JP2012054451A - Method of manufacturing bonded substrate and semiconductor substrate cleaning liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a bonded substrate in which damage on a substrate can be avoided by enhancing the bonding strength even when substrates having significantly different heat expansion coefficients are bonded.SOLUTION: The method of manufacturing a bonded substrate includes a step for cleaning a handle substrate with a solution, where the capacity of NHOH in terms of 29% aqueous solution for the capacity of HOin terms of 30% aqueous solution is 1-200 in volume ratio, and then bonding the handle substrate and a donor substrate.

Description

  The present invention relates to a method for manufacturing a bonded substrate, and more particularly to a method for cleaning a silicon on sapphire (SOS) substrate before bonding.

  Conventionally, a silicon on sapphire (SOS) substrate using sapphire having a high insulating property, low dielectric loss, and high thermal conductivity as a handle substrate has been put into practical use since the 1960s and has been used up to now. The SOS substrate is the oldest silicon on insulator (SOI) substrate, and the SOI structure is realized by heteroepitaxially growing silicon on the R surface (1102) of sapphire.

  However, in recent years, SOI using the SIMOX method or the bonding method has become the mainstream, and the SOS substrate is used only for a high-frequency device that requires a low dielectric loss, for example, an SOI substrate in which the handle substrate is not compatible with silicon. Yes. Heteroepi SOS is known to cause many defects due to lattice size mismatch because silicon is heteroepitaxially grown on sapphire having a lattice constant different by 12% (see, for example, Non-Patent Document 1).

  In recent years, the demand for high-frequency devices has increased due to the widespread use of mobile communications such as mobile phones, but the use of SOS is considered in this field. However, in heteroepi SOS, the defect density is high, and the actual usage is limited to small individual parts (switches and the like).

The surface defect density of the heteroepi SOS is determined by the Secco defect detection method (K ₂ Cr ₂ O ₇ or a mixed solution of Cr ₂ O ₃ and HF) or the selective etching defect detection method (mixture of HF, KI, I and CH ₃ OH). In the case of (solution) etc., it is reported that it is about 10 ⁹ pieces / cm ² (for example, see Non-Patent Document 1).

  In order to reduce this hetero-epi SOS defect, high-concentration Si is ion-implanted in the vicinity of the interface between the Si film and the sapphire substrate to leave the Si surface and change to amorphous, and annealed near 600 ° C. A method of recrystallizing an amorphous layer at a slow position has been proposed, which is called single solid phase growth. In addition, a method (double solid phase growth method) in which this treatment is repeated twice to attempt further defect reduction has been proposed (for example, see Non-Patent Document 1).

However, even if the double solid phase growth method is used, the defect density is about 10 ⁶ to 10 ⁷ pieces / cm ² , and it is difficult to make a leading-edge device that has been miniaturized in recent years. It is also difficult to produce a relatively large device such as a system chip that incorporates many functions. This can be said to be rooted in the essential problem of heteroepi growth (epi growth of materials having different lattice constants).

A method of transferring a single crystal thin film from bulk silicon onto sapphire (bonding method) can be easily inferred as a method for solving the fundamental problem of the above heteroepi method. However, sapphire is a thermal expansion coefficient very high ^{_{(α sapphire = 7.7x10 -6 / K}} : C axis parallel), when compared to that ^{_{(α si = 2.6x10 -6 / K}} ) of silicon, of about 3 times Has a value. Therefore, the bonding method in which sapphire and a silicon substrate are bonded and the bond strength is increased by high-temperature heat treatment has a drawback that the bonded substrate is warped during the heat treatment, resulting in damage to the substrate.

  In order to prevent the substrate from being damaged, a method of increasing the bond strength by low-temperature heat treatment after bonding is conceivable, but it is difficult to obtain sufficient strength by the conventional methods.

