TW201740079A - Film-thickness-distribution measuring method - Google Patents

Abstract

The present invention provides a film-thickness-distribution measuring method for measuring, by way of reflectance spectroscopy using a line light source, a film thickness distribution of a thin film or films of a thin-film-coated wafer having at least one thin-film layer formed on a surface of a substrate, the film-thickness-distribution measuring method including: a step, executed simultaneously when scanning the surface of the thin-film-coated wafer with a beam of light radiated from a line light source and detecting reflected light by using a line light source having a light source longer than the diameter of the thin-film-coated wafer as the line light source, for irradiating a reference with a portion of the beam of light and also detecting light reflected therefrom; a step for correcting the intensity of light reflected from the thin-film-coated wafer by using the intensity of the light reflected from the reference; and a step for calculating a film thickness distribution from the corrected intensity of the light reflected from the thin-film-coated wafer. This provides a film-thickness-distribution measuring method that enables stable and precise film-thickness-distribution measurement when a film thickness distribution of a thin-film-coated wafer is measured by way of reflectance spectroscopy using a line light source.

Description

Film thickness distribution detection method

The present invention relates to a film thickness distribution measuring method for measuring a film thickness distribution of a film with a thin film wafer having at least one film.

In recent years, with the miniaturization of design rules, SOI devices such as Fully Depleted SOI (FD-SOI) devices, FinFET devices, and nanowire transistors have been used, especially in demand. An SOI wafer having an extremely thin film SOI layer having a uniform film thickness has begun to be used. In such devices, the film thickness of the SOI layer and the uniformity of the film thickness of the buried oxide film (hereinafter referred to as BOX film) are important items in determining the characteristics of the crystal.

As a method of measuring the film thickness of a film with a thin film wafer such as an SOI wafer, there is a reflection spectroscopy method. A conventional reflection spectroscopy method is to irradiate light to a film with a thin film wafer, and to split the reflected light by a spectrometer to obtain a spectrum of the reflected light. Next, the interference from the reflected light from the surface of the film and the inner surface utilizes a change in optical path difference (OPD) depending on the wavelength and the thickness of the film, and uses the peak wavelength in the spectrum. Or the value of the refractive index of the film or the like, and the thickness of the film is calculated. However, in such a reflection spectroscopy, since the measurement of the entire surface of the wafer is performed with high precision, the number of measurement points is extremely increased, and a large amount of calculation and time are required, so that it is impossible to measure the entire surface in reality. .

On the other hand, the method described in Patent Document 1 is a method in which the thickness of the overcoat film of the measurement target having a film (film) on the surface is measured two-dimensionally with a higher throughput. In this method, linear light is irradiated on the surface of the measurement object, and the reflected light from the irradiation region of the linear light is split by a spectrometer (imaging spectrometer) that can perform spectroscopic analysis by continuously maintaining position information. Together, the thickness of the tomographic film in the irradiation region of the linear light is calculated together. Further, by continuously repeating the irradiation region in a direction perpendicular to the irradiation region of the linear light, and calculating the thickness of the film in the irradiation region together, the thickness of the film on the object to be measured is repeated. The measurement of the secondary element was performed.

Further, as a method for measuring a film thickness distribution capable of measuring a film thickness distribution over the entire surface of a thin film wafer such as an SOI wafer with high precision and high throughput, it is proposed to measure crystal by reflection spectroscopy using a line source. Method for measuring film thickness distribution of film thickness distribution on a full surface of a circle (Patent Document 2).

According to the method of Patent Document 2, in the film thickness distribution measuring apparatus 10 shown in Fig. 8, the incident angle from the incident light from the line light source 11 reflected by the thin film and detected by the detector 13 can be used. The geometric deviation is corrected, and the overall film thickness distribution of the film-coated wafer 3 is measured with high precision and high throughput. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] JP-A-2000-314612 (Patent Document 2) JP-A-2015-17804

However, even in the case of using the film thickness distribution measuring method using the reflection spectroscopy method using a line light source such as Patent Document 2, there are light sources, detection systems, optical systems, and the like (hereinafter, these are collectively referred to as In order to measure the temporal variation of the overall reflected light intensity caused by the measurement system, the stability, reproducibility, and repeated measurement accuracy of the film thickness measurement are insufficient. In particular, the SOI layer and the BOX layer of the SOI wafer for the ultra-thin film used for the highest-end device are required to have higher film thickness measurement accuracy than conventional ones, and thus the conventional film thickness distribution measurement method cannot be sufficiently satisfied. These requirements.

