JP2005064341A - Silicon single crystal wafer and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon single crystal wafer which has gettering capability even against slight contaminations and is applicable to a device manufacturing process, and also to provide its manufacturing method. <P>SOLUTION: The silicon single crystal wafer has such a structure that an intermediate layer and a silicon oxide film are laminated in order on a rear face of a silicon single crystal substrate. A solubility of heavy metal impurities is larger in the intermediate layer than in the silicon oxide film. For the intermediate layer, a titanium oxide film or a titanium film is used. The intermediate layer which has a solubility of heavy metal impurities larger than the silicon oxide film is formed on the rear face of the silicon single crystal substrate, and the silicon oxide film is formed by the CVD method on a rear face of the intermediate layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an improvement of a gettering method, which is a technique for removing heavy metal impurities that adversely affect device operation, and more particularly to a silicon single crystal wafer for device manufacture having a high gettering capability and a method for manufacturing the same.

  As the density of devices such as semiconductor integrated circuits is increased and the integration is increased, stabilization of device operation has been desired. In particular, improvement of characteristic values such as leakage current and oxide film breakdown voltage is an important issue.

  However, in the manufacturing process of semiconductor integrated circuits, the possibility of contamination with impurities such as undesired heavy metals such as Cu, Fe, and Ni cannot be denied. It is widely known that these heavy metal impurities are significantly dissolved in the silicon single crystal and the above-described leakage current and oxide film breakdown voltage characteristics are remarkably deteriorated.

  Therefore, various gettering techniques have been developed as a method for removing these heavy metal impurities out of the device operating region. For example, an IG (Internal Gettering) method in which oxygen atoms contained in a silicon single crystal produced by the CZ method are precipitated and heavy metals are captured in the strain around the precipitate, or a polycrystalline silicon film is formed on the back surface of a silicon wafer. A method of forming and capturing impurities in the distortion of the polycrystalline grain boundary. The latter is a representative example of the EG (External Gettering) method. Since these two types have different impurity trapping mechanisms, they are selectively used depending on the application. Briefly, the former is effective in the case of a large amount of contamination but may not be effective in a small amount of contamination, whereas the latter is effective even in the case of a small amount of contamination (Non-Patent Document 1).

  However, with the higher integration of devices, the concentration of impurities that affect device operation is considerably lower than before. Therefore, there is a possibility that it is impossible to cope with the lower concentration of impurities by using the backside polycrystalline silicon film which is a conventional technique that is effective even in the case of trace contamination.

In order to cope with a slight amount of contamination, a layer different from the silicon single crystal and having a high solubility with respect to impurities may be used because of its capture mechanism. A typical example is the aforementioned polycrystalline silicon film. Recently, a p / p ⁺ epiwafer in which an epitaxial layer with a low boron concentration is formed on the surface of a high-concentration boron-added silicon single crystal substrate (p ⁺ substrate) containing boron at a high concentration is also considered for that purpose. There may be. In both of these examples, silicon with various contrivances is used for another layer as a gettering layer. All of these devices have the effect of improving the solubility of heavy metal impurities. However, these methods cannot dramatically increase the solubility of impurities.

In that respect, there is a substance with high impurity solubility, considering another layer of completely different substances. For example, a method using an aluminum film is known (Non-Patent Document 2). This aluminum film has extremely high solubility in impurities, and its gettering capability is so strong that it cannot be compared with that of backside polycrystalline silicon. Specifically, the back surface polycrystalline silicon is on the order of ppm, while aluminum has a solubility of several tens of percent. However, the aluminum film has a melting point as low as 660 ° C. and is dissolved during the device manufacturing process heat treatment, so it is not practical.
"Science of Silicon" edited by UCS Semiconductor Technology Research Group, published by Realize, p. 585-621 “Gettering of metallic impulses in photovoltaic silicon” A. McHugo, H .; Hieslmir, E .; R. Weber; Appl. Phys. A 64 (1997) 127-137

  The present invention has been made in view of such problems, and an object of the present invention is to provide a silicon single crystal wafer that can be applied to a device manufacturing process and has a gettering capability even in a minute amount of contamination, and a manufacturing method thereof. To do.