Yoshii et al. Japan Journal of Applied Physics, Vol. 21 (1982) Supplement 21-1, pp. 175-179 Tong et al. “Semiconductor Wafer Bonding” Chapter 2, Wiley Interscience publication, 1999

  An object of the present invention is to provide a method for manufacturing a bonded substrate that can increase the bonding strength and avoid substrate breakage even when substrates having greatly different thermal expansion coefficients are bonded together. .

The present invention has been made to solve the above problems. The substrate manufacturing method according to the present invention is based on the inventor's knowledge that the handle substrate cleaning method particularly affects the bonding strength after being bonded to the donor substrate. That is, in the method for producing a bonded substrate according to the present invention, in order to achieve the above object, the capacity of NH ₄ OH in terms of 29% aqueous solution to the capacity of H ₂ O _{2 in} terms of 30% aqueous solution is 1 by volume. And a step of cleaning the handle substrate with a solution of 200 or less and then bonding the handle substrate to the donor substrate.

  According to the method for manufacturing a bonded substrate according to the present invention, a bonded substrate having excellent bonding strength can be obtained even when substrates having greatly different thermal expansion coefficients are bonded to each other.

It is a graph which shows the result of Example 1 which compared the bonding intensity | strength about the board | substrate bonded by giving each cleaning method. It is a graph which shows the result of Example 2 which compared the bonding strength about the board | substrate which performed the surface activation process and bonded together after giving each washing | cleaning method. It is a graph which shows the result of Example 3 which compared the bonding strength with what was wash | cleaned by the washing | cleaning method which concerns on this invention, and an unwashed thing.

The present invention is described in detail below. In addition, this invention is not restrict | limited to the form demonstrated below.
RCA cleaning is generally used as a normal silicon substrate cleaning method. As one of the steps, there is ammonia overwater cleaning called SC1 cleaning. SC1 cleaning is performed by mixing three types of solutions of ammonia (NH ₄ OH), hydrogen peroxide (H ₂ O ₂ ), and water (H ₂ O) in a volume ratio of 1: 1: 5 to 1: 1: 200. -It is the method of removing organic substance, a foreign material, etc. on the surface by heating (80-90 degreeC) and immersing a board | substrate in the obtained mixed solution.
The present inventor cleaned a substrate such as a sapphire substrate with a solution that greatly reduces the concentration of hydrogen peroxide solution, which is a component of SC1 cleaning, and greatly increases the ratio of ammonia to hydrogen peroxide solution. It has been found that the bonding strength can be greatly increased by bonding. That is, the cleaning method according to the present invention can be suitably incorporated into the manufacturing process of the bonded substrate.
The substrate that is the target of the cleaning method according to the present invention is not particularly limited, but can be applied as long as it is a material whose surface is not etched by the ammonia-rich modified SC1 or a material that is difficult to be etched. Silicon (oxide film thickness is 2 nm to 500 nm, for example), quartz, glass and the like can be particularly preferably employed. Conversely, silicon or the like that does not have an oxide film is not suitable because it is etched and the surface roughness deteriorates.
The volume ratio of ammonia (NH ₄ OH) to hydrogen peroxide water (H ₂ O ₂ ) in the cleaning solution exceeds 1. The volume ratio is preferably 3 or more, more preferably 4 or more, and further preferably 4.5 or more. The upper limit of the volume ratio can be set to 200, for example, so that the surface oxidation ability by the hydrogen peroxide solution does not decrease too much.
The inventors of the present invention have found that a stable bonding can be achieved with a high bonding strength by bonding a handle substrate to a donor substrate such as a silicon substrate after passing through the above-described cleaning method. is there.
In this ammonia-rich SC1 cleaning, the sapphire itself is not etched. It seems that there is an effect of creating a surface suitable for bonding by strongly removing organic substances on the surface and making the surface strongly hydrophilic.
As a method for measuring the properties of the bonding interface, in addition to the crack opening method described later, for example, a method of measuring the degree of hydrophilicity and hydrophobicity by applying water drops to the surface and measuring the contact angle, etc. These methods can be used to observe the difference from unwashed items.

