JPH06151946A - Semiconductor photodetecting element and manufacture thereof - Google Patents

Abstract

PURPOSE:To prevent deterioration of the conversion efficiency of photoelectric signal by providing a take-out electrode continuously extending to interdigital electrodes for forming a junction on a substrate and by so forming a semiconductor thin film consisting of crystal or polycrystal that it abuts on the interdigital electrodes. CONSTITUTION:Interdigital electrodes 2, 2 are arranged on a thin semiconductor film F. A join structure is formed in which the surface where the electrodes 2, 2 exist faces a substrate S1 which supports a device and also a second take- out electrode 3' formed on the substrate S1 abuts on a take-out part 3 of the interdigital electrodes 2. On the opposite side to the join surface, an antireflection surface is placed and the optical signals from element surface is taken in a film F without reflection and received. Also, the film F makes a structure that a finger part 2a of the interdigital electrodes 2 faces the substrate through a gap. Accordingly, the conversion efficiency of optical signals becomes large.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light receiving element used for an optical wiring, an optical signal processing circuit, etc. in an optical transmission system or an information processing apparatus, and a method for manufacturing the same. The device is specifically a metal-semiconductor-metal Schottky photodiode (MSMPD: Metal).
-Semiconductor-Metal Photo
or a phototransistor having a Schottky junction in the gate portion.

[0002]

2. Description of the Related Art A conventional MSM PD is shown in FIG.
As shown in (b), paired metal electrodes 2 and 2 are arranged on the surface of a semiconductor substrate 1 such as GaAs or Si, and
-Has a structure that forms a Schottky junction due to semiconductor contact. The electrode 2 has a plurality of finger-shaped projections (finger-shaped portions; counter-counter electrodes) 2a, 2a, and the electrodes 2, 2 oppose the finger-shaped portions 2a and are arranged alternately. Hereinafter, the counter electrodes having the finger-shaped portions, which are opposed to each other and which are alternately arranged, will be described below.
digital) type electrode.

When the Schottky junction is biased, the semiconductor in the junction and its vicinity is irradiated with light having a wavelength equal to or shorter than the wavelength determined by the band gap of the semiconductor, and electrons are excited in the semiconductor. The MSM PD shown in FIG. 1 performs a basic operation as a light receiving element by detecting the current generated by the excited electrons.

This MSM PD is a pin junction type photodiode (pin PD: pin) which is another light receiving element.
Photodiode) and avalanche photodiode (APD: Avaranche Photodiode)
Compared to de), the structure is simple and ultra-high speed operation is possible. However, as can be seen from FIG. 1, since an optical signal is emitted from the upper part of the substrate 1 between the paired electrodes 2 and 2, the light is emitted to the exposed portion of the semiconductor without the finger-shaped portions 2a. Irradiation causes the electrons to be excited and detected as a current. However, since the optical signal of the finger-shaped portion 2a is blocked by the electrode metal, it does not reach the semiconductor. In this portion, there is no excitation of electrons and it does not contribute to the output current. As a result, the photoelectric conversion efficiency of this device is reduced. To increase efficiency, the finger-shaped part 2 of the electrode 2
It is sufficient to make a thin, but if this is done, the electric field is less likely to be applied and the resistance of the finger-shaped portions 2a becomes large, so the electrical energy converted from light is converted into heat energy, and as a result, conversion is performed. It will appear as a decrease in efficiency.

In order to avoid this, a method of irradiating an optical signal from the back surface of the substrate is used. However, in order for the optical signal to affect the Schottky junction characteristics, it is necessary to irradiate the semiconductor near the electrode where the electric field strength is high. Therefore, when the substrate 1 is thick, light is attenuated near the irradiation surface,
It does not reach near the electrode 2 on the back surface. For this reason, a method is employed in which a hole is dug on the back surface of the substrate to a portion just below the electrode on the surface by etching, and the substrate is processed so that the light hits the hole. However, this method not only complicates the process but also requires access to an electric signal on one side of the chip and an optical signal on the back side, which also complicates the mounting side, resulting in poor productivity and high cost. There was a big problem.

[0006]

SUMMARY OF THE INVENTION The present invention is a simple manufacturing method in which the deterioration of the photoelectric conversion efficiency due to the shielding of the light irradiation surface by the electrodes and the increase of the electrode resistance of the finger-shaped portions of the electrodes is prevented. It realizes an MSM PD that can be configured based on the technology and simple mounting technology.