  The silicon single crystal wafer of the present invention is a silicon single crystal wafer having a structure in which an intermediate layer and a silicon oxide film are sequentially laminated on the back surface of a silicon single crystal substrate, and the solubility of heavy metal impurities in the intermediate layer is determined by silicon oxide. It is characterized by being larger than the membrane.

  In the method for producing a silicon single crystal wafer of the present invention, an intermediate layer having a higher solubility of heavy metal impurities than a silicon oxide film is formed on the back surface of the silicon single crystal substrate, and a silicon oxide film is formed on the surface of the intermediate layer by a CVD method. It is characterized by doing.

  As the intermediate layer, it is preferable to use a titanium oxide film or a titanium film, and these films can be formed by a sputtering method. A typical example of the heavy metal is Fe.

  In this specification, a material substrate for forming a silicon oxide film or an intermediate layer is referred to as a “silicon single crystal substrate”, and a silicon single crystal substrate having a silicon oxide film or an intermediate layer formed thereon is described as “ "Silicon single crystal wafer".

  The silicon single crystal wafer of the present invention has a great effect that it has gettering capability even in a small amount of contamination and can be applied to a device manufacturing process. According to the method of the present invention, the silicon single crystal wafer of the present invention can be efficiently produced.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. However, the illustrated examples are shown by way of example, and various modifications can be made without departing from the technical idea of the present invention. Needless to say.

  As described above, in order to cope with a minute amount of contamination, a layer that is separate from the silicon single crystal and has a high solubility in impurities may be used because of its trapping mechanism. However, in the case of a film having a melting point of less than 1000 ° C. such as an aluminum film, it is not effective because it is often not applicable to a device process.

  Therefore, if the silicon oxide film having a melting point much higher than 1000 ° C. can be used, the present inventor will not dissolve during the device manufacturing process, and the gettering ability is maintained at any stage of device manufacturing. The present invention was completed with the idea of dripping.

  That is, since the silicon oxide film is a constituent element of a normal silicon single crystal wafer for manufacturing a semiconductor device, it is not harmful in the silicon single crystal wafer. In addition, the diffusion coefficient of heavy metal in the silicon oxide film is often several orders of magnitude lower than that in the silicon single crystal, and the heavy metal once gettered in the oxide film is difficult to re-emit. Thus, the silicon oxide film has many desirable properties as the properties of the back surface gettering layer.

  In addition, in the most common thermal oxidation method in the oxide film formation method, the reaction at the interface with the silicon single crystal is the driving force for the growth of the oxide film, so the oxide film is formed on the original surface of the silicon single crystal substrate. At the same time it grows outside, it grows inside the silicon single crystal substrate. Therefore, when the heavy metal impurity is already dissolved in the silicon single crystal substrate, the oxide film grows inward so that the heavy metal is taken into the oxide film, which is advantageous. In other words, the oxide film growth and the heavy metal impurity gettering reaction proceed simultaneously. A technique for removing heavy metal impurities using this phenomenon is generally known as a so-called sacrificial oxidation process (a process for removing the thermal oxide film after the thermal oxide film is formed). According to the sacrificial oxidation, heavy metal impurities can be removed from the system of the silicon single crystal substrate semi-permanently.

  However, performing impurity gettering simultaneously during the oxidation process of the sacrificial oxidation treatment is based on the premise that impurities exist in the silicon single crystal substrate in advance, and the silicon single crystal wafer with an oxide film after the oxidation process It does not necessarily guarantee the gettering ability against heavy metal contamination. This is because it is consistent with the high ability of the oxide film as a gettering layer and depends on whether heavy metal impurities in the silicon single crystal wafer can move into the oxide film. In general, when impurities migrate to adjacent layers, it is necessary to undergo some kind of interfacial reaction in addition to the diffusion behavior of each layer. If the interface reaction is promoted, the impurities are easily transferred to a stable layer in a solid solution state (that is, a layer having a high solubility (solid solubility)).

