JPH11111674A - Method for improving surface roughness of silicon wafer and silicon wafer having improved surface roughness - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve both micro-roughness and haze level of a silicon wafer at the same time by heat treating of a mirror finished silicon wafer in oxidative atmosphere to form a thermal oxide film of specified thickness on the surface thereof and then removing the thermal oxide film. SOLUTION: A mirror finished silicon wafer is heat treated in oxidizing atmosphere to form a thermal oxide film of 300 nm thick or above on the surface thereof, and then the thermal oxide film is removed thus improving the surface roughness of the silicon wafer. Heat treatment in oxidizing atmosphere is suitably conducted at a relatively high temperature of 1,100-1,300 deg.C in order to improve the haze level, while shortening the oxidation time. The thermal oxide film is suitably removed by etching the silicon wafer using an aqueous solution containing hydrofluoric acid, in order to remove the thermal oxide film easily at low cost. In this case, an aqueous solution having HF concentration of 10% or less is suitably employed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving so-called surface roughness such as micro-roughness or haze of a silicon wafer, and a silicon wafer having improved surface roughness by this method.

[0002]

2. Description of the Related Art The quality required for silicon wafers is becoming increasingly sophisticated due to the recent high integration and high precision of devices, and in particular, improving the flatness and surface roughness of the silicon wafer surface requires the improvement of device performance. Needed to improve electrical properties.

That is, it has been found that microroughness, which is microscopic unevenness at the atomic level on the wafer surface, affects the electrical characteristics of the device.
For example, if the micro roughness is large, the oxide film breakdown voltage (T
im Zero Dielectric Break
It is known that, when the micro roughness increases in the channel below the gate oxide film, electron scattering occurs and the electron mobility decreases. Regarding haze, which is undulation having a periodicity of about several to several tens of nm on the wafer surface, a reliability test, which is an electrical property of the device, particularly, a time-dependent dielectric breakdown property of an oxide film (Time Dependent Diel)
It has been found to affect strict breakdown (TDDB).

Therefore, in order to improve the electrical characteristics of devices in the future, it is necessary to improve the surface roughness of the silicon wafer, such as micro roughness or haze.

Conventionally, as a method for improving the micro roughness of such a silicon wafer, a method of performing a high-temperature heat treatment in a hydrogen atmosphere has been known (JP-A-7-23).
No. 5534). However, with this method, although the micro roughness is improved, the haze tends to worsen, and the surface roughness as a whole cannot be completely solved.

As another method for improving micro-roughness, it has been reported that micro-roughness is improved by removing an oxide film formed on a surface after oxidizing a silicon wafer (Symposiu).
mon VLSI Technology, Seat
tle, p24-25, Jun 1992). But,
Again, the haze level is not improved or even worse.

[0007]

That is, no method has been studied for improving both the micro-roughness and the haze level at the same time, and the deterioration of the electrical characteristics due to the surface roughness is completely solved. I couldn't do it. This is due to the fact that the area to be measured differs between micro-roughness and haze, micro-roughness measures a narrow area, and haze level measures a wider area. It seems to be.

Accordingly, the present invention has been made in view of such problems, and an object of the present invention is to provide a method capable of simultaneously improving the micro roughness and haze level of a silicon wafer, or at least a method of improving the haze level. It is an object of the present invention to provide a method capable of improving the micro roughness without deteriorating the micro roughness. Thus, an object of the present invention is to provide a silicon wafer which does not cause a problem of deterioration of electrical characteristics such as an oxide film breakdown voltage and a reliability test due to the surface roughness of the silicon wafer.

[0009]

According to the first aspect of the present invention, there is provided a mirror-polished silicon wafer which is subjected to a heat treatment in an oxidizing atmosphere so that the surface of the silicon wafer has a thickness of 300 nm or more. Forming the thermal oxide film and then removing the thermal oxide film to improve the surface roughness of the silicon wafer.

[0010] As described above, after a silicon wafer is subjected to an oxidizing heat treatment to form a thermal oxide film of 300 nm or more on the surface,
By removing this, it is possible to improve both the surface roughness of a minute region such as micro roughness and the surface roughness of a wider region such as haze.

