JP2017146288A - Film thickness distribution measuring method - Google Patents

Abstract

The present invention provides a film thickness distribution measuring method capable of performing film thickness distribution measurement stably and with high accuracy when measuring the film thickness distribution of a wafer with a thin film by reflection spectroscopy using a line light source.
A film thickness distribution measuring method for measuring a film thickness distribution of a thin film with a thin film having at least one thin film formed on a surface of a substrate by reflection spectroscopy using a line light source. When using a line light source having a light source longer than the diameter of the wafer with a thin film as the line light source and detecting the reflected light by scanning the surface of the wafer with the thin film with linear light emitted from the line light source, A step of irradiating the reference 2 with a part of the linear light 4 and detecting the reflected light, a step of correcting the reflected light intensity from the wafer with a thin film using the reflected light intensity from the reference, and the correction And a step of calculating a film thickness distribution from the reflected light intensity of the wafer with a thin film.
[Selection] Figure 1

Description

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

  In recent years, with the miniaturization of design rules, an ultra-thin SOI that is used for SOI devices such as FD-SOI (Fully Depleted SOI) devices, FinFET devices, Si nanowire transistors and the like, and particularly requires high film thickness uniformity. SOI wafers with layers have begun to be used. In these devices, the uniformity of the thickness of the SOI layer and the thickness of the buried oxide film (hereinafter referred to as a BOX film) are important items in determining the characteristics of the transistor.

  As a method for measuring the thickness of a thin film of a wafer with a thin film, such as an SOI wafer, there is reflection spectroscopy. In the conventional reflection spectroscopy, the thin film of the wafer with a thin film is irradiated with light, and the reflected light is dispersed by a spectroscope to obtain the spectrum of the reflected light. Using the fact that the interference of reflected light from the front and back surfaces of the thin film changes depending on the optical path difference depending on the wavelength and the thickness of the thin film, the peak wavelength in the spectrum, the refractive index value of the thin film, etc. To calculate the thickness of the thin film. However, in such reflection spectroscopy, when the whole wafer surface is measured with high accuracy, the number of measurement points increases extremely, so a huge amount of calculation and time are required. It was impossible.

  On the other hand, there is a method described in Patent Document 1 as a method for two-dimensionally measuring the film thickness of a measurement object having a film (thin film) on the surface with higher throughput. The method uses a spectroscope (imaging spectroscope) that irradiates the surface of the measurement object with linear light, and can spectroscopically reflect the reflected light from the irradiation area of the linear light while maintaining the position information. The film thickness in the irradiation region of the linear light is collectively calculated by performing the spectroscopy. Then, by repeatedly performing the operation of collectively calculating the film thickness in the irradiation region while moving the irradiation region in the direction perpendicular to the linear light irradiation region, the film on the measurement object The film thickness is measured two-dimensionally.

  Furthermore, as a film thickness distribution measuring method capable of measuring the film thickness distribution on the entire surface of a wafer with a thin film such as an SOI wafer with high accuracy and high throughput, the film thickness distribution on the entire surface of the wafer is measured by reflection spectroscopy using a line light source. A film thickness distribution measuring method has been proposed (Patent Document 2).

  According to the method of Patent Document 2, in the film thickness distribution measuring apparatus 10 as shown in FIG. 8, the geometry of the incident angle when the incident light from the line light source 11 is reflected by the thin film and detected by the detector 13. By correcting the general deviation, the film thickness distribution on the entire surface of the wafer with thin film 3 can be measured with high accuracy and high throughput.

JP 2000-314612 A JP, 2015-17804, A

  However, even when the film thickness distribution measurement method by reflection spectroscopy using a line light source as in Patent Document 2 is used, the light source, detection system, optical system, etc. (hereinafter, these may be collectively referred to as a measurement system). ) Due to the time variation of the total reflected light intensity due to the above), the stability of film thickness measurement, reproducibility, and repeated measurement accuracy were not sufficient. In particular, extremely high film thickness measurement accuracy is required for SOI layers and BOX layers of ultra-thin SOI wafers for the production of cutting-edge devices. Conventional film thickness distribution measurement methods require these requirements. However, it was not always enough.

  The present invention has been made in view of the above problems, and when measuring the film thickness distribution of a wafer with a thin film by reflection spectroscopy using a line light source, the film thickness distribution is measured stably and with high accuracy. An object of the present invention is to provide a film thickness distribution measuring method that can be used.

