JP2010216854A - Film thickness measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide new information related to the reliability of measured values. <P>SOLUTION: A correlation diagram 36 (refer to the figure) showing the correlation between each fitting level obtained for each theoretical interference waveform in the curve fitting method and the film thickness of each theoretical interference waveform corresponding to each fitting level is created and displayed. For the peak value of a valley of the waveform of the correlation diagram 36 which changes by film thickness variations, thresholds L1, L2 are set. When the peak value of the valley falls within an alarm range provided by the thresholds L1, L2, an alarm indicating that measurement is not being performed stably is output. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical film thickness measuring apparatus.

  In an optical film thickness measurement device, when light is applied to a substrate on which a thin film is formed, the light reflected on the surface of the thin film interferes with the light reflected on the boundary surface between the thin film and the substrate. The intensity of light varies depending on the thickness of the thin film, and there is a film thickness measuring device that uses the principle of optical interference in which the intensity of interference light changes depending on the wavelength of light irradiated on the same substrate, even on the same substrate.

  In such a film thickness measuring apparatus, a light source that emits light distributed in a predetermined wavelength region is irradiated onto the substrate of the measurement object, and reflected light from the substrate is composed of a spectral filter and a plurality of light receiving elements. It is guided to the light receiving part and extracted into a plurality of wavelength components, and the measured waveform of the reflection spectrum showing the degree of reflection for each wavelength component and the theoretical reflection spectrum when the thickness of the thin film is a predetermined value. The thickness of the thin film on the substrate is measured by a curve fitting method in which the theoretical waveform is compared in order (see, for example, Patent Document 1).

JP 2002-81916 A

  In the above curve fitting method, the theoretical waveform that minimizes the fitting level, which is the level related to the square sum of the difference between the measured waveform of the reflected spectrum and the theoretical waveform of the reflected spectrum for each wavelength, is identified, and the theoretical waveform is supported. The film thickness to be measured is the film thickness of the measurement object.

  In a film thickness measuring apparatus using such a curve fitting method, the obtained film thickness and the minimum fitting level are output as measurement results.

  If the thin film that is the object to be measured has a uniform film thickness, accurate measurement values can be obtained. However, if the film thickness is uneven, the film thickness measurement becomes unstable, which is the worst case. In some cases, different measurements may be obtained.

  In the conventional film thickness measuring apparatus, even if the measurement value is not reliable, the obtained film thickness and the minimum fitting level are output as measurement results.

  For this reason, for example, when a completely different measurement object is measured, the fitting level changes greatly, so that it can be determined that the measurement object is different. When a value is obtained, it cannot be determined whether or not the obtained measurement value is reliable, and it is mistakenly recognized as a correct measurement value, or a stylus type It was necessary to measure again with another measuring device such as the above measuring device and confirm.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide new information regarding the reliability of measurement values.

  (1) The film thickness measuring apparatus of the present invention irradiates a measurement object with light and spectrally analyzes the reflected light, and a plurality of theoretical interference waveforms respectively corresponding to a plurality of predicted film thicknesses. And the film thickness corresponding to the theoretical interference waveform that minimizes the fitting level related to the sum of squares of the differences between the measured interference waveform and the theoretical interference waveform for each wavelength, is the film thickness of the measurement object. And a creation means for creating a correlation diagram showing a correlation between the fitting level obtained for each theoretical interference waveform and the film thickness corresponding to the theoretical interference waveform from which the fitting level is obtained. I have.

  The fitting level related to the square sum of the difference between the measured interference waveform and the theoretical interference waveform for each wavelength is a level related to the square sum of the difference between the measured interference waveform and the theoretical interference waveform for each wavelength, or The level corresponding to the sum of squares of differences, for example, may be the sum of squares of the differences itself, or may be a result of multiplying the sum of squares of the differences by a coefficient or adding or subtracting a predetermined number. May be.

  The generated correlation diagram is preferably displayed and output, but may be printed out.

  As a result of earnest research, the present inventor has obtained the fitting levels of a plurality of theoretical interference waveforms with respect to the actually measured interference waveforms in the curve fitting method with respect to the film thickness. In the correlation diagram plotted in the above, the shape has a plurality of valleys with a small fitting level at a cycle of about 200 nm, and the valleys of the measurement object are uniform when the film thickness is uniform and when the film thickness is uneven. We found that the peak changed.

