JPH05166689A - Method for joining semiconductor substrates - Google Patents

Abstract

PURPOSE:To introduce proper internal stress into the firms of substrates for formation of semiconductor elements by bringing two substrates of different temperatures into contact with each other. CONSTITUTION:Two silicon substrates (or wafers) are prepared, and a thermal oxide film 2 is made on each surface. One substrate 1 is put so that the surface may turn up on the surface of the hot plate placed inside a clean room at room temperature, keeping the surface of said hot plate at approximately 60 deg.C. Just as the substrate 1 gets to fit the temperature of the hot plate, another wafer 1 is placed on it, and they are joined temporally. This is put in a furnace to do heat treatment in a nitrogen atmosphere. Hereby, it becomes possible to introduce internal stress of optional magnitude into the film of the substrate manufactured by lamination 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 laminating method.

[0002]

2. Description of the Related Art A direct bonding method is used as a method for obtaining an SOI (Silicon on Insulator) substrate having a large area and good quality silicon thin film single crystal, or as a method for obtaining a substrate having a steep impurity concentration gradient from a surface to a deep position. Used. In order to obtain an SOI substrate, first, two silicon substrates 1 whose surfaces are mirror-finished are prepared as shown in FIG. 2, and an oxide film 2 serving as an insulating film is formed on the surface of one or both substrates. Next, the insulating films (mirror surfaces) of the substrates are lightly contacted with each other to make a temporary bonding state, and this is heat-treated at high temperature to be integrated to complete the bonding. Finally, one substrate is removed by polishing, etching, etc., leaving a desired thickness, and the SOI film 3 is formed, whereby the SOI substrate is completed. When a steep impurity concentration gradient is intended, a substrate having a desired impurity distribution is prepared, and 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
The internal stress of a film) may affect the performance of the device and the manufacturing yield. The problem of the internal stress of the film is more serious in a device having a structure such as a diaphragm or a beam. 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. It is generally considered that the tensile stress is not limited to the diaphragm application, but if it is extremely large, the substrate warps or 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. For this reason, the stress distribution in the film is dominated by unstable factors such as warpage of the substrate, unevenness of the surface, or deformation of the substrate due to handling. The present invention provides a method of introducing an appropriate internal stress into a film of a substrate manufactured by a laminating method.

[0004]

According to the experiment, the internal stress of the film of the manufactured substrate is determined by the state at the time of temporary joining, 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. It has been found that 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, and in the present invention, the heat of the substrate is used to perform such temporary bonding. The expansion is used to temporarily bond two substrates having different temperatures. The present invention is a direct bonding method in which two semiconductor element-forming substrates whose surfaces are mirror-finished are temporarily bonded by bringing their mirror surfaces into contact with each other, and then heat-bonded to be integrated into one. The method for joining semiconductor element formation substrates is characterized in that the semiconductor element formation substrates are brought into contact with each other with a temperature difference and stress is introduced inside.

[0005]

When a temperature difference is applied to the two substrates, one of the substrates expands with respect to the other by an amount proportional to the coefficient of thermal expansion and the temperature difference. When both are brought into contact with each other in this state, they are adsorbed to each other and the temporary joining is instantly completed. Since the heat transfer between the substrates from the contact to the completion of the temporary bonding can be ignored, the stress equivalent to the extension amount of the substrate before the temporary bonding was introduced into the temporary bonded substrate when these reached the thermal equilibrium state. It will be. 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 thin film, 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 extension amount of one substrate before temporary bonding Are introduced into the membrane. Since the stress introduced into the film is determined only by the initial extension amount of the substrate, that is, the temperature difference between the substrates before temporary bonding, it is easy to control the magnitude of the stress. Further, even when the film thickness cannot be ignored, the temperature difference required for temporary bonding can be easily designed from the final film thickness, the substrate thickness, and the magnitude of stress to be introduced.

