JP2001044085A - Laminating substrate and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminating substrate and its manufacturing method, that completely eliminate defects on a device preparation side, and improve electrical characteristics. SOLUTION: A laminating silicon substrate 13, that is laminated under normal conditions and is subjected to lamination heat treatment is inserted into the crystal reaction pipe of an annealing oven and is subjected to heat treatment in an atmosphere of hydrogen gas at 1,200 deg.C for one hour, thus greatly diffusing oxygen existing in a wafer 11 for an active layer outwardly. It is thought that the diffusion into the gaseous phase of the oxygen on the surface of the wafer is increased. Through hydrogen anneal treatment, the concentration of the oxygen of the wafer 11 for the active layer is greatly reduced, thus nearly completely eliminating an oxygen induced lamination faults (OSF) in the wafer 11, achieving a state having no defects, and hence improving the electrical characteristics, such as oxide film breakdown voltage characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bonded substrate and a method of manufacturing the same, and more particularly, to a bonded substrate having a small number of small defects in an element formation region and a method of manufacturing the same.

[0002]

2. Description of the Related Art When manufacturing an SOI wafer, which is a kind of a bonded substrate, first, a single crystal silicon ingot pulled up by a CZ method is sliced to prepare two silicon wafers. Next, with the insulating film (silicon oxide film) interposed therebetween, one wafer is used as an active layer wafer and the other wafer is used as a support substrate wafer, and both wafers are superposed at room temperature. Then, a predetermined bonding heat treatment is performed. Subsequently, the outer peripheral portion of the active layer wafer is chamfered. Thereafter, the surface of the active layer wafer is ground and polished. By the way, the single crystal silicon ingot contains oxygen as an impurity in a supersaturated state. The supersaturated oxygen plays a useful role such as increasing the mechanical strength of the single crystal silicon ingot and a gettering site for impurities. On the other hand, a minute oxygen-induced stacking fault (OSF; Oxidat)
ion Induced Stacking Foul
t) and COP (Crystal Originate)
d Particle) and BMD (Bulk Mic)
(Ro Defect).

[0003]

In general, the depth of a device formation region in a silicon wafer is 10
μm or less. In the case of SOI wafer, thickness is several tens
A device is formed on the surface layer of the active layer wafer having a thickness of μm to several μm. The crystal characteristics of the active layer wafer become important. That is, the wafer surface must be completely defect-free, and it is required that the surface layer be uniform and defect-free. However, the active layer wafer is also C
Since the wafer is a Z wafer, oxygen exists in a supersaturated state in the wafer. Therefore, this causes a minute defect (oxygen-induced stacking fault) in the active layer wafer. As a result, there have been problems in that the oxide film withstand voltage of the oxide film formed on the wafer surface is reduced, and the reverse bias leakage current characteristic of the PN junction is reduced.

[0004] Therefore, if the bonded substrate is subjected to a hydrogen annealing treatment, supersaturated oxygen in a silicon wafer on the side where devices such as a wafer for an active layer are formed is diffused outward, and the oxygen concentration is greatly reduced. Focusing on the fact that the active region is made defect-free, the present invention has been completed.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a bonded substrate capable of making a silicon wafer on which a device is to be formed defect-free and thereby improving electrical characteristics such as an oxide film breakdown voltage, and a method of manufacturing the same. , Its purpose.

[0006]

According to a first aspect of the present invention, there is provided a bonded substrate produced by bonding a first silicon wafer serving as an active layer and a second silicon wafer serving as a support substrate. The first silicon wafer is a bonded substrate that has been subjected to a hydrogen annealing treatment. The type of the bonded substrate is not limited. For example, S
OI wafers and the like. As a condition of hydrogen annealing, a preferable annealing temperature is 1050 to 1250 ° C.
And the preferable annealing time is 1 to 4 hours. For example, heating is performed at 1200 ° C. for 1 hour. These matters also apply to the invention described in claim 2.

The invention according to claim 2 is the bonded substrate according to claim 1, wherein an insulating layer is formed between the first silicon wafer and the second silicon wafer.
A so-called bonded SOI wafer corresponds to this.

