JPH07335847A - Manufacture of silicon substrate having embedded oxide film - Google Patents

Abstract

PURPOSE:To make a surface silicon layer into a thin film while maintaining good crystallinity in the manufacture of a silicon substrate having an embedded oxide film inside the silicon substrate through oxygen ion implantation and subsequent heat treatment. CONSTITUTION:Following an oxygen ion implantation 2, an appropriate film thickness of a surface silicon layer 4 of an as-implanted wafer is etched off, say dry etching, and high-temperature heat treatment is thereafter performed. This enables a silicon substrate having an embedded oxide film 7, hose surface silicon layer 6 is made into a thin film, to be manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a so-called S in which a single crystal silicon film is grown on a silicon oxide film which is an insulator.
The present invention relates to a method of manufacturing a silicon substrate having a buried oxide film inside a single crystal silicon substrate by ion-implanting oxygen, which is a kind of OI (Silicon-On-Insulator) structure. Is a method of manufacturing a silicon substrate having a buried oxide film, which has excellent uniformity in crystallinity with the surface silicon layer and the buried oxide film and is obtained by a simplified process.

[0002]

2. Description of the Related Art Since a semiconductor device formed on an SOI structure has improved electrical characteristics, a silicon substrate having an SOI structure has been attracting attention as a substrate for a large scale integrated circuit. In particular, when the surface silicon layer is made sufficiently thin to completely deplete the electrically active region of the semiconductor device formed on the substrate, it is demonstrated that the electrical characteristics of the device will be dramatically improved. It is expected to be applied to high-performance devices. Thus, in order to completely deplete the electroactive region of the device, the surface silicon layer needs to be thinned to 100 nm or less. Further, in such a thin film SOI device in which the device active region is completely depleted, the film thickness of the surface silicon layer affects the device characteristics.
The surface silicon layer needs to be thinned uniformly.

There are several methods for forming an SOI structure, but as a method for achieving the specifications required for a large-scale integrated circuit substrate with appropriate productivity, oxygen ions are implanted from one surface of a silicon wafer, The most promising method is to form a buried oxide film in the silicon single crystal substrate by subsequently performing heat treatment.

FIG. 2 shows an example of a conventional method of manufacturing a silicon substrate having a buried oxide film. First, as shown in FIG. 2A, oxygen ions 2 are implanted from one surface of the single crystal silicon substrate 1 at an acceleration energy of 180 keV with an implantation amount of 1.7 × 10 ¹⁸ cm ⁻² , and oxygen of the oxygen is injected into the substrate. The high concentration layer 3 is formed, and subsequently, heat treatment is performed at 1300 ° C. or higher for about 6 hours. As a result, as shown in FIG. 2B, a buried oxide film 9 is formed inside the vicinity of the surface of the single crystal silicon substrate 1. At this time, the thickness of the monocrystalline surface silicon layer 10 is 130 nm.
Then, the thickness of the buried oxide film 9 becomes 430 nm. Therefore, in order to use this substrate for, for example, a thin film SOI device, the layer 11 of 30 nm or more of the surface silicon layer 10 shown in FIG. 2C is scraped off, and then the substrate shown in FIG. As shown, thin film SOI of 100 nm or less
Obtain the layer 12.

