Semiconductor substrate evaluation method

Abstract

To provide a semiconductor substrate evaluation method capable of highly accurately evaluating the surface quality of a semiconductor substrate influencing a film thickness of a thermal oxide film.SOLUTION: A semiconductor substrate evaluation method includes preparing a plurality of semiconductor substrates having the same surface quality standard as the semiconductor substrate to be evaluated, cleaning the plurality of semiconductor substrates under the same cleaning conditions, individually manufacturing a semiconductor substrate in which a dry oxide film is formed by dry oxidation without removing a natural oxide film formed due to the cleaning and a semiconductor substrate in which a pyrogenic oxide film is formed by pyrogenic oxidation without removing the natural oxide film formed due to the cleaning from the plurality of semiconductor substrates, and evaluating the surface quality of the semiconductor substrates on the basis of a ratio between the film thickness of the dry oxide film and the film thickness of the pyrogenic oxide film.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for evaluating a semiconductor substrate. [Background technology]

[0002] As semiconductor integrated circuit elements become more multi-layered and thinner, there is a demand for even thinner films that compose the elements. In order to form such ultra-thin silicon oxide films uniformly and reproducibly within a surface or between substrates, it is impossible to ignore the influence of the natural oxide film that is formed in advance on the semiconductor substrate (Patent Document 1). In this specification, the oxide film (sometimes called a chemical oxide film) formed by cleaning the semiconductor substrate is also included in the natural oxide film. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-49217 A [Patent Document 2] Patent No. 6791453 [Patent Document 3] Patent No. 6791454 [Non-patent literature]

[0004] [Non-Patent Document 1] BEDeal and ASGrove, “General Relationship for the Thermal Oxidation of Silicon”, J.Apply.Phys., 36, 3770(1965). Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors' research and studies have revealed that, for example, when the cleaning method for semiconductor substrates is different, the thickness of the thermal oxide film formed thereafter differs (Patent Documents 2 and 3). For example, it is known that even a change of just 5°C in the SC1 cleaning temperature can have a significant effect depending on the temperature range used for cleaning. Furthermore, there are concerns that differences in the oxide film after thermal oxidation can cause problems such as variations in the characteristics of semiconductor integrated circuit elements and reduced yields.

[0006] However, it is known that this difference in film thickness does not necessarily depend on the thickness of the native oxide film before thermal oxidation, but because the film thickness variation is small, it requires a great deal of effort to distinguish whether the variation is due to disturbance or the influence of the actual surface (for example, fluctuations in cleaning conditions).A method is needed to accurately evaluate the surface condition of the semiconductor substrate that affects the thickness of the thermal oxide film.

[0007] The present invention has been made to solve the above problems, and has an object to provide a method for evaluating a semiconductor substrate, which is capable of evaluating with high accuracy the surface quality of a semiconductor substrate, which affects the thickness of a thermal oxide film. [Means for solving the problem]

[0008] The present invention has been made in order to achieve the above-mentioned object, and provides a method for evaluating semiconductor substrates, comprising the steps of: preparing a plurality of semiconductor substrates having the same surface quality level as semiconductor substrates to be evaluated; cleaning the plurality of semiconductor substrates under the same cleaning conditions; individually producing, from the plurality of semiconductor substrates, a semiconductor substrate on which a dry oxide film is formed by dry oxidization without removing a native oxide film formed by the cleaning; and a semiconductor substrate on which a pyrogenic oxide film is formed by pyrogenic oxidization without removing a native oxide film formed by the cleaning; and evaluating the surface quality of the semiconductor substrates based on a ratio of the film thickness of the dry oxide film to the film thickness of the pyrogenic oxide film.

[0009] According to such a semiconductor substrate evaluation method, it is possible to provide a semiconductor substrate evaluation method that can evaluate the surface quality of a semiconductor substrate with high accuracy based on the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film.

[0010] In this case, the film thickness of the dry oxide film and the pyrogenic oxide film can be set to 0.1 to 10 nm.

[0011] In this manner, when the film thickness is in the thin range, the surface quality of the semiconductor substrate can be evaluated with a high degree of accuracy.

[0012] In this case, the surface quality may be the film quality and / or thickness of a native oxide film formed in the final cleaning of the semiconductor substrate, or the surface quality may be the surface roughness of the semiconductor substrate.

[0013] The method for evaluating a semiconductor substrate according to the present invention is particularly suitable for evaluating the surface quality of such semiconductor substrates.

