JPS6243348B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical semiconductor device, and more particularly to a light receiving semiconductor device suitable for a light receiving section of a photocoupler, etc., in which a transistor amplification stage and a photodiode are formed on the same substrate.

A photocoupler is a composite element in which a light-emitting element and a light-receiving element face each other, and is a new type of device in which an electrical signal is first converted into light by the light-emitting element, and then converted into an electric signal in the light-receiving part. Since signals are propagated by light, it is possible to electrically isolate input/output sections, and it is expected to be in great demand as high-speed switches for electromagnetic relays, signal transformers, and microcomputer peripheral terminal equipment.

Traditionally, the anode of a photodiode was formed by diffusion from the epitaxial surface at the same time as the base of the NPN transistor. Therefore, the only way to increase the sensitivity of a photodiode is to increase the anode area, increase the epitaxial thickness, or increase the epitaxial resistivity. However, increasing the anode area not only increases the chip area but also increases the anode-cathode capacitance, which is undesirable. On the other hand, increasing the epitaxial thickness and increasing the epitaxial resistivity increases the series resistance of transistors formed on the same semiconductor substrate, which tends to become saturated, and the storage time also increases rapidly.
Usually, a Schottky diode is added in parallel to the base-collector junction of a transistor to reduce the storage time, but as the epitaxial resistivity and thickness increase, the series resistance increases.
The shot key clamp will no longer work and the high frequency characteristics of the circuit will deteriorate.

A possible solution to the above-mentioned drawbacks would be to make the photodiode a high-speed PIN photodiode and fabricate the transistor gain stage as a separate chip in a hybrid configuration, but this would make the integrated circuit expensive.

In view of the above circumstances, it is an object of the present invention to provide a semiconductor light receiving device that has superior performance in terms of speed and current transfer rate than conventional light receiving devices, and is suitable for the light receiving section of a photocoupler. purpose.

The present invention is characterized in that one of the two regions constituting the photodiode has a multi-stage structure. That is, one region includes a first portion embedded inside the other region, a second portion disposed on the surface of the other region so as to face the first portion, and a first portion. and a third portion connecting the second portion.

Since such a photodiode has an anode region with a multi-stage structure, light incident on the anode can be efficiently absorbed and light sensitivity can be increased. Furthermore, the impurity concentration of the epitaxial layer constituting the cathode region, for example, makes it possible to obtain sufficiently high photosensitivity even to meet the requirements of an amplification transistor formed on the same substrate, making it easy to combine a photodiode and an amplification transistor. can be formed on the same semiconductor substrate.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a cross-sectional view of a first embodiment of the invention in which a photodiode and a transistor gain stage are formed on the same chip. In FIG. 1, the left side of an insulating region 3 in the center, which will be described later, is a photodiode, and the right side is one transistor constituting a transistor gain stage (the same applies to FIGS. 2 and 3, which will be described later). Antimony was selectively diffused onto a P-type silicon substrate 1 with a specific resistance of about 20 to 40 Ωcm.
N ⁺ type buried layer 2 and specific resistance 0.5Ω-cm thickness 3~4μ
An N-type epitaxial layer 4 is provided. Next, boron is selectively diffused into a portion that will form part of the anode region of the photodiode to form the first anode region 6. The selective diffusion of impurities mentioned above is
As is well known, an insulating film (not shown) such as an oxide film is formed on a semiconductor, and this is selectively removed to diffuse impurities into the exposed semiconductor portion.

After that, the whole has a specific resistance of 1 to 2 Ω-cm and a thickness of 5
Form an N-type epitaxial layer 5 of ~6μ. Next, an insulating region 3 for electrically insulating the photodiode and the transistor is formed. At the same time, a connection region 3' reaching the first anode region 6 is formed by selective diffusion of boron. After this, boron and phosphorous are sequentially selectively diffused in the same manner as in the conventional method to form the second anode region 7 of the photodiode section, the cathode electrode extraction region 8, the region 7 that will become the base of the transistor section, and the emitter and collector extraction regions. ⁺ Form area 8. After this, although not shown, as is well known, the surface is covered with an insulating film, contact holes for each region of the photodiode and transistor are formed in the insulating film, and interconnected with a conductive layer such as aluminum to form the photodiode. The detection current is amplified by a transistor. As an example of this, when converting a photoelectric conversion current from a photodiode into a voltage with a resistor and amplifying this with a transistor, the cathode extraction region 8 of the photodiode is connected to a reverse bias source, and the electrode from the second anode 7 is is connected to one end of the resistor and to the base 7 of the transistor. The emitter 8 of the transistor is connected to the other end of the resistor.

The photodiode according to the first embodiment of the present invention has excellent photosensitivity due to the two anode regions 6 and 7 placed apart in the vertical direction of the semiconductor substrate, and the area may be smaller than that of an ordinary photodiode. . Also, since the depletion layer completely extends between the two anode regions 6 and 7 and between the anode 6 and the antimony buried region 2, the speed is high. For this reason,
Good characteristics can be obtained in both speed and current transfer rate.

