JP5179401B2 - Bonded wafer and manufacturing method thereof - Google Patents

Description

  The present invention relates to a heat conducting member provided with a low stress / diffusion barrier film.

Aluminum nitride (AlN) has a thermal conductivity about 10 times that of alumina, and has recently attracted much attention as an insulating heat dissipation substrate for semiconductor devices. In addition, the coefficient of thermal expansion (about 4.6 × 10 ⁻⁶ / K: less temperature dependency) is related to the coefficient of thermal expansion of silicon (2.6 to 4.5 × 10 ⁻⁶ / K: temperature dependency). Since it is relatively close, it is a material that can be expected to have high affinity with silicon devices. In addition, since it has high heat resistance and plasma resistance, it is widely used for electrostatic chucks, heaters, and the like.

  However, this material also has fatal defects. It has hydrolyzability, and this means that the substrate is eroded during wet processes frequently used in semiconductor processes (see Non-Patent Document 1). Also in the dry process, there is a concern that the component aluminum diffuses at high temperatures.

“Hydrolysis behavior of aluminum nitride in various solutions” Journal of Materials Sciences, 35 (2000), pp.2743-2748

  In view of the above-mentioned present situation, the present invention provides a heat conducting member that has excellent hydrolysis resistance, can suppress diffusion of an aluminum component, and has high affinity with a silicon substrate, and a bonded wafer using the same. For the purpose.

In order to solve this problem, the present inventor has devised the following production method.
That is, the present invention is a bonded wafer provided with a single crystal silicon thin film on a heat conducting member in which a silicon nitride film is deposited on both surfaces of an aluminum nitride substrate.
The present invention also includes a step of implanting ions from the surface of the single crystal silicon substrate to form an ion implantation layer, and bonding the single crystal silicon substrate and a heat conducting member having a silicon nitride film on both surfaces of the aluminum nitride substrate. Both surfaces of the aluminum nitride substrate, including a step of obtaining a bonded body together, and a step of embrittlement of an interface of the ion implantation layer to transfer a part of the single crystal silicon substrate to the heat conductive member to obtain a bonded wafer. This is a method for manufacturing a bonded wafer having a single crystal silicon thin film on a heat conducting member having a silicon nitride film .

  According to the present invention, it is possible to obtain a heat conductive member that is excellent in hydrolysis resistance, can suppress diffusion of an aluminum component, and has high affinity with a silicon substrate, and a bonded wafer using the heat conductive member.

It is a schematic diagram of the heat conductive member concerning this invention. It is typical process drawing which shows the one aspect | mode of the manufacturing process of the bonded wafer concerning this invention.

Hereinafter, the present invention will be described in detail with reference to FIG.
A heat conducting member 1 according to the present invention is obtained by forming silicon nitride films 3 (SiN) on both surfaces of an AlN substrate 2 by a CVD method or the like. By forming the silicon nitride film 3 (SiN), the chemical resistance can be improved and the diffusion of aluminum and other impurity metals from the AlN substrate during the high temperature process can be prevented.
As the silicon nitride film 3 (SiN), either a stoichiometric silicon nitride film (Si ₃ N ₄ ) or a silicon rich silicon nitride film (SRN) compared to the stoichiometric composition can be used.

When the process is relatively low temperature (800 ° C. or lower), a normal stoichiometric silicon nitride film (Si ₃ N ₄ ) can play a sufficient role.
However, since a normal stoichiometric silicon nitride film (Si ₃ N ₄ ) is a very hard material (Young's modulus = 290 GPa-300 GPa), it is deposited on AlN as it is, and the temperature is increased and decreased in the semiconductor processing step. Repeating may cause problems such as cracks and other defects due to differences in thermal expansion coefficient. Therefore, by using a silicon rich silicon nitride film (SRN: Silicon rich nitride) having more silicon components than a normal stoichiometric silicon nitride film (Si ₃ N ₄ ) as the nitride film 3, the Young's modulus is reduced ( For example, see Sensors and Actuators A, 35 (1992), pp. 153-159) and succeeded in making the substrate flexible and maintaining resistance to chemicals.