  That is, according to the film thickness measuring apparatus of the present invention, a correlation diagram showing the correlation between each fitting level obtained for each theoretical interference waveform and the film thickness is created, so that the created correlation diagram is displayed or printed. By observing the correlation diagram, the user can observe the peak of the valley when the film thickness is uniform and stable, and the measurement is unstable due to uneven film thickness. Based on the difference from the peak of the trough, a determination regarding the reliability of the measurement can be made.

  (2) In one embodiment of the film thickness measurement apparatus of the present invention, the film thickness measuring device includes display means for displaying the correlation diagram created by the creation means, wherein the correlation diagram takes the thickness on the horizontal axis and the vertical axis It is the figure which took the fitting level.

  In this embodiment, the magnitude of the fitting level corresponds to the vertical direction of the correlation diagram, so that it becomes easy to observe the peak of the valley with a small fitting level.

  (3) In another embodiment of the film thickness measuring apparatus of the present invention, the peak value of the first valley with the lowest fitting level and the peak of the second valley with the next lowest fitting level in the correlation diagram. Output means for outputting an alarm when at least one of the peak values satisfies a set condition.

  When the film thickness is uniform and stable measurement is performed, the peak value of the first valley with the lowest fitting level corresponding to the measurement value and the peak of the second valley with the next lowest fitting level The difference is relatively large, but if the film thickness is uneven, the difference between the two peak values becomes smaller and close, and finally the peak value of the second trough is reversed to the first value. It becomes smaller than the peak value of the trough part, and the measured value becomes an incorrect value.

  The alarm only needs to be output when the peak value of the first valley and the peak value of the second valley are close to each other due to the unevenness of the film thickness, and the setting condition may be that both peak values are close. .

  According to this embodiment, when the film thickness of the object to be measured is uneven and the measurement becomes unstable, and the peak value of the first valley and the peak value of the second valley are close to each other, a preset value is set. Since the alarm can be output while satisfying the set conditions, the user does not have to monitor whether or not the film thickness is uneven by visually observing the change in the peak value of the correlation diagram.

  (4) In still another embodiment of the film thickness measuring apparatus of the present invention, the output means includes a setting unit that sets a threshold value for the at least one peak value.

  According to this embodiment, an alarm can be output when one peak value exceeds the threshold and approaches the other peak value.

  (5) In another embodiment of the film thickness measuring apparatus of the present invention, the output means sets an alarm range for a difference between the peak value of the first valley and the peak value of the second valley. A setting unit is provided.

  According to this embodiment, an alarm can be output when both peak values are close to each other and enter the alarm range.

  According to the present invention, since the correlation diagram showing the correlation between each fitting level of each of the plurality of theoretical interference waveforms and the film thickness with respect to the actually measured interference waveform in the curve fitting method is created, whether or not the measured value is reliable is determined. The information of the correlation diagram can be used to determine

It is a perspective view showing the appearance of the film thickness measuring device concerning the embodiment of the present invention. It is a schematic block diagram of the film thickness measuring apparatus of FIG. It is a figure explaining the principle of the curve fitting method. It is a figure which shows a mode that it reflects on a board | substrate. It is a fitting level overview chart. FIG. 6 is a fitting level overview diagram when there is uneven thickness. FIG. 5 is a fitting level overview diagram when film thickness unevenness increases. It is a figure which shows a main display screen. It is a flowchart with which operation | movement description is provided. It is a figure which shows a parameter set edit screen.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a perspective view showing an appearance of a film thickness measuring apparatus according to an embodiment of the present invention. This film thickness measuring apparatus is formed by connecting a sensor head 1 and a controller 2 by an optical fiber cable 3. The controller 2 incorporates a light projecting unit 5, a light receiving unit 6, a control circuit 7 and the like shown in FIG. The optical fiber cable 3 is a bundle of a plurality of light projecting optical fibers and light receiving optical fibers, each of which includes a cable 3a that collects light projecting optical fibers at a predetermined position and a light receiving optical fiber. The collected cables 3b are divided and connected to the controller 2. In the figure, reference numeral 4 denotes a personal computer which is an external device, and is connected to the control circuit of the controller 2 by cable. This personal computer 4 is used for inputting setting data related to the substrate 8 to be measured, or for receiving and displaying a film thickness measurement result from the controller 2.

