Semiconductor substrate evaluation method

Abstract

To provide a semiconductor substrate evaluation method capable of highly accurately evaluating the surface quality of a semiconductor substrate from differences between film thicknesses of thermal oxide films.SOLUTION: A semiconductor substrate evaluation method forms a pyrogenic oxide film on a surface of the semiconductor substrate by subjecting the semiconductor substrate to pyrogenic oxidation without removing a natural oxide film formed on the surface of the semiconductor substrate, and evaluates the surface quality of the semiconductor substrate on the basis of a film thickness of the pyrogenic oxidation 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 has revealed that, for example, when the cleaning method of a semiconductor substrate is different, the thickness of the thermally oxidized film after the thermal oxidation differs. Furthermore, there are concerns that the difference in the oxide film after the thermal oxidation may cause problems such as variations in the characteristics of semiconductor integrated circuit elements and a decrease in yield. It has also been found that the difference in the film thickness does not necessarily depend on the native oxide film thickness before the thermal oxidation (Patent Documents 2 and 3).

[0006] However, this difference in thickness of the thermal oxide film is very small, and in order to determine whether the variation is due to external disturbances or to the surface quality of the substrate, a method is needed to make the difference in thickness of the thermal oxide film larger and more clear.

[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 can evaluate the surface quality of a semiconductor substrate with high accuracy based on differences in the thickness of a thermal oxide film. [Means for solving the problem]

[0008] The present invention has been made to achieve the above-mentioned object, and provides a method for evaluating a semiconductor substrate, comprising the steps of: pyrogenically oxidizing the semiconductor substrate to form a pyrogenic oxide film on the surface of the semiconductor substrate without removing a native oxide film formed on the surface of the semiconductor substrate; and evaluating the surface quality of the semiconductor substrate based on 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 difference in thickness of the thermal oxide film.

[0010] In this case, the pyrogenic oxide film may have a thickness of 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 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 pyrogenic oxide film may be a silicon oxide film.

[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 can provide a semiconductor substrate evaluation method that can accurately evaluate the surface quality of a semiconductor substrate based on the difference in the thickness of the thermal 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] 1 shows the relationship between the SC1 cleaning temperature and the thickness of the thermal oxide film in an example and a comparative example. 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 of evaluating a semiconductor substrate that can accurately evaluate the surface quality of the semiconductor substrate based on differences in the thickness of the thermal oxide film.

[0020] As a result of intensive research into the above-mentioned problems, the inventors have discovered that the surface quality of a semiconductor substrate can be evaluated with high accuracy by a method for evaluating a semiconductor substrate, which comprises pyrogenically oxidizing the semiconductor substrate to form a pyrogenic oxide film on the surface of the semiconductor substrate without removing a native oxide film formed on the surface of the semiconductor substrate, and evaluating the surface quality of the semiconductor substrate based on the thickness of the pyrogenic oxide film, and have completed 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 the 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 inventors further investigated and compared thermal oxidation methods, particularly dry oxidation and pyrogenic oxidation, and found that the thickness of the oxide film formed by pyrogenic oxidation is more strongly affected by the cleaning conditions of the semiconductor substrate. This is because, as mentioned above, a thin oxide film is strongly affected by the oxide film / semiconductor interface in addition to the diffusion of oxidizing species.

[0028] The present inventors have conceived the idea that the surface quality of a semiconductor substrate can be evaluated with high accuracy by oxidizing a semiconductor substrate having a native oxide film by a heat treatment method for the semiconductor substrate that increases the difference in thickness of the thermal oxide film, which is influenced by the difference in surface quality of the semiconductor substrate, i.e., by pyrogenic oxidation that is likely to reflect the influence of the film quality of the native oxide film.The present inventors have then found that it is possible to form a pyrogenic oxide film on the surface of the semiconductor substrate by pyrogenic oxidation without removing the native oxide film formed on the surface of the semiconductor substrate, and to evaluate the surface quality of the semiconductor substrate with high accuracy based on the thickness of the pyrogenic oxide film.

[0029] For example, a standard thickness of a pyrogenic oxide film is set, and a change in the surface quality of a semiconductor substrate can be grasped by comparing with this standard value.

[0030] 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 quality of the semiconductor substrate. As shown in the examples described later, the change in film thickness due to pyrogenic oxidation reflects the change 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 treating normal products and grasping the transition in the thickness of the thermal oxide film, it is possible to detect changes in the cleaning conditions and the occurrence of abnormalities.

[0031] In addition, the thickness of the pyrogenic oxide film is preferably 1 to 10 nm, taking into consideration the influence on thinning of semiconductor integrated circuit elements. The semiconductor substrate evaluation method according to the present invention can more accurately evaluate the surface quality of the semiconductor substrate, particularly when the thickness is in such a thin range.

