JP6520795B2 - Film thickness distribution measurement method - Google Patents

Description

  The present invention relates to a film thickness distribution measuring method of measuring the film thickness distribution of a thin film of a thin film-coated wafer having at least one thin film.

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

  Reflection spectroscopy is a method of measuring the film thickness of a thin film-attached wafer such as an SOI wafer. In the conventional reflection spectroscopy, a thin film of a thin film-attached wafer is irradiated with light, and the reflected light is dispersed by a spectroscope to obtain a spectrum of the reflected light. Then, using the fact that the interference condition of the light reflected from the front and back of the thin film changes depending on the wavelength and the optical path difference due to the thickness of the thin film, the peak wavelength in the spectrum, the value of the refractive index of the thin film, etc. The thickness of the thin film is calculated using this. However, in such reflection spectroscopy, when it is intended to measure the entire surface of the wafer with high accuracy, the number of measurement points extremely increases, so a huge amount of calculation and time are required, and in reality, it is necessary to measure the entire surface. It was impossible.

  On the other hand, there is a method described in Patent Document 1 as a method of two-dimensionally measuring the film thickness of a film to be measured with a film (thin film) on the surface with higher throughput. In the method, linear light is irradiated to the surface of the measurement object, and reflected light from the irradiation area of the linear light is dispersed using a spectroscope (imaging spectroscope) that can disperse the light while holding positional information. By spectrally separating, the film thickness in the irradiation area of the linear light is calculated at once. Then, while moving the irradiation area in a direction perpendicular to the irradiation area of the linear light, the coating film on the measurement object is repeatedly performed by repeatedly performing an operation of calculating the film thickness in the irradiation area at one time. The film thickness is measured two-dimensionally.

  Furthermore, as a film thickness distribution measuring method capable of accurately measuring the film thickness distribution on the entire surface of a thin film-attached wafer such as an SOI wafer with 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 such a deviation, the film thickness distribution on the entire surface of the thin film-coated wafer 3 can be measured with high accuracy and high throughput.

Japanese Patent Laid-Open No. 2000-314612 JP, 2015-17804, A

  However, even when the film thickness distribution measuring method by reflection spectroscopy using a line light source as in Patent Document 2 is used, a light source, a detection system, an optical system, etc. (these may be collectively referred to as a measurement system Stability of the film thickness measurement, reproducibility, and repeated measurement accuracy were not sufficient. In particular, extremely high film thickness measurement accuracy is required for the SOI layer and BOX layer of ultrathin film SOI wafers for advanced device fabrication, and these requirements are required in the conventional film thickness distribution measurement method. It did not necessarily correspond sufficiently to.

  The present invention has been made in view of the above problems, and when the film thickness distribution of a thin film-attached wafer is measured by reflection spectroscopy using a line light source, the film thickness distribution is stably and accurately measured. It is an object of the present invention to provide a film thickness distribution measuring method that can

In order to achieve the above object, the present invention measures a film thickness distribution of a thin film-coated wafer having at least one thin film formed on the surface of a substrate by reflection spectroscopy using a line light source. Thickness distribution measurement method,
As the line light source, a line light source having a light source longer than the diameter of the thin film-coated wafer is used.
When scanning the surface of the thin film-coated wafer with linear light emitted from the line light source to detect reflected light, at the same time, a part of the linear light is irradiated to the reference, and the reflected light is also transmitted. A process of detecting
Correcting the reflected light intensity from the thin film-coated wafer using the reflected light intensity from the reference;
And calculating a film thickness distribution from the corrected light intensity of the thin film-attached wafer.

  Thus, using the line light source having a light source longer than the diameter of the thin film-coated wafer, the reflected light from the thin film-coated wafer and the reference can be simultaneously detected, and the fluctuation of the total reflected light intensity caused by the measurement system of the measuring apparatus By calculating the film thickness distribution of the thin film by correction, the film thickness distribution measurement of the thin film-coated wafer can be stably and accurately performed.

  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 an extremely flat surface and has extremely high in-plane reflectance uniformity, and thus can be suitably used as a reference.

