JPH05145051A - Optical semiconductor device - Google Patents

Abstract

PURPOSE:To constitute a common cathode type photodiode group of high sensitivity as an IC, by providing a 2-step epitaxial layer and high concentration buried layers. CONSTITUTION:A first epitaxial layer 14 and a second epitaxial layer 15 are formed on a substrate 13, and a peripheral circuit is constituted by using the second epitaxial layer 15. A photodiode part 11 is constituted by forming a plurality of P-type anode regions 21 on the surface of a second epitaxial layer 15 and applying the first and the second epitaxial layers 14, 15 to a common cathode. On the surface of the substrate 13, first N<+> type buried layer 23 is formed so as to correspond with the respective anode regions 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device in which a plurality of cathode common type photodiodes and peripheral circuits are integrated.

[0002]

2. Description of the Related Art An optical semiconductor device in which a light-receiving element and a peripheral circuit are integrated to form a monolithic device can be expected to reduce costs, unlike a hybrid IC in which a light-receiving element and a circuit element are separately formed. , It has a merit that it is strong against noise caused by an external electromagnetic field. Therefore, there is a movement to expand such an apparatus not only for optical communication for converting an electric signal into an optical signal for transmission but also for use as a pickup for an optical storage device such as a CD or LD. .

In a conventional optical semiconductor device (discrete) for an optical pickup, a P-type region is formed on the surface of an N-type substrate to form a PN junction photodiode, and six photodiodes PD1 to PD6 are arranged as shown in FIG. It was done. PD1 and PD6 are tracking photodiodes, and are provided for controlling the beam for signal detection so as not to shift from the track. PD2 to PD4 are photodiodes for focusing, which convert the signals recorded on the board into electrical signals and, at the same time, compare the photocurrents of PD2 to PD4 to determine whether the light beams are in focus. It is provided to do so.

When such a photodiode group for optical pickup is integrated into an IC, the P-type substrate is GND (ground potential).
Therefore, the anode common type in which the N type epitaxial layer is separated by the P ⁺ isolation region and the PN junction between the substrate and the epi is used as a photodiode is more advantageous in manufacturing.
However, from the background that all conventional discrete products were manufactured with common cathode and circuit technology was developed corresponding to common cathode,
There is a strong demand for a cathode common type when converting to C.

Therefore, FIG. 4 shows an example in which a cathode common type photodiode group is formed in order to meet the above requirements.
That is, the N-type epitaxial layer (2) formed on the P-type substrate (1) is separated by the P ⁺ -type separation region (3) to form a common cathode region, and six P layers are formed on the surface of the epitaxial layer (2). ^{The +} type anode region (4) is formed.

[0006]

However, since the light having a wavelength of 780 nm used for CD pickup and the like can sufficiently reach the depth of about 15 to 20 .mu.m from the silicon surface, how much deeply penetrating light is converted into a photocurrent. Whether it can be recovered or not will affect the sensitivity of the photodiode.
Therefore, the anode common type using the P-type substrate as the common anode can contribute to the photocurrent by the photo-generated carriers generated in the deep portion of the substrate, while the cathode common type in FIG. Since the photo-generated carriers become a reactive current, there is a drawback that the sensitivity is low.

Although the conversion efficiency is improved by increasing the thickness of the epitaxial layer (2), the epitaxial layer (2)
Is greatly related to the characteristics of other coexisting elements (NPN transistor, etc.), and cannot be simply increased from the viewpoint of fine processing. Furthermore, all the minority carriers (holes) generated in the epitaxial layer (2) do not always flow to the anode region (4), and some flow to the substrate (1), resulting in a reactive current. Therefore, there is a drawback that the sensitivity of the photodiode is further deteriorated.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, in which first and second epitaxial layers (14) and (15) are formed on a substrate (13) and a second epitaxial layer (15) is formed. A plurality of anode regions (21) forming a photodiode group are formed on the surface of the epitaxial layer (15), each of which corresponds to an individual anode region (21) on the surface of the substrate (13) under the anode region (21). By forming a plurality of N ⁺ -type buried layers (23), the common cathode type photodiode having high sensitivity to incident light and improved crosstalk between the diodes is provided.