When a large amount of oxygen ions are implanted to form a buried oxide film in this way, a high density of crystal defects is generated in the surface silicon layer 10 after the heat treatment due to damage caused to the silicon by a large amount of ion irradiation. It will be. A surface silicon layer of a silicon substrate having a buried oxide film obtained by implanting oxygen ions at an implantation dose of 1.7 × 10 ¹⁸ cm ^-2 and then performing heat treatment at 1300 ° C. for 6 hours has a concentration of 1 × 10 ⁸ cm 2. Dislocations with a density of ^-2 are present. Since these defects may cause deterioration of electrical characteristics or occurrence of defects when a device is formed on a substrate, it is preferable to reduce them. On the other hand, S. Nak
Ashima et al. Electronic Letterster
s vol. 26 p. 1647 (1990), a method of forming a buried oxide film by a low implantation amount of oxygen ions for lowering the crystal defect density of the surface silicon layer was shown. A silicon substrate having a buried oxide film manufactured by such a low implantation has, for example, oxygen ions of 0.40 × with an acceleration energy of 180 keV.
The dislocation density in the surface silicon layer after implantation at 10 ¹⁸ cm ^-2 and heat treatment at 1300 ° C. or higher is reduced to about 10 ² cm ^-2 . At this time, the buried oxide film thickness is 90 nm and the surface silicon layer thickness is about 300 nm. Although the thickness of the buried oxide film is reduced when the implantation amount is reduced as described above, the dielectric strength is 40 V or more in this case as well, and there is no problem as a substrate for an integrated circuit. However, in this case, the film thickness of the surface silicon layer becomes thicker. Therefore, when a silicon substrate having a buried oxide film manufactured by such a low implantation amount is used as a substrate for a thin film SOI device, the surface silicon after heat treatment is used. The layer should be thinner than 200 nm. In the prior art, in order to reduce the thickness of the surface silicon layer of a silicon substrate having a buried oxide film, heat treatment is performed following implantation to form a buried oxide film, and then the thin film of the surface silicon layer to be removed is oxidized by wet or dry thermal oxidation. The thermal oxide film has been removed by etching with diluted hydrofluoric acid, for example.

In addition, F. Namava et al., Proc.
1989 IEEE SOS / SOI Tech. Co
nf. p. 117, Oct. 3-5, Statelin
e, NE. In, the acceleration energy at the time of oxygen ion implantation is reduced to form an oxygen atom high concentration layer in a shallower region of the substrate, and subsequently heat treatment is performed to form a buried oxide film in the shallow portion of the single crystal silicon substrate. A method for obtaining a silicon substrate having a buried oxide film with a thin surface silicon layer is reported.

[0007]

Problems to be Solved by the Invention 1 after oxygen ion implantation
In the case where the surface silicon layer is thinned after the buried oxide film is formed by performing the high temperature heat treatment at 300 ° C. or higher, for example, the thickness of the oxide film to be reduced by thermal oxidation is the oxide film,
Then, when the oxide film is removed by cleaning with dilute hydrofluoric acid, a much thicker oxide film must be grown than in the normal gate oxide film growth.
This step requires a relatively long oxidation time and a subsequent oxide film removing step, which complicates the process and reduces productivity. Since it is necessary to grow a thick oxide film, it becomes more difficult to ensure the uniformity of the remaining surface silicon film. Furthermore, in this case, stacking dislocations due to oxidation may appear in the residual surface silicon layer. In addition, since the growth rate of the thermal oxide film is different for each substrate due to the difference in the dopant concentration of the substrate, it is difficult to reduce the film thickness equally for each substrate by the same heat treatment process.

Similarly, when the surface silicon layer is thinned after the buried oxide film is formed by performing high temperature heat treatment at 1300 ° C. or higher, for example, when the surface silicon layer is thinned by dry etching with a reactive gas, Exposure of the silicon surface to plasma may introduce defects into the silicon, which may lead to deterioration of electrical characteristics. Therefore, it is necessary to anneal those defects by appropriate heat treatment after thinning them.

Particularly, in the case of the above-mentioned substrate in which the buried oxide film is formed by oxygen ion implantation with a relatively low dose of about 0.4 × 10 ¹⁸ cm ^-2 and subsequent heat treatment, it should be removed in order to thin the film. Since the film thickness becomes thicker, the above-mentioned problems become more apparent.

On the other hand, in the case of thinning the surface silicon layer, for example, the acceleration energy at the time of oxygen ion implantation is further lowered, a high concentration layer of oxygen atoms is formed in a shallower region of the substrate surface, and the subsequent heat treatment When a buried oxide film is formed in the shallow region of the surface by using, low-energy oxygen ions introduce more implantation damage into the implantation region near the surface. Will result in the generation of dislocations. For example, Y. Li is Journal of
Electrochemical Society
vol. 140p. According to 1780,
The implantation energy of oxygen ions is 70 keV, and the dose is 0.4 × 10 ¹⁸ cm ^-2.
As a result of heat treatment for a time, the surface silicon layer thickness is as thin as 124 nm immediately after the heat treatment, but the dislocation density of the surface silicon layer at this time is 1.1 × 10 ⁹ cm ⁻² , and the implantation energy is 180 keV and the same dose amount. Compared to the case of, it is about 7 digits more.

