JP3213131B2 - Phototransistor and photocoupler using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a phototransistor and a phototransistor.
And a photocoupler using the same .

[0002]

2. Description of the Related Art As is well known, a phototransistor is used as a light receiving element such as a photocoupler or a photointerrupter. The schematic configuration of the phototransistor is as follows. Hereinafter, a conventional example will be described with reference to FIGS. FIG. 6 is a sectional view, and FIG. 7 is an equivalent circuit diagram.

In FIGS. 6 and 7, 1 is a phototransistor, 2 is a semiconductor substrate constituting an n ^{+ -type} collector substrate, and 3 is an n ^{− -type} collector laminated on the upper surface of the semiconductor substrate 2. Reference numeral 4 denotes a p ^{+ -type} base diffusion layer formed on the upper surface of the collector layer 3, and reference numeral 5 denotes an n ⁺ -type emitter diffusion layer formed on the upper surface of the base diffusion layer 4. Reference numeral 6 denotes an emitter electrode provided on the emitter diffusion layer 5, reference numeral 7 denotes a collector electrode provided on the lower surface of the semiconductor substrate 2, and reference numeral 8 denotes a collector electrode provided so as to insulate the upper surfaces of the layers 3, 4, and 5. Oxide film.

In such a structure, the pn junction between the collector layer 3 and the base diffusion layer 4 becomes a light-sensitive junction, and the light incident thereon is converted into a photocurrent, so that the emitter electrode 6 and the collector electrode 7 is output. Phototransistor 1 Therefore, as shown in the equivalent circuit diagram of FIG. 7, the base diffusion layer 4 and the collector layer 3 and cathode Cp
Is used as an anode Ap, the pn junction of both layers 3 and 4 functions as a photodiode 9 to convert incident light into a photocurrent, and converts the photocurrent into a collector C, a base diffusion layer 4 and an emitter diffusion layer 5 respectively. , Base B, and emitter E.

[0005] Usually, in the phototransistor 1,
In order to reduce the series resistance of the device, the semiconductor substrate 2 constituting the collector base has a high impurity concentration, and the lifetime of minority carriers generated by incident light is lengthened to effectively contribute to photocurrent. The collector layer 3 has a low impurity concentration in order to ensure the following.

On the other hand, the phototransistor 1 performs a saturation operation when the load of the bipolar transistor 10 is large and the amount of incident light is large. In this saturated operation state, the base-emitter junction and the base-collector junction are both forward-biased.
, Minority carriers are injected from the base diffusion layer 4.

For this reason, when a switching operation in which the saturation operation state and the blocking of the incident light are repeated when the amount of incident light is large is performed, the incident light is blocked because the minority carriers injected into the collector layer 3 have a long lifetime. It remains in the collector layer 3 for a long time, and the “ON” of the phototransistor 1
The operation speed of switching from "OFF" to "OFF" becomes slow, that is, the so-called accumulation time becomes long.

In order to improve the decrease in the operation speed during the switching operation, the lifetime of the minority carrier in the collector layer 3 is shortened, for example, by controlling the lifetime of the minority carrier by irradiating an electron beam or by changing the lifetime of the minority carrier. A method of spreading a lifetime killer such as (Au) has been considered. However, in these methods, the lifetime of the collector layer 3 which is a light absorbing layer is shortened, so that the photocurrent which should contribute to the photocurrent is reduced, and the light receiving sensitivity of the phototransistor 1 is significantly reduced. I will.

Further, according to these methods, the number of manufacturing steps of the phototransistor 1 increases, and the cost increases.

[0010]

As described above, the conventional phototransistor has a low operating speed when the switching operation is performed in a saturated operation state with a large amount of incident light, and the operating speed will be increased. In this case, the light receiving sensitivity is significantly reduced, and the cost may be further increased. The present invention has been made in view of such a situation, and the object thereof is to reduce the light receiving sensitivity and increase the cost, improve the switching operation speed in the saturation operation state where the incident light amount is large, and a phototransistor. Use this
To provide a photocoupler .

