JP2009147207A - Plasma processing equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma processing apparatus capable of improving wavelength accuracy and accurately monitoring plasma emission. <P>SOLUTION: The plasma processing apparatus includes: an optical fiber 6 for introducing the plasma emission generated inside the plasma processing apparatus; a diffraction grating 9 for dividing the plasma emission introduced through the optical fiber into a plurality of spectrums; photodetectors 10 in a row for detecting the emission intensities of the spectrums divided with the diffraction grating for each spectrum; and a signal processor 12 for computing a plasma emission wavelength on the basis of a prescribed operational expression on the basis of the detection outputs of the photodetectors in a row. The signal processor compares the theoretical spectrum wavelength of a processing gas to be used in plasma processing or a material to be processed with a spectrum wavelength obtained when processing the material to be processed using the processing gas and corrects the operational expression on the basis of the compared result. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a plasma processing apparatus, and more particularly to a plasma processing apparatus capable of accurately monitoring plasma emission.

  Many plasma processing apparatuses are equipped with a multi-channel spectroscope capable of observing the emission intensity of a plurality of wavelengths (spectrums) and monitoring the plasma emission of a plurality of wavelengths.

  The multi-channel spectrometer includes a light receiving element of about 1000 pixels, for example, and each of the 1000 pixels receives light corresponding to a wavelength of, for example, 200 nm to 800 nm. The relationship between the pixel of the light receiving element and the wavelength is given in advance as a parameter expressed by a polynomial by the manufacturer of the spectrometer, and the corresponding wavelength can be specified for each pixel of the light receiving element.

As a wavelength calibration technique in such a spectroscope, Patent Document 1 is known. In this prior art, wavelength calibration using a gas cell is performed as a wavelength calibration method in a spectrometer that rotates a diffraction grating and extracts light of a specific wavelength. That is, the light split by the diffraction grating is incident on the gas cell, the light transmitted through the gas cell is incident on the photodetector, and the wavelength calibration of the spectrometer is performed using the absorption spectrum of the gas cell.
JP 2004-108808 A

  According to the prior art, the following problems occur. (1) The wavelength range of a multichannel spectrometer is generally wide (for example, 200 nm to 800 nm), and a wide wavelength calibration cannot be performed with a single gas. (2) The entrance slit, diffraction grating, and light receiving element constituting the multichannel spectrometer are fixed and hermetically sealed, and are relatively small. Therefore, it is difficult to install the gas cell between the diffraction grating and the light receiving element. (3) Since a gas cell is arranged, it is not strictly equivalent to a measurement system that actually observes light.

  In general, in order to monitor plasma emission of a plurality of wavelengths generated in a vacuum container, an optical fiber is attached to the vacuum vessel, and an iris (aperture) is attached to the other end of the optical fiber. Attach another optical fiber and attach this optical fiber to the multichannel spectrometer. The iris is a device that adjusts the amount of received light of the plasma emission intensity by changing its opening.

  Since many devices are connected between the vacuum vessel in which plasma is generated and the spectrometer that monitors the emission, when monitoring the plasma emission with the spectrometer, the wavelength shifts due to the influence of these devices alone or the connected part. May occur. In addition, although wavelength calibration of the spectrometer is performed at the time of shipment, wavelength shift may occur due to impact during transportation.

  The plasma processing apparatus detects, for example, an etching end point of a wafer based on a change in emission intensity of a specific wavelength obtained from a spectroscope. However, if there is a wavelength shift for the above reason, the detected emission intensity change is different from that of the correct wavelength, so that the etching end point cannot be detected correctly. If no change in emission intensity is obtained, the end point cannot be detected, resulting in an etching failure.

  The present invention has been made in view of these problems, and provides a plasma processing apparatus capable of improving wavelength accuracy and accurately monitoring plasma emission.

  In order to solve the above problems, the present invention employs the following means.

