JP2006013179A - Method for manufacturing soi wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem in which surface uniformity deteriorates when an SOI layer of an SOI structure is made into a thin film. <P>SOLUTION: On a substrate which has the SOI structure, the SOI layer is made into a thin film through a stage of injecting hydrogen ions into the SOI layer surface and a 1st heat-treating stage performed thereafter. Consequently, the SOI layer of the SOI structure can be made into the thin film without making the in-surface film thickness distribution worse. Further, a 2nd heat treatment in an oxidizing atmosphere and/or a reducing atmosphere after the stage of injecting hydrogen ions into the surface of the SOI layer and the 1st heat treatment is performed to remove a damage layer formed as a result of the film thinning processing, recrystallize the damage layer, and improve surface roughness. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing an SOI (Silicon On Insulator) wafer, and more particularly to a method for manufacturing an SOI wafer in which an SOI layer is thinned while suppressing deterioration of in-plane film thickness variation of the SOI layer as much as possible. .

  Compared with conventional silicon wafers, SOI wafers have superiority such as isolation between elements, reduction in parasitic capacitance between the elements and the substrate, and a three-dimensional structure, and are used in high-speed and low-power consumption LSIs. As a method for manufacturing an SOI wafer, there is a bonding method in which two silicon wafers each having an oxide film formed on at least one silicon wafer are bonded and then ground and polished to form an SOI layer. In a wafer having this SOI structure, the active layer (SOI layer) becomes thinner to 100 nm or less as the pattern becomes finer, and the uniformity of the SOI layer thickness is strictly demanded. Until now, the following method has been proposed as a method of manufacturing a thin film SOI substrate having excellent in-plane uniformity.

(1) Grind back (GB) method: This is a method of thinning by grinding and polishing from the back side of the SOI layer side substrate after bonding, and the wafer outer peripheral part becomes thinner (roll-off) or thicker than the central part. (Roll-up), and in-plane uniformity of the SOI layer surface may be deteriorated. Also, there is almost no polishing allowance control for a thin film SOI of 100 nm or less.
(2) CMP (Chemical Mechanical Polishing): Compared with the GB method, it is superior in controlling the absolute film thickness and in-plane uniformity, and has been applied to the smart-cut method for thinning. It cannot cope with SOI layer thickness of 100 nm or less and in-plane uniformity ± 10% or less.
(3) Sacrificial oxidation method: A method in which the SOI layer is heat treated in an oxidizing atmosphere to oxidize the surface, and then the oxide film is etched with an HF solution to thin the SOI layer. The property is determined by the thickness distribution of the oxide film. Oxide film formation is usually performed in a vertical furnace, but due to its structural reasons, the oxidizing gas flow and temperature distribution are not necessarily uniform in the substrate surface, and the oxide film thickness varies. In particular, when the oxide film thickness is thick, the film thickness non-uniformity becomes large, and as a result, the SOI film thickness uniformity deteriorates. In other words, it is not suitable as a method for thinning a thick SOI layer to a very thin SOI layer.
(4) Hydrogen ion stripping method (smart cut method: registered trademark): For example, in this method disclosed in Patent Document 1, thinning by polishing is not performed, and an oxide film is formed on at least one of two semiconductor substrates. In addition, hydrogen ions or rare gas ions are implanted from the upper surface of one semiconductor substrate to form a microbubble layer (encapsulation layer) inside the semiconductor substrate, and then the surface on which the ions are implanted is formed on an oxide film. The semiconductor substrate is in close contact with the other semiconductor substrate, and then a heat treatment is applied to separate the one semiconductor substrate into a thin film with the microbubble layer as a cleavage plane, and a heat treatment is further applied to form a SOI substrate. is there. In this method, an SOI substrate having a relatively good mirror surface and a highly uniform SOI layer thickness can be obtained relatively easily. However, this smart cut method also requires a step of thinning by CMP or sacrificial oxidation after peeling for the reasons described later, and becomes problematic when the polishing allowance (etching allowance) for thinning is large.

  As described above, the GB method, the CMP method, and the sacrificial oxidation method all have a problem that the in-plane uniformity of the SOI layer is deteriorated by the thinning, and a very thin SOI layer of 100 nm or less is uniformly formed. Can't get to. Also, in the smart cut method, as a method of reducing the thickness of the SOI layer immediately after stripping according to hydrogen ion implantation conditions, when hydrogen ions are implanted after the BOX layer is formed, in order to reduce the thinning allowance after stripping, It is conceivable to reduce the ion acceleration voltage.