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

  As described above, the reference was placed on both sides of the thin film-coated wafer, and the reflected light intensity from the thin film-coated wafer was corrected using the reflected light intensities from the references on both sides, resulting in the measurement system of the measuring apparatus. It is possible to more reliably suppress the influence of the fluctuation of the overall reflected light intensity. Thereby, film thickness distribution measurement of the thin film-attached wafer can be performed more stably and with higher accuracy.

  At this time, the references are fixedly disposed one by one on both sides in the linear irradiation area of the line light source, and the linear light and the wafer with the thin film are disposed between the two separated references. It is preferable to scan the surface of the thin film-coated wafer with the linear light by disposing the thin film-coated wafer at a position where the diameters of the thin film-coated wafers overlap and rotating the thin film-coated wafer about its center.

  In this way, if the wafer with a thin film disposed between the two separated references is scanned so that the surface is rotated about its center, it is moved so as to pass between the two separated references. The occupied area for performing the film thickness distribution measurement can be approximately halved while maintaining the same measurement accuracy. Also, by adopting a scanning method using a wafer rotation mechanism as described above, it is possible to easily incorporate a film thickness distribution measurement function using a line light source into another device 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 perform the correction of the reflected light intensity for each wavelength of the reflected light used when calculating the film thickness distribution.

  As described above, by performing correction of the reflected light intensity for each wavelength of the reflected light used when calculating the film thickness distribution, it is possible to perform film thickness distribution measurement 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 the light source longer than the diameter of the thin film-attached wafer is detected by the reference, and the reflected light intensity from the thin film-attached wafer is referred to The film thickness distribution measurement of the thin film of the thin film-attached wafer can be stably and accurately performed by correcting using the reflected light intensity from the above.

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 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 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 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 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 by way 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 FIG. 1 and FIG.

  FIG. 1 is a schematic view (as viewed from above) showing an example of the embodiment of the film thickness distribution measuring method of the present invention, and FIG. 2 is a diagram showing the process flow of the film thickness distribution measuring method of the present invention . In the film thickness distribution measuring method of the present invention, the film thickness distribution of a thin film-attached wafer having at least one thin film formed on the surface of a substrate is measured by reflection spectroscopy using a line light source. As the line light source, various types 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, the line light source 1 having a light source longer than the diameter of the thin film-coated wafer 3 is used as the line light source (A in FIG. 2). Further, according to the film thickness distribution measuring method of the present invention, when the surface of the thin film-coated wafer 3 is scanned with the linear light 4 emitted from the line light source 1 to detect the reflected light, the reference 2 is linear simultaneously. Irradiating a part of the light 4 and detecting the reflected light (FIG. 2B), and 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 the step of calculating the film thickness distribution from the corrected light intensity of the thin film-attached wafer 3 (D in FIG. 2).

  Here, when scanning the surface of the thin film-coated wafer 3 with the linear light 4 emitted 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 moving it relative to 2. However, the thin film wafer 3 may be fixed, and the line light source 1 and the reference 2 may be moved relative to the thin film wafer 3 to scan the linear light 4.

  As described above, the line light source 1 having the light source longer than the diameter of the thin film-coated wafer 3 simultaneously detects the reflected light from the thin film-coated wafer 3 and the reference 2 and corrects the fluctuation of the reflected light intensity from the thin film-coated wafer 3 By calculating the film thickness distribution of the thin film, the film thickness distribution measurement of the thin film-coated wafer 3 can be stably and accurately performed. In the method of the present invention, the film thickness distribution of the entire surface of the thin film-coated wafer 3 can be measured.

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

  Further, as the reference 2, one having a uniform surface reflectance is preferable, and one having a variation in the in-plane reflectance of 1% or less is more preferable. If the reflectance of the surface is uniform, even if a slight deviation occurs in the positional relationship between the reference 2 and the line light source 1, the reflected light intensity from the reference 2 hardly changes, so the reflection of the thin film-coated wafer 3 The correction of the light intensity can always be done very accurately. Furthermore, as the reference 2, as long as the reflectance of the surface is appropriate, not only a silicon single crystal wafer but also other semiconductor wafers and other materials can be used.

  Further, as shown in FIG. 1, the reference 2 is fixedly disposed one by one on both sides in the linear irradiation area 4 of the line light source 1 and the thin film-coated wafer 3 is separated from both the references 2. It is preferable to move so as to pass between and scan the surface of the thin film-coated wafer 3 with the linear light 4.