In view of the above problems, an object of the present invention is to provide a method for measuring a film thickness distribution, which can be stably and accurately measured by using a reflection spectroscopy method using a line source to measure a film thickness distribution of a film-coated wafer. Determination of film thickness distribution.

In order to achieve the above object, the present invention provides a film thickness distribution measuring method for measuring a film thickness distribution of a film having a film-formed wafer having at least one film formed on a surface of a substrate by a reflectance spectroscopy using a line source, The film thickness distribution measuring method comprises the steps of: using a line light source having a light source longer than the film-coated wafer as the line light source; and scanning the strip with linear light irradiated from the line light source While detecting the reflected light on the surface of the thin film wafer, a part of the linear light is irradiated onto the reference member to detect the reflected light; and the intensity of the reflected light from the reference member is used to face the film from the thin film. The intensity of the reflected light of the circle is corrected; the film thickness distribution is calculated based on the intensity of the reflected light of the modified film-coated wafer.

In this manner, a line source having a light source having a longer diameter than the film-coated wafer is used, and the reflected light from the film-coated wafer and the reference member is simultaneously detected and caused by the measurement system of the measuring device. The change in the intensity of the entire reflected light is corrected to calculate the film thickness distribution of the film, and the film thickness distribution measurement of the film-coated wafer can be performed stably and accurately.

At this time, preferably, as the reference member, a mirror-polished single crystal germanium wafer is used.

Such a mirror-polished single crystal germanium wafer can be suitably used as a reference member because of its extremely flat surface and extremely high reflectance in the surface.

In this case, preferably, the reference member is fixedly disposed on both sides of the linear illumination region of the line source, and the reference film is fixedly disposed to move the film-coated wafer through the two reference members that are separated by phase separation. The surface of the film-coated wafer is scanned with the linear light.

In this way, the reference members are disposed on both sides of the film-coated wafer, and the intensity of the reflected light from the reference members on both sides is used, and the intensity of the reflected light from the film-coated wafer is corrected to more reliably suppress the measurement. The influence of the fluctuation of the overall reflected light intensity caused by the measurement of the device. Thereby, the film thickness distribution measurement of the film-coated wafer can be performed more stably and with higher precision.

In this case, preferably, the reference member is fixedly disposed on both sides of the linear illumination region of the line source, and is disposed between the two separated reference members. The thin film wafer is disposed at a position where the linear light overlaps with the diameter of the thin film wafer, and the strip film is rotated by the center of the film, and the strip film is scanned by the linear light. The surface of the wafer.

In this way, the film-coated wafer disposed between the two phase-separated reference sheets is scanned by scanning the surface of the film-coated wafer by rotating at the center thereof, and then maintaining two separated phases. At the same time as the measurement accuracy of the movement between the reference members, the occupied area for measuring the film thickness distribution can be reduced by nearly half. Further, by using the scanning method using the wafer rotating mechanism as described above, it is possible to easily incorporate the film thickness distribution measuring function using the line light source into another device having a wafer rotating mechanism such as an aligner. Thereby, the installation area of the apparatus in the clean room can be reduced, and the clean room can be effectively used.

At this time, preferably, the correction of the intensity of the reflected light is performed for the wavelength of each of the reflected lights used when calculating the film thickness distribution.

As described above, by correcting the reflected light intensity for the wavelength of each of the reflected lights used for calculating the film thickness distribution, it is possible to perform film thickness distribution measurement with higher accuracy.

As described above, by the film thickness distribution measuring method of the present invention, the intensity of reflected light from a line source having a light source having a relatively long diameter with a thin film wafer can be detected with a reference member, and the intensity of reflected light from the reference member can be used. By correcting the intensity of the reflected light from the film-coated wafer, the film thickness distribution of the film with the thin film wafer can be measured stably and accurately.