  An optical fiber that introduces plasma emission generated in the plasma processing apparatus, a diffraction grating that splits the plasma emission introduced through the optical fiber into multiple spectra, and the emission intensity of the spectrum dispersed by the diffraction grating for each spectrum And a signal processing device for calculating a plasma emission wavelength based on a predetermined calculation formula based on a detection output of the column-shaped light receiving device, the signal processing device for plasma processing. The theoretical spectral wavelength of the processing gas or material to be used is compared with the spectral wavelength obtained when the processing material is processed using the processing gas using the plasma processing apparatus, and the comparison result is obtained. Based on the above, the arithmetic expression is calibrated.

  Since the present invention has the above-described configuration, it is possible to provide a plasma processing apparatus capable of improving wavelength accuracy and accurately monitoring plasma emission.

  Hereinafter, the best embodiment will be described with reference to the accompanying drawings. FIG. 1 is a diagram illustrating an etching processing apparatus according to the present embodiment. The etching processing apparatus (plasma processing apparatus) 1 includes a vacuum vessel 2, into which an etching gas is introduced through a gas introduction unit (not shown), and the introduced gas is irradiated with microwave power to generate plasma 3. Generate. The plasma 3 etches the material to be processed 4 such as a semiconductor wafer on the sample stage 5.

  Multi-wavelength light generated from the plasma 3 is guided to the spectroscope 11 via the optical fiber 6. A lens (not shown) is attached between the vacuum vessel 2 and the optical fiber 6. This lens plays a role of condensing the plasma light in the vacuum vessel 2 onto the optical fiber 6. An iris (aperture) 7 is provided in the middle of the optical fiber 6, and the emission intensity incident on the spectroscope 11 can be adjusted by the iris 7. Lenses (not shown) are attached to both ends of the iris 7 connected to the optical fiber 6. Light incident on the iris 7 from the optical fiber 6 is converted into parallel light by the lens and guided to the iris 7. The light whose intensity is adjusted by the iris 7 is collected by the other lens and introduced into the optical fiber 6 connected to the spectroscope 11.

  The amount of incident light of the multi-wavelength light guided to the spectroscope 11 is limited by the slit 8. Thereafter, the multi-wavelength light is split by the diffraction grating 9 and is incident on the light receiving element 10 for each wavelength. In the light receiving element 10, an optical signal is converted into an electric signal by the photoelectric effect, and an electric signal corresponding to the light intensity is sent to the digital processing device 12. The digital processing device 12 monitors the signal intensity corresponding to the light intensity of multiple wavelengths, and detects the end point of etching based on this signal intensity change.

  FIG. 2 is a diagram for explaining the relationship between the light receiving element in the spectrometer and the light wavelength. The light receiving element inside the spectroscope 11 is composed of a CCD line sensor of 1000 pixels, for example. Light of each wavelength split by the diffraction grating 9 shown in FIG. 1 is incident on this light receiving element. At this time, the relationship between the wavelength of the incident light and the pixel number of the light receiving element is given by, for example, a polynomial expression (1). Note that, in this optical system of the spectroscope, the image sensor in which the CCD pixel elements that receive the light from the spectral grating are arranged is not arranged so that all the wavelengths of light are parallel. This is used to correct the difference in the output of the element even if the wavelength is the same for each wavelength.

λ = a + b * Pix + c * Pix * Pix + d * Pix * Pix * Pix
+ C * Pix * Pix * Pix * Pix (1)
Here, a, b, c, d, e indicate wavelength parameters, λ indicates a wavelength, and Pix indicates a pixel number (Pix: 1-1000) of the light receiving element. The wavelength parameters of a, b, c, d, and e are determined in advance by the manufacturer when the spectrometer is shipped. The pixel number of the light receiving element corresponding to the intensity of a certain wavelength can be known from the equation (1) and the wavelength parameters of a, b, c, d, and e.

  As shown in FIG. 2, for example, the first pixel (leftmost pixel) of the light receiving element detects the spectral intensity having a wavelength λ of 200 nm.

