JP2013048183A - Etching monitoring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate depth of hole or step with high precision by eliminating the effect of thickness of resist film during execution of etching.SOLUTION: The light of predetermined wavelength width is radiated to a sample 50, and the light containing interference with the light reflected on a bottom surface of a hole 52 or an upper surface of a substrate 51, and the like is subjected to spectral detection by a spectroscope unit 25. At a data processing part 30, an interference spectrum is obtained that is provided by removing effects or the like of an emission spectrum of a light source 21 from spectral profile, which is then subjected to Fourier transformation to provide a peak interval, for calculating depth of a hole, film thickness, or the like. Since a chopper 103 periodically allows shielding/passing of external reference light that is reflected on an external reference surface 104, a data processing part 30 provides data with external reference light and data with no external reference light. For example, during the period when a resist layer 53 is thick, a depth of hole or the like is calculated based on the data with no external reference light which has higher resolution, but when the resist layer 53 becomes thinner as etching proceeds, a depth of a hole or the like is calculated based on the data with external reference light which is hard to be affected by disturbance.

Description

  The present invention relates to an etching monitoring apparatus for measuring a depth or a step of a fine hole formed in a semiconductor substrate or the like by etching processing, for example, TSV (= Through Silicon Via) substantially in real time during processing. About.

  In the manufacturing process of a semiconductor integrated circuit, an etching process using low-pressure plasma or the like is performed in order to form very fine holes or grooves in a semiconductor substrate such as a silicon wafer. Usually, in the etching step, first, etching is performed after masking a portion of the substrate where a hole or groove is not formed with a resist film. As a result, only the unmasked portion is selectively scraped, so that it is possible to form holes or grooves of any shape by removing the resist film after processing. Since the depth of the hole or groove formed at this time depends on various conditions such as etching time, gas type, gas pressure, etc., in order to set the hole or groove depth to the target depth, Control is performed to determine the end point of etching and adjust the conditions while monitoring the actual depth.

  Conventionally, those described in Patent Documents 1 to 3 are known as techniques for optically measuring the depth of fine holes formed by etching. In order to measure the depth of a fine hole formed on a substrate by etching, the apparatuses described in these documents include a monochromatic light source, an optical system that irradiates the hole to be measured with light from the monochromatic light source, and the hole. A detector for measuring the intensity of the reflected light from the light source. Light that enters the detector due to interference between the reflected light from the bottom surface of the hole and the reflected light from the surface surrounding the opening of the hole when the microhole, which is the etched part, becomes deeper as the etching progresses The intensity changes repeatedly. That is, as shown in FIG. 9A, as the etching depth advances by λ / 2 (λ: wavelength of monochromatic light), the signal intensity by the detector repeats a cycle of strength. Therefore, conventionally, the hole depth is measured by counting the peak (maximum or minimum) of the temporal change in the signal intensity.

  In the devices described in Patent Documents 1 to 3, apart from the hole depth measurement, a light source for spectroscopic measurement, an optical system for irradiating the mask layer to be measured with light from the light source for spectroscopic measurement, and a mask layer Equipped with a spectroscopic detector that spectroscopically detects the reflected light from the surface, which is used to measure the thickness of the mask layer that masks the substrate surface other than the part to be etched. Does not matter.

  The conventional etching depth (step) measurement method of obtaining the hole depth by simply counting the peak (or bottom) with respect to the temporal change of the light intensity described above is used when there are two light reflecting surfaces. There is no particular problem. However, when the state of the reflecting surface changes, such as when there are three or more light reflecting surfaces due to the resist film or other layer structure, the temporal variation in the amplitude of the interference light is as shown in FIG. It becomes complicated. This makes it difficult to accurately count peaks. In particular, when the hole formed by etching has a very fine diameter or is deep, the reflected light from the bottom surface of the hole becomes dominant because the reflected light from the bottom of the hole becomes weak, Since the amplitude of interference reflecting the depth of the etched portion is reduced, the possibility of causing a counting error increases. For this reason, the accuracy of measurement of the depth and level difference of the hole, which is the etched portion, is reduced, which causes a large etching failure.

Japanese Patent No. 2859159 JP 10-325708 A JP 2001-284323 A

  The present invention has been made to solve the above-mentioned problems, and its main purpose is the influence of the film thickness of the resist layer and other film structures, the size and depth of the hole to be etched, Etching monitoring with little or no decrease in measurement accuracy, such as hole depth, step, or resist film thickness, even when the interference light amplitude varies or decreases due to various factors such as uniform etching Is to provide a device.