According to the second aspect of the present invention, the oxidation heat treatment is performed at 1100 to 1300 ° C. Thus, if the heat treatment is performed at a relatively high temperature, the haze level can be further improved and the oxidation time can be shortened.

According to a third aspect of the present invention, the thermal oxide film is removed by etching with an aqueous solution containing hydrofluoric acid. As described above, if the thermal oxide film is removed by etching with an aqueous solution containing hydrofluoric acid, the oxide film can be removed easily and at low cost.

In this case, the thermal oxide film is preferably removed by etching with an aqueous solution containing hydrofluoric acid having an HF concentration of 10% or less. This is because if the HF concentration is too high, the surface of the silicon wafer may be newly roughened.

As described above, according to the method described in claims 1 to 4 of the present invention, it is possible to obtain a silicon wafer having improved surface roughness at both the micro roughness and the haze level. Therefore, such a silicon wafer has improved surface roughness even in a minute area or a wider area, so that not only an oxide film withstand voltage but also an electrical property such as a reliability test has been improved. (Claim 5).

Hereinafter, the present invention will be described in more detail. Prior to the description, first, the micro roughness and the haze referred to in the present invention will be described again. The micro-roughness is a fine unevenness on an atomic level on a wafer surface, and is a surface roughness obtained mainly by measuring a narrow area of about 1 micron square or less with an AFM (atomic force microscope). The haze is a undulation having a periodicity of about several to several tens of nm on the wafer surface, and is mainly a particle counter using a laser (for example, LS-6000: trade name of Hitachi Electronics Electronics Co., Ltd.). Scan the entire surface of the wafer with a laser,
The surface roughness is evaluated semi-quantitatively as the haze level of the entire surface of the wafer by measuring the irregular reflection intensity.

The present inventors have studied a method that can improve both the surface roughness of a micro area such as micro roughness and the surface roughness of a wider area such as haze. As a result, after oxidizing a silicon wafer, In the method of removing the oxide film formed on the surface, the improvement of the micro roughness and the haze level is affected by the oxide film thickness formed on the surface, and that the haze level is further affected by the oxidation heat treatment temperature. The present invention has been completed under the heading.

In other words, the inventors of the present invention have proposed a method for removing a oxidized film formed on a surface after oxidizing a silicon wafer, which is a conventional method for improving micro roughness, despite the fact that the micro roughness is improved. In order to investigate the cause of the haze level not being improved or worsening, an oxide film was grown under various conditions, and the influence on the surface roughness was examined.

FIG. 1 shows that a mirror-polished silicon wafer whose micro roughness has been measured in advance is subjected to a heat treatment in an oxidizing atmosphere so that the surface of the silicon wafer is about 100 to 1 mm.
After forming a thermal oxide film of 2,000 nm, the thermal oxide film is removed with hydrofluoric acid, and then the surface roughness of the silicon wafer (R
(MS: root mean square roughness) measured by AFM is shown as micro-roughness (RMS) with respect to thermal oxide film thickness.

As is apparent from this figure, there is a strong correlation between the oxide film thickness and the micro roughness, and it is understood that the larger the oxide film thickness, the better the micro roughness. In particular, when the oxide film thickness is set to 300 nm or more, the RMS value which was about 0.146 nm at the beginning is changed to about 0.4 mm.
It is greatly improved to 12 nm or less. Therefore, in order to improve the micro roughness, the oxide film thickness is preferably set to 300 nm or more.

The reason why the micro-roughness is improved by the formation of the oxide film is considered to be due to the effect of the interstitial silicon generated by the oxidation to fill the atomic vacancies. Therefore, it can be interpreted that the larger the oxide film thickness is, the more the vacancies are filled, thereby improving the micro roughness.

On the other hand, as for the oxidation heat treatment temperature, although the improvement effect tends to be higher as the temperature is higher, a clear correlation is not found.

