JPH06196377A - Bonding method for semiconductor substrates - Google Patents

Abstract

PURPOSE:To obtain a method wherein a proper internal stress is introduced into a film on a substrate manufactured by a pasting method by utilizing a change in the length of the surface when a substrate to be bonded is deformed elastically. CONSTITUTION:1) Two silicon wafers 1 whose diameter is 100mm and whose thickness is 500mum are prepared, thermal oxide films 2 whose thickness is 0.5mum are formed on individual surfaces. 2) One substrate is sucked to a vacuum suction-type plate whose surface has been formed to be a protrusion shape in a radius of curvature of 50 m, it is deformed, and another substrate is overlapped on it and bonded temporarily. 3) A vacuum suction operation is released, it is confirmed that no exfoliation due to a stress has been caused, the substrates are inserted in a heat treatment furnace, and a heat treatment is executed in a nitrogen atmosphere at 1100 deg.C for two hours. 4) The substrates are polished from the side of the substrate which has been deformed previously, and a film 3 in a thickness of 2 um is left. Thereby, it is possible to introduce a uniform compressive or tensile stress into the inside of a film on a substrate formed by a pasting method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a substrate for forming a semiconductor element (hereinafter referred to as a substrate) using a bonding method.

[0002]

2. Description of the Related Art As a method for obtaining an SOI (Silicon on Insulator) substrate having a large area and good quality silicon thin film single crystal, or a method for obtaining a semiconductor substrate having a steep impurity concentration gradient at a deep position from the surface, direct contact is performed. Legal is used. In order to obtain an SOI substrate, first, two silicon substrates whose surfaces are mirror-finished are prepared, and an insulating film is formed on the surface of one or both substrates. Next, the insulating film on the substrate (mirror surface)
The two are lightly contacted with each other to be in a temporarily joined state, which is then heat treated at a high temperature to be integrated to complete joining. Finally, one of the substrates is removed by polishing, etching, etc., leaving a desired thickness to complete the SOI substrate. For the purpose of a steep impurity concentration gradient, prepare a substrate with the desired impurity distribution,
The substrates are directly bonded to each other by the procedure described above without forming an insulating film.

[0003]

When an element is formed on the substrate thus manufactured, a thinned substrate (hereinafter, referred to as
Internal stress (which is called a film) may affect the performance of the device and the manufacturing yield. The problem of film stress is more serious in devices having structures such as diaphragms and beams. For example, when a compressive stress is present in the film, the diaphragm or beam formed by using the film is bent, and a sensor or the like using this has a large dead zone near the origin. The tensile stress is generally considered to be preferable not only for the diaphragm application, but if it is extremely large, the substrate warps and the like, which becomes an obstacle to the element manufacturing process. Further, if the stress is unevenly distributed in the film, it appears as variations in device characteristics. In the conventional method, it was impossible to introduce internal stress into the film. Therefore, the stress distribution in the film is dominated by unstable factors such as the warp of the substrate, the unevenness of the surface, or the deformation of the substrate due to handling. The present invention provides a method for introducing an appropriate internal stress into a film of a substrate manufactured by a laminating method.

[0004]

[Means for Solving the Problem] According to experiments, the internal stress of the film of the manufactured substrate is determined by the state at the time of temporary bonding, and there is almost no relaxation of stress in the subsequent heat treatment and processing steps for thinning. . That is, by applying tensile and compressive stress to each of the temporarily bonded substrates, the stress can be left in the finally finished film. The magnitude of the internal stress of the film is determined by the initial thickness of the two substrates, the thickness of the remaining film, and the initial stress. In the present invention, a change in the surface length when the substrates are elastically deformed is used to perform such bonding. When a mechanical external force in the thickness direction of the substrate is applied to deform the substrate so that its surface becomes convex, the surface expands according to the degree of curvature. When another substrate is placed on top of this, if the surfaces are mirror surfaces, they will stick to each other and the stacked substrates will be deformed concavely along the previously deformed substrate. At this time, the external force acting on the stacked substrates is only in the thickness direction, so that the surface of the substrate is compressed. Here, if the initial mechanical force is released, stress can be left on the substrate. At this time, tensile and compressive stresses are present in each substrate depending on its thickness, and this distribution is preserved even after the heat treatment for joining and unifying. When one of the substrates is thinned to the target substrate, the stress concentrates on the thin film, and if the film thickness is sufficiently smaller than the total thickness of the substrate, the stress equivalent to the expansion and contraction of the substrate surface at the time of temporary bonding is generated. be introduced. Since the stress introduced into the film is determined by the amount of initial expansion and contraction of the substrate, that is, the degree of bending of the substrate during temporary bonding, it is easy to control the stress.
Further, even when the film thickness cannot be ignored, the curvature required for temporary bonding can be easily designed from the final film thickness, the substrate thickness, and the magnitude of the stress to be introduced.