The present invention, which has been made to solve the above problems, is an etching monitoring apparatus that measures at least the depth or step of etching when etching a portion to be etched on a sample surface that is not masked. A light source that generates measurement light having a predetermined wavelength width, and the measurement light from the light source is guided to the sample, and a light spot formed on the sample surface is applied to the etched site and the surrounding masking site. An introduction optical system that irradiates the sample surface with the measurement light so as to straddle, and interference that causes the reflected light from the etched portion and masking portion on the sample surface to interfere with the measurement light irradiation by the introduction optical system An optical system, a spectroscopic unit that wavelength-disperses interference light from the interference optical system, and a detection unit that detects, for each wavelength, the light wavelength-dispersed by the spectroscopic unit. In the etching monitoring apparatus,
a) external reference light generating means for extracting a part of the light in the middle of the optical path of the introduction optical system and reflecting it on the external reference surface and then introducing it into the optical path of the interference optical system as external reference light to be mixed into the interference light; ,
b) An external for obtaining an interference spectrum which is an intensity distribution in a predetermined wavelength range of the interference light based on a detection signal obtained by the detection means for the light in which the external reference light is mixed into the interference light reflected from the sample Spectrum acquisition means with reference light;
c) a spectrum acquisition means without external reference light for obtaining an interference spectrum based on a detection signal obtained by the detection means for interference light reflected from the sample and not mixed with the external reference light;
d) an etching amount calculation means for calculating an etching depth or a step by an analysis process that selectively uses one of the interference spectrum by the spectrum acquisition means with external reference light or the interference spectrum by the spectrum acquisition means without external reference light;
It is characterized by having.

  In the etching monitoring apparatus according to the present invention, a light source having a certain wavelength width is used to measure the depth and level difference of the etching hole, and the interference light returned from the hole and level difference formed by etching is spectroscopically measured. The spectrum acquisition means with external reference light and the spectrum acquisition means without external reference light create an interference spectrum based on the detection signal obtained by the detection means. The etching amount calculation means extracts a spectrum interference waveform appearing in the interference spectrum, performs frequency analysis by Fourier transform, and converts a wavelength (or wave number) of the interference spectrum into a distance between the reference surface and the reflection surface. The hole depth from the reference surface (for example, the substrate surface), the groove step, or the masking layer thickness is calculated from the peak appearing in the graph. At this time, in order to avoid that the masking layer (usually the resist layer) on the substrate to be etched becomes too thin due to etching and the position of the reference surface such as the upper surface of the resist layer for measuring the interference distance is ambiguous, Separately, an external reference plane is provided. However, there are advantages and disadvantages both when the external reference light reflected by the external reference surface is used and when it is not used.

  That is, when external reference light is not used, a reference surface such as a substrate upper surface or resist layer upper surface that is very close to the bottom of the hole to be measured on one optical path is used. Thus, the depth of the etching hole (distance from the bottom of the structure to be etched) and the like can be stably measured with high accuracy. On the other hand, if the resist layer is removed by etching and the film thickness is less than the measurable distance (depending on the wavelength band used), the reference surface position becomes ambiguous, and the measurement accuracy of the etching hole depth decreases. End up. On the other hand, when the external reference light is used, the external reference surface is not an object to be etched, so that the structure and distance thereof do not change, and there is an advantage that measurement can be performed stably and with relatively high accuracy regardless of the etching state. On the other hand, at least a part of the optical path for generating the external reference light is different from the optical path for measuring the object to be measured, so that it is easily affected by disturbances such as vibrations. Stability is not obtained. In addition, since extra light called external reference light is mixed, the influence of noise increases.

  In the etching monitoring apparatus according to the present invention, in order to make use of the advantages while compensating for the above-described defect with / without the external reference light, information that can be used to estimate the state of the detected signal and the reliability of the measurement result during the etching, etc. On the basis of the above, the interference spectrum with which the external reference light is used or the interference spectrum without the external reference light is used as the interference spectrum from which the hole depth, groove step, masking layer thickness, and the like are calculated.

  That is, in the etching monitoring apparatus according to the present invention, the etching amount calculation means is configured to output the external reference light based on a detection signal obtained by the detection means during the progress of etching or a processing result obtained by analysis processing on the detection signal. A determination unit that determines whether to use an interference spectrum with or without an external reference light, and an etching hole depth or step by analysis using the interference spectrum selected based on the determination; It may be configured to calculate.

  Specifically, when there is a periodic signal intensity fluctuation (such as a periodic disturbance or a large fluctuation in amplitude) that appears with a change in the hole depth, or in the graph after Fourier transform In a situation where multiple peaks overlap and cannot be separated, or when the thickness of the masking layer obtained by measurement is thinner than a predetermined threshold, the interference spectrum without external reference light is sufficiently accurate. Since the hole depth and the like cannot be calculated, switching to use an interference spectrum with external reference light is preferable.

