JP5766901B2 - Manufacturing method of bonded wafer - Google Patents

Description

  The present invention relates to a method for manufacturing a bonded wafer, and more particularly, to a method for manufacturing a bonded wafer in which an oxygen ion implanted layer is effectively used as a stop layer when reducing the thickness.

As a general method for manufacturing a bonded wafer, another silicon wafer is bonded to one silicon wafer on which an oxide film (insulating film) is formed, and one of the bonded silicon wafers is ground. Polishing method to form SOI (Silicon On Insulator) layer (grinding polishing method) and implanting hydrogen ions etc. into the surface layer part of silicon wafer (active layer wafer) on the S OI layer side to form ion implantation layer After the, bonded to the silicon wafer and silicon wafer for support substrate and then a method of forming an SOI layer by delamination at the ion implanted layer (smart cut method) and the like that are known by heat treatment.

  However, each of the above methods has a problem that the film thickness uniformity of the active layer is inferior (± 30% or more).

Therefore, as a solution to the above problem, the present inventors firstly combined the oxygen ion implantation method and the grinding and polishing method, ie, “active layer wafer with or without an insulating film on the surface, A method for producing a bonded wafer comprising directly bonding to a support layer wafer and then thinning the active layer wafer portion,
Injecting oxygen ions into the active layer wafer to form an oxygen ion implanted layer in the active layer;
A step of heat-treating the active layer wafer at a temperature of 1100 ° C. or higher in a non-oxidizing atmosphere;
Bonding the active layer wafer and the support layer wafer together;
A heat treatment step for improving the bonding strength of the bonded wafers;
Grinding the wafer part for the active layer of the bonded wafer to the front of the oxygen ion implantation layer;
Further polishing or etching the wafer portion for the active layer of the bonded wafer to expose the oxygen ion implantation layer;
Oxidizing the bonded wafer to form an oxide film on the exposed surface of the oxygen ion implantation layer; and
Removing the oxide film;
Applying a heat treatment at a temperature of 1100 ° C. or less in a non-oxidizing atmosphere to flatten the wafer portion for the active layer of the bonded wafer;
A method for producing a bonded wafer, characterized in that the time-series coupling is as follows. "
Was developed and disclosed (see Patent Document 2).
According to this method, it is possible to provide a directly bonded wafer having relatively excellent thickness uniformity of the active layer and relatively few defects as evaluated by a transmission electron microscope (TEM) .
JP 2008-16534 A

  However, in the method disclosed in Patent Document 2, although it is described that the oxygen ion implanted layer works as a polishing stop layer, the conditions of the oxygen ion implanted layer desirable as a polishing stop layer are not shown. There is a problem that the oxygen ion implantation layer to be obtained is not necessarily optimized as a polishing stop layer.

That is, in the above method, oxygen ions are implanted only once at a high temperature exceeding 200 ° C. based on a conventional method, so that the formed oxygen ion implanted layer is shown in a cross-sectional TEM photograph in FIG. 4 (a) to 4 (c), the surface on the oxygen ion implantation side (lower side in FIG. 4) of the wafer portion for the active layer (the boundary between the BOX layer and the SOI layer in the figure) ) Near the layer (implantation damage maximum region) A and a layer farther from the oxygen ion implantation side surface (implantation ion maximum region) B, there is a case where such a two-layer structure. Then, the volume fraction of SiO ₂ particles dispersed in the silicon of the oxygen ion implanted layer becomes low, and the SiO ₂ particles fall off from the oxygen ion implanted layer during polishing from the layer B side. As shown in FIG. 4 (a), unevenness tends to remain on the surface of the oxygen ion implanted layer.

  For this reason, when an oxidation process is performed thereafter, as shown in FIG. 4B, the oxide film C oxidized to a predetermined depth including the oxygen ion implanted layer corresponds to the unevenness of the surface of the oxygen ion implanted layer. As shown in FIG. 4C, unevenness tends to remain on the surface of the SOI layer after the oxide film C is removed. Therefore, in the above method, the surface of the wafer portion for the active layer is flattened in the subsequent heat treatment step to obtain the thickness uniformity of the active layer, but it is desirable to solve the problem that the heat treatment takes time and man-hours. There was a problem.

  The present invention advantageously solves the above-mentioned problems, and proposes an advantageous method for producing a bonded wafer in which an oxygen ion implantation layer having a sufficiently high polishing stop function, which is desirable as a polishing stop layer, can be obtained. Objective.

Now, in order to solve the above problems, the present inventor has made extensive studies on the polishing stop conditions in the oxygen ion implanted layer. As a result, the oxygen ion implanted layer desirable as the polishing stop layer has an average oxygen concentration in the thickness direction. The knowledge that the distribution has a single peak was obtained.
Further, the present inventor said that it is effective to combine the implantation at a high substrate temperature and the implantation at a low temperature by oxygen ion implantation in order for the average oxygen concentration distribution in the thickness direction to have a single peak. Obtained knowledge.
The present invention is based on the above findings.