  The silicon single crystal wafer 10 of the present invention has been made in consideration of this point, and as shown in FIG. 1, the solubility of heavy metal impurities at the interface between the silicon oxide film 16 and the silicon single crystal substrate 12 is a silicon oxide film. By inserting a larger separate layer (intermediate layer) 14, impurities contaminating the front and back surfaces of the silicon single crystal wafer 10 can be easily moved into the oxide film layer 16. . An example of the heavy metal is Fe.

  This makes it possible to obtain an impurity gettering effect in the formed oxide film 16 during the device fabrication heat treatment after the oxide film 16 is formed.

For example, a titanium oxide film (TiO ₂ ) or a titanium film (Ti) can be suitably used as another layer (intermediate layer) 14 in which the solubility of heavy metal impurities is larger than that of the silicon oxide film. These have a melting point higher than the heat treatment temperature (several hundred to 1400 ° C.) in which silicon single crystal wafers are usually used, and there is no fear of melting during the device manufacturing process heat treatment as described above. Further, the solubility of TiO ₂ and Ti with respect to heavy metal impurities such as Cu, Fe, and Ni is larger than the solubility of the silicon oxide film (in the case of Fe, 3.2 × 10 ²¹ atoms / cm ³ at 1000 ° C.). ₂ and Ti function effectively as a buffer layer for gettering these heavy metal impurities into the silicon oxide film.

  FIG. 2 schematically shows the relationship between the cross-sectional structure of the silicon single crystal wafer 10 (silicon single crystal substrate 12, intermediate layer 14, and silicon oxide film 16) of the present invention and the solubility of heavy metal impurities in each layer. .

  The method of the present invention is a method of manufacturing the above-described silicon single crystal wafer of the present invention. As shown in FIG. 3, a step of preparing a silicon single crystal substrate (step 100), on the back surface of the silicon single crystal substrate The process includes a step of forming an intermediate layer in which the solubility of heavy metal impurities is larger than that of the silicon oxide film (step 102), and a step of forming a silicon oxide film on the surface of the intermediate layer by the CVD method (step 104). An example of the heavy metal is Fe.

  As the intermediate layer, it is preferable to form a titanium oxide film or a titanium film by a sputtering method.

The present invention will be described more specifically with reference to the following examples. However, it is needless to say that these examples are shown by way of illustration and should not be construed in a limited manner.
(Example 1)

  A crystal rod having a diameter of 6 inches, an initial oxygen concentration of 14 ppma (JEIDA scale), and an orientation <100> was pulled at a normal pulling rate (1.2 mm / min) by the CZ method. This crystal rod is processed by slicing, lapping, etching, mirror polishing, etc. to produce a silicon single crystal substrate having one surface (front surface) as a mirror surface, and a titanium oxide film is formed on the back surface (chemical etching surface) by sputtering. After that, a silicon oxide film having a thickness of 0.1 μm is deposited on the titanium oxide film by using the CVD method, so that an intermediate layer (titanium oxide film) and a silicon oxide film are sequentially laminated on the back surface. A silicon single crystal wafer was produced. JEIDA is an abbreviation for Japan Electronics Industry Promotion Association (currently renamed JEITA: Japan Electronics Information Technology Association).

A silicon single crystal wafer fabricated in this manner was prepared by coating Fe with a concentration of 4 × 10 ¹³ cm ⁻² on the oxide film on the back surface and a wafer contaminated with the same concentration from the mirror surface. At a temperature of 1000 ° C., the Fe atoms were diffused in the wafer depth direction by changing the heat treatment time from 30 minutes to 8 hours.

  Thereafter, the depth distribution of the Fe concentration of the silicon single crystal substrate was measured by a DLTS (Deep Level Transient Spectroscopy) method. In a wafer contaminated from the mirror surface side, Fe was detected from the mirror surface side after 30 minutes of heat treatment. However, as it became deeper toward the back surface, Fe was not detected. Further, when heat treatment was performed for 1 hour or longer, Fe was not detected at any position in the depth direction. This is because Fe contaminated from the mirror surface side quickly transferred to the silicon oxide film and the titanium oxide film layer, which are high-concentration solid solution layers, indicating that almost no Fe remained on the single crystal silicon side.