The cleaning method according to the present invention may be performed, for example, by immersing the handle substrate in the above solution for 1 to 30 minutes, or supplying and flowing the solution while rotating the handle substrate at 50 to 1500 rpm for cleaning. May be performed.
In the cleaning method according to the present invention, ultrasonic waves (20 kHz or higher), two-fluid spray, cavitation jet, bubble jet are used in combination with the above-described chemical cleaning method or in a separate process from the chemical cleaning method. Further, physical cleaning with a brush scrub or the like may be performed. In addition, as the cleaning temperature, for example, in the case of normal immersion, it can be set to 70 ° C. to 90 ° C., but when used together with physical cleaning by the above ultrasonic waves or the like, it is allowed even at a lower temperature. 40 ° C to 60 ° C.
After the cleaning method according to the present invention, rinsing may be performed with pure water or deionized water as appropriate. The drying step after the cleaning method according to the present invention can be performed under the same conditions and apparatus as in the prior art.

After cleaning the handle substrate as described above, a surface activation treatment may be performed on the cleaning surface of the handle substrate before bonding.
Examples of the surface activation treatment include plasma treatment, ozone water treatment, UV ozone treatment, and ion beam treatment.
When processing with plasma, the cleaned substrate is placed in a vacuum chamber, a plasma gas is introduced under reduced pressure, and then the surface is exposed to high-frequency plasma of about 100 W for about 5 to 10 seconds to perform plasma processing. As a plasma gas, when processing a silicon substrate, when oxidizing the surface, plasma of oxygen gas, when not oxidizing, hydrogen gas, argon gas, or a mixed gas thereof or a mixture of hydrogen gas and helium gas A mixed gas can be used. When processing a sapphire substrate, any gas may be used. By treating with plasma, organic substances on the surface of the substrate are oxidized and removed, and OH groups on the surface are increased and activated.
When processing with ozone, ozone gas can be introduced into pure water and the wafer surface can be activated with active ozone.
When UV ozone treatment is performed, the surface can be activated by irradiating the atmosphere or oxygen gas with short wavelength UV light (wavelength of about 195 nm) to generate active ozone.
The ion beam treatment can be performed by exposing an ion beam of Ar or the like to the wafer surface in a high vacuum (<1 × 10 ⁻⁶ Torr) and exposing a dangling bond having high activity.
The surface activation treatment is preferably performed not only on the bonding surface of the handle substrate but also on the ion-implanted surface of the donor substrate, but may be performed only on the bonding surface of the handle substrate.

Next, the surface of the handle substrate subjected to the surface activation treatment is bonded to the donor substrate at a temperature of 50 ° C. or higher and 350 ° C. or lower using the bonding surface as a bonding surface. If it exceeds 350 ° C., the stress generated at the bonding interface may be unfavorable because (bonding temperature−room temperature) becomes a large factor.
After the pasting, a heat treatment step for obtaining a joined body as described later may be performed and then cooled to room temperature, or after the pasting, after cooling to room temperature, a heat treatment step for obtaining a joined body again. May be performed.
The cooling step is a step in which stress is generated, and the cooling rate can be, for example, 5 ° C./min to 50 ° C./min.

Next, the bonded substrate is subjected to heat treatment at 150 ° C. or higher and 350 ° C. or lower to obtain a bonded body. The reason for performing the heat treatment is to prevent the introduction of crystal defects due to a sudden rise in temperature when the bonding interface becomes a high temperature by visible light irradiation in a subsequent process, thereby improving the bond strength. The reason why the temperature is set to 150 ° C. or higher and 350 ° C. or lower is that the bonding strength does not increase when the temperature is lower than 150 ° C., and the bonded substrate may be damaged when the temperature exceeds 350 ° C.
The heat treatment time is preferably 12 hours to 72 hours depending on the temperature to some extent.