[0007]

In the semiconductor light receiving element of the present invention, a counter-type counter electrode for forming a junction and a take-out electrode continuous with the counter electrode are provided on a substrate so that the counter-type counter electrode contacts the counter-type counter electrode. A semiconductor thin film made of a crystal or polycrystal is formed on the back surface, whereby a Schottky junction is formed between the counter-type counter electrode and the semiconductor thin film, and the back surface of the semiconductor thin film which is not in contact with the counter-type counter electrode. It is characterized in that an optical signal is received from a direction, and a current accompanied therewith is obtained as an output signal from the extraction electrode.

Here, the lead-out electrode is a first lead-out electrode integrated with the counter-type counter electrode formed on one surface of the semiconductor thin film, and at least one pair formed on the substrate. A second lead-out electrode of the semiconductor thin film, and the first lead-out electrode on the semiconductor thin film and the second lead-out electrode on the substrate are in contact with each other. The back surface of the semiconductor thin film may be a light receiving surface.

A space may be provided between the counter electrode and the substrate.

Further, the counter type counter electrode and the take-out electrode may be installed on a substrate, and the semiconductor thin film may be laminated thereon.

The method of manufacturing the semiconductor light receiving element is
A lift-off etching layer having an extremely high etching rate for a specific solution is epitaxially grown on a first substrate, and a semiconductor thin film for mounting a device is epitaxially grown thereon, and an electrode is formed on the surface of the semiconductor thin film. To form a Schottky junction, and thereafter, the etching layer is etched with the specific solution, the semiconductor thin film having the Schottky junction is peeled from the first substrate, and the semiconductor thin film is previously formed into another device. It is characterized in that it is adhered onto a second substrate on which is mounted so that the electrodes come into contact with the second substrate.

More specifically, the method of manufacturing the semiconductor light receiving element is a method of forming the MSM PD by using a so-called epitaxial lift-off technique. That is, for example, a lift-off etching layer made of AlAs is epitaxially grown on a GaAs substrate, a device mounting layer for PD is epitaxially grown thereon, and a Schottky junction is formed on the surface of the device mounting layer. After the device was constructed, the Al was treated with hydrofluoric acid.
The As layer is etched and the device layer is peeled off as a film. Then, the film is MSM-coated onto a substrate on which other devices such as an amplifier and a reproduction identification circuit are mounted in advance.
The electrodes are bonded so that the electrode part of the substrate comes into contact with the substrate and thus the peeled surface appears on the surface. At this time, the arrangement is such that the extraction electrode of the MSM PD and the electrode on the substrate are in contact with each other, the finger-shaped portions of the MSM PD electrode are not in direct contact with the substrate, or they are laminated on the substrate. Make contact with a thin film made of a material having a low dielectric constant. With such a structure, it is possible to irradiate the signal light from the etching surface portion at the time of lift-off. That is, considering the conventional example in which the electrodes do not block, irradiation from the back surface direction is possible.

[0013]

With the above-described structure, in the device of the present invention, even if the signal light is incident on the substrate surface, the signal light is emitted from the portion of the etching surface at the time of lift-off, that is, from the direction not blocked by the electrode. Moreover, since the film thickness of the film can be selected from several 1000 A to several μm or more, a region where the electric field strength in the vicinity of the finger-shaped portions of the electrodes is relatively large can be selected as the light incident point. Therefore, it is not necessary to thin the substrate by etching as in the conventional example. Also, from the viewpoint of device characteristics, there is no problem of light shielding, there is no need to reduce the width of the finger-shaped portion of the electrode, and there is no loss due to electrode resistance, so it is possible to have a large conversion efficiency. is there. Further, since the low dielectric constant film or air is arranged under the finger-shaped portions of the electrodes, and the thin film thickness of the semiconductor, the electric field is concentrated in the interaction region with light. As a result, there is a feature that the deterioration of the high frequency characteristics due to the extra capacitance is small.

The present invention is different from the conventional one in that it has extra steps of the epitaxial growth of the thin film and the lift-off process, but the substrate on which the thin film is initially mounted can be repeatedly used, and the thin film growth is also a mass production technique. Therefore, the film lift-off and the step of attaching the film to the mounting substrate can be mass-produced by a new method, which is not a technical or cost problem. According to the present invention, since the manufacturing is realized not in a continuous process but in separate processes, non-defective products can be combined with each other after inspecting the devices on the film and the mounting substrate, and thus the product yield can be significantly increased. It is possible to improve. Further, in the present invention, the element on the mounting film may be a state in which not only the MSMPD alone but also a compound semiconductor circuit such as GaAs is mounted, and the technology has a great degree of freedom of application range. There is.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings.

