JP2747232B2 - Semiconductor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to 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. 2. Description of the Related Art Light emitting and receiving devices such as a semiconductor laser (LD), a light emitting diode (LED), and a photodetector, and an FE
A so-called integrated optical device, in which electronic devices such as T and bipolar transistors are monolithically integrated on the same substrate, is capable of improving performance by increasing the operation speed.
Since it has many advantages such as reliability improvement and cost reduction due to integration, it is desired to realize it in the field of optical communication. Also, with the speeding up of semiconductor electronic devices, signal transmission delay between LSI chips integrated at a high density cannot be ignored. Therefore, it is extremely effective to monolithically integrate an optical semiconductor device on an LSI chip and perform signal transmission between the chips by an optical signal instead of an electric signal in order to increase the speed of the theoretical value arithmetic circuit. . From such a point, it is strongly desired to realize a technology for monolithically integrating the light emitting / receiving device on the same substrate as the electronic device. However, a Si substrate on which an electronic device is formed and GaAs, GaAlAs, InP, InGaAs of direct transition type constituting a light emitting / receiving device.
Since the lattice constant is significantly different from that of a compound semiconductor mixed crystal such as P or InGaAs, it is extremely difficult to obtain a high-quality compound semiconductor mixed crystal on a Si substrate by an epitaxial growth method. That is, since the two have different lattice constants, lattice defects such as dislocations are introduced at a high density at the crystal growth interface, which penetrate into the epitaxial growth layer together with the crystal growth, and act as non-emission coupling centers. Departure
In the light receiving device, the light emitting efficiency and the light receiving sensitivity are reduced, and the life of the device is deteriorated. This is a major obstacle in integrating the light emitting / receiving device on the same substrate as the electronic device. 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 is laminated and integrated via electrodes, but can be easily realized. And the electrode area of the contact portion increases. For this reason, there is a disadvantage that the parasitic capacitance and the inductance are increased as compared with the monolithic integrated semiconductor device, and the inherent performance of the element cannot be brought out. [0005] As described above, conventionally,
If the light receiving device is integrated on the same substrate as the electronic device, the light emitting efficiency and the light receiving sensitivity of the light emitting / receiving device are reduced, and the life of the device is shortened. Further, in 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, parasitic capacitance and parasitic capacitance are lower than those of a monolithically integrated semiconductor device. There is a problem that the inductance becomes large and the original performance of the element cannot be obtained. The present invention has been made in view of the above circumstances, and has as its object to integrate a light emitting / receiving device and an electronic device, and to improve element characteristics. To provide a semiconductor device that can be obtained. The gist of the present invention is to form a light emitting / receiving device formed of a compound semiconductor mixed crystal on a semiconductor substrate having a lattice constant very close to that of the device. An object of the present invention is to integrate a light emitting / receiving device with an electronic device by bonding the semiconductor device to a semiconductor substrate suitable for forming an electronic device. The present inventors have found that two different types of crystals, for example, the surface of a compound semiconductor mixed crystal substrate on which a light emitting / receiving device is formed and the surface of a Si substrate suitable for forming an electronic device,
In the case of flat surfaces having a surface roughness of 50 [nm] or less, those surfaces are washed with water and dried, and then, for example, the dust floating amount 2
In a clean room of 0 [pieces / m ³ ] or less, the two flat crystals are heated to a temperature of 200 ° C. or more by being brought into close contact with each other under the condition that substantially no foreign substance intervenes between the flat surfaces. I found that my body joined tightly. Conventionally, when semiconductor wafers that have been mirror-polished 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 a liquid such as water, and has not been observed on a dried wafer. The present invention is capable of sufficiently cleaning the surface of a mirror-polished compound semiconductor such as GaAs or InP or silicon and firmly bonding two surfaces of the same type or different types under a highly clean atmosphere. I found that I got a body. Furthermore, it was found that a heat treatment at 200 ° C. or more was essential to sufficiently increase the bonding strength of the joined body thus obtained. As a result of further investigating this phenomenon of adhesion,