Next, a surface thinning process is performed on the donor substrate side of the bonded body.
As a 1st aspect which thins a donor substrate, the grinding and polishing method is mentioned, for example. Examples of the grinding / polishing method include CMP polishing, polishing with fixed abrasive grains, etching with an alkaline aqueous solution such as ammonia hydrogen peroxide and KOH, and the like.
As a second aspect of thinning the donor substrate, for example, before bonding to the handle substrate, ion implantation is performed on one main surface of the donor substrate to form an ion implantation layer, and then bonding to the donor substrate is performed. A technique of embrittlement and separation using the ion implantation layer as a boundary interface after the alignment can be employed.
When an ion implantation layer is formed by implanting ions into the donor substrate, a predetermined dose of hydrogen ions (H ⁺ ) or hydrogen molecular ions is implanted with an implantation energy that can form the ion implantation layer from the surface to a desired depth. Inject (H ₂ ⁺ ). As a condition at this time, for example, the implantation energy can be set to 30 to 100 keV.
The dose of hydrogen ions (H ⁺ ) implanted into the donor substrate is preferably 5.0 × 10 ¹⁶ atoms / cm ^{2 to} 2.0 × 10 ¹⁷ atoms / cm ² . If it is less than 5.0 × 10 ¹⁶ atom / cm ² , the interface may not be embrittled. If it exceeds 2.0 × 10 ¹⁷ atom / cm ² , bubbles are transferred during heat treatment after bonding. It may become defective. A more preferable dose amount is 7.0 × 10 ¹⁶ atoms / cm ² .
When hydrogen molecular ions (H ₂ ⁺ ) are used as implanted ions, the dose is preferably 2.5 × 10 ¹⁵ atoms / cm ^{2 to} 1.0 × 10 ¹⁷ atoms / cm ² . If it is less than 2.5 × 10 ¹⁵ 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 2.5 × 10 ¹⁶ atoms / cm ² .

  As a method for embrittlement of the interface of the ion implantation layer, for example, a method of irradiating visible light from any one of the bonded bodies toward the ion implantation layer formed on the donor substrate can be given. For visible light irradiation, laser light, heat treatment temperature of 1200 ° C. or higher, heat treatment time of 1 to 120 seconds, including spike annealing RTA (Rapid Thermal Anneal), annealing by flash lamp, etc. Can do. The temperature of the bonded body at the time of irradiation with visible light is preferably ± 50 ° C. at the time of bonding and is heated to 50 ° C. or higher and 350 ° C. or lower. By performing light irradiation at a high temperature, it is possible to avoid introduction of defects into the transferred donor thin film and damage to the substrate.

If transfer of the donor thin film to the handle substrate cannot be confirmed after laser light irradiation, RTA treatment, or flash lamp irradiation, the donor thin film is peeled along the interface by applying a mechanical impact to the interface of the ion implantation layer. Is transferred to the handle substrate.
In order to give a mechanical impact to the interface of the ion-implanted layer, for example, a jet of fluid such as gas or liquid may be blown continuously or intermittently from the side surface of the wafer, but mechanical peeling occurs due to the impact. The method is not particularly limited.
The peeling instrument is capable of applying a mechanical impact from the side surface of the hydrogen ion implanted layer of the joined body heat-treated at a temperature of 150 ° C. or higher and 350 ° C. or lower, preferably, the portion corresponding to the side surface of the hydrogen ion implanted layer is pointed, It is movable along the ion-implanted layer, preferably using a scissor-shaped sharp tool or a scissor-shaped sharp blade, and the material thereof is plastic (for example, polyetheretherketone) or zirconia, Silicon, diamond, or the like can be used, and metal or the like can be used because it does not stick to contamination. If you are particular about contamination, plastic may be used. A blade such as scissors may be used as a wedge-shaped sharp tool.

  Through the peeling step, the bonded substrate of the present invention in which the donor thin film is formed on the handle substrate is obtained.

