JP2815001B2 - Method for manufacturing thin film SOI substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an SOI substrate (Si
on Insulator or Semicond
In particular, the present invention relates to a method for uniformly thinning a semiconductor layer on an insulating film.

[0002]

2. Description of the Related Art SOI having a semiconductor active layer on an insulator
As one of the methods for forming a substrate, a bonding method is known. In this method, at least one of the two silicon substrates is oxidized to form a silicon oxide film as an insulator,
After stacking the silicon oxide films in an interposed arrangement, heat treatment is applied and the silicon oxide films are bonded to each other, and the silicon substrate serving as an active layer is further thinned. In this method, since the silicon substrate layer which is a single crystal is thinned in the first place, the crystallinity of the active layer is extremely good.

Conventionally, as a method of thinning the active layer, for example, Journal of Electric Materials, Vol. 21, pp. 669-676, 1992 (Jour)
nalof Electronic Material
1, Vol. 21, No. 7,669-676,199
Although detailed in 2), a method of mechanically polishing and a method of etching using an epitaxial layer as an etch stop are known.

However, it is difficult to obtain a uniform film thickness by the former method, and a typical active layer film thickness and uniformity obtained by this method is, for example, 3 μm ± 0.5 μm. A useful thin film (for example, 0.1 μm) could not be formed. Further, the latter method has a drawback that the process of performing epitaxial growth is complicated and the production cost is increased.

Further, for example, in 1992, I Triple E International SOI Conference Proceedings, pp. 152-153 (1992 IEEE
International SOI Confere
nce Proceedings, pp152-15
As described in 3), there is a method in which the thickness of the active layer is precisely measured after mechanically polishing, and a thick region is etched longer by local plasma etching than other regions, but the process is complicated. In addition, there is a problem of causing damage and contamination by plasma.

Further, for the purpose of overcoming the above-mentioned problems, for example, Japanese Journal of Applied Physics, Vol. 35, pp. L71-L73 (Japanese)
Journal of Applied Physic
s, Vol. 35, (1996) pp. L71-L7
3) proposes a method of applying a DC voltage between the supporting substrate layer and the etching solution to the bonded SOI to reduce the thickness of the active layer. However, since this method applies a DC voltage, the effect of automatically stopping the etching when a leakage current is present is reduced, and the uniformity of the obtained active layer film thickness and the process reproducibility are poor. .

As described above, although the bonded SOI has a great advantage of good crystallinity, it is difficult to make the thickness of the active layer uniform, and the thin film SOI is effective for improving the performance of the device.
Was difficult to form.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has been made in view of the above circumstances. An object of the present invention is to provide a manufacturing apparatus used for this.

[0009]

According to the present invention, a supporting substrate and a semiconductor substrate are bonded together with an insulating layer interposed therebetween.
Contacting the surface of the semiconductor substrate layer with a solution or gas capable of etching while applying a pulse voltage between the bonded support substrate layer and the semiconductor substrate layer to reduce the thickness of the semiconductor substrate layer. A method for producing the

[0010] The present invention also provides a supporting substrate and a semiconductor substrate.
Bonding a semiconductor compound layer that can be removed by reacting a semiconductor on the surface of the semiconductor substrate layer while applying a pulse voltage between the supporting substrate layer and the semiconductor substrate layer after bonding, and The present invention relates to a method for manufacturing a thin-film SOI substrate including a step of forming and a step of removing the semiconductor compound layer and thinning a semiconductor substrate layer.

In the present invention, the pulse voltage is applied by connecting one terminal of a pulse power source to a supporting substrate layer and bringing the other terminal into contact with a solution or gas insulated from the supporting substrate layer. Is preferably applied.

In the present invention, it is preferable that the pulse voltage is applied by connecting one terminal of a pulse power supply to a support substrate layer and connecting the other terminal to a semiconductor substrate layer to apply the pulse voltage.

