JP2002009263A - Simox substrate and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a higher quality SIMOX substrate its manufacturing method in which the problems of conventional ITOX are overcome by specifying in detail thermal treatment conditions in the manufacturing method of SIMOX substrate. SOLUTION: In a manufacturing method of a SIMOX substrate is which a silicon single crystal wafer is doped by ion implantation of oxygen ions and an embedded oxide layer and a surface single crystal silicon layer are formed by applying heat treatment at high temperature, this invention is a manufacturing method of a SIMOX substrate characterized in that after applying the heat treatment at a temperature lower than the melting point of silicon, and higher than 1300 deg.C, in an atmosphere of an inert gas including oxygen of less than 2 vol%, an ITOX process of the embedded oxide layer is performed at a temperature of lower than 1300 deg.C, as well as a SIMOX substrate formed by the manufacturing method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a buried oxide layer disposed near the surface of a silicon substrate, and a single crystal silicon layer (hereinafter referred to as SOI (Silicon-on-insul)
a)) layer is formed on the SOI substrate. More specifically, SIMOX (Separation
1 is an SOI substrate and a method of manufacturing the same using an (Implanted Oxygen) technique.

[0002]

2. Description of the Related Art As an SOI substrate on which a single crystal silicon layer is formed on an insulator such as silicon oxide, SIMO is used.
A wafer bonded to an X wafer is mainly known. A SIMOX wafer is obtained by implanting oxygen ions into a single crystal silicon substrate by ion implantation of oxygen ions, and subsequently performing a chemical reaction between these oxygen ions and silicon atoms by an annealing treatment to form a buried oxide layer. It is a substrate. On the other hand, a bonded wafer is an SOI substrate obtained by bonding two single-crystal silicon wafers with an oxide layer interposed therebetween and thinning one of the two wafers.

A MOSFET (Metal-oxide-Semico) formed in the SOI layer of these SOI substrates
nductor Field Effect Tran
Sistor) has high radiation resistance and latch-up resistance, exhibits high reliability, suppresses a short channel effect due to device miniaturization, and enables low power consumption operation. In addition, since the device operation region is capacitively insulated from the substrate itself, the signal transmission speed is improved, and high-speed operation of the device can be realized. For these reasons, the SOI substrate is expected as a high-performance semiconductor substrate for the next-generation MOS-LSI.

[0004] Among these SOI substrates, the SIMOX wafer has a feature that the uniformity of the thickness of the SOI layer is particularly excellent. In a SIMOX wafer, a thickness of 0.3 μm or less can be formed as an SOI layer, and a thickness of 0.1 μm
The thickness of the SOI layer before, after, and even less can be well controlled. In particular, an SOI layer having a thickness of 0.1 μm or less is often applied to the formation of a MOS-LSI of a fully depleted operation, in which case the thickness of the SOI layer itself is proportional to the threshold voltage of the MOSFET operation. Therefore, in order to manufacture a high-performance device with high yield, the uniformity of the thickness of the SOI layer is an important factor. From this viewpoint, a SIMOX wafer having excellent SOI film thickness uniformity is expected as a substrate for a next-generation MOSFET.

In the production of a SIMOX substrate, usually,
Oxygen ions are implanted using a single acceleration energy, typically about 200 keV. In this case, the amount of implanted oxygen ions is 1.5 × 10 ¹⁸ / cm ^2.
Only in one of the above-mentioned regions or a limited region in the range of 2.5 to 4.5 × 10 ¹⁷ / cm ² , in the SIMOX structure obtained after the high-temperature heat treatment, continuous and uniform quality is excellent. It is well known that a buried oxide layer can be obtained (eg, S. Nakashima and
dK. Izumi, Journal of Mate
reals Research, vol. 8523 (1
993)). SIMOX substrates fabricated using these oxygen ion implantation doses are conventionally manufactured using the former oxygen ion implantation dose region at high dose SIMOX.
A substrate manufactured using the latter oxygen ion implantation region is called a low-dose SIMOX substrate.

