Standard samples for film thickness measuring devices and methods for managing film thickness measuring devices

Abstract

This invention provides a standard sample for a film thickness measuring device that does not undergo oxide film growth even when left in the atmosphere for a long period of time, and a method for managing a film thickness management device using that sample. [Solution] A standard sample for a film thickness measuring device, characterized in that it includes a silicon substrate, an oxide film of a predetermined thickness formed on the silicon substrate, and a nitride film formed on the oxide film.

Description

Technical Field

[0001] The present invention relates to a standard sample for a film thickness measuring device that can be used to measure the film thickness of a thin oxide film and a method for managing the film thickness measuring device.

Background Art

[0002] A silicon oxide film formed on a semiconductor silicon substrate is a material that is not only easy to fabricate but also has strong insulating properties and is indispensable for manufacturing semiconductor devices on the silicon substrate. In particular, in recent semiconductor devices, very thin silicon oxide films of 1 nm or 5 nm (hereinafter simply referred to as oxide films) are often used.

[0003] Naturally, when such a thin oxide film is fabricated, it is necessary to guarantee its thickness. Film thickness measurement is generally performed using an ellipsometer.

[0004] At this time, in order to guarantee the measured film thickness, it is necessary to calibrate and manage the film thickness measuring device using a standard sample with a known oxide film thickness. However, it is known that a thin oxide film, for example, a 1 nm oxide film, reacts with oxygen in the air in the atmosphere and gradually becomes thicker over time. Therefore, a standard wafer that simply forms a thin oxide film on a silicon substrate is not suitable as a standard sample for guaranteeing the oxide film thickness.

[0005] This change in film thickness over time is a phenomenon peculiar to thin oxide films, and such a change over time does not occur in oxide films with a film thickness of about 20 nm. Therefore, as a standard sample for managing a film thickness measuring device, it is common to use one with a thick oxide film formed. However, in order to improve the measurement accuracy in the thin film thickness region to be actually measured, a standard sample with an oxide film thickness of 1 nm to 1 nm is desired.

[0006] Patent Document 1 discloses a set of standard samples that can stably and accurately measure oxide films and manage the film thickness measuring device, even when the oxide film thickness is very thin. However, even with this method, if stored in the air for a long period of time, the thickness of the oxide film increases, albeit more slowly than with normal cleaning treatment. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2023-112235 [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention was made to solve the above problems and aims to provide a standard sample for a film thickness measuring device that does not undergo oxide film growth even when left in the atmosphere for a long period of time, and a method for managing a film thickness measuring device using the sample. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides: The present invention provides a standard sample for a film thickness measuring device, characterized in that it includes a silicon substrate, an oxide film of a predetermined thickness formed on the silicon substrate, and a nitride film formed on the oxide film.

[0010] With such a standard sample for a film thickness measuring device, the nitride film formed on the oxide film inhibits the growth of the oxide film, so even when left in the air for a long period of time, a standard sample for a film thickness measuring device can be provided in which the oxide film does not grow.

[0011] Furthermore, the thickness of the oxide film formed on the silicon substrate may be 1 to 10 nm.

[0012] The standard sample for the film thickness measuring device of the present invention is preferable because it prevents the growth of oxide film even when the oxide film thickness is as thin as 1 to 10 nm, thereby improving the measurement accuracy in the thin film thickness region being measured.

[0013] Furthermore, it is preferable that the thickness of the nitride film formed on the oxide film of the predetermined thickness is 1 to 20 nm.

[0014] Such standard samples for film thickness measuring devices are preferable because the nitride film functions more effectively as a gas barrier film, thereby reliably inhibiting the growth of the oxide film.

[0015] Furthermore, the present invention provides a method for managing a film thickness measuring device, which involves performing daily maintenance of the device using a standard sample for the film thickness measuring device.

[0016] The standard sample for the film thickness measuring device of the present invention can be used for the daily maintenance of the film thickness measuring device because the thickness of the oxide film does not change even when left in the air for a long period of time. In other words, according to the maintenance method of the present invention, the film thickness measuring device can be managed with high accuracy over a long period of time by using the standard sample for the film thickness measuring device of the present invention as a guarantee sample.

[0017] Furthermore, the present invention is suitable for controlling the measurement of the thickness of an oxide film on a silicon substrate having an oxide film thickness of 1 to 10 nm using the aforementioned film thickness measuring device.