It has been found that the formation of a natural oxide film on the surface of these crystals is an essential condition for bonding. The presence of the natural oxide film can be confirmed by a method such as ellipsometry, but it can be more 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 presence of a native oxide film. Although this natural oxide film is formed under various conditions, according to the experiments of the present invention and the like, a normal washing step of at most several minutes was sufficient. The thus obtained wafers having a hydrophilic and normal surface can be easily bonded to each other. On the other hand, the natural oxide film is removed by immersion in, for example, hydrofluoric acid or the like, and then the natural acid film is removed again. Care was taken to prevent the formation of the surface, and an attempt was made to bond the surface having a water-repellent surface, but it was found that a sufficient bonded body could not be obtained. Further, the reason why heat treatment at 200 [° C.] or more is necessary to obtain sufficient adhesive strength is that active OH groups existing on the surface of the natural oxide film react around this temperature, and the semiconductor-O-semiconductor Probably to make a strong bond. It was also confirmed that the semiconductors bonded in this manner were electrically connected. The present invention pays attention to such a point, and in a semiconductor device including an optical semiconductor element such as a light emitting element and a light receiving element and a normal electronic element, a semiconductor light emitting element or a semiconductor light receiving element is formed on the surface side; A first semiconductor substrate having a front surface formed in a mirror state; and a second semiconductor formed of a semiconductor material different from the first semiconductor substrate, wherein an electronic element is formed on the front side and the front side is formed in a mirror state. A substrate, and each of the semiconductor substrates has a surface side thereof,
The surface is directly bonded without melting and integrated. According to the present invention, since the light emitting / receiving device and the electronic device can be manufactured by independent processes, the manufacturing becomes extremely easy. In addition, since the characteristics of each element can be optimized, the element performance after integration can be greatly improved as compared with a conventional monolithic optoelectronic integrated semiconductor device. Furthermore, since the bonding surface is a mirror-polished surface, there is no electrode or insulating film projection on the top,
Adhesion is easy. Moreover, since there is no unnecessary electrode on the bonding surface, the parasitic capacitance can be reduced. This effect is particularly noticeable when a semi-insulating substrate is used. Further, a compound semiconductor mixed crystal emitting / receiving device formed on another substrate such as a Si substrate, which is suitable for forming an electronic device, can be formed without using the conventional epitaxial growth method. Even when the constants are significantly different, the light emitting / receiving device can be constituted by good crystals, and the characteristics of these devices do not deteriorate. For this reason, it is possible to form the light emitting / receiving device and the electronic device on a substrate suitable for each of the electronic devices, regardless of the difference in the lattice constant. The range of application can be expanded by expanding the degree of freedom of alignment. As a result, the effect on the fields of optical communication and computers using these devices is enormous. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the embodiments, the basic principle of the present invention will be described. Conventionally, it has been known that when a smooth surface of a glass plate is kept extremely normal and such two glass plates are 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 if the surfaces of the glass plates are slid against each other, cracks may be generated by removing the joint surfaces. On the other hand, the fact that a bonding method such as the above-mentioned glass between semiconductor crystals has not been known is that it has been difficult to strictly maintain the smoothness and cleanliness of the surface to be bonded of the semiconductor crystals. It can be said that it was the biggest cause. Therefore, it has been found that the present invention and the like can perform bonding between semiconductor crystals like bonding between glasses by performing the following treatment. That is, the surface to be joined between the two semiconductor crystals was smoothed to a surface roughness of 50 [nm] or less, and washed with water for 5 minutes. The smoothing is performed by forming an epitaxial growth layer by mirror polishing or a method that does not impair the flatness on the mirror polished surface, for example, MOCVD or MBE. The surface of the obtained semiconductor was well wetted by water, and it was presumed that a natural oxide layer was formed. Thereafter, methanol replacement and Freon drying are performed, and the semiconductor crystals obtained in this manner are directly adhered to each other in a clean room with a dust floating amount of 20 [pieces / m ³ ] substantially free of dust. Let me 200
When heat-treated at a temperature of [° C.] or more, the two were bonded very firmly. The bonding strength of this bonded body was set at a heat treatment temperature of 2
When the temperature is higher than 00 [° C.], the temperature rises remarkably. From the above, the surface of a polished clean semiconductor becomes hydrophilic only by washing with water, and if bonded under a clean environment and at a temperature of 200 ° C. or more, an adhesive can be obtained firmly. Can be. On the other hand, at a heating temperature of about 200 ° C.,
In addition to semiconductor constituent atoms,
It is well known that the diffusion rate of a valence ion in a semiconductor crystal is usually negligibly small. In addition, this 2
At a temperature around 00 [° C.], the water molecules adsorbed on the surface of the oxide film are almost desorbed, and the —OH formed by the chemical adsorption is removed.