  The substrate cleaning liquid used in the substrate manufacturing method according to the present invention is also one aspect of the present invention. A substrate cleaning aqueous solution containing concentrated ammonia water, hydrogen peroxide water and dilution water (preferably pure water or deionized water), wherein the volume ratio of the concentrated ammonia water is 10 when the volume of the dilution water is 10. However, the volume ratio of the hydrogen peroxide solution is 0.01 to 0.5 in terms of a 30% aqueous solution, and the concentrated ammonia water and the hydrogen peroxide solution are Is a substrate cleaning aqueous solution having a volume ratio of more than 1.

The sapphire substrate having a diameter of 150 mm was cleaned by any of the following cleaning methods.
1. No washing 2. 3. Wash with pure water 3.2% HF for 10 minutes 4. Immerse in normal SC1 (80 ° C.) of ammonia: hydrogen peroxide: water = 1: 1: 10 (volume ratio) for 10 minutes 5. Immerse in normal SC2 (80 ° C.) of hydrochloric acid: hydrogen peroxide: water = 1: 1: 10 (volume ratio) for 10 minutes 6. Immerse in a solution (80 ° C.) of ammonia: hydrogen peroxide: water = 1: 0: 10 (volume ratio) for 10 minutes 7. Immerse in 10% KOH solution for 10 minutes Immersion in modified SC1-A (80 ° C.) of ammonia: hydrogen peroxide: water = 1: 0.7: 10 (volume ratio) for 10 minutes (invention)
9. Immersion in modified SC1-B (80 ° C.) of ammonia: hydrogen peroxide water: water = 1: 0.3: 10 (volume ratio) for 10 minutes (invention)
10. Immersion for 10 minutes in modified SC1-C (80 ° C.) of ammonia: hydrogen peroxide water: water = 1: 0.2: 10 (volume ratio) (invention)
However, the concentration of NH ₄ OH and H ₂ O ₂ is the case of 29% aqueous solution conversion and 30% aqueous solution conversion, respectively.

_{Incidentally,} NH 4 _OH, H 2 _{O 2} concentrations were 29% aqueous solution in terms of a case of a 30% aqueous solution of terms. This sapphire was bonded to a silicon substrate (thickness: 625 μm) having a diameter of 150 mm on which an oxide film was grown in advance by 200 nm. The bonded substrates were heated in an atmosphere at 150 ° C. for 24 hours, and then the surface energy (bonding strength) was measured using a crack opening method. The crack opening method is a method in which a blade is inserted into the bonding interface and the bonding strength is measured in an open area (see, for example, Non-Patent Document 2). The blade used was Special Grade, product number: EF-SLZ15 (blade span: about 1 mm, thickness: 0.38 mm, material: zirconia).
The results are shown in FIG.

  From this result, it can be seen that the method of manufacturing a bonded substrate employing the modified SC1-A, B, C of the present invention has the highest bonding strength. Even in the case of ammonia water excluding the hydrogen peroxide solution or KOH solution, it can be seen that mere alkali cleaning is insufficient because the surface energy is lower than that of the cleaning method of the present invention. Further, comparing the normal SC1 and the modified SC1 of the present invention, the modified SC1 of the present invention has a higher surface energy, so that the ammonia concentration is somewhat high and addition of a small amount of hydrogen peroxide is important. I understood it.

The sapphire substrate with a diameter of 150 mm was cleaned by each cleaning method in the same manner as in Example 1.
_{Incidentally,} NH 4 _OH, H 2 _{O 2} concentrations were 29% aqueous solution in terms of a case of a 30% aqueous solution of terms. The surface activation treatment was performed on the sapphire surface, and then a silicon substrate (thickness: 625 μm) having a diameter of 150 mm on which an oxide film was grown in advance by 200 nm was bonded. The bonded substrates were heated in an atmosphere of 150 ° C. for 24 hours, and then the surface energy (bonding strength) was measured using the crack opening method in the same manner as in Example 1.
The results are shown in FIG.

  Although the value increased as a whole as compared with Example 1, it was found that the tendency was almost the same. It has been found that this method is effective even when the activation treatment after washing is used in combination.

