JP5502227B1 - Film thickness distribution measurement method - Google Patents

Abstract

The present invention provides a film thickness distribution measuring method capable of measuring the film thickness distribution on the entire surface of a wafer with a thin film with high accuracy and high throughput.
[Solution]
Using a wafer with a thin film having a thin film with a known thickness, the reflectance at the center of the wafer with the thin film is measured, and the corrected incidence at the center of the wafer is measured from the measured reflectance and the known thickness. Calculate the corner. Using the wafer with the thin film to be measured and the corrected incident angle at the calculated wafer center, the wafer center line at the center position of the line light source is moved while moving the wafer with the thin film in the wafer surface direction perpendicular to the line light source. The film thickness distribution in the region along the line is measured. Then, after rotating the wafer with thin film by 90 °, the reflectance distribution of the measured region is measured at each point in the line light source direction, and the corrected incident angle at each point in the line light source direction is calculated from the measured reflectance distribution. calculate. The film thickness distribution of the thin film of the wafer with a thin film is measured using the corrected incident angle.
[Selection] Figure 1

Description

  The present invention relates to a film thickness distribution measuring method for measuring the film thickness distribution of the entire surface of a wafer with a thin film of one or more layers used in a semiconductor device by reflection spectroscopy using a line light source.

  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, which requires particularly high film thickness uniformity. SOI wafers with layers have begun to be used. In these devices, the uniformity of the SOI film thickness and the buried oxide film (BOX film) thickness is an important item in determining the characteristics of the transistor.

  The current film thickness measurement method for calculating the film thickness distribution of such a thin film-attached wafer having a thin film on the surface of the substrate is generally a film thickness measurement at each point by spectroscopic ellipsometry or reflection spectroscopy. However, a film thickness distribution measuring apparatus capable of measuring the film thickness distribution with high throughput and high accuracy over the entire wafer surface is not commercially available.

In point measurement by spectroscopic ellipsometry or reflection spectroscopy, a spectrum in a certain wavelength range (generally, visible light region) is taken for each measurement point, and the spectrum is fitted to the model film structure. The film thickness at each measurement point is obtained. Therefore, if it is attempted to measure the entire wafer surface with high throughput and high accuracy, the number of measurement points increases extremely, making it impossible to measure practically due to the amount of calculation and time constraints.
Therefore, for example, it is a problem to measure the film thickness distribution of a wafer with a thin film such as an SOI wafer having a diameter of 300 mm or more with high density and accuracy in a short time.

  In contrast, a method of measuring the film thickness while irradiating a measurement object with linear light from the line light source and scanning the measurement object in a direction perpendicular to the line light source by spectral reflection using a line light source. Is known (see Patent Document 1).

JP 2000-314612 A

However, there is a problem that sufficient measurement accuracy cannot be obtained even when film thickness is measured by this method. When the inventors investigated the cause, the following was found.
In film thickness distribution measurement by scanning spectral reflection method using a line light source, the incident angle when the incident light from the light source is reflected by the thin film and detected by the detector (camera) Different at measurement points. Therefore, it is necessary to calculate the incident angle for each measurement point in advance and set it to a predetermined value (theoretical incident angle).

  However, in an actual measurement system, some geometrical deviation of the optical system occurs, and thus a deviation from the theoretical incident angle cannot be avoided, and an error occurs in the measurement result of the thin film. The degree of error is not negligible as the film thickness of the thin film to be measured is thinner. In particular, in the thin film SOI layer (for example, the SOI film thickness is 20 nm or less) that requires high film thickness uniformity. It becomes a problem.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a film thickness distribution measuring method capable of measuring the film thickness distribution on the entire surface of a thin film-coated wafer with high accuracy and high throughput.

  In order to achieve the above object, according to the present invention, the film thickness distribution of the thin film of a 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. A film thickness distribution measuring method, which corrects an incident angle at each point in a line light source direction on the wafer with a thin film, and includes the following first step, second step, and third step. A fourth step of measuring a film thickness distribution of the thin film of the wafer with a thin film using an incident angle, and using the wafer with a thin film having a thin film with a known film thickness in the first step, The reflectivity at the center of the wafer with the thin film is measured, and the corrected incident angle at the wafer center is calculated from the measured reflectivity and the previously known film thickness. In the second step, the first step Before used in the process Using the thin film-coated wafer having a thin film of the same material as the thin film of the thin film-coated wafer and the corrected incident angle at the calculated wafer center, the thin film-coated wafer is perpendicular to the line light source. While moving in the wafer in-plane direction, the film thickness distribution of the region along the wafer center line at the center position of the line light source is measured, and in the third step, the thin film-coated wafer after the second step is measured. After rotating 90 °, the reflectance distribution of the region measured in the second step is measured at each point in the line light source direction, and the measured reflectance distribution and the film thickness distribution measured in the second step are measured. A film thickness distribution measuring method is provided that calculates a corrected incident angle at each point in the line light source direction.

