JP3522482B2 - Method for manufacturing SOI substrate - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an oxide layer formed.
After performing hydrogen ion implantation on the first semiconductor substrate,
Separate the semiconductor substrate as the supporting substrate with the oxide layer as the bonding surface.
Bonded to the second semiconductor substrate of the
By separating from the second semiconductor substrate at the injection part,
SOI substrate having single crystal thin film on surface of second semiconductor substrate
The present invention relates to a method of manufacturing .

[0002]

2. Description of the Related Art An SOI substrate is a typical example of a semiconductor substrate having a single crystal thin film on the substrate. This SO
The I substrate has attracted attention as a future ultra-high integrated circuit (ULSI) substrate. This SOI substrate manufacturing method includes:
A method of bonding silicon substrates to each other via an insulating film,
A method of depositing a silicon thin film on an insulative substrate or a substrate having an insulative thin film on the surface, a high concentration of oxygen ions is implanted into the inside of the silicon substrate, and then annealed at high temperature to obtain a predetermined amount from the surface of the silicon substrate. There is a SIMOX method in which a buried silicon oxide layer is formed in the depth region and the Si layer on the surface side is used as the active region. Also recently, the first
After hydrogen ion implantation is performed on the semiconductor substrate, this semiconductor substrate is bonded to another second semiconductor substrate that serves as a supporting substrate with the ion implantation surface as a bonding surface, and the first semiconductor substrate is bonded to the second semiconductor substrate at the hydrogen ion implantation portion. A method has been proposed in which a semiconductor substrate having a thin film on the surface of the second semiconductor substrate is manufactured by separating it from the substrate (Japanese Patent Laid-Open No. 511128/1993). In this method, if the ions can be uniformly injected into the inside of the semiconductor substrate from the surface, a semiconductor substrate having a thin film having a uniform thickness can be obtained. Further, if an oxide layer is provided in advance on the surface of the second semiconductor substrate to be the supporting substrate, the SOI substrate can be manufactured by this method.

On the other hand, in recent years, with the high integration of microelectronic devices and the reduction of the minimum device size, the cleanliness of the wafer surface as well as the micro-roughness of the wafer surface have been emphasized. There is. In particular, it is recognized that microroughness has a great influence on the electrical characteristics such as the breakdown voltage of the oxide film of the device ((M. Morita, et al., "Effect of Si Wa
fer surface micro-roughness on electrical properti
es of very-thin gate oxide films ", ULSI Science an
d Technology / 1991, pp.400-408, Electrochem, Society
(1991)). Here, the microroughness means a surface roughness on the order of 1 μm or less and several nm.

The average roughness of the thin film existing on the surface of the second semiconductor substrate immediately after the first semiconductor substrate is separated by the method disclosed in Japanese Patent Laid-Open No. 511128/1993 is the average roughness of the initial surface of the silicon substrate. Is 0.1 nm or less, the average roughness is 10 times or more, and the microroughness is relatively large, which may adversely affect the electrical characteristics such as the oxide film withstand voltage. In particular, according to this method, the surface of the thin film formed by separating the first semiconductor substrate has a large microroughness because the shape of minute bubbles due to the heat treatment remains, and is not suitable for device fabrication. In order to solve this problem, the thin film surface on the second semiconductor substrate after the first semiconductor substrate is separated is touch-polished.
The surface roughness is made to be microroughness equivalent to the roughness of the initial substrate surface, called "polishing" (M.Bruel et al., "A Promising New SOI").
Material Technology "IEEE International SOI Confer
ence proceedings, pp.178-179 (1995)).

[0005]

However, when the current touch polishing technique is applied to an extremely thin thin film having a thickness of several hundreds nm or less produced by the above method, the thin film surface can be flattened. However, there is a problem that the thickness distribution of the thin film becomes large due to the variation in the polishing amount within the surface. Since the thickness distribution of this thin film is large, there is a problem in that when the device is manufactured using the thin film semiconductor substrate after polishing, the device characteristics vary. An object of the present invention is to provide a single crystal thin film formed on a second semiconductor substrate, which is an extremely thin thin film having a thickness of several hundreds nm or less, without changing the thickness of the thin film and in-plane thickness variation. SO for improving the average surface roughness of thin films to the order of 0.1 nm without increasing the thickness
It is to provide a method for manufacturing an I substrate .