[0032] The surface quality can be the quality and / or thickness of a native oxide film formed in the final cleaning of the semiconductor substrate. In particular, the method for evaluating a semiconductor substrate according to the present invention can perform more accurate evaluation because the quality of the native oxide film formed in the final cleaning of the semiconductor substrate strongly affects the thickness of the oxide film formed by pyrogenic oxidation.

[0033] 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 pyrogenic oxidation that more strongly reflects the influence of the oxide film / semiconductor interface, can also evaluate the surface roughness of the semiconductor substrate with high accuracy.

[0034] The semiconductor substrate is preferably a silicon substrate. In this case, the pyrogenic oxide film is a silicon oxide film. The method for evaluating a semiconductor substrate according to the present invention is particularly effective in evaluating a silicon substrate. EXAMPLES

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

[0036] (Example) A boron-doped silicon substrate with a diameter of 300 mm and normal resistivity (approximately 10 Ω cm) was prepared. After cleaning with 0.5% HF to eliminate the influence of the natural oxide film formed on the silicon substrate surface and to initialize it, SC1 cleaning (NH4OH concentration: 3%) was performed with the cleaning solution temperatures set to 40, 45, 50, 60, and 70°C.

[0037] After this, these silicon substrates were thermally oxidized by pyro-oxidation (700°C, N2 dilution, oxidation time: 23 minutes) to form a thermal oxide film. The thermal oxide film thickness after thermal oxidation was measured at five points on the substrate with a spectroscopic ellipsometer to evaluate the effect of the SC1 cleaning temperature on the thermal oxide film thickness. As a result, as shown in Figure 1 (plot of the average of the five points on the substrate and the maximum (MAX) and minimum (MIN)), it was found that the higher the SC1 cleaning temperature, the thicker the thermal oxide film became.

[0038] It is believed 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, when pyro-oxidation is performed without removing the natural oxide film, the thickness of the pyro-oxidation film can sensitively reflect the difference in quality, so 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 thickness of the pyro-oxidation film.

[0039] Based on these results, it is possible to perform daily management of the cleaning equipment. In other words, if the oxide film thickness becomes different from normal, it is clear 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 oxide film thickness is determined and monitored for daily management, fluctuations in the cleaning conditions can be detected.

[0040] (Comparative Example) A boron-doped silicon substrate with a diameter of 300 mm and normal resistivity (approximately 10 Ωcm) was prepared. The silicon substrate surface was washed with 0.5% HF for initialization, and then washed with SC1 (NH4OH concentration: 3%) at a cleaning solution temperature of 40 to 70°C.

[0041] After that, these silicon substrates were thermally oxidized by dry oxidation (900°C, N2 dilution, oxidation time: 23 minutes) to form a thermal oxide film. The thermal oxide film thickness after thermal oxidation was measured at five points on the substrate with a spectroscopic ellipsometer to evaluate the effect of the SC1 cleaning temperature on the thermal oxide film thickness. As a result, as shown in FIG. 1 (plot of the average of the five points on the substrate and the maximum (MAX) and minimum (MIN)), the thermal oxide film thickness tended to increase as the SC1 cleaning temperature increased, but the difference in the thermal oxide film thickness due to the SC1 cleaning temperature was smaller than that in the pyro-oxidation of the embodiment. As shown in FIG. 1, in the comparative example, it is clear that there is a difference in the oxide film thickness due to the chemical solution temperature, but when the variation in the substrate surface during oxidation is taken into account, the effect of the chemical solution temperature becomes smaller and the difference is unclear.

[0042] Thus, in the comparative example in which dry oxidation was performed instead of the pyro-oxidation of the embodiment, the change in the thickness of the dry oxide film relative to the change in the quality of the silicon substrate surface was small, and it was found that the accuracy of the evaluation of the silicon substrate surface was low.

[0043] As described above, according to the embodiment of the present invention, it was found that the thickness of the thermal oxide film (pyro-oxide film) formed by pyro-oxidation accurately reflects the fluctuations in the SC1 cleaning conditions (temperature). It was found that pyro-oxidation allows the quality of the semiconductor substrate to be evaluated with high accuracy, and the effects of changes in the cleaning conditions to be evaluated with even higher accuracy. It was also found that this method can be applied to the management of cleaning processes and cleaning machines. Furthermore, it is believed that it is possible to evaluate changes in the surface quality of semiconductor substrates that could not be measured or evaluated by conventional methods.

[0044] 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: A method for evaluating a semiconductor substrate, comprising: pyrogenically oxidizing a semiconductor substrate to form a pyrogenic oxide film on the surface of the semiconductor substrate without removing a native oxide film formed on the surface of the semiconductor substrate; and evaluating the surface roughness, which is the surface quality of the semiconductor substrate, based on the film thickness of the pyrogenic oxide film.

2. 2. The method for evaluating a semiconductor substrate according to claim 1, wherein the thickness of the pyrogenic oxide film is set to 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. 4. The method for evaluating a semiconductor substrate according to claim 1, wherein the semiconductor substrate is a silicon substrate, and the pyrogenic oxide film is a silicon oxide film.

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