  With such a film thickness distribution measuring method, the corrected incident angle at each point in the direction of the line light source can be obtained with high accuracy. Therefore, the film thickness distribution on the entire surface of the wafer with a thin film can be accurately obtained using this incident angle. It can be measured with good and high throughput.

At this time, a silicon oxide film having a thickness of 200 nm or more calibrated with an ellipsometer is formed on the surface of the silicon single crystal wafer as the wafer with a thin film used in the first step and / or the wafer with a thin film to be measured. It is preferable to use a different wafer.
By doing so, the absolute value of the reflectance with respect to the change in the wavelength of the incident light from the light source becomes sufficiently large, so that the measurement accuracy of the incident angle can be increased.

  According to the film thickness distribution measuring method of the present invention, in the film thickness distribution measurement by reflection spectroscopy using a line light source, the incident angle at each point in the line light source direction is corrected, and the thin film is obtained using the corrected incident angle. Measure the film thickness distribution of the thin film on the attached wafer. For example, measure the film thickness distribution on the entire surface of the wafer with the thin film such as an SOI wafer having an ultrathin SOI layer or an ultrathin BOX layer with high accuracy and practical high throughput. Is possible. Therefore, for example, the wafer process management and quality control with high uniformity of SOI layer thickness and BOX layer film thickness distribution as required by the FD-SOI device can be realized.

It is a flowchart of an example of the film thickness distribution measuring method of this invention. It is the schematic which shows an example of the measuring apparatus for enforcing the film thickness distribution measuring method of this invention. It is a figure which shows the film thickness distribution measured at the 2nd process in the Example. It is a figure which shows the correction | amendment incident angle in an Example, and the theoretical incident angle in a comparative example. It is a figure which shows the SOI film thickness distribution measurement result in an Example. It is a figure which shows the SOI film thickness distribution measurement result in a comparative example.

  Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to this.

The present invention is a film thickness distribution measuring method for measuring a film thickness distribution of a thin film of a wafer with a thin film by reflection spectroscopy using a line light source.
The wafer with a thin film to be measured has at least one thin film formed on the surface of the substrate. As an example of a wafer with a thin film having a single layer of thin film, a silicon single crystal wafer with a silicon oxide film can be given. An example of a wafer with a thin film having two thin films is an SOI wafer in which a buried oxide film (BOX film) is formed on a silicon substrate and an SOI layer made of silicon single crystal is formed thereon. It is done. However, the present invention is not limited to these wafers, and can be applied to a thin film structure having three or more layers.

  Here, the film thickness distribution measuring method of the present invention will be described with reference to FIGS. 1 and 2 by taking as an example a case where a silicon single crystal wafer with a silicon oxide film is used as a wafer with a thin film to be measured.

The film thickness distribution measuring method of the present invention can be implemented using a measuring apparatus as shown in FIG.
As shown in FIG. 2, the measuring apparatus 1 includes a line light source 2 and a detector (camera and spectroscope) 3. Linear light is irradiated from the line light source 2 onto the wafer W with a thin film to be measured. By detecting the reflected light of the irradiated light with the detector 3 and performing spectrum analysis, the film thickness distribution of the thin film at each measurement point in the direction of the line light source on the wafer with the thin film can be measured.

When the reflected light of the light emitted from the line light source 2 is detected by the detector 3 and subjected to spectrum analysis, the incident angle at each measurement point in the direction of the line light source is used, so it is necessary to set in advance. This incident angle has a different value at each measurement point in the line light source direction.
In the conventional film thickness distribution measuring method, the theoretical incident angle is set in advance and used for measuring the film thickness distribution. However, in an actual measurement system, there is a geometrical deviation of the optical system. Deviation occurs between the incident angle and the theoretical incident angle, which causes a measurement error in the film thickness distribution.