That is, the summary structure of the manufacturing method of the bonded wafer of this invention is as follows.
1. A method for manufacturing a bonded wafer by bonding an active layer wafer and a support layer wafer,
(1) a step of implanting oxygen ions into the active layer wafer to form an oxygen ion implanted layer;
(2) After the step of forming the oxygen ion implantation layer of (1), a step of heat-treating the active layer wafer at a temperature of 1100 ° C. or higher in a non-oxidizing atmosphere;
( 3 ) bonding the surface of the active layer wafer on the oxygen ion implantation side and the support layer wafer directly or via an insulating film;
( 4 ) a heat treatment process for improving the bonding strength of the bonded wafers;
( 5 ) The thickness of the wafer portion for the active layer of the bonded wafer is reduced using the oxygen ion implanted layer as a stop layer to expose the oxygen ion implanted layer;
( 6 ) removing the oxygen ion implanted layer from the wafer portion for the active layer of the bonded wafer;
Including a series of processes including
In the step of implanting oxygen ions into the active layer wafer described in (1) above, oxygen ions are implanted into the active layer wafer at a high temperature exceeding 200 ° C., and then accelerated from the oxygen ion implantation at the high temperature. At least once including the case where the voltage is increased, oxygen ion implantation is performed at a low temperature of 200 ° C. or lower to form an oxygen ion implanted layer ,
In the heat treatment step (2), the maximum ion implantation region by oxygen ion implantation at a high temperature and the amorphous layer by oxygen ion implantation at a low temperature are combined into one, and the oxygen ion implantation layer is formed as an average oxygen in the thickness direction. A method for producing a bonded wafer, wherein the concentration distribution has a single peak .

2. In the oxygen ion implantation at the low temperature in the oxygen ion implantation step (1) in the active layer wafer, the oxygen ion implantation at the high temperature is the same as the acceleration voltage and the oxygen ion implantation at the high temperature. The method for producing a bonded wafer according to claim 1, wherein oxygen ions are implanted a plurality of times including the case where the acceleration voltage is increased.

3. In the step (1) of implanting oxygen ions into the active layer wafer, VH is an acceleration voltage at the time of oxygen ion implantation at the high temperature, and at least one acceleration voltage at the time of the oxygen ion implantation at the low temperature. VL, 1.0 × VH <VL <1.2 × VH
The method for producing a bonded wafer according to claim 2, wherein:

4). In the step of implanting oxygen ions into the active layer wafer of (1) above, the dose amount at the time of oxygen ion implantation at the high temperature is 1.0 × 10 ^{16 to} 1.0 × 10 ¹⁸ atoms / cm ² , the oxygen at the low temperature The method for manufacturing a bonded wafer according to any one of claims 1 to 3, wherein a dose amount during ion implantation is set to 1.0 × 10 ^{15 to} 1.0 × 10 ¹⁷ atoms / cm ² .

5. In the step of implanting oxygen ions into the active layer wafer of (1), the oxygen ions are implanted a plurality of times at the low temperature, and the wafer is rotated 360 degrees and the resting during the plurality of oxygen ion implantations. The method for producing a bonded wafer according to any one of claims 1 to 4, wherein the wafer is rotated by a predetermined angle other than a multiple.

When the average oxygen concentration distribution in the thickness direction of the oxygen ion implanted layer has multiple peaks, the SiO ₂ particles are too far apart, so polishing is performed to reduce the thickness of the active layer wafer. The polishing stop function is not sufficiently high because SiO ₂ particles easily fall off during the process. That is, unevenness tends to remain on the surface of the oxygen ion implanted layer after polishing is stopped.
On the other hand, when the average oxygen concentration distribution in the thickness direction in the oxygen ion implanted layer has a single peak, the SiO ₂ particles are densely solidified, so the thickness of the active layer wafer portion is reduced. Therefore, since SiO ₂ particles are difficult to fall off during polishing, a sufficiently high polishing stop function can be achieved.

  In the present invention, in the step of implanting oxygen ions into the active layer wafer, oxygen ions are implanted into the active layer wafer at a high temperature exceeding 200 ° C., and then accelerated than the oxygen ion implantation at the high temperature. Since the oxygen ion implantation layer is formed by performing oxygen ion implantation at a low temperature of 200 ° C. or less at least once including the case where the voltage is increased, the maximum ion implantation region can be obtained by oxygen ion implantation at a high temperature. After the formation, an amorphous layer (maximum implantation damage region) is formed deeply near the previous implantation ion maximum region by oxygen ion implantation at a low temperature with an increased acceleration voltage. Since the amorphous layer formed by low temperature implantation can be combined into one, a single peak stop layer is formed even by heat treatment at a temperature of 1200 ° C. or lower.

