JP2000241121A - Step-difference measuring apparatus, etching monitor using the same, and etching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable to measure a step-difference of fine depth formed on a transparent substrate, from the rear of the transparent substrate. SOLUTION: Two light beams having coherency are cost from the rear of a transparent substrate, and reflected by the respective step-difference surfaces. The two reflected beams are synthesized to be an interference beam. In this case, the optical distance of one optical path is changed continuously in time. This interference beam is received with a photo detector 34 and converted to an electric signal. An output signal of the photo detector 34 contains phase information caused by the step-difference and phase information which is compulsorily introduced. A signal processing circuit 35 stores the relation between time and photo detector output intensity. By comparing phase information before the step-difference is formed with phase information after the step- difference is formed, the phase information caused by the step-difference can be led out as the amount of phase shift.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a step measuring device having a resolution of about 0.1 nm, an etching monitor using the step measuring device, and an etching method.

[0002]

2. Description of the Related Art Along with a reduction in the line width of an LSI, a phase shift mask is used as a photomask having a higher resolution limit. In this phase shift mask, a light-shielding pattern that defines a plurality of light transmission openings is formed on a glass substrate,
It is configured to give a phase difference of λ / 2 between the exposure lights passing through the light transmission openings adjacent to each other with the light shielding pattern interposed therebetween. As an actual configuration of the phase shift mask, a light-shielding pattern that defines a light-transmitting opening is formed on a glass substrate, and every other concave portion that provides a phase difference of λ / 2 with respect to the light-transmitting opening is formed. Alternatively, a portion where no concave portion is formed functions as a phase shifter. The concave portion constituting the phase shifter is formed by etching, and has a depth of about several 100 nm.

In a phase shift mask, the phase difference between light passing through an opening in which a phase shifter is formed and light passing through an opening in which no phase shifter is formed is designed to be λ / 2. As it deviates, the resolution decreases and the quality as a photomask decreases. For this reason,
In the manufacturing process of the phase shift mask, there is a strong demand for the development of a step measuring device capable of accurately measuring the depth of the concave portion constituting the phase shifter. In particular, a step measuring device capable of measuring the concave depth of about 0.1 nm has been demanded. Development is strongly demanded.

As a defect inspection apparatus for a phase shift mask,
There is an apparatus described in Japanese Patent Application No. 8-339522 proposed by the present applicant. In this defect inspection apparatus, the depth of a concave portion formed in a transparent substrate is extracted as phase information with reference to the surface of the light-shielding pattern, and the presence of a defect is detected from the phase information.

[0005]

Since the depth of the recess constituting the phase shifter is about 100 nm, it is necessary to detect a depth error of about 0.1 nm when performing a defect inspection. Inspection of mask defects was extremely difficult. On the other hand, the above-described defect inspection apparatus proposed by the present applicant has an advantage that defect inspection can be performed with extremely high accuracy because the depth of the concave portion is extracted as phase information.

On the other hand, if the depth of the concave portion, ie, the depth (level) of the step can be measured with a resolution of about 0.1 nm during the etching step for forming the phase shifter, the production yield of the phase shift mask can be further improved. Can be. That is, when a step is formed on a transparent substrate by an etching process, the transparent substrate can no longer be used as a product if it is excessively etched beyond a specified amount. On the other hand, if the etching amount is less than the specified amount, it is sufficient to add the etching by an insufficient amount, but it is extremely difficult to measure the etching amount of the transparent substrate on which the resist pattern is formed, that is, the step, with a conventional measuring device, In addition, since the thickness of the resist pattern varies depending on the progress of the etching, there is an inconvenience that the range of use of an apparatus for measuring a level difference by projecting a light beam from the side performing the etching process is limited.

Further, measurement of a step at a minute height level of about 0.1 nm is performed not only by the above-described phase shift mask but also by forming various optical elements such as waveguides on an optically transparent substrate. There is also a strong demand in the field of optical integrated circuits.

Accordingly, it is an object of the present invention to provide a step measuring apparatus and a step measuring method capable of measuring a step at a minute height level with high resolution.

