JP6759626B2 - Epitaxial wafer manufacturing method and epitaxial wafer - Google Patents

Description

The present invention relates to a method for manufacturing an epitaxial wafer and an epitaxial wafer.

In the semiconductor wafer manufacturing process and the device forming process, if heavy metals are mixed in the semiconductor wafer that is the substrate of the device, the device characteristics such as pause time failure, retention failure, junction leakage failure, and dielectric breakdown of the oxide film are significantly adversely affected. Therefore, conventionally, in order to prevent heavy metals from diffusing into a device forming region, which is a region for forming a device, on the surface of a silicon wafer, which is a typical substrate, a gettering ability has been imparted by a gettering method.

The gettering method includes an intrinsic gettering method (IG method) in which oxygen is precipitated inside a silicon wafer and the formed oxygen precipitate is used as a gettering site, and a back surface of the silicon wafer. There is an Extrinsic Gettering method (EG method) in which mechanical strain is applied by using a sandblast method or the like, or a polycrystalline silicon film or the like is formed to form a gettering site.

However, in recent years, due to the lower temperature of the device forming process and the larger diameter of the silicon wafer, there has been a problem that the gettering ability cannot be sufficiently imparted to the silicon wafer. That is, in the IG method, it is difficult to form oxygen precipitates inside the silicon wafer due to the low temperature of the manufacturing process.

Regarding the EG method, for a silicon wafer having a diameter of 300 mm or more, it is customary to perform a mirror polishing treatment not only on the main surface but also on the back surface, and mechanical strain is applied to the back surface of the silicon wafer. It is in a situation where it is not possible to give a wafer or form a polycrystalline silicon film or the like.

If a silicon wafer cannot be provided with sufficient gettering capacity, if metals with very slow diffusion rates such as titanium (Ti), molybdenum (Mo), and tungsten (W) adhere to the wafer surface, the temperature of the device forming process will be lowered. Therefore, the device cannot be sufficiently separated from the device forming region, and device characteristic defects (for example, white scratch defects in the case of a solid-state image sensor) occur. Therefore, it is necessary to form a gettering layer directly under the device forming region so that such a metal having a slow diffusion rate can be captured.

Further, in recent years, it has been required that no crystal defects exist in the device forming region, and an epitaxial layer is formed on a silicon wafer, and this epitaxial layer is used as a device forming region. Therefore, the wafer manufacturing process is a process of forming a gettering layer on the surface layer region of the support substrate wafer and then forming an epitaxial layer on the surface of the support substrate wafer by a known CVD method or the like.

As a method for forming a gettering layer on such an epitaxial wafer, Patent Document 1 states that carbon ions are injected into the surface of a silicon wafer to form a gettering layer containing a high concentration of carbon in the surface layer region of the wafer, and then the silicon is formed. A method of forming an epitaxial layer on the surface of a wafer is described.

When the gettering layer is formed by the above carbon ion implantation method, the carbon ion implantation range is increased to avoid the diffusion of carbon into the epitaxial layer as much as possible, and the position is relatively deep from the wafer surface. Ion implantation treatment is performed so that a gettering layer is formed in the wafer.

However, when the gettering layer is formed at a position relatively deep from the wafer surface, the heavy metal having a slow diffusion rate cannot be separated from the device forming region due to the low temperature of the device forming process described above, and the heavy metal is captured by the gettering layer. There is a concern that it cannot be done.

Further, in order to form a gettering layer by injecting carbon ions at a high concentration from the wafer surface, it is necessary to increase the accelerating voltage of the carbon ions, but in that case, the crystallinity of the wafer surface deteriorates. There is also a problem that crystal defects occur in the epitaxial layer grown on the epitaxial layer.

Therefore, in Patent Document 2, the constituent elements of the molecular ions are introduced into the silicon wafer in a state where the acceleration voltage per atom is reduced by irradiating the surface of the silicon wafer as the wafer for the support substrate with the molecular ions. A technique capable of improving the gettering ability without increasing the crystal defects of the epitaxial layer by forming a modified layer containing the above-mentioned constituent elements and using the modified layer as a gettering layer is described. There is.

Japanese Patent No. 3384506 International Publication No. 2012/157162

However, when a gettering layer is formed in the surface layer region of a silicon wafer as a wafer for a support substrate by the method of Patent Document 2 and an epitaxial layer is formed on the gettering layer to manufacture an epitaxial wafer, the process of forming the epitaxial layer becomes high temperature. Since this is a process, the constituent elements of the gettering layer and impurities such as dopants and oxygen contained in the silicon wafer diffuse from the silicon wafer as the wafer for the support substrate to the epitaxial layer, and the photodiode is used in the subsequent device formation process. There was a risk that device characteristics such as abnormal charge status and pn junction leak would occur.

Therefore, an object of the present invention is a method for manufacturing an epitaxial wafer, which can suppress the diffusion of constituent elements of the gettering layer and impurities such as oxygen in the wafer for the support substrate to the epitaxial layer when the epitaxial layer is formed. And to provide epitaxial wafers.

The present inventor has diligently studied ways to solve the above problems. As described above, in the conventional method for manufacturing an epitaxial wafer, the support substrate wafer having the gettering layer is inevitably exposed to a high temperature environment when the epitaxial layer is formed. Therefore, the gettering layer in the support substrate wafer is used. In principle, it is difficult to prevent impurities such as constituent elements and oxygen from diffusing into the epitaxial layer.

