JP5045498B2 - Method and apparatus for detecting end point of dry etching - Google Patents

Description

  The present invention relates to end point detection in an etching process used for manufacturing a photomask or a reticle used in lithography in semiconductor manufacturing.

  With the recent miniaturization and higher integration of semiconductors, the aperture ratio (area to be etched of a semiconductor wafer) in a semiconductor wafer is decreasing. Since the photomask is an original plate, the aperture ratio tends to be reduced similarly, and it is difficult to determine the etching end point of the pattern at the time of manufacturing the photomask.

  In lithography using a light source with a wavelength of 13.5 nm, which is an extreme ultraviolet (EUV) region, which is being developed in recent years, the reduced projection exposure method is a conventional KrF laser (wavelength 248 nm), Similar to ArF laser (wavelength 193 nm), the photomask magnification is expected to be 4 or 5 times. Therefore, compared to conventional light sources using KrF laser and ArF laser, the pattern size on the photomask is also made smaller at the same magnification, and the end point of etching must be determined from this fine pattern. Judgment is difficult.

  As a method for forming a fine pattern, a dry etching method using gas plasma has become an essential technique. Such an etching process is a method of generating a plasma using a reactive gas in a vacuum and removing an object to be etched using ions, neutral radicals, atoms, molecules, etc. in the plasma.

  As a conventional end point determination method, there are known a method in which a predetermined time is set as the end point, and a method in which plasma emission generated in the etching chamber is optically measured and determined. As an example, a method of measuring an emission spectrum by a spectroscopic method (Patent Document 1) and a method using an optical fiber to guide emitted light to a detector are known (Patent Document 2). Further, a method (Patent Document 3) for processing an image obtained from an area sensor is known.

  In addition to the end point detector / device, these devices using an optical technique for determining the end point may be called an end point monitor or a plasma monitor.

  A common problem in the above-described method for optically measuring and determining plasma emission is that sufficient emission intensity cannot be obtained when the etching area (aperture ratio) that changes the emission is small. In addition to the gas introduced for etching, the light that exists in the plasma includes light emission that depends on various chemical species, such as reaction products with the material to be etched, and only light that depends on the material to be etched. is not.

  Further, when the emission spectrum of the underlying material of the object to be etched is approximate, the end point determination itself is impossible. As a countermeasure against this, there is an application that limits the wavelength region used for determination (Patent Document 4). However, in the spectroscopic methods of these prior applications, the wavelength range is limited to the wavelength range of 200 nm to 800 nm, which is the near-infrared to near-infrared region.

  As a method other than detecting the plasma emission, there is an apparatus for irradiating lamp light and using a reflection spectrum from an etching object and a mask material to determine from the difference (Patent Document 5). However, in this case, since a wide range of wavelengths are always irradiated, the so-called resist mask method in which the mask material of the pattern in etching uses an ultraviolet curable resin is excessively photosensitive, and the resistance is deteriorated due to deterioration. In some cases, there is a risk that the pattern dimensions may change due to the shrinkage phenomenon of the ultraviolet curable resin.

  Since the photomask for lithography using a conventional KrF laser (wavelength 248 nm) and ArF laser (wavelength 193 nm) as a light source is a transmission type, the reflection of the laser light is actually reflected on the quartz glass surface of the substrate, Rather than detecting the reflectivity, this determined the point in time when the reflection disappeared due to transmission. This conventional method is effective for a transmissive mask, but in principle, a reflective mask such as a mask for extreme ultraviolet (EUV) exposure lithography cannot use the method of determining the transmission point, and a new means is required. It is said that.

JP 2001-176851 A Japanese Patent No. 2559731 Japanese Patent No. 3637324 JP-A-7-66173 JP-A 61-149955

  Therefore, the present invention has been made to solve the above-described problems. Unlike the plasma emission method, the present invention selects and selects only a unique wavelength that provides an optical contrast between an etching material and its underlying material. An object of the present invention is to provide a method and an apparatus for irradiating irradiated light and determining an etching end point from the intensity of reflected light.