  On the other hand, the flattening method has a problem that the surface (peeled surface) of the SOI wafer after peeling becomes rough as compared with a normal mirror wafer due to damage at the time of peeling. To solve this problem, for example, in the method for manufacturing an SOI wafer described in Patent Document 2, the surface of the wafer after peeling is oxidized and then heat-treated in a reducing atmosphere containing hydrogen to flatten the surface. Techniques to do this have been proposed.

JP-A-4-264594 Japanese Patent Laid-Open No. 11-307472

  All of the GB, CMP, and sacrificial oxidation method thinning and planarization methods have a problem that the in-plane uniformity of the SOI layer deteriorates due to the thinning. In the smart cut method, it is necessary to reduce the thickness of the SOI layer immediately after delamination depending on the hydrogen ion implantation conditions. For that purpose, the relationship between the acceleration voltage and the bonding defect (blister) was examined in detail, and as a result, the thickness was reduced to 50 keV or less. It was found that when hydrogen ions are implanted at an accelerating voltage, the lower the accelerating voltage, the higher the probability of blistering (Fig. 2).

  This can be explained by assuming a blister generation mechanism in which the injected hydrogen diffuses the silicon layer and the BOX layer to the bonding interface during the bonding and peeling process and becomes a gas state and becomes a blister defect. That is, it is considered that the smaller the acceleration voltage of hydrogen ion implantation, the shorter the distance to the bonding interface, the greater the amount of hydrogen diffusion, and the higher the probability of blistering. In addition, it is considered that the thickness of the SOI layer + BOX layer to be peeled is reduced, the mechanical strength is lowered, and defects are more likely to occur. As a result of the above, the thinning allowance after peeling can be reduced by low acceleration voltage injection. As a result, even in a thin SOI layer, the uniformity of the in-plane film thickness is not impaired, but there is a problem that many bonding defects occur. .

  The present invention has been made in view of the above-described problems, in which hydrogen ions are implanted into the surface of a substrate having an SOI structure, and then heat treatment is performed to peel off the surface of the SOI layer to obtain a predetermined thickness. A method of thinning the film is provided. Since the implantation depth of hydrogen ion implantation is uniquely determined by the acceleration voltage of ion implantation, it is possible to reduce the thickness of the wafer without substantially degrading variations in the SOI layer surface of the entire wafer.

  According to a first aspect of the present invention, there is provided an SOI wafer characterized in that, in a substrate having an SOI structure, the SOI layer is thinned by a step of implanting hydrogen ions into the surface of the SOI layer and a subsequent first heat treatment step. It is a manufacturing method.

  According to the invention of claim 1, in the substrate having the SOI structure, the implanted hydrogen ions are aggregated and bubbles are formed by heat treatment in the step of implanting hydrogen ions into the surface of the SOI layer and the subsequent first heat treatment step. The SOI layer is thinned by peeling the surface side from the implantation depth. Thereby, the SOI layer can be thinned without deteriorating the in-plane thickness distribution of the SOI layer.

  According to a second aspect of the present invention, the second heat treatment is performed in an oxidizing atmosphere or a reducing atmosphere after the step of implanting hydrogen ions into the surface of the SOI layer and the first heat treatment. It is the manufacturing method of this SOI wafer.

  According to the invention of claim 2, after the step of implanting hydrogen ions into the surface of the SOI layer and the first heat treatment, the second heat treatment is performed in an oxidizing atmosphere to form an oxide film in the vicinity of the surface. It is possible to remove the damaged layer generated by the crystallization treatment. In addition, by performing heat treatment in a reducing atmosphere, the damaged layer generated by the thinning treatment can be removed by recrystallizing the damaged layer generated by the thinning processing.

  The invention according to claim 3 is characterized in that after the step of implanting hydrogen ions into the surface of the SOI layer and the first heat treatment, a second heat treatment is performed in an oxidizing atmosphere and a reducing atmosphere. It is a manufacturing method of the described SOI wafer.

  According to the invention of claim 3, after the step of implanting hydrogen ions on the surface of the SOI layer and the first heat treatment, the peeling damage layer is removed by forming an oxide film in an oxidizing atmosphere, and HF cleaning or the like. After removing the oxide film, the second heat treatment is performed in a reducing atmosphere, so that the removal of the peeling damage layer and the completeness of the surface crystallinity are more complete as compared with the heat treatment in the single atmosphere of claim 2. It is possible to improve the surface roughness.