In order to achieve the above object, the present invention provides a film for measuring a film thickness distribution of a thin film of a wafer with a thin film having at least one thin film formed on a surface of a substrate by reflection spectroscopy using a line light source. A thickness distribution measuring method,
As the line light source, using a line light source having a light source longer than the diameter of the wafer with the thin film,
When detecting the reflected light by scanning the surface of the wafer with thin film with the linear light emitted from the line light source, simultaneously irradiating a part of the linear light to the reference, the reflected light also Detecting step;
Correcting the reflected light intensity from the wafer with the thin film using the reflected light intensity from the reference;
And a step of calculating the film thickness distribution from the corrected reflected light intensity of the wafer with a thin film.

  In this way, using a line light source with a light source longer than the diameter of the wafer with thin film, the reflected light from the wafer with thin film and the reference is detected at the same time, and the fluctuation of the total reflected light intensity caused by the measurement system of the measuring device is detected. By correcting and calculating the film thickness distribution of the thin film, the film thickness distribution measurement of the wafer with the thin film can be performed stably and with high accuracy.

  At this time, it is preferable to use a mirror-polished silicon single crystal wafer as the reference.

  Such a mirror-polished silicon single crystal wafer has a very flat surface and has a very high uniformity of in-plane reflectivity, and thus can be suitably used as a reference.

  At this time, the reference is fixedly arranged one by one on both sides in the linear irradiation region of the line light source, and the wafer with a thin film is moved so as to pass between the two separated references. It is preferable to scan the surface of the wafer with the thin film with the linear light.

  In this way, the reference was placed on both sides of the thin film wafer, and the reflected light intensity from the reference on both sides was used to correct the reflected light intensity from the thin film wafer, resulting in the measurement system of the measuring device. It is possible to more reliably suppress the influence of fluctuations in the overall reflected light intensity. Thereby, the film thickness distribution measurement of the wafer with a thin film can be performed more stably and with higher accuracy.

  At this time, the reference is fixedly arranged separately on both sides in the linear irradiation region of the line light source, and the linear light and the thin film-attached wafer are placed between the separated references. It is preferable that the surface of the wafer with a thin film is scanned with the linear light by disposing the wafer with a thin film at a position where the diameters overlap, and rotating the wafer with a thin film around its center.

  In this way, when the surface of the wafer with a thin film placed between the two separated references is rotated about its center, the surface is scanned so that it passes between the two separated references. The area occupied for film thickness distribution measurement can be almost halved while maintaining the same measurement accuracy. In addition, by adopting a scanning method using a wafer rotation mechanism in this way, it is possible to easily incorporate a film thickness distribution measurement function using a line light source into another apparatus having a wafer rotation mechanism such as an aligner. Become. Thereby, the installation area of the device in the clean room can be reduced, and the clean room can be used effectively.

  At this time, it is preferable to correct the reflected light intensity for each wavelength of the reflected light used when calculating the film thickness distribution.

  In this way, by performing the correction of the reflected light intensity for each wavelength of the reflected light used when calculating the film thickness distribution, the film thickness distribution can be measured with higher accuracy.

  As described above, according to the film thickness distribution measuring method of the present invention, the reflected light intensity from the line light source having a light source longer than the diameter of the wafer with the thin film is detected by the reference, and the reflected light intensity from the wafer with the thin film is referred to. By correcting using the reflected light intensity from, the film thickness distribution measurement of the thin film of the wafer with the thin film can be performed stably and with high accuracy.

It is a schematic diagram which shows an example of the embodiment of the film thickness distribution measuring method of this invention. It is a figure which shows the process flow of the film thickness distribution measuring method of this invention. It is a schematic diagram which shows the other example of the embodiment of the film thickness distribution measuring method of this invention. It is a graph which shows the film thickness of the SOI layer of the SOI wafer of an Example, and the relationship of a measurement time. It is a graph which shows the film thickness of the BOX layer of the SOI wafer of an Example, and the relationship of a measurement time. It is a graph which shows the film thickness of the SOI layer of the SOI wafer of a comparative example, and the relationship of a measurement time. It is a graph which shows the film thickness of the BOX layer of the SOI wafer of a comparative example, and the relationship of a measurement time. It is the schematic which shows an example of the film thickness distribution measuring apparatus by the reflection spectroscopy using the conventional line light source. It is a schematic diagram which shows the further another example of the embodiment of the film thickness distribution measuring method of this invention.