According to a third aspect of the present invention, there is provided a method of superposing a first silicon wafer and a second silicon wafer, both of which are pulled up by the CZ method, and a step of superimposing the first and second silicon wafers. A method of manufacturing a bonded substrate, comprising: performing a bonding heat treatment on a wafer; and performing a hydrogen annealing process on the bonded substrate after the bonding heat treatment. First silicon wafer and second silicon wafer
Is usually superimposed at room temperature. The heating temperature of the lamination heat treatment is 800 ° C or more,
Usually, it is 1100 ° C to 1200 ° C. The bonding heat treatment time is usually 2 hours. Oxygen or the like is used as an atmosphere gas in the furnace.

[0009]

According to the present invention, a hydrogen annealing treatment is performed on the bonded substrate that has been subjected to the bonding heat treatment. Thereby, supersaturated oxygen in the surface layer portion of the silicon wafer on which the device is manufactured is diffused outward. Therefore, the surface layer is made defect-free. Therefore, the electric characteristics can be improved. For example, oxide film breakdown voltage characteristics can be improved.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. Here, a bonded SOI wafer is taken as an example of the bonded substrate. FIG. 1 is a flowchart showing a method for manufacturing a bonded substrate according to one embodiment of the present invention. As shown in FIG. 1, in the step of pulling a single crystal silicon ingot by the CZ method in advance, the single crystal silicon ingot pulled up at a predetermined pulling speed is subjected to block cutting, slicing, chamfering, polishing, etc., to a thickness of 620 μm. , Diameter 150m
An active layer wafer (first silicon wafer) 11 of m (6 inches) is prepared. Further, a wafer (second silicon wafer) 12 for a support substrate having the same thickness and the same diameter as the active layer wafer 11 is prepared by the same manufacturing method. The silicon oxide film 12 serving as an insulating film is formed on the surface of the support substrate wafer 12 by wet O ₂ oxidation.
a is formed with a thickness of 1 μm.

Next, the active layer wafer 11 and the supporting substrate wafer 12 are subjected to SC1 cleaning, and then rinsed with pure water and dried. Subsequently, the mirror surfaces of both wafers 11 and 12 are superimposed at room temperature in a clean room. The bonded silicon substrate 13 is manufactured. Thereafter, the bonded silicon substrate 13 is inserted into a quartz reaction tube of a bonding furnace, and subjected to a bonding heat treatment in an oxygen gas atmosphere. The bonding temperature is 1100 ° C. and the heat treatment time is 2 hours. Subsequently, a void inspection by ultrasonic irradiation is performed, the non-defective bonded silicon substrate 13 is chamfered, and the active layer wafer 11 is ground and polished. Thus, the thickness of the active layer wafer 11 is reduced to a predetermined thickness.

Thereafter, the bonded silicon substrate 13 is
A hydrogen annealing treatment is performed in a hydrogen gas atmosphere. Specifically, the bonded silicon substrate 13 is placed in a quartz reaction tube of an annealing furnace, and heated at 1200 ° C. for one hour in a hydrogen gas atmosphere. As described above, when the bonded silicon substrate 13 is heated at a high temperature in a hydrogen gas atmosphere, oxygen present in the active layer wafer 11 is greatly increased as compared with other atmosphere gases such as nitrogen gas and oxygen gas. Spread. This is considered to be due to an increase in diffusion of oxygen into the gas phase on the wafer surface.

By the hydrogen annealing treatment, the oxygen concentration of the active layer wafer 11 is greatly reduced. As a result, the oxygen-induced stacking fault OSF in the active layer wafer 11 is almost completely eliminated, and this region is made defect-free. Therefore, electrical characteristics such as oxide film breakdown voltage characteristics can be improved. After the thus obtained bonded substrate is washed, it is packed in a wafer case or the like and shipped to a device maker or the like.

Here, based on FIG. 2 and FIG. 3, the results of an evaluation test of an oxide film breakdown voltage on each silicon wafer are described by comparing the bonded substrate of the conventional method with the bonded substrate of the present invention. . FIG. 2 is an explanatory diagram showing an evaluation test method of the oxide film breakdown voltage of the bonded substrate. FIG. 3A is an explanatory diagram showing a distribution state of measurement points of oxide film breakdown voltage in the bonded substrate according to one embodiment of the present invention. FIG. 3B is an explanatory diagram showing a distribution state of measurement points of the oxide film breakdown voltage in the bonded substrate according to the conventional means.