[0014] In this case, the semiconductor substrate may be a silicon substrate, and the dry oxide film and the pyrogenic oxide film may be silicon oxide films.

[0015] The method for evaluating a semiconductor substrate according to the present invention is particularly suitable for evaluating a silicon oxide film formed on a silicon substrate. Effect of the Invention

[0016] As described above, the semiconductor substrate evaluation method of the present invention provides a method for evaluating the surface quality of a semiconductor substrate with high accuracy based on the difference in the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film. Also, it becomes possible to clarify the process conditions related to the manufacture of a semiconductor substrate that affect the thickness of the thermal oxide film. [Brief description of the drawings]

[0017] [Figure 1]The relationship between the SC1 cleaning temperature and the oxide film thickness by dry oxidation and pyrogenic oxidation, and the ratio of the dry oxide film thickness to the pyrogenic oxide film thickness is shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The present invention will be described in detail below, but the present invention is not limited thereto.

[0019] As described above, there has been a demand for a method for evaluating a semiconductor substrate that can accurately evaluate the surface quality of the semiconductor substrate, which affects the thickness of the thermal oxide film.

[0020] As a result of intensive investigations into the above-mentioned problems, the inventors have found that the surface quality of a semiconductor substrate can be evaluated with high accuracy by a method for evaluating a semiconductor substrate, comprising the steps of: preparing a plurality of semiconductor substrates having the same surface quality level as semiconductor substrates to be evaluated; cleaning the plurality of semiconductor substrates under the same cleaning conditions; individually preparing, from the plurality of semiconductor substrates, a semiconductor substrate on which a dry oxide film is formed by dry oxidizing without removing the native oxide film formed by the cleaning; and a semiconductor substrate on which a pyrogenic oxide film is formed by pyrogenic oxidizing without removing the native oxide film formed by the cleaning; and evaluating the surface quality of the semiconductor substrates based on the ratio of the film thickness of the dry oxide film to the film thickness of the pyrogenic oxide film, thereby completing the present invention.

[0021] The following description will be given with reference to the drawings.

[0022] To form a thin thermal oxide film on a semiconductor substrate such as a silicon substrate, the semiconductor substrate is generally placed in a heat treatment furnace equipped with a heater or lamp on the outside of a quartz tube, and oxygen is introduced into the furnace while the semiconductor substrate is heated to oxidize the semiconductor, producing a semiconductor oxide film. To form a thin thermal oxide film of 10 nm or less using this method, measures such as lowering the temperature to 900°C or lowering the partial pressure of oxygen are taken. This method of using oxygen as the oxidizing species is generally called dry oxidation, and the oxide film formed is sometimes called a dry oxide film.

[0023] On the other hand, there is a method called pyrogenic oxidation (also called pyro-oxidation or wet oxidation) that uses water (heated steam) as an oxidizing species. The oxide film formed by such a pyrogenic oxidation method is sometimes called a pyrogenic oxide film (pyro-oxidation film). Methods for introducing heated steam include a method in which water is bubbled with oxygen and supplied to the furnace, and a method in which oxygen and hydrogen are separately introduced into the furnace and burned in the furnace to generate water. In particular, in consideration of cleanliness, stability, and safety, a method has become common in recent years in which a preliminary combustion chamber is provided at the gas introduction section, and oxygen and hydrogen are burned in advance in this preliminary combustion chamber and introduced into the heat treatment furnace. The oxidation rate of this pyro-oxidation process is higher than that of dry oxidation, and it is generally used to form a thick oxide film (Non-Patent Document 1).

[0024] For this semiconductor oxidation, the oxidizing species must diffuse through the oxide film to reach the oxide film / semiconductor interface, and since the oxidation rate is determined by the diffusion of the oxidizing species, it slows down with oxidation time (as the thermal oxide film thickness increases). However, when the oxide film is thin or the effect of the diffusion of the oxidizing species is small, such as in the early stages of oxidation, the effect of diffusion is small, and the oxide film thickness also depends on the reaction (structure) at the oxide film / semiconductor interface.

[0025] Thus, in the case of a thin oxide film, the influence of the natural oxide film formed on the surface of the semiconductor substrate cannot be ignored, and the thickness and quality of the natural oxide film also affect the thickness of the thermal oxide film.