(Embodiment 1) FIGS. 2A and 2B show a first embodiment of the present invention. In the figure, S1 is a substrate on which the device is mounted, 2 and 2 are interdigital electrodes, and 2a is a finger-shaped portion thereof. Reference numerals 3 and 3'represent first and second extraction portions of the electrode, A is an antireflection film, and F is an epitaxial lift-off semiconductor film.

2A shows a top view taken along the line AA in FIG. 2B, and FIG. 2B shows a side view of the element. In this embodiment, interdigital electrodes 2 and 2 are arranged on a thin semiconductor film F, and the electrodes 2 and 2 are formed on the substrate S1 so that the surface on which the electrodes 2 and 2 face the substrate S1 holding the device. It has a structure in which the second extraction electrode 3'and the (first) extraction portion 3 of the interdigital electrode 2 are in contact with each other. An antireflection surface is disposed on the surface opposite to the bonding surface of the film F (upper surface in FIG. 6B), and the film is non-reflective so as to be received in the film so as to receive an optical signal from the upper surface of the element. Has become. The film F has a structure in which the finger portions 2a of the interdigital electrodes 2 face the substrate 1 with a gap.

The material of the semiconductor of the film F is a compound semiconductor such as GaAs in this embodiment, and the film thickness thereof is on the order of dimensions such as the line / space of the interdigital electrode 2. In principle, the material of the electrode 2 may be any material as long as it has good Schottky diode characteristics with the semiconductor 1. The material of the substrate S1 may be a semiconductor such as Si, a compound semiconductor similar to that of the film F, or any material such as piezoelectric material / magnetic material / glass / dielectric material.

As described in the conventional example, the basic operation of the MSM PD having such a structure is that an optical signal is incident from the surface of the substrate 1 with a bias applied to both terminals of the interdigital electrode 2. (However, the wavelength of light is shorter than the absorption edge wavelength determined by the band gap of the semiconductor and has a large energy.) Electrons are excited in accordance with the incident optical signal. The excited electrons are accelerated by the bias electric field, flow through the semiconductor, tunnel through the junction, or cross the barrier to be extracted as a current to the interdigital electrode 2. Since the number of excited electrons increases according to the light intensity and the current increases, an operation of converting an optical signal into an electric signal is performed.

In this structure, air is arranged below the finger-shaped portions 2a, and the semiconductor film F
Has a small film thickness. Further, a material having a small relative dielectric constant can be selected as the substrate material. For these reasons, the applied electric field is concentrated in the region of interaction with light, and the extra capacitance is reduced. This shows that the high frequency characteristics of this element are excellent.

(Embodiment 2) Here, FIGS. 3A to 3H.
An example of the manufacturing process of the element having the structure shown in the first embodiment is shown in FIG.

FIG. 3 schematically shows an example of the procedure of the manufacturing process of the embodiment of the present invention shown in FIG. 2 and a sectional view of the device at each step. This process basically applies a technique known as epitaxial lift-off. This technique aims to realize a monolithic device by individually building near-ideal devices on a perfect crystal and then laminating this laminated body on a substrate. With this technology, AlAs
Since the etching rate of hydrofluoric acid is extremely high, which is about 10 7 compared to other materials such as GaAs, the lower layer is thin (10 n
(about m to 50 nm) AlAs is inserted, and a layer for realizing a device is grown thereon. After device formation (or in the middle of formation or before formation), AlA is formed by wet etching with hydrofluoric acid.
s is eluted and the layer above the AlAs layer is taken up (lifted off). This lift-off operation avoids damage to the membrane due to bubbles emerging during lift-off.
Select the etching conditions that do not cause a violent reaction,
Also, since technology that applied apiezon wax to the surface of the release film before lift-off and used the stress caused by it to escape the bubbles that came out, it became fully usable. The thickness of the lifted-off film depends on the structure of the device and the presence / absence of a buffer layer.
Usually, it is about several 100 nm to several μm, and the dimension is 1
It can be up to about 2 cm. There is also a method of using an adhesive to attach the film to the substrate, but from the viewpoint of preventing contamination of the substrate, ensuring flatness, etc., the method of using an adhesive is not preferable, and adhesion by Van der Waals force is most suitable. It is a method. Conventionally, there is a demand for thinning a chip on which a device is mounted by etching in a power device and the like.Therefore, a method of scraping a substrate by mechanical polishing is adopted. There is a limit (100 μm order). Although there is a method of melting the entire substrate by etching, it is not a practical method due to the complicated process. On the other hand, although the lift-off method is a method based on a simple technique called lift-off, there is almost no damage to the device by lift-off, and there is no problem of defects such as a film formed by epitaxial growth. Moreover, since the film thickness is extremely small, it is possible to perform an integrated circuit process after the attachment.