A sapphire substrate having a diameter of 150 mm, a SiC substrate, a quartz substrate, a silicon substrate with an oxide film (100 nm), and a silicon substrate (without an oxide film) were used as a handle substrate, and the following cleaning method was performed.
1. No washing 2. Immersion in modified SC1 (80 ° C.) of ammonia: hydrogen peroxide: water = 1: 0.2: 10 (volume ratio) for 10 minutes (present invention)
_{Incidentally,} NH 4 _OH, H 2 _{O 2} concentrations were 29% aqueous solution in terms of a case of a 30% aqueous solution of terms. A surface activation treatment using plasma and a silicon substrate (thickness: 625 μm) having a diameter of 150 mm on which an oxide film was previously grown to 200 nm were bonded to these substrates. The bonded substrates are heated in an atmosphere of 150 ° C. for 24 hours, and then the surface energy (bonding strength) is crack-opening method (a blade is inserted at the bonding interface and the bonding strength is measured in an open area) (See, for example, Non-Patent Document 2.) The results are shown in FIG.

  It was found that the bonding force was increased by applying the cleaning method of the present invention except when the handle substrate was made of silicon. The decrease in the surface energy after cleaning observed in the case of silicon is thought to be because the surface was etched by the cleaning of the present invention and the surface roughness was deteriorated. Therefore, it has been found that when applying the cleaning method according to the present invention, it is preferable to select a material whose surface is not excessively etched.

Claims (11)

The handle substrate is made of a mixed solution in which the volume ratio of concentrated ammonia water [NH ₄ OH] in terms of 29% aqueous solution with respect to the volume of hydrogen peroxide water [H ₂ O ₂ ] in terms of 30% aqueous solution is more than 1 and not more than 200 in volume ratio A method for manufacturing a bonded substrate, comprising: cleaning the substrate, and thereafter bonding the handle substrate to a donor substrate. The composition of the mixed solution, when of _{H 2} O and 10, _NH 4 OH composition (in terms of volume) is 0.5 to _2, the composition of the H 2 _{O 2} is 0.01 to 0.5 The method for producing a bonded substrate according to claim 1.   The method for manufacturing a bonded substrate according to claim 1, wherein the handle substrate is sapphire, SiC, glass, quartz, or silicon with an oxide film.   4. The method for manufacturing a bonded substrate according to claim 1, wherein the donor substrate is silicon or silicon with an oxide film. The bonded substrate according to any one of claims 1 to 4, wherein the donor substrate is GaN, single crystal SiC, or a semiconductor material having a silicon oxide film (SiO ₂ ) formed on a surface thereof. Production method.   6. The method of manufacturing a bonded substrate according to claim 1, wherein surface activation is performed on the handle substrate before bonding.   The method for manufacturing a bonded substrate according to claim 6, wherein the surface activation is performed by any one or a combination of ozone water treatment, UV ozone treatment, ion beam treatment, and plasma treatment.   The method for manufacturing a bonded substrate according to claim 1, further comprising a step of thinning the donor substrate by a grinding / polishing method after the bonding.   Including a step of thinning the donor substrate by performing ion implantation on one main surface of the donor substrate before being bonded to the handle substrate, and performing peeling on the ion-implanted layer after the bonding step. 8. A method for manufacturing a bonded substrate according to claim 1, wherein   A bonded substrate obtained by the method for manufacturing a bonded substrate according to claim 1. A substrate cleaning aqueous solution containing concentrated aqueous ammonia, hydrogen peroxide and dilution water,
When the volume of the dilution water is 10, the volume ratio of the concentrated ammonia water is 0.5 to 2 in terms of 29% aqueous solution, and the volume ratio of the hydrogen peroxide solution is 0.01 in terms of 30% aqueous solution. A substrate cleaning aqueous solution having a volume ratio of ˜0.5 and a concentrated ammonia water and hydrogen peroxide solution exceeding 1.

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