JP3175323B2 - Semiconductor substrate manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a power device,
The present invention relates to a method for manufacturing a semiconductor substrate widely used as a VLSI substrate including a composite element, and particularly relates to a method for manufacturing a semiconductor substrate in which two silicon crystal plates are directly bonded.

[0002]

2. Description of the Related Art Conventionally, in order to manufacture one semiconductor substrate by directly bonding two silicon wafers made of a silicon crystal body, first, as shown in FIG. Silicon wafer made of silicon crystal
Perform 11 washes. This cleaning process allows the silicon wafer
An oxide film 12 is formed on the surface of 11.

The silicon wafer 11 having the oxide film formed on the surface by the cleaning step is immersed in 1 to 10 wt% dilute hydrofluoric acid as shown in FIG. After removing the oxide film 12 formed on the surface, for example, 90 ° C.
Of Kyarosu solution _{[H 2 SO 4 (4)} : H 2 O 2 (1)] performs Kyarosu oxide immersing about 3-5 minutes in the surface of the silicon wafer 11, as shown in FIG. 6 (C) For example, 50Å
A thin oxide film 13 is formed. As a result, the surface of the silicon wafer 11 is made hydrophilic.

[0004] Once the hydrophilic treatment is completed,
The silicon wafer 11 is immersed in ultrapure water for about 30 minutes as shown in FIG. 6D to adsorb water molecules on the surface of the silicon wafer 11 so that the surface is covered with OH groups. Thereafter, as shown in FIG. 6E, the two silicon wafers 111 and 112 subjected to such processing are adhered to each other, and heat-treated as shown in FIG.
Join 111 and 112 together.

In such a manufacturing method, a thin oxide film 13 is formed on the surface of the silicon wafer 11 by performing Carros oxidation, thereby making the surface hydrophilic. 11 is covered with OH groups. 2 thus covered by OH groups
When the surfaces of the silicon wafers 11 are brought close to each other, they are bonded by hydrogen bonding.

Here, if Carros oxidation is not performed,
Since the surface of the dil hydrofluoric acid-treated silicon wafer 11 is not hydrophilic and the two silicon wafers 111 and 112 cannot be bonded, the carlos oxidation step is indispensable.

However, oxide film 13 formed by carross oxidation has its oxide film localized at and near the junction interface even after heat treatment, and increases the electrical resistance in the direction passing through the junction interface. . In addition, the localized oxide film causes crystal defects, and has a problem in the characteristics of a device formed using the semiconductor substrate.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has been made in consideration of the above-described circumstances. Oxygen is not localized in
It is an object of the present invention to provide a method of manufacturing a semiconductor substrate in which a device having stable characteristics can be surely formed by lowering resistance at a bonding interface.

[0009]

SUMMARY OF THE INVENTION In a method of manufacturing a semiconductor substrate according to the present invention, at least one surface of each of a first silicon crystal plate and a second silicon crystal plate is mirror-polished, and after cleaning the surface, the silicon crystal plate is cleaned. While removing the oxide film on the surface of
The OH group is directly terminated to the silicon atom bond on the surface. Thereafter, the first and second silicon crystal plates are bonded.

The oxide film on the surface of the silicon crystal plate after the cleaning and the termination of the OH group are removed by removing the oxide film existing on the surface of the silicon crystal plate and removing the bond between the silicon atoms first. Termination is performed with a high-degree atom, and then the terminated high-negativity atom is replaced with an OH group.

In this case, it is necessary to terminate the surface of the silicon crystal plate with more atoms having high electronegativity. In other words, it is necessary to minimize the ratio of “Si—H” bonds on the surface of the silicon crystal plate before bonding the two silicon crystal plates.

This is realized, for example, by immersion in ultrapure water after immersion in concHF. In this case, the surface of the silicon crystal plate has a structure terminated by many fluorine atoms, and by immersing the silicon crystal plate in ultrapure water, the fluorine atoms terminated on the surface are replaced by OH groups. Become so.

As described above, the two silicon crystal plates are bonded by hydrogen bonding based on the OH group, and oxygen is not localized at the bonding interface, so that the resistance can be reliably reduced.

