JPH0626944A - Method for measuring stress of thin film, and method and device for manufacturing test piece for stress measurement - Google Patents

Abstract

PURPOSE:To precisely measure the stress of a thin film having a thin film thickness by bringing an O-ring into contact with the surface or reverse side of a base, conducting etching to manufacture a test piece, anisotropically etching the base reverse side after forming a thin film, and then measuring warp. CONSTITUTION:A silicon base 4 to which a thin film 5 is adhered is enclosed by vessels 1, 2, and the reverse side of the base 4 is exposed to the surface to make contact with an etching solution 7. An O-ring 3 is arranged on the reverse side of the base 4 to prevent the etching solution 7 from making contact with the thin film 5 adhered to the surface of the base 4. The vessels 1, 2 are dipped in an outer vessel 6 filled with the etching solution 7, and the etching solution 7 is heated by a heater 10 to increase etching speed. The thin film can be thinned to have an uniform thickness by use of a solution of potassium hydroxide which is an etching solution highly anisotropic to the etching solution 7. Further, sealing is conducted by use of the ring 3, whereby the natural characteristic of the thin film 5 can be measured without corroding the thin film 5, and the stress of the extremely thin film 5 can be precisely measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stress measuring method for a test piece and a method for producing a stress measuring test piece, which are most suitable for measuring the mechanical properties of a thin film.

[0002]

2. Description of the Related Art Up to now, thin film materials have been widely used for semiconductors and magnetic recording media. In these thin film applied products, the residual stress of the thin film may cause cracking or peeling of the thin film to prevent the desired performance, or adverse effects such as the introduction of crystal defects into the thin film forming substrate. Is generally reported. Therefore, the residual stress of the thin film has been widely measured as one of the important parameters of the physical properties of materials. The simplest method for measuring the residual stress of this thin film is to measure the amount of elastic deformation of the substrate provided with the thin film. As described in Applied Physics, Vol. 56, No. 7, 1987, pages 923 to 924, this is a thin film formed on a disc-shaped or strip-shaped substrate, and is obtained from the warp thereof. From r, in the case of a disk-shaped substrate, the residual stress σ of the thin film is calculated as σ = Et ² / {6 (1-ν) rd} (Equation 1). Here, E is the Young's modulus of the substrate, t is the thickness of the substrate, d is the thickness of the thin film, and ν is the Poisson's ratio. The expression 1 is based on the approximation of d << t << r.

[0003]

Since a circular substrate is generally used in the manufacturing process of semiconductor products and the like, it is generally performed to form a thin film on the circular substrate and measure the warp to obtain the stress of the thin film. . For example, a thin film stress measuring device manufactured by Flexus Co., Ltd. can measure the stress of a thin film formed on a silicon wafer, and can be used for quality control of a thin film in a manufacturing line. However, in recent years, the frequency of use of a very thin (1 μm or less) thin film has increased due to the miniaturization of products, but when measuring the stress of this very thin thin film, the measurement may become difficult. For example, in recent years, most of thin layers used in highly integrated semiconductor devices have a thickness of 0.1 μm or less, and most of them have become thinner. However, the thickness of the usable wafer is not only limited due to the wafer handling in the manufacturing apparatus, but also the thickness thereof tends to increase as the diameter of the wafer increases. Then, even when measuring the same stress value, it becomes necessary to measure a smaller warp. For example, silicon substrate thickness t is 0.3 mm
From 0.5 to 0.5 mm, and the thin film thickness d from 0.5 μm to 0.1 μm decreases from Equation 1, and when measuring the same stress value, a warpage amount of about 1/14 is obtained with the same accuracy. It must be measurable. Therefore, the measurement resolution of the warpage measuring device becomes lower than the measurement resolution, and the measurement may be impossible.