Another object of the present invention is to accurately determine the amount of etching, that is, the amount of step or the depth of a concave portion of a transparent substrate on which a resist pattern is being formed while the resist pattern is being formed. An object of the present invention is to realize an etching monitor device capable of measuring.

Still another object of the present invention is to provide an etching method capable of accurately etching to a predetermined depth.

It is a further object of the present invention to provide an etching apparatus capable of accurately etching to a predetermined depth.

[0012]

SUMMARY OF THE INVENTION According to the present invention, there is provided a step measuring apparatus comprising: an optically transparent substrate having a first surface and a second surface opposite to the first surface; And a second interface formed of two media having different refractive indexes similarly to the first interface formed of two media having different refractive indexes and formed on or above the surface. A step measuring device for optically measuring a step which is a distance in a direction orthogonal to these interfaces, comprising: a light source device for generating a light beam; and two light source devices having a coherence from the light beam generated from the light source device. An optical system for generating a light beam, an objective lens for projecting these two light beams toward a second surface, which is the back surface of the transparent substrate, and a first lens which transmits through the second surface of the transparent substrate. 2 reflected at the interface and the second interface, respectively.
An interference optical system that relatively shifts the phases of the two reflected beams and combines the two reflected beams to generate an interference beam; and receives the interference beam emitted from the interference optical system and receives the interference beam. A photodetector that outputs the amplitude of the interference beam corresponding to the amount of phase shift given by
The first phase information, which is connected to the photodetector and includes information on a change in the amplitude of the interference beam with respect to the phase shift amount in the first measurement of the transparent substrate, and a second measurement different from the first measurement A signal processing device for determining a phase displacement amount between the phase shift amount and second phase information including information on an amplitude change of the interference beam, and determining a magnitude of a step to be measured from the obtained phase displacement amount. It is characterized by

The basic idea of the present invention is to project a light beam toward a second surface opposite to the first surface on which a step or a recess is formed, and to determine the depth of the step or the recess by a phase shift method. Is to determine. The present invention is based on the recognition that if two adjacent light beams are projected with a large numerical aperture, these two light beams can be considered to propagate along a common optical path. Based on such recognition, two light beams are projected on the transparent substrate or the transparent layer, and reflected on the interface located on the opposite side of the transparent substrate.
If the reflected beams are combined to generate an interference beam,
This interference beam includes a phase difference between the two reflected beams. Therefore, if the phase difference information included in the interference beam can be detected, the size of the step formed by the two interfaces formed on the transparent substrate can be detected. In the present invention, the phase difference between the reflected beams respectively reflected at the two interfaces forming the step is detected by the phase shift method. By using this phase shift method, a step of about 10 nm can be accurately detected, and a step having a small depth formed in a phase shift mask or an optical integrated circuit can be accurately measured.

On the other hand, when a concave portion is formed by an etching process in a phase shift mask or an optical integrated circuit, a resist pattern is formed on the surface side, and the thickness of the resist pattern changes according to the progress of the etching. Therefore, even if a light beam is projected from the side on which the resist pattern is formed, an accurate step difference cannot be measured. On the other hand, if a light beam is projected from the back side,
Depth measurement can be performed without being affected by the resist pattern, and depth measurement can be performed on a substrate during etching.

When there is a phase difference of Δθ between reflected beams reflected at two interfaces forming a step located on the opposite side of the transparent substrate, the phase difference Δθ can be expressed by the following equation. Δθ = 2π2nd / λ (1) where n is the refractive index of the transparent substrate, d is the distance in the direction orthogonal to the interface between the two substrates, that is, the height level of the step,
And λ are the wavelengths of the measurement light. Therefore, this phase difference Δθ
Can be detected, the height level d of the step can be obtained based on the equation (1).