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

  First, the film thickness distribution measuring method of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic diagram showing an example of an embodiment of the film thickness distribution measuring method of the present invention (viewed from substantially above), and FIG. 2 is a diagram showing a process flow of the film thickness measuring method of the present invention. . In the film thickness distribution measuring method of the present invention, the film thickness distribution of the thin film of the wafer with a thin film having at least one thin film formed on the surface of the substrate is measured by reflection spectroscopy using a line light source. Any line light source can be used as long as it can irradiate linear light.

  In the film thickness distribution measuring method of the present invention, as shown in FIG. 1, a line light source 1 having a light source longer than the diameter of the wafer 3 with a thin film is used as the line light source (A in FIG. 2). Furthermore, the film thickness distribution measuring method of the present invention is arranged so that the reference 2 is linear when scanning the surface of the thin film-coated wafer 3 with the linear light 4 irradiated from the line light source 1 and detecting the reflected light. Irradiating a part of the light 4 and detecting the reflected light (B in FIG. 2), correcting the reflected light intensity from the thin film-coated wafer 3 using the reflected light intensity from the reference 2 (C in FIG. 2) includes a step of calculating a film thickness distribution from the corrected reflected light intensity of the wafer with thin film 3 (D in FIG. 2).

  Here, when the surface of the wafer with thin film 3 is scanned with the linear light 4 irradiated from the line light source 1, the line light source 1 and the reference 2 are fixed in FIG. The linear light 4 is scanned by being moved with respect to 2. However, the linear light 4 may be scanned by fixing the wafer 3 with thin film and moving the line light source 1 and the reference 2 with respect to the wafer 3 with thin film.

  In this way, by using the line light source 1 having a light source longer than the diameter of the wafer with thin film 3, the reflected light from the wafer with thin film 3 and the reference 2 is simultaneously detected, and the fluctuation of the reflected light intensity from the wafer with thin film 3 is corrected. By calculating the film thickness distribution of the thin film, the film thickness distribution measurement of the wafer with thin film 3 can be performed stably and with high accuracy. Moreover, in the method of this invention, the film thickness distribution of the wafer whole surface of the wafer 3 with a thin film can be measured.

  Moreover, it is preferable to use a mirror-polished silicon single crystal wafer as the reference 2. A mirror-polished silicon single crystal wafer produced for manufacturing a semiconductor device has a very flat surface and is highly suitable for the reference 2 because of its extremely high in-plane reflectance uniformity. Specifically, for example, a mirror-polished silicon single crystal wafer having a diameter of 125 mm can be used as the reference 2.

  Further, the reference 2 preferably has a uniform surface reflectance, and more preferably has an in-plane reflectance variation of 1% or less. If the reflectance of the surface is uniform, the reflected light intensity from the reference 2 hardly changes even if the positional relationship between the reference 2 and the line light source 1 is slightly changed. The light intensity can always be corrected extremely accurately. Further, the reference 2 is not limited to a silicon single crystal wafer as long as the surface reflectance is appropriate, and other semiconductor wafers and other materials can be used.

  In addition, as shown in FIG. 1, the reference 2 is fixedly arranged one by one on both sides in the linear irradiation region 4 of the line light source 1, and the thin film-attached wafers 3 are separated from each other. It is preferable to scan the surface of the thin film-coated wafer 3 with the linear light 4 while moving so as to pass between them.

  Thus, in the state where the reference 2 is arranged on both sides of the wafer 3 with thin film to be measured, the reflected light is detected simultaneously from the wafer 3 with thin film and the reference 2, for example, reflection from the reference 2 on both sides. By calculating the average value of the light intensity and correcting the reflected light intensity from the wafer with thin film 3 on the basis of the average value, it is possible to sufficiently suppress the influence of fluctuation of the reflected light intensity from the wafer with thin film 3 on time. It becomes.

  However, the reference 2 is disposed in the linear irradiation region 4 of the line light source 1, and when the thin film-coated wafer 3 is scanned with the linear light from the line light source 1, reflected light from the reference 2 is also simultaneously generated. As long as it can be detected, its arrangement and size are not particularly limited. For example, when measuring the film thickness distribution of a thin film of a wafer 3 with a large diameter having a diameter exceeding 300 mm, the length of the line light source 1 becomes very long if the reference 2 is arranged on both sides of the wafer 3 with a thin film. As shown in FIG. 3, the length of the line light source 1 may be suppressed by arranging the reference 2 only on one side of the wafer 3 with a thin film. Further, the shape of the reference 2 may be a rectangle or another shape. Since the reference 2 only needs to be able to measure the reflected light when a part of the linear light 4 is irradiated, the linear light 4 may cross the reference 2 as shown in FIG. The end of the linear light 4 may be located on the surface of the reference 2.

