerated into the device by the built-in electric field, and thus carrier loss due to recombination mediated by surface levels. Can be ignored. This also makes it possible to increase the sensitivity of the photodiode 100.

Further, in the light receiving device with a built-in circuit shown in FIG. 5, instead of the n-type silicon crystal growth layer 2 on the p-type silicon substrate 1, an n-type silicon germanium mixed crystal layer 3 is formed.
0 can also be used. In this case, discontinuity occurs in the valence band due to the heterojunction between the p-type silicon substrate 1 and the n-type silicon-germanium mixed crystal layer 30. But,
The n-type silicon-germanium mixed crystal layer 30 is usually made to have a low impurity concentration, and p-type impurities diffuse from the p-type semiconductor substrate 1 into the n-type silicon germanium mixed crystal layer 30.
The junction center is formed displaced slightly toward the surface side from the hetero junction center. Therefore, when a reverse bias voltage is applied to draw a light detection current from the photodiode,
As in the energy band diagram shown in FIG. 8, the potential barrier against holes due to the discontinuity of the valence band can be set to a negligible level.

As shown in FIG.
Germanium mixed crystal has larger light absorption coefficient than silicon
The n-type silicon germanium mixed crystal growth layer 3
0 is set to be thinner than the silicon crystal growth layer 1.
Can be For example, normally used for photocouplers, etc.
For light of wavelength 950 nm used, 1000 cm ^-1
Using silicon-germanium mixed crystal with absorption coefficient of
The distance from the surface needed to absorb 90% of the light
Can be reduced from about 58 μm to about 22 μm. this thing
Can shorten the carrier mileage,
Speed up of photodiode 100 and transistor 200
Can be done. In addition, the photodiode section 100 has a silicon
A bond between the germanium mixed crystal layers 8, 30 is formed.
So that silicon has no sensitivity for long wavelength light, e.g.
Light receiving device for optical fiber using 1.3 μm long light
It is also applicable as.

Further, the n-type silicon-germanium mixed crystal layer 30 gradually decreases the germanium concentration as it grows from the p-type semiconductor substrate 1 and gradually increases the germanium concentration after a certain thickness. May be formed. That is, as shown in FIG. 9, the position having the minimum germanium concentration in the n-type silicon-germanium mixed crystal layer 30 is the position where the p-type semiconductor substrate 1 and the n-type silicon-germanium mixed crystal layer 30 and their n-type The region is set at a position other than the depleted region near both pn junctions by the silicon germanium mixed crystal layer 30 and the p-type silicon germanium mixed crystal layer 8 and at a position where the direction of the electric field is reversed. By setting the germanium concentration in this way, the minority carriers (holes) generated in the n-type silicon-germanium mixed crystal layer 30 in the photodiode unit 100 are accelerated toward both pn junction interfaces by the built-in electric field. Therefore, the speed of the photodiode can be increased.

(Embodiment 3) In FIG. 10, the structure of a light receiving device with a built-in circuit according to Embodiment 3 of the present invention is illustrated in a schematic sectional view. The light receiving device with a built-in circuit in FIG. 10 is similar to that in FIG.
In FIG. 00, an n-type buried diffusion layer 31 having a high impurity concentration is formed at the bottom of the n-type semiconductor crystal growth layers 2 and 30. This n-type buried diffusion layer 31 has n
It is connected to the metal cathode electrode 21 via the mold impurity region 32. That is, the n-type buried diffusion layer 31 having a high impurity concentration acts as a low-resistance cathode region in the photodiode. Also, n from the buried diffusion layer 31
Since the center of the pn junction with the p-type silicon substrate 1 is displaced into the substrate due to diffusion of the p-type impurity, the distance that minority carriers (electrons) generated inside the p-type substrate travel to the pn junction decreases. This can also contribute to speeding up the photodiode.

(Embodiment 4) In FIG. 11, the structure of a light receiving device with a built-in circuit according to Embodiment 4 of the present invention is illustrated in a schematic sectional view. 11 is similar to that of FIG. 5 except that the antireflection film 3 on the silicon-germanium mixed crystal layer 8 in the photodiode portion 100 is formed.
3 in that they are formed.

