JPH08111409A - Manufacturing for semiconductor device - Google Patents

Abstract

PURPOSE: To provide a manufacturing method for a semiconductor device in a CVD process, in which a warp in semiconductor wafer is prevented in a heating process and a uniform film formation step or a uniform treatment step is carried out. CONSTITUTION: In a manufacturing method for a semiconductor device, a film formation step and an etching step are carried out to form a semiconductor element on a semiconductor wafer 1. After that, the semiconductor wafer 1 is diced. At least an oxide film 1a made of the same material as the wafer 1 is formed on the rear face of the semiconductor wafer 1 before a CVD film formation step on a face of the semiconductor wafer 1. The oxide film 1a on the rear face of the semiconductor wafer 1 is left as it is still after a last film formation step is carried out in the CVD method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device. More specifically, the present invention relates to a method for manufacturing a semiconductor device that eliminates process unevenness such as film unevenness due to warpage of a semiconductor wafer when forming a film in a high temperature state such as a CVD method.

[0002]

2. Description of the Related Art Semiconductor devices such as ICs are generally manufactured as follows. That is, each process such as a film forming process on a semiconductor wafer having a diameter of 6 inches or 5 inches by epitaxial growth or a CVD method, patterning by a series of photolithography techniques such as photoresist coating, exposure, development, etching, and ion implantation. After that, a plurality of the same semiconductor elements are formed on one wafer. After each process on the semiconductor wafer is completed, the semiconductor wafer is diced to be separated into individual chips, and the chips are bonded to a lead frame or the like and molded to manufacture a semiconductor device.

The above-mentioned semiconductor wafer is formed by cutting an ingot, which is a lump of semiconductor single crystals, into a thin wafer. The semiconductor wafer is cut and polished to a thickness suitable for the purpose of each semiconductor device, or a wafer obtained by cutting. Lapping and polishing with an abrasive are performed to smooth the rough surface. In the thickness adjustment stage, cutting, chemical treatment, polishing with a relatively rough abrasive, etc. are performed, and the surface side of the semiconductor wafer is for epitaxial growth or film formation later, so
It is mirror-finished with a fine abrasive. Therefore, in general, a semiconductor wafer has a mirror surface on the front surface and a relatively rough surface on the back surface that does not reach the mirror surface.

[0004]

As described above, the semiconductor wafer has different finishing surfaces on the front surface side and the back surface side, and when the temperature rises in the heating process, tensile thermal stress is applied to the rough surface on the back surface side. Therefore, for example, 400 ° C in the CVD process
When the film is formed to a certain degree, the semiconductor wafer 1 is warped so that the bottom is convex as shown in FIG. This warp is so large that it can be clearly confirmed with the naked eye when viewed from outside the reaction tube during film formation. Therefore, the periphery of the semiconductor wafer 1 floats up from the susceptor 2 heated to about 400 ° C., and the temperature around the semiconductor wafer 1 becomes low, and the flow range of the reaction gas 3 becomes narrow. As a result, the growth of the film is slow around the semiconductor wafer 1 and it is difficult to form a film, and there is a case where the film is hardly formed at the edge. The unevenness of the film thickness on the surface of the semiconductor wafer is, for example, 0.1 to 0.2 μm. growing. Therefore, when the chips are diced and separated into chips, there arises a problem that chip defects occur, yield decreases, and reliability decreases.

The present invention solves such a problem, and CVD
It is an object of the present invention to provide a method for manufacturing a semiconductor device that can suppress the warp of the semiconductor wafer as much as possible in a heating process of the semiconductor wafer such as steps and can perform uniform film formation and processing.

[0006]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made diligent studies in order to eliminate variations in the treatment of the surface of a semiconductor wafer in the heating process, such as variations in film formation due to the warp of the semiconductor wafer in the above heating process. As a result of
By forming an oxide film made of SiO ₂ etc. on the back surface of the semiconductor wafer, a compressive force that cancels the tensile force of thermal stress due to the rough surface works on the back surface side, and the warp of the semiconductor wafer hardly occurs during heating. It was found that a uniform film thickness can be obtained in the central portion and the peripheral portion of the semiconductor wafer even in the film forming process of the CVD method, for example.

According to the method of manufacturing a semiconductor device of the present invention, a semiconductor device is formed by subjecting a semiconductor wafer to a process including at least a film forming step by a CVD method, and dicing the semiconductor wafer on which the semiconductor device is formed to form a semiconductor device. A method of manufacturing, wherein an oxide film of the semiconductor wafer material is formed on the back surface of the semiconductor wafer before at least the first step of forming a film by the CVD method on the front surface of the semiconductor wafer, and the back surface of the semiconductor wafer is oxidized. It is characterized in that the film is left as it is at least until after the last film forming step by the CVD method.

When the oxide film on the back surface of the semiconductor wafer is formed simultaneously with the oxide film formed as a mask on the front surface of the semiconductor wafer by the thermal oxidation method, no special film forming step is required, and when etching or the like is performed. Since it is only necessary to attach the protective film to the oxide film on the back surface, even if there are many heating processes, it is not necessary to provide the oxide film on the back surface each time, which is preferable.