[0011]

A phototransistor according to the present invention.
Stars and photocouplers using the same
The collector region and the base region on the semiconductor substrate.
And an emitter region is formed on the upper surface of the base region.
And a pn junction between the collector region and the base region is exposed to light.
In a phototransistor having a sensitive junction, the collector
At least a portion of the data region penetrates the base region.
Forming an island-shaped exposed surface on the upper surface of the base region;
A Schottky barrier at the contact between the data region and the base region.
The exposed surface of the collector region and the vicinity of the vicinity of the exposed surface.
Metal electrodes are provided to cover the base area
Is intended, characterized in, also photocoupler, emission
The collector and base are used as the light receiving element facing the element.
Using a phototransistor with a light-sensitive junction as the pn junction
In the photocoupler,
Connect a Schottky barrier diode in parallel with the pn junction
It is intended, characterized in was also opposed to the light emitting element
Collector area on semiconductor substrate as light receiving element to be arranged
And a base region, and an upper surface of the base region is etched.
A mitter region is formed, and the collector region and the base region are formed.
Using a phototransistor with a light-sensitive junction as the pn junction
In the photocoupler,
At least a portion of the collector region is in contact with the base region.
Connect between and shot to the contact area of the collector area
Metal electrodes are provided to form a barrier
And a small collector area.
At least in part, an island-shaped exposed surface is formed in the upper surface of the base region.
Is provided through the base region to be formed,
Covering the exposed surface and the base region in the vicinity of the exposed surface
Characterized by being provided with a metal electrode
And a metal electrode is provided in the emitter region.
That it is formed of the same metal material as the emitter electrode
It is a feature.

[0012]

According to the present invention, the phototransistor and the phototransistor constructed as described above are provided.
And photocouplers that use this
Through the base region in the same manufacturing process as the emitter electrode
On the island-shaped exposed surface of the collector region
Toki metal electrode is formed and pn junction between collector and base
A Schottky barrier diode connected in parallel to
When a large amount of incident light saturates, the Schottky barrier becomes higher than the forward voltage of the base-collector junction.
The forward voltage of the Schottky junction of the diode decreases, and a current flows in the forward direction of the Schottky junction. Thereby, the forward current of the base-collector junction is suppressed, and the injection of minority carriers from the base to the collector is suppressed. Therefore, the amount of charge stored in the collector is reduced, the storage time is shortened, and the switching operation speed is increased. Further, since the switching operation speed is increased without shortening the lifetime of minority carriers of the collector, the light receiving sensitivity does not decrease. As a result, the phototransistor
Or reduce the receiving sensitivity of the static, it no to or increasing the cost, it is possible to improve the switching operation speed of the incident light amount is large saturation operating state, switch
It is possible to construct a photocoupler with fast switching operation.
You.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. 1 is a cross-sectional view of a phototransistor, FIG. 2 is an equivalent circuit diagram, FIG. 3 is a top view in the middle of a manufacturing process of the phototransistor, and FIG. 4 is a circuit diagram shown for explaining an operation state. FIG. 5 is a sectional view showing a schematic configuration of a photocoupler.

First, in FIGS. 1 to 3, reference numeral 11 denotes a phototransistor having a chip size of about 1 mm square, which is formed by adding a high concentration of antimony to a silicon semiconductor substrate 12 of n ^{+ type} as a collector base. It is configured. An n ⁻ -type collector layer 13 is laminated on the upper surface of the semiconductor substrate 12 by an epitaxial method in which a silane compound and a phosphorus compound are reacted at a high temperature. The thickness and impurity concentration of the collector layer 13 determine the light receiving sensitivity and other characteristics of the phototransistor. For example, a light receiving device having a wavelength of 950 nm and a collector withstand voltage of 80 V has a thickness of 20 μm. ４０40 μm and an impurity concentration of 10 ¹⁴ cm ⁻³ to 10 ¹⁵ cm ^−3.
It is of the order.