In claim 1 of the present invention, in the process of etching the material to be etched on the surface of the substrate installed in the vacuum vessel using plasma formed by introducing gas into the vacuum vessel and applying high frequency power,
A light source that generates light including light in a wavelength range of less than 200 nm;
A spectroscope for spectrally separating light from the light source;
Irradiation light wavelength selection means for selecting light in a predetermined wavelength region from the dispersed light and passing it as irradiation light;
A first beam splitter that reflects a portion of the illumination light and transmits another portion;
A first condensing optical system for condensing and irradiating a part of the irradiation light reflected by the first beam splitter onto a substrate surface;
First reflected light detection means for detecting reflected light reflected from the substrate surface by irradiation light from the first condensing optical system and generating a first detection signal;
A light chopper disposed in the optical path of the irradiation light transmitted through the first beam splitter;
A second beam splitter that reflects part of the irradiation light that has passed through the light chopper and transmits another part;
A second condensing optical system for condensing and irradiating a part of the irradiation light reflected by the second beam splitter onto a substrate surface;
Second reflected light detection means for detecting a reflected light reflected from the substrate surface by irradiation light from the second condensing optical system and generating a second detection signal;
A window for introducing irradiation light from the first and second condensing optical systems into the vacuum vessel;
A memory for receiving and storing the first and second detection signals;
The first and second detection signals obtained at an arbitrary time during the etching process of the substrate stored in the memory, and a detection signal of reflected light from the material of the layer below the etching target material on the substrate surface Comparing means for calculating the difference, and
Determination means for determining that the etching of the material to be etched is completed using the calculation result of the comparison means;
Display means for displaying the determination result;
The dry etching end point detection device is characterized by comprising:

In claim 2 of the present invention,
In the process of etching the material to be etched on the surface of the substrate installed in the vacuum vessel using plasma formed by introducing gas into the vacuum vessel and applying high frequency power,
A light generation stage for generating light including light in a wavelength range of less than 200 nm;
A spectroscopic step of splitting light from the light source;
An irradiation light wavelength selection step of selecting light in a predetermined wavelength region from the dispersed light and passing it as irradiation light;
A first optical path splitting step for reflecting a part of the irradiation light and transmitting another part;
A first condensing irradiation step of condensing and irradiating a part of the irradiation light reflected in the first optical path dividing step onto the substrate surface;
A first reflected light detection step of detecting a reflected light reflected by the substrate surface by the irradiation light irradiated in the first focused irradiation step to generate a first detection signal;
An irradiation light intensity fluctuation step for periodically changing the intensity of the irradiation light transmitted through the first optical path dividing step;
A second optical path splitting step of reflecting a part of the irradiation light whose intensity is varied by the irradiation light intensity fluctuation stage and transmitting another part thereof;
A second condensing irradiation step of condensing and irradiating a part of the irradiation light reflected in the second optical path dividing step onto the substrate surface;
A second reflected light detection step of detecting a reflected light reflected by the substrate surface by the irradiation light irradiated in the second focused irradiation step and generating a second detection signal;
An irradiation light introduction step for introducing irradiation light into the vacuum vessel in the first and second focused irradiation steps;
A detection signal storing step of receiving and storing the first and second detection signals;
From the first and second detection signals obtained at any time during the etching process of the substrate stored in the detection signal storing step, and from the material of the layer under the material to be etched on the substrate surface A comparison stage for comparing the detection signals of the reflected light and calculating the difference;
A determination step of determining that the etching of the etching target material is completed using the calculation result in the comparison step;
A display stage for displaying the judgment result;
This is a dry etching end point detection method characterized by comprising:

  The dry etching end point detection method and apparatus according to the present invention is characterized in that, in the manufacture of a photomask for extreme ultraviolet exposure, the etching end point is detected by using a difference in reflectance at a specific wavelength between the material to be etched and its underlayer. To do.

  Hereinafter, embodiments of the dry etching end point determination apparatus of the present invention will be described. This embodiment shows a case where the present invention is applied to a photomask or reticle (hereinafter referred to as EUV mask) for extreme ultraviolet lithography.