Hereinafter, the present invention will be described in detail with reference to the drawings as an example, but the invention is not limited thereto.

First, the film thickness distribution measuring method of the present invention will be described with reference to Figs. 1 and 2 .

Fig. 1 is a schematic view showing an example of an embodiment of a method for measuring a film thickness distribution of the present invention (a view seen from a substantial portion), and Fig. 2 is a flow chart showing the steps of a method for measuring a film thickness distribution of the present invention. The film thickness distribution measuring method of the present invention is a method for measuring a film thickness distribution of a film of a film-coated wafer having at least one film formed on a surface of a substrate by a reflectance spectroscopy using a line source. As the line light source, various types of illuminants can be used as long as they can emit linear light.

In the film thickness distribution measuring method of the present invention, as shown in Fig. 1, as the line light source, a line light source 1 (A of Fig. 2) having a light source having a longer diameter than the film-coated wafer 3 is used. Further, the film thickness distribution measuring method of the present invention comprises the steps of: scanning the surface of the film-coated wafer 3 with the linear light 4 irradiated from the line light source 1 to detect the reflected light while linearly detecting A part of the light 4 is irradiated onto the reference member 2 to detect the reflected light (B of FIG. 2); and the intensity of the reflected light from the coated film 3 is corrected using the intensity of the reflected light from the reference member 2 ( C) of Fig. 2; the film thickness distribution (D of Fig. 2) is calculated based on the intensity of the reflected light of the modified film-coated wafer 3.

Here, in the case where the surface of the film-coated wafer 3 is scanned with the linear light 4 emitted from the line light source 1, the line light source 1 and the reference member 2 are fixed in the first drawing to make the tape The thin film wafer 3 is scanned with respect to the line light source 1 and the reference member 2 to perform linear light 4 scanning. However, the thin film wafer 3 may be fixed, and the line light source 1 and the reference member 2 may be moved relative to the film-coated wafer 3 to scan linear light.

Thus, the line source 1 having a light source having a longer diameter than the film-coated wafer 3 is used, and the reflected light from the film-coated wafer 3 and the reference member 2 is simultaneously detected, and by the film-derived wafer 3 The variation in the intensity of the reflected light is corrected to calculate the film thickness distribution of the film, and the film thickness distribution of the film-coated wafer 3 can be measured stably and accurately. In addition, the method of the present invention can measure the film thickness distribution of the entire surface of the wafer with the thin film wafer 3.

Further, preferably, as the reference member 2, a mirror-polished single crystal germanium wafer is used. The mirror-polished single crystal germanium wafer produced by manufacturing a semiconductor device has an extremely flat surface, and is suitable as the reference member 2 because of the high uniformity of reflectance in the surface. Specifically, for example, a mirror-polished single crystal germanium wafer having a diameter of 125 mm can be used as the reference member 2.

Further, as the reference member 2, it is preferable that the reflectance of the surface is uniform, and the amount of the reflectance in the surface is preferably within 1%. If the reflectance of the surface is uniform, even if the positional relationship between the reference member 2 and the line light source 1 is slightly deviated, the intensity of the reflected light from the reference member 2 hardly changes. The correction of the intensity of the reflected light with the thin film wafer 3 can always be performed extremely accurately. Further, as the reference material 2, if the reflectance of the surface is appropriate, it is not limited to a single crystal germanium wafer, and other semiconductor wafers or other materials can be used.

Further, as shown in Fig. 1, preferably, each of the reference members 2 is fixedly disposed on both sides in the linear irradiation region 4 of the line light source 1, and the film-coated wafer 3 is moved and passed. Between the two reference members 2 separated by phase, the surface of the film-coated wafer 3 is scanned with linear light 4.

In this manner, in the state where the reference member 2 is disposed on both sides of the thin film-formed wafer 3 to be measured, the reflected light from the thin film-formed wafer 3 and the reference member 2 is simultaneously detected, for example, from both sides. The average value of the reflected light intensity of the reference member 2 is corrected based on the intensity of the reflected light from the film-coated wafer 3, and the intensity of the reflected light from the film-coated wafer 3 can be sufficiently suppressed. The impact of changes in time.