  The sensor head 1 is constructed by incorporating a condensing objective lens 1a shown in FIG. 2 and the like in a cylindrical case body, and the lens surface is disposed at a position above the substrate 8 to be measured by a predetermined distance. It is installed in a state facing the surface. The light from the light projecting unit 5 is irradiated onto the substrate surface from the sensor head 1 through the optical fiber cable 3a, and the reflected light from the substrate with respect to the irradiated light is received from the sensor head 1 through the optical fiber cable 3b. Guided to part 6.

  FIG. 2 is a block diagram showing a configuration of the film thickness measuring apparatus of FIG.

  This film thickness measuring device includes a light projecting unit 5, optical fibers 3a and 3b, a light receiving unit 6, and a control circuit 7, all of which are incorporated in the controller 2 described above.

  The light projecting unit 5 includes three LEDs 11, 12, 13 having different output wavelength characteristics, two dichroic mirrors 14, 15 having different transmission characteristics, and a condensing lens (not shown). Have a light source. For each of the LEDs 11 to 13, LEDs for red light emission, white light emission, and blue light emission are used.

  Light from the light projecting unit 5 is irradiated from the tip of the sensor head 1 to the surface of the substrate 8 to be measured via the optical fiber cable 3a. This light is reflected on the surface of the thin film 8a on the substrate body 8b and the boundary surface between the thin film 8a and the substrate body 8b. The reflected light is incident on the sensor head 1 and then received through the optical fiber cable 3b. Guided to part 6.

  The light receiving unit 6 includes a spectral filter 20 using an optical multilayer film, and a line CCD (a plurality of CCDs one-dimensionally arranged) 21. The reflected light is split into wavelengths by the spectral filter 20, and each of the split lights is taken into each CCD of the line CCD 21 to extract the intensity of the reflected light in the wavelength unit.

  The control circuit 7 includes an A / D conversion unit 23, a light projection amount, and a control unit 22 mainly composed of a microcomputer having various functions such as a function for creating a correlation diagram to be described later and a means for outputting an alarm. The adjustment unit 24, the light receiving sensitivity adjustment unit 25, the display control unit 26, the input / output unit 27, and the like are connected. The A / D converter 23 extracts received light from each CCD of the line CCD 21 and digitally converts it, thereby generating received light data indicating the intensity distribution (interference waveform) of the reflected light for each wavelength unit. The control unit 22 takes in the received light data and executes a film thickness measurement process.

  The input / output unit 27 is for fetching setting data such as material and optical constants for the substrate body 8b and the thin film 8a of the substrate 8 to be measured, and for outputting the film thickness measurement result to the outside of the apparatus. The display control unit 26 displays data on the display screen by giving display data such as the measurement result.

  The light projection amount adjusting unit 24 adjusts the output level of the light projecting unit 5 by controlling the drive circuit for the LEDs 11 to 13 of the light projecting unit 5 to adjust the light emission pulse interval. The light reception sensitivity adjustment unit 25 adjusts the light reception sensitivity by controlling the shutter time interval of the line CCD 21 or adjusting the gain of the amplification circuit 28 between the line CCD 21 and the A / D conversion unit 23.

  In such a film thickness measuring apparatus, the film thickness measuring process is started after the output level of the line CCD 21 is automatically adjusted by the adjusting units 24 and 25 in accordance with the type of substrate of the measurement object. In this measurement process, the control unit 22 sets data indicating a theoretical interference waveform when the thickness of the thin film is assumed to be a predetermined value for each predetermined number of film thicknesses, and then calculates the theoretical theoretical interference waveform and The thickness of the thin film is specified by a curve fitting method in which the measured interference waveform indicated by the received light data input from the A / D converter 23 is sequentially compared.

FIG. 3 is a diagram illustrating the principle of the curve fitting method. In the figure, S is a measured interference waveform indicated by measured light reception data. R _{A to} R _E are theoretical theoretical interference waveforms obtained by the following equation (1) for each film thickness, and each has different distribution shapes reflecting the phenomenon that the degree of light interference varies depending on the film thickness. Take.
R = 1−A / {B + C la cos [(4π / λ) ra n ra d]}... 1
Here, as shown in FIG. 4, R (%) is the reflectance of the thin film 30 when light having a wavelength λ is incident on the substrate 31 on which the thin film 30 is formed, λ is the incident light wavelength, and n is the thin film. The refractive index of 30, d is the thickness of the thin film 30, and A, B, and C are constants determined by the refractive indexes of the substrate 31 and the thin film 30.