Therefore, the present inventor has diligently studied a method of providing an epitaxial layer on the support substrate wafer without exposing the support substrate wafer to a high temperature environment. As a result, the epitaxial layer is not directly formed on the support substrate wafer having the gettering layer, but is formed on the active layer wafer prepared separately, and the active layer wafer and the support substrate wafer are vacuumed. In addition, after laminating in an environment at room temperature, he came up with a method for removing the wafer for the active layer, and completed the present invention.

That is, the gist structure of the present invention is as follows.
(1) An epitaxial layer forming step of forming a silicon epitaxial layer on the surface of a silicon wafer for an active layer, a silicon wafer for a support substrate having an oxygen concentration of 8 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or more, and the above. A gettering layer forming step of forming a gettering layer containing an element that contributes to heavy metal gettering inside at least one of the silicon epitaxial layers, and the surface of the silicon epitaxial layer and the supporting substrate in a vacuum and normal temperature environment. After the surface of the silicon wafer for use is activated to form amorphous layers on both surfaces, the silicon wafer for the active layer and the silicon wafer for the support substrate are attached via the amorphous layers on both surfaces. It has a bonding step of joining and a substrate removing step of removing the silicon wafer for the active layer to expose the silicon epitaxial layer, and the silicon wafer for the support substrate and the amorphous layer on the silicon wafer for the support substrate. And the silicon epitaxial layer on the amorphous layer, and the silicon epitaxial layer on the amorphous layer has an oxygen concentration of 1 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) over the entire thickness direction. A method for manufacturing an epitaxial wafer, which comprises the following.

(2) The epitaxial according to (1) above, wherein the activation treatment is a process of causing an ionized neutral element to collide with the surface of the silicon epitaxial layer or the silicon wafer for a support substrate and sputtering the surface. Wafer manufacturing method.

(3) The method for producing an epitaxial wafer according to (2) above, wherein the neutral element is at least one selected from the group consisting of argon, neon, xenon, hydrogen, helium and silicon.

(4) The method for manufacturing an epitaxial wafer according to any one of (1) to (3) above, wherein the activation treatment is a plasma etching treatment.

(5) The method for manufacturing an epitaxial wafer according to any one of (1) to (4) above, wherein the activation treatment is performed so that the thickness of the amorphous layer is 2 nm or more.

(6) The method for manufacturing an epitaxial wafer according to any one of (1) to (4) above, wherein the activation treatment is performed so that the thickness of the amorphous layer is 10 nm or more.

(7) Between the epitaxial layer forming step or the gettering layer forming step and the bonding step, hydrogen, nitrogen, and hydrogen, nitrogen, are formed on at least one of the surface of the silicon epitaxial layer and the surface of the silicon wafer for the support substrate. The method for producing an epitaxial wafer according to any one of (1) to (6) above, which comprises a step of containing an element consisting of at least one selected from the group consisting of fluorine and oxygen.

(8) The method for producing an epitaxial wafer according to (7) above, wherein a Group 3B element is contained together with an element consisting of at least one selected from the group consisting of hydrogen, nitrogen, fluorine and oxygen.

(9) The gettering layer forming step is performed by irradiating at least one surface of the silicon wafer for a support substrate and the silicon epitaxial layer with molecular ions containing an element that contributes to gettering of a heavy metal. )-(8). The method for manufacturing an epitaxial wafer according to any one of the items.

(10) The gettering layer forming step is performed by injecting monomer ions of an element that contributes to heavy metal gettering into at least one surface of the silicon wafer for a support substrate and the silicon epitaxial layer. The method for manufacturing an epitaxial wafer according to any one of (8).

(11) A silicon wafer having an oxygen concentration of 8 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or more, an amorphous layer on the silicon wafer, a silicon epitaxial layer on the amorphous layer, the silicon epitaxial layer, and the silicon wafer. A gettering layer is provided inside at least one of the silicon wafers, and the oxygen concentration over the entire thickness direction of the silicon epitaxial layer is 1 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less. Epitaxial wafer.

(12) The epitaxial wafer according to (11) above, wherein the amorphous layer has a thickness of 2 nm or more.

(13) The epitaxial wafer according to (11) above, wherein the amorphous layer has a thickness of 10 nm or more.

(14) The epitaxial wafer according to any one of (11) to (13 ) above, wherein the amorphous layer contains at least one selected from the group consisting of hydrogen, nitrogen, fluorine and oxygen.

(15) The epitaxial wafer according to (14) above, wherein the amorphous layer further contains a Group 3B element.

According to the present invention, the epitaxial layer is not directly formed on the support substrate wafer having the gettering layer, but is formed on the active layer wafer prepared separately, and the active layer wafer and the support substrate wafer are formed. Since the wafers for the active layer are removed after the wafers are bonded together in a vacuum and at room temperature, the constituent elements of the gettering layer and impurities such as oxygen in the wafer for the support substrate are epitaxial when the epitaxial layer is formed. It is possible to suppress the diffusion to the layer.
Further, according to the present invention, since the amorphous layer is provided at the interface between the epitaxial layer and the wafer for the support substrate, the diffusion of impurities such as oxygen from the wafer for the support substrate to the epitaxial layer is suppressed in the device forming process. be able to.