  In addition, both the interference spectrum without external reference light and the interference spectrum with external reference light may be always acquired regardless of necessity, or conversely, only those necessary for calculation of hole depth etc. May be acquired selectively. That is, in one embodiment of the present invention, the external reference light generating means includes switching means for switching presence / absence of external reference light, and by switching the presence / absence of external reference light by the switching means, The interference spectrum with reference light and the interference spectrum without external reference light can always be obtained.

  Further, in the configuration in which the processing is switched so as to use the interference spectrum with the external reference light according to the film thickness of the masking layer as described above, the external reference light generation unit switches the presence / absence of the external reference light to be mixed. The external reference light is not mixed by the switching means while the thickness of the masking layer is greater than or equal to a predetermined value, and the external reference light is supplied by the switching means when the thickness of the masking layer is less than the predetermined value. It is good also as a structure which switches the presence or absence of mixing of external reference light so that it may mix.

  In general, since the reflectance of the external reference surface is higher than that of the sample surface, there is a difference in the amount of light reaching the detection means depending on the presence or absence of external reference light, and the upper limit of the amount of light that can be received by the detection means (Upper limit of the dynamic range of the detection means) may be exceeded, or conversely, if such an overage is not caused, the sensitivity may be lowered. Therefore, in the etching monitoring apparatus according to the present invention, preferably, the amount of emitted light of the light source, the amount of light incident on the detection means, and the measurement light irradiated on the sample surface depending on whether or not external reference light is mixed. It is preferable to adjust at least one of the amount of light, the amount of light reflected from the sample surface, and the detection sensitivity of the detection means. According to this configuration, even when there is a difference in the amount of light reaching the detection unit due to the presence or absence of external reference light, the amount of light can be appropriately adjusted according to the presence or absence of external reference light or the gain of the detection unit The dynamic range of the detection means can be used effectively by adjusting the

  According to the etching monitoring apparatus according to the present invention, the depth and level difference of a target hole formed by etching can be accurately and with high resolution without being affected by the film thickness of a masking layer such as a resist or the change thereof. It can be measured. In addition, since such measurement can be performed with high real-time properties, it is suitable for controlling etching end point detection and condition change.

1 is a schematic configuration diagram of an etching monitoring apparatus according to an embodiment of the present invention. The schematic of the interference spectrum obtained in the etching monitoring apparatus of a present Example. The figure which shows an example of the observed spectral spectrum when not using external reference light, the interference spectrum after normalization calculated | required from this spectral spectrum, and the signal waveform after Fourier-transforming this interference spectrum. The figure which shows an example of the observed spectral spectrum when not using external reference light, the interference spectrum after normalization calculated | required from this spectral spectrum, and the signal waveform after Fourier-transforming this interference spectrum. The figure which shows an example of the observed spectral spectrum when not using external reference light, the interference spectrum after normalization calculated | required from this spectral spectrum, and the signal waveform after Fourier-transforming this interference spectrum. The figure which shows an example in the case of using external reference light, the observed spectral spectrum, the interference spectrum after normalization calculated | required from this spectral spectrum, and the signal waveform after Fourier-transforming this interference spectrum. The figure which shows the flowchart of the hole depth measurement control and process in execution of the etching in the etching monitoring apparatus of a present Example. The figure which shows the flowchart of the hole depth measurement control and process in execution of the etching in the etching monitoring apparatus of another Example. The figure which shows an example of the time change of reflected light intensity when monochromatic light is irradiated to the to-be-etched part.

  An etching monitoring apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of an etching monitoring apparatus according to this embodiment.

  This etching monitoring device is a device that monitors the depth of a microhole formed in a sample 50 that is a processing target placed in the vacuum chamber 1 of the etching device, a step of a groove, and the like. A light source / spectral detection unit 20, a data processing unit 30, and a control unit 31. The measurement unit 10 and the light source / spectral detection unit 20 are connected via an optical fiber 24.

  The light source / spectral detection unit 20 includes a measurement light source 21 that emits light having a high emission intensity while having low coherence and having a wavelength width necessary for measurement of a target hole depth. As the measurement light source 21, for example, a super luminescent diode (SLD) having a center wavelength of 835 nm and a full width at half maximum of 40 nm can be used. The measurement light emitted from the measurement light source 21 is taken into the incident side optical fiber 22, travels through the optical fiber 24 via the fiber coupler 23, and proceeds to the measurement unit 10. The measurement light emitted from the end of the optical fiber 24 in the measurement unit 10 is bent toward the sample 50 by the next beam splitter 13 through the collimator lens 18 and the beam splitter 100. The measurement light is irradiated onto the sample 50 through the objective lens 12 and the measurement window 11 provided in the vacuum chamber 1.