  In the curve fitting method, the theoretical interference waveform having the shape closest to the measured interference waveform, that is, the square is obtained by sequentially obtaining the square sum of the difference for each wavelength with respect to each theoretical interference waveform for the measured interference waveform obtained from the measured light reception data. The theoretical interference waveform that minimizes the sum is specified, and the film thickness d (1000 nm in the illustrated example) corresponding to the theoretical interference waveform is set as the thickness of the thin film to be measured.

  Since the conventional film thickness measuring device only outputs the obtained film thickness and the fitting level related to the sum of squares of the minimum difference, there is information for judging the reliability of the obtained film thickness value. For example, when an uneven measurement occurs and the measurement becomes unstable and an erroneous measurement value is obtained, it is difficult to determine whether the measurement value is incorrect.

  Therefore, as a result of earnest research, the present inventors have plotted each fitting level of each of the plurality of theoretical interference waveforms with respect to the actually measured interference waveform against the film thickness. For example, as shown in FIG. It was found to be wavy with a peak in the part.

  FIG. 5 shows an actually measured interference waveform obtained by measuring a thin film having a thickness of 500 nm and theoretical interference waveforms having a thickness of 0 nm, 1 nm, 2 nm,. 4 is a correlation diagram in which 2001 fitting levels related to the sum of squares of differences are displayed in correspondence with film thicknesses of theoretical interference waveforms. In this embodiment, the square sum of the difference itself is used as each fitting level related to the square sum of the difference between the actually measured interference waveform and each theoretical interference waveform.

  The correlation diagram of FIG. 5 can be seen through the entire fitting level, and is also referred to as “fitting level overview diagram” hereinafter.

  As shown in FIG. 5, the true film thickness is 500 nm and the fitting level is minimum, and the conventional film thickness measuring device outputs the film thickness of 500 nm and the fitting level as a measurement result. become.

  As shown in FIG. 5, in the fitting level overview chart, the fitting level is usually minimized with a true film thickness, and has a wave shape having peaks at a plurality of valleys having a period of about 200 nm.

  Furthermore, according to the research of the present inventors, if the thickness of the 500 nm thin film to be measured is uneven, the actually measured interference waveform becomes a distorted waveform different from the theoretical waveform, and as a result, the fitting level overview chart For example, as shown in FIG. 6, the peak P1 of the first valley having a true film thickness of 500 nm and the peak P2 of the second valley having a thickness of 300 nm shifted by about 200 nm come close to each other.

  Further, when the non-uniformity of the film thickness increases and the distortion of the actually measured interference waveform increases, as shown in FIG. 7, the peak P1 of the first valley having a true film thickness of 500 nm and the second peak having a film thickness of 300 nm are obtained. The trough peak P2 is reversed, and an erroneous film thickness of 300 nm is output as a measurement value.

  In the conventional film thickness measuring device, only the measurement value of the film thickness and the value of the fitting level corresponding to the measurement value are output as the measurement result. Therefore, for example, the measurement is performed by flowing a substrate on which a 500 nm thin film is formed. If the measured value that was 500 nm is changed to 300 nm in the case where the thickness of the substrate is 300 nm, or whether the measured value is erroneously obtained due to the unevenness of the film thickness? It was not possible to judge.

  Therefore, in the film thickness measuring apparatus of this embodiment, in addition to the film thickness and the fitting level, the above-described fitting level overview chart can be displayed as a measurement result.

  Furthermore, the measurement becomes unstable before the peak P2 of the first trough portion having a true film thickness and the peak P2 of the second trough portion having another film thickness are reversed due to unevenness of the film thickness. The alarm range can be set between the peak value P1 of the first trough portion and the peak value P2 of the second trough portion of the true film thickness so that the user can be notified of this. When both the peak values P1 and P2 come close to each other, an alarm by display or sound is issued.

  FIG. 8 shows a main display screen displayed on the display of the film thickness measuring apparatus of this embodiment. Waveform data, film thickness measurement values, fitting level values, etc. are displayed together with various buttons. ing.

