JPH05145107A - Optical semiconductor device - Google Patents

Abstract

PURPOSE:To develop a further integrated circuit from a high sensibility cathode common type photodiode group by partially increasing the thickness of the N type region which serves as a cathode. CONSTITUTION:An epitaxial layer 14 is adopted for a common cathode. On the surface of the epitaxial layer are formed a plurality of P<+> type anode regions 17, thereby forming photodiode groups. There are formed N type well regions 19 having low concentration impurities respectively on the surface of a board 13 equivalent to each of the anode regions 17.

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 to meet the above demand.
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.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks. Under the plurality of P ⁺ -type anode regions (17) forming a photodiode group, each anode region (17) is formed. By providing an N-type well region (19) diffused from the surface of the substrate (13) so as to correspond to the above, a common cathode type photodiode having high sensitivity to incident light and improved crosstalk between the diodes is provided. To do.

[0009]

According to the present invention, the P ⁺ type anode region (17)
Since each has an N-type well region (19) underneath,
The thickness of the region serving as the cathode can be increased by the amount of the mold well region (19). In addition, since the N ⁺ well region (19) is provided in each of the P ⁺ -type anode regions (17), photo-generated carriers generated in the P-type substrate (13) between the well regions (19) can contribute to photocurrent. Instead, it becomes a reactive 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. The figure shows a photodiode section (11) forming PD1 to PD6 of FIG. 2 and an NPN transistor section (12) as a part of a peripheral circuit. In FIG. 1, (13) is a P-type silicon semiconductor substrate, (14) is an N-type epitaxial layer formed on the substrate (13) by a vapor phase growth method, and (15) is N formed on the surface of the substrate (13). ⁺
Type buried layer, (16) is epitaxial layer (14)
Is a P ⁺ -type isolation region for junction isolation.

On the surface of the epitaxial layer (14) surrounded by the isolation region (16), a plurality of P ⁺ type anode regions (17) are formed in the pattern shown in FIG. 3, and the anode region (17) and the epitaxial layer are formed. The tracking photodiodes PD1 and PD6 and the focusing photodiodes PD2 to PD4 are formed by the PN junction with (14). Epitaxial layer between the tracking photodiode PD1, PD6 and focusing photodiode PD2～PD4 (14) surface and the epitaxial layer (14) surface surrounding the photodiode group, N ⁺ -type which is a and the cathode of the extraction were separated both photodiodes A cathode contact region (18) is formed. Since the epitaxial layer (14) serving as the cathode is shared by all the photodiodes, these photodiodes are constructed as a cathode common type.

The substrate (1) below the photodiode portion (11)
3) On the surface, a plurality of N-type well regions (19) are formed at positions corresponding to the P ⁺ -type anode regions (17). The N-type well region (19) has a shape that suppresses rising to the epitaxial layer (14) side and is diffused sufficiently deep inside the substrate (13). The surface of the other epitaxial layer (14) surrounded by the isolation region (16) has P
A type base region (20), an N ⁺ type emitter region (21) and an N ⁺ type collector contact region (22) are formed to form an NPN transistor (12). If the impurity concentration of the epitaxial layer (14) does not match between the photodiode portion (11) and the NPN transistor portion (12), match the impurity concentration with the photodiode portion (11), and
The PN transistor section (12) may have a structure in which an N type well is diffused to increase the impurity concentration.

The surface of the epitaxial layer (14) is covered with an insulating film (23) such as silicon oxide (SiO ₂ ).
By providing the l electrode (24), the elements are connected to each other. Insulating film (2) on the photodiode part (11)
3) is selected to have an appropriate film thickness as an antireflection film, and a region other than the photodiode portion (11) is covered with a light shielding film (not shown) so as to prevent excessive light incidence. Then, for example, the signal light having a wavelength of 780 nm is supplied to the photodiode section (11).
So as to reach the optical semiconductor device.

Since the optical semiconductor device according to the present invention described above is provided with the N-type well region (19) on the surface of the substrate (13), the thickness of the epitaxial layer (14) is substantially increased in the photodiode portion (11). This is equivalent to the above, and the thickness of the N-type region serving as the cathode can be increased by the amount of the well region (19). For example, assuming that the thickness of the epitaxial layer (14) is 6 μm and the incident light is the light having the wavelength of 780 nm, the light is 1 from the surface of the epitaxial layer (14).
Since the depth reaches about 5 to 20 μ, if the diffusion depth of the N-type well region (19) is set to 8 to 10 μ, most of the region where the incident light reaches can be the N-type cathode and the incident light Most can contribute to photocurrent.