[0004]

In order to solve the above problems, the board thickness t of the substrate may be reduced. From Equation 1, when measuring the same stress, the radius of curvature r is proportional to the square of the plate thickness t of the substrate. Therefore, by reducing t, r becomes smaller,
Therefore, the sled becomes large. However, since the substrate must be thick during film formation due to the handling of the substrate in the film forming apparatus, it is necessary to uniformly remove the film from the back surface of the substrate and thin it after the film formation. Further, in this case, in order to keep the deformation of the substrate uniform, the plate thickness of the substrate must be uniform. It has been found that etching using an anisotropic etching solution is effective for this purpose. It was also found that an O-ring was necessary to protect the thin film from corrosion by the etching solution.

Of the present invention, typical ones will be briefly described again briefly. That is, (1) in the residual stress measuring method of a thin film for obtaining the residual stress of the thin film from the measurement of the warp of the substrate with the thin film, the warpage is measured after anisotropically etching the back surface of the substrate after forming the thin film. Characteristic thin film stress measurement method.

(2) Obtaining the residual stress of a thin film from the measurement of the warpage of a substrate with a thin film. In the method of measuring the residual stress of a thin film, after the thin film is formed, the back surface of the substrate is potassium hydroxide, sodium hydroxide, cesium hydroxide, Alkaline aqueous solution containing ammonium, ethylenediamine, hydrazine,
A method for measuring stress in a thin film, which comprises measuring warpage after etching with an organic solution containing choline, tetramethylammonium hydroxide, tetraethylammonium hydroxide, etc.

(3) Obtaining the residual stress of a thin film from the measurement of the warp of a substrate with a thin film In the method of measuring the residual stress of a thin film, it is necessary to measure the warp after anisotropically etching the back surface of the substrate after forming the thin film. Characteristic thin film stress measurement method.

(4) In the method for producing a stress measuring test piece according to any one of (1) to (3) above, etching is performed by bringing an O-ring into contact with the front surface or the back surface of the substrate. Method of manufacturing test piece for stress measurement.

[0009]

From the formula 1, for example, the thickness d of the thin film is 0.5 μm.
From 0.1 to 0.1 μm, the same accuracy as when the thickness d of the thin film is 0.5 μm can be obtained by reducing the thickness t of the silicon substrate from 0.3 mm to 0.13 mm. To be In addition, since the deformation of the silicon substrate becomes non-uniform even after the plate thickness of the silicon substrate is thinned, the plate thickness must be uniform. Therefore, when the silicon substrate is thinned by etching the back surface of the silicon substrate without the thin film, potassium hydroxide, sodium hydroxide, cesium hydroxide, and ammonium hydroxide, which are highly anisotropic etchants to this etchant, are used. By using an alkaline aqueous solution containing ethylene or an organic solution containing ethylenediamine, hydrazine, choline, tetramethylammonium hydroxide, tetraethylammonium hydroxide, etc., the thickness of the substrate will be uniform even after etching, resulting in a measurement error. Hateful.

Further, when the etching solution comes into contact with the substrate surface to which the thin film is attached during the etching process, the thin film itself may be corroded. Therefore, by placing an O-ring on the front surface or the back surface of the substrate and sealing it, the thin film on the front surface of the substrate can be protected from corrosion. Therefore, since the original characteristics of the thin film can be measured, a measurement error is unlikely to occur.

[0011]

EXAMPLE FIG. 1 shows an explanatory view of an apparatus for producing a stress measuring test piece which is a first example of the present invention. The silicon substrate 4 with the thin film 5 attached is a Teflon container (top) 1 and a container (bottom)
It is surrounded by 2 and the back surface of the silicon substrate is exposed on the surface so as to come into contact with the etching liquid 7. Further, the O-ring 3 is arranged on the back surface of the silicon substrate to prevent the etching liquid 7 from coming into contact with the thin film 5 attached to the front surface of the silicon substrate. Further, the container 1 and the container 2 are immersed in the outer container 6 filled with the etching liquid 7, and the etching liquid 7 is heated by the heater 10 in order to increase the etching rate.