On the other hand, in the film thickness distribution measuring method of the present invention, the incident angle at each measurement point in the line light source direction is corrected using an actual measurement system, and the corrected incident angle is set to measure the film thickness distribution. Use.
Therefore, it is possible to eliminate the incident angle error caused by the geometrical deviation of the optical system, and to measure the film thickness distribution with high accuracy.

Here, a method of correcting the incident angle will be described.
As shown in FIG. 1, the correction of the incident angle is calculated through a first process, a second process, and a third process described below.
First, in the first step, a thin film-attached wafer having a thin film with a known thickness is prepared. This wafer with a thin film has a thin film made of the same material as the thin film of the wafer with a thin film to be measured. For example, a silicon single crystal wafer having a silicon oxide film as the thin film (hereinafter referred to as a standard oxide film wafer) is prepared. be able to.

The thickness of the silicon oxide film of the standard oxide film-attached wafer is preferably 200 nm or more, and more preferably 1000 nm or more.
The reason is as follows. In order to improve the measurement accuracy of the oxide film thickness by reflection spectroscopy, it is necessary that the reflectance varies greatly with changes in the wavelength of incident light, and that the absolute value of the reflectance is large. At this time, if the oxide film is thin, the change in reflectivity is small, the reflectivity is also small, and the measurement accuracy cannot be increased. When the thickness of the silicon oxide film is 200 nm or more, a reflectance of 25 to 35% is obtained, the fluctuation range of the reflectance is increased, and the measurement accuracy can be increased. When the oxide film thickness is further increased, particularly 1000 nm or more, the periodic fluctuation of the reflectance becomes remarkable with respect to the change of the wavelength of the incident light, so that the measurement accuracy can be further improved.
Note that the same tendency as described above is shown with respect to the reflectance even for thin films other than silicon oxide films.

  At this time, if the thickness of the silicon oxide film of the wafer with the standard oxide film to be prepared is measured in advance with an ellipsometer at one point in the center of the wafer, the film thickness can be measured with high accuracy and the measurement time is also short. This is preferable because it takes time.

  Using the measuring apparatus shown in FIG. 2, the wafer with standard oxide film is irradiated with linear light from the line light source 2 so that the center of the line light source 2 corresponds to the center of the wafer, The reflectance of the silicon oxide film at the wafer center position is measured. Since the reflectivity is determined by the film thickness and the incident angle, the corrected incident angle θ at the center of the wafer, that is, the center of the line light source is calculated using the reflectivity measured in this way and the previously known film thickness. .

  Next, as shown in FIG. 1, a second step is performed. In the second step, the film thickness distribution of the thin film of the wafer with the thin film to be measured is measured using the corrected incident angle θ at the wafer center calculated in the first step as the incident angle. Here, as described above, the wafer with a thin film to be measured has a thin film of the same material as the thin film of the wafer with the standard oxide film used in the first step, that is, a silicon oxide film. A silicon single crystal wafer having an oxide film can be obtained.

Similarly to the above, the thickness of the silicon oxide film of the silicon single crystal wafer to be measured is preferably 200 nm or more, and more preferably 1000 nm or more.
The wafer center line at the center position of the line light source 2 while moving (scanning) this silicon single crystal wafer in the wafer surface direction A perpendicular to the line light source 2 using the measuring apparatus 1 as shown in FIG. The film thickness distribution in the region along the wafer diameter direction is measured.

  Next, as shown in FIG. 1, a third step is performed. In the third step, the silicon single crystal wafer after the second step is rotated by 90 ° so that the region where the film thickness distribution is measured in the second step is parallel to the line light source. Thereafter, the reflectance distribution in this region is measured at each point in the line light source direction. Using the measured reflectance distribution and the film thickness distribution measured in the second step, the corrected incident angle θ at each point in the line light source direction is calculated based on the geometric relationship.

Through the above steps, the corrected incident angle can be obtained with high accuracy.
Next, as shown in FIG. 1, a fourth step is performed. In the fourth step, the thickness distribution of the silicon oxide film of the silicon single crystal wafer is measured using the corrected incident angle θ calculated in the third step.
In this way, the film thickness on the entire surface of the wafer can be measured with high accuracy and high throughput using the corrected incident angle.