  Therefore, according to the present invention, it is possible to have an oxygen ion implanted layer that stably exhibits a sufficiently high polishing stop function desirable as a polishing stop layer during the production of a bonded wafer, and the thickness uniformity of the active layer is excellent. A bonded wafer can be manufactured at low cost.

  In the case of oxygen ion implantation at a low temperature in the process of implanting oxygen ions into the active layer wafer, when the acceleration voltage is the same as the oxygen ion implantation at a high temperature and when the acceleration voltage is higher than the oxygen ion implantation at a high temperature If oxygen ions are implanted in multiple steps, including oxygen, the oxygen ions can be implanted evenly, so that the generation of pinholes in the stop layer can be suppressed and the polishing stop function can be stably obtained. it can.

Also, in the process of implanting oxygen ions into the active layer wafer, if acceleration voltage at the time of oxygen ion implantation at high temperature is VH, and acceleration voltage at least once at the time of oxygen ion implantation at low temperature is VL,
1.0 × VH <VL <1.2 × VH
This is preferable because the acceleration voltage VL at the time of oxygen ion implantation at a low temperature can be appropriately increased from the acceleration voltage VH for oxygen ion implantation at a high temperature.

Furthermore, in the process of implanting oxygen ions into the active layer wafer, the dose amount at the time of oxygen ion implantation at high temperature is 1.0 × 10 ^{16 to} 1.0 × 10 ¹⁸ atoms / cm ² , and at the time of oxygen ion implantation at low temperature If the dose is set to 1.0 × 10 ^{15 to} 1.0 × 10 ¹⁷ atoms / cm ² , an implanted ion maximum region is formed by oxygen ion implantation at a high temperature, and then an amorphous layer (implantation damage maximum region is formed by oxygen ion implantation at a low temperature. ) Can be formed deeply up to the maximum ion implantation region.

  Then, in the oxygen ion implantation step into the active layer wafer, the oxygen ion implantation is performed a plurality of times at the low temperature, and the wafer is moved to other than 360 degrees and an integral multiple thereof during the pause between the plurality of oxygen ion implantations. If the predetermined angle is rotated, the influence of the temperature distribution in the wafer surface during oxygen ion implantation can be reduced, and the in-plane uniformity of the active layer can be further improved. Here, the reason other than 360 degrees or an integral multiple thereof is that even if the angle is rotated by 360 degrees or an integral multiple thereof, only the original state is restored.

Hereinafter, embodiments of the present invention will be specifically described.
First, the bonded wafer as a target in the present embodiment and each manufacturing process of the present embodiment according to the process flow shown in FIG. 1 will be specifically described.
To prepare a-bonded rehabilitation Ri combined wafer by the wafer this embodiment is not bonded to the active layer wafer two silicon wafers of the support layer wafer, but the present embodiment is of both wafers The bonding can be applied not only when the insulating film (oxide film) is interposed, but also when the bonding is performed directly without using such an insulating film.
Note that the type, concentration, oxygen concentration, and the like of the dopant are not limited as long as the bonded wafer has good surface roughness suitable for bonding. However, in order to further reduce defects, a wafer having no or few COPs (Crystal Oriented Particles) is preferable. Here, COP can be reduced by optimizing the CZ pulling conditions to reduce COP, performing high-temperature heat treatment at 1000 ° C or higher in a reducing atmosphere after wafer mirror processing, and epitaxially growing Si on the wafer by CVD or the like. Methods etc. can be applied.

(1) Step of implanting oxygen ions into active layer wafer First, in this embodiment, oxygen ions are implanted into an active layer wafer.
In the present embodiment, the acceleration voltage at the time of oxygen ion implantation can be appropriately selected according to the thickness of the active layer of the final product, and is not particularly limited. Accordingly, the acceleration voltage of a normal oxygen ion implanter may be about 100 to 300 keV.
However, in this embodiment, as the oxygen ion implantation, a high temperature implantation in which oxygen ions are implanted at a high temperature exceeding 200 ° C. (for example, 450 ° C.) and a substrate temperature of 200 ° C. or less (for example, 100 ° C. or 20 ° C. (for example) Room temperature)) and low-temperature implantation in which oxygen ions are implanted at a low temperature.
If the acceleration voltage at the time of oxygen ion implantation at high temperature is VH, and the acceleration voltage at the time of oxygen ion implantation at low temperature is VL,
1.0 × VH <VL <1.2 × VH
Thus, the acceleration voltage VL at the time of oxygen ion implantation at a low temperature is slightly higher than the acceleration voltage VH for oxygen ion implantation at a high temperature.
On the other hand, in the present embodiment, the dose during oxygen ion implantation is high so that the average oxygen concentration distribution in the thickness direction in the oxygen ion implanted layer has a single peak after the heat treatment of the active layer wafer. The dose amount during oxygen ion implantation is 1.0 × 10 ^{16 to} 1.0 × 10 ¹⁸ atoms / cm ² , and the dose amount during oxygen ion implantation at low temperature is 1.0 × 10 ^{15 to} 1.0 × 10 ¹⁷ atoms / cm ² . Set.