As described above, according to the method of manufacturing a semiconductor substrate according to the present invention, two silicon crystal plates can be bonded without employing the Carros oxidation process.
In this case, bonding can be performed in a state where oxygen is not localized at the bonding interface. For this reason, a reduction in resistance at the junction interface can be reliably realized, and a device having stable characteristics can be easily formed.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments with reference to the drawings. FIG. 1 shows a process of bonding a silicon wafer 11 made of a silicon single crystal, and at least one surface of the silicon wafer 11 is polished to a mirror surface. Although two silicon wafers are prepared for bonding, FIGS. 1A to 1C show only one of the silicon wafers 11. Hereinafter, a manufacturing process according to an embodiment of the present invention will be described with reference to FIG. FIG. 1A shows a cleaning step, and FIG.
HF immersion step, FIG. 1C shows ultrapure water immersion step, FIG.
FIG. 1 (D) shows a wafer bonding step of bonding a wafer by hydrogen bonding based on an OH group, and FIG. 1 (E) shows a bonding step of forming a covalent bond by heat treatment to firmly bond the wafer. 1 (B) concHF dipping process and FIG.
In the step (C) of immersion in ultrapure water, a natural oxide film on the wafer surface is removed, and OH groups are directly terminated on the wafer surface.

First, as shown in FIG. 1A, a silicon wafer 11 is, for example, SC2 [HCl (1): H ₂ O ₂ (1): H].
₂ O (4)]. By this cleaning step, a natural oxide film 12 of silicon oxide having a thickness of about 50 ° is formed on the surface of the silicon wafer 11.

After the cleaning step of the silicon wafer 11 is completed, the silicon wafer 11 is immersed in concHF (concentrated hydrofluoric acid solution: （50 wt% aq.) As shown in FIG. The native oxide film 12 formed on the substrate is removed. For example, it is immersed in concHF for about 3 minutes.

When the immersion process for concHF is completed as described above, a process for immersing the silicon wafer 11 in ultrapure water is performed as shown in FIG. The time of immersion in the ultrapure water is a time sufficient for most of the fluorine atoms terminating the surface of the silicon wafer 11 to react with water molecules and replace them with OH groups, for example, about 0.5 to 1 hour. It is.

When the immersion processing in the ultrapure water is completed, excess water droplets adhering to the wafer edge and the wafer carrier are removed by means such as spin drying, and then the two sheets thus processed are removed. Silicon wafer 111 and
As shown in FIG. 1 (D), 112 is brought into close contact with its mirror-polished surfaces facing each other. And the silicon wafer 111 and
O 2 formed to cover most of the surface of each of
With the hydrogen bonding force based on H group, this silicon wafer 111
Adhere 112. Then, as shown in FIG.
A covalent bond is formed by performing a heat treatment at a temperature in the range of 1 to 1200 ° C. to complete the strong bonding process.

The processing atmosphere in this heat treatment step is usually performed in N ₂ gas, but may be performed in oxygen, argon or hydrogen in a controlled atmosphere.

In the conventional method shown in FIG. 6, the silicon wafer 11 after the cleaning step is immersed in a dilute hydrofluoric acid solution of 1 to 10 wt% to form an oxide film 12 on the surface of the silicon wafer 11.
Is removed, for example, in a Carros solution at 90 ° C.
It is soaked for about 10 minutes to form a thin oxide film 13 on the surface. Then, as a result, the surface of the silicon wafer 11 is made to be hydrophilic. Then, by immersion in ultrapure water, water molecules are adsorbed on the surface of the silicon wafer 11, and the surface is covered with OH groups. I am trying to be.
Here, the surface of the silicon wafer after immersion in ultrapure water according to the conventional method has been made hydrophilic in a state of being wet with water,
Making the silicon surface hydrophilic before bonding was an essential condition. On the other hand, in the manufacturing method shown in the embodiment, the silicon wafer after the treatment of being immersed in ultrapure water is used.
The surface of 11 is hydrophobic so that it flips water,
The silicon surface before bonding does not need to be particularly hydrophilic.

FIG. 2A is a schematic diagram of the chemical structure of the surface of the silicon wafer 11 treated with conc HF (about 50 wt%), and FIG. 2B is the schematic diagram of the surface of the silicon wafer treated with dil HF (1 wt%). 1 shows a schematic diagram of a chemical structure.

When the silicon wafer 11 is immersed in conc HF, 0.38 fluorine atoms exist per silicon atom as shown in FIG. 2A, and dil HF as shown in FIG. When the immersion treatment is performed, 0.08 fluorine atoms are present per silicon atom. The remaining silicon atoms are terminated by hydrogen atoms.

When the silicon wafer 11 is immersed in water in such a state, the bond of "Si-F" is changed to the bond of "Si-OH" by the attack of water molecules as shown in FIG. However, the "Si-H" bond remains.
As a result, about 38% of the surface of the silicon wafer 11 treated with concHF shown in FIG. 3A is covered with OH groups. On the other hand, dil shown in FIG.
The surface of the silicon wafer 11 treated with HF is covered with OH groups only at most about 8%. When two wafers are brought close to each other in this state, the wafers treated with concHF are bonded to each other by hydrogen bonding based on OH groups, whereas the silicon wafers treated with 1 wt% HF are not bonded to each other. Therefore, it is considered necessary to keep the ratio of "Si-H" bonds as low as possible before bonding the wafer.