Further, the present invention relates to an apparatus for manufacturing a thin-film SOI substrate for thinning a substrate obtained by bonding a supporting substrate and a semiconductor substrate with an insulating layer interposed therebetween, wherein the bonded supporting substrate layer and the semiconductor substrate are bonded together. A pulse power supply for applying a pulse voltage between the layers, a solution or gas capable of being etched, a solution or gas capable of forming a removable semiconductor compound layer by reacting with a semiconductor, or a solution capable of removing the semiconductor compound layer or The present invention relates to an apparatus for manufacturing a thin film SOI substrate having a sealing means for bringing only a predetermined region of a semiconductor substrate layer surface into contact with a gas.

This manufacturing apparatus preferably further comprises means for connecting one terminal of the pulse power source to the support substrate layer, and means for bringing the other terminal into contact with a solution or gas insulated from the support substrate layer. .

It is preferable that the manufacturing apparatus further includes a means for connecting one terminal of the pulse power supply to the supporting substrate layer and a means for connecting the other terminal to the semiconductor substrate layer.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In electrochemical reactions such as a semiconductor etching reaction (liquid phase etching using an etchant, gas phase etching with a partial gas) and an electrode reaction (for example, anodic oxidation or anodic formation), The reaction rate such as the etching rate greatly depends on the presence or absence of the carrier or its concentration. Therefore, if a depletion layer containing no carrier is formed in the semiconductor layer, the reaction speed of etching or the like becomes extremely slow. The depletion layer functions as an etch stop or a reaction stop layer, and a uniform active layer film corresponding to the uniform depletion layer can be obtained.

As an example, a fluorinated nitric acid solution (HF / H
The principle in which a depletion layer acts as an etch stop in chemical etching using a mixed solution of NO ₃ / CH ₃ COOH) will be described. HF using CH ₃ COOH as a buffer
When etching Si with the / HNO ₃ solution, the etching proceeds according to a series of reactions expressed by the following equations. ^{Si + 2h + → Si 2+ (} 1) Si 2+ + 2OH - → SiO 2 + H 2 (2) SiO 2 + 6HF → H 2 SiF 6 ( water soluble) + H ₂ O (3)

Therefore, the presence or absence of carriers (holes in this case) as seen in the equation (1) depends on the progress of etching.
Play a big role in the line . Therefore, when the etching progress surface reaches the end of the depletion layer, a shortage of holes causes an etch stop mechanism to operate.

At this time, the formation of a similar depletion layer can be expected in principle even if a DC voltage is applied. However, in reality, carriers such as electrons injected into the depletion layer at the time of a chemical reaction of etching cause depletion. It has the function of extinguishing the layer, and consequently has disadvantages such as deterioration in uniformity of the film thickness after the etch stop and poor reproducibility of the etch stop.

Therefore, in the present invention, a pulse voltage is applied between the supporting substrate layer and the semiconductor substrate layer of the bonded SOI substrate instead of a DC voltage. By applying the pulse voltage, the process of once discharging the carriers injected into the depletion layer and forming the depletion layer again is repeated, so that the carriers do not extinguish the depletion layer. Therefore, in the present invention, a uniform depletion layer is always formed at the bonding interface (interface with the insulating film) of the semiconductor substrate layer, and this acts as a stop layer at the time of etching or electrode reaction. This makes it possible to form a thin film with high precision and uniformity.

The semiconductor substrate used in the present invention includes:
Although a compound semiconductor substrate such as GaAs or an intrinsic semiconductor substrate such as Ge or silicon can be used, a silicon substrate is preferable because an insulating film can be easily formed on the surface by thermal oxidation or the like.

The support substrate used in the present invention is not particularly limited as long as it has conductivity, but usually a semiconductor substrate, particularly a silicon substrate, is preferably used. This is because it is preferable that the compatibility with the current semiconductor process is good, and that the coefficient of thermal expansion and the like do not greatly differ from the semiconductor substrate to be bonded.

As the insulating film of the present invention, when the semiconductor substrate or the supporting substrate is silicon, an oxide film formed on the surface by thermal oxidation or the like as described above can be used.