[0009]

According to the present invention, the two-stage epitaxial structure allows the photodiode portion (11) and the peripheral circuit portion to have appropriate film thicknesses, so that the thickness of the N-type region serving as the anode is increased. it can. In addition, minority carriers (holes) generated in the N-type region serving as the cathode are generated in the substrate (13) by the N / N ⁺ barrier between the N ⁺ -type buried layer (23) and the N-type first epitaxial layer (14). Since it has a structure that does not easily flow out, most of the minority carriers generated by light incidence can be recovered as an anode current.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a sectional structure of an IC with a built-in photodiode according to the present invention. This figure shows the photodiode section (11) forming PD1 to PD6 of FIG. 2 and the NPN transistor section (12) as a part of the same side circuit. In FIG. 1, (13) is a P-type silicon semiconductor substrate, and (14) is an N-type first substrate formed on the substrate (13) by vapor phase epitaxy.
Epitaxial layer, (15) is an N-type second epitaxial layer also formed on the first epitaxial layer (14) by vapor phase epitaxy, and (16) is the first and second epitaxial layers ( 14) A P ⁺ type isolation region for junction isolation of (15). First and second epitaxial layers (14)
Both (15) have an impurity concentration of about 1.0 to 2.0 Ω · cm, and the first epitaxial layer (14) has a film thickness of 1
The thickness of the second epitaxial layer (15) is about 5 μm and is about 5 to 7 in conformity with the configuration of the peripheral circuit.

A plurality of anode regions (21) are formed on the surface of the second epitaxial layer (15) surrounded by the isolation region (16) in the pattern shown in FIG. 3, and the first and second epitaxial layers are formed. (14) The tracking photodiode P is formed by the PN junction of both with the common cathode of (15).
D1 and PD6 and focusing photodiodes PD2 to P2
D4 is formed. Tracking photodiode PD
1, PD6 and focusing photodiodes PD2 to PD
4 between the second epitaxial layer (15) and the surface of the second epitaxial layer (15) surrounding the photodiode groups PD1 to PD6, an N ⁺ -type cathode which separates both diodes and serves as a common cathode is taken out. A contact area (22) is formed.

The substrate (1) below the photodiode portion (11)
3) On the surface, an N ⁺ -type first buried layer (23) is formed so as to correspond to the P ⁺ -type anode region (21). The first buried layer (23) is vertically diffused by about 6 to 7 μm from the surface of the substrate (13), and forms a barrier between itself and the first epitaxial layer (14) by making the concentration high.

The NPN transistor portion (12) has a second epitaxial layer (15) surrounded by an isolation region (16).
On the surface of the P type base region (17), N ⁺ type emitter region (18) and N ⁺ type collector contact region (19)
To form an NPN transistor. The first and second epitaxial layers (1) below the NPN transistor section (12)
4) An N ⁺ -type second buried layer (20) is formed at the boundary of (15). On the surface of the substrate (13) further below the second buried layer (20), the photodiode part (11) is formed.
A first buried layer (23) similar to the above may be formed.
The P-type base region (17) and the anode region (21)
It is convenient to form the N ⁺ type emitter region (18) and the cathode contact region (22) in the same process.

The surface of the second epitaxial layer (15) is covered with an insulating film (24) such as silicon oxide (SiO ₂ ), and an Al electrode (25) is provided to connect the elements to each other. ing. The insulating film (24) on the photodiode part (11) is selected to have an appropriate film thickness as an antireflection film, and the region other than the photodiode part (11) is covered with a light-shielding film (not shown) so as to prevent excessive light incidence. Has been done. Then, for example, in order that signal light having a wavelength of 780 nm can reach the photodiode section (11), it is housed in a package with a window or a resin mold package that can transmit light having the wavelength, thereby forming an optical semiconductor device.

The optical semiconductor device according to the present invention described above has four characteristics. First of all, since the epitaxial layer has a two-stage structure, the circuit element of the peripheral circuit can be miniaturized and densified by using the second epitaxial layer (14), and the photodiode portion (11) can be made finer. By using the first and second epitaxial layers (14) and (15), the thickness of the N-type region which becomes the cathode can be increased.
Since light having a wavelength of 780 nm used for CD pickup can reach a depth of 15 to 20 μ inside silicon, if the second epitaxial layer (15) has a thickness of 5 μ, the film of the second epitaxial layer (14) is formed. Thickness 15
If it is set to about μ, 90% or more of the incident light can be collected. Therefore, the miniaturized NPN transistor (12) and the highly sensitive photodiode section (11) can coexist.

