JPH0740603B2 - Method for manufacturing semiconductor device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a semiconductor device in which an optical semiconductor element such as a light emitting element or a light receiving element and an electronic element are integrally formed.

[Technical background of the invention and its problems]

A so-called integrated optical device in which a light emitting / receiving device such as a semiconductor laser (LD), a light emitting diode (LED), and a photodetector and an electronic device such as a FET and a bipolar transistor are monolithically integrated on the same substrate is Performance improvement due to high-speed operation, reliability improvement due to integration,
Since it has many advantages such as cost reduction, its realization in the field of optical communication is desired. In addition, with the increase in speed of semiconductor electronic devices, the signal transmission delay between high-density integrated LSI chips is becoming non-negligible. For this reason, monolithically integrating optical semiconductor devices on an LSI chip and performing signal transmission between chips by optical signals instead of electrical signals is an extremely effective means for increasing the speed of a logical operation circuit. From this point of view, it is strongly desired to realize a technique for monolithically integrating a light emitting / receiving device on the same substrate as an electronic device.

However, the Si substrate on which electronic devices are formed and the direct transition type GaAs, GaA that constitutes the light emitting and receiving devices.
Since the lattice constant is remarkably different from that of the compound semiconductor mixed crystal such as lAs, InP, InGaAsP and InGaAs, it is extremely difficult to obtain the above compound semiconductor mixed crystal of high quality on the Si substrate by the epitaxial growth method. That is, since the lattice constants of the two are different, lattice defects such as dislocations are introduced at a high density at the crystal growth interface, and these penetrate into the epitaxial growth layer together with the crystal growth, and as a result, they act as non-radiative coupling centers. In the light emitting / receiving device, the luminous efficiency and the light receiving sensitivity are deteriorated and the device life is deteriorated, which has a fatal adverse effect on the device characteristics. This is a major obstacle in integrating the light emitting / receiving device with the electronic device on the same substrate.

On the other hand, a conventional hybrid integrated circuit in which a semiconductor substrate on which an electronic device is formed and a semiconductor substrate on which a light emitting / receiving device is formed are laminated and integrated via electrodes can be easily realized, but in this case the wiring becomes long. Or the electrode area of the contact part becomes large. Therefore, the parasitic capacitance and the inductance are larger than those of the monolithic integrated semiconductor device, and there is a drawback that the original performance of the element cannot be obtained.

[Object of the Invention]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor device that can easily integrate and integrate a light emitting / receiving device and an electronic device without using a conventional epitaxial method. It is to provide a manufacturing method of.

[Outline of Invention]

The essence of the present invention is to form a light emitting / receiving device formed of a compound semiconductor mixed crystal or the like on a semiconductor substrate having a lattice constant extremely close to that of the light emitting / receiving device, and to bond it to a semiconductor substrate suitable for forming an electronic device. Thus, the light emitting / receiving device and the electronic device are integrated and integrated.

The inventors of the present invention have found that two different types of crystal bodies, for example, a compound semiconductor mixed crystal substrate surface on which a light emitting / receiving device is formed and a Si substrate surface suitable for forming an electronic device have a surface roughness of 500.
In the case of flat surfaces of [Å] or less, after washing and drying those surfaces, for example, in a clean room with a dust floating amount of 20 [pieces / m ³ ] or less, substantially no foreign matter is present between the flat surfaces. It has been found that the two crystals are strongly bonded by bringing them into close contact with each other and heating at a temperature of 200 [° C.] or more under the condition of not intervening.

Conventionally, when mirror-polished semiconductor wafers are brought into contact with each other in a wet state with water, alcohol or the like, a phenomenon in which the two adhere to each other is often experienced. However, this is due to the surface tension of liquids such as water and has not been observed on dried wafers. The inventors of the present invention have made the surface of a compound semiconductor such as GaAs, InP or the like, which has been mirror-polished, or silicon surfaces sufficiently clean, and when two surfaces of the same kind or different kinds are brought into contact with each other under a highly clean atmosphere, a strong bond is obtained. It was found that the body can be obtained. Furthermore, it has been found that a heat treatment of 200 [° C.] or higher is indispensable in order to sufficiently enhance the adhesive strength of the bonded body thus obtained. As a result of further detailed investigation of this adhesion phenomenon, it was found that the formation of a natural oxide film on the surface of these crystals is an essential condition for adhesion. The presence of this natural oxide film is confirmed by, for example, a method such as ellipsometry, but more simply, it can be easily determined by placing a water droplet on the cleaned surface and spreading it. That is, the change of the surface from volatile to hydrophilic is evidence of the existence of a natural oxide film. This natural oxide film is formed under various conditions, but according to the experiments conducted by the present inventors, a normal water washing step of at most several minutes was sufficient.