The stoichiometric silicon nitride film (Si ₃ N ₄ ) has a refractive index of approximately 2.0 at a wavelength l = 633 nm, whereas SRN has a refractive index of over 2.0 and 2.5 due to excess silicon. Since it becomes the following, discrimination is easy. A more preferable upper limit of the refractive index is 2.35, and a further preferable upper limit is 2.3. If the refractive index exceeds 2.5, a special method such as low-frequency plasma CVD needs to be employed, which may be difficult in terms of cost.
As a method for measuring the refractive index, an optical interference type film thickness measuring device or the like is used in the embodiments. However, an ellipsometry method using a wavelength l = 633 nm HeNe laser or a spectroscopic ellipsometry method using a xenon short arc lamp may be employed.

As used herein, “silicon rich” means that the stoichiometric ratio is less than 1.33.
As a specific composition of the SRN, for example, in the case of Si3N4 (refractive index 2.0) in the N / Si ratio, it is 1.33, whereas the SRN having a refractive index of 2.3 is 0.8. There is a report.

A stoichiometric silicon nitride film (Si ₃ N ₄ ) and SRN are generally deposited by a method called LPCVD [Low Pressure CVD] method, and SiH ₂ Cl ₂ and NH ₃ which are source gases are generally used. The composition of the film can be easily changed by changing the composition of the gas. The normal deposition temperature is about 800 ° C. Further, since films are formed on both surfaces of the wafer, there is a characteristic that warpage does not normally occur.
As another method, there is a PECVD [Plasma Enhanced CVD] method, in which a film is formed only on one side of a wafer, so that it is necessary to repeat the process of the front and back twice, and the deposition temperature is as low as around 400 ° C. Therefore, it is necessary to perform a high-temperature treatment at about 1000 ° C. called baking, and it is feasible although it is inconvenient than the LPCVD method.

The thickness of the silicon nitride film 3 is preferably 50 nm to 500 nm. If it is less than 50 nm, the hydrolysis resistance may be inferior, and if it exceeds 500 nm, the thermal process may not follow the expansion of aluminum nitride, and defects such as cracks may be introduced.
The thickness of the aluminum nitride substrate depends on the application, but when used for a semiconductor device element, it is 400 μm to 800 μm in consideration of the affinity with a normal silicon wafer process, and the diameter is 100 mm to 200 mm. can do.

Since the heat conducting member 1 according to the present invention has a high heat-resistant temperature and plasma resistance, it can be suitably used alone for a heater, an electrostatic chuck, etc., but a silicon thin film, particularly a single crystal silicon thin film is used. The stacked SOI bonding structure is expected to be applied to semiconductor support members such as power devices that generate a lot of heat.
In the present specification, the semiconductor support member includes all members that are in contact with a semiconductor regardless of whether or not the semiconductor support member is chemically bonded to the semiconductor. The semiconductor support member can be particularly preferably used as a member in contact with the semiconductor in the semiconductor processing step. Examples of such a semiconductor support member include an electrostatic chuck and a printed circuit board.
Since the heat conducting member 1 is obtained by coating both surfaces of an aluminum nitride substrate with a silicon nitride film, the silicon nitride film functions as a diffusion prevention film and a chemical erosion resistant film. It can be put into a semiconductor process (CMOS process) involving a wet process such as etching using an acid aqueous solution or the like, or a dry process such as high-temperature annealing at 900 ° C. or higher. By using the heat conductive member 1 as a handle substrate and bonding to a donor substrate described later, a bonded wafer having high heat dissipation can be realized.

FIG. 2 shows an example of a manufacturing process of a bonded wafer according to the present invention.
First, as the donor substrate 4, for example, a silicon wafer 5 or a silicon wafer 5 with an oxide film 9 (hereinafter simply referred to as a silicon wafer 5 unless otherwise distinguished) is prepared, and ions are implanted from one surface 11 to form an ion implantation layer 7. Form.
The ion implantation layer 7 is formed in the silicon wafer 5. At this time, a predetermined dose of hydrogen ions (H ⁺ ) or hydrogen molecular ions (H ₂ ⁺ ) is implanted with an implantation energy that can form the ion implantation layer 7 at a desired depth from the surface 11 of the donor substrate 4. . As a condition at this time, for example, the implantation energy can be set to 50 to 100 keV.