  As shown in the enlarged view of FIG. 1, the sample 50 includes a substrate 51 that is an object to be etched, a resist layer 53 that is a resist for etching protection thinly applied on the upper surface thereof, and a substrate that is not coated with a resist. 51 to be etched. This figure shows a state in which the etched portion 52 has been etched and fine holes have been formed in the etched portion 52. As described above, the spot diameter of the light beam 40 irradiated on the sample 50 is adjusted so as to straddle the etched portion 52 on the sample 50 and the surrounding resist layer 53. Therefore, on the sample 50, the reflected light 43 from the surface of the resist layer 53, the reflected light 42 from the surface of the substrate 51 with respect to the light entering the resist layer 53, and the etched portion 52 (the bottom surface of the hole in FIG. 1). And the reflected light 41 is mainly generated.

  These reflected lights 41 to 43 are directed in various directions. Of these, the light that has traveled again in the direction of the measurement window 11 is applied to the objective lens 12, the beam splitter 13, the beam splitter 100, and the collimator lens 18 during the light irradiation. On the contrary, the light enters the optical fiber 24. Then, the light returns to the light source / spectral detection unit 20 through the optical fiber 24, and reaches the spectral unit 25 through the fiber coupler 23. As described above, a plurality of reflected lights 41 to 43 having optical path differences are generated from the sample 50. These reflected lights 41 to 43 mainly interfere with each wavelength in the process of passing through the optical fiber 24, thereby causing interference light. It becomes.

  In the spectroscopic unit 25, the interference light is wavelength-dispersed by a spectroscope 26 such as a diffraction grating, and light of a plurality of wavelengths is simultaneously detected by an array detector 27 such as a CCD line sensor. Detection signals corresponding to the respective wavelengths from the array detector 27 are input to the data processing unit 30, and the data processing unit 30 executes processing to be described later, whereby the depth of the hole, which is the etched portion 52, and the film of the resist layer 53. Thickness etc. are calculated.

  The observation camera 17 included in the measurement unit 10 is for observing the entire upper surface or a specific part of the sample 50. That is, the auxiliary light emitted from the observation auxiliary light source 16 illuminates the sample 50 along substantially the same optical axis as the main light beam coming from the measurement light source 21 via the collimator lens 15 and the beam splitters 14 and 13. An image obtained by photographing the reflected light with respect to the auxiliary light by the observation camera 17 is used for confirming the position of the etched portion 52 on the sample 50.

  Further, in the etching monitoring apparatus of the present embodiment, in order to form a virtual external reference surface 104 ′ in the vicinity of the upper surface of the sample 50, a chopper that is rotationally driven by the reflecting mirror 101 and the motor 102 in addition to the beam splitter 100. 103, an external reference surface 104 that is a reflecting mirror, and a piezoelectric element 105 that finely moves the external reference surface 104 in a direction parallel to the optical axis.

  The beam splitter 100 divides a part of the measurement light emitted from the end of the optical fiber 24 and directed to the beam splitter 13, and reciprocates an optical path to the external reference surface 104 via the reflecting mirror 101. The reciprocating distance (external reference surface reciprocating distance) between 100 and the external reference surface 104 is set to be slightly different from the reciprocating distance (sample surface reciprocating distance) between the beam splitter 100 and the sample 50 surface. Thereby, the virtual external reference surface 104 ′ can be set at a position slightly away from the upper surface of the sample 50.

  The optical path for generating the external reference light may not be branched using the beam splitter 100, but may use light that has passed straight through the beam splitter 13, or may be branched from the fiber coupler 23. The light emitted from another arm (not shown) other than the optical fiber 24 may be used.

  Moreover, the substance of the data processing unit 30 and the control unit 31 is a personal computer, and functions as the data processing unit 30 and the control unit 31 by executing control / processing software installed in the computer in advance. You can make it.

  In the etching monitoring apparatus of the present embodiment, the intensity distribution of the interference light derived from the reflected light in the vicinity of the part to be etched 52 on the sample 50 is determined at predetermined time intervals during execution of the etching process on the sample 50 in the vacuum chamber 1. Get repeatedly. Therefore, as shown in FIG. 2, an interference spectrum indicating the relationship between wavelength and signal intensity is obtained at predetermined time intervals. Information reflecting the hole depth of the etched portion 52 to be measured and the film thickness of the resist layer 53 around the hole is included in one interference spectrum. The data processing unit 30 extracts such information from the obtained data, and calculates and outputs the hole depth that changes momentarily as the etching proceeds.

  Next, in the etching monitoring apparatus of the present embodiment, a basic method of hole depth calculation using an interference spectrum executed by the data processing unit 30 will be described.