  As described above, in a state where the reference 2 is disposed on both sides of the thin film-attached wafer 3 to be measured, reflected light is simultaneously detected from the thin film-attached wafer 3 and the reference 2. For example, reflection from the reference 2 on both sides By determining the average value of the light intensity and correcting the reflected light intensity from the thin film-coated wafer 3 on the basis thereof, it is possible to sufficiently suppress the influence of the fluctuation of the reflected light intensity from the thin film attached wafer 3 with respect to time. It becomes.

  However, the reference 2 is disposed in the linear irradiation area 4 of the line light source 1, and when scanning the thin film-coated wafer 3 with the linear light from the line light source 1, the reflected light from the reference 2 is also simultaneously The arrangement and size thereof are not particularly limited as long as they can be detected. For example, when measuring the film thickness distribution of the thin film-coated wafer 3 having a large diameter exceeding 300 mm, the length of the line light source 1 becomes extremely long when the reference 2 is disposed on both sides of the thin film-coated wafer 3. As shown in FIG. 3, the reference 2 may be disposed only on one side of the thin film-coated wafer 3 to suppress the length of the line light source 1. Also, the shape of the reference 2 may be rectangular or another shape. Further, as long as the reference 2 can measure the reflected light when it is irradiated with a part of the linear light 4, the linear light 4 may be configured to cross the reference 2 as shown in FIG. 1. 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 according to the present invention, as shown in FIG. 9, the reference 2 is separately disposed one by one on both sides within the linear irradiation area of the line light source 1 and both disposed apart. The thin film-coated wafer 3 is disposed between the reference 2 at a position where the linear light 4 and the thin film-coated wafer 3 overlap in diameter, and the thin film-coated wafer 3 is rotated about its center to form linear light 4. The surface of the thin film-coated wafer 3 may be scanned.

  As described above, if the thin film-coated wafer 3 is rotated about its center to scan the surface, the thin-film coated wafer 3 shown in FIG. The size of the apparatus used for the measurement can be greatly reduced, as described below, while maintaining the same measurement accuracy as in the previous case.

  In the film thickness distribution measuring apparatus applicable to the film thickness distribution measuring method of the present invention, the wafer 3 with a thin film is held and moved or rotated, and the entire surface is scanned with linear light 4 to measure the film thickness distribution. The part to do is called the measurement part. When scanning linear light 4, in FIG. 1, in order to scan from the lower end to the upper end of thin film-coated wafer 3 by linear light 4, thin films are attached to the upper and lower sides of at least linear light 4. A measuring unit having a space for one wafer is required. On the other hand, when the thin film wafer 3 is rotated and scanned, the occupied area of the measurement unit may be about one thin film attached wafer, so the occupied area of the measurement unit is reduced to about half compared to when linearly scanned. can do.

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

  Further, in the film thickness distribution measuring method of the present invention, it is preferable to correct the reflected light intensity for each wavelength of the reflected light used when calculating the film thickness distribution.

  It is simple to correct the reflected light intensity collectively for all the 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 the reflected light used when calculating the film thickness distribution, it is possible to cope with the case where the wavelength distribution of the light source fluctuates, and to improve the accuracy of the film thickness distribution measurement of the thin film. be able to.

In this case, for example, when the reflected light from each point on the wafer is detected by a CCD, the correction for each wavelength is divided into wavelength components by dispersing the reflected light from each point by a spectroscope, which is divided by the CCD For example, by developing each pixel in the vertical direction, each pixel in the vertical direction is configured to receive light of a certain wavelength (range), and the correction can be performed for each pixel.
At that time, the computational complexity can be reduced by using an average of several pixels corresponding to a certain wavelength range.

  EXAMPLES The present invention will be more specifically described below with reference to examples and comparative examples, but the present invention is not limited to these.