[0026] The inventors have previously elucidated that, for example, differences in cleaning conditions for semiconductor substrates (such as the type and composition of cleaning solution) affect the structure (quality such as film quality and film thickness) of the native oxide film formed on the surface of the semiconductor substrate by cleaning (Patent Documents 2 and 3).

[0027] The present inventors further studied and focused on the difference in oxidation species between the thermal oxidation method, specifically the dry oxidation and the pyrogenic oxidation, and came up with the idea of ​​utilizing the difference in oxidation species and oxidation mechanism. A plurality of semiconductor substrates having the same surface quality level are prepared as semiconductor substrates to be evaluated, and are cleaned under the same cleaning conditions to obtain semiconductor substrates with the same surface quality. These semiconductor substrates are individually subjected to dry oxidation and pyrogenic oxidation without removing the natural oxide film formed by cleaning, to produce a semiconductor substrate with a dry oxide film and a semiconductor substrate with a pyrogenic oxide film. The surface quality of the semiconductor substrate is evaluated based on the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film (hereinafter, sometimes simply referred to as the "oxide film thickness ratio") obtained by measuring the thickness of the thermal oxide film of the semiconductor substrate thus produced. At this time, the standard cleaning conditions are determined, and the difference in the oxide film thickness when the cleaning conditions are changed is calculated, and the ratio of the dry oxidation to the pyrogenic oxidation can be obtained using this difference. The inventors have found that by doing this, it is possible to evaluate the surface quality of semiconductor substrates with high accuracy, and furthermore, it is possible to evaluate differences in surface quality, and have thus completed the present invention.

[0028] For example, a reference oxide film thickness ratio is set, and a change in the surface quality of the semiconductor substrate can be grasped by comparing with this reference value.

[0029] Furthermore, by using the semiconductor substrate evaluation method according to the present invention, it is possible to manage processes before thermal oxidation, such as a cleaning process, based on the evaluation of the surface quality of the semiconductor substrate. As shown in the examples described later, changes in the oxide film thickness ratio reflect changes in the cleaning conditions of the semiconductor substrate with high sensitivity. It is also preferable to utilize this to evaluate the cleaning process. For example, by periodically monitoring the cleaning process for processing normal products and grasping the transition of the oxide film thickness ratio, it is possible to detect changes in the cleaning conditions and the occurrence of abnormalities.

[0030] In addition, the target oxide film thickness in the oxidation process for forming the dry oxide film and the pyrogenic oxide film is preferably approximately the same for the dry oxidation and the pyrogenic oxidation, and the range of the film thickness is preferably 0.1 to 10 nm. The method for evaluating a semiconductor substrate according to the present invention can more accurately evaluate the surface quality of the semiconductor substrate, particularly in the case of such a film thickness range.

[0031] The surface quality can be the quality and / or thickness of a native oxide film formed in the final cleaning of a semiconductor substrate. In particular, the quality of the native oxide film formed in the final cleaning of a semiconductor substrate strongly affects the ratio of the thickness of a dry oxide film to the thickness of a pyrogenic oxide film, and therefore, the semiconductor substrate evaluation method according to the present invention can perform evaluation with higher accuracy.

[0032] The surface quality can also be the surface roughness of the semiconductor substrate. The cleaning conditions of the semiconductor substrate also affect the surface roughness of the semiconductor substrate. Therefore, the semiconductor substrate evaluation method according to the present invention, which uses the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film, which strongly reflects the influence of the oxide film / semiconductor interface, can also evaluate the surface roughness of the semiconductor substrate with high accuracy.

[0033] The semiconductor substrate is preferably a silicon substrate. In this case, the dry oxide film and the pyrogenic oxide film are silicon oxide films. The method for evaluating a semiconductor substrate according to the present invention is particularly effective in evaluating a silicon substrate.

[0034] The ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film may be calculated as either pyrogenic oxide film thickness / dry oxide film thickness or dry oxide film thickness / pyrogenic oxide film thickness. EXAMPLES

[0035] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

[0036] (Example) Several silicon substrates with a diameter of 300 mm and normal resistivity (approximately 10 Ωcm) doped with boron were prepared. All of the silicon substrates prepared had the same surface quality level. First, they were cleaned with 0.5% HF (common to all silicon substrates) to eliminate the effects of the natural oxide film formed on the silicon substrate surface and to initialize it. Next, they were cleaned with SC1 (NH4OH concentration: 3%) with cleaning solution temperatures of 40, 45, 50, 60, and 70°C. Several silicon substrates were cleaned for each cleaning solution temperature level.