  The spectral spectrum shown in FIG. 3A shows the etching hole depth, that is, the distance (h1) between the hole bottom surface 52a as the etched portion 52 and the upper surface of the substrate 51 (interface between the substrate 51 and the resist layer 53) 51a. Is a spectral spectrum acquired by the array detector 27 when the refractive index of the resist layer 53 is n = 2.0 and the film thickness thereof is 10 μm. This spectral spectrum includes wavelength-dependent factors other than interference of reflected light, such as an emission spectrum of the measurement light source 21. Therefore, the spectral spectrum is normalized by using the intensity distribution obtained in advance with respect to the reference light in a state where there is no interference, and the original interference spectrum is obtained. FIG. 3B is an interference spectrum after normalization obtained by calculation from the spectral spectrum of FIG. Further, by performing Fourier transform on the interference spectrum in which the horizontal axis is converted from wavelength to wave number, a graph in which the horizontal axis indicates the distance between the reference surface and the reflecting surface as shown in FIG.

In this case, that is, when the virtual external reference surface 104 ′ is not used, the interference spectrum includes interference light derived from a combination of the following three types of reflection surfaces.
[I] Resist layer 53 upper surface 53 a-upper surface 51 a of substrate 51
[Ii] Upper surface 51a of substrate 51-hole bottom surface 52a (distance h1) of etched portion 52
[Iii] Hole bottom surface 52a of etched portion 52-Upper surface 53a of resist layer 53 (distance h2)

  In the signal waveform after Fourier transform shown in FIG. 3C, peaks appear at three positions corresponding to the optical distances [i], [ii], and [iii]. In this case, the peak position showing the longest distance is usually determined by the method of fitting a generally known Gaussian function, and the distance from the resist layer 53 upper surface 53a to the hole bottom surface 52a corresponding to the above [iii]. As soon as possible. Here, the distance between the peaks corresponding to the above [ii] and [iii] corresponds to the film thickness of the resist layer 53. In FIG. 3C, it can be seen that the peak intervals corresponding to [ii] and [iii] are intervals corresponding to the optical distance of the resist layer 53 of about 20 μm.

  As the etching progresses, the portion to be etched (hole) 52 becomes deeper, but the resist layer 53 is gradually removed by etching, but the film thickness gradually decreases. Therefore, the peak intervals corresponding to [ii] and [iii] on the signal waveform after the Fourier transform are gradually narrowed and eventually overlap.

  FIG. 4 shows a simulation result when only the thickness of the resist layer 53 is changed to 3.05 μm from the state shown in FIG. Since the distance between the upper surface 51a of the substrate 51 and the upper surface 53a of the resist layer 53 is reduced, the peaks corresponding to [ii] and [iii] overlap in the signal waveform after Fourier transform (see FIG. 4C). Thus, it can be seen that the position of each peak top is unclear.

  FIG. 5 shows a simulation result when the thickness of the resist layer 53 is further reduced to 3.00 μm. In FIG. 5, it can be seen that peaks corresponding to [ii] and [iii] are separated in the signal waveform after Fourier transform (see FIG. 5C). As described above, when the two reflecting surfaces are close to each other on the sample 50, if the distance is changed little by little, the distance only changes in nano order, and the peaks overlap on the signal waveform after Fourier transform. Or repeat the separation. As shown in FIG. 9B, this is the effect of the amplitude of the signal intensity being reduced and the period of the periodic change being disturbed. In this case, it is very difficult to specify the position of the peak top on the signal waveform after the Fourier transform, and even if the position of the peak top can be specified, the accuracy of calculation such as the hole depth is considerably low. End up.

  Therefore, in the etching monitoring apparatus of the present embodiment, the external reference surface 104 is used in order to avoid the ambiguity of the peak position in the signal waveform after the Fourier transform as described above. As shown in FIG. 1, in the actual apparatus, the external reference plane 104 is used, but on the principle of calculation, a virtual external reference plane 104 ′ is considered corresponding to the external reference plane 104. Considering interference of reflected light on the three surfaces of the virtual external reference surface 104 ′, the upper surface 53 a of the resist layer 53, and the hole bottom surface 52 a of the etched portion 52, the relationship between the interference surfaces can be easily understood.

As shown in the enlarged view of FIG. 1, the virtual external reference surface 104 ′ is considered as a reference plane, and the distance between the resist layer 53 upper surface 53a and the hole bottom surface 52a that is the etched portion 52 is h2, and the substrate 51 upper surface 51a. And h1 is the distance between the hole bottom surface 52a, which is the etched portion 52. Here, since the resist layer 53 may have a multilayer structure instead of a single layer film, for example, a silicon oxide film (SiO ₂ ) formed on the substrate 51 may be included in the resist layer 53. The difference between h1 and h2 is slight, and cannot normally be separated by Fourier transform of the interference waveform involving the upper surface 53a of the resist layer 53, and the peaks overlap on the signal waveform after Fourier transform as described above. Therefore, if the interference between the virtual external reference surface 104 ′ that is not influenced by etching and the hole bottom surface 52 a of the etched portion 52 can be obtained satisfactorily, it is advantageous in accurately calculating the hole depth of the etched portion 52. is there.