[0009]

According to the present invention, since the oxide film is formed on the back surface which is the rough surface of the semiconductor wafer, the tensile force on the back surface of the semiconductor wafer based on the thermal stress due to the rough surface and the semiconductor wafer made of silicon or the like and the SiO film are formed. The compressive force of the oxide film based on the difference in thermal expansion coefficient from the oxide film of ₂ or the like is offset, so that the semiconductor wafer does not warp at a high temperature in a heating process such as a CVD process.

As a result, even when a film is formed in, for example, a CVD process, the semiconductor wafer comes into contact with the susceptor over the entire surface, the temperature becomes uniform, and the flow state of the surrounding reaction gas becomes uniform, so that the uniform film thickness is obtained. Can be used to form a film.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a method of manufacturing a semiconductor device of the present invention will be described with reference to the drawings. FIG. 1 is a schematic explanatory view of a CVD process in a method for manufacturing a semiconductor device of the present invention, and FIG. 2 is a diagram showing a relationship between the thickness of an oxide film and a warp when the oxide film is provided on the back surface of a semiconductor wafer.

As described above, the inventors of the present invention have investigated the cause of non-uniformity of the film thickness in the film forming process by the CVD method, and as a result, when forming a film at a high temperature of about 400 ° C., as shown in FIG. It was also found that the reason is that the circumference of the semiconductor wafer 1 is warped, the temperature of the peripheral edge of the semiconductor wafer 1 is lowered, and the reaction gas in the atmosphere is not sufficient because the reaction region is narrowed. In order to eliminate this warpage during film formation, the present inventors have conducted further diligent studies, and as a result, found that the cause of the warpage is due to the difference in roughness between the front and back surfaces of the semiconductor wafer, and By providing an oxide film having a thermal expansion coefficient smaller than that of the material of the semiconductor wafer, the tensile force based on the rough surface and the compression force based on the oxide film with a small thermal expansion coefficient work on the back surface of the semiconductor wafer,
It has been found that the two are offset and the warp of the semiconductor wafer during heating can be suppressed.

Although it is not possible to measure the warp of a semiconductor wafer during heating, 400
When the PSG film is formed by the CVD method at about ℃, it can be confirmed visually that the surrounding area is warped from the outside of the reaction tube, and about 1 to 2 mm is warped from the susceptor. Was there. On the other hand, as shown in FIG. 1, an oxide film 1a is provided on the back surface of the semiconductor wafer 1, and the warp of the semiconductor wafer 1 when the film is formed with various thicknesses is examined. As a result, the results shown in FIG. I got it. That is,
The oxide film 1a is formed on the surface of the semiconductor wafer 1 by SiO _{2 on} the surface of the semiconductor wafer 1 for patterning in the next step at the beginning of the process.
An oxide film such as is formed by a thermal oxidation method at about 1000 to 1200 ° C., but the oxide film 1a formed on the back surface at that time is formed.
Is applied and protected by a resist or the like in a later etching step so as not to be removed, and the thickness of the oxide film is changed by controlling the time of this thermal oxidation. FIG. 2A is a graph showing the relationship between the thickness of the oxide film 1a by measuring the warp of the semiconductor wafer 1 at room temperature after forming the oxide film 1a, and FIG. 400 ℃ when changing the thickness
The warp of the semiconductor wafer 1 in the CVD step of forming the PSG film in a certain degree is shown in the figure as a tendency by visual observation from outside the reaction tube.

As described above, since the oxide film 1a is formed by the thermal oxidation method at a high temperature of about 1000 ° C., the oxide film 1a is formed when the thickness of the oxide film 1a is about 0.6 μm or more at room temperature. Shrinkage is smaller than the semiconductor wafer 1,
Bend it so that the bottom is convex. On the other hand, when the oxide film 1a is thinner, the contraction force of the oxide film 1a does not work, and the oxide film 1a is bent so as to be convex upward. When this semiconductor wafer 1 is heated to about 400 ° C. to form a film by the CVD method, as shown in FIG. 2B, when the oxide film 1a is thin, a large downward warp appears, but the oxide film 1a When the thickness is about 0.6 μm or more, almost no warp is observed with the naked eye, and a film can be formed in a flat semiconductor wafer 1.

The method of manufacturing the semiconductor device of the present invention was carried out on the basis of the above findings, and will be specifically described below.

FIG. 1 is an explanatory view of a semiconductor wafer 1 in a thermal process such as a CVD process of the present invention. In FIG. 1, 1 has a thickness of 200 to 2 made of, for example, silicon.
It is a semiconductor wafer of 50 μm and 5 inches.
For example, the oxide film 1a made of SiO ₂ has a thickness of 0.7 to
It is formed to a thickness of 1.0 μm.