  According to the present invention, the SOI layer can be thinned by a step of implanting hydrogen ions into the surface of the SOI layer of the substrate having the SOI structure, and the first heat treatment step and the second heat treatment step thereafter. It is possible to remove the damaged layer caused by the crystallization treatment, recrystallize the damaged layer, improve the surface roughness, and make the film thickness uniform.

  Hereinafter, although the form of the manufacturing method of the SOI wafer which concerns on this invention is demonstrated based on drawing, this invention is not limited to them.

  A substrate having an SOI structure as a base to which the present invention is applied may be either a substrate that has been grind-backed after bonding or a substrate that has been created by a smart cut method. However, as a high-precision thin-film SOI substrate, an SOI substrate prepared by a smart cut method is preferable in terms of in-plane uniformity of the SOI layer. When applying the present invention to an SOI substrate manufactured by the smart cut method, (a) after bonding, the substrate is peeled off by an ion implantation layer is used. (B) After bonding, peeling with an ion-implanted layer, followed by planarization treatment (high temperature treatment in an Ar atmosphere or an oxidizing atmosphere) is used. These two processes (a) and (b) can be considered.

  However, in the process (a), the roughness of the SOI layer surface is large (RMS to several nm), and the depth of implanted ions varies due to the influence. Therefore, the SOI layer surface roughness after the thin film heat treatment (hydrogen is bubbled and the SOI layer surface is removed) is further increased, which makes post-step planarization difficult. Therefore, it is preferable that the surface is once flattened by the process (b) and then the thinning treatment of the present invention is performed. Further, the hydrogen ion implantation acceleration voltage for producing a smart cut substrate for performing the thinning treatment according to the present invention is preferably 40 keV or more, more preferably 50 to 80 kev for reducing bonding defects (blister). . If it is 80 kev or more, the surface roughness after peeling becomes large, and the flattening process in the subsequent process becomes difficult.

  As conditions for hydrogen ion implantation for thinning, an accelerating voltage so as to obtain a desired SOI layer thickness and an implantation amount (dose amount) are appropriately selected such that the surface of the SOI layer can be peeled off by heat treatment. The implantation acceleration voltage is preferably selected so as to be an implantation depth corresponding to a desired difference in SOI layer thickness from the SOI layer thickness of the SOI substrate to be thinned. However, since a damaged layer (about 500 to 1000 mm) is formed at the time of surface peeling, when removing the damaged layer by sacrificial oxidation, it is necessary to select an acceleration voltage in consideration of the thickness.

The peeling process by hydrogen ion implantation for thinning the SOI layer of the present invention does not have a bonded wafer at the time of surface peeling unlike the peeling process by normal smart cut. For this reason, in order to peel the SOI surface uniformly, a dose of 4 to 15 × 10 ¹⁶ atoms / cm ² is preferable, and a hydrogen ion implantation dose of 6 to 10 × 10 ¹⁶ atoms / cm ² is more preferable. preferable. If it is 15 × 10 ¹⁶ atoms / cm ² or more, a peeling phenomenon occurs at the time of hydrogen ion implantation and there is a risk of particle contamination of the hydrogen ion implanter. The first heat treatment after the hydrogen ion implantation requires 400 ° C. or higher at which hydrogen bubbles form, and preferably 500 to 700 ° C. The holding time depends on the heat treatment temperature, but is preferably 5 minutes or more at 500 ° C. As the heat treatment furnace, a batch furnace (vertical furnace, horizontal furnace) or a single wafer furnace (RTP furnace, rapid temperature rising and high temperature furnace) can be applied. As the heat treatment atmosphere, a nitrogen atmosphere, an oxygen atmosphere, an argon atmosphere, a mixed atmosphere thereof, or the like can be applied.

After the thinning process, as the second heat treatment for removing the damaged layer, it is necessary to perform an oxidation heat treatment or a high-temperature heat treatment in a reducing atmosphere for recrystallization of the damaged region. In the case of oxidation treatment, dry oxidation (heat treatment with flowing oxygen gas), wet oxidation (heat treatment in an H ₂ O atmosphere generated by reacting oxygen and hydrogen gas), hydrochloric acid oxidation (in an oxygen atmosphere containing HCl). Oxidation) can be selected.