In order to realize the N-type well region having a large diffusion depth as described above, the device of the present application can be manufactured by the following flow, for example. First, a selection mask for forming the N-type well region (19) is formed on the surface of the substrate (13), and an N-type impurity such as phosphorus (P) is dosed with the selection mask at a dose of 10
^{About 13} ions are selectively implanted, and the entire substrate (13) is heat-treated at high temperature for a long time to diffuse the N-type well region (19) to a sufficient depth. After that, the N ⁺ type buried layer (15) is formed, the epitaxial layer (14) is formed, the P ⁺ type isolation region (16) is formed, and the base diffusion process and the emitter diffusion process are performed. By thus diffusing and forming the N-type well region (19) first, it is possible to obtain a structure in which there is almost no rise to the epitaxial layer (14) side. Also, a low impurity concentration N-type well region (19)
The substrate (13) having a specific resistance of 6 to 12 Ω · cm or 40 to 60 Ω · cm, which is lower in impurity concentration than a general substrate, is preferably used so that the substrate can be formed deep easily. The manufacturing process can be simplified by forming the base region (20) and the anode region (17) in the same process and the emitter region (21) and the cathode contact region (18) in the same process.

As one index showing the performance of such a photodiode group, there is a cross stroke characteristic representing the resolution between adjacent photodiodes. As shown in the enlarged cross-sectional view of FIG.
This is because the photo-generated carriers (25) generated in the region between 7) and the anode region (17) reach one of the anode regions (17) by diffusion and are detected as an anode current. Therefore, if the amount of photogenerated carriers (25) generated in such a region is small and if the generated photogenerated carriers (25) do not reach the anode region (17), the crosstalk characteristics can be improved. For the IC with a built-in photodiode, the substrate (13) is connected to the ground potential (GN
D), about + 5V in the epitaxial layer (14) which becomes the cathode, and + 3V in the anode region (17).
The photodiode is operated in a reverse bias state by applying a potential of the order.

According to the structure of the present invention, the N-type well region (19) is partially removed, so that the region between the anode regions (17) and (17) serves as a cathode. The thickness of the region is smaller than the thickness of the portion where the well region (19) is provided. Furthermore, the substrate (1
The thickness is further reduced by the amount (27) of upward diffusion from 3). Therefore, the generation of photogenerated carriers (25) at the cathode is small. Photogenerated carriers (26) are also generated in the P-type substrate (13) sandwiched between the well regions (19). The photogenerated carriers (26) generated here are generated in the substrate (13) and the epitaxial layer (14). ), The diode current, and does not contribute to the photodiode current. Therefore, the crosstalk characteristic can be improved rather than forming the well region (19) on the entire surface.

[0018]

As described above, according to the present invention, since each anode region (17) has an N-type well region (19), a group of high-sensitivity cathode common type photodiodes having a high light absorption rate can be provided. It has the advantage of being integrated into an IC. Moreover, since the N-type well regions (19) are individually provided, there is an advantage that crosstalk between adjacent photodiodes can be reduced.

[Brief description of drawings]

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

FIG. 2 is an enlarged sectional view for explaining the present invention.

FIG. 3 is a plan view showing a photodiode group.

FIG. 4 is a cross-sectional view for explaining a conventional example.

Claims (3)

[Claims] 1. An optical semiconductor device in which a photodiode for light reception and a peripheral circuit are integrated, wherein an epitaxial layer of opposite conductivity type formed on a semiconductor substrate of one conductivity type and a surface of the epitaxial layer are close to each other. A plurality of one-conductivity-type anode regions formed as described above, and a plurality of reverse-conductivity-type well regions of low impurity concentration formed on the surface of the substrate so as to correspond to the individual anode regions. An optical semiconductor device characterized by: 2. The optical semiconductor device according to claim 1, wherein the well region of the opposite conductivity type is formed deeper downward from the surface of the substrate. 3. The optical semiconductor device according to claim 1, further comprising a vertical bipolar transistor in another region of the epitaxial layer.