It is a flowchart of the manufacturing method of the epitaxial wafer which concerns on one Embodiment of this invention. It is a figure which shows an example of a vacuum room temperature bonding apparatus. It is a flowchart of the manufacturing method of the epitaxial wafer which concerns on a preferable embodiment of this invention. It is a carbon concentration profile with respect to (a) conventional example and (b) invention example 1. It is an oxygen concentration profile with respect to (a) conventional example and (b) invention example 1. It is a figure which shows the result of infrared ray observation with respect to the epitaxial wafer manufactured in Invention Example 1. FIG. It is a cross-sectional TEM image of an epitaxial wafer immediately after being manufactured in Invention Example 1.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a flowchart of a method for manufacturing an epitaxial wafer according to an embodiment of the present invention. The methods shown in this figure include an epitaxial layer forming step (FIGS. 1 (A) and 1 (B)) for forming an epitaxial layer 17 on the surface of the active layer wafer 11, and the support substrate wafer 12 and the epitaxial layer. A gettering layer forming step (FIGS. 1 (C) and 1 (D)) for forming a gettering layer 16 containing an element that contributes to heavy metal gettering inside at least one of 17 and an environment of vacuum and normal temperature. After the surface of the epitaxial layer 17 and the surface of the support substrate wafer 12 are activated to form the amorphous layer 18 on both surfaces (FIG. 1 (E)), the active layer wafer 11 and the support substrate are formed. A bonding step (FIG. 1 (F)) in which the wafer 12 for bonding is bonded via the amorphous layers 18 on both surfaces, and a substrate removing step (FIG. 1) in which the wafer 11 for the active layer is removed to expose the epitaxial layer 17. It is characterized by having (G)). Hereinafter, each step will be described.

First, as shown in FIG. 1A, the active layer wafer 11 and the support substrate wafer 12 are prepared. The active layer wafer 11 is a wafer used as a temporary support substrate for the epitaxial layer 16 used as a device forming region. As the active layer wafer 11, a single crystal silicon wafer made of a silicon single crystal can be used.

As the single crystal silicon wafer, a single crystal silicon ingot grown by a known method such as the Czochralski (CZ) method or the floating zone melting (Floating Zone, FZ) method is sliced with a wire saw or the like. can do. Further, an arbitrary impurity can be added to obtain an n-type or a p-type, and the resistivity, oxygen concentration, etc. can be adjusted by adjusting the concentration of the impurity.

Regarding the oxygen concentration of the active layer wafer 11, when the epitaxial layer 17 is formed on the active layer wafer 11, if the oxygen concentration of the active layer wafer 11 is high, the oxygen diffusion into the epitaxial layer 17 is large. Become. Therefore, it is preferable to use a wafer 11 for an active layer having a low oxygen concentration. In this case, for example, a silicon wafer prepared by the FZ method or a silicon wafer having a low oxygen concentration of 3 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less prepared by the CZ method can be used as the wafer 11 for the active layer. it can.

Further, regarding the dopant concentration in the active layer wafer 11, the same specifications as the epitaxial layer 17 (the dopant type and its concentration are the same) from the viewpoint of reducing the diffusion of the dopant in the active layer wafer 11 into the epitaxial layer 17. ), A non-doped silicon wafer to which no dopant is added, a high resistance silicon wafer having a resistance of 100 Ω · cm or more, and the like are preferably used as the active layer wafer 11.

When a low oxygen silicon wafer, a high resistance silicon wafer, or the like is not used as the active layer wafer 11, the diffusion region in which the dopant has diffused into the epitaxial layer 17 during the formation of the epitaxial layer 17 is thinned (polishing treatment). ), It is possible to obtain an epitaxial layer 17 having a quality level that does not cause any problem as a product. In this case, the epitaxial layer 17 that is thick enough to be thinned and deleted is formed in advance.

Further, the support substrate wafer 12 is a wafer that supports the epitaxial layer 17 that is a device forming region, and a gettering layer 16 that captures heavy metals adhering to the epitaxial layer 16 is formed in the surface layer region thereof. As the support substrate wafer 12, it is desirable to use a single crystal silicon wafer made of a silicon single crystal, similarly to the active layer wafer 11. Further, an arbitrary impurity can be added to obtain an n-type or a p-type, and the resistivity, oxygen concentration, etc. can be adjusted by adjusting the concentration of the impurity.

When the oxygen concentration in the support substrate wafer 12 is high, the amount of oxygen diffused into the epitaxial layer 17 in the device forming process increases, so that the oxygen concentration is preferably low. On the other hand, when the oxygen concentration in the support substrate wafer 12 is low, the gettering effect due to BMD formation in the support substrate wafer 12 becomes low. Therefore, from the viewpoint of forming the BMD and obtaining the gettering ability, the oxygen concentration of the support substrate wafer 12 is preferably 8 × 10 ¹⁷ atoms / cm ³ or more.

Further, the dopant concentration of the support substrate wafer 12 can be appropriately set based on the specifications.

Next, as shown in FIG. 1B, an epitaxial layer forming step of forming the epitaxial layer 17 on the surface of the active layer wafer 11 is performed. Examples of the epitaxial layer 17 include a silicon epitaxial layer, which can be formed under general conditions. For example, hydrogen (H) is used as a carrier gas, and a source gas such as dichlorosilane (H ₂ Cl ₂ Si) or trichlorosilane (HCl ₃ Si) is introduced into the chamber, and the growth temperature differs depending on the source gas used. The silicon epitaxial layer 17 can be epitaxially grown on the active layer wafer 11 by a CVD (Chemical Vapor Deposition) method at a temperature in a temperature range of approximately 1000 to 1200 ° C. The thickness of the epitaxial layer 17 is not particularly limited, and may be appropriately set based on the specifications of the device forming region.

Further, the oxygen concentration of the epitaxial layer 17 is preferably 1 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less over the entire thickness direction of the epitaxial layer 17.