High dose SIMOX substrate and low dose SIM
Each of the OX substrates has a characteristic, and is appropriately used according to the characteristics. Among these, the low-dose SIMOX substrate is expected to be a technology that can reduce the threading dislocation density of the surface silicon layer and can realize low cost because the oxygen ion implantation amount is relatively small. On the other hand, the low-dose SIMOX substrate has a problem that a leak defect is frequently generated due to a thin buried oxide layer, and there is a high probability that insulation resistance becomes insufficient.

As a technique for contributing to the improvement of the quality of the buried oxide layer of the low-dose SIMOX substrate, a high-temperature IT
OX treatment (Internal Thermal Oxi
A technology utilizing the aging process (also referred to as internal oxidation treatment) has been proposed (Nakajima et al., JP-A-7-263538, or S. Nakashi).
ma et al. , Journal of Elec
Trochemical Society, vol. 14
3244). According to the ITOX technology, a thermal oxide film grows on the substrate surface due to the oxidation treatment at a high temperature, and at the same time, a small amount of oxide film grows on the upper interface of the buried oxide film, so that the buried oxide film can be made thicker. Become. As a result,
It is reported that both reduction of leak defects and improvement of dielectric strength can be achieved.

On the other hand, the surface silicon layer of low dose SIMOX substrate, although that is reduced compared to the high dose SIMOX substrate, density 10 ² to 10 ⁴ / cm ² of about or more threading dislocation remains However, in the process of manufacturing such a low-dose SIMOX substrate, when an ITOX process (internal oxidation process) is performed at a high temperature of about 1350 ° C., which is generally used, a threading dislocation is mainly formed on the SOI layer surface. It is pointed out that a pit having a diameter of about 2 μm and a depth of about 10 nm is generated (WP Maszara).
et al. , Proceedings 1997 I
EEE International SOI Con
reference, p. 18). Typically, a fully depleted device using a thin SOI thickness of 100 nm or less has an operating threshold value that varies depending on the SOI thickness. When a fully depleted device is manufactured on such a substrate, there is a possibility that the operation performance is restricted.

[0009]

As described above, as described above, ITO
A low-dose SIMOX substrate manufactured using X technology
Although the quality of the buried oxide layer was improved by the TOX effect, a pit having a diameter of 2 μm and a depth of about 10 nm was generated in the threading dislocation portion remaining in the surface silicon layer. Therefore, on these substrates, typically 100
When a fully-depleted device using a thin SOI thickness of nm or less is formed, its operation threshold is affected by local fluctuations in the SOI thickness, and there is a possibility that improvement in its operation performance may be restricted. There was such a problem.

The present invention overcomes this problem in the conventional type of ITOX by specifying the heat treatment conditions in the method of manufacturing a SIMOX substrate in detail, and realizes a higher quality SOX.
An IMOX substrate and a method for manufacturing the same can be provided.

[0011]

[MEANS FOR SOLVING THE PROBLEMS] SOMO by SIMOX method
In the high-temperature heat treatment after oxygen ion implantation in the process of forming the I-structure, if the ITOX treatment is performed in a predetermined temperature range, it is possible to avoid the formation of a depression around the dislocation on the surface of the SOI layer while maintaining the ITOX effect. The inventors have newly found this. That is, the present invention relates to an SOI substrate and a method of manufacturing the same to solve the above-mentioned problems, and is based on the following means.

That is, the present invention relates to a method for manufacturing a SIMOX substrate in which a buried oxide layer and a surface single-crystal silicon layer are formed by implanting oxygen ions into a silicon single-crystal substrate and then performing a high-temperature heat treatment. Performing a first heat treatment at 1300 ° C. or more and a melting point of silicon in an atmosphere in which oxygen is added to an inert gas at a concentration of 2 vol% or less, and then subject the buried oxide layer to ITOX at a temperature of 1300 ° C. or less. S
This is a method for manufacturing an IMOX substrate.