When the dose during oxygen ion implantation at high temperature is less than 1.0 × 10 ¹⁶ atoms / cm ² or when the dose during oxygen ion implantation at low temperature is less than 1.0 × 10 ¹⁵ atoms / cm ² is, (2) Si amorphous layer containing oxygen atoms are not formed or fully formed of a two-layer structure without settled in a single layer in the oxygen ion implanted layer after the heat treatment in the heat treatment step, SiO ₂ Since the particles are too far apart, the SiO ₂ particles easily fall off when polishing to reduce the thickness of the active layer wafer part in the step (5) after bonding, which will be described later. The polishing stop cannot be performed accurately.
On the other hand, when the dose amount during oxygen ion implantation at a high temperature exceeds 1.0 × 10 ¹⁸ atoms / cm ² or when the dose amount during oxygen ion implantation at a low temperature exceeds 1.0 × 10 ¹⁷ atoms / cm ² Since oxygen is required for oxygen ion implantation, oxygen ion implantation is expensive.

Although the substrate temperature at the time of oxygen ion implantation at the low temperature can be carried out even at room temperature or lower, it is necessary to add a function for forcibly cooling the wafer to the implanter.
Further, the oxygen ion implantation at the low temperature may be divided implantation, and during the implantation pause, the wafer may be rotated by a predetermined angle excluding 360 degrees and an integral multiple thereof. The influence of the temperature distribution in the wafer surface during implantation can be reduced, and the in-plane uniformity of the active layer can be further increased.
Further, the cleaning may be performed between the oxygen ion implantation at the high temperature and the oxygen ion implantation at the low temperature, or between the divided ion implantation at the low temperature. As the cleaning method, cleaning with SC1, HF, O ₃ and organic acid having excellent particle removal capability is suitable.

(2) Step of heat-treating active layer wafer Next, in this embodiment, heat treatment is performed at a temperature of 1100 ° C. or higher and 1200 ° C. or lower for 2 hours after oxygen ion implantation and before bonding. If the temperature is less than 1100 ° C., the oxygen ion implanted layer is not combined into a single layer but has a two-layer structure, or is not sufficiently amorphous, and the polishing stop function is not sufficiently high.
During this heat treatment, by processing in a non-oxidizing atmosphere, oxygen implanted near the outermost surface during oxygen ion implantation is diffused outward to lower the oxygen concentration, and oxygen near the outermost surface during bonding strengthening heat treatment This contributes to the suppression of precipitates, and as a result, the defect density can be further reduced. As the non-oxidizing atmosphere, Ar, H ₂ or a mixed atmosphere thereof is advantageously adapted.

2 (a) and 2 (b) show a comparison of cross-sectional TEM photographs of wafers that have been bonded to each other after oxygen ions have been implanted according to the conditions of the present embodiment and the conventional conditions, respectively, and then heat-treated.
The oxygen ion implantation conditions and heat treatment conditions are as follows.
・ Conventional conditions Oxygen ion implantation High temperature implantation: acceleration voltage: 200 keV, dose: 1.0 × 10 ¹⁶ atoms / cm ² , substrate temperature: 450 ° C.
Low-temperature implantation: acceleration voltage: 180 keV, dose: 0.04 × 10 ¹⁶ atoms / cm ²
Heat treatment 1100 ℃, 2h
-Conditions of the present invention Oxygen ion implantation treatment High temperature implantation: acceleration voltage: 200 keV, dose: 1.0 × 10 ¹⁷ atoms / cm ² , substrate temperature: 450 ° C.
Low temperature implantation: acceleration voltage: 210 keV, dose: 0.04 × 10 ¹⁶ atoms / cm ² , substrate temperature: 100 ° C.
Heat treatment 1100 ℃, 2h
As can be seen from the photograph, under the conventional conditions, irregularities are observed on the surface of the oxygen ion implanted layer (SiO ₂ layer), so that the Si layer after bonding as shown in FIGS. The surface of the active layer after polishing and removing the oxide film is inevitable.
On the other hand, under the conditions of this embodiment, the interface between the oxygen ion implanted layer (SiO ₂ layer) and the Si layer on the surface is smooth, so that it has a sufficiently high polishing stop function and is inexpensive as a polishing stop layer. It can be seen that an oxygen ion implanted layer capable of oxygen ion implantation is formed.
3 (a) and 3 (b) show TEM photographs after oxygen ion implantation. The accelerating voltage for low-temperature implantation is the same as that for high-temperature implantation (FIG. 3 (b)). In the case of 210 keV (Fig. 3 (a)), it can be seen that the amorphous layer covers the oxygen ion implanted layer (black part) formed by high temperature implantation deeply. The oxygen ion implantation layer is prevented from being separated into two layers.