When a silicon oxide film is formed as the antireflection film 33, reducing the germanium concentration on the surface side of the silicon-germanium mixed crystal layer 8 makes it possible to form a stable silicon oxide film. When a silicon oxide film is formed on the surface of the silicon-germanium mixed crystal layer 8 having a low germanium concentration, a good interface is obtained, so that loss due to carrier recombination at the interface can be reduced. The thickness of the silicon oxide film 33 needs to be selected so as to minimize the reflectance in accordance with the wavelength of the signal light to be used and the semiconductor material in the surface layer of the photodiode 100. For example, when the outermost surface of the semiconductor layer of the photodiode 100 is silicon, the wavelength of the incident signal light is 950.
12, the reflectance is 6 when the thickness of the silicon oxide film 33 is about 160 nm, as shown in FIG.
%.

When a silicon nitride film is used as the anti-reflection film 33, the wavelength of the signal light to be used and the film thickness that minimizes the reflectance in conformity with the outermost surface of the semiconductor material in the photodiode 100 are determined. You have to choose.
For example, when the outermost surface of the semiconductor material of the photodiode 100 is silicon, the wavelength of the incident signal light is 9
If it is 50 nm, the reflectivity can be reduced to about 1% when the film thickness is about 120 nm as shown in FIG.

When the antireflection film 33 is formed as a laminated film of a silicon oxide film and a silicon nitride film, the silicon-germanium mixed crystal layer 8 is formed with a reduced germanium concentration on the surface side, and the silicon oxide film is formed on the surface. Preferably, a film is formed, and a silicon nitride film is formed thereon. Also in this case, it is necessary to select a silicon oxide film thickness and a silicon nitride film thickness that minimize the reflectance in accordance with the wavelength of the signal light to be used and the semiconductor material on the outermost surface of the photodiode 100. For example, if the outermost surface of the photodiode is silicon and the wavelength of incident light is 780 nm, the reflectance can be reduced to 1% or less when the oxide film thickness is 65 nm and the nitride film thickness is 50 nm.
As described above, if a silicon oxide film is formed on the outermost surface of the semiconductor of the photodiode 100, a favorable interface state can be obtained. Therefore, a stacked film in which a silicon oxide film and a silicon nitride film are formed in this order is It is also preferable to reduce loss due to recombination of carriers at the interface.

As the antireflection film 33, an amorphous carbon film may be formed. In this case, a silicon oxide film (about 900 ° C.) or a silicon nitride film (about 750 ° C.) having a high process temperature is used.
In comparison, the amorphous carbon film can be grown at a low temperature. Therefore, the anti-reflection film 33 can be formed without affecting the device structure such as the diffusion region formed before the formation process of the anti-reflection film 33 and without deteriorating the high-speed response.

In all of the first to fourth embodiments as described above, the silicon-germanium mixed crystal layer may be grown while mixing several percent of carbon atoms. The reason why it is preferable to grow the silicon-germanium mixed crystal layer while mixing carbon atoms is as follows. That is, since germanium atoms are larger than silicon atoms, if a heterojunction between a silicon crystal and a silicon-germanium mixed crystal is formed, a large number of interface states tend to exist at the junction interface. In order to reduce such interface states, it is possible to form a silicon-germanium mixed crystal at a very low growth rate on a silicon crystal so as to maintain lattice matching at the interface, but elastic strain exists at the interface. Therefore, it is not easy to grow the mixed crystal layer thick while maintaining lattice matching at the interface. In such a situation, by growing the silicon-germanium mixed crystal layer while mixing carbon atoms smaller than that of silicon, the lattice constant with the underlying silicon crystal can be easily matched. As a result, a thermally stable device can be obtained, and the mixed crystal layer can be grown thick without increasing the interface state. Also preferred.

[0051]

As described above, according to the present invention, the silicon-germanium mixed crystal layer in the photodiode portion has a higher carrier mobility than silicon and the carrier traveling speed is increased. It is possible to provide a semiconductor light receiving device with a higher speed. In addition, since the light absorption coefficient of the silicon-germanium mixed crystal layer is larger than that of silicon, the light penetration length is shortened, and the light-receiving layer of the photodiode can be made thinner than before. That is, by setting the thickness of the silicon-germanium mixed crystal layer so as to satisfy the required response speed, a high-speed light receiving device that satisfies desired specifications can be provided.