It is preferable that the temperature of the ITOX treatment is 1150 ° C. or more and 1280 ° C. or less.

The temperature of the ITOX treatment is more desirably 1150 ° C. or more and 1250 ° C. or less.

The oxygen concentration in the ITOX treatment is 2
It is desirable that it be 0 vol% or more.

It is preferable that the temperature of the first heat treatment is not less than 1350 ° C. and not more than the melting point of silicon.

Further, the SI manufactured by the above manufacturing method
MOX substrate.

The thickness of the surface single crystal silicon layer is 10
not less than 120 nm and not more than 120 nm, and the thickness of the buried oxide layer is 80
A SIMOX substrate characterized by having a thickness of not less than 200 nm and not more than 200 nm and an uneven width of the silicon layer surface of not more than 8 nm.

[0019]

Next, an embodiment according to the present invention will be described.

The present invention relates to a high-temperature heat treatment condition in a method for manufacturing a SIMOX substrate manufactured by performing high-temperature heat treatment after oxygen ion implantation into a single crystal silicon substrate. After performing the first heat treatment of the high-temperature heat treatment in an atmosphere in which oxygen is added to the inert gas at 2 vol% or less,
At least a part of the ITOX treatment performed by increasing the oxygen concentration is performed at a temperature of 1300 ° C. or lower.

The first heat treatment is preferably performed at a temperature of 1300 ° C. or higher and a melting point of single crystal silicon (about 1414 ° C.) or lower in order to recover damage caused by oxygen ion implantation. From the viewpoint of reducing the density of crystal defects such as threading dislocations,
It is more preferable that the temperature be 1350 ° C. or higher and the melting point of single crystal silicon or lower. Representative examples of the inert gas include argon and nitrogen, but are not particularly limited as long as they are inert. The processing time in this step is not particularly limited as long as the damage in the crystal is sufficiently recovered, but a time of about 1 to 6 hours is typically used.

The atmosphere of the first heat treatment is preferably added with a trace amount of oxygen from the viewpoint of preventing the surface of the silicon layer from being roughened. On the other hand, the damage caused by the oxygen ion implantation is recovered during the first heat treatment. However, if the added oxygen concentration is too high, the oxygen precipitates at the damaged portion as a nucleus before the damage is recovered. An object is formed and a good SIMOX structure is not formed. In order to prevent the formation of this oxygen precipitate, the amount of added oxygen must be kept to a necessary minimum, and is desirably 2 vol% or less.

The ITOX processing temperature is set to 1150 ° C. in order to generate an increment at the upper interface of the buried oxide film.
It is preferable to set the above temperature. On the other hand, in order to suppress the occurrence of pits around dislocations on the silicon layer surface,
It is necessary to be 1300 ° C. or lower. More preferably 12
The temperature is 80 ° C. or lower, more preferably 1250 ° C. or lower. The mechanism that suppresses the occurrence of pits around dislocations by using the above-described temperature is considered as follows.
That is, in the 1350 ° C. ITOX treatment, the amount of oxygen diffused from the substrate surface to the inside can be sufficiently secured.
The oxidation reaction at the interface between the surface oxide film and the silicon layer is a so-called reaction rate-limiting. Since there is a high index surface with a high reaction rate constant at the place where threading dislocation exists, local accelerated oxidation occurs at the dislocation part under the condition of reaction control, and as a result,
At that portion, a local depression occurs in the silicon layer. On the other hand, when the ITOX processing temperature is lowered from 1350 ° C.,
Since the amount of oxygen that diffuses from the surface to the inside decreases as the temperature decreases, the oxidation reaction at the interface between the surface oxide film and the silicon layer changes from the reaction rate-limiting to the oxygen supply-limiting. If the oxidation reaction is controlled by the supply of oxygen, the reaction rate is determined uniquely by the supply amount of oxygen regardless of the reaction constant of the interface to be oxidized. Does not occur, and as a result, local depression of the silicon layer can be suppressed. In order for the reaction at the oxidized interface to be controlled by the supply of oxygen, the ITOX treatment temperature is preferably reduced to 1280 ° C., and more preferably 1250 ° C.