Second, the first buried layer (2) diffused to the side of the substrate (13) under the photodiode portion (11).
Since it has 3), the diffused portion serves as a cathode N
The thickness of the mold area can be increased. Therefore, the recovery rate of incident light can be increased more than that of the two-stage epitaxial structure. Third
In addition, by making the first burying layer (23) a high-concentration burying layer, outflow of minority carriers (holes) generated by light incidence to the substrate (13) is prevented. The IC with a built-in photodiode has a substrate (13) with a ground potential (GN
D) is applied, a potential of about +5 V is applied to the first and second epitaxial layers (14) and (15) serving as cathodes, and a potential of about +3 V is applied to the anode region (21) to reverse-bias the PN junction of the photodiode. To work with. When light is incident on the anode or cathode region, electron-hole pairs are generated, and minority carriers of the electron-hole pairs reach the cathode or anode region to generate photocurrent. The movement of the minority carriers is due to the diffusion current in the region other than the depletion layer generated in the PN junction. Therefore, the minority carriers generated in the first and second epitaxial layers (14) and (15) serving as cathodes flow to the anode region (21) and become photocurrent or the substrate (13) due to the potential relationship. Flows into the reactive current. According to the structure of the present application, as shown in the energy band diagram of FIG. 2, since the N / N ⁺ type barrier is formed by the first epitaxial layer (14) and the first buried layer (23), The holes (1
It becomes difficult to flow out to 3). Therefore, the majority of the generated holes can be converted into photocurrent, so that the sensitivity of the photodiode can be further improved.

Fourth, the first buried layer (23) below the photodiode portion (11) is formed into individual anode regions (21).
Since it is provided corresponding to, it is possible to improve the crosstalk characteristic representing the resolution between adjacent photodiodes. As shown in the enlarged cross-sectional view of FIG. 3, the crosstalk characteristic is that photogenerated carriers (26) generated in a region between the anode region (21) and the anode region (21) are diffused so that either one of the anode regions (21 ) And is detected as anode current. Therefore, if the amount of photogenerated carriers (26) generated in such an area is small, and the photogenerated carriers (26) generated are in the anode area (21).
If not, the crosstalk characteristic can be improved. According to the structure of the present invention, the first buried layer (23) is first partially removed, so that the anode region (2
In the region between 1) and the anode region (21), the thickness of the N-type region serving as the cathode is smaller than the thickness of the portion provided with the first buried layer (23). Therefore, the amount of photogenerated carriers (26) generated is small. Furthermore, the thickness thereof becomes smaller due to the amount of diffusion (27) rising from the substrate (13). In addition, the photo-generated carriers (26) generated in the region between the anode region (21) and the anode region (21).
Has no N / N ⁺ barrier described above, and therefore has a high probability of flowing out to the P-type substrate (13). Crosstalk characteristics are improved for these two reasons. The photogenerated carriers (28) are also generated by the light incident on the substrate (13) between the first buried layers (23). The photogenerated carriers (28) generated here are the same as those on the substrate (13). Diode current between the epitaxial layers (14) of
It does not contribute to the current of the photodiode. Therefore, it does not contribute to the crosstalk characteristic. Therefore, the crosstalk characteristics can be improved as compared with the case where the first burying layer (23) is provided on the entire surface.

[0018]

As described above, according to the present invention, by adopting the two-stage epitaxial structure, the film thickness of the N-type region which becomes the cathode of the photodiode part (11) can be greatly increased, and therefore, most of the incident light can be obtained. Has the advantage that it can be used for photocurrent. Further, since the photo-generated carriers generated by the first embedded layer (23) are prevented from flowing out to the substrate (13), there is an advantage that most of the photo-generated carriers can be collected as a photocurrent. Furthermore, since the first buried layer (23) is formed for each of the anode regions (21), the crosstalk characteristic between adjacent photodiodes can be improved. Therefore, a common cathode type photodiode group with high sensitivity to light incidence and reduced crosstalk is
It can be converted to C.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining the present invention.

FIG. 2 is an energy band diagram for explaining the present invention.

FIG. 3 is an enlarged cross-sectional view for explaining the present invention.

FIG. 4 is a plan view showing a photodiode group.

FIG. 5 is a sectional view for explaining a conventional example.

Claims (3)

[Claims] 1. An optical semiconductor device in which a light-receiving photodiode and a peripheral circuit are integrated, wherein first and second opposite conductivity type epitaxial layers are sequentially formed on a semiconductor substrate of one conductivity type, and An isolation region of one conductivity type that separates the first and second epitaxial layers, a plurality of anode regions formed on the surface of the second epitaxial layer surrounded by the isolation regions, and a substrate surface under the anode region And a plurality of reverse-conductivity-type high-concentration buried layers formed so as to correspond to the individual anode regions, and a circuit element forming the peripheral circuit formed on the surface of the second epitaxial layer. An optical semiconductor device characterized by: 2. The optical semiconductor device according to claim 1, further comprising a second reverse-conductivity-type high-concentration buried layer at the boundary between the first and second epitaxial layers below the circuit element. 3. The optical semiconductor device according to claim 1, wherein the circuit element is a bipolar element.