[0018] The standard sample for the film thickness measuring device of the present invention prevents oxide film growth even when the oxide film thickness is as thin as 1 to 10 nm, thereby improving the measurement accuracy in the thin film thickness range that is actually measured. In other words, according to the management method of the present invention, by using the standard sample for the film thickness measuring device of the present invention as a guarantee sample, the film thickness measuring device can be managed with high accuracy over a long period of time. [Effects of the Invention]

[0019] As described above, the standard sample for a film thickness measuring device of the present invention, in which a nitride film is formed on an oxide film, can be used as a standard sample for a film thickness measuring device in which the film thickness of the oxide film does not change even when left in the atmosphere for a long time. Therefore, the standard sample for a film thickness measuring device of the present invention can be used in a method for managing a film thickness measuring device in the same thickness range as the thickness range to be actually measured. Further, according to the management method of the present invention, by using the standard sample for a film thickness measuring device of the present invention as a guarantee sample, the film thickness measuring device can be managed with high precision over a long period of time.

Brief Description of the Drawings

[0020] [Figure 1] It is a schematic diagram showing an example of a standard sample for a film thickness measuring device of the present invention. [Figure 2] It is a graph showing the film thickness changes of Example 1 and Comparative Example 1. [Figure 3] It is a graph showing the film thickness changes of Example 2 and Comparative Example 2. [Figure 4] It is a graph showing the film thickness change of Comparative Example 3. [Figure 5] It is a graph showing a comparison between the present invention and thickness correction by extrapolation.

Modes for Carrying Out the Invention

[0021] As described above, there has been a demand for the development of a standard sample for a film thickness measuring device in which the growth of an oxide film does not occur even when left in the atmosphere for a long time.

[0022] As a result of intensive studies on the above problems, the present inventor has found that a standard sample for a film thickness measuring device including a silicon substrate, an oxide film having a predetermined film thickness formed on the silicon substrate, and a nitride film formed on the oxide film is a standard sample in which the growth of the oxide film does not occur even when left in the atmosphere for a long time, and the above standard sample can be used in a method for managing a film thickness measuring device, thereby completing the present invention.

[0023] In other words, the present invention is a standard sample for a film thickness measuring device, characterized in that it includes a silicon substrate, an oxide film of a predetermined thickness formed on the silicon substrate, and a nitride film formed on the oxide film.

[0024] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0025] [Standard samples for film thickness measuring devices] For example, as shown in Figure 1, the standard sample 10 for the film thickness measuring device of the present invention includes a silicon substrate 1, an oxide film 2 of a predetermined thickness formed on the silicon substrate 1, and a nitride film 3 formed on the oxide film 2.

[0026] The known mechanism for silicon oxide film growth involves oxygen atoms permeating through oxide film 2 from its surface, reaching the SiO2 / Si interface, and reacting with Si to form SiO2. Regardless of the thickness of oxide film 2, the mechanism by which oxygen reacts to form an oxide remains the same, but the growth of silicon oxide film is rate-limited by the phenomenon of oxygen passing through oxide film 2. Therefore, as the thickness of oxide film 2 increases, the oxidation reaction slows down, and oxide film 2 hardly grows at all in thick oxide films. In this mechanism, if oxygen atoms do not reach the SiO2 / Si interface, oxide film 2 will not grow. Therefore, we considered covering the surface of a thin oxide film with a substance that inhibits oxygen passage. Specifically, by covering the surface of a thin oxide film 2 with nitride film 3, a two-layer film of nitride film / oxide film / Si is formed on the silicon substrate. Nitride film 3 acts as a gas barrier film and can inhibit the growth of oxide film 2. Therefore, the standard sample 10 for the film thickness measuring device of the present invention can be a standard sample 10 for a film thickness measuring device in which no oxide film 2 grows even when left in the air for a long period of time.

[0027] The configuration of the standard sample for the film thickness measuring device of the present invention will be described in detail below.

[0028] (Silicon substrate) The silicon substrate 1 included in the standard sample 10 for the film thickness measuring device of the present invention preferably has a diameter of 50 mm to 300 mm and a thickness of 280 to 775 μm if it is circular, and the conductivity type may be either P-type or N-type, and it is preferable that the silicon substrate 1 has a resistivity of 0.005 to 1000 Ω·cm. However, the shape of the silicon substrate 1 used is not particularly limited as long as the thickness of the oxide film 2 formed on the silicon substrate 1 can be measured with an ellipsometer.