The dose of hydrogen ions (H ⁺ ) implanted into the donor substrate 4 is preferably 1.0 × 10 ¹⁶ atoms / cm ^{2 to} 1.0 × 10 ¹⁷ atoms / cm ² . If it is less than 1.0 × 10 ¹⁶ atoms / cm ² , the interface may not be embrittled. If it exceeds 1.0 × 10 ¹⁷ atoms / cm ² , bubbles are transferred during heat treatment after bonding. It may become defective. A more preferable dose amount is 5.0 × 10 ¹⁶ atoms / cm ² .
When hydrogen molecular ions (H ₂ ⁺ ) are used as implanted ions, the dose is preferably 5.0 × 10 ¹⁵ atoms / cm ^{2 to} 5.0 × 10 ¹⁶ atoms / cm ² . If it is less than 5.0 × 10 ¹⁵ atoms / cm ² , embrittlement of the interface may not occur, and if it exceeds 5.0 × 10 ¹⁶ atoms / cm ² , bubbles are transferred during heat treatment after bonding. It may become defective. A more preferable dose amount is 2.5 × 10 ¹⁶ atoms / cm ² .
If the donor substrate 4 has an insulating film such as a silicon oxide film 9 having a thickness of several nanometers to 500 nm formed around it in advance, if hydrogen ions or hydrogen molecular ions are implanted therethrough, channeling of the implanted ions is performed. The effect which suppresses is acquired.

Next, prior to the bonding of the donor substrate 4 and the heat conducting member 1, the ion-implanted surface 11 of the donor substrate 4 and / or the bonding surface 6 of the heat conducting member 3 can be activated. Examples of the surface activation treatment include plasma treatment and ozone treatment.
When processing with plasma, the donor substrate 4 and / or the heat conduction member 1 cleaned by RCA cleaning or the like is placed in a vacuum chamber, the plasma gas is introduced under reduced pressure, and then the high-frequency plasma of about 100 W is applied. The surface is exposed to plasma for about 5 to 10 seconds. As a plasma gas, when processing a silicon wafer, when oxidizing the surface, plasma of oxygen gas, when not oxidizing, hydrogen gas, argon gas, or a mixed gas thereof or a mixed gas of hydrogen gas and helium gas Can be used. Any gas may be used when the heat conducting member 1 is processed.
By treating with plasma, organic substances on the bonding surface 6 of the donor substrate 4 and / or the heat conducting member 1 are oxidized and removed, and the OH groups on the surface are increased and activated. The treatment is more preferably performed on both the ion-implanted surface 11 of the silicon wafer 5 and the bonding surface of the heat conducting member 1, but only one of them may be performed.
When processing with ozone, the silicon wafer 5 and / or the heat conducting member 1 cleaned by RCA cleaning or the like was placed in a chamber into which air was introduced, and a plasma gas such as nitrogen gas or argon gas was introduced. Then, the surface is subjected to ozone treatment by generating high-frequency plasma and converting atmospheric oxygen into ozone. Either or both of plasma treatment and ozone treatment can be performed.
The surface of the donor substrate 4 on which the surface activation process is performed is preferably the surface 11 on which ion implantation has been performed.

Prior to bonding between the bonding surface 6 of the heat conducting member 1 and the surface 11 into which the ions of the donor substrate 4 are implanted, the silicon nitride film bonding surface 6 of the heat conducting member 1 is subjected to chemical mechanical polishing or the like. And polishing to make the smoothness 0.5 nm or less by RMS is essential. By including such a step, the bonding strength is synergistically increased by surface activation and surface roughness reduction. If the thickness exceeds 0.5 nm, the bonding itself may not proceed.
The RMS is a value obtained by measurement based on the AFM image.

  Next, the bonded body 13 is obtained by bonding the surface 11 into which ions of the donor substrate 4 are implanted and the surface 6 of the heat conducting member 1 treated with plasma and / or ozone as bonding surfaces.

Next, the bonded body 13 is preferably subjected to a heat treatment of 150 ° C. or more and 400 ° C. or less to increase the bond strength. The reason why the preferable temperature is 150 ° C. or higher is that the bond strength does not increase when the temperature is lower than 150 ° C., and the reason why the temperature is 400 ° C. or lower is that if the temperature exceeds 400 ° C., the bonded substrate may be damaged. . A more preferable upper temperature limit is 350 ° C.
The heat treatment time is preferably 12 hours to 72 hours depending on the temperature to some extent.

After the heat treatment step, thin film transfer is performed in which the vicinity of the interface of the ion implantation layer 7 of the donor substrate 4 is embrittled and a part (15, 17) of the donor substrate 4 is transferred to the heat conducting member 1.
The embrittlement process may include, for example, a process of peeling by applying a mechanical impact.
In order to give a mechanical impact to the vicinity of the interface of the ion implantation layer 7, for example, a jet of fluid such as gas or liquid may be sprayed continuously or intermittently from the side surface of the wafer. There is no particular limitation as long as it is a method in which the above occurs.
Although the thickness of the thin film to be transferred can be changed depending on the energy at the time of ion implantation, it can usually be set to 100 nm to 1000 nm.
By the peeling process, a bonded wafer 19 in which a part (15, 17) of the silicon wafer 5 is formed on the heat conducting member 1 is obtained.