Subsequently, as shown in FIG. 1C, a gettering layer forming step of forming a gettering layer 16 containing an element contributing to metal gettering inside at least one of the support substrate wafer 12 and the epitaxial layer 17. I do. FIG. 1 illustrates a case where the gettering layer 16 is formed inside the support substrate wafer 12. In this gettering layer forming step, ion (monomer ion) of an element that contributes to gettering of heavy metals is injected into the wafer surface, or as shown in FIG. 1C, molecular ions are injected into the support substrate wafer 12. This can be done by irradiating the surface.

Here, the "molecular ion" is not only an ion obtained by applying a positive charge or a negative charge to a single molecule, but also an ion obtained by combining a plurality of molecules into a mass, and one or more molecules. It also includes an ionized mass formed by bonding one or more atoms. The number of such molecules and atoms can be, for example, 2 to 200.

The element constituting the monomer ion or the molecular ion is not particularly limited as long as it is an element that contributes to gettering. For example, it is preferably at least one selected from the group consisting of hydrogen (H), helium (He), carbon (C), argon (Ar) and silicon (Si). This is because the above elements do not affect the resistivity of the epitaxial wafer. By ionizing these elements and introducing them into at least one of the support substrate wafer 12 and the epitaxial layer 17, the gettering layer 16 can be formed directly under the device forming region.

From the viewpoint of obtaining higher gettering ability, the formation of the gettering layer 16 is performed by forming molecular ions on at least one of the surface 12A of the support substrate wafer 12 and the surface of the epitaxial layer 17, as shown in FIG. 1C. It is preferable to carry out by irradiating. That is, when the gettering layer 16 is formed by irradiating at least one of the wafer surface 12A and the surface of the epitaxial layer 17 with molecular ions, the accelerating voltage per atom is smaller than that in the case of forming by injecting monomer ions. In this state, the constituent elements of the molecular ions can be introduced into the wafer.

Therefore, the constituent elements of the molecular ions can be confined in a narrow region in the wafer thickness direction, and the peak concentration of the constituent elements can be increased to enhance the gettering ability. Moreover, as described above, since the acceleration energy per atom can be reduced, the damage when the constituent elements of the molecular ions are introduced into the wafer can be reduced, and the epitaxial defects caused by the introduction of the ions can be reduced. It can be reduced.

For the conditions for injecting (irradiating) monomer ions or molecular ions into the substrate, for example, the acceleration voltage, the dose amount, etc., known or general conditions may be adopted while considering the gettering ability. Further, as a monomer ion generator or a molecular ion generator, a conventional device can also be used. The epitaxial layer forming step and the gettering layer forming step may be performed first or in parallel.

Subsequently, as shown in FIG. 1 (E), the surface of the epitaxial layer 17 and the surface of the support substrate wafer 12 on the gettering layer 16 side are subjected to activation treatment in a vacuum and normal temperature environment. An amorphous layer 18 is formed on the surface, and subsequently, as shown in FIG. 1 (F), a bonding step of bonding the active layer wafer 11 and the support substrate wafer 12 via the amorphous layers 18 on both surfaces. I do.

In the present invention, the active layer wafer 11 and the support substrate wafer 12 that have undergone the steps up to FIG. 1 (D) are bonded together in a vacuum and normal temperature environment (hereinafter, this bonding process is referred to as "vacuum room temperature bonding". Also called). As a pretreatment for that purpose, when the bonding surface of the active layer wafer 11 and the support substrate wafer 12, that is, the gettering layer 16 is formed inside the support substrate wafer 12 in a vacuum and normal temperature environment. When the gettering layer 16 is formed inside the epitaxial layer 17 on each of the surface of the epitaxial layer 17 of the active layer wafer 11 and the surface of the support substrate wafer 12 on the gettering layer 16 side, epitaxial Each of the surface of the layer 17 and one surface of the support substrate wafer 12 is subjected to an activation treatment for activating the bonded surface.

By the above activation treatment, an amorphous layer 18 is formed on each bonded surface, and a dangling bond of an element constituting the amorphous layer 18 is formed on the surface thereof. Since this dangling bond is energetically unstable, when both bonded surfaces are brought into contact with each other in the subsequent processing, a bonding force acts between the wafers so as to eliminate the dangling bonds on both surfaces, and a treatment such as heat treatment is performed. The active layer wafer 11 and the support substrate wafer 12 can be firmly bonded to each other without a non-bonding region (void).

In the activation treatment of the bonded surface, the ionized neutral element accelerated by the ion beam device is made to collide with the bonded surface to sputter the surface, or the neutral element ionized in the plasma atmosphere is accelerated to the wafer surface. It can be performed by performing a plasma etching process for etching.

FIG. 2 shows an example of a vacuum room temperature bonding apparatus in which two wafers are bonded after activating the bonding surface by a plasma etching method. The device 50 includes a plasma chamber 51, a gas introduction port 52, a vacuum pump 53, a pulse voltage application device 54, and wafer fixing bases 55A and 55B.

First, the active layer wafer 11 and the support substrate wafer 12 are placed and fixed on the wafer fixing bases 55A and 55B in the plasma chamber 51, respectively. Next, after depressurizing the inside of the plasma chamber 51 by the vacuum pump 53, the raw material gas is introduced into the plasma chamber 51 from the gas introduction port 52. Subsequently, the pulse voltage applying device 54 applies a negative voltage to the wafer fixing bases 55A and 55B (wafers 11 and 12) in a pulsed manner. As a result, a plasma of the raw material gas is generated, and ions of the raw material gas contained in the generated plasma are accelerated and irradiated toward the wafers 11 and 12, and an amorphous layer 18 is formed on the wafer surface to form an amorphous layer 18 on the irradiated surface. , Dangling bonds of elements constituting the amorphous layer 18 can be formed.