The surface layer of the as-implanted wafer is contaminated with the metal introduced at the time of implantation and implantation damage, and a large amount of crystal defects will remain if the substrate is directly heat-treated. Further, since the surface is sputtered by the irradiation of ions or voids are formed in the vicinity of the surface, when the heat treatment is performed as it is, the surface morphology after the heat treatment may be deteriorated.

[0012]

In order to solve these problems, the present invention provides (1) a method of manufacturing a silicon substrate having a buried oxide film in a single crystal silicon substrate by oxygen ion implantation and a heat treatment process, A first step of implanting oxygen ions from one surface of the single crystal silicon substrate,
Then, a second step of reducing the thickness of the implanted substrate surface, and a third step of heat treating the substrate.
And a method of manufacturing a silicon substrate having a buried oxide film in a single crystal silicon substrate.

The present invention also provides (2) dry etching using a reactive gas as a method for reducing the film thickness of the surface of a single crystal silicon substrate after oxygen ion implantation in the second step shown in (1) above. A method of manufacturing a silicon substrate having a buried oxide film as described in (1) above is provided.

[0014]

In the method of manufacturing a silicon substrate having a buried oxide film according to the present invention, oxygen ions are implanted before the heat treatment (following the first step of implanting oxygen ions from one surface of the single crystal silicon substrate). Hereinafter, this state is referred to as “as-implanted”), and a suitable thickness of a part of the silicon wafer is etched by a second step, for example, by dry etching using a reactive gas to reduce 130
By going through the third step of performing the high temperature heat treatment of 0 to 1410 ° C., a silicon substrate having a buried oxide film with a thin surface silicon layer can be prepared.

In the oxygen ion implantation step, which is the first step, depending on the acceleration energy and the implantation amount of oxygen ions, which are ion implantation conditions, the oxygen high concentration layer 3 in FIG. The implantation depth and thickness are determined. Therefore, the acceleration energy and implantation amount of oxygen ions are in the range of conditions that can obtain the surface silicon layer film thickness and the buried oxide film thickness suitable for forming an electronic device on the silicon substrate having the buried oxide film formed through the subsequent steps. To be determined within. In addition to this, since the defect density tends to increase as the implantation amount of oxygen ions increases and as the acceleration energy decreases, these implantation conditions are conditions under which crystal defects do not remain after the high temperature heat treatment step. It is preferably in the range. Therefore, in the oxygen ion implantation step which is the first step, the single crystal silicon substrate is heated to 400 to 700 ° C., and the acceleration energy is 100 to 200 keV from one surface of the silicon substrate.
Preferably, the oxygen ion dose is 0.30 to 0.43 × 10 ¹⁸ cm ^-2 or 1.35 at 150 to 200 keV.
~ 2.2 × 10 ¹⁸ cm ^-2 , preferably 0.35 to 0.4
3 × 10 ¹⁸ cm ^-2 or 1.5 to 2.0 × 10 ¹⁸ cm ^-2
To form a high concentration layer of oxygen inside the silicon substrate. That is, the acceleration energy is 100 keV
If oxygen ions are implanted at less than 100 nm, a large amount of crystal defects remain in the surface silicon layer even after high-temperature heat treatment, since the surface layer of the silicon substrate is damaged, and the electronic device It will adversely affect the characteristics. If the voltage exceeds 200 keV, it is necessary to newly develop an ion implanter that is an ultra-high-current machine and a high-energy machine, and the high-concentration layer of oxygen formed inside the silicon substrate becomes deep. Inconvenience occurs, for example, it is necessary to extremely increase the amount of decrease in the thickness of the surface layer in the process. When the dose amount is small, for example, the acceleration energy is 180 keV and the dose amount is 0.2 × 10 ¹⁸ cm 2.
^{In the case of -2} , the high concentration layer of oxygen formed in the silicon substrate by oxygen ion implantation does not become a continuous buried oxide film, so that the withstand voltage required for a substrate for integrated circuits cannot be obtained. And the dose amount is 2.2 × 10 ¹⁸ cm ^-2
If it exceeds 1.0, the dislocation density remaining in the surface silicon layer after the heat treatment increases, which deteriorates the crystal quality of the substrate, which is not preferable, and since the surface silicon layer after the high temperature heat treatment becomes extremely thin, device fabrication is performed thereafter. The process may cause the surface silicon layer to disappear.

