JPH05335395A - Method for making soi film thickness uniform in soil substrate - Google Patents

Abstract

PURPOSE:To suppress an irregularity in an SOI film thickness to + or -0.3mum or less over the whole face of an SOI substrate even in the SOI substrate whose SOI film thickness is 10mum or more by a method wherein the SOI film thickness in each section inside the face of the SOI substrate is measured and an SOI film is etched by a prescribed etching margin. CONSTITUTION:The face of an SOI substrate 11 is partitioned into a plurality of sections; the SOI film thickness of individual sections W1 to Wn is measured individually by using a Fourier-transform infrared spectrometer; a film-thickness map is formed. Then, an etching margin which sets the SOI film thickness of the individual sections to a specific value is computed for the individual sections W1 to Wn on the basis of the film-thickness map. After that, a dry etching apparatus 30 which can selectively etch only a prescribed region is scanned on the SOI substrate 11, the SOI film of the individual sections W1 to Wn is etched and treated by a prescribed etching margin. The dry etching apparatus can selectively etch only a region having a diameter of, e.g. 8 to 14mm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for making an SOI film thickness uniform over the entire surface of an SOI substrate.

[0002]

2. Description of the Related Art Conventionally, as a method of forming a single crystal semiconductor thin film having a thickness of 1 μm or more on a dielectric substrate, a technique of epitaxially growing a single crystal silicon film or the like on a single crystal sapphire substrate is well known. However, in this technique, a large number of crystal defects occur in the silicon vapor phase growth layer due to the mismatch of the lattice constants between the dielectric substrate and the vapor-grown silicon single crystal. The technology is lacking in practicality.

Therefore, in recent years, SOI (Si On Insulato)
A bonded wafer having a r) structure (hereinafter referred to as an SOI substrate) has particularly attracted attention. This SOI substrate is, for example, 2
At least one of the semiconductor substrates is oxidized to form an oxide film on the surface of at least one of the substrates.
After stacking the semiconductor substrates on each other so that the oxide film serves as an intermediate layer, these are heated to a predetermined temperature to be bonded,
It is obtained by subjecting one of the semiconductor substrates to surface grinding, and then further polishing to thin this to obtain a single crystal silicon thin film (hereinafter referred to as an SOI film).

By the way, SOI used for power
The substrate has a relatively large SOI film thickness of 10 μm or more, but the thickness is uniform and the variation is at least ± 0.3.
It is required to be less than μm.

[0005]

However, there is a limit to the uniformization of the SOI film thickness under the current management method in polishing, and it is impossible to make the SOI film thickness uniform by suppressing the variation to ± 0.3 μm or less. It was impossible.

The present invention has been made in view of the above problems. The object of the present invention is to provide a SOI substrate having an SOI film thickness of 10 μm or more with a variation in the SOI film thickness of ± 0.3 μm over the entire surface of the substrate. SO that can be kept below
An object of the present invention is to provide a method for uniforming the SOI film thickness on an I substrate.

[0007]

In order to achieve the above object, the present invention divides the surface of an SOI substrate into a plurality of sections, and measures the SOI film thickness of each section using a Fourier transform infrared spectrometer. A dry etching apparatus capable of creating a thickness map, calculating an etching allowance for the SOI film thickness of each section to become a predetermined value for each section based on the film thickness map, and selectively etching only a predetermined area Is scanned on the SOI substrate and the SOI film in each section is etched by a predetermined etching amount.

[0008]

[Function] The present inventors have made a Fourier transform infrared spectrometer (hereinafter,
A method for measuring the SOI film thickness using FTIR (hereinafter referred to as the FTIR method) was previously proposed, but this method provides high accuracy even if the SOI film thickness is 10 μm or more. It turns out that it can measure.

Therefore, as in the present invention, the SOI film thickness of each section of the SOI substrate surface is measured by the FTIR method to create a film thickness map, and the etching allowance of the SOI film in each section is determined based on this film thickness map. Even if the SOI film having a thickness of 10 μm or more is calculated and the SOI film of each section is etched by the dry etching apparatus, the thickness of the SOI film can be made uniform within ± 0.3 μm. can do.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

In the method of the present invention, as shown in FIG. 1, first, the SOI substrate 11 is divided into a plurality of sections W1, W2 ... Wn.
And the SOI film thickness of each section W1, W2 ... Wn is F
A film thickness map is created by measurement by the TIR method.