FIG. 2 shows that a mirror-polished silicon wafer whose haze level has been measured in advance is subjected to a heat treatment in an oxidizing atmosphere so that the surface of the silicon wafer is
After forming a thermal oxide film of nm, the thermal oxide film was removed with hydrofluoric acid, and then the haze level of the silicon wafer was measured with a particle counter, and the result is shown as the haze level (bit) relative to the thermal oxide film thickness. It is.

As is clear from this figure, the haze level has a peak at an oxide film thickness of around 200 nm even when oxidized at any temperature zone. In other words, when an oxide film of about 200 nm is grown, the haze level is most deteriorated. In the region where the oxide film thickness is 200 nm or less, the haze level becomes worse as the oxide film thickness increases, and in the region where the oxide film thickness is 200 nm or more, the haze level improves as the oxide film thickness increases. Is done. In particular, depending on the oxidation heat treatment temperature, the oxide film thickness is set to 300 nm.
In this case, the improvement effect is large. Therefore, in order to improve or at least prevent the haze level from being deteriorated, the oxide film thickness is preferably set to 300 nm or more.

On the other hand, as for the oxidation heat treatment temperature, when the oxide film thickness is 300 nm or more, the higher the temperature, the higher the improvement effect tends to be. In particular, it can be seen that if the heat treatment is performed at a temperature of 1100 ° C. or more, the haze level of the silicon wafer can be improved from the initial haze level. Therefore, it is desirable to perform the oxidation heat treatment at a temperature of 1100 ° C. or higher.

It can be said that it is preferable to perform the heat treatment at a high temperature in order to shorten the oxidation treatment time and improve the productivity. However, if the heat treatment is performed at a temperature exceeding 1300 ° C., there is a high possibility that contamination accompanying the heat treatment of the wafer occurs, and a problem of durability of the heat treatment furnace occurs.
Processing at temperatures up to 1300 ° C. is preferred.

The reason why the haze level has a peak near the oxide film thickness of 200 nm, and
Although the details of the reason why the haze level is improved by increasing the thickness are not clear at present, clear reproducibility can be seen.
When the thickness was set to be not less than 00 nm, the haze level could be surely improved.

As described above, in order to simultaneously improve the micro roughness and the haze level of the mirror-polished silicon wafer, or at least to improve the micro roughness without deteriorating the haze level, the silicon wafer is subjected to a heat treatment in an oxidizing atmosphere. It is found that the thermal oxide film may be removed after forming a thermal oxide film of 300 nm or more on the surface of the silicon wafer. However, it is sufficient to increase the thickness of the oxide film, but it is sufficient to grow the oxide film as much as 2 microns. If an oxide film having a thickness greater than that is to be formed, it takes too much oxidation time.
Not practical.

In this case, the oxidation heat treatment is performed at 1100-1.
If the heat treatment is performed at 300 ° C., the haze level can be improved compared to the original silicon wafer, and the oxidation time can be shortened.

It is not necessary to use a special gas composition or the like as the oxidizing atmosphere, and the oxidizing atmosphere may be an atmosphere used for an ordinary oxidation treatment of a silicon wafer. For example, so-called dry oxidation with pure oxygen, wet oxidation with oxygen saturated with water vapor, or a mixture of these with an inert gas such as nitrogen or argon, or a mixture of high-temperature water vapor and hydrogen chloride, etc. are used. I can do it.

The furnace for performing the oxidation treatment may be a commonly used furnace, and is not particularly limited. That is, as long as heat treatment can be applied to a silicon wafer in an oxidizing atmosphere, any heat treatment furnace can be used in principle.

After forming the oxide film, the thermal oxide film may be removed by etching with an aqueous solution containing hydrofluoric acid. As described above, if the oxide film is removed by etching with an aqueous solution containing hydrofluoric acid, only the oxide film is removed by etching, and a silicon wafer having improved surface roughness by oxidizing heat treatment can be obtained. Moreover, such a hydrofluoric acid treatment of the silicon wafer has an advantage that it is simple and low in cost.