  The wavelength parameters a, b, c, d, and e are parameters obtained by the manufacturer by entering appropriate light at the time of shipment of the spectrometer. However, when the actual plasma emission is monitored after being attached to the etching apparatus. The emission wavelength may be shifted. There are two reasons for this, and one of them is the case where the position of the diffraction grating or the light receiving element inside the spectroscope is shifted due to vibration during transportation, and the emission wavelength is thereby shifted. In the other, hardware such as the optical fiber 6, the iris 7, and the spectroscope 11 is interposed in the path for monitoring the plasma intensity generated in the etching chamber. It is known that a wavelength shift occurs when it is attached in a state where the is applied. That is, the wavelength shift occurs not only by a single component but also by a component joint.

  In this embodiment, in order to solve the above-described wavelength shift, wavelength calibration is performed for the entire spectroscope system including the optical fiber 6, the iris 7, and the spectroscope 11.

The emission spectrum at the time of etching shows different intensities depending on the gas used for etching and the wafer film type, and becomes an intensity spectrum depending on the etching gas and the wafer film type. Therefore, in this embodiment, Ar and Cl ₂ are used as the etching gas, a Si wafer is used as the wafer, and wavelength calibration is performed using the emission intensity spectrum when the wafer is etched.

  In this example, the above-mentioned wafer and gas are selected as gas and wafer that are easy to use in the operation of the apparatus, but other types of gas and wafer may be used. In this case, the shape of the emission spectrum is different from the example of this embodiment.

  When performing calibration of wavelength calibration of the spectrometer system, the calibration is performed in a state where a calibration wafer having a specific film structure is placed on the sample stage 5. The test wafer is placed on a cassette table stored in the cassette and arranged on the atmosphere side of the apparatus, and is mounted on the cassette table using the transfer means of the etching apparatus. The test wafer may be a dummy wafer used for cleaning or the like.

FIG. 3 is a diagram showing main emission spectrum wavelengths (theoretical wavelengths) of Ar, Cl ₂ and Si used in etching performed for wavelength calibration. The emission spectrum at the time of etching has an intensity peak mainly at the wavelength shown in FIG.

FIG. 4 is a diagram showing an emission spectrum when the Si wafer is etched using the etching gas Ar, Cl ₂ .

  It can be seen that a peak exists in the emission spectrum near the wavelength shown in FIG. If the peak wavelength of the emission spectrum matches the theoretical wavelength shown in FIG. 3, it can be said that the wavelength shift has not occurred.

  When the peak wavelength of the emission spectrum does not match the theoretical wavelength shown in FIG. 3, a wavelength shift has occurred, and the wavelength parameter expressed by a, b, c, d, e in Equation (1). Need to be recalculated. For recalculation of the wavelength parameter, emission spectrum data at the time of actual etching is used.

  In the recalculation, the number and wavelength (peak pixel) of the pixel (peak pixel) that detected the peak of the spectral intensity at the 14 wavelengths (9 wavelengths of Ar, 3 wavelengths of Si, 2 wavelengths of Cl) for each element shown in FIG. The relationship of the theoretical wavelength) is extracted, and the wavelength parameter of equation (1) is obtained by linear regression approximation.

  In this example, the 14-wavelength data shown in FIG. 3 is used to obtain the wavelength parameter shown in Expression (1). However, in the case of Expression (1), the wavelength parameter is obtained if there is data for at least 5 wavelengths. be able to.

FIG. 5 is a diagram for explaining wavelength calibration processing. First, in step 501, a Si wafer used for wavelength calibration is transferred into the vacuum container (etching chamber) 2 (steps 501 and 502). Next, etching is performed on the Si wafer carried in using Ar, Cl ₂ gas (step 503). At this time, the emission spectrum during etching is stored in the digital processor 12 (step 504).

  Next, it is determined whether or not the peak wavelengths in the stored emission spectrum match, for example, the 14 peak wavelengths (theoretical values) shown in FIG. 3 (less than an allowable value) (step 505).