The neutral element to be irradiated is preferably at least one selected from the group consisting of argon (Ar), neon (Ne), xenon (Xe), hydrogen (H), helium (He) and silicon (Si). ..

The pressure (vacuum degree) in the plasma chamber 51 is preferably 1 × 10 ⁻⁵ Pa or less. As a result, it is possible to suppress the reattachment of the sputtered elements to the wafer surface and perform the activation treatment without lowering the dangling bond formation rate.

The pulse voltage applied to the active layer wafer 11 and the support substrate wafer 12 is set so that the acceleration energy of the irradiation element with respect to the wafer surface is 100 eV or more and 10 keV or less. If the acceleration energy is less than 100 eV, the irradiated neutral element is deposited on the wafer surface, and a dangling bond cannot be formed on the wafer surface. On the other hand, when the acceleration energy exceeds 10 keV, the irradiated element is injected into the wafer, and even in this case, a dangling bond cannot be formed on the wafer surface.

The frequency of the pulse voltage determines the number of times the wafers 11 and 12 are irradiated with ions. The frequency of the pulse voltage is preferably 10 Hz or more and 10 kHz or less. Here, by setting the frequency to 10 Hz or higher, variations in ion irradiation can be absorbed and the amount of ion irradiation becomes stable. Further, by setting the frequency to 10 kHz or less, plasma formation due to glow discharge is stabilized.

The pulse width of the pulse voltage determines the time during which the wafers 11 and 12 are irradiated with ions. The pulse width is preferably 1 μsec or more and 10 msec or less. By setting the time to 1 μsec or more, ions can be stably irradiated to the wafers 11 and 12. Further, by setting the time to 10 msec or less, plasma formation by glow discharge is stabilized.

Since the wafers 11 and 12 are not heated in the above process, the temperature thereof is normal temperature (usually 30 ° C. to 90 ° C.).

Further, the activation treatment is preferably performed so that the thickness of the amorphous layer 18 is 2 nm or more. Thereby, the function of the amorphous layer 18 as a block layer for blocking the heat diffusion of impurities in the support substrate wafer 12 to the epitaxial layer 16 can be further enhanced. The thickness of the amorphous layer 18 can be adjusted by adjusting the accelerating voltage of ions.

Further, the activation treatment is preferably performed so that the thickness of the amorphous layer 18 is 10 nm or more. As a result, the amorphous layer 18 can be further enhanced in function as a block layer that suppresses heat diffusion of interstitial oxygen in the support substrate wafer 12 to the epitaxial layer 16.

As described above, in the present invention, since the active layer wafer 11 and the support substrate wafer 12 are bonded together in a vacuum and normal temperature environment, the support substrate wafer 12 on which the gettering layer 16 is formed is formed. It is not exposed to the high temperature environment associated with the formation of the epitaxial layer 17. As a result, when the epitaxial layer 17 is formed, thermal diffusion of the elements constituting the gettering layer 16 and impurities such as dopants and oxygen contained in the support substrate wafer 12 does not occur in principle.

Further, during the activation treatment in the bonding step, an amorphous layer 18 is formed on the bonding surface, and the amorphous layer 18 functions as a diffusion block layer of impurities in the support substrate wafer 18. Therefore, it is possible to prevent oxygen contained in the support substrate wafer 12 from being thermally diffused into the epitaxial layer 17 during the heat treatment in the subsequent device forming process.

Further, since the epitaxial layer 17 is not formed on the wafer surface to which the monomer ion implantation or the molecular ion irradiation for forming the gettering layer 16 is performed as in the conventional case, there is an epitaxial defect due to the implantation (irradiation) damage. do not do.

Finally, as shown in FIG. 1 (G), a substrate removing step of removing the active layer wafer 11 to expose the epitaxial layer 17 is performed. Well-known surface grinding and mirror polishing methods can be preferably used in this substrate removing step. Further, this substrate removing step may be performed by using another technique such as a well-known smart cutting method. After removing the active layer wafer 11, the epitaxial layer 17 may be thinned to a predetermined thickness. In this way, the epitaxial wafer 1 according to the present invention can be manufactured.

The epitaxial wafer 1 according to the present invention thus obtained is a novel epitaxial wafer formed by laminating, that is, joining, two wafers, unlike a conventional wafer in which an epitaxial layer is directly formed on a wafer for a support substrate. Is. Such an epitaxial wafer 1 according to the present invention can be referred to as a "bonded epitaxial wafer" or a "bonded epitaxial wafer".

As shown in FIG. 3, at least one of the surface of the epitaxial layer 17 and the surface of the support substrate wafer 12 on the gettering layer 16 side between the epitaxial layer forming step or the gettering layer forming step and the bonding step. It is preferable to further have a step (FIG. 3 (H)) of containing an element consisting of at least one selected from the group consisting of hydrogen, nitrogen, fluorine and oxygen. Thereby, during the heat treatment in the device forming process, the above elements can be thermally diffused to terminate the residual (End Of Range, EOR) defects caused by ion implantation in the device forming process and to be electrically inactivated. ..

Specifically, in the above step, at least one of the surface of the epitaxial layer 17 and the surface of the wafer 12 for the support substrate on the gettering layer 16 side is selected from at least one selected from the group consisting of hydrogen, nitrogen, fluorine and oxygen. It can be carried out by immersing in a liquid containing the above element.

Specific examples of the liquid containing the above elements include aqueous solutions such as hydrofluoric acid (containing hydrogen and fluorine), aqueous ammonia (containing nitrogen), hydrogen peroxide solution and ozone water (containing oxygen). Can be done. The concentration of the liquid can be 0.05% by weight to 50% by weight, and the immersion time can be 1 minute to 30 minutes.