First, referring to FIG. 2, a specific test method for evaluating the withstand voltage of an oxide film on a bonded substrate will be described. As shown in FIG. 2, the bonded substrate 10 has a thickness of 5 to 10 μm.
The active layer wafer 11 is bonded to one surface of the support substrate wafer 12 via a 1 μm thick silicon oxide film 12a, and then subjected to a hydrogen annealing treatment. In this case, the oxygen concentration of the active layer wafer 11 is [Oi] = 1.30 × 10 ¹⁸ / cm ³ . Note that, unlike the bonded substrate 10 according to the present invention, the conventional bonded substrate 100 is not subjected to the hydrogen annealing treatment after the bonded substrate is manufactured.

The surface layer of the active layer wafer 11 is doped with phosphorus P, and this portion becomes an N ⁺ region. An aluminum electrode 14 is provided on this region.
Are formed. A gate oxide film 15 having a thickness of 25 nm and a film area of 20 mm ² is formed at a position separated from the electrode 14 by a predetermined distance. Gate oxide film 15
A polysilicon electrode 16 is provided thereon. This electrode 16 has a thickness of 500 nm and is doped with phosphorus. These electrodes 14 and 16 have an oxide film breakdown voltage measuring device 20 having a DC power source 17, an ammeter 18 and a voltmeter 19.
Are connected respectively.

In the oxide film breakdown voltage test of the gate oxide film 15, a DC applied voltage of 10 MV / cm is applied for 10 seconds, and then the voltage is applied again only once. At this time, the amount of current flowing through the electrodes 14 and 16 was measured, and it was determined that dielectric breakdown had occurred in the gate oxide film 15 only when the current density exceeded 100 μA / cm ² . A total of 181 measurement points were arranged on the active layer wafer 11, and the state of dielectric breakdown of the gate oxide film 15 at each point was examined. The result is shown in FIG.

As apparent from FIG. 3A, in the case of the bonded substrate 10 according to one embodiment of the present invention, no dielectric breakdown occurred at all the measurement points 181. On the other hand, FIG.
The conventional bonded substrate 100 shown in FIG.
Of the points, dielectric breakdown occurred at 20 points. Note that FIG.
3A and 3B, a white area indicates no dielectric breakdown and a black area indicates a dielectric breakdown. From the above experiments, it has been proved that, after the bonded substrate 10 is manufactured, the hydrogen annealing treatment is performed on the bonded substrate 10 to increase the oxide film breakdown voltage in the active layer.

[0019]

According to the present invention, since the hydrogen annealing treatment is performed on the bonded substrate after fabrication, the silicon wafer on which the device is fabricated can be made defect-free. Thereby, electrical characteristics such as oxide film breakdown voltage can be improved.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a method for manufacturing a bonded substrate according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing an evaluation test method of an oxide film breakdown voltage of the bonded substrate.

FIG. 3A is an explanatory view showing a distribution of measurement points of oxide film breakdown voltage in a bonded substrate according to one embodiment of the present invention. (B) is an explanatory view showing a measurement point distribution of an oxide film breakdown voltage in a bonded substrate according to a conventional means.

[Explanation of symbols]

Reference Signs List 10 bonded substrate, 11 wafer for active layer (first silicon wafer), 12 wafer for support substrate (second silicon wafer).

Claims (3)

[Claims] 1. A bonded substrate produced by bonding a first silicon wafer serving as an active layer and a second silicon wafer serving as a support substrate, wherein the first silicon wafer is subjected to a hydrogen annealing treatment. Bonded substrate. 2. The bonded substrate according to claim 1, wherein an insulating layer is formed between the first silicon wafer and the second silicon wafer. 3. A step of laminating a first silicon wafer and a second silicon wafer, both of which have been lifted up by the CZ method, and a lamination heat treatment on the superimposed first and second silicon wafers. Performing a hydrogen annealing process on the bonded substrate after the bonding heat treatment.