Further, by forming a silicon germanium mixed crystal layer as a base layer of a transistor included in a signal processing circuit at the same time as forming a silicon germanium mixed crystal layer of a photodiode, the transistor can be cut off without complicating the manufacturing process. The frequency and the current amplification factor can be increased. This makes it possible to provide a light receiving device with a built-in circuit in which the speed of the photodiode can be increased and the performance of the transistor is also improved.

Further, since an internal electric field can be generated by appropriately setting the germanium gradient in the silicon-germanium mixed crystal layer, the moving speed of carriers can be further increased. By utilizing this, it is possible to provide a light receiving device that is further speeded up to satisfy the required response speed.

Further, by providing a high-concentration buried cathode region inside the photodiode, a pn junction is formed inside the substrate, so that the pn junction is generated inside the substrate, which causes a delay in response speed. The distance that the carrier travels to the joining end is reduced. With this effect, the response speed of the photodiode can be further increased.

Further, by forming an antireflection film conforming to the surface semiconductor material of the photodiode, the loss due to the reflection of signal light can be reduced, and the sensitivity of the photodiode can be improved.

Further, by mixing carbon atoms in the silicon-germanium mixed crystal, it is easy to realize lattice matching with silicon, and a more stable photodetector with a built-in circuit can be provided.

As described above, according to the present invention, by using a silicon-germanium mixed crystal layer, a photodiode with high sensitivity and high speed can be obtained, and a transistor formed on the same semiconductor substrate can be obtained. And a high-sensitivity and high-speed light receiving device with a built-in circuit that further includes:

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a light-receiving device with a built-in circuit according to Embodiment 1 of the present invention.

FIG. 2 is a graph showing a relationship between a light absorption coefficient and a light wavelength in silicon and germanium.

FIG. 3 is a schematic cross-sectional view illustrating a manufacturing process of the light receiving device with a built-in circuit in FIG. 1;

FIG. 4 is a schematic cross-sectional view illustrating a step that follows the step of the manufacturing process in FIG.

FIG. 5 is a schematic sectional view showing a light receiving device with a built-in circuit according to a second embodiment of the present invention.

6A is a graph showing a relationship between a germanium concentration gradient in a silicon germanium mixed crystal layer of a photodiode portion included in the photodetector with a built-in circuit in FIG. 5 and an energy band structure, and FIG. 4 is a graph showing a relationship between a germanium concentration gradient in a silicon germanium mixed crystal layer of a processing circuit unit and an energy band structure.

FIG. 7 is a graph showing a preferable germanium concentration gradient and an energy band structure in a photodiode surface layer when long-wavelength light is incident.

8 is a graph showing an energy band structure that can be applied to a photodiode part in the circuit built-in light receiving device of FIG.

9 is a graph showing a relationship between a germanium concentration distribution and an energy band structure that can be employed in a photodiode portion of the light receiving device with a built-in circuit as shown in FIG.

FIG. 10 is a schematic sectional view showing a light receiving device with a built-in circuit according to a third embodiment of the present invention.

FIG. 11 is a schematic sectional view showing a light receiving device with a built-in circuit according to a fourth embodiment of the present invention.

FIG. 12 is a graph showing the relationship between the silicon oxide film thickness and the reflectance when the wavelength of light is 950 nm.

FIG. 13 is a graph showing the relationship between the silicon nitride film thickness and the reflectance when the light wavelength is 950 nm.