In this case, the HF concentration of the aqueous solution containing hydrofluoric acid is preferably 10% or less, more preferably 5% or less. This is because if the HF concentration is higher than these values, the surface of the silicon wafer may be newly roughened. Therefore, it is preferable to immediately perform a treatment such as washing with water and drying the wafer after the etching for removing the oxide film with an aqueous solution containing hydrofluoric acid.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to examples, but the present invention is not limited thereto.

[0034]

【Example】

Example First, a silicon wafer having a diameter of 8 inches and a crystal orientation of <100> prepared by slicing a silicon ingot manufactured by the Czochralski method by a commonly used method and mirror-finished was prepared. .

The micro-roughness and haze level of the surface of these silicon wafers were measured before applying the oxidizing heat treatment. Microroughness was measured by AFM (SPA360: trade name, manufactured by Seiko Denshi Kogyo Co., Ltd.), and haze level was measured by a particle counter (LS-6000, trade name, manufactured by Hitachi Electronics Engineering Co., Ltd.) in the 900 V range. These measuring methods are generally used methods.

The silicon wafers whose surface roughness was measured were subjected to an oxidizing heat treatment at 1100 ° C. in a wet oxygen atmosphere to form a thermal oxide film of about 600 nm on the surface. Next, the silicon wafer having a thermal oxide film on the surface was immersed in a hydrofluoric acid aqueous solution having a HF concentration of 5% to completely remove the thermal oxide film on the surface. In this case, the wafer was immediately washed with water after the completion of the etching and dried to prevent the occurrence of a new surface roughness due to the etching.

The surface roughness of the treated silicon wafer was measured again by the same method as described above. Table 1 shows the results.

[0038]

[Table 1]

As is clear from Table 1, it can be seen that the method of the present invention can improve both the micro roughness and the haze level. Therefore, the silicon wafer obtained by the method of the present invention can improve not only the withstand voltage of the oxide film but also the reliability test when a subsequent device is manufactured, and the deterioration of the electrical characteristics of the device due to the surface roughness can be improved. Can solve the problem.

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of the present invention. It is included in the technical scope of the invention.

For example, in the above embodiment, a silicon wafer having a diameter of 8 inches and a crystal orientation of <100> was used. However, the present invention is applicable regardless of the specifications of the silicon wafer such as the diameter, orientation, and resistance. Needless to say.

[0042]

As described above in detail, according to the method of the present invention, it is possible to improve both the micro roughness and the haze level surface roughness of a silicon wafer. Therefore, the obtained silicon wafer has improved surface roughness even in a minute area or a wider area, so that not only the oxide film breakdown voltage but also the electrical characteristics such as reliability tests are improved. be able to. Moreover, it is simple, low-cost, and does not require the use of special equipment.

[Brief description of the drawings]

FIG. 1 shows a result of measuring the micro roughness of a silicon wafer by AFM after performing an oxidation heat treatment on a mirror-polished silicon wafer and then removing a thermal oxide film with hydrofluoric acid as a micro roughness to a thermal oxide film thickness. FIG.

FIG. 2 shows an oxidizing heat treatment performed on a mirror-polished silicon wafer, and after removing the thermal oxide film with hydrofluoric acid, the haze level of the silicon wafer is measured with a particle counter. FIG.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI // H01L 21/316 H01L 21/316 P 21/306 D

Claims (5)

[Claims] 1. A silicon wafer characterized in that a mirror-polished silicon wafer is heat-treated in an oxidizing atmosphere to form a thermal oxide film having a thickness of 300 nm or more on the surface of the silicon wafer, and then the thermal oxide film is removed. A method for improving the surface roughness of a wafer. 2. The method for improving the surface roughness of a silicon wafer according to claim 1, wherein the heat treatment is performed at 1100 to 1300 ° C. 3. The method for improving the surface roughness of a silicon wafer according to claim 1, wherein the thermal oxide film is removed by etching with an aqueous solution containing hydrofluoric acid. . 4. The method according to claim 1, wherein the thermal oxide film is removed at an HF concentration of 10%.
3. The method for improving the surface roughness of a silicon wafer according to claim 1, wherein the removal is performed by etching with an aqueous solution containing hydrofluoric acid of not more than%. 5. A silicon wafer whose surface roughness is improved by the method according to claim 1.