  Since the position of the virtual external reference surface 104 ′ can be adjusted by fine adjustment of the position of the external reference surface 104 by the piezoelectric element 105, the position of the virtual external reference surface 104 ′ is the same as that of the external reference surface 104 ′. What is necessary is just to preset to the distance by which interference with the hole bottom face 52a of the etching part 52 is emphasized. On the other hand, the chopper 103 is for controlling the blocking / passing of the light beam reaching the external reference surface 104 under the control of the control unit 31. The chopper 103 blocks / passes, for example, 60 times / second by rotating the motor 102. If they are alternately performed, the interference spectral waveforms with the external reference surface 104 (that is, with external reference light mixed) and without the external reference surface 104 (that is with no external reference light mixed) are alternately 60 times / second. Can get to.

FIG. 6 shows an actually measured spectral spectrum when the virtual external reference surface 104 ′ is installed such that the distance from the beam splitter 100 is minus 100 μm as compared with the upper surface 51a of the substrate 51. It is a calculation result of the signal spectrum after the interference spectrum and Fourier transform for. In this case, the interference spectrum includes interference light derived from the combination of the following six types of reflecting surfaces.
[I] Upper surface 53a of resist layer 53-Upper surface 51a of substrate 51
[Ii] Upper surface 51a of substrate 51-hole bottom surface 52a (distance h1) of etched portion 52
[Iii] Hole bottom surface 52a of etched portion 52-Upper surface 53a of resist layer 53 (distance h2)
[Iv] Virtual external reference surface 104′-upper surface 53a of resist layer 53 (distance d2)
[V] Virtual external reference surface 104'-upper surface 51a of substrate 51 (distance d1)
[Vi] Virtual external reference surface 104'-hole bottom surface 52a (distance d3) of the etched portion 52

  Among them, the interference due to [vi] is uncertain even when the resist layer 53 is very thin because the external reference surface 104 (and the virtual external reference surface 104 ′) is a single surface. Instead, it appears as a clear isolated peak as shown by [vi] in FIG. Therefore, as described above, the position of the peak indicating the longest distance is immediately determined as the distance from the virtual external reference surface 104 ′ corresponding to the above [vi] to the hole bottom surface 52a by the method of fitting the Gaussian function. Can be requested.

  On the other hand, as can be seen by comparing the magnitudes of noise other than the signal peak portions in FIGS. 5 and 6, the disadvantage of using the external reference surface 104 is that the optical shot noise in accordance with the intensity of the external reference light is disadvantageous. There is an increase. In addition, due to restrictions on the mechanical accuracy of the fixed position of the external reference surface 104, it is difficult to avoid nano-order fluctuations in the measurement accuracy of the etching hole depth, unlike when the external reference surface 104 is not used. Therefore, in order to overcome these drawbacks, in the etching monitoring apparatus of the present embodiment, data acquired with the external reference surface 104 and data acquired without the external reference surface 104 are used properly. Thereby, both the advantages of having the external reference surface 104 as described above can be enjoyed simultaneously.

  A specific example of hole depth measurement control / processing during execution of etching in the etching monitoring apparatus of the present embodiment will be described with reference to the flowchart shown in FIG.

  That is, when etching monitoring is started with the start of etching, as described above, the chopper 103 is driven to rotate by the motor 102, whereby data with and without the external reference surface 104 is alternately acquired at a predetermined cycle. (Step S1). In the data processing unit 30, for example, based on the data without the external reference surface 104, the temporal change in the signal intensity of an appropriate wavelength such as the center wavelength in the acquired predetermined wavelength width is monitored (step S2), and the intensity change Is greater than or equal to a predetermined threshold (step S3). When the intensity change is equal to or greater than the threshold value, a graph having a clear peak position as shown in FIG. 3C can be obtained as a signal waveform after Fourier transform without using the external reference plane 104. Therefore, the interference spectrum is obtained as described above based on the data without the external reference surface 104, and the hole depth, the step difference, the film thickness of the resist layer 53, and the like are calculated by performing Fourier transform (step S4).

  On the other hand, when it is determined in step S3 that the intensity change is less than the threshold value, a peak as shown in FIG. 4C is obtained as a signal waveform after Fourier transform when the external reference surface 104 is not used. There is a possibility of overlapping. Accordingly, the interference spectrum is obtained as described above based on the data with the external reference surface 104, and the hole depth, the step difference, the film thickness of the resist layer 53, and the like are calculated by performing Fourier transform (step S5). In either case of steps S4 and S5, if information such as hole depth is obtained, the result is output (step S6), and if the measurement is not completed (No in step S7), the process returns to step S1.