In the figure, S0 is the film F to be lifted off.
Of the compound semiconductor substrate, LF is an etching layer for lift-off, W is a stress applying film, CF1,
CF2 is a carrier sheet for moving the film.

As shown in the figure, first, the compound semiconductor substrate S0
AlAs as etching layer LF during lift-off
Are grown epitaxially. This etching layer L
A semiconductor film substrate F is epitaxially grown on F as a device layer. Then, the interdigital electrode 2 is formed on the substrate F to form the MSM PD (step (a)), and then the LF at the time of lift-off is formed.
A stress-applying film (wax film) W is attached so that the film F is not destroyed by the air bubbles generated with the etching. The wax film W plays a role of releasing bubbles to the outside as a result of the film F being warped as the etching progresses and the film F is warped (step (b)). Then have elasticity,
In addition, the carrier sheet CF1 having a hole through which etching and air bubbles can freely move up and down is adhered. The carrier sheet CF1 has a structure in which small holes are formed in a polymer film such as polyimide. Therefore, the sheet has elasticity and can absorb the strain applied to the sheet even if it is distorted. The size of the hole and the film thickness are not specified, but the size must be less than a fraction of the film size because the film to be peeled must be supported. Can be as thin as it can be mechanically handled as a film. In the case of a polymer film, a size of about several μm will be possible (step (c)). When the laminated product in this state is dipped in an etching solution composed of a thin aqueous solution of hydrofluoric acid to dissolve and remove AlAs (LF), the semiconductor film F is lifted off while being adhered to the carrier sheet CF1 (step (d)). In this state, the other carrier CF2 is attached to the lifted-off surface side of the semiconductor film F (step (e)). When immersed in an organic solvent in this state, the stress imparting film W is dissolved, the carrier sheet CF1 is removed, and the surface of the semiconductor film F can be cleaned (step (f)). Next, a lead-out electrode 3'for the interdigital electrode 2 is formed at a predetermined position on the S1 substrate constituting the device, and the lead-out electrode 3 of the electrode 2 and the connection lead-out electrode 3'are aligned so that their positions overlap. , And adhere (steps (g) and (h)). As the bonding method, there are various methods such as utilizing adsorption by van der Waals force, fusing by interposing the metals of the extraction electrodes 3, 3'or low-melting metal between them, or bonding with a conductive adhesive. It is possible. Finally, the device is completed by attaching the antireflection film A to the region where the optical signal is incident.

(Embodiment 3) Various modifications can be made without changing the basic idea of the present invention, and this embodiment is one of them. As shown in FIGS. 4A and 4B, in this embodiment, the interdigital electrodes 2 are connected to the semiconductor film F as shown in FIGS.
Instead of being configured above, it is arranged on the substrate S1 in advance, and the semiconductor film F is covered and pressure-welded on the substrate S1. The semiconductor film F may be in a state in which no electrode is attached, or in the state in which an electrode is attached also to the semiconductor film F side. Even with such a structure, it is clear that a device similar to that shown in FIG. 2 can be realized if consideration is given to complete connection between the electrode and the film.

(Fourth Embodiment) FIG. 5 shows a third embodiment of the present invention. In this embodiment, an insulating film I having a small dielectric constant is arranged on the surface of the substrate S1, and a film-shaped photodiode (PD) including an interdigital electrode 2, a semiconductor film F and an antireflection film A is arranged thereon. Is. In this case, the electrode capacitance can be reduced and high speed operation becomes possible. The principle of operation and the characteristics obtained match the characteristics of the device shown in FIG.

(Embodiment 5) The fourth embodiment shown in FIG. 6 is characterized in that a mirror M is arranged immediately below the light receiving portion of the PD of the embodiment 3 shown in FIG. The mirror M may be made of any material such as a metal or a semiconductor superlattice as long as the material efficiently reflects an optical signal. In this example, the light not absorbed by the semiconductor film F is transmitted from the finger-shaped space portion of the interdigital electrode 2 to the substrate S1.
This is an example in which the conversion efficiency is further increased by reflecting the light leaking in the direction and returning it to the semiconductor film F again. (Embodiment 6) FIG. 7 shows a fifth embodiment of the present invention. In this embodiment, the semiconductor film F is arranged only on the light receiving portion of the interdigital electrode 2, and in this case, there is an advantage that the electrostatic capacity can be reduced.