(3) Step of bonding the active layer wafer and the support layer wafer Next, in this embodiment, the active layer wafer and the support layer wafer are bonded together, but this bonding may be performed through an insulating film. However, it can also be bonded directly without using an insulating film.
When bonding is performed through an insulating film, an oxide film (SiO ₂ ) such as a BOX, a nitride film (Si ₃ N ₄ ), or the like is preferable as the insulating film. As a film forming method, heat treatment (thermal oxidation, thermal nitridation), CVD, or the like in an oxidizing atmosphere or a nitrogen atmosphere is preferable. As thermal oxidation, in addition to oxygen gas, wet oxidation using water vapor or the like can also be used.

Further, the insulating film may be formed before oxygen ion implantation or after implantation.
The insulating film can be formed on the active layer wafer, the support layer wafer, or both the active layer and support layer wafers.

Further, before bonding, it is advantageous to perform a cleaning process in order to suppress generation of voids due to particles.
As a cleaning method, SC1 + SC2, HF + O ₃ , an organic acid, or a combination thereof, which is a general silicon wafer cleaning method, is effective.
Furthermore, if the bonding temperature is less than 1000 ° C, the bonding strength is not sufficient, and if there is a risk of peeling depending on the conditions (pressure / speed) of the grinding / polishing process after bonding, the bonding strength In order to improve the above, it is advantageous to subject the silicon surface before bonding to an activation treatment by plasma using oxygen, nitrogen, He, H ₂ , Ar, or a mixed atmosphere thereof. In this case, the temperature of the bonding strengthening heat treatment may be about 300 to 500 ° C.

In the case of direct bonding, H ₂ O adsorbed on the bonding surface changes to SiO ₂ in the subsequent heat treatment and exists at the bonding interface, so the bonding surface is washed with HF, and hydrophobic surface bonding is performed. And a method for suppressing SiO ₂ may be performed. Thereby, the oxide at the interface can be reduced, which leads to improvement of device characteristics.

(4) Heat treatment step for improving the bonding strength Next, in this embodiment, a heat treatment for increasing the bonding strength is performed. In order to sufficiently increase the bond strength, this heat treatment is preferably performed at a temperature of 1000 ° C. or higher for 1 hour or longer. Although the atmosphere is not particularly limited, it is preferable to provide an oxide film having a thickness of 150 nm or more as the oxidizing atmosphere in order to protect the back surface of the wafer in the next grinding step.

(5) Step of reducing the thickness of the active layer wafer and exposing the oxygen ion implanted layer In this embodiment, the thickness of the active layer wafer is then reduced by grinding and polishing to expose the oxygen ion implanted layer.
・ Grinding The active layer wafer of the bonded wafer is ground by mechanical processing. In this grinding, a part of the active layer wafer is left on the surface side of the oxygen ion implanted layer. The film thickness of a part of the remaining active layer wafer is not limited.
In order to shorten the polishing process time in the next process, it is preferable to perform grinding until just before the oxygen ion implanted layer. However, considering the accuracy of the grinding apparatus and the damage depth (about 2 μm) due to grinding, the remaining film Si thickness Is preferably about 3 to 10 μm.

-Polishing Following the grinding, the wafer for active layer of the bonded wafer is polished to expose the oxygen ion implanted layer.
This polishing method is preferably performed while supplying an abrasive having an abrasive concentration of 1% by mass or less. Examples of such a polishing liquid include an alkaline solution having an abrasive grain (for example, silica) concentration of 1% by mass or less. As the alkaline solution, an inorganic alkaline solution (KOH, NaOH, etc.), an organic alkaline solution (for example, piperazine or ethylenediamine containing amine as a main component) or a mixed solution thereof is suitable.
In this polishing method, the abrasive concentration is 1% by mass or less, and therefore there is almost no mechanical polishing action by the abrasive grains, and the chemical polishing action is prioritized. And a part (Si layer) of the wafer for active layers is grind | polished by the chemical grinding | polishing effect | action by this alkaline solution. Since the alkaline solution has a high etching rate ratio of Si / (Si amorphous layer containing oxygen atoms or a layer in which SiO ₂ particles are dispersed in Si), the Si layer that is part of the wafer for the active layer is efficiently polished. However, the Si amorphous layer containing oxygen atoms or the layer in which SiO ₂ particles are dispersed in Si is hardly polished. Therefore, even if the mechanical accuracy of the polishing apparatus is not sufficient, the oxygen ion implanted layer is hardly polished, and only the Si layer is polished. As a result, the oxygen ion implanted layer can be uniformly exposed.
That is, the oxygen ion implanted layer in the present embodiment functions as a polishing stop layer having a sufficiently high polishing stop function.