On the upper surface of the collector layer 13, a region having a size of about 0.7 mm square formed by photolithography or the like is provided in the vicinity of one corner of this region. Boron is thermally diffused so as not to be diffused to the portion, so that a p-type base diffusion layer 14 is formed.
In this manner, as shown in FIG. 3, on the upper surface of the base diffusion layer 14, an exposed portion 15 in which a part of the collector layer 13 is exposed in an approximately 50 μm square island shape is formed as shown in FIG.
The four surroundings are surrounded by the base diffusion layer 14.

Further, at a predetermined portion on the upper surface of the base diffusion layer 14, an emitter formation region is patterned by photolithography or the like, and phosphorus is thermally diffused therein to form an n ^{+ type} emitter diffusion layer 16. Have been.

Further, an oxide film 17 such as silicon oxide (SiO ₂ ) is formed on the surface of the device thus formed. Then, the emitter diffusion layer 1 of the oxide film 17 is formed.
6 and a portion of the exposed portion 15 of the collector layer 13 and a portion of the upper surface of the base diffusion layer 14 in the vicinity of the exposed portion 15 are then removed. The electrode 18 and the Schottky metal electrode 19 are formed in the same manufacturing process. Reference numeral 20 denotes a collector electrode provided on the lower surface of the semiconductor substrate 12.

Since the phototransistor 11 is configured as described above, its equivalent circuit diagram is as shown in FIG. That is, the collector layer 13 is connected to the cathode Cp
The base diffusion layer 14 is an anode Ap, and both layers 13,
Photodiode 21 a pn junction 14 as photosensitizers junction
Are formed, and the collector layer 13, the base diffusion layer 14,
The emitter diffusion layer 16 is divided into a collector C, a base B,
A bipolar transistor 22 is formed as the emitter E. The light incident on the photodiode 21 is pn
The junction is converted into a photocurrent, and the photocurrent obtained by the conversion operates so as to be amplified by the bipolar transistor 22.

Further, in the phototransistor 11, an exposed portion 1 of the collector layer 13 exposed in the base diffusion layer 14 is provided.
By 5 a Schottky metal electrode 19 Schottky barrier da
An ion 23 is formed. This Schottky barrier die
Ord 23 has its cathode Cs photodiode 2
It is connected to the collector C of the first cathode Cp and bipolar transistor 22, the anode As a photodiode 2
One anode Ap and the base B of the bipolar transistor 22 are connected.

For this reason, when the phototransistor 11 performs a saturated operation by receiving strong incident light, that is, in the circuit diagram showing the operation state of FIG. 4, the incident light causes the photocurrent _IPB to flow through the photodiode 21, and this photocurrent If the ratio is greater than the I _PB load _{R L} flowing through the load current _{I C} and the amplification factor _{h FE} of the bipolar transistor 22 _(I PB> _{I C}
/ H _FE ) is the base of the bipolar transistor 22.
Schottky barrier from forward voltage V _BC of collector junction
The forward voltage _Vf of the Schottky junction of the diode 23 is low, so that a current flows in the forward direction of the Schottky junction and the forward current of the base-collector junction is suppressed.

Since minority carriers injected from the base diffusion layer 14 into the collector layer 13 are suppressed at the base-collector junction, the amount of charges stored in the collector layer 13 is reduced, and the storage time is shortened. Operating speed at the time of switching operation of the bipolar transistor 22,
That is, the switching operation speed of the phototransistor 11 increases. However, in this case, since the lifetime of minority carriers in the collector layer 13 is not shortened in order to increase the switching operation speed, the light receiving sensitivity does not decrease.

The Schottky metal electrode 19 is formed of the same metal material as that of the emitter electrode 18. Since the Schottky metal electrode 19 is formed simultaneously in the aluminum deposition step of forming the emitter electrode 18, the Schottky metal electrode 19 is formed of a different metal material. The manufacturing process is simpler than in the case of performing the above.

Further, the phototransistor 11 configured as described above is used as a light receiving element 24, a GaAs LED is used as a light emitting element 25, and the two elements 24 and 25 are optically coupled to form a photocoupler 26 whose sectional view is shown in FIG. Formed and their properties were measured. Reference numeral 27 denotes a light-transmitting resin that covers the two elements 24 and 25 in a state where they are optically coupled.
Is a lead, and 30 is an envelope formed of a light-impermeable resin.