In each of the above embodiments, the semiconductor film was manufactured by the epitaxial lift-off method. However, any semiconductor film having a similar structure may be used, for example, a thin film on a foreign semiconductor. May be grown, a device may be produced on it, and the substrate itself may be melted away. Also, for polycrystalline semiconductors,
Since there is no requirement for epitaxial growth, a method of forming a polycrystalline film on an organic material such as a resist or an amorphous material such as glass and peeling it together with the device structure may be used.

Although the electrode structure has been described as an interdigital type, it is clear that it is not necessary, and any structure of the counter type electrode may be used.

[0030]

As described above, according to the present invention,
An optical signal is not blocked by the electrodes, the electrode resistance does not increase, and therefore the conversion efficiency is high, and the MSM PD with excellent high-frequency characteristics can be used under a simple process with a small capacitance. realizable. Further, the present invention can be realized in a monolithic form on a different substrate or on another substrate on which other electronic circuits and optical circuits are formed.

[Brief description of drawings]

FIG. 1 shows a conventional example of MSM PD, in which (a) is a plan configuration diagram and (b) is a side sectional view.

2A and 2B show a first embodiment of the present invention, in which FIG. 2A is a plan configuration view taken along line AA of FIG. 2B, and FIG. 2B is a side sectional view of the device of the present invention. .

FIG. 3 shows a second embodiment of the present invention, in which (a)-
(H) is a side sectional view of the device for explaining each manufacturing process of the device of the present invention.

4A and 4B show a third embodiment of the present invention, wherein FIG. 4A is a plan configuration diagram showing a partially exfoliated state of the device of the present invention, and FIG. 4B is a side sectional view of the same device. .

FIG. 5 shows a fourth embodiment of the present invention and is a side sectional view of the device of the present invention.

FIG. 6 shows a fifth embodiment of the present invention and is a side sectional view of the device of the present invention.

FIG. 7 shows a sixth embodiment of the present invention, (a) is a plan configuration view of the present invention device, and (b) is a side sectional view.

[Explanation of symbols] Substrate on which S1 device is mounted 2 Counter electrode (interdigital electrode) of MSM PD 2a Finger-shaped portion of counter electrode 3,3 'Electrode take-out portion A Antireflection film F Epitaxial lift-off semiconductor film S0 Liftoff The compound semiconductor substrate on which the film F is produced LF The etching layer when lifted off W The stress imparting film CF1, CF2 The carrier sheet for moving the film I The low dielectric constant insulating film M Mirror

Claims (5)

[Claims] 1. A counter-type counter electrode for forming a junction and an extraction electrode continuous with the counter electrode are provided on a substrate, and a semiconductor thin film made of a crystal or a polycrystal is formed so as to contact the counter-type counter electrode. As a result, a Schottky junction is formed between the counter type counter electrode and the semiconductor thin film, and an optical signal is received from the back surface direction which is not in contact with the counter type counter electrode of the semiconductor thin film, and the accompanying current is generated. A semiconductor light receiving element characterized in that an output signal is obtained from the extraction electrode. 2. The first extraction electrode, wherein the extraction electrode is integrated with the counter-type counter electrode formed on one surface of the semiconductor thin film, and at least one pair of electrodes formed on the substrate. A second lead electrode, a first lead electrode on the semiconductor thin film and a second lead electrode on the substrate.
2. The semiconductor light receiving element according to claim 1, wherein the semiconductor thin film and the substrate are adhered to each other so that the extraction electrodes of the semiconductor thin film contact each other, and the back surface of the semiconductor thin film serves as a light receiving surface. 3. The semiconductor light receiving element according to claim 2, wherein an air gap is provided between the counter electrode and the substrate. 4. A semiconductor light receiving element, wherein the counter type counter electrode and a take-out electrode are provided on a substrate, and the semiconductor thin film is laminated thereon. 5. A lift-off etching layer having an extremely high etching rate for a specific solution is epitaxially grown on a first substrate, and a semiconductor thin film for device mounting is epitaxially grown on the lift-off etching layer. An electrode is formed on the surface to form a Schottky junction, and then the etching layer is etched with the specific solution, the semiconductor thin film having the Schottky junction is peeled off from the first substrate, and the semiconductor thin film is removed. A method for manufacturing a semiconductor light receiving element, comprising: adhering the electrode on a second substrate on which another device is preliminarily mounted so that the electrode comes into contact with the second substrate.