The bonding of the substrates can be performed by laminating the supporting substrate and the semiconductor substrate with an insulating film therebetween and heating at a predetermined temperature as in the case of manufacturing an ordinary SOI substrate. After that, before thinning the semiconductor substrate layer of the bonded substrate with high accuracy, it is preferable to reduce the thickness to some extent in advance by using a mechanochemical polishing method or the like because the time of the next thinning process can be shortened.

In order to reduce the thickness of the semiconductor substrate layer by an etching reaction, any of wet etching using an etchant, dry etching using an etching gas, and the like can be used as long as the etching rate varies depending on the carrier. it can.

For example, wet etching using an etching solution such as a hydrofluoric-nitric acid-based solution, a KOH-based solution, or a hydrazine-based solution, or a halogen-based gas such as Cl ₂ , HCl, CCl _4, etc.
Gas etching such as plasma etching using a plasma source such as CR, high frequency, and helicon, and temperature-rising etching using a halogen-based gas such as Cl ₂ , HCl, and CCl ₄ can be used.

Further, in the present invention, the semiconductor compound layer is formed by reacting the surface of the semiconductor substrate layer even if the reaction and dissolution (or gasification) of the semiconductor do not proceed simultaneously as in the case of ordinary etching. The semiconductor substrate layer can be thinned by repeating the step of removing it once or many times. Here, the semiconductor compound layer refers not only to a semiconductor compound that has changed to a different compound due to a reaction of the semiconductor, but also to a material that has changed to a state in which it is easily removed physically.

In this case, the present invention can be applied to a method in which the formation speed of the semiconductor compound layer changes depending on the presence of carriers. It is preferable that this semiconductor compound layer can be easily removed in the next step.

As an example of this, when the semiconductor substrate is silicon, a method of oxidizing an electrode on the surface of the silicon substrate layer and then removing the oxide film with hydrofluoric acid or the like, or a method of making the surface of the silicon substrate layer porous And a method of performing etching removal with hydrofluoric / nitric acid.

In the present invention, any method of applying a pulse voltage may be used as long as a voltage is applied between the supporting substrate layer and the semiconductor substrate layer with the insulating film interposed therebetween.

For example, one terminal of the pulse power supply can be connected to the back side of the support substrate layer, and the other terminal can be connected to the surface of the semiconductor substrate layer. In addition, if in a solution, one terminal may be connected to the supporting substrate layer, an appropriate electrode may be provided in the solution, and the other terminal may be connected to this electrode. In the case of a solution, it is particularly preferable to provide a suitable sealing means so that the etching solution or the like does not come into contact with the supporting substrate layer side. Accordingly, the support substrate layer is not exposed to a reaction solution such as etching, and a circuit is not short-circuited, so that a pulse voltage can be reliably applied between the support substrate layer and the semiconductor substrate layer.

In the case of plasma etching or the like, one terminal is connected to the supporting substrate layer, and the other terminal is
It can also be connected to a suitable electrode or a device wall provided at a position at least insulated from the supporting substrate layer and in contact with the plasma.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following embodiments will be described in detail with reference to the drawings.

[Example 1] A bonded SOI was manufactured by using a P-type Si substrate (specific resistance: 1 to 3 Ω · cm, thickness: 625 μm) as a support substrate.
m) and a P-type Si substrate (resistivity 1) as a semiconductor substrate.
To 3 Ω · cm) to form a silicon oxide film having a thickness of about 1 μm. The thickness of the semiconductor substrate is 3 to 5 μm by the usual mechanical and chemical polishing from the surface opposite to the bonding surface,
The thickness was reduced to a film thickness accuracy of ± 0.5 μm.

A number of such SOI substrates were prepared, mounted on the thinning apparatus shown in FIG. 1, and a highly accurate thinning process was performed.
That is, the bonded SOI substrate 20 is fixed to the substrate holder 10 via the O-ring 40 made of a material having excellent chemical resistance for solution separation so that the bonded SOI substrate 20 is in contact with the gold-coated support substrate electrode 30 for pulse voltage application. did.