Further, in the above step, at least one of the surface of the epitaxial layer 16 and the surface of the wafer 12 for the support substrate on the gettering layer 16 side is an element composed of at least one selected from the group consisting of hydrogen, nitrogen, fluorine and oxygen. This can be done by supplying the contained ions. For the supply of the ions, the ion implantation method or the molecular ion irradiation method used in the formation of the gettering layer 16 can be used.

When the above ions are supplied by the ion implantation method, specifically, ions such as H, N, and O are implanted by an ion implantation device with an accelerating voltage: 0.1 keV to 10 keV and a dose amount of 1 × 10 ¹⁴ atoms / cm. It can be carried out under the condition of ² to 1 × 10 ¹⁸ ions / cm ² .

When the ions are supplied by the molecular ion irradiation method, specifically, molecules such as C ₃ H ₅ and C ₁₆ H ₁₀ are accelerated by a cluster ion irradiation device with an accelerating voltage: 0.3 keV / molecule to 30 keV. / Molecule, dose amount: 1 × 10 ¹⁴ atoms / cm ² to 1 × 10 ¹⁸ atoms / cm ² .

The element consisting of at least one selected from the group consisting of hydrogen, nitrogen, fluorine and oxygen is preferably contained together with the Group 3B element. As described above, the step of containing an element consisting of at least one selected from the group consisting of hydrogen, nitrogen, fluorine and oxygen is performed between the epitaxial layer forming step or the gettering layer forming step and the bonding step. However, there is a risk that heat diffuses out of the amorphous layer 18 before the EOR defect is terminated in the device forming process. Here, when a Group 3B element is supplied together with the above element, a stable and strong bond is generated between the above element and the Group 3B element. As a result, the above elements are less likely to be thermally diffused from the amorphous layer 18, and EOR defects can be more effectively terminated in the device forming process.

The Group 3B element is a Group 3B (Group 13) element in the periodic table, and is an element such as boron (B), aluminum (Al), and gallium (Ga), and these can be used. Of these, boron (B) is preferably used because it forms a strong and stable bond with hydrogen, nitrogen, fluorine or oxygen.

(Epitaxial wafer)
Next, the epitaxial wafer according to the present invention will be described. The epitaxial wafer 1 according to the present invention shown in FIG. 1 (G) includes a support substrate wafer 11, an amorphous layer 18 on the support substrate wafer 11, and an epitaxial layer 17 on the amorphous layer 18. A gettering layer 16 is provided inside at least one of the layer 17 and the support substrate wafer 12.

In the epitaxial wafer 1 according to the present invention, the epitaxial layer 17 is not directly formed on the support substrate wafer 12 having the gettering layer 16, but is formed on a separately prepared active layer wafer 11. The active layer wafer 11 and the support substrate wafer 12 are bonded together in a vacuum and normal temperature environment, and then the active layer wafer 11 is removed to form the wafer. Therefore, when the epitaxial layer 17 is formed, thermal diffusion of elements constituting the gettering layer 16 and impurities such as dopants and oxygen contained in the support substrate wafer 12 does not occur in principle.

Further, the amorphous layer 18 functions as a diffusion block layer of impurities such as oxygen and elements contained in the gettering layer 16 in the support substrate wafer 12. Therefore, it is possible to prevent impurities contained in the support substrate wafer 12 from thermally diffusing into the epitaxial layer 17 during the heat treatment in the subsequent device forming process.

Here, by setting the thickness of the amorphous layer 18 to 2 nm or more, the function of blocking impurities of the amorphous layer 18 can be enhanced, and further, by setting the thickness of the amorphous layer to 10 nm or more, the amorphous layer 18 has a thickness of 10 nm or more. As described above, the function as a block layer for blocking the heat diffusion of interstitial oxygen in the support substrate wafer 12 to the epitaxial layer 16 can be further enhanced.

Further, as described above, it is preferable that the amorphous layer 18 contains at least one selected from the group consisting of hydrogen, nitrogen, fluorine and oxygen, and that the amorphous layer 18 further contains a Group 3B element. is there.

Further, the oxygen concentration of the epitaxial layer 17 is preferably 1 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less over the entire thickness direction of the epitaxial layer 17, and the oxygen concentration of the wafer for the support substrate is high. As described above, it is preferable that the size is 8 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or more.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

(Invention Example 1)
An epitaxial wafer according to Invention Example 1 was manufactured according to the flowchart shown in FIG. First, as a wafer for the active layer, a silicon wafer having a diameter of 200 mm and a thickness of 725 μm (oxygen concentration: 2.0 × 10 ¹⁷ atoms / cm ³ , dopant: phosphorus, dopant concentration: 4.4 × 10 ¹⁴ atoms / cm ^3). , Target resistivity: 10Ω · cm) was prepared. Further, as a wafer for a support substrate, a silicon wafer having a diameter of 200 mm and a thickness of 725 μm (oxygen concentration: 8.0 × 10 ¹⁷ atoms / cm ³ , dopant: phosphorus, dopant concentration: 1.4 × 10 ¹⁴ atoms / cm ^3). , Target resistivity: 30 Ω · cm) was prepared.

Next, an epitaxial layer of silicon (thickness: 8 μm, dopant: phosphorus, 4.4 × 10 ¹⁴ atoms / cm ³ ) was placed on the wafer for the active layer by a CVD method at 1150 ° C. using hydrogen as a carrier gas and dichlorosilane as a source gas. , Target resistivity: 10 Ω · cm) was formed.