  In particular, by etching Si before polishing, the boundary between the terrace (the outermost 1 to 3 mm area where the two wafers are not bonded together) and the bonded area becomes smooth, and the generation of particles is suppressed. Note that only the terrace portion may be polished before polishing.

(6) Oxygen ion implantation layer removal step In this embodiment, the exposed oxygen ion implantation layer is then removed. This oxygen ion implantation layer is made of Si amorphous containing oxygen atoms, partially recrystallized Si, and SiO ₂ . As a removal method, an etching method, an oxidation + etching method, polishing, or the like can be applied.
・ Etching method Oxygen ion implantation layer is a complete SiO ₂ layer (BOX layer). Oxygen dose amount and heat treatment are not sufficient conditions. Therefore, HF solution that removes SiO ₂ is used for etching. Etching conditions such as an alkaline solution for removing Si or an SC1 solution or ozone solution for oxidizing Si and an HF solution for removing SiO ₂ formed by oxidation are preferred.
In any case, after immersing in the HF solution and using the HF solution, it is preferable to repeat the oxidation + HF until the entire wafer surface becomes a water-repellent surface, which is a measure for removing SiO ₂ .

Oxidation method This method comprises a step of forming an oxide film having a predetermined thickness on the exposed surface of the oxygen ion implanted layer and a step of removing the oxide film.
This oxidation treatment may be performed in an oxidizing atmosphere, and the treatment temperature is not particularly limited, but is preferably an oxidizing atmosphere at 600 to 1000 ° C.
However, in order to suppress the deterioration of the surface roughness due to the SiO ₂ particles generated by recrystallization of the amorphous of the oxygen ion implanted layer, it is preferable to perform the treatment at a low temperature, more preferably 600 to 900 ° C. .
When performing oxidation treatment at low temperature, we can apply wet oxidation using H ₂ O vapor or hydrochloric acid oxidation of oxidizing gas treatment containing HCl gas to increase the growth rate of the oxide film, and high throughput is achieved. More preferred for obtaining.
The thickness of the oxide film is not particularly limited. However, when a crystal defect layer is present in the oxygen ion implanted layer, it is preferable to set the thickness to be equal to or greater than the thickness. Is preferably about 100 to 500 nm. If the thickness of the oxide film is less than 100 nm, the Si amorphous layer cannot be sufficiently removed under the oxygen ion implantation conditions of the present embodiment, while if it exceeds 500 nm, the active layer is broken due to the collapse of the in-plane uniformity of the oxide film. The film thickness uniformity deteriorates.
In order to remove the oxide film, cleaning with HF solution or etching by annealing using hydrogen gas, Ar gas, or gas containing HF may be used. Here, the above oxidation treatment and removal treatment may be performed a plurality of times. As a result, it is possible to further reduce the thickness of the active layer while maintaining the flattened surface roughness.
After removing the oxide film, for example, it is advantageous to immerse the bonded wafer in a mixed solution of organic acid and hydrofluoric acid to remove particles and metal impurities adhering to the surface of the bonded wafer.

(7) Planarization and / or thinning step of wafer surface for active layer In this embodiment, the surface of the wafer for active layer is then planarized.
Since the bonded wafer surface after removal of the oxygen ion implanted layer is rough as compared with mirror polishing, it is desirable to make it flat.
As a planarization method, heat treatment in a reducing atmosphere, gas etching made of gas, ions, radicals, etc. capable of polishing and Si etching can be applied.
・ Polishing method The surface to be bonded is slightly polished to improve roughness. The polishing allowance is preferably about 10 to 500 nm. If the thickness is less than 10 nm, the roughness cannot be improved sufficiently, while if it exceeds 500 nm, the film thickness uniformity of the active layer deteriorates. By this treatment, the surface roughness (RMS) can be reduced to 0.5 nm or less.

・ Reducing atmosphere heat treatment
The roughness of the bonded wafer surface is improved by heat treatment in an atmosphere of Ar, H ₂ or a mixture thereof. The treatment temperature is preferably about 1000 ° C to 1300 ° C. The treatment time needs to be longer as the temperature is lower, preferably about 1 to 2 hours at 1000 to 1200 ° C, about 10 to 30 minutes at 1200 to 1250 ° C, and about 1 to 5 minutes at 1250 ° C or higher. When heat treatment is performed at a high temperature for a long time exceeding the above temperature and time, the in-plane uniformity of the active layer may be deteriorated due to the etching action in the reducing atmosphere.
In the present embodiment, sufficient bonding strength is not always obtained by heat treatment after bonding to removal of the oxygen ion implantation layer. Accordingly, a planarization treatment at a temperature of 1100 ° C. or higher that improves the bonding strength after removing the oxygen ion implanted layer is more preferable.
When surface activation is performed by plasma or the like in the pre-bonding treatment, heat treatment at 1100 ° C. or higher is not necessarily required.
As the heat treatment furnace, a resistance heating type vertical furnace capable of processing a plurality of sheets at the same time or a lamp heating type RTA (high speed heating / cooling furnace) for processing each sheet is suitable. In particular, RTA is effective for treatments above 1200 ° C.
By the above heat treatment, the surface roughness (RMS) can be reduced to 0.5 nm or less, as in the case of the polishing method.
The removal of the surface oxide film generated by this heat treatment may be performed by cleaning with HF liquid, or etching by annealing using a gas containing hydrogen gas, Ar gas, or HF.