  By repeating the processing of steps S1 to S7 during the execution of etching, it is possible to output measurement values such as the depth and level difference of the hole to be cut by etching or the film thickness of the resist layer 53 in substantially real time. In the control and processing shown in FIG. 7, not only the calculation accuracy such as the hole depth decreases due to the thin film thickness of the resist layer 53, but also the signal intensity decreases due to another factor such as disturbance. Even in this case, the external reference plane 104 is used, and a significant decrease in calculation accuracy can be avoided. Specifically, when the resist layer 53 has a film thickness that corresponds to an anti-reflection coating, the signal intensity decreases drastically. In such a case, by using the external reference surface 104, the hole depth can be reduced. Etc. can be obtained.

  Note that when monitoring the change in signal intensity, the signal intensity based on the light amount of the entire predetermined wavelength width may be used instead of the signal intensity based on the light amount of one specific wavelength. Further, instead of monitoring the signal intensity change, it is determined whether or not the peaks of [ii] and [iii] are separable on the signal waveform after Fourier transform based on the data without the external reference plane, and the determination result is Based on this, the process in step S4 or S5 may be selected.

  FIG. 8 is a flowchart of hole depth measurement control / processing during etching in the etching monitoring apparatus of another embodiment. In this case, instead of the chopper 103 that periodically passes and blocks light, a shutter that switches between passing and blocking light based on an instruction from the control unit 31 is installed.

  When etching monitoring is started with the start of etching, the shutter is set in a light blocking state as described above, and data without the external reference surface 104 is acquired (step S11). The data processing unit 30 obtains the interference spectrum as described above based on the data without the external reference surface 104, and performs Fourier transform to calculate the hole depth, the step difference, the film thickness of the resist layer 53, and the like (step S12). ). If information such as the hole depth is obtained, the result is output (step S13). Next, it is determined whether or not the calculated film thickness of the resist layer 53 is less than a predetermined value (step S14). If the film thickness is equal to or greater than the predetermined value and there is no instruction to end the measurement (No in step S15). ) Return to step S11. Therefore, while the thickness of the resist layer 53 is equal to or greater than a predetermined value from the etching start time, the hole depth, the step, and the like are calculated based on the data without the external reference surface 104.

  When the etching progresses and the film thickness of the resist layer 53 becomes less than the predetermined value, the process proceeds from step S14 to S16, the shutter is set in the light passing state, and data with the external reference surface 104 is acquired (step S16). The data processing unit 30 obtains the interference spectrum as described above based on the data with the external reference surface 104 and performs Fourier transform to calculate the hole depth, the step difference, the film thickness of the resist layer 53, and the like (step S17). ). If information such as the hole depth is obtained, the result is output (step S18), and if there is no measurement end instruction (No in step S19), the process returns to step S16. Therefore, after the etching progresses and the film thickness of the resist layer 53 becomes less than the predetermined value, the hole depth, the step, and the like are calculated based on the data with the external reference surface 104 until the measurement is completed.

  When the external reference light is blocked by the chopper 103 or the shutter, the external reference light is not mixed in the light introduced into the spectroscopic unit 25, and the external reference light is passed by the chopper 103 or the shutter. The light introduced into the spectroscopic unit 25 is a mixture of external reference light. In general, when the external reference light is mixed, the amount of light incident on the array detector 27 increases accordingly, and the incident light amount falls within the dynamic range of the array detector 27 without the external reference light. If the amount of light is adjusted so that it falls within the range, the amount of incident light may exceed the dynamic range of the array detector 27 in the presence of external reference light. On the other hand, if the light amount adjustment is performed so that the incident light amount falls within the dynamic range of the array detector 27 in the presence of the external reference light, the incident light amount becomes too small in the absence of the external reference light, and the measurement sensitivity may decrease. There is.

  Therefore, in order to avoid such a problem, for example, the amount of light emitted from the measurement light source 21 is changed in accordance with the presence or absence of the external reference light, and the dynamic range of the array detector 27 is sufficiently increased with or without the external reference light. It is good to make it available for use. Instead of changing the amount of emitted light of the measurement light source 21, depending on the presence or absence of the external reference light, it is in front of the array detector 27, between the measurement light source 21 and the incident end of the incident side optical fiber 22, or on the incident side. A dimming element such as an ND filter or an attenuator may be inserted into or removed from the optical path such as in the middle of the optical fiber 22 or the optical fiber 24. Further, the gain of the array detector 27 itself may be switched according to the presence or absence of external reference light. Further, the amount of the measurement light 40 irradiated on the sample 50 or the amount of the reflected light 41, 42, 43 from the sample 50 may be adjusted using a neutral density filter or the like according to the presence or absence of external reference light. Good. Furthermore, there is also means for adjusting the external reference light amount when the surface intensity of the sample 50 becomes rough or the signal intensity obtained from the sample 50 becomes extremely small due to the state corresponding to the non-reflective coating as described above. It is valid.