Next, etching was performed using a mixed solution of hydrofluoric acid / nitric acid / acetic acid having a mixing ratio of 1: 3: 10 or a solution obtained by adding acetic acid saturated with iodine instead of pure acetic acid.

The potential of each electrode during etching is a Pt electrode 8
0 is grounded, and a pulse voltage is applied to the supporting substrate electrode using a pulse voltage generator 50 with a pulse height of +0.5 V to 1 with respect to 0 V.
A different pulse waveform was applied to each sample while changing the frequency between 0 V and 1 Hz to 10 MHz.

The solution during the etching was stirred by a stirrer 70 and further controlled by a computer-controlled heater 60 between room temperature and 100 ° C. Etching stopped automatically after about 10-30 minutes had elapsed depending on the sample.

The thickness of the semiconductor substrate layer measured by an optical film thickness measuring device was 0.5 to 3 μm according to the applied voltage, and the accuracy was ± 1 nm, and the thickness could be extremely uniformly reduced.

Since the obtained depletion layer width depends not only on the height of the pulse voltage but also on the specific resistance of the semiconductor substrate, it is necessary to calculate the depletion layer width for each sample and adjust the voltage in consideration of these factors. Thus, a desired film thickness can be accurately obtained.

Further, when acetic acid saturated with iodine was used, the flatness of the sample surface after the completion of etching was more excellent than that of a solution to which pure acetic acid was added.

Example 2 The same SOI substrate as that used in Example 1 was prepared, and etching was performed using a 10% to 40% aqueous solution of KOH as a solution using the same arrangement and the same value of applied voltage. When etching was performed while maintaining the solution temperature at 50 to 80 ° C., the etching was stopped in about 5 to 10 minutes.

With respect to the thickness and distribution of the semiconductor substrate layer after the etching, the same result was obtained when the potential of each electrode was the same as in the first embodiment. Therefore, according to the present invention, it was confirmed that the film thickness of the semiconductor substrate layer after the etching was defined by the width of the depletion layer depending on the type of the solution.

Example 3 The same SOI substrate as that used in Example 1 was prepared, and using the same apparatus, ethylene glycol was used for the solution. Further, an electrode was provided on the surface of the silicon substrate layer, and a current was passed between the silicon substrate layer (anode) and the Pt electrode to perform anodic oxidation. The current density is 20 mA / cm ²
When the voltage between the silicon substrate layer (anode) and the Pt electrode voltage increases by 50 V, 1
An oxide film having a thickness of 100 to 300 Å was formed.

Next, the SOI substrate was taken out and immersed in diluted hydrofluoric acid to dissolve and remove the oxide film. Further, the anodic oxidation and the removal of the oxide film by hydrofluoric acid were repeated many times to reduce the thickness. As a result, the oxidation reaction was stopped halfway, and the thinning did not proceed any further. As a result, Examples 1 and 2
With the same film thickness and film thickness distribution as in Example 5, a uniform thin film could be obtained.

In order to carry out the anodic oxidation, a mixture of sodium tetraborate and boric acid may be used instead of ethylene glycol.

Example 4 The same SOI substrate as that used in Example 1 was prepared, and the solution was treated with hydrofluoric acid / hydrofluoric acid using the same apparatus.
A pulse voltage having a height of 5 to 15 V was applied using a 2: 3 solution of ethyl alcohol, and a constant current of about 20 to 80 mA / cm ² was applied in the same manner as in Example 3. This reaction was known as anodization, and porous Si was formed on the surface of the semiconductor substrate layer. The reaction was stopped in 5-15 minutes. Next, when only the porous Si layer was removed with a fluorinated nitric acid solution, the film was uniformly thinned with the same thickness and distribution as in Examples 1 to 3.

Example 5 Same as that used in Example 1
Set the SOI substrate in the plasma etching equipment and support it
Connect the pulse power supply terminals to the substrate layer and the semiconductor substrate layer, respectively.
To the supporting substrate layer side with reference to the semiconductor substrate layer side.
A pulse voltage of 1 to 5 V is applied and CCl _FourUsing gas
Plasma etching was performed.