It is also known that dehydration of the group begins to occur. Considering these facts, the mutual bonding of the semiconductor crystals is not due to the mutual diffusion known as a joint between metals, but the interaction between the hydrated layers of the surface oxide film of the semiconductor crystal and the -OH Semiconductor -O-
It is considered that a strong bonding structure serving as a semiconductor is formed. This fact means that a high adhesive strength can be obtained by making the surface of the semiconductor crystal hydrophilic and subjecting it to a heat treatment at 200 ° C. or more after the close bonding. Hereinafter, the present invention will be described in detail with reference to the illustrated embodiment. (Embodiment 1) FIGS. 1 and 2 are a perspective view and a side view showing a manufacturing process of a semiconductor device according to a first embodiment of the present invention. In this embodiment, a GaAlAs-based semiconductor laser and an electronic device are integrated and integrated to be monolithically formed. First, as shown in FIG. 1A, n-GaAs
After the upper surface of the substrate 11 is mirror-polished to a surface roughness of 50 [nm] or less, n-Ga _0.65 Al _0.35 As is formed on the substrate 11.
Clad layer 12, undoped GaAs active layer 13, p-
Ga _0.65 Al _0.35 As clad layer 14 and n-GaAs
The contact layers 15 are sequentially grown and formed. At this time, it is desirable that the growth layer be formed by MOCVD or MBE so as not to impair the flatness of the mirror-polished substrate surface. Next, using SiN as a mask, FIG.
As shown in (b), Zn is diffused into the surface of the stripe-shaped portion having a width of about 5 [μm] to form the n-GaAs contact layer 1.
The p-type GaAs contact layer 16 is formed by converting a part of 5 into a p-type. This is for narrowing the current flowing through the GaAs active layer 13 in a stripe shape. Next, using a photoresist or the like as a mask, the cavity end face 18 is made perpendicular to the current stripe (p-type contact layer) 16 as shown in FIG. 1C by a reactive ion etching method using a mixed gas of BCl ₃ + Cl ₂ . And unnecessary portions are removed by etching. Thus, the semiconductor laser substrate 10 is formed. Next, as shown in FIG. 2D, the surface of the Si substrate 19 suitable for manufacturing an electronic device is
Mirror polishing was performed to a thickness of [nm] or less, and the substrate was bonded to the semiconductor laser substrate 10 by the procedure described above. The heat treatment was performed in a H ₂ atmosphere at 500 [° C.] for 1 hour. As the Si substrate 19, a substrate having p-type conductivity by ion implantation or diffusion of an appropriate impurity such as B was used. Thus, a GaAs-GaAlAs semiconductor laser is obtained on the Si substrate 19. It is desirable that the electronic device formed on the Si substrate 19 be formed in advance before the above-mentioned bonding step. If necessary, NH ₄ —H ₂ O ₂ —H ₂ O
As shown in FIG. 2 (e), using an etching solution such as
-The GaAs substrate 11 may be finally removed. In the semiconductor device thus obtained,
The semiconductor laser 10 shows good characteristics and the p-GaAs
The s-contact layer 16 and the surface of the p-type Si substrate 19 exhibited good electric conduction characteristics. Therefore, according to the present embodiment, the semiconductor laser and the ordinary electronic device can be formed monolithically, and the characteristics can be made the same as when the semiconductor laser and the electronic device are each manufactured alone. For this reason, 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 enormous. (Embodiment 2) FIGS. 3 and 4 are cross-sectional views showing steps of manufacturing a semiconductor device according to a second embodiment of the present invention. In this embodiment, an InGaAsP semiconductor laser and a GaAs MESFET for driving the laser are integrated and integrated. First, as shown in FIG.
A recess 22 is formed on the surface of the nP substrate 21 and the recess 22 is formed.
As shown in FIG. 3 (b) within _{^{p + -In 1-u Ga u}} As v
A P _{1 -V} electrode extraction layer 23, a p-InP cladding layer 24,
Sequentially grown and formed an undoped _{In 1-x Ga x As y} P 1-Y active layer 25 and the n-InP cladding layer 26. Next, as shown in FIG. 3 (c), the cladding layers 24 and 26 and the active layer 25 are mesa-etched except for the laser oscillation region, and then the side of the mesa is n-type as shown in FIG. 3 (d). Embedded with an -InP buried layer 27 and a p-InP buried layer 28. Next, as shown in FIG. 3E, all unnecessary portions in the concave portion 22 are removed by mesa etching, and finally an ohmic electrode 29 is formed on the p ⁺ -type electrode extraction layer 23. Thereby, the semiconductor laser substrate 20 is formed. Here, the height of the mesa portion to be grown is substantially
The height is adjusted so as to be the same as the outside of 2, and the final mirror polishing is performed so that the height is completely the same. Although not shown in the drawing, in order to perform polishing at the end, the semiconductor laser substrate and an electronic element portion base to be described later shall be provided with a protective film before polishing, as necessary, on the main part of the element in the recess. . On the other hand, as shown in FIG.