That is, in the manufacturing method shown in the embodiment, on the surface of the silicon wafer 11, the fluorine atom which terminates the bond of the silicon atom reacts with the water molecule and is replaced by the OH group. The presence of the group causes the adhesive effect. In the state where the two silicon wafers are bonded, the remaining hydrogen atoms are hydrogen atoms or O 2 terminated on the surface of the other silicon wafer.
A hydrogen atom or OH via a water molecule
It is considered to be opposite to the base.

When heat treatment is performed to complete the bonding process in such a state, the reaction between the opposing atoms proceeds by thermal energy, and the "Si-Si" bond and the "Si-OS"
The i ″ bond and the H ₂ molecule are formed, completing a strong bond.

When the silicon wafers are bonded to each other in such a process, the number of oxygen atoms present at the bonding interface is based only on OH groups and is reduced to one atomic layer or less. This oxygen is easily diffused into the inside by a subsequent heat treatment at, for example, 1150 ° C. for 1 hour. Therefore, there is no increase in interface resistance due to the localization of oxygen atoms.

On the other hand, in the manufacturing method in which the carross treatment is performed as shown in FIG.
酸化) The oxide film layer exists at the bonding interface. This oxide film layer is not easily diffused into the interior even by the subsequent heat treatment, which causes an increase in interface resistance.

FIG. 4 shows the result of an investigation of the change in the resistance value near the bonding interface of the bonded wafer manufactured in the above embodiment by spread resistance measurement. Conc shown by a solid line in this figure
In the example manufacturing method in which the HF processing is performed, the spreading resistance near the interface is equal to the value of bulk silicon. On the other hand, the resistance value near the bonding interface of the bonded wafer obtained by the conventional manufacturing method (using Carross oxidation) indicated by the broken line is:
It is a very high value.

FIG. 5 shows the bonding strength between the silicon wafers 111 and 112 bonded by the method shown in the embodiment in comparison with the values shown in the conventional method and the literature. In this figure, (A) is the bonding strength obtained by the example, (B)
Shows the bonding strength obtained according to the conventional method of Carros oxidation, and (C) and (D) show examples shown in the literature, respectively. As is clear from FIG. 5, when the bonding is performed by the method shown in the embodiment, a result is obtained in which the tensile strength is 2-2.5 times higher than the conventional method or the literature value.

As described above, according to the method of manufacturing a semiconductor substrate according to this embodiment, two silicon crystal plates can be bonded without employing the Carross oxidation process, and in this case, the bonding interface Bonding can be performed in a state where oxygen is not localized in the substrate. For this reason, a reduction in resistance at the junction interface can be reliably realized, and a device having stable characteristics can be easily formed.

In the above embodiment, 50 wt% of concHF is used as a step of removing a natural oxide film and adding a fluorine atom.
Although the treatment was performed, the treatment can be similarly performed by using a hydrofluoric acid solution having a concentration higher than 1 wt%.

Further, the conc shown in FIG.
Instead of the HF treatment, a treatment with an ammonium fluoride solution or a mixed solution of hydrofluoric acid and alkali may be performed as a step of removing a natural oxide film and adding a fluorine atom. In that case, the processing may be performed in the same manner as shown in FIGS. By performing such a treatment, the concentration of H ⁺ ions in the aqueous solution decreases, and accordingly, the number of hydrogen atoms terminating on the surface of the silicon wafer decreases according to the principle of chemical equilibrium. The proportion terminated by the group increases.

In the embodiment described with reference to FIG. 1, the concentration of the hydrofluoric acid solution to be immersed was set to concHF (about 50 wt%). However, this hydrofluoric acid concentration is not particularly limited. After irradiating the surface of the silicon wafer 11 with ultraviolet rays having a wavelength of, for example, 4000 ° or less in the ultrapure water, the two silicon wafers 111 subjected to such processing are irradiated with the ultraviolet rays.
And 112 may be adhered. By irradiating the ultraviolet rays, the “Si—H” bonds of hydrogen that have terminated the surface of the silicon wafer after the immersion in the hydrofluoric acid solution are broken, whereby the OH groups can be replaced. The wavelength of the ultraviolet light applied here is desirably not more than about 4073 ° corresponding to the Si—H bond energy of 3.05 eV. Furthermore, since the bond energy of the Si-O bond is 3.85 eV and the wavelength of the corresponding ultraviolet light is 3243 °, it is preferable that the wavelength of the ultraviolet light to be irradiated does not include light of 3243 ° or less.