  Unlike the conventional photomask structure using a wavelength of 248 nm (KrF laser) or 193 nm (ArF laser), the EUV mask uses light with a wavelength of 13.5 nm that does not pass through a quartz material. It becomes. FIG. 1 shows an example of the cross-sectional structure. It is composed of a multilayer film. From the incident direction of light, the low reflection part (film) 10, the absorption part (film) 20, the buffer part (film) 30, the protection part (film) 40, the multilayer reflection part (film) 50, and the substrate 60 The back surface conductive portion (film) 70.

  The portions that form the optical contrast (brightness and darkness) to be a pattern are basically the multilayer reflecting portion (film) 50 and the absorbing portion (film) 20. However, a wavelength other than 13.5 nm may be used for pattern inspection. For such a case, the contrast (reflected light Rf / reflected light Rm) with the multilayer reflective portion (film) 50 is improved. For the purpose, a low reflection portion (film) 10 may be formed.

  The buffer portion (film) 30 is a sacrificial portion (film) that protects the reflective portion from damage when the mask is corrected by a physical or chemical reaction. The protective part (film) 40 is for protecting the reflective part (film) 50 from alteration due to surface oxidation or the like. The back surface conductive portion (film) 70 is used when the electrostatic adsorption principle is used for mounting on an exposure apparatus.

Specific materials of each part of the EUV mask are as follows.
The low reflection part (film) 10 and the absorption part (film) 20 are mainly composed of tantalum (Ta) and contain at least one of silicon (Si), oxygen (O), and nitrogen (N). The buffer part (film) 30 is mainly composed of chromium (Cr) or zirconium (Zr) and contains at least one of oxygen (O), nitrogen (N), and silicon (Si). The protective part (film) 40 is made of silicon (Si), ruthenium (Ru), or the like. The multilayer reflecting portion (film) 50 is formed of a multi-layered film including silicon (Si) and molybdenum (Mo) as a pair.

  Quartz is used for the substrate 60, and synthetic quartz added with titanium (Ti) or titanium oxide (TiO) is particularly preferably used. It is known that this synthetic quartz has a lower thermal expansion coefficient than quartz without addition. The back surface conductive portion (film) 70 is mainly composed of chromium (Cr) and contains at least one of oxygen (O) and nitrogen (N).

  The reflection spectrum of an EUV mask manufactured using the above materials is shown in FIG. Rf is reflected light from the low reflection portion (film) 10, and Rm is reflected light from the protection portion (film) 40. From the difference between Rf and Rm indicated by (Rm−Rf) in FIG. 2, it can be seen that the etching end point has a contrast at a wavelength of less than 200 nm and can be used for end point determination.

Hereinafter, the configuration of a dry etching end point determination apparatus according to an embodiment of the present invention will be described with reference to FIG.
This apparatus includes an optical unit 200 and a control unit 300. The optical unit 200 is connected to the mask 100 installed in the dry etching apparatus 400 through the window 500.

  For convenience of explanation, in FIG. 3, the mask 100 shows the state where the resist pattern 80 before etching is formed on the left side and the state where there is no resist pattern 80 on the right side as in FIG. The light emitted from the light source 210 installed in the optical unit 200 is divided by the half mirror 220A, and one is irradiated as incident light Im (solid line) to the mask 100 by the condensing optical system 230A in the unit Rm.

  The reflected light Rm (dotted line) from the mask 100 is transmitted again through the condensing optical system 230A and the half mirror 220A and enters the detector 240A. The detector 240 </ b> A photoelectrically converts the reflected light Rm and outputs a detection signal Rm corresponding to the light intensity to the memory 310 installed in the control unit 300.

  The other light Ia divided by the half mirror 220A enters the half mirror 220B of the unit Ra. The reflected light Ra (dotted line) from the mask 100 is transmitted again through the condensing optical system 230B and the half mirror 220B and enters the detector 240B. The detector 240B photoelectrically converts the reflected light Ra, and outputs a detection signal Ra corresponding to the light intensity to the memory 310 installed in the control unit 300.

  The comparator 320 outputs the difference between the detection signal Rm input to the memory 310 and the reflected light Rm3 from the M3 unit input in advance to the memory 310 to the determination unit 330.