(Example)
Wafer with thin film for measurement of thin film SOI wafer (diameter 300 mm, thickness of SOI layer: 88 nm, thickness of BOX layer: 145 nm, both film thickness set in SOI wafer manufacture) manufactured by ion implantation peeling method As No. 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, as a reference 2, a mirror-polished silicon single crystal wafer (diameter 125 mm) was spaced apart on both sides in a linear irradiation area 4 as shown in FIG. Then, in a state where the linear irradiation area 4 of the line light source 1 and both reference wafers are fixed, the thin film SOI wafer is scanned (moved) at right angles to the linear direction of the irradiation area between both reference wafers. The

  As the line light source 1, using a visible light source of a wavelength band of 450 to 750 nm, film thickness measurement on the entire surface of the thin film SOI wafer was performed at 1 mm pitch to calculate an in-plane average value. At this time, with regard to the reflected light intensity of 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. Correction was performed using the average value of the reflected light intensity from two reference wafers simultaneously irradiated 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 thicknesses (film thickness distributions) of the SOI layer and the BOX layer calculated in this manner, the average value of the in-plane film thickness on the wafer is determined and used as the respective film thickness. FIG. 4 (SOI layer) and FIG. 5 (BOX layer) show the relationship between the measurement times (once to 30 times) and the film thickness of each time in the 30 times repeated measurement of film thickness distribution.

  In 30 repetitive measurements of the film thickness of the SOI layer shown in FIG. 4, there is no tendency for the average film thickness 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 value of the film thickness of the SOI layer which was 07 nm and was very stable through 30 measurements was obtained. From this, it can be said that the measurement accuracy of the film thickness of each time is also high.

  Also, in the case of 30 repeated measurements of the film thickness of the BOX layer shown in FIG. 5, there is no tendency for the film thickness to fluctuate in one direction, and the difference between the maximum value and the minimum value of the repeated measurement is about 0. A sufficiently small value of 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 the film thickness of each time is also high.

(Comparative example)
The film thickness of the SOI layer and the film thickness of the BOX layer were repeatedly measured 30 times using the same thin film SOI wafer as used in the example. At this time, the reference wafer used in the example was not disposed, 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.

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

  In 30 repetitive measurements of the film thickness of the SOI layer shown in FIG. 6, the film thickness of the SOI layer fluctuates as the process progresses, and the difference between the maximum value and the minimum value of the repeated measurement is about It was 0.47 nm. This value is much larger than that of the example, and stable film thickness measurement was difficult.

  Further, in the repeated measurement of the film thickness of the BOX layer 30 times shown in FIG. 7, the film thickness of the BOX layer fluctuates as the time goes on, and the difference between the maximum value and the minimum value of the repeated measurement Has reached about 2.9 nm. This value is also much larger than in the examples, and stable film thickness measurement was difficult.

  As described above, according to the film thickness distribution measuring method of the present invention, the stability, the reproducibility, and the repeated measurement accuracy of the film thickness distribution measurement can be improved as compared with the conventional method.

  The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and it has substantially the same configuration as the technical idea described in the claims of the present invention, and any one having the same function and effect can be used. It is included in the technical scope of the invention.

1 ... line light source, 2 ... reference, 3 ... wafer with thin film,
4 linear light (linear irradiation area) 10 film thickness distribution measuring device
11: Line light source (conventional technology) 13: Detector.

Claims (3)

A film thickness distribution measuring method of measuring a film thickness distribution of a thin film-attached wafer 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, a line light source having a light source longer than the diameter of the thin film-coated wafer is used.
When scanning the surface of the thin film-coated wafer with linear light emitted from the line light source to detect reflected light, at the same time, a part of the linear light is irradiated to the reference, and the reflected light is also transmitted. A process of detecting
Correcting the reflected light intensity from the thin film-coated wafer using the reflected light intensity from the reference;
From the reflected light intensity of the corrected film with wafers, saw including a step of calculating the film thickness distribution,
The reference is fixedly disposed one by one on both sides in a linear irradiation area of the line light source,
The thin film-coated wafer is moved so as to pass between the spaced references, or the linear light and the thin film-deposited wafer overlap each other between the spaced references. The surface of the thin film-coated wafer is scanned with the linear light by arranging the thin film-coated wafer and rotating the thin film-coated wafer about its center,
A method of measuring a film thickness distribution comprising: calculating an average value of reflected light intensities from the references on both sides, and correcting the reflected light intensity from the thin film-coated wafer based on the average value .   2. The film thickness distribution measuring method according to claim 1, wherein a mirror-polished silicon single crystal wafer is used as the reference. 3. The film thickness distribution measuring method according to claim 1, wherein the correction of the reflected light intensity is performed for each wavelength of the reflected light used when calculating the film thickness distribution.

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