(Reference Example 1)
A 150 nm diameter, 600 μm thick AlN substrate with a stoichiometric silicon nitride film (Si ₃ N ₄ : refractive index = 2.0) of 200 nm deposited on both sides and an SRN of 200 nm with a refractive index of 2.25 Prepared on both sides.
The process of raising and lowering the temperature from 300 ° C. to 800 ° C. and repeating the temperature reduction (2 ° C./min) was repeated 10 times, and surface cracks and the like were observed under an optical microscope of 1000 magnifications, but no cracks were observed.

(Reference Example 2)
A 150 nm diameter, 600 μm thick AlN substrate with a stoichiometric silicon nitride film (Si ₃ N ₄ : refractive index = 2.0) of 500 nm deposited on both sides and an SRN of 500 nm with a refractive index of 2.25 Prepared on both sides.
The process of repeatedly raising and lowering both temperatures from 300 ° C. to 1000 ° C. and lowering the temperature (2 ° C./min) was repeated 10 times, and surface cracks and the like were observed under an optical microscope with a magnification of 1000. Si ₃ N ₄ Cracks were observed, but SRN was not observed.

(Reference Example 3)
A 150 nm diameter, 600 μm thick AlN substrate with a stoichiometric silicon nitride film (Si ₃ N ₄ : refractive index = 2.0) of 200 nm deposited on both sides and an SRN of 200 nm with a refractive index of 2.25 Prepared on both sides.
Both were subjected to either RCA cleaning, which is a general cleaning method for semiconductor cleaning, or HF cleaning (10%), but no change was observed in the state of the cleaning surface. On the other hand, when the bare AlN not coated with the silicon nitride film was observed under a condenser lamp under both RCA cleaning and HF cleaning, an increase in haze due to an increase in surface roughness was observed. Was visually observed, and it was found that hydrolysis was progressing.

A stoichiometric silicon nitride film (Si ₃ N ₄ : refractive index = 2.0) on an AlN substrate (150 mm diameter, manufactured by Toshiba Materials), a heat conduction member formed by depositing 200 nm, and a refractive index of 2.25 A heat conductive member formed by depositing SRN 200 nm on both sides of the substrate was prepared as a handle substrate.
Separately, after an oxide film is grown to a thickness of 100 nm on the surface of a single crystal silicon substrate (diameter 150 mm, manufactured by Shin-Etsu Semiconductor Co., Ltd.), hydrogen ions are implanted at a dose of 8.0 × 10 ¹⁶ atoms / cm ^2. A substrate was prepared.
One surface of the heat conduction member is mirror-polished until the root mean square roughness [RMS] is 0.25 nm, and the surface activated surface of the single crystal silicon substrate (donor substrate) is bonded onto the polished surface. To obtain a joined body.
The obtained bonded body was subjected to a heat treatment at 250 ° C., and a mechanical impact was applied to the hydrogen ion implanted interface to transfer a thin film of single crystal silicon.
The obtained bonded wafer was repeatedly subjected to a process of repeatedly raising and lowering the temperature from 300 ° C. to 800 ° C. under a nitrogen atmosphere (2 ° C./min) 10 times, and the surface was observed under an optical microscope of 1000 magnifications. Was not observed.

A stoichiometric silicon nitride film (Si ₃ N ₄ : refractive index = 2.0) on an AlN substrate (150 mm diameter, manufactured by Toshiba Materials), a heat conduction member formed by depositing 200 nm, and a refractive index of 2.25 A heat conductive member formed by depositing SRN 200 nm on both sides of the substrate was prepared as a handle substrate.
Separately, an oxide film was grown to a thickness of 100 nm on the surface of a single crystal silicon substrate (diameter 150 mm), and then a hydrogen ion was implanted at a dose of 8.0 × 10 ¹⁶ atoms / cm ² to prepare a donor substrate.
Next, one surface of the heat conducting member is mirror-polished until the root mean square roughness [RMS] is 0.25 nm, and the surface of the single crystal silicon substrate (donor substrate) is subjected to surface activation treatment on the polished surface. A bonded body was obtained by bonding.
The obtained bonded body was subjected to a heat treatment at 250 ° C., and a mechanical impact was applied to the hydrogen ion implanted interface to transfer a thin film of single crystal silicon.
About the obtained bonded wafer, the process of repeating the temperature increase from 300 ° C. to 1000 ° C. and the temperature decrease (2 ° C./min) in a nitrogen atmosphere was repeated 10 times, and surface cracks and the like were observed under an optical microscope of 1000 magnifications. However, although microcracks (about 2 to 10 μm) were observed at the periphery of the substrate on which Si ₃ N ₄ was deposited, no cracks or the like were observed on the substrate on which SRN was deposited.