The oxygen concentration in the ITOX treatment is ITOX
The range is not particularly limited as long as the effect can be obtained, but it is desirable to increase the oxygen concentration from the viewpoint of shortening the processing time. Preferably 20 vol% or more 10
0 vol% or less, more preferably 50 vol% or more and 10
The oxygen concentration is preferably 0 vol% or less. Oxygen concentration 1
In the case of less than 00 vol%, the gas to be mixed may be an inert gas, and typically includes argon, nitrogen, and the like, but is not particularly limited thereto.

The ITOX processing time is adjusted so as to finally obtain a desired SOI layer thickness.
Since it changes depending on the X temperature, it cannot be unconditionally specified.
50 nm to 2 typically used for the SOI layer thickness
In the case of 00 nm, the ITOX processing time is about 3 hours to 8 hours, but is not particularly limited to this range.

The apparatus for performing the high-temperature heat treatment is not particularly limited as long as the heat treatment at a desired temperature can be performed for a desired time. As a preferred apparatus, a high-temperature heat treatment furnace can be mentioned as a representative, but a lamp annealing furnace can be used if the performance such as the processing temperature and the processing time is satisfied. Conditions other than the processing temperature and the processing time in the heat treatment furnace, such as the insertion temperature, the heating rate, and the cooling rate, are not particularly limited, and the heating and cooling conditions may be a plurality of stages.

The conditions for implanting oxygen ions in the manufacture of a SIMOX substrate are not particularly limited. The dose of oxygen ions may be a low dose or a high dose, but may be other conditions. Further, oxygen ion implantation may be performed plural times. Typically, when 180 keV is used as the acceleration energy, the low dose is in the range of 2.5 × 10 ^{17 to} 4.5 × 10 ¹⁷ / cm ² , and the high dose is 1.2 × 10 ¹⁸ / cm ^2. When a dose of cm ² or more is used, a buried oxide film having few pinholes and excellent in withstand voltage characteristics can be formed. In that case,
From the viewpoint of reducing crystal defects in the SOI layer, it is desirable that the substrate temperature during the ion implantation be about 500 to 600 ° C.

According to the present invention, an acceleration energy of 150 to 250 k commonly used for manufacturing a SIMOX substrate is used.
When a low-dose SIMOX substrate is manufactured using an eV ion implanter, a fully depleted field-effect transistor can be fabricated on a buried oxide layer having a thickness of 80 to 200 nm, the quality of which has been improved by ITOX processing. It becomes possible to manufacture a required SOI layer having a thickness of 120 nm or less with a surface irregularity of 8 nm or less. In the fully depleted type operation, the threshold voltage changes according to the thickness of the SOI layer. However, in a frequently used thickness of 50 to 120 nm, the threshold voltage changes by 10 mV due to the change of 1 nm in thickness. . A typical threshold voltage in fully depleted operation using a SIMOX substrate is 400 mV,
Since the allowable range of the change is about 20%,
It is desirable to suppress the I thickness variation to 8 nm or less.
According to the SIMOX substrate of the present invention, since the local unevenness of the SOI layer is suppressed to 8 nm or less, the threshold voltage of the fully depleted type field effect transistor element formed thereon is reduced in variation. Can be realized.
Although the lower limit of the thickness of the SOI layer is not particularly limited, it is preferable that the thickness of the SOI layer be 10 nm or more in consideration of the case where the unevenness width is about 8 nm.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific examples of the present invention will be described.

Seven silicon wafers were prepared, and oxygen ions were implanted at a substrate temperature of 550 ° C., an acceleration voltage of 180 keV, and an implantation amount of 4 × 10 ¹⁷ / cm ² . Next, each of these wafers was individually placed in a heat treatment furnace and subjected to high-temperature heat treatment under different conditions. The high-temperature heat treatment had a two-step configuration. The first heat treatment uses conditions common to all wafers,
The temperature was 1350 ° C., the atmosphere was argon + 0.5 vol% oxygen, and the treatment time was 4 hours. After that, 70
In an atmosphere to which vol.% of oxygen is added, 1100 to 13
Using a different temperature for each sample in the range of 50 ° C
An OX treatment step was performed. The processing time was adjusted for each temperature so that the finally obtained SOI layer thickness was 100 nm.