[0006]

The invention according to claim 1 is
As shown in FIGS. 1A to 1E , an oxide layer 1 is formed on the substrate surface.
Inject hydrogen ions into the first semiconductor substrate 11 on which 1a is formed.
By ion implantation into the first semiconductor substrate 11
A damaged region 11b is formed, and the semiconductor substrate 11 is treated with the above acid.
Another surface that serves as a support substrate with the surface of the oxidization layer 11a as a bonding surface.
2 Joined to the semiconductor substrate 12, these two joined semiconductors
The first semiconductor substrate is formed by heat-treating the body substrates 11 and 12.
The plate 11 is divided at the damaged area 11b to separate the second semiconductor.
Separated from the body substrate 12 and attached to the bonding surface of the second semiconductor substrate 12.
Immediately after this separation or after the single crystal thin film 13 remains
The second semiconductor substrate 12 having the crystalline thin film 13 by heat treatment.
Immediately after strengthening the chemical bond of the single crystal thin film 13 of
The second semiconductor substrate 12 having the single crystal thin film 13 is heat-treated in an active atmosphere at a temperature of 1000 to 1300 ° C. for 10 minutes to 5 hours to obtain an average surface roughness of the upper thin film of 0.1 nm.
Method for manufacturing SOI substrate, which is characterized in that when the semiconductor substrate is heat-treated under the above conditions, atoms on the surface of the thin film on the substrate are in an active state and easily move, and the average surface roughness of the thin film is 0. Set to 1 nm order. Claim 2
The invention according to claim 1 is the invention according to claim 1, wherein the thin film 13
There a silicon thin film, inert atmosphere is a hydrogen atmosphere, SOI heat treatment temperature of about 1000 to 1300 ° C.
It is a method of manufacturing a substrate . By heat treating the silicon thin film in a hydrogen atmosphere under the above conditions, in addition to reducing the surface roughness of the thin film, minute defects existing in silicon are reduced, and the concentration of boron contained as a dopant in silicon is reduced. Can be controlled.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION As the active atmosphere during the heat treatment of the present invention, there are a hydrogen atmosphere, a hydrochloric acid atmosphere, and a fluorocarbon atmosphere, and the hydrogen atmosphere is preferable from the viewpoint of easy control of the surface treatment. If the heat treatment temperature is less than the above lower limit and the heat treatment time is less than the above lower limit, the activity of atoms on the thin film surface is low,
The surface roughness cannot be set to the order of 0.1 nm. If the heat treatment temperature exceeds the upper limit value and the heat treatment time exceeds the upper limit value, etching by the active element proceeds, and the thin film surface becomes rough rather than before the heat treatment. In both claim 1 and claim 2, the heat treatment temperature is 1100 to 120.
The temperature is preferably 0 ° C., and the heat treatment time is preferably 1 to 2 hours.

The object to be treated of the present invention is a semiconductor substrate having a single crystal thin film having an average surface roughness of at least 0.2 nm on the substrate. If it is less than 0.2 nm, the surface roughness cannot be made smaller than this value by the treatment method of the present invention. As an example of such a semiconductor substrate, high-concentration oxygen ions are implanted into the silicon substrate by the SIMOX method and then annealed at a high temperature to form a buried silicon oxide layer in a region of a predetermined depth from the surface of the silicon substrate. Did S
Examples thereof include an OI substrate and a second semiconductor substrate having a thin film immediately after separating the first semiconductor substrate by the method disclosed in JP-A-5-211128.