[0029] (Oxide film) The oxide film 2 included in the standard sample 10 for the film thickness measuring device of the present invention preferably has an oxide film thickness of 1 nm to 10 nm. The oxide film 2 can be formed, for example, by heat-treating a bare silicon substrate 1. The heat treatment conditions are a temperature of 600°C to 1100°C, a time of 10 minutes to 600 minutes, and an oxidizing atmosphere with an oxygen concentration of 1 to 100%. For example, a 5 nm thermal oxide film can be grown by heat treatment at 800°C, dry oxidation (N2 / 13SLM, O2 / 0.6SLM), for 400 minutes.

[0030] (nitride film) The nitride film 3 included in the standard sample 10 for the film thickness measuring device of the present invention preferably has a nitride film thickness of 1 to 20 nm. The nitride film 3 can be formed, for example, by vapor deposition using CVD at a temperature of 600°C to 800°C for 10 to 600 minutes in an atmosphere of a mixed gas of ammonia and dichlorosilane. The CVD conditions can be either reduced pressure CVD or atmospheric pressure CVD. For example, a nitride film 3 of 6 nm can be formed under reduced pressure CVD conditions of 610°C / 130 minutes, NH3 flow rate of 1.2 SLM, and DCS of 0.12 SLM. As the nitride film 3, for example, Si3N4 can be used.

[0031] However, the thickness of the nitride film 3 is important, and the formation conditions are not particularly limited as long as a nitride film 3 of a predetermined thickness can be formed.

[0032] Among the CVD films that can be applied in this case, nitride films are superior in terms of film quality stability and uniformity of film thickness.

[0033] For example, in SOI where a silicon single crystal film is formed on oxide film 2, if oxide film 2 is made thin, it will change into Si during the bonding heat treatment, so the thickness of oxide film 2 needs to be 10 nm or more. Also, if a poly-Si film is formed on oxide film 2, microscopic variations in film thickness occur, making it unsuitable for standard samples.

[0034] [Management methods for film thickness measuring devices] The present invention provides a management method for a film thickness measuring device, which involves performing daily maintenance on the device using a standard sample for the present invention. Furthermore, it provides a management method for a film thickness measuring device that measures the thickness of an oxide film on a silicon substrate having an oxide film with a thickness of 1 to 10 nm.

[0035] Routine maintenance methods for film thickness measuring devices include using the same standard sample and measuring it with the device to confirm that the measurement value is the same. For long-term maintenance, a standard sample with a guaranteed constant thickness is measured, and the device is adjusted and calibrated so that the measurement value matches the guaranteed value. Standard samples for daily maintenance must be samples that do not vary from day to day, while standard samples for long-term maintenance must have a film thickness that does not change over the long term and whose film thickness is guaranteed.

[0036] In other words, samples whose film thickness changes during storage are not suitable as guarantee samples. The standard sample for the film thickness measuring device of the present invention does not change in film thickness and is therefore suitable for use as a guarantee sample. That is, according to the management method of the present invention, the film thickness measuring device can be managed over a long period of time by using the standard sample for the film thickness measuring device of the present invention as a guarantee sample. [Examples]

[0037] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to these.

[0038] [Example 1] A standard sample was prepared by forming a 1.34 nm thick oxide film on a P-type silicon substrate with a diameter of 300 mm and a resistivity of 10 Ω·cm, and then forming a 6 nm thick nitride film on top of it.

[0039] [Example 2] A standard sample was prepared by forming a 7.97 nm thick oxide film on a P-type silicon substrate with a diameter of 300 mm and a resistivity of 10 Ω·cm, and then forming a 6 nm thick nitride film on top of it.

[0040] [Comparative Example 1] A standard sample was prepared by forming an oxide film with a thickness of 1.34 nm on a P-type silicon substrate with a diameter of 300 mm and a resistivity of 10 Ω·cm.

[0041] [Comparative Example 2] A standard sample was prepared by forming an oxide film with a thickness of 7.97 nm on a P-type silicon substrate with a diameter of 300 mm and a resistivity of 10 Ω·cm.

[0042] [Comparative Example 3] A standard sample was prepared by forming a 20nm thick oxide film on a P-type silicon substrate with a diameter of 300mm and a resistivity of 10Ω·cm.

[0043] These standard samples were left in the air, and the change in oxide film thickness was measured.

[0044] The ellipsometer used at this time was a JAWoollam M-2000. Measurements were taken at a single point in the center.