  The determination unit 330 determines that the etching is completed when a signal indicating that the difference between the detection signal Rm and the detection signal Rm3 input in advance is zero, and ends the etching on the display unit 340 to end the etching.

  The detection signal Ra is observed to monitor how the film thickness of the resist pattern 80 is reduced as the etching progresses. The reflected light intensity signal value Rm0 on the mask surface is measured by the unit Rm simultaneously with the start of etching and is input to the memory 310. When the resist pattern 80 finally disappears, the detection signal Ra becomes equal to the reflected light intensity signal value Rm0, so that the comparator 320 transmits to the determiner 330 that the difference between Rm0 and Ra is zero. The determination unit 330 determines that the resist pattern 80 has disappeared, displays the disappearance of the resist pattern 80 on the display 340, and ends the etching.

  Here, the light chopper 250 will be described with reference to FIGS. In the above description, the reflected lights Rm and Ra from the mask 100 are simultaneously incident on the detectors 240A and 240B, respectively. At this time, as indicated by a two-dot chain line in FIG. 4, a part of the reflected light Ra enters the detector 240A via the half mirror 220B and the half mirror 220A. In this case, a part of the reflected light Ra is added to the detector 240A in addition to the original reflected light Rm, and the change of the reflected light Rm due to the original etching cannot be obtained.

  Therefore, as shown in FIG. 4, a light chopper 250 is disposed between the half mirror 220A and the half mirror 220B so that signals of Ra and Rm are obtained alternately and periodically. As schematically shown in FIG. 5, the light chopper 250 includes a rotating disk 251 and a rotating motor 252. An opening 253 and a light shielding part 254 are periodically provided in a part of the circumference of the rotating disk 251. By rotating this with a rotary motor 252, a state where light from the light source 210 is transmitted and a state where it is shielded are created.

  FIG. 6 is a timing chart showing the state of transmission and light shielding. The light receiving timings at the detectors 240A and 240B are as shown in FIGS. 6 (a) and 6 (b), respectively. Since the detector 240A is located closer to the light source 210 than the light chopper 250, it is always in a light receiving state. On the other hand, the detector 240 </ b> B is in a light receiving state only when the opening 253 of the light chopper 250 transmits light from the light source 210.

  As described above, part of the reflected light Ra is incident on the detector 240A via the half mirror 220B and the half mirror 220A (see FIG. 4). Therefore, when the detector 240B is in the light receiving state, the detector 240A The detected light does not represent the fluctuation of the reflected light Rm accompanying the original etching.

  Therefore, the detector 240A stops signal output when the detector 240B is in the light receiving state, and the detector 240A may restart signal output when the detector 240B is in the light shielding state. FIG. 6 (aa) shows the timing. FIG. 6 (aa) is an inversion of FIG. 6 (b), and can be obtained as a trigger when the input to the detector 240B becomes zero.

  Next, the light source 210 will be described with reference to FIG. Using the deuterium lamp 211 as a radiation source, the light is condensed by an elliptical mirror 212 and dispersed by a diffraction grating 213. The diffraction grating 213 rotates to irradiate the slit 214 with light that is continuously dispersed. In the slit 214, only light in a desired wavelength region is selectively passed and irradiated on the parabolic mirror 215. The reflected light from the parabolic mirror 215 is parallel light, and this parallel light is incident on the half mirror 220A shown in FIGS.

  3 and 4, the half mirrors 220A and 220B installed in the optical unit 200 and the window 500 are quartz to which calcium fluoride (CaF2) or fluorine (F), which is a material that transmits vacuum ultraviolet rays, is added. It is preferable to use a plate.

  Next, detectors 240A and 240B will be described with reference to FIG. For detection of light having a wavelength of less than 200 nm, reflected light Ra or Rm from the mask is received by a quartz plate 242 coated with sodium salicylate 241, and fluorescence generated there is photoelectrically converted by a photomultiplier tube 244, and an electric signal Get.

  A coating material for the quartz plate 242 other than sodium salicylate may be Coronene (C24H12). Further, a charge coupled device (CCD) may be used for photoelectric conversion. Incidentally, in order to improve the photoelectric conversion efficiency of the secondary light, an integrating sphere 243 for condensing, etc. is installed in the front stage of the photomultiplier tube 244. In addition, a filter 245 that blocks light having a wavelength longer than 200 nm is installed in front of the quartz plate 242.