While the wafers thus obtained having hydrophilic and normal surfaces can be easily bonded to each other, the natural oxide film is removed by immersing it in hydrofluoric acid or the like so that the natural oxide film is not formed again. After careful handling, an attempt was made to adhere to the surface having a water-repellent surface, but it was found that a sufficient adhesive body could not be obtained. Also, to obtain sufficient adhesive strength
It is considered that the reason why the heat treatment of 200 [° C.] or more is necessary is that active OH groups existing on the surface of the natural oxide film react around this temperature to form a strong bond of semiconductor-O-semiconductor. In addition, it was also confirmed that the semiconductors bonded in this way are electrically connected.

The present invention focuses on such a point, and in a method of manufacturing a semiconductor device including an optical semiconductor element such as a light emitting element and a light receiving element and an ordinary electronic element, a semiconductor light emitting element or a semiconductor is provided on the front surface side of a first semiconductor substrate. Forming a light receiving element and flattening the surface side thereof, forming an electronic element on the surface side of the second semiconductor substrate and flattening the surface side thereof, and then washing the flattened flat surface with water and then drying; Then, in a clean atmosphere, directly attach the above flat surfaces to each other, and
This is a method in which each substrate is bonded by heat treatment at a temperature of [° C.] or higher.

〔The invention's effect〕

According to the present invention, since the light emitting / receiving device and the electronic device can be manufactured by independent processes, the manufacturing thereof becomes extremely easy. Further, since the characteristics of each element can be optimized, the element performance after integration can be greatly improved as compared with the conventional monolithic optoelectronic integrated semiconductor device. Further, since the bonding surface is a mirror-polished surface, there is no convex portion of the electrode or the insulating film on the upper portion, and the bonding is easy. Moreover, since there is no unnecessary electrode on the adhesive surface, the parasitic capacitance can be reduced. This effect is particularly remarkable when a semi-insulating substrate is used.

Further, since it is possible to integrate and form a compound semiconductor mixed crystal emitting / receiving device, which is suitable for forming an electronic device, for example, on a Si substrate and formed on another substrate, without using the conventional epitaxial growth method, the lattice constants of both are significantly increased. Even if they are different, a light emitting / receiving device can be formed of a good crystal, and the characteristics of these devices are not deteriorated. Therefore, it is possible to form them on a substrate suitable for each of the light emitting / receiving device and the electronic device without being affected by the difference in lattice constant, and it is possible to improve the characteristics of the light emitting / receiving device-electronic device integrated device and to combine them. The range of application can be expanded by expanding the degree of freedom in alignment. As a result, the effects on the fields of optical communication and computers using these devices are enormous.

Example of Invention

First, before describing the embodiments, the basic principle of the present invention will be described.

Conventionally, it is known that when the smooth surface of a glass plate is kept extremely normal and such two glass plates are directly brought into close contact with each other, the friction coefficient between them is increased and a bonded state is obtained. It is also known that when the surfaces of the glass plates are slid against each other, cracks are generated due to the peeling of the bonding surface. On the other hand, it has been difficult to keep the smoothness and the cleanliness of the surfaces of the semiconductor crystals to be bonded strictly because the bonding method of the above-mentioned glass of semiconductor crystals is not known. It can be said that it was the biggest cause.

Therefore, the present inventors have found that the semiconductor crystal members can be bonded to each other like the glass members by performing the following process. That is, the surfaces to be joined of the two semiconductor crystal bodies are smoothed to have a surface roughness of 500 [Å] or less, and 5
It was washed with water for a minute. The smoothing method is a mirror-polished method or a method that does not impair the flatness on the mirror-polished surface, such as MOCV.
The epitaxial growth layer is formed by the D method or the MBE method. It was presumed that the surface of the obtained semiconductor was well wetted with water and a layer of natural oxide was formed. After that, methanol replacement and freon drying are performed, and the semiconductor crystal bodies thus obtained are directly adhered to each other in the above-mentioned bonding surface in a substantially dust-free clean room with a dust floating amount of 20 [pieces / m ³ ]. Then, when heat-treated at a temperature of 200 [° C.] or higher, the two were extremely strongly bonded. The adhesive strength of this bonded body increases remarkably at a heat treatment temperature of 200 ° C. or higher.

From the above, the surface of a clean, polished semiconductor becomes hydrophilic only by washing with water, and the surface becomes 200 [° C] in a clean environment.
If bonded under the above temperature, an adhesive body can be strongly obtained.

On the other hand, at a heating temperature of about 200 ° C., it is well known that the diffusion rate in a semiconductor crystal is usually small enough to be ignored, not only for the semiconductor constituent atoms but also for the most easily diffused monovalent ions.