FIG. 14 is a schematic cross-sectional view illustrating an example of a conventional photodetector with a built-in circuit.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 First conductivity type semiconductor substrate, 2 Second conductivity type semiconductor crystal growth layer, 3 Base region, 4 Emitter region, 6, 7
1st conductivity type isolation region, 8 1st conductivity type silicon germanium mixed crystal layer, 9 1st conductivity type contact region, 10 2nd conductivity type contact region, 11 2nd conductivity type buried layer, 1
2 second conductivity type compensation region, 13 base region, 14 emitter region, 15 insulating layer, 16 silicon oxide film, 1
7 silicon nitride film, 18 side wall, 19 polysilicon emitter electrode, 20 polysilicon base electrode, 21 metal cathode electrode, 22 metal anode electrode, 23 metal base electrode, 24 metal emitter electrode,
25 metal collector electrode, 26 first conductivity type silicon germanium base region, 27 emitter region, 28 first
Conductive type polysilicon anode electrode, 29 first conductive type polysilicon base electrode, 30 second conductive type silicon germanium mixed crystal growth layer, 31 second conductive type buried layer, 32
Second conductivity type impurity region, 33 anti-reflection film, 100 photodiode unit, 200 signal processing circuit unit.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naoki Fukunaga 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka Inside (72) Inventor Takahiro Takimoto 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka Sharp Inside (72) Inventor Kazuhiro Natsuaki 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Zenpei 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation F Term (reference) 5F049 MA03 MB03 NA03 NB01 NB08 QA15 QA19 RA06 RA10 SS03 SZ02 WA01

Claims (11)

[Claims] A first conductivity type semiconductor substrate and a second conductivity type semiconductor crystal growth layer on the first conductivity type semiconductor substrate, wherein the second conductivity type semiconductor crystal growth layer is formed by a plurality of second conductivity type isolation regions by a first conductivity type isolation region. A first conductivity-type silicon-germanium mixed crystal layer formed on at least one of the second conductivity-type islands; the first conductivity-type silicon-germanium mixed crystal layer;
A semiconductor light receiving device, wherein a photodiode including a semiconductor junction between the conductive island and the conductive island is formed. 2. A signal processing circuit for processing a photoelectric conversion signal from the photodiode is formed on at least one island different from the island on which the photodiode is formed. The semiconductor light receiving device according to claim 1. 3. The first conductive type silicon-germanium mixed crystal layer is also formed on the second conductive type island where the signal processing circuit portion is formed, and is used as a base of a transistor. 3. The semiconductor light receiving device according to claim 2, wherein the first conductivity type silicon germanium mixed crystal layer on the second conductivity type island on which a photodiode is formed is used as a light receiving layer of the photodiode. . 4. The silicon germanium mixed crystal layer of the first conductivity type, wherein the germanium concentration is reduced from the interface side with the second conductivity type semiconductor crystal growth layer toward the surface side. Item 4. The semiconductor light receiving device according to any one of Items 1 to 3. 5. The semiconductor device according to claim 1, wherein the second conductive type semiconductor crystal growth layer is a
The semiconductor light receiving device according to any one of claims 1 to 4, wherein the semiconductor light receiving device is made of a conductive silicon germanium mixed crystal layer. 6. In the second conductivity type silicon-germanium mixed crystal layer, the germanium concentration is minimized at a predetermined position in the thickness direction, and the germanium concentration increases in the thickness direction from the minimum position of the germanium concentration. 6. The semiconductor light receiving device according to claim 5, wherein the concentration is increased. 7. A buried layer having a high impurity concentration and acting as an extraction electrode of the photodiode is formed at the bottom of the second semiconductor crystal growth layer of the photodiode. The semiconductor light receiving device according to claim 1. 8. The photodiode according to claim 1, wherein the anti-reflection film on the surface of the photodiode includes one selected from a silicon oxide film, a silicon nitride film, and an amorphous carbon film. A semiconductor light receiving device according to any one of the above. 9. The photodiode according to claim 1, wherein a laminated structure of a silicon oxide film and a silicon nitride film is formed as an antireflection film on the surface of the photodiode. Semiconductor light receiving device. 10. The semiconductor light receiving device according to claim 1, wherein the first conductivity type silicon-germanium mixed crystal layer contains carbon. 11. The semiconductor device according to claim 5, wherein at least one of the first conductivity type silicon-germanium mixed crystal layer and the second conductivity type silicon-germanium mixed crystal layer contains carbon.
10. The semiconductor light receiving device according to any one of items 1 to 9.