For example, when the user wants to measure the SiO ₂ film on Si, the measurement is performed according to the procedure shown in FIG.

  First, the user clicks a “parameter set edit” button 39 on the main display screen of FIG. 8 to move to the parameter set edit screen shown in step n1 and FIG.

In this parameter set edit screen,
Parameter set name: (Test) SiO ₂ on Si
Film type: SiO ₂
Substrate type: Si
Optical wavelength range to be measured: 460 to 680 nm
Step n2 is set, and the save button 40 is clicked to return to the main display screen in FIG.

Next, when a Si substrate without a film is installed at the measurement position and the “reference” button 32 is clicked on the main display screen of FIG. 8, step n4, and the application software refracts “Si” used when acquiring the reference. Based on the rate, absorption coefficient, and reflected light from the filmless Si substrate, the projecting and receiving parts are controlled to optimize the LED light emission amount and the light receiving dynamic range light receiving sensitivity of the CCD for SiO ₂ on Si. Set.

  In this state, a measurement is performed by flowing a substrate with a SiO2 film and measuring n5. When the “Measurement” button 33 on the main screen in FIG. 8 is clicked, the application software controls the light projecting unit and the light receiving unit, the received light data is taken into the control unit, and the film thickness is calculated based on the curve fitting method. The

  The calculation result is displayed in the waveform display area 34 on the main display screen of FIG. 8 as the theoretical waveform selected by the actually measured received light waveform / curve fitting method, and in the numerical value column 35 on the right side thereof, the film thickness is displayed. Values and fitting levels are displayed.

  Furthermore, in this embodiment, the above-mentioned fitting level overview chart 36 is displayed at the bottom of the display screen, and the threshold value L is displayed.

  The user operates the threshold value change button 37 as the setting unit to set the threshold value L to the peak P1 of the first valley portion having the true film thickness and the peak value of the second valley portion having another film thickness. Steps n6 and n7) are set at an appropriate level between P2 and the threshold value decision button 38 is clicked to confirm (step n8).

  Next, measurement is performed by flowing a substrate with a SiO2 film, and it is determined whether or not there are two or more peaks below the threshold value L in step n9 (step n10). Only the peak P1 of the first valley portion of the film thickness is below the threshold value and can be measured stably (step n11). In step n10, when there are two or more peaks that are lower than the threshold value L, the threshold level L is set so that there is only one peak that is lower than the threshold value by looking at the fitting level overview chart 36 on the main display screen. Adjust (step n12), then go to step n8.

  By performing several stable measurements as described above, an appropriate threshold value L is set, and after that, when an alarm is set and there are two or more peaks below the threshold value, An alarm is displayed when stable measurement is not performed.

  Note that threshold values may be set up and down, and the alarm range may be set between them.

  The present invention is useful as a film thickness measuring apparatus.

1 Sensor head 8 Substrate 20 Spectral filter 36 Fitting level overview

Claims (5)

The measured interference waveform obtained by irradiating the measurement object with light and dispersing the reflected light is compared with a plurality of theoretical interference waveforms respectively corresponding to the predicted plurality of film thicknesses, and the measured interference waveform and the A film thickness measuring apparatus that uses the film thickness of the measurement object as the film thickness corresponding to the theoretical interference waveform that minimizes the fitting level related to the square sum of the difference between the theoretical interference waveform and each wavelength,
A film thickness measuring apparatus comprising: a creation unit that creates a correlation diagram indicating a correlation between the fitting level obtained for each theoretical interference waveform and the film thickness corresponding to the theoretical interference waveform from which the fitting level is obtained. Display means for displaying the correlation diagram created by the creation means;
2. The film thickness measuring apparatus according to claim 1, wherein the correlation diagram is a diagram in which the horizontal axis indicates the film thickness and the vertical axis indicates the fitting level.   When at least one of the peak values of the first valley having the lowest fitting level in the correlation diagram and the peak value of the second valley having the second lowest fitting level satisfies the setting condition, The film thickness measuring apparatus according to claim 1, further comprising an output unit that outputs an alarm.   The film thickness measuring apparatus according to claim 3, wherein the output unit includes a setting unit that sets a threshold for the at least one peak value.   The film thickness measuring apparatus according to claim 3, wherein the output unit includes a setting unit that sets an alarm range for a difference between the peak value of the first valley and the peak value of the second valley.

Images