It is also known that at a temperature of around 200 [° C.], most of the water molecules adsorbed on the surface of the oxide film are desorbed, and the dehydration bond of the —OH group formed by chemisorption starts to occur. Considering these facts, the mutual bonding of the semiconductor crystal bodies is not due to mutual diffusion known as metal-metal bonding, but the interaction between hydrated layers of the surface oxide film of the semiconductor crystal body, It is considered that a strong junction structure of semiconductor-OH-semiconductor is formed by dehydration polymerization of OH groups.

This fact makes the surface of the semiconductor crystal hydrophilic,
If heat treatment of 200 [℃] or more is performed after the close bonding,
This means that high adhesive strength can be obtained.

Hereinafter, the details of the present invention will be described with reference to the illustrated embodiments.

1A to 1E are a perspective view and a side view showing a manufacturing process of a semiconductor device according to an embodiment of the present invention. In this embodiment, a GaAlAs semiconductor laser and an electronic device are integrated and monolithically formed.

First, as shown in FIG. 1 (a), the upper surface of the N-GaAs substrate 11 is mirror-polished to have a surface roughness of 500 [Å] or less, and then the substrate 1
N-Ga _0.65 Al _0.35 As cladding layer 12, undoped GaAs on 1
Active layer 13, P-Ga _0.65 Al _0.35 As cladding layer 14 and N-GaAs
The contact layer 15 is sequentially grown and formed. At this time, it is preferable that the growth layer is grown and formed by the MOCVD method or the MBE method so as not to impair the flatness of the initially mirror-polished substrate surface.

Then, using SiN as a mask, Zn diffusion is performed on the surface of a stripe-shaped portion having a width of about 5 [μm] as shown in FIG.
The GaAs contact layer 16 is formed. This is the GaAs active layer 13
It is for narrowing the current flowing through the stripes.

Then, using the photoresist as a mask, BCl ₃ + Cl ₂
First by reactive ion etching method with mixed gas
As shown in FIG. 3C, the resonator end face 18 is formed perpendicular to the current stripe (P-type contact layer) 16 and the unnecessary portion is removed by etching. As a result, the semiconductor laser substrate 10 is formed.

Next, as shown in FIG. 1 (d), the surface of the Si substrate 19 suitable for manufacturing an electronic device is mirror-polished to have a surface roughness of 500 [Å] or less, and the semiconductor laser substrate 10 is manufactured by the procedure described above. I glued it. The heat treatment was performed at 500 [° C.] in H ₂ atmosphere for 1 hour. Further, as the Si substrate 19, a substrate whose surface is P-type conductive by ion implantation or diffusion of an appropriate impurity such as B is used. Thus, a GaAs-GaAlAs semiconductor laser can be obtained on the Si substrate 19.

The electronic device formed on the Si substrate 19 is preferably formed in advance before the above-mentioned bonding step. If necessary, the N-GaAs substrate 11 is finally removed by using an etching solution such as NH ₄ —H ₂ O ₂ —H ₂ O system as shown in FIG. 1 (e). Good.

In the semiconductor device thus obtained, a semiconductor laser
No. 10 showed good characteristics, and the P-GaAs contact layer 16 and the surface of the P-type Si substrate 19 showed good electric transfer characteristics.
Therefore, according to this embodiment, the semiconductor laser and the ordinary electronic device can be formed monolithically, and the characteristics can be the same as those obtained when the semiconductor laser and the electronic device are individually manufactured. Therefore, the characteristics of the integrated device of the semiconductor laser electronic device can be improved and the degree of freedom in combination can be increased, and the effect on the field of optical communication is great.

2A to 2H are cross-sectional views showing the manufacturing process of a semiconductor device according to another embodiment. In this example, InGaAs
P-based semiconductor laser and GaAs-based MESFET driving this laser
It is an integrated integration of and.

First, as shown in FIG. 2 (a), a recess 22 is formed on the surface of a semi-insulating InP substrate 21, and in this recess 22, as shown in FIG. 2 (b), P ⁺ -In _1-u Ga _u AS _v P _1-v electrode extraction layer 23, P-InP clad layer 24, undoped In _1-x Ga _x AS _y P _1-y active layer 25 and N-
The InP clad layer 26 is sequentially grown and formed.

Next, as shown in FIG. 2 (c), the cladding layers 24, 26 and the active layer 25 are mesa-etched except for the laser oscillation region portion, and then the side portions of the mesa are N-InP as shown in FIG. 2 (d).
The buried layer 27 and the P-InP buried layer 28 were buried. Next, as shown in FIG. 2 (e), all unnecessary portions in the recess 22 are removed by mesa etching, and finally an ohmic electrode 29 is formed on the P ⁺ -type electrode extraction layer 23. As a result, the semiconductor laser substrate 20 is formed.

Here, the height of the growing mesa portion is adjusted to be substantially the same as the outside of the concave portion 22, and the same height is obtained by the final mirror polishing. Although not shown in the figure, in order to carry out polishing lastly, a protective film is to be attached to the semiconductor laser substrate and the electronic element substrate described later on the element main portion in the recess before polishing if necessary. .