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

(Example)
The first step is performed using a silicon single crystal wafer having a silicon oxide film with a thickness of 1000 nm calibrated by an ellipsometer (standard oxide film wafer: diameter 300 mm, crystal orientation <100>), and the incident angle at the center of the line light source Asked.
As a result, the incident angle was calculated to be 3.28 degrees, and it was found that a deviation of about 10% occurred compared to the set value (theoretical incident angle) of 3 degrees.

Next, a second process is performed using a silicon oxide single crystal wafer with a total oxide film thickness of 4800 nm, and the film thickness distribution of the oxide film (in the diameter direction of the wafer) is measured along the wafer center line at the center of the line light source. It was measured. The result of this film thickness distribution is shown in FIG.
Thereafter, the wafer after the second step was rotated by 90 °, and the reflectance of the region where the film thickness distribution was obtained in the second step was measured at each point in the direction parallel to the line light source. Using the measured reflectance of each point and the oxide film thickness distribution measured in the second step, the incident angle (corrected incident angle) of each point in the line light source direction was obtained. The result of this incident angle is shown in FIG.

Using the corrected incident angle obtained, the SOI film thickness of an SOI wafer having a diameter of 300 mm was measured. The SOI film thickness was measured by scanning the wafer in the direction perpendicular to the notch position formed on the wafer. After the first measurement, the wafer was rotated 180 degrees and the second measurement was performed.
FIG. 5 shows the film thickness distribution of the wafer center line in the direction parallel to the notch (that is, the wafer center line parallel to the line light source) and the difference between the first measurement and the second measurement.
The second measurement is performed by rotating the wafer by 180 degrees. In FIG. 5, the first and second measurement positions are plotted so as to coincide with each other.

  As shown in FIG. 5, according to the line graph showing the film thickness difference, it can be seen that the two coincide with each other with an accuracy of ± 0.1 nm or less.

(Comparative example)
The SOI film thickness was measured on the entire surface of the same SOI wafer as in the example without correcting the incident angle and setting the theoretical incident angle as the initial setting value.
FIG. 4 shows the theoretical incident angle set in the comparative example. As shown in FIG. 4, it can be seen that there is a difference between the theoretical incident angle and the corrected incident angle.

FIG. 6 shows the film thickness distribution of the wafer center line in the direction parallel to the notch (that is, the wafer center line parallel to the line light source) and the difference between the first measurement and the second measurement rotated 180 degrees. .
The second measurement is performed by rotating the wafer by 180 degrees, but FIG. 6 is plotted so that the first and second measurement positions coincide.
As shown in FIG. 6, according to the line graph showing the film thickness difference, a difference of ± 0.5 nm or more is observed between the two. This indicates that the initial theoretical incidence angle is not accurate, so the measured value varies depending on the wafer scan direction. ing.

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

  DESCRIPTION OF SYMBOLS 1 ... Measuring apparatus, 2 ... Line light source, 3 ... Detector.

Claims (2)

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,
The following first, second, and third steps for correcting the incident angle at each point in the line light source direction on the thin film-attached wafer, and the thin film-attached wafer using the corrected incident angle. A fourth step of measuring the film thickness distribution of the thin film;
In the first step, using a wafer with a thin film having a thin film having a known thickness, the reflectance at the center of the wafer with the thin film is measured, and the measured reflectance and the previously known thickness are measured. To calculate the corrected angle of incidence at the wafer center,
In the second step, the wafer with a thin film to be measured for the film thickness distribution having a thin film of the same material as the thin film of the wafer with the thin film used in the first step, and the correction at the calculated wafer center Using the incident angle, while moving the wafer with thin film in the wafer surface direction perpendicular to the line light source, measure the film thickness distribution of the region along the wafer center line at the center position of the line light source,
In the third step, after rotating the wafer with a thin film after the second step by 90 °, the reflectance distribution of the region measured in the second step is measured at each point in the line light source direction, A film thickness distribution measuring method, comprising: calculating a corrected incident angle at each point in the direction of the line light source from the measured reflectance distribution and the film thickness distribution measured in the second step.   As a wafer with a thin film used in the first step and / or a wafer with a thin film to be measured, a wafer in which a silicon oxide film having a thickness of 200 nm or more calibrated with an ellipsometer is formed on the surface of a silicon single crystal wafer. The film thickness distribution measuring method according to claim 1, wherein the film thickness distribution measuring method is used.

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