However, when the reference member 2 is disposed in the linear irradiation region 4 of the line light source 1 and the linear light from the line light source 1 is scanned with the thin film wafer 3, the reference piece 2 can be detected at the same time. For those who reflect light, there are no special restrictions on their configuration and size. For example, in the case of measuring the film thickness distribution of the film of the large-diameter film-coated wafer 3 having a diameter of more than 300 mm, the length of the line light source 1 is extremely long since the reference member 2 is disposed on both sides of the film-coated wafer 3. Therefore, as shown in FIG. 3, the reference member 2 can be disposed only on one side of the film-coated wafer 3, and the length of the line light source 1 can be suppressed. In addition, the shape of the reference member 2 may also be a square shape or other shapes. Further, since the reference member 2 can measure the reflected light when a part of the linear light 4 is irradiated, the linear light 4 as in the first embodiment may be configured to straddle the reference member 2 or may be The end of the linear light 4 is located on the surface of the reference member 2.

Further, as shown in Fig. 9, the film thickness distribution measuring method of the present invention may be disposed on both sides of the linear irradiation region of the line light source 1 so as to be separated from each other, and each of the reference members 2 is fixedly disposed. Between the two separated reference members 2, the film-coated wafer 3 is disposed at a position where the diameter of the linear light 4 and the thin film-formed wafer 3 overlap, by making the film-coated wafer 3 centered on the center thereof. Rotation is performed, and the surface of the film-coated wafer 3 is scanned with linear light 4.

In this manner, when the film-coated wafer 3 is rotated about the center of the film-coated wafer 3 and the surface of the film-coated wafer 3 is scanned, the two films which are separated from the film-coated wafer 3 shown in FIG. 1 are maintained. The same measurement accuracy can be obtained while scanning the straight line between the reference members 2, and the size of the device for measurement can be greatly reduced as described below.

In the film thickness distribution measuring apparatus to which the film thickness distribution measuring method of the present invention is applied, the film-formed wafer 3 is supported and moved or rotated for scanning the entire surface of the linear light 4 to measure the film thickness distribution. The part is called the measuring part. In the case where the linear light 4 is linearly scanned, in the first drawing, in order to scan the lower end to the upper end of the thin film wafer 3 by the linear light 4, at least the linear light 4 must be used. A measurement unit having a space with a thin film wafer on the upper and lower sides. On the other hand, in the case where the film-formed wafer 3 is rotated and scanned, it is only necessary to have a space for the film-formed wafer in the area occupied by the measuring unit, and the measuring unit can be made more than the state of the linear scanning. The area occupied has been reduced by nearly half.

In addition, by using a scanning method using the wafer rotating mechanism described above, it is possible to easily incorporate a film thickness distribution measuring device (function) using a line light source into a wafer rotating mechanism having an aligner or the like. Other devices (manufacturing device, inspection device, evaluation device). Thereby, the installation area of the apparatus in the clean room can be reduced, and the clean room can be effectively used.

Further, in the film thickness distribution measuring method of the present invention, preferably, the correction of the reflected light intensity is performed for the wavelength of each of the reflected lights used for calculating the film thickness distribution.

The correction of the reflected light intensity is the easiest to perform the total wavelength of the linear four irradiated with the thin film wafer 3, and the film thickness measurement (calculation) time is also shortened. In addition, by correcting the intensity of the reflected light for the wavelength of each of the reflected lights used in calculating the film thickness distribution, the wavelength distribution of the light source can be varied, and the film thickness distribution of the film can be further improved. The accuracy of the measurement.

In this case, when the correction of each wavelength is performed, for example, when the reflected light from each point on the wafer is detected by the CCD, the reflected light from each point is split by the spectrometer to separate the wavelength component, and the light is separated. For example, in each vertical pixel of the CCD, each pixel in the vertical direction is configured to receive light of a certain wavelength (range), and correction can be performed for each pixel. At this time, the amount of calculation can also be reduced by using an average value of several pixels corresponding to a certain wavelength range. [Examples]

Hereinafter, the present invention will be more specifically described by showing examples and comparative examples, but the present invention is not limited to the examples.