Further, in the embodiment, the concentration of the hydrofluoric acid solution to be immersed was set to concHF (up to 50% by weight). Was obtained, and the bonding strength was comparable to that of bulk. However, the concentration of hydrofluoric acid solution is 10wt
%, It becomes difficult to adhere when two silicon wafers are brought into close contact at room temperature.
If it is less than almost all of the adhesive will not be adhered. Therefore, it is desirable that the concentration of the hydrofluoric acid used is at least 10 wt% or more. FIGS. 7 (A) and 7 (B) show the amounts of fluorine and oxygen on the HF-etched silicon wafer surface.
It shows the concentration dependence and the change due to immersion in pure water. The amount of fluorine terminated on the surface was reduced by immersion in water, and instead an equivalent amount of oxygen was increased, indicating that "Si-F"
It can be seen that the bonds are hydrolyzed and converted into “Si—OH” bonds. However, the higher the hydrofluoric acid concentration, the more fluorine atoms can be terminated to the silicon wafer surface, and the more “Si—OH” bonds. "A bond can be formed. Further, since the effect of reducing the interface resistance and the high bonding strength are obtained when the hydrofluoric acid concentration is 10 wt% or more, at least 0.2 fluorine atoms per silicon atom before immersion in ultrapure water. Is considered to be terminated.

In the above embodiment, the surface of the silicon wafer is terminated with fluorine atoms. Instead, the surface of the silicon wafer is terminated with atoms having high electronegativity like fluorine atoms, for example, other halogen elements such as chlorine. You may. For example, when a chlorine atom is to be terminated, a silicon wafer may be heated to, for example, 1000 ° C. or more in a hydrogen atmosphere to which chlorine has been added using, for example, HCl gas to remove a natural oxide film on the surface. . Then, after removing the natural oxide film, the silicon wafer is cooled to about 200 ° C. while maintaining the chlorine atmosphere, and then switched to the inert gas atmosphere to take out the silicon wafer, whereby the silicon wafer surface can be terminated with chlorine atoms and hydrogen atoms. Thereafter, as in FIG. 1 (C), if immersed in ultrapure water, the terminated chlorine atom is replaced by an OH group, so if the treatment is performed in the same manner as shown in FIGS. 1 (D) and 1 (E), Good. Further, the ultraviolet rays may be irradiated during the immersion in the ultrapure water as described above.

Further, in the above embodiment, the natural oxide film on the surface was removed by immersing the silicon wafer in a hydrofluoric acid-based aqueous solution, and the surface was terminated with a large number of fluorine atoms. The step of removing the film and the step of terminating the surface with many fluorine atoms may be performed separately, and the atoms terminating the surface have a high electronegativity. It may be. In this case, the step of removing the oxide film on the surface may be a step of heating in a vacuum, preferably an ultra-high vacuum, or a step of sputtering in a vacuum. Next, as a step of terminating the surface with atoms having a high electronegativity, in the same vacuum as that from which the oxide film has been removed, exposure to a chlorine gas atmosphere such as HCl or Cl ₂ or its plasma atmosphere, or exposed to the fluorine gas atmosphere or a plasma atmosphere, such as HF or SF _6, or may be a step of exposure to bromine gas atmosphere or a plasma atmosphere such as HBr. Thereafter, as in FIG. 1 (C), if immersed in ultrapure water, the terminated chlorine, fluorine or bromine atoms are replaced by OH groups, and therefore, as shown in FIGS. 1 (D) and (E). Should be processed. Further, the ultraviolet rays may be irradiated during the immersion in the ultrapure water as described above.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a manufacturing process of a semiconductor substrate according to one embodiment of the present invention.

FIGS. 2A and 2B are schematic diagrams showing chemical structures of a silicon wafer surface after a conc HF treatment and a silicon wafer surface after a 1 wt% HF treatment, respectively.

FIGS. 3 (A) and (B) show 50 wt% HF treatment after hydrofluoric acid treatment, pure water washing, and further drying, respectively.
It is a schematic diagram which shows the chemical structure of the silicon wafer surface which processed wt%.

FIG. 4 is a diagram showing a junction interface resistance of a joined semiconductor substrate in comparison between an embodiment and a conventional example.

FIG. 5 is a diagram showing bonding strength in comparison with an example and a conventional example.