[0045] Figures 2-4 show the results of measuring the oxide film thickness over 257 days in the case with a nitride film (Examples 1 and 2) and in the case without a nitride film (Comparative Examples 1-3).

[0046] The results in Figures 2 and 3 show that the oxide films without nitride coatings in Comparative Examples 1 and 2 gradually increased in thickness over time. In Comparative Example 1, a 1.34 nm oxide film was formed on a silicon substrate and left in the air. After 257 days, the oxide film became 1.57 nm thick, an increase of approximately 17%. Samples whose thickness changes over time in this manner are not suitable as standard samples. On the other hand, the thickness of the oxide films coated with nitride coatings in Examples 1 and 2 remained unchanged.

[0047] As shown in Figure 4, the thickness of the oxide film in Comparative Example 3 did not change over time. This is presumed to be because as the thickness of the oxide film increases, the oxidation reaction slows down, and in thick oxide films, the oxide film hardly grows at all.

[0048] When determining the thickness of a thin oxide film using a device calibrated with a thick oxide film, the thickness is obtained by extrapolating a constant determined by the existing calibration and applying it to the thin oxide film, but this process introduces errors. Ideally, calibration should be performed using a standard sample close to the thickness to be measured, but until now, it has been difficult to produce standard samples of thin oxide films. The standard samples for the film thickness measuring devices in Examples 1 and 2 are standard samples with constant film thickness because the oxide film thickness does not change, making them suitable for controlling thin film measurements.

[0049] When using a standard sample with only an oxide film formed on it, it is necessary to form a thick film, for example, 10-20 nm thick. In this case, when measuring the thickness of a thin oxide film, thickness correction is performed by extrapolation, and in cases where the thickness value becomes negative for particularly thin films such as 1 nm, this can occur. On the other hand, when using a standard sample in which an oxide film of the same thickness as the object to be measured, 1-10 nm, is formed and a 6 nm nitride film is formed on its surface, such thickness correction is not necessary, so no errors occur, and there is no change in oxide film thickness over time, making it an excellent standard sample for film thickness measuring devices. For example, as shown in Figure 5, it can be seen that calibration using a standard sample in which an oxide film of the same thickness as the object to be measured, 1-10 nm, is formed and a 6 nm nitride film is formed on its surface is more accurate than extrapolating the results of calibration with an oxide film of thicker than 10 nm and applying them to an oxide film of 1-10 nm.

[0050] [1]: A standard sample for a film thickness measuring device, characterized in that it includes a silicon substrate, an oxide film of a predetermined thickness formed on the silicon substrate, and a nitride film formed on the oxide film. [2]: A standard sample for a film thickness measuring device according to [1], characterized in that the thickness of the oxide film formed on the silicon substrate is 1 to 10 nm. [3]: A standard sample for a film thickness measuring device according to [1] or [2], characterized in that the film thickness of the nitride film formed on the oxide film of the predetermined thickness is 1 to 20 nm. [4]: A method for managing a film thickness measuring device, characterized by performing daily management of the film thickness measuring device using a standard sample for the film thickness measuring device described in any one of items [1] to [3]. [5]: A method for managing a film thickness measuring device according to [4], characterized in that the film thickness measuring device measures the film thickness of an oxide film on a silicon substrate having an oxide film with a film thickness of 1 to 10 nm.

[0051] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention. [Explanation of Symbols]

[0052] 1...Silicon substrate, 2...Oxide film, 3...Nitride film, 10...Standard sample for film thickness measuring device

Claims

1. A standard sample for a film thickness measuring device, characterized in that it includes a silicon substrate, an oxide film of a predetermined thickness formed on the silicon substrate, and a nitride film formed on the oxide film.

2. The standard sample for a film thickness measuring device according to claim 1, characterized in that the thickness of the oxide film formed on the silicon substrate is 1 to 10 nm.

3. The standard sample for a film thickness measuring device according to claim 1, characterized in that the film thickness of the nitride film formed on the oxide film of the predetermined thickness is 1 to 20 nm.

4. A method for managing a film thickness measuring device, characterized by performing daily management of the film thickness measuring device using a standard sample for the film thickness measuring device described in any one of claims 1 to 3.

5. The method for managing a film thickness measuring device according to claim 4, characterized in that the film thickness measuring device measures the film thickness of an oxide film on a silicon substrate having an oxide film with a film thickness of 1 to 10 nm.

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