  Thus, according to the present embodiment, it is possible to obtain a bonded wafer that is excellent in film thickness uniformity, has few defects, and has a markedly improved surface roughness.

In order to confirm the feasibility of this embodiment, the method of performing oxygen ion implantation once is similar to this embodiment, but the average oxygen concentration distribution in the thickness direction in the oxygen ion implanted layer has a single peak. Reference examples and comparative examples in which bonded wafers having two peaks close to each other are manufactured will be described below.
Prepare two silicon wafers each having a diameter of 300 mm and grown from the silicon ingot grown by the CZ method and boron as a dopant. The other silicon wafer was used as a support layer wafer.
Each set of active layer wafers was heat-treated at 1000 ° C. for 10 minutes in an oxidizing atmosphere to form an oxide film having a thickness of 10 nm.
Next, high-temperature oxygen ion implantation was performed from the surface of each group of active layer wafers at an acceleration voltage of 200 keV and a dose of 1.0 × 10 ¹⁷ atoms / cm ² . In each set of low-temperature implantation, the substrate temperature was set to room temperature to 200 ° C., the acceleration voltage was set to 180 keV to 240 keV, and the dose was set to 0.04 × 10 ¹⁷ atoms / cm ² . In some samples, the low temperature implantation is divided into two parts with a dose of 0.02 × 10 ¹⁷ atoms / cm ² , the first acceleration voltage is 200 keV, the second acceleration voltage is 210 keV, and each wafer is held. Injection was performed with the position rotated to 0 and 180 degrees, and HF + O ₃ was cleaned during the injection.
As a result, an oxygen ion implanted layer was formed at a depth of about 600 to 800 nm from the surface of each group of active layer wafers.
Next, each pair of active layer wafers was heat-treated before bonding (annealing) in a non-oxidizing (Ar) atmosphere, the heat treatment temperature was 1100 ° C., and the heat treatment time was 5 hours.

Next, HF + ozone cleaning was performed on both wafers in each group to remove particles on the bonding surface, and then both wafers in each group were bonded.
Thereafter, post-bonding heat treatment (annealing) was performed to firmly bond the bonding interfaces of both wafers in each group. The heat treatment conditions were 1100 ° C. for 2 hours in a wet oxidizing gas atmosphere, and an oxide film having a thickness of about 600 nm was formed on the front and back surfaces of the bonded wafer to form a back surface protective film during post-processing.
Next, the active layer wafer of each bonded wafer was ground by a predetermined thickness from the surface using a grinding apparatus. That is, a grinding process was performed to leave only a part of the active layer wafer (film thickness of about 5 μm) on the surface side of the oxygen ion implanted layer.
Subsequently, the surface of each bonded wafer after grinding was polished while supplying a polishing agent containing abrasive grains having an abrasive grain (silica) concentration of 1% by mass or less to expose the oxygen ion implanted layer. As an abrasive | polishing agent, the alkaline solution whose abrasive grain concentration is 1 mass% or less was used. This alkaline solution is an organic alkaline solution, and contains an amine as a main component (for example, piperazine, ethylenediamine, etc.).

Thereafter, each bonded wafer was subjected to a wet oxidation treatment at a temperature of 950 ° C. for 0.5 hours in an oxidizing atmosphere. As a result, an oxide film having a predetermined thickness was formed on the exposed surface of the oxygen ion-implanted layer, and the Si amorphous layer containing oxygen atoms became an oxide film (SiO ₂ ). Next, the oxide film was removed by HF etching (HF liquid composition: 10%, temperature: 20 ° C.). As a result, after the oxide film was removed, the exposed active layer had a uniform thickness in the surface and a thin film.

Next, each bonded wafer was cleaned by the following process. First, in a dissolved ozone aqueous solution having an ozone concentration of 5 ppm, then in an aqueous solution in which 0.06% by mass of citric acid as an organic acid is mixed with pure water, and in an aqueous solution in which 0.05% by mass of hydrofluoric acid is added, Finally, the sample was immersed in an aqueous solution containing 0.6% by mass of citric acid, which is an organic acid, and finally in a room temperature dissolved ozone aqueous solution having an ozone concentration of 5 ppm. The treatment time was 5 minutes each, and the temperature was room temperature. By this cleaning treatment, metal impurities and particles were removed from the surface of each bonded wafer.
After the cleaning, heat treatment was performed at 1100 ° C. for 2 hours in an argon gas atmosphere to complete each bonded wafer.