  The heat treatment temperature and holding time may be arbitrarily selected as long as the film can be formed with an oxide film thickness that can remove the damaged layer. Since the peeling damage due to hydrogen ion implantation + heat treatment is generally about 50 to 100 nm, the damaged layer can be removed if the oxide film thickness is about 100 to 200 nm. For example, the dry oxidation may be performed at 1000 ° C. for 5 hours, and the wet oxidation may be performed at 950 ° C. for about 30 minutes. Although the damaged layer can be removed by forming an oxide film having a thickness of 200 nm or more, in-plane non-uniformity of the oxide film thickness is increased, and an oxide film thickness as small as possible is preferable.

In high-temperature heat treatment in a reducing atmosphere, Ar, H ₂ or a mixed atmosphere thereof is suitable as the atmosphere. The heat treatment temperature is required to be 1050 ° C. or higher and the holding time is 1 hour or longer. Preferably, holding in the temperature range of 1150 ° C. for 2 hours or more is effective for recrystallization of the damaged layer and improvement of surface roughness. However, although the above improvement effect can be expected more at 1200 ° C. or higher, there is a risk that the occurrence probability of slip increases, and the etching cost of the SOI layer by the reducing atmosphere gas becomes large and the SOI layer in-plane uniformity is lost. Moreover, you may combine the said oxidation process and high temperature heat processing in a reducing atmosphere.

  Next, a specific example of the actual case using the method according to the present invention will be described with reference to FIG.

Bonded silicon wafers 10 and 20 used in this example were doped with boron, p-type, specific resistance: 10 to 20 Ωcm, oxygen concentration: 12 to 14 × 10 ¹⁷ atoms / cm ³ [ASTM F-121 1979] 200 mm Wafers were prepared for the active layer and the support substrate, respectively (FIG. 1 (a)). One silicon wafer 10 was heat-treated in a dry oxygen atmosphere at 1000 ° C. for 5 hours to form a BOX oxide film with a thickness of 1500 mm as the oxide film 10a (FIG. 1B). Thereafter, hydrogen ions were accelerated at 50 keV, the dose was 6 × 10 ¹⁶ atoms / cm ² , the ion implantation depth was about 5300 mm, and the SOI (active) layer substrate side having the hydrogen ion implanted layer 10b was used ( FIG. 1 (c)). The ion implantation surface 10A on the SOI layer substrate side and the other silicon wafer 20 were bonded together to obtain a bonded substrate 30 (FIG. 1D).

  Thereafter, a peeling heat treatment is performed in a nitrogen atmosphere at 500 ° C. for 30 minutes, the peeling substrate 40 from which the silicon wafer 10 is peeled by the hydrogen ion implantation layer 10b, and the silicon wafer 20 as a supporting substrate, and the hydrogen of the silicon wafer 10 through the oxide film 10a. A bonded substrate 50 having the ion-implanted layer 10b as a surface was obtained (FIG. 1E). The damage removal treatment was performed at 1000 ° C. for 5 hours in a dry oxygen atmosphere, the entire bonded substrate 50 was covered with the oxide film 10c, and the damaged layer was an oxide film. The oxide film thickness was aimed at 1500 mm (FIG. 1 (f)). In order to remove the damaged layer, the oxide film was removed by washing with a 50% HF solution for 5 minutes to obtain an SOI substrate 60 from which damage on the peeled surface was removed (FIG. 1G).

  Here, the SOI substrate once manufactured was evaluated. The evaluation was performed by spectroscopic ellipsometry to measure the in-plane distribution of the SOI layer thickness (49-point measurement, measurement exclusion value outer circumference 5 mm). As a result, the SOI layer average film thickness was 3100 mm, and the in-plane variation was p-v30 mm. (Pv: SOI layer maximum film thickness value-SOI layer minimum film thickness value)

Next, a thinning process was performed, in which hydrogen ions were implanted into the SOI substrate according to the present invention and heat treatment was performed. The SOI substrate 60 obtained in FIG. 1G is an SOI substrate having hydrogen ions implanted layer 10e with hydrogen ions at an acceleration voltage of 10 keV and a dose of 8 × 10 ¹⁶ atoms / cm ² . The ion implantation depth was aimed at 1500 mm (left of FIG. 1 (h)).

  Next, heat treatment for separating the SOI layer surface with the hydrogen ion implanted layer 10e was performed in a nitrogen atmosphere at 500 ° C. for 30 minutes (left of FIG. 1 (i)). The damage removal treatment of the hydrogen ion implanted layer 10e was performed at 1000 ° C. for 5 hours in a dry oxygen atmosphere, the entire bonded substrate was covered with the oxide film 10f, and the damaged layer was an oxide film. The oxide film thickness was aimed at 1500 mm (FIG. 1 (j) left).

