JPH04360584A - Optical semiconductor device - Google Patents

Abstract

PURPOSE:To provide an optical semiconductor device which intends to enhance high sensitivity and low power consumption of a phototransistor and to reduce in size a package. CONSTITUTION:An optical semiconductor device having an n<+> type buried epitaxial part 6 in a phototransistor operation section B in a boundary between an epitaxial layer 2 and an n<+> type silicon substrate 1 as a structure of a phototransistor. The part 6 is provided thereby to reduce a collector resistance, and hence a high sensitivity, low power consumption can be performed without altering the size of a chip, and further a package can be also reduced in size.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an optical semiconductor device.
In particular, the present invention relates to an optical semiconductor device having a feature in the structure of a phototransistor.

0002

2. Description of the Related Art The structure and operation of a conventional phototransistor will be explained with reference to FIGS. 4 to 6. FIG. 4 is a cross-sectional view of a conventional semiconductor chip, and FIG. 5 is a plan view (top view) of FIG. 4. Moreover, FIG. 6 is an equivalent circuit diagram of a phototransistor. A conventional phototransistor has a relatively low concentration collector region 2 epitaxially grown on a substrate 21, as shown in FIGS. 4 and 5.
2, and has a base region 23 and an emitter region 24 formed within this collector region 22 by ion implantation or thermal diffusion. Here, the base area 23 has two functions.
It has two parts, namely a photodiode part A and a transistor operation part B. In FIGS. 4 to 6, 25 and 26 are element isolation portions, 27 is a back collector electrode, 28 is external light (incident light), and 29 is a collector current.

Next, the operation of the conventional phototransistor will be explained.
Carriers generated by external light (incident light) 28 that has entered the depletion layer region formed by the -n junction and its surroundings are injected into the transistor operating portion B, and the collector current 29
flows. At this time, in order to obtain high light-receiving efficiency, either (1) the impurity concentration of the collector region 22 is lowered and the impurity concentration of the base region 23 is increased to widen the depletion layer region, or, (2) It is common to employ means to increase the area of the photodiode portion A. Note that an equivalent circuit diagram of the phototransistor is added to FIG. 6.

0004

[Problems to be Solved by the Invention] In the above-mentioned conventional phototransistor, in order to increase the light receiving efficiency, it is necessary to increase the impurity concentration of the collector region 22 in order to widen the width of the depletion layer between the collector and the base, which is the light receiving region. If the voltage is lowered, the collector resistance increases and the DC current amplification factor of the transistor decreases in a high current range, resulting in a problem that a large current cannot flow. Furthermore, there is a problem in that increasing the area of the photodiode portion A increases the size of the package.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical semiconductor device that solves the above-mentioned problems. Specifically, the collector resistance is reduced, and the high sensitivity of the phototransistor is improved.
It is an object of the present invention to provide an optical semiconductor device which is intended to reduce power consumption and also to reduce the size of the package.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides that, in the collector portion of a phototransistor, all or part of the bulk portion through which the collector current flows is doped with an impurity concentration higher than that in the collector portion. This is an optical semiconductor device characterized by having a high portion, and also includes a built-in phototransistor having such characteristics.

As described above, the phototransistor of the present invention is a phototransistor having a structure in which all or part of the bulk portion through which the collector current flows has a portion with high impurity concentration. It has a structure in which a buried epitaxial layer having an impurity concentration higher than that of the collector portion is buried in the collector portion of the semiconductor device, and has one or more such buried epitaxial layers. It has a structure in which the photodiode portion and the transistor operating portion are clearly separated in function.

[0008]

[Function] By providing the above-mentioned buried epitaxial layer, the low impurity concentration = high resistance part is reduced in the transistor operating part, the collector resistance is reduced, the direct current amplification factor of the transistor is prevented from decreasing, and the large current An effect occurs that allows the flow of water. In addition, in the present invention, since there is no need to increase the area of the photodiode portion, the problem of increasing the size of the package does not occur, and the package size increases.
This results in the effect that the size of the engine can be reduced. In other words, by providing a buried epitaxial layer, the collector resistance can be reduced, resulting in higher sensitivity and lower power consumption without changing the chip size.
can also be made smaller.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail based on FIGS. 1 to 3. FIG. 1 is a cross-sectional view of a semiconductor chip that is an example (Example 1) of the present invention, and FIG. 2 is a plan view (top view) of FIG. Further, FIG. 3 is a cross-sectional view of a semiconductor chip which is another embodiment (Embodiment 2) of the present invention.

(Example 1) In this example, as shown in FIGS. 1 and 2, an n- epitaxial layer (collector portion) with a resistivity of 100 Ω·cm and a layer thickness of about 50 μm is formed on an n+ type silicon substrate 1. 2, this epitaxial layer 2
Inside, there is a base region 3,0 having an area of about 0,5 mm2.
, an n+ buried epitaxial layer 6 having a resistivity of about 0.01 Ω·cm is buried in the interface between the emitter region 4 having an area of about 1 mm 2 and the epitaxial layer 2 below this emitter region 4 and the n+ type silicon substrate 1. It has a similar structure. In FIGS. 1 and 2, 5 is an element isolation part, 7 is a back collector electrode, 8 is an emitter electrode, 9 is a base electrode, and 1
0 is an oxide film, 11 is a passivation film, 12 is a buried epitaxial thickness, A is a photodiode portion, and B is a transistor operating portion.