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 a model, two 0.5 mm thick thermal oxide films were formed on two silicon substrates with a diameter of 100 mm and a thickness of 500 μm.
An SO with one of these joined to form a film with a thickness of 1 μm
Consider the I structure. 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.
It is estimated to be 9 × 10 ⁶ dyn / cm ² . Next, the stress introduced into the film by the unevenness of the substrate surface is estimated. The model has a diameter of 100 mm and a thickness of 500 μm, and the surface has a radius of curvature of 10 m.
Consider a structure in which a sufficiently thick substrate with a completely flat surface is bonded to the convex substrate of and the film is finished to a thickness of 1 μm. 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. 2 flat substrates with a diameter of 100 mm and a thickness of 500 μm
If one substrate is prepared and bonded with a temperature difference ΔT between the substrates, and the substrates that were at high temperature are thinned to a film with a thickness of 1 μm, the internal stress of the film is tensile and the size is ΔT ×
It becomes 3.3 × 10 ⁶ dyn / cm ² . For example, when the temperature difference between the substrates at the time of temporary bonding is 30 ° C., a tensile stress of about 10 ⁸ dyn / cm ² is introduced into the film. This is large enough to neglect the stress estimated in the previous method that may remain in the film by the conventional bonding method.

[0007]

【Example】

(Embodiment 1) An embodiment according to the present invention will be described with reference to FIG. 1) Two silicon substrates (or wafers) each having a diameter of 100 mm and a thickness of 500 μm were prepared, and a thermal oxide film 2 having a thickness of 0.5 μm was formed on each surface (see FIGS. 1A and 1B). 2) The surface of a hot plate placed in a clean room at room temperature of 23 ° C. was kept at about 60 ° C., and one substrate was placed on the hot plate so that the surface thereof faced upward (see FIG. 1 (c)). 3) Where the substrate has been adjusted to the temperature of the hot plate,
Another wafer was stacked from above and temporary bonding was performed (Fig. 1
(See (d)). 4) After confirming that there is no peeling due to stress when left at room temperature, insert this into a heat treatment furnace and place it in a nitrogen atmosphere for 11
Heat treatment was performed at 00 ° C. for 2 hours. 5) This substrate was polished from the side of the substrate previously placed on the hot plate to form the SOI film 3 while leaving a film having a thickness of 2 μm (see FIG. 1 (e)). 6) For comparison, a sample prepared by the conventional method was prepared, and when both were gradually thinned from the supporting substrate side, the thin film was deformed to be convex. This deformation is due to the 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.

Example 2 An example of quantitatively evaluating the effect of the present invention will be described. 1) Two silicon substrates (or wafers) having a diameter of 100 mm and a thickness of 500 μm were prepared, and a sample was manufactured by the procedure of 2) to 5) of Example 1. However, the surface temperature of the hot plate was set to three types of 40, 60 and 80 ° C. 2) When the supporting substrate of the sample was processed and thinned to a thickness of 200 μm, the film surface was deformed concavely. In that state, the radius of curvature of the wafer was measured, and the internal stress of the film was calculated from the sample size and the material constant. It can be seen that the internal stress of the film is controlled by the substrate temperature difference during temporary bonding.

[0009]

[Table 1]

[0010]

According to the present invention, it becomes possible to introduce an arbitrary amount of internal stress into the inside of the film of the substrate manufactured by the bonding method. By using this substrate, the element characteristics on the substrate are made uniform, and the yield and productivity are improved.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram illustrating an embodiment of the present invention.

FIG. 2 is an explanatory view showing a manufacturing process of a bonded substrate by a conventional method.

[Explanation of symbols]

 1 Silicon substrate 2 Oxide film 3 SOI film 4 Hot plate

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 of heat-treating and bonding-integrating, for temporary bonding, two semiconductor element forming substrates are brought into contact with each other with a temperature difference, and stress is introduced into the inside. Substrate bonding method.