Table 1 shows the results of each condition. Although the SOI film thickness uniformity is improved by performing the low temperature implantation (Reference Example 1 and Comparative Examples 2 and 3), in Examples 1 and 2 of the present invention in which the acceleration voltage is slightly increased compared to the high temperature implantation, the film thickness is further increased. It can be seen that the uniformity is improved.
Further, in Example 3 of the present invention in which the low temperature implantation was divided into two, the SOI film thickness uniformity showed the best value of 4 nm.

  Thus, according to the method for producing a bonded wafer of the present invention, it is possible to have an oxygen ion implanted layer having a sufficiently high polishing stop function, which is desirable as a polishing stop layer, during the production of the bonded wafer. A bonded wafer having excellent film thickness uniformity can be manufactured at low cost.

It is a figure which shows the process flow of one Embodiment of this invention. (a) is a cross-sectional TEM photograph after bonding of wafers subjected to heat treatment after implantation of oxygen ions in accordance with the conditions of the above-described embodiment and (b) according to conventional conditions, respectively. A wafer in which oxygen ion implantation is performed in two stages of high-temperature implantation and low-temperature implantation as in the above embodiment, where (a) is an acceleration voltage of low-temperature implantation larger than that of high-temperature implantation, and (b) is a low-temperature implantation. Although the acceleration voltage for implantation is slightly lower than that for high-temperature implantation, each is a cross-sectional TEM photograph after implantation of oxygen ions. (a), (b), and (c) show the influence of the polished surface state after polishing stop of the bonded wafer subjected to oxygen ion implantation and pre-bonding heat treatment by the conventional method on the surface state after oxide film removal. It is sectional drawing which shows this typically.

Claims (5)

A method for manufacturing a bonded wafer by bonding an active layer wafer and a support layer wafer,
(1) a step of implanting oxygen ions into the active layer wafer to form an oxygen ion implanted layer;
(2) After the step of forming the oxygen ion implantation layer of (1), a step of heat-treating the active layer wafer at a temperature of 1100 ° C. or higher in a non-oxidizing atmosphere;
( 3 ) bonding the surface of the active layer wafer on the oxygen ion implantation side and the support layer wafer directly or via an insulating film;
( 4 ) a heat treatment process for improving the bonding strength of the bonded wafers;
( 5 ) The thickness of the wafer portion for the active layer of the bonded wafer is reduced using the oxygen ion implanted layer as a stop layer to expose the oxygen ion implanted layer;
( 6 ) removing the oxygen ion implanted layer from the wafer portion for the active layer of the bonded wafer;
Including a series of processes including
In the step of implanting oxygen ions into the active layer wafer described in (1) above, oxygen ions are implanted into the active layer wafer at a high temperature exceeding 200 ° C., and then accelerated from the oxygen ion implantation at the high temperature. At least once including the case where the voltage is increased, oxygen ion implantation is performed at a low temperature of 200 ° C. or lower to form an oxygen ion implanted layer ,
In the heat treatment step (2), the maximum ion implantation region by oxygen ion implantation at a high temperature and the amorphous layer by oxygen ion implantation at a low temperature are combined into one, and the oxygen ion implantation layer is formed as an average oxygen in the thickness direction. A method for producing a bonded wafer, wherein the concentration distribution has a single peak .   In the oxygen ion implantation at the low temperature in the oxygen ion implantation step (1) in the active layer wafer, the oxygen ion implantation at the high temperature is the same as the acceleration voltage and the oxygen ion implantation at the high temperature. The method for producing a bonded wafer according to claim 1, wherein oxygen ions are implanted a plurality of times including the case where the acceleration voltage is increased. In the step of implanting oxygen ions into the active layer wafer of (1) above, the acceleration voltage at the time of oxygen ion implantation at the high temperature is VH, and the acceleration voltage at the time of oxygen ion implantation at the low temperature is VL. , At least once low temperature injection under the following conditions
1.0 × VH <VL <1.2 × VH
The method for producing a bonded wafer according to claim 2, wherein: In the step of implanting oxygen ions into the active layer wafer of (1) above, the dose amount at the time of oxygen ion implantation at the high temperature is 1.0 × 10 ^{16 to} 1.0 × 10 ¹⁸ atoms / cm ² , the oxygen at the low temperature The method for manufacturing a bonded wafer according to any one of claims 1 to 3, wherein a dose amount during ion implantation is set to 1.0 × 10 ^{15 to} 1.0 × 10 ¹⁷ atoms / cm ² .   In the step of implanting oxygen ions into the active layer wafer of (1), the oxygen ions are implanted a plurality of times at the low temperature, and the wafer is rotated 360 degrees and the resting during the plurality of oxygen ion implantations. The method for producing a bonded wafer according to any one of claims 1 to 4, wherein the wafer is rotated by a predetermined angle other than an integral multiple.

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