The method of measuring the SOI film thickness by FTIR will be outlined with reference to FIGS. 2 to 4. 2 is F
Basic configuration diagram of SOI film thickness measurement system by TIR method, FIG. 3 is a diagram showing a relationship between optical path difference in an SOI substrate and reflected infrared light intensity, and FIG. 4 is 5 to 32 μ on oxide film thicknesses 1, 2 and 3 μm.
It is a figure which shows the correlation of the SOI film thickness measured by the FTIR method, and the SOI film thickness measured by the scanning electron microscope (SEM) with respect to the SOI film which has a film thickness of m.

As shown in FIG. 2, an infrared ray generating lamp 1
The continuous infrared light having a wavelength of 2.5 to 25 μm generated by is converted into interference light by using a Michelson interferometer composed of the fixed mirror 2, the movable mirror 3 and the beam splitter 4, and the interference light is placed on the SOI substrate 11. Irradiation is performed on the SOI film 12.

When the SOI film 12 is irradiated with the interference light obtained by continuously changing the optical path difference Δ between the fixed mirror 2 and the movable mirror 3, the optical path difference between the fixed mirror 2 and the movable mirror 3 is irradiated. When Δ has a certain specific value, the combined reflected light exhibits a peculiar behavior. That is, on the optical path difference-reflected infrared light intensity curve shown in FIG. 3, there occurs a portion called a side burst (peak aggregation portion) where the reflected light intensity has a peak value.

The present inventors have found a correlation existing between the optical path difference Δ at which the reflected light intensity has a peak and the SOI film thickness on the optical path difference-reflected infrared light intensity curve. That is, of the minimum peaks present in each of the plurality of side bursts in the optical path difference-reflected infrared light intensity curve, the minimum peak having the smallest absolute value of the optical path difference Δ has its optical path difference (in the example shown in FIG. It was found that the optical path difference (Δmin) of 1 corresponds to the SOI film thickness.

According to the above correlation, the thickness is 10 μm.
Even with the above SOI film, its thickness can be measured with high accuracy. FIG. 4 shows the relationship between the SOI film thickness measured by the FTIR method and the SOI film thickness measured by using a scanning electron microscope (SEM). According to this, the correlation coefficient of both data is 0. It is 999, and it can be seen that the two have a very high correlation.

When the SOI film thickness is measured for each of the sections W1, W2 ... Wn of the SOI substrate 11 by the FTIR method described above and a film thickness map is created,
Wn is calculated for each of the sections W1, W2 ... Wn based on the film thickness map so that the SOI film thickness of each section W1, W2 ... Wn becomes a predetermined value.

Next, as shown in FIG. 5, the SOI substrate 11
In the reaction chamber 20, the SOI film 12 is etched and removed by the dry etching device 30 by the etching amount calculated for each of the sections W1, W2 ... Wn. That is, an XY table 40 that can move in an XY plane (horizontal plane) is housed in the reaction chamber 20, and a disk-shaped lower electrode 31 is fixed on the XY table 40. ing. In addition, a cylindrical upper electrode 3 is provided in the reaction chamber 20.
2 is housed, and an AC power source 3 is placed on both electrodes 31, 32.
3 is connected. The electrodes 31, 32 and the AC power supply 33 constitute a dry etching device 30, and the dry etching device 30 has a diameter of 8 to 14 mmφ.
It is possible to selectively etch only the area.

Thus, as shown in FIG. 5, the SOI substrate 1
1 is fixed on the lower electrode 31 in the reaction chamber 20, and the reaction gas (SF ₆ / O ₂ gas) is supplied into the reaction chamber 20. Then, the XY table 40 is driven so that the upper electrode 32 of the dry etching device 30 scans the SOI substrate 11 in the order of sections W1, W2 ... Wn, and the dry etching device 30 is discharged by the electrodes 31 and 32. The SOI film 12 of the SOI substrate 11 is thinned by etching a predetermined etching allowance for each of the sections W1, W2 ... Wn.
When the etching process is completed for all the sections W1, W2 ... Wn of the OI substrate 11, the SOI film thickness becomes a desired value and a desired variation (± 0.3 μm) or less, and the SOI substrate 1
1 is made uniform over the entire surface. In addition, the scanning speed of the dry etching apparatus 30 depends on each section W on the surface of the SOI substrate 11.
1, W2 ... Wn are determined by the etching allowance and the etching rate.