A stoichiometric silicon nitride film (Si ₃ N ₄ : refractive index = 2.0) on an AlN substrate (150 mm diameter, manufactured by Toshiba Materials), a heat conduction member formed by depositing 200 nm, and a refractive index of 2.25 A heat conductive member formed by depositing SRN 200 nm on both sides of the substrate was prepared as a handle substrate.
Separately, after an oxide film is grown to a thickness of 100 nm on the surface of a single crystal silicon substrate (diameter 150 mm, manufactured by Shin-Etsu Semiconductor Co., Ltd.), hydrogen ions are implanted at a dose of 8.0 × 10 ¹⁶ atoms / cm ^2. A substrate was prepared.
Next, one surface of the heat conducting member is mirror-polished until the root mean square roughness [RMS] is 0.25 nm, and the surface of the single crystal silicon substrate (donor substrate) is subjected to surface activation treatment on the polished surface. A bonded body was obtained by bonding.
The obtained bonded body was subjected to a heat treatment at 250 ° C., and a mechanical impact was applied to the hydrogen ion implanted interface to transfer a thin film of single crystal silicon.
The obtained bonded wafer is subjected to high-temperature annealing at 950 ° C. for 1 hour in a nitrogen atmosphere, the surface is brought into contact with an HF solution, and the HF solution is subjected to mass spectrometry using an inductively coupled plasma mass spectrometer [ICP-MS]. As a result, the Al concentration on the surface of the SiN film of the heat conducting member is 5 × 10 ¹⁰ atoms / cm ² or less for both the stoichiometric silicon nitride film and the SRN, and Al inside the AlN is hardly diffused. found.

1 Thermal Conductive Member 2 Aluminum Nitride 3 Silicon Nitride 4 Donor Substrate 5 Silicon Substrate 6 Bonding Surface 7 Ion Implanted Layer 9 Silicon Oxide Film 11 Ion Implanted Surface 13 Joint 15 and 17 Part of Donor Substrate 19 Bonded Wafer

Claims (8)

A bonded wafer comprising a single crystal silicon thin film on a heat conducting member comprising silicon nitride films on both sides of an aluminum nitride substrate. 2. The bonded wafer according to claim 1, wherein the silicon nitride film is silicon rich as compared to a stoichiometric composition and has a refractive index exceeding 2.0 at a wavelength l = 633 nm. The bonded wafer according to claim 1, wherein the silicon nitride film is stoichiometric (Si ₃ N ₄ ). The bonded wafer according to claim 1 , wherein the heat conducting member is a semiconductor support member. A step of implanting ions from the surface of the single crystal silicon substrate to form an ion implantation layer;
Bonding the single crystal silicon substrate and a heat conductive member having a silicon nitride film on both sides of an aluminum nitride substrate to obtain a bonded body; and
A heat conductive member comprising silicon nitride films on both surfaces of an aluminum nitride substrate, the method including embrittlement of an interface of the ion implantation layer and transferring a part of the single crystal silicon substrate to the heat conductive member to obtain a bonded wafer. A method for manufacturing a bonded wafer provided with a single crystal silicon thin film on top . Prior to the step of obtaining the joined body, the surface of the silicon nitride film of the heat conducting member, which becomes the bonding surface of the single crystal silicon substrate, is polished, and the smoothness is 0.5 nm or less in terms of root mean square roughness (RMS). The method for producing a bonded wafer according to claim 5 , comprising a step of: Prior to the step of obtaining the joined body, the method includes a step of performing a surface activation process on the surface of the heat conducting member or at least one of the surfaces of the single crystal silicon substrate into which the ions have been implanted. The manufacturing method of the bonded wafer of Claim 5 . The heat treatment of 400 ° C. or less to the bonded body addition method for producing a bonded wafer according to claim 5 to 7, characterized in that to increase the bonding strength.

Images