Next, in the second step, which is the step of reducing the film thickness of the surface of the single crystal silicon substrate, the appropriate thickness of a part of the surface of the silicon wafer of As-In-Pla on the side where oxygen is ion-implanted is decreased. The surface silicon layer is thinned. The appropriate amount of thin film reduction depends on the ion implantation conditions such as the depth and thickness of the oxygen-enriched layer inside the silicon substrate and the factors required by the device formed on the surface silicon layer after the high temperature heat treatment. It is determined by

When the amount of decrease in the film thickness is too large, when the depth of the oxygen-enriched layer inside the silicon substrate is shallow, the surface required for recovering the damage due to the ion implantation in the subsequent high temperature heat treatment step. By completely erasing the crystal region, sufficient crystallinity is not recovered and a large amount of crystal defects remain in the surface silicon layer after the high temperature heat treatment.

Further, the film thickness of the surface silicon layer suitable for forming the device varies depending on the device formed on the SOI substrate, but especially the device has excellent device characteristics by completely depleting the electroactive region of the device. To get
The thickness of the surface silicon layer is usually 80-
It is necessary to reduce the thickness to 120 nm, preferably 90 to 110 nm, and make it uniform. For this reason, if the reduction amount of the surface silicon layer of the as-implanted wafer is too small, the process of thinning the surface silicon layer again has to be performed after the high temperature heat treatment.

Therefore, the reduction amount of the surface silicon layer of the az-implanted wafer in which oxygen ions are implanted under the above-mentioned ion implantation conditions is 40 to 370 nm, preferably 50 to 350 nm.

As a method of reducing the film thickness of the surface layer of the silicon substrate after the oxygen ion implantation, dry etching using a reactive gas is generally preferable. However, in some cases, for example, wet etching using a chemical solution that is corrosive to silicon may be used. Further, a mechanical or mechanochemical polishing method may be used.

Dry etching with a reactive gas, which is a suitable means, includes plasma etching utilizing a chemical reaction of active particles in plasma generated by applying a high frequency electric field to an introduced gas, and both a chemical reaction and a sputtering action. Any of reactive ion etching (RIE) utilizing the above, sputter etching utilizing only a sputtering action by ions accelerated by an electric field, and ion beam etching can be applied. In the dry etching, it is necessary to control the physical quantity involved in the reaction to achieve high processing performance, particularly processing accuracy and flatness of the processing surface in the present invention. Therefore, isotropic plasma etching,
For example, chemical dry etching (CDE) is suitable.

Next, as the reactive gas used for the dry etching of silicon, for example, CF ₄ , SF ₆ , NF ₃ ,
F-based gas such as SiF ₄ , BF ₃ , CBrF ₃ , XeF ₂ , CCl ₂ F ₂ , CCl ₃ F, C ₂ Cl ₂ F ₅ , C ₂
Cl-F-based gas such as _{Cl 2 F 4, CCl 4,} SiCl
Cl-based gases such as ₄ , PCl ₃ , BCl ₃ , Cl ₂ and HCl can be used alone or in combination, and various additive gases such as Ar and N ₂ gas can be mixed therewith.