  Further, in the film thickness distribution measuring method of the present invention, as shown in FIG. 9, the reference 2 is fixedly arranged separately on both sides in the linear irradiation region of the line light source 1, and the two separated Between the reference 2, the thin film-attached wafer 3 is arranged at a position where the diameter of the linear light 4 and the thin film-attached wafer 3 overlaps, and the thin film-attached wafer 3 is rotated about the center thereof to thereby form the linear light 4. The surface of the thin film-coated wafer 3 may be scanned.

  In this way, when the surface of the thin film-coated wafer 3 is rotated about its center and the surface is scanned, the thin film-coated wafer 3 shown in FIG. As will be described below, the size of the apparatus used for measurement can be greatly reduced while maintaining the same measurement accuracy as in the case of doing so.

  In a film thickness distribution measuring apparatus that can be applied to the film thickness distribution measuring method of the present invention, the thin film-coated wafer 3 is held and moved or rotated, and its entire surface is scanned with linear light 4 to measure the film thickness distribution. A portion for performing the above will be referred to as a measurement unit. When the linear light 4 is scanned linearly, in order to scan from the lower end to the upper end of the thin film-coated wafer 3 with the linear light 4 in FIG. A measuring part having a space for one wafer is required. On the other hand, when the wafer with thin film 3 is rotated and scanned, the area occupied by the measurement unit may be approximately one wafer with a thin film, so that the area occupied by the measurement unit is almost halved compared with the case of scanning linearly. can do.

  In addition, by adopting the scanning method using the wafer rotation mechanism as described above, the film thickness using a line light source for other apparatuses (manufacturing apparatus, inspection apparatus, evaluation apparatus) having a wafer rotation mechanism such as an aligner. It becomes possible to easily incorporate the distribution measuring device (function). Thereby, the installation area of the device in the clean room can be reduced, and the clean room can be used effectively.

  Moreover, in the film thickness distribution measuring method of this invention, it is preferable to correct | amend reflected light intensity for every wavelength of the reflected light used when calculating a film thickness distribution.

  The correction of the reflected light intensity can be easily performed collectively for all wavelengths of the linear light 4 irradiated to the thin film-coated wafer 3, and the film thickness measurement (calculation) time is also shortened. However, by correcting the reflected light intensity for each wavelength of reflected light used when calculating the film thickness distribution, it is possible to cope with fluctuations in the wavelength distribution of the light source, and further improve the accuracy of the film thickness distribution measurement of the thin film. be able to.

In this case, for each wavelength, for example, when the reflected light from each point on the wafer is detected by the CCD, the reflected light from each point is divided into wavelength components by separating the reflected light from each point with a spectrometer. For example, it can be realized by developing each pixel in the vertical direction so that each pixel in the vertical direction receives light of a certain wavelength (range), and performing correction for each pixel.
At this time, the calculation amount can be reduced by using the average of several pixels corresponding to a certain wavelength range.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.

(Example)
A thin film SOI wafer (diameter 300 mm, SOI layer film thickness: 88 nm, BOX layer film thickness: 145 nm, both film thicknesses set at the time of manufacturing an SOI wafer) manufactured by an ion implantation delamination method is used. 3, 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 for the same thin film SOI wafer.

  At this time, a mirror-polished silicon single crystal wafer (diameter: 125 mm) was arranged as a reference 2 on both sides in the linear irradiation region 4 as shown in FIG. Then, with the linear irradiation area 4 of the line light source 1 and both reference wafers fixed, the thin film SOI wafer is scanned (moved) at right angles to the linear direction of the irradiation area between the reference wafers. It was.

  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 in-plane average value. At this time, for the reflected light intensity at each measurement point in the region irradiated with the linear light 4 on the thin film SOI wafer, the reflected light intensity of the entire wavelength band of 450 to 750 nm is detected, and the reflected light intensity is Correction was performed using the average value of the reflected light intensity from two reference wafers irradiated simultaneously on the same line (line), and the film thickness distribution of the thin film was calculated using the corrected reflected light intensity.