[0005]

For comparison with this method, the internal stress of the film of the bonded substrate when the conventional method is used will be estimated. First, the stress introduced into the film by the thermal expansion of the material is estimated.
As an model, consider an SOI structure in which two silicon substrates each having a diameter of 100 mm and a thickness of 500 μm are formed with a thermal oxide film having a thickness of 0.5 μm and bonded to each other to finish one of them into a film having a thickness of 1 μm. It is assumed that the surface of the substrate used is perfectly flat and there is no stress at the oxidation temperature (1000 ⁰ C). At this time, the internal stress of the film is tensile and its magnitude is 2.9X1.
It is estimated to be 0 ⁶ dyn / cm ² . Next, the stress introduced into the film by the unevenness of the substrate surface is estimated. Diameter 1 as a model
Consider a structure in which a sufficiently thick substrate having a completely flat surface is bonded to a convex substrate having a radius of curvature of 10 m and a surface of 00 mm and a thickness of 500 μm, and a film having a thickness of 1 μm is finished. The internal stress of this film is estimated to be 5,5 × 10 ⁶ dyn / cm ² . Here, the magnitude of stress that can be introduced by this method is shown. Two flat substrates having a diameter of 100 mm and a thickness of 500 μm are prepared, and one is curved to have a radius of curvature R (cm). If another substrate is joined along this, and the curved substrate is thinned to a film with a thickness of 1 μm, the internal stress of the film is tensile and its size is 6. 6 x ^{10 10}
Calculated as / Rdyn / cm ² . For example, when the radius of curvature is 70 m, a tensile stress of about 10 ⁷ dyn / cm ² is introduced into the film. This is a value sufficient to leave tensile stress over the entire surface of the film.

[0006]

EXAMPLES Example 1 An example according to the present invention will be described. 1) 2 silicon wafers with a diameter of 100 mm and a thickness of 500 μm
One piece was prepared, and a thermal oxide film having a thickness of 0.5 μm was formed on each surface. 2) The substrate was adsorbed and deformed by a vacuum adsorption type plate whose surface had a convex shape with a radius of curvature of 50 m, and another substrate was overlaid and temporarily bonded. 3) After releasing the vacuum adsorption and confirming that there is no peeling due to stress, insert this into a heat treatment furnace and place it in a nitrogen atmosphere for 1
Heat treatment was performed at 100 ° C. for 2 hours. 4) This substrate was polished from the side of the substrate that was previously deformed to leave a film having a thickness of 2 μm. 5) For comparison, a sample prepared by the conventional method was prepared, and both were gradually thinned from the side of the supporting substrate. This deformation is due to compressive stress in the oxide film caused by the difference in thermal expansion coefficient between silicon and the thermal oxide film. The degree of deformation was obviously smaller in the sample produced by this method, and it was confirmed that the film had tensile stress.

(Embodiment 2) 1) Four silicon wafers having a diameter of 100 mm and a thickness of 500 μm are prepared.
One sheet was prepared, and a thermal oxide film having a thickness of 0.1 μm was formed on each surface. 2) Two sets of bonded substrates a, as in 2) and 3) of the first embodiment,
b is manufactured, and for a, the substrate side that has been previously deformed is
For the other side, thin the substrate on the opposite side to a thickness of 5μ.
An m 2 SOI film was left. 3) A part of the supporting substrate of these substrates was removed by wet etching, and an SOI diaphragm of about 3 mm square was formed and observed. As a result, the film remained taut in a, whereas the film in b did not. I was slack. Considering the method of manufacturing the sample and this result, it is concluded that the internal stress of the film is tensile on the substrate a and the internal stress of the film is compressive on the substrate b.

[0008]

According to the present invention, it is possible to uniformly introduce a compressive or tensile stress into the inside of a film of a substrate manufactured by a bonding method.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a manufacturing process of a bonded substrate by a conventional method.

FIG. 2 is a manufacturing process diagram illustrating an embodiment of the present invention.

[Procedure amendment]

[Submission date] December 26, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

Claims (1)

[Claims] 1. After two mirror-finished substrates for semiconductor element formation are brought into contact with each other and the mirror-finished surfaces are temporarily joined,
In the direct bonding method in which heat treatment is performed to bond and integrate, during temporary bonding, one of the semiconductor element forming substrates is curved so that the bonding surface is convex and the other substrate is superposed along it. A method for joining semiconductor substrates, wherein stress is introduced into the inside.