(Example) A thin film SOI wafer (diameter 300 mm, SOI layer film thickness: 88 nm, BOX layer film thickness: 145 nm) prepared by ion implantation stripping method, and two film thicknesses were set film thicknesses at the time of SOI wafer fabrication As the film-coated wafer 3 for film thickness measurement, the film thickness distribution of the SOI layer and the film thickness distribution of the BOX layer were measured by the film thickness distribution measuring method of the present invention. The film thickness distribution measurement was repeated 30 times on the same thin film SOI wafer.

At this time, as the reference material 2, the mirror-polished single crystal germanium wafer (diameter 125 mm) was disposed to be separated from each other on both sides in the linear irradiation region 4 of Fig. 1 . Next, in a state where the linear irradiation region 4 of the line light source 1 and the two reference wafers are fixed, the thin film SOI wafer is perpendicular to the linear direction of the irradiation region between the two reference wafers. Ground scan (moving).

As the line light source 1, a visible light source having a wavelength band of 450 to 750 nm was used, and the film thickness of the entire surface of the thin film SOI wafer was measured at a pitch of 1 mm to calculate an average value in the surface. At this time, the reflected light intensity of the entire wavelength band of 450 to 750 nm is detected for the intensity of the reflected light at each measurement point of the region irradiated by the linear light 4 on the thin film SOI wafer, and the intensity of the reflected light is used. The average value of the reflected light intensity of the two reference wafers simultaneously irradiated on the same line is corrected, and the film thickness distribution of the film is calculated using the corrected reflected light intensity.

Based on the film thickness (film thickness distribution) of the SOI layer and the BOX layer thus calculated, the obtained film surface in-film thickness was determined as the film thickness of each. The relationship between the number of measurements (first to 30th) in the measurement of the film thickness distribution repeated 30 times and the film thickness of each time is shown in Fig. 4 (SOI layer) and Fig. 5 (BOX layer).

In the measurement in which the film thickness of the SOI layer shown in FIG. 4 was repeated 30 times, there was no tendency for the average film thickness to fluctuate in a certain direction, and the difference between the maximum value and the minimum value of the repeated measurement was only about 0.07 nm. The value of the film thickness of the extremely stable SOI layer was obtained by 30 measurements. According to this case, the measurement accuracy of each film thickness can also be referred to as high.

Further, in the measurement in which the film thickness of the BOX layer shown in Fig. 5 was repeated 30 times, the film thickness did not tend to fluctuate in a certain direction, and the difference between the maximum value and the minimum value of the repeated measurement was extremely small. A value of about 0.46 nm was obtained by measuring 30 times to obtain a stable film thickness of the BOX layer. Therefore, it can also be said that the measurement accuracy of each film thickness is high.

(Comparative Example) The film thickness of the SOI layer and the film thickness of the BOX layer were measured 30 times using the same thin film SOI wafer as used in the examples. At this time, the reference wafer used in the embodiment is not disposed. Therefore, the detection of the reflected light from the reference member and the correction of the reflected light intensity of the thin film SOI wafer are not performed.

The same procedure as in the example was carried out, and the relationship between the number of measurements and the film thickness of each of the SOI layer and the BOX layer was determined, and the relationship was shown in FIGS. 6 and 7 respectively.

In the measurement of the film thickness of the SOI layer shown in FIG. 6 repeated 30 times, the film thickness of the SOI layer fluctuated in the increasing direction as the number of times of measurement progressed, and the maximum value and the minimum value of the repeated measurement were repeated. The difference is about 0.47 nm. This value is very large compared to the examples, so that it is difficult to perform stable film thickness measurement.

Further, in the measurement of the film thickness of the BOX layer shown in Fig. 7 repeated 30 times, the film thickness of the BOX layer fluctuated in the decreasing direction as the number of times of measurement progressed, and the maximum value and the minimum of the repeated measurement were repeated. The difference in values reached approximately 2.9 nm. This value is also very large compared to the examples, so that it is difficult to perform stable film thickness measurement.