In parallel with the formation of the epitaxial layer, the molecular ion generator (Nissin Ion Equipment Co., model number: CLARIS) generates a C ₃ H ₅ ion with an acceleration voltage 80 keV / molecular, dose: 1 The surface of the support substrate wafer was irradiated under the condition of × 10 ¹⁵ molecules / cm ² , and a gettering layer was formed inside the support substrate wafer.

Subsequently, the wafer for the active layer and the wafer for the support substrate were bonded together in a vacuum and normal temperature environment. Specifically, the wafer for the active layer and the wafer for the support substrate are introduced into the vacuum room temperature bonding apparatus shown in FIG. 2, the pressure in the chamber is set to 5.0 × ^10-5 Pa, and then Ar ions are accelerated. Under the conditions of voltage: 1.0 keV, frequency: 140 Hz, pulse width: 55 × ^10-6 seconds, it is injected into the surface of the epitaxial layer and the surface of the support substrate wafer 12 on the gettering layer side, and both are activated. An amorphous layer was formed on the surface. After that, the wafer for the active layer and the wafer for the support substrate were bonded together via the amorphous layers on both surfaces.

Finally, the surface of the active layer wafer is ground and polished to remove the active layer wafer and thinn it so as to leave an epitaxial layer of 4 μm to obtain an epitaxial wafer according to an embodiment of the present invention. It was.

(Conventional example)
An epitaxial wafer according to a conventional example of the present invention was manufactured in the same manner as in Invention Example 1. However, in the epitaxial layer forming step, the epitaxial layer was not formed on the active layer wafer, but was formed on the support substrate wafer after the gettering layer was formed, and the bonding step and the substrate removing step were not performed. All other conditions are the same as in Invention Example 1.

(Invention Example 2)
Similar to Invention Example 1, an epitaxial wafer according to an embodiment of the present invention was manufactured. However, according to the flowchart shown in FIG. 3, both the surface of the epitaxial layer and the surface of the wafer for the support substrate on the gettering layer side are formed between the epitaxial layer forming step (gettering layer forming step) and the bonding step. Fluorine and hydrogen were supplied to the wafer surface and contained in a 0.5 wt% aqueous solution of hydrofluoric acid for 10 minutes. All other conditions are the same as in Invention Example 1.

(Invention Example 3)
Similar to Invention Example 2, an epitaxial wafer according to an embodiment of the present invention was manufactured. However, the element feeding step, the molecular ion generator (Nissin Ion Equipment Co., model number: CLARIS) was used to generate the _B 5 _{H 5} ion, acceleration voltage: 80 keV / molecule dose: 2 × ^{10 14} molecules The surface of the support substrate wafer was irradiated under the condition of / cm ² , and boron (B) and hydrogen (H) were supplied and contained. Other conditions are all the same as in Invention Example 2.

<Carbon concentration profile>
SIMS measurement was performed on the epitaxial wafer immediately after being manufactured in the conventional example and the first invention to obtain a carbon concentration profile. FIG. 4A shows a conventional example, and FIG. 4B shows a carbon concentration profile with respect to Invention Example 1.

From FIG. 4A, it can be seen that in the epitaxial wafer produced in the conventional example, the carbon contained in the reformed layer is largely diffused in the epitaxial layer. On the other hand, from FIG. 4B, in the epitaxial wafer produced in Invention Example 1, the carbon contained in the modified layer is not diffused in the epitaxial layer, and the carbon concentration of the concentration profile peak is the conventional example. You can see that it is higher than that.

<Oxygen concentration profile>
SIMS measurement was performed on the epitaxial wafer immediately after being produced in the conventional example and the first invention to obtain an oxygen concentration profile. FIG. 5A shows a conventional example, and FIG. 5B shows an oxygen concentration profile with respect to Invention Example 1.

From FIG. 5A, in the epitaxial wafer produced in the conventional example, the oxygen concentration in the support substrate wafer is diffused and captured in the modified layer and has a high peak oxygen concentration, while in the support substrate wafer. It can be seen that oxygen is diffused in the epitaxial layer. On the other hand, from FIG. 5B, in the epitaxial wafer produced in Invention Example 1, oxygen in the support substrate wafer is not diffused into the epitaxial layer, and the interface between the epitaxial layer and the support substrate wafer It can be seen that the oxygen concentration changes sharply.

<Quality evaluation of epitaxial wafer>
FIG. 6 shows the results of infrared observation of the epitaxial wafer manufactured in Invention Example 1. As is clear from this figure, in the epitaxial wafer of Invention Example 1, no void, which is a non-bonding region, is formed between the wafers in the bonding step of bonding the active layer wafer and the support substrate wafer. It can be seen that a good bonding interface is formed. Similarly, in the epitaxial wafers of Invention Examples 2 and 3, a good bonding interface was formed.

Further, FIG. 7 shows a cross-sectional TEM image of the epitaxial wafer immediately after being manufactured in Invention Example 1. As is clear from FIG. 7, in the epitaxial wafer of Invention Example 1, it can be seen that the amorphous layer is formed between the epitaxial layer and the silicon wafer which is the wafer for the support substrate. Further, it can be seen that the epitaxial layer does not have secondary defects such as dislocations due to the crystal structure of the supporting wafer.

<Device formation process simulation process>
The device forming process simulation process was performed on the epitaxial wafers of Invention Examples 2 and 3 prepared as described above and the conventional example. Specifically, as a pre-stage treatment, the epitaxial layer is forcibly injected by implanting He ions from the surface side of the epitaxial layer at a dose amount of 1 × 10 ¹² cm- ² and an accelerating voltage of 200 keV using an ion implantation device. After forming the implantation defect inside, as a simulated heat treatment, an epitaxial wafer was introduced into the heat treatment furnace, the temperature was raised at a heating rate of 5 ° C./sec, and then the temperature was maintained at 1100 ° C. for 2 hours to 2.5 ° C. The temperature was lowered to room temperature at a temperature lowering rate of seconds.