On the other hand, no Fe was detected in the single crystal silicon at the wafer contaminated from the back oxide film side, at any heat treatment time, or at any depth. This indicates that Fe hardly diffused to the single crystal silicon side due to the presence of the silicon oxide film and the titanium oxide film as the high concentration solid solution layer on the contaminated surface side.
(Comparative Example 1)

  A crystal rod having a diameter of 6 inches, an initial oxygen concentration of 14 ppma (JEIDA scale), and an orientation <100> was pulled at a normal pulling rate (1.2 mm / min) by the CZ method. This crystal rod is processed by slicing, lapping, etching, mirror polishing, etc. to produce a silicon single crystal substrate having one surface (front surface) as a mirror surface, and the back surface (chemical etching surface) is formed using a CVD method. By depositing a 0.1 μm silicon oxide film, a silicon single crystal wafer having only a silicon oxide film formed on the back surface was produced.

In the same manner as in Example 1, the wafers contaminated on either side were heat-treated, and Fe atoms were diffused in the wafer depth direction. After that, when the depth distribution of the Fe concentration on the silicon single crystal substrate side was measured, the Fe concentration in the silicon single crystal was uniformly distributed in the depth direction regardless of the contaminated surface when the heat treatment was performed for 4 hours or more. Saturated at. However, the saturated average concentration was uniform at a concentration of 2 × 10 ¹³ cm ⁻³ when contaminated from the oxide film side, whereas the surface concentration of the wafer contaminated from the mirror surface side was 1 × 10 ¹⁴ cm. ^The oxide film was not necessarily effectively acting as a gettering layer. Therefore, the effective function of the oxide film as the gettering layer has been limited to contamination from the oxide film side. This indicates that Fe could not be rapidly transferred from the single crystal silicon side to the oxide film.

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

  For example, in the first embodiment, a titanium oxide film layer is used as a layer between the silicon single crystal and the silicon oxide film, but the present invention is not limited to this, and a titanium film layer, a tungsten oxide film layer, or the like is used. If the same effect is obtained, it is included in the scope of the present invention. In addition, the formation method of the intermediate layer used for the layer between the single crystal Si and the oxide film is not limited, and the same effect can be obtained by using sputtering, vapor deposition, CVD (chemical vapor deposition), etc. Is included in the scope of the present invention.

It is an expanded partial sectional view of the silicon single crystal wafer of the present invention. It is a schematic diagram which shows the relationship between the cross-sectional structure of the silicon single crystal wafer of this invention, and the solubility of a heavy metal impurity. It is a flowchart which shows the process order of this invention method.

Explanation of symbols

10: silicon single crystal wafer, 12: silicon single crystal substrate, 14: intermediate layer, 16: silicon oxide film.

Claims (6)

  A silicon single crystal wafer having a structure in which an intermediate layer and a silicon oxide film are sequentially stacked on the back surface of a silicon single crystal substrate, wherein the solubility of heavy metal impurities in the intermediate layer is larger than that of a silicon oxide film Single crystal wafer.   The silicon single crystal wafer according to claim 1, wherein the intermediate layer is a titanium oxide film or a titanium film.   The silicon single crystal wafer according to claim 1, wherein the heavy metal is Fe.   A silicon single crystal wafer is produced by forming an intermediate layer having a higher solubility of heavy metal impurities on the back surface of a silicon single crystal substrate than a silicon oxide film, and forming a silicon oxide film on the surface of the intermediate layer by a CVD method. Method.   The method for producing a silicon single crystal wafer according to claim 4, wherein a titanium oxide film or a titanium film is formed as the intermediate layer by a sputtering method. 6. The method for producing a silicon single crystal wafer according to claim 4, wherein the heavy metal is Fe.

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