  From the film thickness (film thickness distribution) of the SOI layer and the BOX layer calculated in this way, the average value of the film thickness in the wafer surface was obtained and used as each film thickness. FIG. 4 (SOI layer) and FIG. 5 (BOX layer) show the relationship between the measurement times (1 to 30 times) and the film thicknesses of each time in 30 times of repeated film thickness distribution measurement.

  In the repeated measurement of the film thickness of the SOI layer shown in FIG. 4 for 30 times, the average film thickness does not tend to fluctuate in one direction, and the difference between the maximum value and the minimum value of the repeated measurement is only about 0. The film thickness of the SOI layer was very stable through 30 measurements. From this, it can be said that the measurement accuracy of each film thickness is high.

  In addition, even in 30 repeated measurements of the film thickness of the BOX layer shown in FIG. 5, the film thickness does not tend to fluctuate in one direction, and the difference between the maximum value and the minimum value of the repeated measurement is about 0. 0. The film thickness was as small as 46 nm, and a stable BOX layer thickness value was obtained through 30 measurements. For this reason, it can be said that the measurement accuracy of each film thickness is high.

(Comparative example)
Using the same thin film SOI wafer used in the examples, the film thickness of the SOI layer and the film thickness of the BOX layer were measured 30 times. At this time, the reference wafer used in the example was not arranged, and therefore, the detection of the reflected light from the reference and the correction of the reflected light intensity of the thin film SOI wafer were not performed.

  In the same manner as in the example, the relationship between the measurement times and the film thicknesses of the SOI layer and the BOX layer at each time was obtained and shown in FIGS. 6 and 7, respectively.

  In the repeated measurement of the film thickness of the SOI layer shown in FIG. 6 in 30 times, the film thickness of the SOI layer fluctuates in an increasing direction as the time advances, and the difference between the maximum value and the minimum value of the repeated measurement is about It was 0.47 nm. This value was much larger than that of the example, and it was difficult to measure the film thickness stably.

  Further, in the repeated measurement of the thickness of the BOX layer shown in FIG. 7 in 30 times, the thickness of the BOX layer varies in the direction of decreasing, and the difference between the maximum value and the minimum value of the repeated measurement is increased. Was about 2.9 nm. This value was also much larger than that of the example, and it was difficult to measure the film thickness stably.

  As described above, the film thickness distribution measuring method of the present invention can improve the stability, reproducibility, and repeated measurement accuracy of the film thickness distribution measurement as compared with the prior art.

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

1 ... Line light source, 2 ... Reference, 3 ... Thin film wafer,
4 ... linear light (linear irradiation region), 10 ... film thickness distribution measuring device,
11: Line light source (prior art), 13: Detector.

Claims (5)

A film thickness distribution measuring method for measuring a film thickness distribution of a thin film of a wafer with a thin film having at least one thin film formed on a surface of a substrate by reflection spectroscopy using a line light source,
As the line light source, using a line light source having a light source longer than the diameter of the wafer with the thin film,
When detecting the reflected light by scanning the surface of the wafer with thin film with the linear light emitted from the line light source, simultaneously irradiating a part of the linear light to the reference, the reflected light also Detecting step;
Correcting the reflected light intensity from the wafer with the thin film using the reflected light intensity from the reference;
And a step of calculating the film thickness distribution from the corrected reflected light intensity of the wafer with a thin film.   2. The film thickness distribution measuring method according to claim 1, wherein a mirror-polished silicon single crystal wafer is used as the reference.   The reference is fixedly spaced one by one on both sides in the linear irradiation region of the line light source, and the wafer with a thin film is moved so as to pass between the two separated references, The film thickness distribution measuring method according to claim 1 or 2, wherein the surface of the wafer with a thin film is scanned with the linear light.   The reference is fixedly arranged one by one on both sides in the linear irradiation region of the line light source, and the diameter of the linear light and the wafer with the thin film is between the two separated references. 2. The surface of the wafer with thin film is scanned with the linear light by disposing the wafer with thin film in an overlapping position and rotating the wafer with thin film about its center. The film thickness distribution measuring method according to claim 2. 5. The film thickness distribution measuring method according to claim 1, wherein the correction of the reflected light intensity is performed for each wavelength of reflected light used when calculating the film thickness distribution. 6. .

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