  In the present invention, light in the vacuum ultraviolet region having a wavelength of less than 200 nm is used, and therefore, the optical path inside the optical unit 200 is preferably a reduced pressure or nitrogen atmosphere with a vacuum pump.

  A specific detection flow of the dry etching end point detection apparatus of the present invention described above will be described with reference to FIG.

<Step 1>
A mask to be etched is placed in a dry etching apparatus. The start-up operation of the entire dry etching end point detection apparatus of the present invention is performed, and measurement is started.

<Step 2>
The reflection spectrum Sm3 of the etching end surface M3 measured in advance is input to the memory 310.

<Step 3>
The mask surface is left in a state where the resist pattern M1 and the etching surface M2 are exposed. The reflection spectra Sm 1 and Sm 2 of these two surfaces are measured and input to the memory 310. Here, the measurement of the reflection spectra Sm1 and Sm2 is to measure the intensity of the reflected light with the detectors 240A and 240B while rotating the diffraction grating 213 in the light source 210 to change the wavelength of the irradiation light.

<Step 4>
The difference spectrum between the reflection spectra Sm2 and Sm3 is calculated, and the wavelength at which the difference value of the light intensity is maximum is selected as the measurement wavelength Ir. The larger the difference value, the larger the signal width of the reflectance transition due to etching, and the end point determination accuracy increases.

<Step 5>
For the measurement wavelength Ir obtained in Step 4, the reflectance intensities Rm1, Rm2, and Rm3 at the corresponding wavelengths in the reflection spectra Sm1, Sm2, and Sm3 are extracted from the memory 310 and stored in the memory 310 again.

<Step 6>
Etching is started, and the reflected light intensity Rm2 of the etched portion M2 is measured with the unit Rm, and the reflected light intensity Rm1 of the resist pattern portion M1 is measured with time by the unit Ra.

<Step 7>
In order to determine the disappearance of the resist pattern, the difference between the reflected light intensity Rm2 and Rm1 at the start of etching is calculated, and when it is zero, it is determined that it has disappeared (Yes) and the etching is stopped (Steps 10 to 12). If it is not zero, it is determined that it has not disappeared (No) and etching is continued.

<Step 8>
When the etching is continued at Step 7, the end point is determined. In this determination, the difference between the reflected light intensities Rm2 and Rm3 is calculated, and when it is zero, it is determined that the end point has been reached (Yes), and the etching is stopped (Steps 10 to 12). If it is not zero, it is determined that the end point has not been reached (No), and etching is continued (Step 9), and the process returns to Step 6.

  By the processing procedure as described above, the etching end point can be detected.

The dry etching end point detection method and apparatus of the present invention are expected to be used in a manufacturing process using a dry etching method in a semiconductor device or the like in which fine pattern formation is desired.

It is sectional drawing which shows the structure of the mask for extreme ultraviolet exposure. It is a figure which shows the wavelength dependence of the reflectance of each part of the mask for extreme ultraviolet exposure. It is a schematic block diagram of the dry etching end point determination apparatus of the embodiment of the present invention. It is a figure which shows the optical path of the dry etching end point determination apparatus of embodiment of this invention. It is a figure which shows the light chopper of the dry etching end point determination apparatus of embodiment of this invention. It is a figure which shows the light reception timing of the detector of the dry etching end point determination apparatus of embodiment of this invention. It is a lineblock diagram of a light source of dry etching end point judging device of an embodiment of the present invention. It is a block diagram of the detector of the dry etching end point determination apparatus of the embodiment of the present invention. It is a figure which shows an example of the detection flow of the dry etching end point determination apparatus of embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Low reflective layer 20 ... Absorbing layer 30 ... Buffer layer 40 ... Protective layer 50 ... Multilayer reflective layer 60 ... Substrate 70 ... Back surface conductive layer 80 ... Resist pattern 100 ·· Mask 200 · · Optical unit 210 · · Light source
211 ·· Deuterium lamp 212 · · Elliptical mirror 213 · · Diffraction grating 214 · · Slit 220A · · Half mirror 220B · · Half mirror 230A · · Condensing optical system
230B ... Condensing optical system 240A ... Detector 240B ... Detector 241 ... Sodium salicylate 242 ... Quartz plate 243 ... Integrating sphere 244 ... Photomultiplier tube 245 ... Filter 251 ... Rotating plate 252 -Motor 253-Opening 254-Shading unit 300-Control unit 310-Memory 320-Comparator 330-Determinator 340-Display 400-Dry etching apparatus 500-Window