  If all of the peak wavelengths in the stored emission spectrum match the peak wavelengths (theoretical values) shown in FIG. 3, the wavelength calibration result is normal, and the wavelength calibration is terminated (step 507). Here, the allowable value is set to ± 1 nm.

  Here, if even one of the 14 wavelengths is outside the allowable value, it is determined that a wavelength shift has occurred, and the number of the pixel (peak pixel) that has detected each peak at the 14 wavelengths. Then, the wavelength parameters a, b, c, d, and e in the equation (1) are obtained by linear regression from the relationship between the theoretical wavelength and the theoretical wavelength (step 506). The obtained wavelength parameter is used as a correct value from the next time.

  In the above description, an example has been shown in which wavelength calibration is performed using a Si wafer, but calibration may be performed using a dummy wafer of the same film type as the material of the product to be processed after calibration. By performing wavelength calibration with a dummy wafer of the same film type as the product, the wavelength used for end point determination can be included in the wavelength calibration, and more optimal wavelength calibration becomes possible.

  The wavelength calibration is performed after the assembly of the etching apparatus is completed, and the correct wavelength parameter for the spectroscope system is obtained. Further, it is desirable to perform wavelength calibration at the timing when the components constituting the spectroscope system are replaced or when the received light intensity adjustment by the iris 7 is performed.

  As described above, according to the present embodiment, the emission spectrum can be acquired with an accurate wavelength in the plasma emission monitor by the spectrometer system of the plasma processing apparatus.

  In addition, since wavelength calibration is performed using an actual measurement system, it is possible to provide a spectroscope system having no wavelength shift among a plurality of plasma processing apparatuses. As described above, since wavelength calibration including wavelength shift caused by connection between hardware units or devices can be performed, a spectrometer system capable of monitoring the correct wavelength can be provided.

It is a figure explaining the etching processing apparatus concerning this embodiment. It is a figure explaining the relationship between the light receiving element inside a spectrometer, and a light wavelength. It is a figure which shows the gas emission spectrum wavelength (theoretical wavelength) used by the etching performed in wavelength calibration. It is a figure which shows the emission spectrum at the time of etching a Si wafer using etching gas. It is a figure explaining the process of wavelength calibration.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Etching apparatus 2 Vacuum container 3 Plasma 4 Material to be processed 5 Sample stand 6 Optical fiber 7 Iris (aperture)
8 Slit 9 Diffraction grating
10 light receiving element 11 spectroscope 12 digital processing device

Claims (3)

An optical fiber for introducing plasma emission generated in the plasma processing apparatus;
A diffraction grating that splits plasma emission introduced through an optical fiber into a plurality of spectra;
A row of light receiving elements that detect the emission intensity of the spectrum separated by the diffraction grating for each spectrum;
A signal processing device that calculates a plasma emission wavelength based on a predetermined calculation formula based on the detection output of the row-shaped light receiving elements,
The signal processing apparatus includes a theoretical spectrum wavelength of a processing gas or a material to be processed used for plasma processing and a spectrum obtained when the processing material is processed with the processing gas using the plasma processing apparatus. A plasma processing apparatus that compares wavelengths and calibrates the arithmetic expression based on the comparison result. The plasma processing apparatus according to claim 1,
A plasma processing apparatus comprising a diaphragm for adjusting a light amount in a light guide path formed by the optical fiber. A diffraction grating that splits plasma emission introduced from a plasma processing apparatus through an optical fiber into a plurality of spectra;
A row of light receiving elements that detect the emission intensity of the spectrum separated by the diffraction grating for each spectrum;
A signal processing device that calculates a plasma emission wavelength based on a predetermined calculation formula based on the detection output of the row-shaped light receiving elements,
The signal processing apparatus includes a theoretical spectrum wavelength of a processing gas or a material to be processed used for plasma processing and a spectrum obtained when the processing material is processed with the processing gas using the plasma processing apparatus. Comparing wavelengths, calculating the plasma emission wavelength by calibrating the calculation formula based on the comparison result, and detecting the end point of the plasma processing based on the spectrum intensity of the calculated wavelength apparatus.

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