An alkaline aqueous solution containing potassium hydroxide, sodium hydroxide, cesium hydroxide or ammonium, which is a highly anisotropic etching solution, or ethylenediamine, hydrazine, choline, tetramethylammonium hydroxide, or hydroxide is used as the etching solution 7. By using an organic solution containing tetraethylammonium or the like, the silicon substrate could be thinned to have a more uniform thickness as compared with the case where a hydrofluoric acid solution was used. For example,
To etch the back surface of a silicon substrate 4 having a diameter of 2 inches and a thickness of 550 μm to 200 μm, hydrofluoric acid: nitric acid:
When the solution of acetic acid = 3: 5: 3 was used, the thickness of the silicon substrate varied by 10 μm or more depending on the location.
When an aqueous solution of potassium hydroxide was used as the etching solution 7, it was 2 μm or less. Therefore, according to the present invention, the deformation of the substrate with a thin film does not become non-uniform, and the stress of a very thin thin film can be accurately measured.

In the semiconductor manufacturing process, a photoresist is often used as a mask for etching.
It was found that when an alkali-based etching solution is used, even a rubber-based photoresist having alkali resistance is peeled off and cannot be used. Therefore, the O-ring 3 was used for sealing and a trial experiment was conducted. As a result, it was found that the etching liquid can be completely sealed even though the silicon substrate 4 has the step 8 as shown in FIG. 2 during the etching. Therefore, according to the present invention, since the original characteristics of the thin film 5 can be measured without corroding the thin film 5, the stress of the very thin thin film 5 can be accurately measured.

FIG. 3 shows a second embodiment of the present invention. In the present embodiment, the etching solution 7 is sprayed onto the silicon substrate 4 by the shower 9 toward the container 1 and the container 2, whereby the etching proceeds. Further, the etching liquid 7 is heated by the heater 10. In the present invention, since the etching liquid 7 does not stagnate and the etching progresses more uniformly, the plate thickness of the silicon substrate 4 becomes more uniform, and the stress of the thin thin film 5 can be accurately measured.

[0015]

According to the present invention, the stress of a thin film can be accurately measured.

[Brief description of drawings]

FIG. 1 is an explanatory view of a stress measuring test piece manufacturing apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of an effect in the first embodiment of the present invention.

FIG. 3 is an explanatory view of a stress measuring test piece manufacturing apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

1 ... Container (top), 2 ... Container (bottom), 3 ... O-ring, 4 ... Silicon substrate, 5 ... Thin film, 6 ... Outer container, 7 ... Etching liquid,
8 ... step, 9 ... shower, 10 ... heater, 11 ... pump.

Claims (4)

[Claims] 1. A method for measuring a residual stress of a thin film, wherein the residual stress of the thin film is obtained by measuring the warp of a substrate provided with the thin film.
A method for measuring the stress of a thin film, characterized in that after the thin film is formed, the back surface of the substrate is anisotropically etched and then the warpage is measured. 2. A method for measuring a residual stress of a thin film, wherein the residual stress of the thin film is obtained by measuring the warp of a substrate provided with the thin film.
After forming the thin film, an alkaline aqueous solution containing potassium hydroxide, sodium hydroxide, cesium hydroxide, or ammonium on the back surface of the substrate, or ethylenediamine, hydrazine,
A method for measuring stress in a thin film, which comprises measuring warpage after etching with an organic solution containing choline, tetramethylammonium hydroxide, tetraethylammonium hydroxide, etc. 3. A method for measuring a residual stress of a thin film, wherein the residual stress of the thin film is obtained by measuring the warp of a substrate provided with the thin film.
A method for measuring the stress of a thin film, characterized in that after the thin film is formed, the back surface of the substrate is anisotropically etched and then the warpage is measured. 4. The method for manufacturing a stress measuring test piece according to claim 1, wherein the O-ring is brought into contact with the front surface or the back surface of the substrate for etching.