[0024] Then, 1.9Keiomega the load resistance _{R L,} the power supply voltage _{V CC} 5V, the input current _{I F} to the light emitting element 25 5
When the accumulation time of the phototransistor 11 was measured under the condition of mA, the accumulation time was 15 μsec.

On the other hand, a photocoupler was similarly constructed using a conventional phototransistor as a light receiving element, and the accumulation time was measured under the same conditions. The accumulation time of the conventional phototransistor was 30 μsec. By using the transistor 11, the accumulation time can be reduced by half
Thus, the photocoupler 26 having a fast switching operation can be formed.

In the above embodiment, the Schottky metal electrode 19 is formed simultaneously with the same aluminum as the emitter electrode 18. However, the Schottky metal electrode 19 does not have to be formed at the same time. May be formed of another metal or alloy, such as aluminum, tungsten, and molybdenum, to which silicon is added and which forms a Schottky barrier by contacting with silicon. Further, the phototransistor 11 is configured as an npn type, but may be a pnp type.
Bipolar transistor 22, Shotoki barrier diode
Although the phototransistor 11 is formed so that the diode 23 is provided, a portion corresponding to the Schottky barrier diode 23 may be externally provided to form a hybrid structure. The present invention can be implemented with appropriate modifications.

[0027]

As is apparent from the above description, the present invention reduces the light receiving sensitivity of the phototransistor by connecting the Schottky barrier diode in parallel to the pn junction of the collector and the base of the phototransistor. Switching speed in a saturated operation state where the amount of incident light is large without increasing the cost or increasing the cost .
The effect is that the speeding operation can be made faster .

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of one embodiment of the present invention.

FIG. 3 is a top view in the middle of a manufacturing process according to an embodiment of the present invention.

FIG. 4 is a circuit diagram for explaining an operation state of one embodiment of the present invention.

FIG. 5 is a cross-sectional view illustrating a schematic configuration of a photocoupler using one embodiment of the present invention.

FIG. 6 is a sectional view showing a conventional example.

FIG. 7 is an equivalent circuit diagram of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 13 ... Collector layer 14 ... Base diffusion layer 15 ... Exposed part 16 ... Emitter diffusion layer 19 ... Schottky metal electrode

Claims (5)

(57) [Claims] A collector region and a base region are provided on a semiconductor substrate.
And an emitter region on the upper surface of the base region.
Is formed, and a pn junction between the collector region and the base region is formed.
In a phototransistor having a photosensitive junction,
At least a portion of the collector region extends through the base region.
To form an island-shaped exposed surface on the upper surface of the base region,
Schottky failure in the contact area between the collector area and the base area
A wall, and an exposed surface of the collector region and a vicinity of the exposed surface.
A metal electrode is provided so as to cover the adjacent base region.
A phototransistor characterized in that: 2. A light-receiving element disposed opposite to a light-emitting element.
To make the pn junction between the collector and the base a photosensitive junction.
A photocoupler using a phototransistor;
Schottky barrier in parallel with the pn junction of the phototransistor
Photocap, characterized by connecting a diode
La. 3. A light receiving element disposed opposite to a light emitting element.
And a collector region and a base region are formed on the semiconductor substrate.
And an emitter region is formed on the upper surface of the base region.
Pn junction between the collector region and the base region.
For photocouplers using phototransistors as junctions
In this case, the phototransistor has a small collector region.
At least partially, the connection between the base region and
A Schottky barrier is formed at the contact portion of the collector region.
Characterized in that a metal electrode is provided.
Coupler. 4. The method according to claim 1 , wherein at least a part of the collector region includes a base.
The base is formed so that an island-shaped exposed surface is formed in the upper surface of the storage region.
The exposed surface and the exposed surface.
A metal electrode is provided so as to cover the base region near the periphery of the surface.
4. The photo camera according to claim 3, wherein
Plastic. 5. A metal electrode is provided in an emitter region.
It is characterized by being formed of the same metal material as the emitter electrode.
The photocoupler according to claim 3 or 4, wherein