Here, a specific example will be described.

If the desired value of SOI film thickness is 20.0 μm, 5 ″ N type <100>, center thickness is 21.5 μm.
The method of the present invention was applied to the SOI substrate having the SOI film.

First, the SOI substrate is entirely covered by 10 mm.
It was divided into square grids, and the SOI film thickness was measured for each partition by the FTIR method to create a film thickness map.
The variation in the I film thickness was ± 1.0 μm.

Next, the etching allowance was calculated for each section of the SOI substrate, and the dry etching apparatus performed the etching process by the etching allowance. In the etching process, an upper electrode with a diameter of 8 mmφ and a lower electrode with a diameter of 200 mmφ were used, the distance between them was set to 60 mm, and the reaction gas (SF ₆ / O ₂ gas) was supplied at a rate of 45/5 cc / min in the reaction chamber. Frequency of 13.56MH for both electrodes
An alternating current of z and power of 0.2 W was applied. Also, the scanning speed V of the dry etching apparatus is set to X μm for the SOI film in the scanning region.
As V = 8 × 0.06 / (X-20.0) (mm /
min). Here, 8 is the diameter (mm) of the upper electrode, and 0.06 is the etching rate (μm / min) in the depth direction of the SOI film.

As a result, the SOI film thickness distribution after etching is 20.5 ± 0.25 μm.
It was possible to make the SOI film thickness uniform by suppressing the variation in the SOI film thickness to ± 0.3 μm or less.

[0025]

As is apparent from the above description, according to the present invention, the SOI substrate surface is divided into a plurality of sections, and the SOI film thickness of each section is measured by using a Fourier transform infrared spectrometer. A dry etching apparatus capable of creating a thickness map, calculating an etching allowance for the SOI film thickness of each section to become a predetermined value for each section based on the film thickness map, and selectively etching only a predetermined area Since the SOI film is scanned on the SOI substrate and the SOI film in each section is etched only by a predetermined etching allowance, the SOI film thickness of the SOI film having a thickness of 10 μm or more has a variation of ± 0.3 μm or less. An effect that it can be suppressed and uniformed can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view of a partitioned SOI substrate.

FIG. 2 is a basic configuration diagram of an SOI film thickness measurement system by an FTIR method.

FIG. 3 is a diagram showing a relationship between an optical path difference on an SOI substrate and a reflected infrared light intensity.

FIG. 4 is a diagram showing a correlation between an SOI film thickness measured by an FTIR method and an SOI film thickness measured by a scanning electron microscope (SEM).

FIG. 5 is a block diagram of an apparatus for carrying out the method of the present invention.

[Explanation of symbols]

 2 fixed mirror 3 moving mirror 11 SOI substrate 12 SOI film 30 dry etching apparatus

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masatake Katayama 2-13-1 Isobe, Annaka-shi, Gunma Shin-Etsu Semiconductor Co., Ltd.

Claims (4)

[Claims] 1. An SOI substrate surface is divided into a plurality of sections, the SOI film thickness of each section is measured using a Fourier transform infrared spectrometer, and a film thickness map is created. The etching allowance to obtain the value is calculated for each section based on the film thickness map, and a dry etching apparatus capable of selectively etching only a predetermined region is scanned on the SOI substrate to remove the SOI film of each section. A method of uniformizing an SOI film thickness on an SOI substrate, which comprises performing an etching process for a predetermined etching amount. 2. An S using the Fourier transform infrared spectrometer.
The measuring method of the OI film thickness is that the optical path difference-reflected infrared light is obtained by irradiating the SOI substrate with the interference light obtained by continuously changing the optical path difference between the fixed mirror and the moving mirror which constitute the Michelson interferometer. An intensity curve is obtained, and the minimum absolute value of the optical path difference is selected from the minimum peaks present in each of the plurality of side bursts in this curve, and S is determined from the optical path difference of the minimum peak.
The SO according to claim 1, wherein the OI film thickness is obtained.
Method of uniformizing SOI film thickness on I substrate. 3. The dry etching apparatus has a diameter of 8 to
The S in the SOI substrate according to claim 1, wherein only a region of 14 mmφ can be selectively etched.
OI film thickness uniforming method. 4. The method for uniformizing an SOI film thickness on an SOI substrate according to claim 1, wherein the scanning speed of the dry etching apparatus is determined from an etching allowance and an etching speed in each section of the SOI substrate surface.