  In order to remove the damaged layer, the oxide film was removed by washing with a 50% HF solution for 5 minutes to obtain an SOI substrate from which damage on the peeled surface was removed (FIG. 1 (k) left). By performing the above steps, the film thickness was reduced to about 2200 mm.

  Here, the SOI substrate manufactured in this example was evaluated. The evaluation was performed by spectroscopic ellipsometry to measure the in-plane distribution of the SOI layer thickness (49-point measurement, measurement exclusion value outer circumference 5 mm). As a result, the SOI layer average film thickness was 900 mm, and the in-plane variation was p-v42 mm.

  As a comparative example, a method of forming an oxide film by dry oxidation without performing surface peeling by hydrogen ion implantation and a method of performing thinning by sacrificial oxidation by removing the manufactured oxide film was performed. The SOI substrate 60 obtained in FIG. 1G was subjected to 1000 ° C. for 5 hours in a dry oxygen atmosphere, and the entire bonded substrate was covered with an oxide film 10f to form an oxide film. The thickness of the oxide film was aimed at 1500 mm (right of FIG. 1 (j)).

In order to remove the oxide film, the oxide film was removed by washing with a 50% HF solution for 5 minutes to obtain an SOI substrate from which damage on the peeled surface was removed (FIG. 1 (k) right).
The oxide film was formed in this dry atmosphere and the HF cleaning for removing the oxide film was repeated twice to reduce the thickness to about 2200 mm.

  Here, an SOI substrate manufactured as a comparative example was evaluated. The evaluation was performed by spectroscopic ellipsometry to measure the in-plane distribution of the SOI layer thickness (49-point measurement, measurement exclusion value outer circumference 5 mm). As a result, the SOI layer average film thickness was 900 mm, and the in-plane variation was p-v60 mm.

  When the thinning allowance is aimed at 2200 mm, the method of the present invention (hydrogen ion implantation + peeling treatment + damage removal oxidation) is compared with the sacrificial oxidation (oxidation treatment + oxide film removal) shown in the comparative example. It can be seen that there is little degradation of in-plane variation of the SOI layer.

  An example of medium-high temperature heat treatment in a reducing atmosphere for removing the damaged layer and recrystallizing the damaged region after the thinning treatment is shown below.

Hydrogen ion implantation for thinning was performed on an SOI substrate manufactured by the smart cut method at an acceleration voltage of 10 keV and an implantation dose amount of 8 × 10 ¹⁶ atoms / cm ² , and a surface peeling heat treatment was performed at 500 ° C. for 30 minutes in a nitrogen atmosphere. The thing (equivalent to FIG. 1 (i) of Example 1) was prepared. This sample was heat-treated at 1150 ° C. for 2 hours in an argon atmosphere. When the SOI in-plane variation was measured with an ellipsometer in this state, the p-v value was 34 mm, and no significant deterioration in the SOI layer thickness variation was observed compared to 30 mm before the thinning treatment. The surface roughness was also improved from the rms value before argon annealing = 8 nm (AFM measurement, 10 × 10 μm square) to 0.4 nm.

  The SOI layer having an SOI structure can be thinned without greatly degrading the in-plane uniformity of the SOI layer, and can be used for a high-speed and low-power consumption LSI that requires an ultra-thin SOI layer structure.

It is a figure which shows the process of thinning of the SOI substrate of this invention and a comparative example. It is a figure which shows the hydrogen ion implantation acceleration voltage dependence of the blister which is a bonding defect. It is a figure which shows hydrogen ion implantation acceleration voltage and hydrogen ion implantation depth.

Explanation of symbols

10, 20 Silicon wafer,
30 bonded wafers

Claims (3)

  A method for manufacturing an SOI wafer, characterized in that, in a substrate having an SOI structure, the SOI layer is thinned by a step of implanting hydrogen ions on the surface of the SOI layer and a subsequent first heat treatment step.   2. The method for manufacturing an SOI wafer according to claim 1, wherein a second heat treatment is performed in an oxidizing atmosphere or a reducing atmosphere after the step of implanting hydrogen ions into the surface of the SOI layer and the first heat treatment.   2. The method for manufacturing an SOI wafer according to claim 1, wherein after the step of implanting hydrogen ions into the surface of the SOI layer and the first heat treatment, a second heat treatment is performed in an oxidizing atmosphere and a reducing atmosphere.

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