[0037] Using silicon substrates that had been cleaned, without removing the native oxide film formed on the surface, silicon substrates were individually prepared by pyro-oxidation (700°C, N2 dilution, oxidation time: 23 min) to form pyro-oxidation films, and silicon substrates were individually prepared by dry oxidation (900°C, N2 dilution, oxidation time: 23 min) to form dry oxide films. The thermal oxide film thickness after thermal oxidation was measured at five points on the substrate surface with a spectroscopic ellipsometer to calculate the average film thickness, and the oxide film thickness at each SC1 cleaning temperature was taken as the standard with the oxide film thickness at 40°C, and the difference in the oxide film thickness at each SC1 cleaning temperature was calculated to obtain the ratio of the difference between the dry oxide film thickness and the pyrogenic oxide film thickness (pyrogenic oxide film thickness / dry oxide film thickness), and the effect of the SC1 cleaning temperature on the ratio of the dry oxide film thickness and the pyrogenic oxide film thickness was investigated. As a result, it was found that the ratio of the dry oxide film thickness and the pyrogenic oxide film thickness changes depending on the SC1 cleaning temperature, as shown in Figure 1.

[0038] It is considered that the SC1 cleaning temperature affects the roughness of the silicon substrate surface and the quality of the natural oxide film formed on the silicon substrate surface by cleaning. As shown in this embodiment, the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film (pyro-oxide film thickness / dry oxide film thickness in this embodiment), which can be measured and calculated from a silicon substrate that has been dry-oxidized without removing the natural oxide film and a silicon substrate that has been pyro-oxidized without removing the natural oxide film, can reflect the difference in the surface quality of the silicon substrate with high sensitivity. Therefore, it was found that it is possible to accurately evaluate the surface quality of the semiconductor substrate (in this embodiment, the roughness of the silicon substrate surface and the quality of the natural oxide film formed on the silicon substrate surface by cleaning) by performing an evaluation based on the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film.

[0039] Based on these results, it is also possible to estimate cleaning conditions and perform daily management of the cleaning equipment. For example, if the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film becomes different from normal, it can be determined that there is an abnormality in the temperature management of the cleaning equipment. In this example, the chemical temperature is changed for ease of understanding, but if the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film is determined and monitored as part of daily management, it is also possible to detect fluctuations in the cleaning conditions.

[0040] As described above, according to the embodiment of the present invention, it was found that the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film reflects the fluctuation of the SC1 cleaning conditions (temperature) with high accuracy. It was found that the quality of the semiconductor substrate can be evaluated with high accuracy by using the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film. It was also found that by using this, the effect of the change in the cleaning conditions can be evaluated with high accuracy, and it can be applied to the management of the cleaning process and the cleaning machine. Furthermore, it is considered possible to evaluate the change in the surface quality of the semiconductor substrate, which could not be measured and evaluated by the conventional method.

[0041] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention.

Claims

1. A method for evaluating a semiconductor substrate, comprising: preparing a plurality of semiconductor substrates having the same surface quality level as semiconductor substrates to be evaluated, cleaning the plurality of semiconductor substrates under the same cleaning conditions, and individually preparing, from the plurality of semiconductor substrates, a semiconductor substrate on which a dry oxide film is formed by dry oxidation without removing a native oxide film formed by the cleaning, and a semiconductor substrate on which a pyrogenic oxide film is formed by pyrogenic oxidation without removing a native oxide film formed by the cleaning, A method for evaluating a semiconductor substrate, comprising: evaluating a surface quality of the semiconductor substrate based on a ratio of a thickness of the dry oxide film to a thickness of the pyrogenic oxide film.

2. 2. The method for evaluating a semiconductor substrate according to claim 1, wherein the film thickness of said dry oxide film and said pyrogenic oxide film is set to 0.1 to 10 nm.

3. 3. The method for evaluating a semiconductor substrate according to claim 1, wherein the surface quality is determined as a film quality and / or a thickness of a native oxide film formed in a final cleaning of the semiconductor substrate.

4. 3. The method for evaluating a semiconductor substrate according to claim 1, wherein the surface quality is a surface roughness of the semiconductor substrate.

5. 5. The method for evaluating a semiconductor substrate according to claim 1, wherein the semiconductor substrate is a silicon substrate, and the dry oxide film and the pyrogenic oxide film are silicon oxide films.

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