FIG. 6 is a diagram for explaining a conventional semiconductor substrate manufacturing process.

FIGS. 7A and 7B are diagrams showing the HF concentration dependence of the amounts of fluorine and oxygen on the surface of a silicon wafer which has been treated with hydrofluoric acid, and also showing changes caused by immersion in pure water.

[Explanation of symbols]

11, 111, 112 Silicon wafer (silicon single crystal plate) 12 Natural oxide film 13 Oxide film (by Carros oxidation)

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Seiji Fujino 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Inside Denso Co., Ltd. (56) References JP-A-3-123014 (JP, A) JP-A-61- 4221 (JP, A) JP-A-2-183510 (JP, A) JP-A-5-82404 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21 / 02,21 / 304

Claims (8)

(57) [Claims] A cleaning step of cleaning the mirror-polished surfaces of the first and second silicon crystal plates having at least one surface mirror-polished, and the cleaned first and second silicon crystal plates. 10w
By dipping in a hydrofluoric acid solution with a concentration of
Acid present on the mirror polished surface of the recon crystal plate
The oxide film is removed, and the silicon atom is
A fluorine atom adding step of terminating the oxide, and converting the fluorine atom bonded to the silicon atom on the surface to O.
An OH group adding step of substituting with an H group, and combining the mirror-polished surfaces of the first and second silicon crystal plates with the first and second silicon crystal plates via an OH group A method for manufacturing a semiconductor substrate, comprising: a bonding step of bonding by hydrogen bonding. 2. The step of adding an OH group comprises the step of
The first and second silicon crystal plates which have been terminated
Is immersed in ultrapure water for about 0.5 to 1 hour.
The method for manufacturing a semiconductor substrate according to claim 1. 3. The method according to claim 1, wherein at least one surface is mirror-polished.
Mirror-polished surfaces of first and second silicon crystal plates
A cleaning step of cleaning the first and second cleaned silicon crystal plates.
Immerse in ammonium solution or hydrofluoric acid-alkali mixed solution
By mirror polishing the silicon crystal plate
Remove the oxide film present on the surface, and fluorine atoms
With fluorine atom to terminate the bond of silicon atom
And the fluorine atom bonded to the silicon atom on the surface is changed to O.
An OH group adding step of substituting with an H group, and the mirror polishing of the first and second silicon crystal plates
The first and second silicon crystals together
An adhesion process in which the plate is adhered by hydrogen bonding via an OH group;
A method for manufacturing a semiconductor substrate, comprising: 4. The method according to claim 1, wherein at least one surface is mirror-polished.
Mirror-polished surfaces of first and second silicon crystal plates
Cleaning step, and cleaning the first and second silicon crystal plates with chlorine.
The silicon is heated by heating in an added hydrogen atmosphere.
Oxide film present on the mirror-polished surface of the crystalline body plate
And bond the silicon atom with a chlorine atom
A chlorine atom adding step of terminating the chlorine atom bonded to the silicon atom on the surface with OH.
An OH group adding step of substituting with a group, and the mirror polishing of the first and second silicon crystal plates
The first and second silicon crystals together
An adhesion process in which the plate is adhered by hydrogen bonding via an OH group;
A method for manufacturing a semiconductor substrate, comprising: 5. The method of claim 1, wherein at least one surface is mirror-polished.
Mirror-polished surfaces of first and second silicon crystal plates
A cleaning step of cleaning the surface of the cleaned first and second silicon crystal plates.
An oxide film removing step for removing the formed oxide film; and, after the oxide film removing step , the silicon oxide film is removed with atoms having a high electronegativity.
Terminator for terminating the bond of the recon atom
The degree of electronegativity associated with silicon atoms on the surface
An OH group adding step of substituting a hydrogen atom with an OH group, and the mirror polishing of the first and second silicon crystal plates
The first and second silicon crystals together
An adhesion process in which the plate is adhered by hydrogen bonding via an OH group;
A method for manufacturing a semiconductor substrate, comprising: 6. An oxide film removing step includes heating in a vacuum.
Process or sputtering in vacuum.
The method for manufacturing a semiconductor substrate according to claim 5. 7. The terminating step includes removing the oxide film.
In the same vacuum as the removal step, halide gas or
Is a process of exposing to the plasma atmosphere
7. The method for manufacturing a semiconductor substrate according to claim 6, wherein: 8. The method of claim 1, wherein the step of adding an OH group comprises the steps of:
2 while immersing the silicon crystal plate in ultrapure water,
Characterized by the process of irradiating ultraviolet light in pure water
The semiconductor according to any one of claims 1 to 7,
Method for manufacturing body substrate.