Next, the operation of the phototransistor of this embodiment will be explained. Light is incident on the depletion layer region generated at the interface between the epitaxial layer (collector portion) 2 and the base region 3 and its surroundings. The generated carriers are injected into the base region 3 directly below the emitter region 4, and the present phototransistor operates. Here, in order to increase the sensitivity, that is, to bring the depletion layer region closer to the chip surface in order to increase the number of carriers generated, the junction between the base and the emitter is set at a distance of about 2 μm or less from the surface.

At this time, most of the collector current passes through the base region 3 and epitaxial layer 2 directly below the emitter region 4, further passes through the n+ buried epitaxial layer 6, and then passes through the n+ type silicon substrate 1. It is electrically connected to the backside collector electrode 7 via. Although the resistance of the epitaxial layer 2 is the highest in the part where this collector current passes,
Since the n+ buried epitaxial layer 6 is provided, the thickness of the low concentration layer is reduced, the collector resistance can be reduced, and element heat generation and a decrease in the DC current amplification factor in the high current region are prevented, making it possible to handle large currents. That is, in this embodiment, the transistor operating portion B
It has a structure in which the epitaxial layer (collector part) 2 in the middle is provided with a buried epitaxial layer 6 having a higher impurity concentration than the collector part, and by providing this buried epitaxial layer 6, the collector resistance in the transistor operating part B is reduced. This reduces the DC current amplification factor of the transistor and allows a large current to flow.

When a conventional phototransistor not equipped with a buried epitaxial layer 6 is irradiated with light and a photocurrent of 50 μA is applied, the linearity of the DC current amplification factor starts to decrease at a collector current of about 1 μA. As in this embodiment, when the buried epi layer 6 is provided and the buried epi layer thickness 12 is up to about 20 μm, the linearity can be increased to about 4 times for the same photocurrent. Thickness 12 to 30μm
If the thickness is increased to a certain extent, it can be increased to about 9 times.

(Embodiment 2) FIG. 3 is a sectional view of a semiconductor chip according to another embodiment (Embodiment 2) of the present invention, in which only the transistor operating portion B is extracted and illustrated. Reference numerals 1 to 11 in FIG. 3 are the same as the reference numerals in FIGS. 1 and 2 described above, and their explanations will be omitted since they overlap. In the first embodiment, the buried epitaxial layer 6 has a dango shape as shown in FIG. 1, and the collector current is concentrated at the peak of the ridge. Therefore, in the second embodiment, in order to prevent this, a plurality of buried epitaxial layers 6 are buried and arranged as shown in FIG. This has the advantage of preventing current concentration and heat concentration within the chip.

[0015]

Effects of the Invention As described in detail above, the present invention provides that, in the collector portion of a phototransistor, all or part of the bulk portion through which the collector current flows has a higher impurity concentration (buried epitaxial portion) than the collector portion. ), which has the effect of reducing collector resistance. Therefore, the present invention makes it possible to realize a phototransistor with high sensitivity and high load current, and the amount of reduction in collector resistance can be achieved by controlling the size and height of the buried epitaxial layer described above. By doing so, it is possible to freely adjust the resistance from the epitaxial layer concentration to the buried epitaxial layer concentration. Further, according to the present invention, since the size of the chips is the same and heat generation can be suppressed, there is also an effect that the size of the package can be reduced.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a semiconductor chip that is an embodiment of the present invention.

FIG. 2 is a plan view (top view) of FIG. 1;

FIG. 3 is a cross-sectional view of a semiconductor chip that is another embodiment of the present invention.

FIG. 4 is a cross-sectional view of a conventional semiconductor chip.

FIG. 5 is a plan view (top view) of FIG. 4;

FIG. 6 is an equivalent circuit diagram of a phototransistor.

[Explanation of symbols]

1 n+ silicon substrate 2 Epitaxial layer 3 Base area 4 Emitter area 5 Element isolation part 6 Embedded epi 7 Back side collector electrode 8 Emitter electrode 9 Base electrode 10 Oxide film 11 Passivation film 12 Buried epitaxial thickness 21 Substrate 22 Collector area 23 Base area 24 Emitter area 25 Element isolation part 26 Element isolation part 27 Back side collector electrode 28 Incident light 29 Collector current A Photodiode part B Transistor operation part

Claims (2)

[Claims] 1. An optical semiconductor device characterized in that, in a collector portion of a phototransistor, all or part of a bulk portion through which a collector current flows has a portion having a higher impurity concentration than the collector portion. 2. An optical semiconductor device with a built-in phototransistor, comprising a phototransistor having a structure in which all or part of a bulk portion through which a collector current flows has a portion with a high impurity concentration.