As a result, the thickness was 0.5 to 3 μm and the distribution was ±
The thickness was 0.01 μm, which was very uniform as compared with the prior art. The reason why the uniformity is slightly inferior to the above-described embodiment is that the rate of decrease in the etching rate in the depletion layer where no carrier is present is smaller than in the first and second embodiments. However, this method has an effect that, for example, the advantages of dry etching that is cleaner and has less environmental impact can be used.

Here, in addition to CCl ₄ , a gas capable of etching a semiconductor can also be used.

[Embodiment 6] In each of the pulse voltages used in Embodiments 1 to 5, a pulse voltage fluctuating between 0 V and a predetermined voltage on the + side was applied to the support substrate layer side. In the example, the same effect was obtained even when a voltage having a predetermined height was applied so as to swing to the + side with reference to -0.1 to -1 V.

When the conduction type of the active layer is n-type,
The same effect was obtained by reversing the polarity of the pulse voltage applied between the support substrate electrode 30 and the Pt electrode 80 in the solution to that of the p-type.

[0053]

According to the present invention, it is possible to provide a method of manufacturing a thin film SOI substrate having a uniform thickness and a small thickness of a semiconductor substrate layer at low cost and with good reproducibility, and a manufacturing apparatus used for the same.

[Brief description of the drawings]

FIG. 1 is a schematic view of a thinning apparatus of the present invention.

[Explanation of symbols]

 Reference Signs List 10 substrate holder 20 bonded SOI substrate 30 support substrate electrode 40 O-ring 50 pulse voltage generator 60 heater 70 stirrer 80 Pt electrode in solution

Claims (7)

(57) [Claims] 1. A step of bonding a support substrate and a semiconductor substrate with an insulating layer interposed therebetween, and applying a pulse voltage between the bonded support substrate layer and the semiconductor substrate layer while applying a pulse voltage to the surface of the semiconductor substrate layer. Contacting the substrate with an etchable solution or gas to reduce the thickness of the semiconductor substrate layer. 2. A step of bonding a support substrate and a semiconductor substrate with an insulating layer interposed therebetween; and applying a pulse voltage between the bonded support substrate layer and the semiconductor substrate layer while applying a pulse voltage to the surface of the semiconductor substrate layer. A method for manufacturing a thin-film SOI substrate, comprising: a step of forming a removable semiconductor compound layer by reacting a semiconductor; and a step of removing the semiconductor compound layer and thinning a semiconductor substrate layer. 3. The method of applying a pulse voltage according to claim 1, wherein one terminal of the pulse power supply is connected to a supporting substrate layer, and the other terminal is brought into contact with a solution or gas insulated from the supporting substrate layer to apply the pulse voltage 3. The method for manufacturing a thin film SOI substrate according to claim 1, wherein: 4. The method of applying a pulse voltage according to claim 1, wherein one terminal of the pulse power supply is connected to a support substrate layer, and the other terminal is connected to a semiconductor substrate layer to apply the pulse voltage. Item 3. The method for manufacturing a thin film SOI substrate according to item 1 or 2. 5. A thin-film SOI substrate manufacturing apparatus for thinning a substrate obtained by laminating a support substrate and a semiconductor substrate with an insulating layer interposed therebetween, comprising: A pulse power supply for applying a pulse voltage to a solution or gas capable of being etched, a solution or gas capable of forming a removable semiconductor compound layer by reacting with a semiconductor, or a solution or gas capable of removing the semiconductor compound layer; An apparatus for manufacturing a thin film SOI substrate, comprising: a sealing means for contacting only a predetermined area on a surface of a semiconductor substrate layer. 6. The thin film according to claim 5, further comprising: means for connecting one terminal of the pulse power supply to the support substrate layer; and means for bringing the other terminal into contact with a solution or gas insulated from the support substrate layer. SOI substrate manufacturing equipment. 7. The apparatus for manufacturing a thin film SOI substrate according to claim 5, further comprising: means for connecting one terminal of the pulse power supply to a support substrate layer; and means for connecting the other terminal to a semiconductor substrate layer.