This method will be described with reference to the drawings. Figure 1
As shown in (a), the first semiconductor substrate 11 of the silicon wafer is thermally oxidized to form an oxide layer (SiO ₂ layer) on the substrate surface.
After forming 11a, 2 × hydrogen ions are applied to the substrate 11.
Ion implantation is performed at a dose amount of 10 ¹⁶ / cm ² to 1 × 10 ¹⁷ / cm ² . Reference numeral 11b is a damaged region due to hydrogen ion implantation. Next, as shown in FIG. 1B, a second semiconductor substrate 12 made of the same silicon wafer as above is prepared.
As shown in FIG. 1C, after cleaning both the substrates 11 and 12 by the RCA method, the substrate 11 is bonded onto the substrate 12 at room temperature. The substrate 12 acts as a supporting substrate. Figure 1 (d)
As shown in, the two bonded substrates 11 and 12 are subjected to a first heat treatment at 400 to 600 ° C. in an argon atmosphere. As a result, the substrate 11 is broken at the damaged region 11b and separated from the substrate 12. The single crystal silicon thin film 13 remains on the bonding surface of the substrate 12. The average surface roughness of the silicon thin film 13 after the first heat treatment is about 10 nm. As shown in FIG. 1 (e), after separation, about 1 in argon atmosphere
A second heat treatment is performed at 100 ° C. to strengthen the chemical bond of the silicon thin film. As shown in FIG. 1F, the substrate 12 having the thin film 13 is subjected to the third heat treatment in a hydrogen atmosphere at a temperature range of 1000 to 1300 ° C. for 10 minutes to 5 hours. This heat treatment does not change the thickness of the silicon thin film 13 and its distribution, and the average surface roughness is on the order of 0.1 nm. As another method, after the first heat treatment, the heat treatment in the same hydrogen atmosphere as the third heat treatment may be performed. In this case, the same effect as the second heat treatment (increased bonding strength) can be obtained together with the flattening of the silicon surface.

[0010]

EXAMPLES Next, examples of the present invention will be described together with comparative examples. Example 1 A first silicon wafer having a thickness of 625 μm was thermally oxidized to form a thermal oxide film having a thickness of 500 nm on the surface. This silicon wafer has 120 keV and a dose of 5
Hydrogen ions were implanted at × 10 ¹⁶ / cm ² . The same second silicon wafer as above before thermal oxidation is used as a supporting substrate,
The first silicon wafer was bonded to the second silicon wafer. Both wafers were cleaned by the RCA method before bonding. Both bonded wafers were heat treated at 600 ° C. Due to the rearrangement of crystals in the first silicon wafer and the pressure action of the minute bubbles by this heat treatment, the first silicon wafer is broken and separated at the ion-implanted portion inside the wafer, and the silicon having a thickness of 500 nm is formed on the second silicon wafer. An SOI substrate having a thin film was obtained. The variation of the thin film on the wafer surface at this time was ± 3 nm. The average surface roughness Ra is 10 as a result of measurement with an atomic force microscope (AFM).
was nm. The surface roughness of the thin film by this AFM is shown in FIG.
Shown in. The second silicon wafer with the silicon thin film was heat-treated in a hydrogen atmosphere at 1100 ° C. for 3 hours. The thickness of the thin film after heat treatment did not change to 500 ± 3 nm in the wafer surface, and the average surface roughness Ra was measured by AFM.
It was 0.1 nm. This value was similar to the surface roughness of the initial silicon wafer. This surface roughness is shown in FIG.

Example 2 A second silicon wafer with a silicon thin film produced in the same manner as in Example 1 was heat-treated in a hydrogen atmosphere at 1200 ° C. for 2 hours. The thickness of the thin film after the heat treatment does not change to 500 ± 3 nm within the wafer surface, and the average surface roughness Ra is 0.12 nm as measured by AFM.
Met. This surface roughness is shown in FIG.

Comparative Example 1 A second silicon wafer with a silicon thin film prepared in the same manner as in Example 1 was touch-polished. The average surface roughness Ra of the thin film at this time was improved to 0.15 nm, but the thickness of the thin film was deteriorated to 480 ± 7 nm in the plane of the wafer.

<Comparative Example 2> A second silicon wafer with a silicon thin film produced in the same manner as in Example 1 was heat-treated in a hydrogen atmosphere at 1350 ° C. for 1 hour. Due to the heat treatment, the silicon thin film is etched with hydrogen, and the thickness of the thin film deteriorates to 100 ± 8 nm within the wafer surface, and the average surface roughness R
The value of a was 5 nm, which was worse than that of Examples 1 and 2 as a result of measurement by AFM.