On the other hand, a recess 32 is formed on the semi-insulating GaAs substrate 31 as shown in FIG.
The mold active layer 33 is formed. Then, as shown in FIG. 2 (g), a gate Schottky electrode 34 is formed on the upper portion of the FET channel, and an N ⁺ type region 35 is formed by ion implantation using the gate electrode as a mask to form a source electrode 36. This allows
The electronic device substrate 30 will be formed.

When the surfaces of the bases 20 and 30 manufactured as described above are mirror-polished, washed with water and aligned and then pressure-bonded by the procedure described above, the two bases become an integrated semiconductor device. Here, the mirror polishing was performed under the condition that the surface roughness was 500 [Å] or less, and the heat treatment was performed in an H ₂ atmosphere at 500 [° C] for 1 hour.

Since the semiconductor device thus manufactured has a simple manufacturing method, the manufacturing yield and reliability are high, and the characteristics of the semiconductor laser and the electronic device can be optimized respectively. Further, since the connection wiring between the N-InP clad layer 26 of the semiconductor laser and the N ⁺ type layer 35 of the electronic device is unnecessary, and the structure in which the parasitic capacitance and the like can be reduced, high performance is achieved.

The present invention is not limited to the above-mentioned embodiments. For example, as the light emitting / receiving device, a light emitting diode, a PIN photodiode, an avalanche photodiode, or the like can be used instead of the semiconductor laser, and the material thereof is GaAs / GaAlAs, InP /
In addition to III-V compound semiconductors such as InGaAsP, HgCdTe, ZnS, Z
It is also applicable to II-VI group compound semiconductors such as nSe. Similarly, as a substrate suitable for forming electronic devices, Si, InP
Besides, a semiconductor such as GaAs can be used. In addition, it is clear that the mirror polishing step may be omitted if the surface of the semiconductor substrate is in a mirror surface state after the elements are formed on the surface. Therefore, the order of the mirror polishing step and the element forming step is interchanged. May be. In addition, various modifications can be made without departing from the scope of the present invention.

[Brief description of drawings]

1 (a) to 1 (e) are perspective views and side views showing a manufacturing process of a semiconductor device according to an embodiment of the present invention, and FIGS. 2 (a) to 2 (h) are semiconductors according to another embodiment. It is sectional drawing which shows the manufacturing process of an apparatus. 10 ... Semiconductor laser substrate, 11 ... N-GaAs substrate, 12 ... N-Ga
AlAs clad layer, 13 ... Undoped GaAs active layer, 14 ... P-
GaAlAs cladding layer, 15 ... N-GaAs contact layer, 16 ... P
-GaAs contact layer, 18 ... Resonator end face, 19 ... Si substrate, 20
... semiconductor laser substrate, 21 ... semi-insulating InP substrate, 22 ... recess, 23 ... P ⁺ -InGaAsP electrode extraction layer, 24 ... P-InP clad layer, 25 ... undoped InGaAsP active layer, 26 ... N-InP clad layer, 27 ... N-InP buried layer, 28 ... P-InP buried layer,
29 ... Ohmic electrode, 30 ... Electronic device base, 31 ... Si substrate, 32 ... Recess, 33 ... N type active layer, 34 ... Schottky electrode, 35 ... N ⁺ type region, 36 ... Source electrode.

Claims (6)

[Claims] 1. A step of forming a semiconductor light emitting element or a semiconductor light receiving element on the front surface side of a first semiconductor substrate and flattening the front surface side, and forming an electronic element on the front surface side of a second semiconductor substrate. And the step of flattening the surface side, the step of washing the flattened flat surface with water and then drying, and then directly bonding the flat surfaces under a clean atmosphere, and in this state
And a step of adhering the substrates to each other by heat treatment at a temperature of 200 ° C. or higher. 2. The semiconductor device according to claim 1, wherein the step of flattening comprises mirror-polishing the surface side of the substrate to a surface roughness of 500 [Å] or less after forming the element. Production method. 3. The semiconductor device according to claim 1, wherein the step of planarizing is mirror-polishing the surface of the substrate to have a surface roughness of 500 [Å] or less before forming the element. Production method. 4. The flattening step is to form the epitaxial growth layer on the polished surface by the MOCVD method or the MBE method after the mirror surface polishing.
Item 7. A method for manufacturing a semiconductor device. 5. The clean atmosphere means that the amount of dust floating is 20.
The method of manufacturing a semiconductor device according to claim 1, wherein the atmosphere is not more than [pieces / m ³ ]. 6. The semiconductor device according to claim 1, wherein part or all of the first semiconductor substrate is removed after the flat surfaces are bonded by the heat treatment. Production method.