When the appropriate thickness of the surface layer of the as-implanted wafer is etched off by dry etching with a reactive gas to reduce the film thickness, the surface silicon layer of the wafer after the heat treatment is thermally oxidized and formed. As compared with the reduction by removing the formed oxide film, the thick film can be etched off in a short time, and the productivity can be improved. In addition, it is unlikely that stacking faults due to oxidation will occur when a thick thermal oxide film is formed. The rate of dry etching is mainly determined by the type of reactive gas, the power applied during etching, the substrate temperature during etching, and the like, so that it is possible to control variations in the etching amount due to the dopant concentration of the substrate. When the surface silicon layer of the as-implanted wafer after the implantation of oxygen ions is removed by dry etching as described above, damage to the silicon substrate may be introduced by exposure to plasma.
By carrying out a high temperature heat treatment of 0 to 1410 ° C.,
Those damages can be healed.

When the buried oxide film is formed by oxygen ion implantation with a relatively low dose of about 0.4 × 10 ¹⁸ cm ^-2 , the surface silicon layer of the as-implanted wafer is thinned in order to reduce the film thickness. The above-described operation becomes more effective because it is necessary to reduce the film thickness of more.

Next, in the high temperature heat treatment step, which is the third step, the as-implanted wafer after the thickness of the surface layer is reduced is 1300 to 1410 ° C., preferably 1330 to 139.
The heat treatment is performed at a high temperature of 0 ° C. for 1 to 10 hours, preferably 4 to 6 hours. By this high temperature heat treatment, silicon atoms and oxygen atoms chemically react with each other in the vicinity of the high oxygen concentration layer inside the silicon substrate to form SiO ₂ , and a buried oxide film is formed inside the silicon substrate. Further, a large amount of crystal defects caused by the implantation of oxygen ions are recovered to form a good single crystal silicon layer.

If the heat treatment temperature is lower than 1300 ° C., the crystal defects of silicon cannot be sufficiently removed, and
If it exceeds 10 ° C., the shape of the wafer is likely to be deformed because the melting point of silicon is approached, which is not preferable. When the heat treatment time is less than 1 hour, the crystal defects of silicon cannot be sufficiently removed, and when the heat treatment time exceeds 10 hours, most of the defects have already disappeared and the crystallinity has been recovered. It is not preferable because the effect corresponding to the heat treatment is not obtained.

As described above, in the method according to the present invention, it is not necessary to lower the implantation energy at the time of ion implantation in order to thin the surface silicon layer, and therefore the damage introduced to the silicon substrate at the time of ion implantation is not increased. ,
It does not increase the dislocation density of the surface silicon layer after the heat treatment. Rather, depending on the amount of surface reduction by dry etching, damage or contamination introduced at the time of implantation will be partly removed, so crystal defects can be reduced and surface morphology can be improved.

Further, in the present invention, after the heat treatment, epitaxial growth may be performed on the surface silicon layer of the substrate to form a single crystal silicon layer suitable for device formation.

[0029]

FIG. 1 is a state diagram of a silicon substrate in each step showing an example of a method for manufacturing a silicon substrate having a buried oxide film according to an embodiment of the present invention.

First, as shown in FIG. 1A, an acceleration energy of 200 ke is obtained from one surface of the single crystal silicon substrate 1.
Oxygen ion 2 was implanted at a dose of 1.7 × 10 ¹⁸ cm ^-2 . As a result, the oxygen ion-implanted region 3, which is a high concentration layer of oxygen, was formed inside the single crystal silicon substrate 1, and at the same time, the surface silicon layer 4 was formed on the oxygen ion-implanted region 3 of the silicon substrate.

Thereafter, as shown in FIG. 1B, a part of the film thickness of the surface layer 4 of the silicon substrate 1 after the implantation of the oxygen ions 2 (the part 5 removed by the dry etching) was removed.
In this embodiment, as shown in FIG. 1C, the reactive gas is C
Plasma etching is performed for 39 seconds by using a chemical reaction of active particles of CF ₄ in plasma generated by applying a high-frequency electric field to the introduced gas using F _4, thereby forming a film of the surface silicon layer. The thickness was removed by 137 nm to obtain the surface silicon layer 6 remaining after plasma etching.