From this, it can be confirmed that the stability, reproducibility, and repeatability of the measurement of the film thickness distribution can be improved by the film thickness distribution measuring method of the present invention as compared with the prior art.

Further, the present invention is not limited by the foregoing embodiments. The above-described embodiments are exemplified, and have substantially the same configuration as the technical idea described in the patent application scope of the present invention, and the same effects are achieved in the technical scope of the present invention.

1, 11‧‧‧ line source
2‧‧‧ Reference parts
3‧‧‧With thin film wafer
4‧‧‧Linear light
10‧‧‧ Film thickness distribution measuring device
13‧‧‧Detector

[Fig. 1] is a schematic view showing an example of an embodiment of a method for measuring a film thickness distribution of the present invention. [Fig. 2] A flow chart showing the steps of the method for measuring the film thickness distribution of the present invention. [Fig. 3] is a schematic view showing another example of the embodiment of the film thickness distribution measuring method of the present invention. [Fig. 4] is a graph showing the relationship between the film thickness of the SOI layer of the SOI wafer of the example and the number of times of measurement. [Fig. 5] is a graph showing the relationship between the film thickness of the BOX layer of the SOI wafer of the example and the number of times of measurement. [Fig. 6] is a graph showing the relationship between the film thickness of the SOI layer of the SOI wafer of the comparative example and the number of times of measurement. [Fig. 7] is a graph showing the relationship between the film thickness of the BOX layer of the SOI wafer of the comparative example and the number of times of measurement. [Fig. 8] is a schematic view showing an example of a film thickness distribution measuring apparatus by a reflection spectroscopic method using a conventional line source. [Fig. 9] is a schematic view showing still another example of the embodiment of the film thickness distribution measuring method of the present invention.

1‧‧‧ line source

2‧‧‧ Reference parts

3‧‧‧With thin film wafer

4‧‧‧Linear light

Claims (7)

A film thickness distribution measuring method for measuring a film thickness distribution of a film having a film-formed wafer having at least one film formed on a surface of a substrate by a reflectance spectroscopy using a line source, the film thickness distribution measuring method comprising the following steps : using a line light source having a light source longer than the thin film wafer as the line light source; scanning the surface of the thin film wafer with the linear light irradiated from the line light source to reflect light At the time of detection, a part of the linear light is simultaneously irradiated to the reference member to detect the reflected light; and the intensity of the reflected light from the referenced member is used to correct the intensity of the reflected light from the film-coated wafer; The corrected light intensity of the film-coated wafer is calculated to calculate the film thickness distribution. The film thickness distribution measuring method according to claim 1, wherein as the reference member, a mirror-polished single crystal germanium wafer is used. The method for measuring a film thickness distribution according to claim 1, wherein the reference member is fixedly disposed on both sides of the linear irradiation region of the line source, and the film-coated wafer is moved and passed. Between the two reference members that are separated by phase, the surface of the film-coated wafer is scanned with the linear light. The film thickness distribution measuring method according to claim 2, wherein the reference member is fixedly disposed on both sides of the linear irradiation region of the line source, and the film-coated wafer is moved to pass through Between the two reference members separated by phase, the surface of the film-coated wafer is scanned with the linear light. The method for measuring a film thickness distribution according to claim 1, wherein the reference member is fixedly disposed on both sides of the linear irradiation region of the line source, and the reference member is fixedly disposed, and the two phases are separated from each other. Between the members, the thin film wafer is disposed at a position where the linear light and the diameter of the thin film wafer overlap, and the thin film wafer is rotated about the center of the film. The light is scanned across the surface of the film-coated wafer. The method for measuring a film thickness distribution according to claim 2, wherein two of the reference members are fixedly disposed on both sides in the linear irradiation region of the line source, and the two reference portions are separated from each other. Between the members, the thin film wafer is disposed at a position where the linear light and the diameter of the thin film wafer overlap, and the thin film wafer is rotated about the center of the film. The light is scanned across the surface of the film-coated wafer. The film thickness distribution measuring method according to any one of claims 1 to 6, wherein the correction of the intensity of the reflected light is performed for calculating a wavelength of each of the reflected lights used when the film thickness distribution is calculated.