A concave portion 32 is formed on an As substrate 31, and an n-type active layer 33 is formed on the surface of the concave portion 32 by Si ion implantation. Next, as shown in FIG.
4 is formed above the FET channel portion, an n ⁺ -type region 35 is formed by ion implantation using the gate electrode as a mask, and a source electrode 36 is formed. Thereby, the electronic device substrate 3
0 will be formed. The substrates 20, 30 produced as described above
4 is mirror-polished, and after being washed and washed by the above-described procedure, is aligned and pressed, as shown in FIG.
The two substrates 20 and 30 form an integrated semiconductor device. Here, the mirror polishing was performed under the condition that the surface roughness was 50 [nm] or less, and the heat treatment was performed in a H ₂ atmosphere at 500 [° C.] for 1 hour. Since the semiconductor device manufactured in this manner is simple in manufacturing method, the manufacturing yield and the reliability are high, and the characteristics of the semiconductor laser and the electronic device can be optimized. Further, the semiconductor laser n-InP
Since the connection wiring between the cladding layer 26 and the n ⁺ -type layer 35 of the electronic device is not required and the parasitic capacitance and the like can be reduced, high performance can be obtained. The present invention is not limited to the above 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 a semiconductor laser.
II such as aAs / GaAlAs, InP / InGaAsP
HgCdTe, ZnS, Z besides the IV group compound semiconductor
It is also applicable to II-VI group compound semiconductors such as nSe.
Similarly, substrates suitable for electronic device types include S
In addition to i and InP, a semiconductor such as GaAs can be used. In addition, it is clear that the mirror polishing step may be omitted if the surface is mirror-finished after forming the element on the surface of the semiconductor substrate. Therefore, the order of the mirror polishing step and the element forming step is changed. You may. In addition, various modifications can be made without departing from the scope of the present invention. As described in detail above, according to the present invention, a light emitting / receiving device formed of a compound semiconductor mixed crystal can
By forming it on a semiconductor substrate whose lattice constant is very close to this and bonding it to a semiconductor substrate suitable for forming an electronic device, the light emitting / receiving device can be integrated with the electronic device, and A semiconductor device capable of improving element characteristics can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a first half of a manufacturing process of a semiconductor device according to a first embodiment. FIG. 2 is a side view showing the second half of the manufacturing process of the semiconductor device according to the first embodiment. FIG. 3 is a sectional view showing the first half of the manufacturing process of the semiconductor device according to the second embodiment. FIG. 4 is a sectional view showing the latter half of the manufacturing process of the semiconductor device according to the second embodiment. DESCRIPTION OF SYMBOLS 10, 20 semiconductor laser base 11 n-GaAs substrate 12 n-GaAlAs cladding layer 13 undoped GaAs active layer 14 p-GaAlAs cladding layer 15 n-GaAs contact layer 16 p-GaAs Contact layer 18 resonator end faces 19, 31 Si substrate 21 semi-insulating InP substrates 22, 32 recess 23 p ⁺ -InGaAsP electrode extraction layer 24 p-InP clad layer 25 undoped InGaAsP active layer 26 n -InP cladding layer 27 ... n-InP buried layer 28 ... p-InP buried layer 29 ... ohmic electrodes 30 ... electronic device substrate 33 ... n-type active layer 34 ... Schottky electrode 35 ... n ⁺ -type region 36 ... source electrode

   ────────────────────────────────────────────────── ─── Continuation of front page    (56) References JP-A-50-93586 (JP, A)                 JP-A-59-88864 (JP, A)                 JP-A-61-182215 (JP, A)                 Japanese Patent Publication No. 49-26455 (JP, B2)

Claims (1)

(57) [Claims] A first semiconductor substrate in which a semiconductor light emitting element or a semiconductor light receiving element is formed on a front surface side and a front surface side is formed in a mirror state; and a semiconductor material different from the first semiconductor substrate.
A second semiconductor substrate having an electronic element formed on the front surface side and a mirror surface formed on the front surface side, wherein each of the semiconductor substrates has a front surface side that does not melt the surface.
Ku semiconductor device characterized by comprising been integrated directly bonded. 2. Direct bonding surface of first semiconductor substrate and second semiconductor substrate
2. An oxygen atom is segregated in the substrate.
13. The semiconductor device according to claim 1.