After that, as shown in FIG.
By heat treatment at 0 ° C. for 6 hours, a silicon substrate having a buried oxide film 7 was obtained. Damage to the surface silicon layer 6 shown in FIG. 1C due to plasma etching can be removed thereafter by high temperature heat treatment at 1300 ° C. At this time, the film thickness of the surface silicon layer 8 of the thin film obtained by performing the heat treatment after the plasma etching shown in FIG. 1D becomes 93 nm, and the thin film SOI can be obtained without the process of thinning the surface silicon layer after the heat treatment. A device substrate has been obtained. In addition, when thinning by removing the thermal oxide film, it takes about 8 hours to process 100 wafers per batch, so the productivity per wafer is 5 times even if the preparation time before and after is taken into consideration. Improved above.

Dislocations are generated in the surface silicon layer of the silicon substrate having the buried oxide film, which is formed by performing oxygen ion implantation under the same conditions as in this embodiment and subsequently performing heat treatment without thinning the surface silicon layer. 8.4 x 10 ⁷ c
whereas there was a m ^-2, the dislocation density in the present embodiment 5.
It was reduced to 1 × 10 ⁷ cm ^-2 . The surface morphology of the silicon wafer of this example was good.

Similarly to this embodiment, a silicon wafer into which oxygen ions have been implanted at a low dose is subjected to dry etching to remove an appropriate amount of the surface silicon layer after implantation, and then heat treatment is performed to crystallize the surface silicon layer. It could also be obtained relatively easily in excellent condition.

[0035]

As described above, by implanting oxygen ions from one surface of a single crystal silicon substrate, reducing the film thickness of the implanted substrate surface and then performing heat treatment, the substrate can be used as a semiconductor device. A silicon substrate with a buried oxide film, which has the required specifications, is obtained by a simplified process.

[Brief description of drawings]

1A to 1C are state diagrams of a silicon substrate for each step showing an example of a method of manufacturing a silicon substrate having a buried oxide film according to an embodiment of the present invention, in which FIG. FIG. 1B is a state diagram when the surface film thickness is reduced by dry etching after oxygen ion implantation,
FIG. 1 (c) is a state diagram of the result of reducing the surface film thickness, and FIG. 1 (d) is a diagram showing a silicon substrate having an SOI structure having a thin surface silicon layer obtained after heat treatment.

FIG. 2 is a state diagram of a silicon substrate for each step showing an example of a conventional method for manufacturing a silicon substrate having a buried oxide film, wherein FIG. 2A is a state diagram at the time of oxygen ion implantation;
2 (b) is a state diagram after heat treatment, FIG. 2 (c) is a state diagram when the surface silicon layer is reduced, and FIG. 2 (d) is a silicon of SOI structure having the obtained thin film surface silicon layer. It is a figure showing a board.

[Explanation of symbols]

1 ... Silicon substrate, 2 ... Oxygen ion beam, 3 ... Oxygen ion implantation region, 4 ... Surface silicon layer, 5 ... Portion removed by dry etching of surface silicon layer after implantation, 6 ... Surface remaining after dry etching Silicon layer, 7 ... Buried oxide film formed after heat treatment after dry etching, 8 ... Thin film SO obtained by annealing after dry etching
I layer, 9 ... Buried oxide film obtained by implantation followed by heat treatment, 10 ... Surface single crystal silicon layer after heat treatment, 11 ... Portion for reducing film thickness of surface silicon layer after heat treatment, 12 ... Thinning Surface silicon layer.

Claims (2)

[Claims] 1. An oxygen ion implantation and heat treatment process
In a method for manufacturing a silicon substrate having an embedded oxide film in a single crystal silicon substrate, a first step of implanting oxygen ions from one surface of the single crystal silicon substrate and, subsequently, a film thickness of the implanted substrate surface is set. A method of manufacturing a silicon substrate having a buried oxide film, which comprises a second step of reducing the number of steps, and a third step of subsequently heat treating the substrate. 2. The method for producing a silicon substrate having a buried oxide film according to claim 1, wherein in the second step, dry etching with a reactive gas is used as a method for reducing the film thickness on the substrate surface.