In the manufactured SIMOX wafer, after removing the surface oxide layer with hydrofluoric acid, spectroscopic ellipsometry (SOP) was performed.
The thickness of the SOI layer and the buried oxide layer were measured using RAS (MOSS-ES4G). The thickness of the SOI layer of each sample was 100 nm in all samples because the heat treatment time was adjusted as described above. As the thickness of the buried oxide layer, different values were obtained depending on the processing temperature. ITO
The amount of ITOX was derived as a difference from the buried oxide layer thickness of 85 nm when X processing was not performed.

Thereafter, the surface of the SOI layer of each sample was cleaned with an atomic force microscope (AFM).
oscope; Digital Instrument
(Company s, D-5000), and the unevenness was evaluated. FIG. 1 shows an observation example of the cross-sectional profile of the surface of the SOI layer of the sample in which the ITOX temperature was 1350 ° C., and FIG.
The observation example of the cross-sectional profile of the SOI layer surface of the sample in which the TOX temperature is 1250 ° C. is shown. In FIG. 1, a local depression was confirmed, and it was found from the cross-sectional profile that the depth was about 12 nm. In FIG. 2, roughness was observed over the entire profile, but no local depression was observed. These samples were subjected to an etching treatment using a solution in which hydrofluoric acid and chromic acid were mixed at a ratio of 2: 1 to perform etching until ２ of the SOI layer was removed. Observation with a microscope revealed that the local depressions shown in FIG. 1 corresponded to threading dislocations in the silicon layer. Since the existence of threading dislocations was confirmed also in FIG. 2, in FIG.
It was confirmed that no depression occurred at the threading dislocation on the silicon layer surface. The roughness of the surface of the SOI layer observed in FIG. 2 is equivalent to the roughness of the interface between the SOI layer and the buried oxide layer, and is a projection of the interface roughness. It was also confirmed that they did not.

FIG. 3 shows the relationship between the ITOX temperature, the amount of ITOX and the depth of the depression on the surface of the SOI layer for the five samples having different ITOX temperatures. The depression on the silicon layer surface decreases as the ITOX temperature decreases,
Although it is 12 nm at 1350 ° C., it is reduced to 7 nm at 1300 ° C. and 3 nm at 1280 ° C.
In the following, it was found that no depression occurred. on the other hand,
The amount of ITOX also decreases with a decrease in the temperature of the ITOX treatment.
It gradually decreases to 25 nm at 250 ° C., and the IT of 15 nm at 1200 ° C. and 7 nm at 1150 ° C.
Although the amount of OX was secured, it was found that at 1100 ° C., the effect was ineffective when the amount of ITOX was 1 nm or less. Therefore, at a heat treatment temperature of 1250 ° C. or lower, it was confirmed that although the ITOX effect remains at a temperature up to 1150 ° C., a depression on the silicon layer surface can be completely avoided.

Although it is conceivable that the tolerance of the local depression varies depending on the type of device used and the device manufacturing process, one index is SOI.
It is said that the variation in the layer thickness is within ± 5% (199).
9NTSR roadmap prescribed value). Since a substrate having a thin SOI layer is used for a fully depleted device, the requirement for thickness variation becomes severe, but for a typical SOI layer thickness of 100 nm, the variation must be kept within ± 5 nm. In addition, as described above, from the viewpoint of the threshold voltage fluctuation in the fully depleted operation, it is desired to suppress the variation in the thickness of the silicon layer to be within 8 nm by the difference between the maximum value and the minimum value. According to the present invention, this requirement can be realized by using a temperature of 1300 ° C. or lower as the ITOX temperature. It is better to use a temperature of 1280 ° C. or less for more reliably realizing, and it is better to use a temperature of 1250 ° C. or less to completely avoid the influence of the local depression.