Claims (2)

In the process of etching the material to be etched on the surface of the substrate installed in the vacuum vessel using plasma formed by introducing gas into the vacuum vessel and applying high frequency power,
A light source that generates light including light in a wavelength range of less than 200 nm;
A spectroscope for spectrally separating light from the light source;
Irradiation light wavelength selection means for selecting light in a predetermined wavelength region from the dispersed light and passing it as irradiation light;
A first beam splitter that reflects a portion of the illumination light and transmits another portion;
A first condensing optical system for condensing and irradiating a part of the irradiation light reflected by the first beam splitter onto a substrate surface;
First reflected light detection means for detecting reflected light reflected from the substrate surface by irradiation light from the first condensing optical system and generating a first detection signal;
A light chopper disposed in the optical path of the irradiation light transmitted through the first beam splitter;
A second beam splitter that reflects part of the irradiation light that has passed through the light chopper and transmits another part;
A second condensing optical system for condensing and irradiating a part of the irradiation light reflected by the second beam splitter onto a substrate surface;
Second reflected light detection means for detecting a reflected light reflected from the substrate surface by irradiation light from the second condensing optical system and generating a second detection signal;
A window for introducing irradiation light from the first and second condensing optical systems into the vacuum vessel;
A memory for receiving and storing the first and second detection signals;
The first and second detection signals obtained at an arbitrary time during the etching process of the substrate stored in the memory, and a detection signal of reflected light from the material of the layer below the etching target material on the substrate surface Comparing means for calculating the difference, and
Determination means for determining that the etching of the material to be etched is completed using the calculation result of the comparison means;
Display means for displaying the determination result;
An end point detection device for dry etching, comprising:
In the process of etching the material to be etched on the surface of the substrate installed in the vacuum vessel using plasma formed by introducing gas into the vacuum vessel and applying high frequency power,
A light generation stage for generating light including light in a wavelength range of less than 200 nm;
A spectroscopic step of splitting light from the light source;
An irradiation light wavelength selection step of selecting light in a predetermined wavelength region from the dispersed light and passing it as irradiation light;
A first optical path splitting step for reflecting a part of the irradiation light and transmitting another part;
A first condensing irradiation step of condensing and irradiating a part of the irradiation light reflected in the first optical path dividing step onto the substrate surface;
A first reflected light detection step of detecting a reflected light reflected by the substrate surface by the irradiation light irradiated in the first focused irradiation step to generate a first detection signal;
An irradiation light intensity fluctuation step for periodically changing the intensity of the irradiation light transmitted through the first optical path dividing step;
A second optical path splitting step of reflecting a part of the irradiation light whose intensity is varied by the irradiation light intensity fluctuation stage and transmitting another part thereof;
A second condensing irradiation step of condensing and irradiating a part of the irradiation light reflected in the second optical path dividing step onto the substrate surface;
A second reflected light detection step of detecting a reflected light reflected by the substrate surface by the irradiation light irradiated in the second focused irradiation step and generating a second detection signal;
An irradiation light introduction step for introducing irradiation light into the vacuum vessel in the first and second focused irradiation steps;
A detection signal storing step of receiving and storing the first and second detection signals;
From the first and second detection signals obtained at any time during the etching process of the substrate stored in the detection signal storing step, and from the material of the layer under the material to be etched on the substrate surface A comparison stage for comparing the detection signals of the reflected light and calculating the difference;
A determination step of determining that the etching of the etching target material is completed using the calculation result in the comparison step;
A display stage for displaying the judgment result;
A method for detecting the end point of dry etching.