The semiconductor wafer 1 before the oxide film 1a is formed is cut out from the ingot as described above,
The front surface is polished to be a mirror surface, and the back surface is rougher. The oxide film 1a has a thickness of 0.7 to 1.0 μm.
Is formed to a thickness of. In order to form the oxide film 1a, after the semiconductor wafer 1 is cleaned, heat treatment is performed at 1000 to 1200 ° C. in O ₂ or a mixed atmosphere of O ₂ and H ₂ for 50 to 100 minutes after masking in the next step. By doing so, an oxide film formed on the entire surface including the front surface and the back surface can be used, but it may be formed by a thermal oxidation method or a CVD method in another step.

After that, in order to pattern the oxide film on the front surface side, the oxide film is etched after the resist is applied, exposed and developed. At the time of the etching, a resist or the like is applied on the entire surface of the oxide film 1a on the back surface. Set it aside so that it is not removed by the etching solution. Also in the subsequent steps, if there is a step of removing the oxide film 1a with the processing liquid, a protective film is provided so as not to remove the oxide film 1a, and the oxide film 1a on the back surface is removed at least until the film forming step by the final CVD method is completed. Hold.

In the semiconductor wafer process, after the above-mentioned thermal oxidation step, through an etching step, a diffusion step, etc., for example, a protective film and PSG for kettering.
There is a step of forming a film by a CVD method. At the time of this film formation, the oxide film 1a is formed on the back surface of the semiconductor wafer 1 and placed on the susceptor 2 and installed in a reaction tube (not shown). Then, the susceptor 2 is heated to about 400 ° C. and SiH ₄ and O ₂ which are reaction gases 3 are introduced together with the dopant gas, whereby the gases react with each other to form a film on the surface of the semiconductor wafer 1. At this time, since the oxide film 1a was formed on the back surface of the semiconductor wafer 1 to a thickness of 0.7 to 1.0 μm, it was heated to about 400 ° C. as shown in FIG. 2B. In the state, almost no warpage occurred, and a PSG film having a uniform thickness was formed. As a result of actually measuring the film-forming thickness at five measuring points between the peripheral portion and the central portion in the semiconductor wafer after the film-forming, it was within the range of 0.01 to 0.02 μm, Significant improvement was observed for variations of up to 0.2 μm. After that, the normal semiconductor manufacturing process is continued, the oxide film on the back surface is also removed during the contact etching step, the back surface is ground, and then dicing,
Separated into each chip and bonded to the lead frame,
A semiconductor device is obtained by molding.

In the above description, the effect of the oxide film 1a on the back surface of the semiconductor wafer 1 in the film forming process by the CVD method has been described, but the semiconductor wafer at the time of processing is similarly applied to the film forming process by a thermal reaction other than the CVD method. It is possible to prevent the warp of No. 1 and it is effective. However, it is preferable to select an appropriate thickness of the oxide film 1a according to the temperature at the time of this processing, that is, the thicker the processing temperature is, the thicker it is.
The lower the temperature, the better the thinness. However, the CVD process is particularly problematic in the thermal process, and it is preferable to form the oxide film with a thickness suitable for the temperature of the CVD process of about 400 ° C., that is, about 0.7 to 1.0 μm. Most preferred.

Further, when the semiconductor wafer 1 becomes thin, the warp becomes severe, and the thickness of the oxide film 1a needs to be made thick. The thickness of the semiconductor wafer (sub-wafer) 1 before the oxide film is formed is
For example, when it becomes about 150 to 200 μm, the above 400
By forming the oxide film 1a having a thickness of about 1.0 to 1.3 μm even in the heat treatment step at about ° C, it is possible to form a film having a uniform thickness.

[0022]

According to the present invention, since the oxide film is formed on the back surface of the semiconductor wafer, the warp of the semiconductor wafer in the heat treatment process such as the CVD process does not become a problem, and the heat treatment process such as film formation with a uniform thickness is performed. Can be performed uniformly on the entire surface of the semiconductor wafer. As a result, a product yield is improved and a semiconductor device having a constant quality can be obtained. In addition, this tendency becomes more remarkable as the semiconductor wafer becomes thinner.

[Brief description of drawings]

FIG. 1 is an explanatory diagram in a CVD process of a method for manufacturing a semiconductor device of the present invention.

FIG. 2 is a diagram showing the relationship between the thickness and the warp of an oxide film provided on the back surface of a semiconductor wafer.

FIG. 3 is an explanatory diagram in a CVD process of a conventional manufacturing method.

[Explanation of symbols]

 1 semiconductor wafer 1a oxide film 2 susceptor 3 reaction gas

Claims (2)

[Claims] 1. A method of manufacturing a semiconductor device by subjecting a semiconductor wafer to a treatment including at least a film-forming step by a CVD method to form a semiconductor element, and dicing the semiconductor wafer on which the semiconductor element is formed, An oxide film of the semiconductor wafer material is formed on the back surface of the semiconductor wafer before at least the first step of forming a film on the front surface of the semiconductor wafer by the CVD method, and the oxide film on the back surface of the semiconductor wafer is at least the last CVD method. A method for manufacturing a semiconductor device, which is characterized in that the film is left as it is after the film formation step. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the oxide film on the back surface of the semiconductor wafer is formed simultaneously with the oxide film formed on the front surface of the semiconductor wafer as a mask by a thermal oxidation method.