FIG. 2 is a sectional view of a second embodiment of the present invention,
The first anode region 6 is formed using a P-type buried layer which is used as an insulator and a collector of a vertical PNP in an ordinary integrated circuit. That is,
After providing a first anode region 6 by selectively diffusing impurities in the N ⁺ type buried layer 2 of the photodiode portion formed in the same manner as in the first embodiment, an insulating region is formed in the same manner as in the first embodiment. 3 and a connection region 3' are formed, and a photodiode section and a transistor section are formed. Thereafter, connections between elements are made as described in FIG.

The photodiode according to the second embodiment has the disadvantage that the capacitance is larger than the photodiode according to the first embodiment, but since the ordinary integrated circuit process can be used as is, only light sensitivity is required. In this case, the photodiode of the second embodiment is used.

FIG. 3 is a sectional view showing a third embodiment of the present invention, in which an N ⁺ type buried layer 2 is formed by selectively diffusing antimony on a P type silicon substrate 1 having a specific resistance of about 20 to 40 Ω-cm. and specific resistance 0.5Ω-cm, thickness 5~6μ N
The type epitaxial layer 4 is formed in exactly the same manner as before. Next, selective diffusion of impurities is performed to form the first anode region 6 of the photodiode portion, and then the surface of the epitaxial layer 4 other than the portion where the photodiode is to be formed is covered with, for example, an oxide film (not shown). After that, epitaxial growth is performed to a specific resistance of 10 to 15 Ω-cm and a thickness of about 8 to 10 μm.
The epitaxial layer on the oxide film is polycrystalline silicon (not shown), and since there is no oxide film on the region where the photodiode is to be formed, a high quality single crystal region 5 is formed. Then HF―HNO ₃ ―CH ₃ COOH
Polycrystalline silicon is selectively etched using a system solution. That is, the polycrystalline silicon formed on the transistor gain stage portion is removed. Next, insulating diffusion is performed in the same manner as described in the first embodiment to form an insulating region 3 for isolation between elements, and at the same time, a region 3' in contact with the first anode region 6 is formed in the single crystal region 5. form. Thereafter, boron is diffused to form a second anode region 7 spanning the surface portions of the single crystal region 5 and the epitaxial layer 4, and also to form the base region 7 of the transistor. The first and second anode regions 6, 7 are connected by a region 3'. Next, by selectively diffusing phosphorus, a region 8 that will become a cathode lead-out region and the emitter and collector lead-out regions of the transistor is formed. After this, connections between elements (not shown) are made.

The photodiode and transistor according to the third embodiment are each optimally designed. That is, the epitaxial crystal that forms the photodiode has a high specific resistance, so the capacitance is small. Furthermore, since the photodiode part has a thick epitaxial thickness (consisting of layers 4 and 5), the sensitivity is sufficient. On the other hand, since the transistor portion has a low epitaxial resistivity and a thin epitaxial thickness (layer 4 only), the collector series resistance of the transistor is small and the storage time is short. Therefore, the speed and current transfer rate are also very excellent.

As explained above, according to the present invention, a photodiode and a transistor gain stage can be formed on the same chip without deteriorating their electrical characteristics. If the photodiode of the present invention is used in a light receiving section, a photocoupler with high speed and excellent current transfer rate can be obtained. In the above embodiment, the case where the anode is in two stages has been described, but it is obvious that the anode can be expanded to three or more stages. The photodiode according to the present invention can increase the light-receiving sensitivity without increasing the chip area or increasing the anode-cathode capacitance as described above.

[Brief explanation of the drawing]

FIG. 1 is a structural cross-sectional view showing a first embodiment of the optical semiconductor device of the present invention, FIG. 2 is a structural cross-sectional view showing an embodiment of the present invention, and FIG. 3 is a structural cross-sectional view showing a third embodiment of the present invention. FIG. 1...P-type silicon substrate, 2...N ⁺ buried layer,
3, 3'... P ⁺ type insulating region, 4, 5... N type epitaxial layer, 6... Photodiode anode region, 7... Photodiode anode region (NPN transistor base region), 8... ...Photodiode cathode region (NPN transistor emitter, collector N ⁺ region).

Claims (1)

[Claims] 1 first and second semiconductor regions of one conductivity type separated from each other in an island shape by an insulating region;
a high concentration buried region formed at the bottom of the semiconductor region; a third semiconductor region of an opposite conductivity type buried inside the first semiconductor region; and a surface portion of the first semiconductor region. a fourth semiconductor region of an opposite conductivity type disposed to face the third semiconductor region; and a fourth semiconductor region provided in the first semiconductor region so as to connect the third and fourth semiconductor regions. a fifth semiconductor region of opposite conductivity type and an amplification transistor formed in the second semiconductor region;
An optical semiconductor device comprising a light receiving element formed by a PN junction formed by a semiconductor region and the third to fifth semiconductor regions.