[0035]

As described above, the present invention provides a SIM
ITOX of high temperature heat treatment process in OX substrate manufacturing process
By defining the processing temperature, the local depression on the surface of the SOI layer is reduced while maintaining the ITOX effect contributing to the reduction of the leak defect of the buried oxide film and the improvement of the withstand voltage.
It enables the realization of SIMOX substrates with good characteristics.
This contributes to stable production of a fully depleted device having good operation performance.

[Brief description of the drawings]

FIG. 1 is an observation example of a cross-sectional profile of an SOI layer surface of a sample in which an ITOX temperature is 1350 ° C.

FIG. 2 is an observation example of a cross-sectional profile of an SOI layer surface of a sample in which an ITOX temperature is 1250 ° C.

FIG. 3 is an evaluation result in the example of the present invention.

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[Procedure amendment]

[Submission date] July 11, 2000 (2007.1.
1)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0033

[Correction method] Change

[Correction contents]

FIG. 3 shows the relationship among the ITOX temperature, the amount of ITOX, and the depth of the depression on the surface of the SOI layer for the seven samples having different ITOX temperatures. The depression on the silicon layer surface decreases as the ITOX temperature decreases,
Although it is 12 nm at 1350 ° C., it is reduced to 7 nm at 1300 ° C. and 3 nm at 1280 ° C.
In the following, it was found that no depression occurred. on the other hand,
The amount of ITOX also decreases with a decrease in the temperature of the ITOX treatment.
It gradually decreases to 25 nm at 250 ° C., and the IT of 15 nm at 1200 ° C. and 7 nm at 1150 ° C.
Although the amount of OX was secured, it was found that at 1100 ° C., the effect was ineffective when the amount of ITOX was 1 nm or less. Therefore, it was confirmed that at a heat treatment temperature of 1250 ° C. or less, although the ITOX effect remains at a temperature up to 1150 ° C., the depression on the silicon layer surface can be completely avoided.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Toshiyuki Mizutani 20-1 Shintomi, Futtsu-shi, Chiba F-term in the Technology Development Division, Nippon Steel Corporation (reference) 4G077 AA02 BA04 FE03 FE12 FE19

Claims (7)

[Claims] 1. A method for manufacturing a SIMOX substrate in which a buried oxide layer and a surface single-crystal silicon layer are formed by implanting oxygen ions into a silicon single-crystal substrate and then performing a high-temperature heat treatment, wherein the high-temperature heat treatment is performed in an inert manner. The first heat treatment is performed at a temperature of 1300 ° C. or more and the melting point of silicon in an atmosphere in which oxygen is added to the gas at a concentration of 2 vol% or less, and then the ITOX treatment of the buried oxide layer is performed at a temperature of 1300 ° C. or less. A method for manufacturing a SIMOX substrate. 2. The processing temperature in the ITOX processing is 1
2. The method for manufacturing a SIMOX substrate according to claim 1, wherein the temperature is 150 ° C. or more and 1280 ° C. or less. 3. The processing temperature in the ITOX processing is 1
2. The method for manufacturing a SIMOX substrate according to claim 1, wherein the temperature is 150 ° C. or more and 1250 ° C. or less. 4. An oxygen concentration in the ITOX treatment is 2
The method for producing a SIMOX substrate according to any one of claims 1 to 3, wherein the content is 0 vol% or more. 5. The method for manufacturing a SIMOX substrate according to claim 1, wherein the temperature of the first heat treatment is not less than 1350 ° C. and not more than the melting point of silicon. 6. A SIMOX substrate manufactured by the manufacturing method according to claim 1. 7. The thickness of a surface single crystal silicon layer is 10 nm.
Not less than 120 nm and the thickness of the buried oxide layer is 80
not less than 200 nm and not more than 200 nm, and the unevenness width of the substrate surface is 8 n.
m or less.