Comparative Example 3 A second silicon wafer with a silicon thin film prepared in the same manner as in Example 1 was heat-treated in a hydrogen atmosphere at 900 ° C. for 5 hours. There was no change in the thickness of the thin film, its in-plane distribution and the surface roughness.

[0015]

As described above, according to the present invention, the group
Hydrogen ion is formed on the first semiconductor substrate with an oxide layer formed on the plate surface.
Ion implantation into the first semiconductor substrate by ion implantation.
Forming a damaged region on the surface of the oxide layer.
To another second semiconductor substrate that serves as a supporting substrate
And heat treating the two bonded semiconductor substrates together.
And divide the first semiconductor substrate at the damaged area by
Separated from the second semiconductor substrate and bonded to the second semiconductor substrate
Immediately after this separation or after this single crystal
The second semiconductor substrate having the thin film is heat treated to obtain the single crystal thin film.
Immediately after the strong chemical bonding film, a semiconductor substrate having an upper SL single crystal thin film in an active atmosphere 1000 to 1300 ° C.
By performing the heat treatment at the temperature of 10 minutes to 5 hours, even an extremely thin thin film having a thickness of several hundreds nm or less, without changing the thickness of the thin film and without increasing the in-plane thickness variation, The average surface roughness of the thin film can be improved to the order of 0.1 nm.

[Brief description of drawings]

FIG. 1 is a diagram showing a method of manufacturing an SOI substrate according to an embodiment of the present invention in the order of steps.

FIG. 2 is a diagram showing substrate surface roughness by an atomic force microscope before heat treatment in an active atmosphere of Example 1 of the present invention.

FIG. 3 is a diagram showing substrate surface roughness by an atomic force microscope after heat treatment in an active atmosphere of Example 1 of the present invention.

FIG. 4 is a diagram showing substrate surface roughness by an atomic force microscope after heat treatment in an active atmosphere of Example 2 of the present invention.

[Explanation of symbols]

11 First semiconductor substrate (first silicon wafer) 11a oxide layer 12 Second semiconductor substrate (second silicon wafer) 13 Silicon thin film

Continuation of the front page (56) Reference JP-A-5-217821 (JP, A) JP-A-8-264552 (JP, A) JP-A-9-162090 (JP, A) JP-A-7-235534 (JP , A) JP 10-275905 (JP, A) M.S. Bruel, Silicon on insulator material technology, Electronics Letters, July 6, 1995, Vol. 31, No 14, PP. 1201-1202 (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/02 H01L 21/322 H01L 21/324 H01L 21/76 H01L 27/12

Claims (2)

(57) [Claims] 1. A first substrate having an oxide layer (11a) formed on a substrate surface .
1 Injecting hydrogen ions into the semiconductor substrate (11) , the first semiconductor
Body substrate (11) form a damaged region (11b) by ion implantation in the interior
To form the semiconductor substrate (11) on the surface of the oxide layer (11a) .
On another second semiconductor substrate (12) which becomes a supporting substrate as a bonding surface
The two bonded semiconductor substrates (11, 12) are heat treated.
The first semiconductor substrate (11) is damaged by
From pass the divided at the (11b) second semiconductor substrate (12)
Separately , a single crystal thin film is formed on the bonding surface of the second semiconductor substrate (12).
(13) is left, immediately after the separation or the single crystal thin film (13)
The second semiconductor substrate (12) having
Immediately after strengthening the chemical bond of the film (13), the single crystal thin film (1
The second semiconductor substrate (12) having ( 3) is heated to 100 in an active atmosphere.
Heat treatment at a temperature of 0 to 1300 ° C. for 10 minutes to 5 hours
The average surface roughness of the thin film to the order of 0.1 nm
A method of manufacturing an SOI substrate, comprising : 2. The thin film (13) is a silicon thin film, the active atmosphere is a hydrogen atmosphere, and the heat treatment temperature is from 1000 to 1000.
The method for manufacturing an SOI substrate according to claim 1, wherein the method is at 1300 ° C.