In Invention Examples 2 and 3, and conventional examples, EOR defects after the device formation process simulation process were evaluated by the cathodoluminescence (CL) method. Specifically, each epitaxial wafer was irradiated with an electron beam at 34 K and 15 keV, the signal intensity of the D line (1450 nm) was measured, and the defect density was evaluated based on the intensity. As a result, in the conventional example, in the region of the epitaxial layer detects C _i O _i defects, carbon and oxygen is diffused into the epitaxial layer, it was confirmed that the formation of the defects. On the other hand, in Invention Examples 2 and 3, C _i O _i defects were not detected.

According to the present invention, the epitaxial layer is not formed on the support substrate wafer having the gettering layer, but is formed on the active layer wafer prepared separately, and the active layer wafer and the support substrate wafer are vacuumed. In addition, it is configured to remove the active layer wafer after bonding in an environment of room temperature to prevent impurities from diffusing from the support substrate wafer to the epitaxial layer during the epitaxial layer formation and device formation process. It is useful in the semiconductor industry because it can be used.

1, 2, epitaxial wafer 11 active layer wafer 12 support substrate wafer 12A support substrate wafer surface 16 gettering layer 17 epitaxial layer 18 amorphous layer 50 vacuum room temperature bonding device 51 plasma chamber 52 gas inlet 53 vacuum pump 54 pulse voltage Applying device 55A, 55B Wafer fixing base

Claims (15)

An epitaxial layer forming step of forming a silicon epitaxial layer on the surface of a silicon wafer for an active layer,
A silicon wafer for a support substrate having an oxygen concentration of 8 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or more and a gettering layer containing an element contributing to heavy metal gettering are formed inside at least one of the silicon epitaxial layers. Gettering layer forming process and
In an environment of vacuum and room temperature, the surface of the silicon epitaxial layer and the surface of the silicon wafer for the support substrate are activated to form amorphous layers on both surfaces, and then the silicon wafer for the active layer and the surface are described. A bonding step in which a silicon wafer for a support substrate is bonded via the amorphous layers on both surfaces, and
A substrate removing step of removing the silicon wafer for the active layer to expose the silicon epitaxial layer,
Have,
It is composed of the silicon wafer for the support substrate, the amorphous layer on the silicon wafer for the support substrate, and the silicon epitaxial layer on the amorphous layer, and the silicon epitaxial layer on the amorphous layer covers the entire thickness direction. A method for producing an epitaxial wafer, which comprises obtaining an epitaxial wafer having an oxygen concentration of 1 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less. The method for manufacturing an epitaxial wafer according to claim 1, wherein the activation treatment is a process of colliding an ionized neutral element with the surface of the silicon epitaxial layer or the silicon wafer for a support substrate to sputter the surface. .. The method for producing an epitaxial wafer according to claim 2, wherein the neutral element is at least one selected from the group consisting of argon, neon, xenon, hydrogen, helium and silicon. The method for manufacturing an epitaxial wafer according to any one of claims 1 to 3, wherein the activation treatment is a plasma etching treatment. The method for manufacturing an epitaxial wafer according to any one of claims 1 to 4, wherein the activation treatment is performed so that the thickness of the amorphous layer is 2 nm or more. The method for manufacturing an epitaxial wafer according to any one of claims 1 to 4, wherein the activation treatment is performed so that the thickness of the amorphous layer is 10 nm or more. Between the epitaxial layer forming step or the gettering layer forming step and the bonding step, hydrogen, nitrogen, fluorine and oxygen are formed on at least one of the surface of the silicon epitaxial layer and the surface of the silicon wafer for the support substrate. The method for producing an epitaxial wafer according to any one of claims 1 to 6, further comprising a step of containing an element consisting of at least one selected from the group consisting of. The method for producing an epitaxial wafer according to claim 7, wherein a Group 3B element is contained together with an element consisting of at least one selected from the group consisting of hydrogen, nitrogen, fluorine and oxygen. The step of forming a gettering layer is performed by irradiating at least one surface of the silicon wafer for a support substrate and the silicon epitaxial layer with molecular ions containing an element that contributes to gettering of a heavy metal. The method for manufacturing an epitaxial wafer according to any one item. Any of claims 1 to 8, wherein the gettering layer forming step is performed by injecting monomer ions of an element that contributes to gettering of a heavy metal into at least one surface of the silicon wafer for a support substrate and the silicon epitaxial layer. The method for manufacturing an epitaxial wafer according to item 1. A silicon wafer having an oxygen concentration of 8 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or more, an amorphous layer on the silicon wafer, a silicon epitaxial layer on the amorphous layer, the silicon epitaxial layer, and the silicon wafer. With a gettering layer inside at least one of the
An epitaxial wafer having an oxygen concentration of 1 × 10 ¹⁷ atoms / cm ³ (ASTM F121-1979) or less over the entire thickness direction of the silicon epitaxial layer. The epitaxial wafer according to claim 11, wherein the amorphous layer has a thickness of 2 nm or more. The epitaxial wafer according to claim 11, wherein the amorphous layer has a thickness of 10 nm or more. The epitaxial wafer according to any one of claims 11 to 13, wherein the amorphous layer contains at least one selected from the group consisting of hydrogen, nitrogen, fluorine and oxygen. The epitaxial wafer according to claim 14, wherein the amorphous layer further contains a Group 3B element.