  In addition, any of the above-described embodiments is merely an example of the present invention, and it is obvious that modifications, additions, and changes as appropriate within the scope of the present invention are included in the scope of the claims of the present application.

DESCRIPTION OF SYMBOLS 1 ... Vacuum chamber 10 ... Measurement part 11 ... Measurement window 12 ... Objective lens 13, 14, 100 ... Beam splitter 15, 18 ... Collimating lens 16 ... Observation auxiliary light source 17 ... Observation camera 18 ... Collimating lens 20 ... Light source, spectroscopy Detector 21 ... Measurement light source 22 ... Incoming side optical fiber 23 ... Fiber coupler 24 ... Optical fiber 25 ... Spectral unit 26 ... Spectroscope 27 ... Array detector 30 ... Data processing unit 31 ... Control unit 40 ... Light beams 41, 42 43 ... Reflected light 50 ... Sample 51 ... Substrate 51a ... Substrate upper surface 52 ... Etched portion 52a ... Bottom surface 53 ... Resist layer 53a ... Resist layer upper surface 101 ... Reflector 102 ... Motor 103 ... Chopper 104 ... External reference surface 105 ... Piezoelectric element

Claims (6)

An etching monitoring apparatus that measures at least the depth or step of etching when etching a portion to be etched on the sample surface that is not masked, and generates measurement light having a predetermined wavelength width. Introduced optics that directs measurement light onto the sample surface so that the light source and measurement light from the light source are guided to the sample, and the light spot formed on the sample surface straddles the part to be etched and the surrounding masking part System, an interference optical system for causing the light reflected from the etched part and the masking part on the sample surface to interfere with measurement light irradiation by the introduction optical system, and wavelength dispersion of the interference light by the interference optical system In an etching monitoring apparatus comprising: a spectroscopic means for detecting; and a detecting means for detecting, for each wavelength, the light wavelength-dispersed by the spectroscopic means,
a) external reference light generating means for extracting a part of the light in the middle of the optical path of the introduction optical system and reflecting it on the external reference surface and then introducing it into the optical path of the interference optical system as external reference light to be mixed into the interference light; ,
b) An external for obtaining an interference spectrum which is an intensity distribution in a predetermined wavelength range of the interference light based on a detection signal obtained by the detection means for the light in which the external reference light is mixed into the interference light reflected from the sample Spectrum acquisition means with reference light;
c) a spectrum acquisition means without external reference light for obtaining an interference spectrum based on a detection signal obtained by the detection means for interference light reflected from the sample and not mixed with the external reference light;
d) an etching amount calculation means for calculating an etching depth or a step by an analysis process that selectively uses one of the interference spectrum by the spectrum acquisition means with external reference light or the interference spectrum by the spectrum acquisition means without external reference light;
An etching monitoring apparatus comprising: The etching monitoring apparatus according to claim 1,
The etching amount calculation means is configured to detect interference obtained with the external reference light and interference without the external reference light based on a detection signal obtained by the detection means during the progress of etching or a processing result obtained by analyzing the detection signal. An etching monitoring apparatus comprising: a determination means for determining which one of the spectrum is used, and calculating the etching hole depth or step by analysis using the interference spectrum selected based on the determination . The etching monitoring apparatus according to claim 2,
The determination means determines whether the thickness of the masking layer calculated based on the interference spectrum without external reference is less than a predetermined value as the etching progresses, and the thickness is equal to or greater than the predetermined value. In some cases, the etching hole depth or step is calculated using an interference spectrum without external reference light, and if the film thickness is less than a predetermined value, the etching hole depth is analyzed by using the interference spectrum with external reference light. An etching monitoring apparatus that switches to calculation of a height or a step. The etching monitoring apparatus according to any one of claims 1 to 3,
The external reference light generating means includes switching means for switching presence / absence of external reference light, and by alternately switching presence / absence of external reference light by the switching means, interference spectrum with external reference light and external reference light are switched. An etching monitoring apparatus characterized by always obtaining an interference spectrum without noise. An etching monitoring apparatus according to claim 3, wherein
The external reference light generating means includes switching means for switching presence / absence of mixing of external reference light, and the external reference light is not mixed by the switching means while the thickness of the masking layer is not less than a predetermined value. An etching monitoring apparatus, wherein the presence or absence of external reference light is switched by the switching means so that external reference light is mixed when the thickness is less than a predetermined value. The etching monitoring apparatus according to any one of claims 1 to 5,
The amount of light emitted from the light source, the amount of light incident on the detection means, the amount of measurement light applied to the sample, the amount of reflected light from the sample, or the detection, depending on whether or not external reference light is mixed An etching monitoring apparatus that adjusts at least one of detection sensitivities in the means.

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