In the present invention, the phase difference Δθ is obtained by a phase shift method. For this reason, the first step constituting the step of the transparent substrate
An interference optical system is used that relatively shifts the phases of the two reflected beams respectively reflected at the interface and the second interface and combines the two reflected beams to generate an interference beam. Since the interference beam emitted from the interference optical system includes both the phase shift amount given by the interference optical system and the phase information caused by the step, if the interference beam emitted from the interference optical system is received by the photodetector, The amplitude of the interference beam corresponding to the amount of phase shift given by the interference optical system is output. Therefore, for example, the amplitude change of the interference beam corresponding to the amount of phase shift for the transparent substrate before the step is formed is measured, and then the amplitude change of the interference beam corresponding to the amount of phase shift is formed with the step formed. If measured, the amount of phase displacement between these pieces of phase information corresponds to the phase difference Δθ caused by the step.

According to the present invention, the step to be measured is formed both directly on the first surface of the transparent substrate and when the step comprises an interface constituted by various films formed on the first surface. The case can be applied. Further, the medium forming the first interface and the medium forming the second interface can be the same medium, or the medium forming the first interface and the medium forming the second interface are different from each other. The present invention can also be applied to the case where one medium of the two interfaces is the same and the other medium is different.

In a preferred embodiment of the step measuring apparatus according to the present invention, a mirror having an opening formed substantially at the center is disposed on the front side of the photodetector, and light passing through the opening of the mirror is used as the photodetector. To form a confocal optical system so that reflected light from an interface other than the interface to be measured does not enter the photodetector.
When a plurality of interfaces are formed on a sample to be measured for a step, the projected light beam is reflected at each interface. In this case, since the reflected light reflected at an interface other than the interface to be measured shifts from the optical path, the reflected light reflected at an undesired interface can be removed by using a confocal optical system. improves. In particular, it is extremely useful when forming a plurality of layers on a transparent substrate and measuring the step or the film thickness, which is the distance between the interfaces of these layers.

A preferred embodiment of the step measuring device according to the present invention is characterized in that the light source device has a light emitting diode (LED) and a phase diffraction grating. In order to perform highly accurate measurement, it is desirable to remove the influence of stray light as much as possible. However, it is difficult to completely remove the effects of reflection and refraction on the surface of various optical elements. In this case, if laser light is used as the measurement beam, the generated stray light interferes with the laser light because the coherence length of the laser light is long, and noise occurs. On the other hand, since the light beam emitted from the LED has a short coherence length, even if stray light is generated on the reflection surface or refraction surface of various optical elements, the stray light travels over an optical path length longer than the normal optical path length. Therefore, the coherence is lost and no noise occurs. Therefore,
In order to perform a measurement with a high resolution of about 0.1 nm, it is extremely useful to use an LED as a light source. Further, if a phase diffraction grating is used as a beam splitting element for generating two coherent light beams, only ± 1st-order diffracted light is generated, so that there is an advantage that beam splitting can be performed with almost no loss of light quantity. Achieved.

A preferred embodiment of the step measuring device according to the present invention is characterized in that the objective lens is a thickness-corrected objective lens optically corrected for the thickness of the transparent substrate to be measured. When a glass substrate is used as a transparent substrate and a light beam is incident from the back side of the glass substrate, it is necessary to reduce the thickness of the glass substrate. On the other hand, although the thickness of the glass substrate is standardized, a tolerance is allowed. Therefore, it is necessary to use an objective lens in which the aberration such as chromatic aberration and the field of view are corrected within the range.

[0021]

FIG. 1 shows an example of a sample to be measured by a step measuring device according to the present invention. In this example, it is assumed that the depth of the concave portion formed by etching the phase shift mask 1 during the formation of the phase shifter by the etching process, that is, the step is measured. Phase shift mask 1
Comprises a glass substrate 2 which is an optically transparent substrate, a light-shielding pattern 3 defining a light transmission opening is formed on a first surface 2a of the glass substrate 2, and further defines a step which constitutes a phase shifter. An etching resist film 4 is formed. FIG. 1A shows a state before the etching process,
FIG. 1B shows a state in which a step having a depth d is formed during the etching process. In measuring the level difference, two measurement beams L1 and L2 which are coherent from each other from the side of the second surface 2b which is the back surface facing the first surface 2a of the glass substrate 2.
To project. Then, the first measurement beam L1 is made incident on a first step surface 5a which is one of two surfaces forming a step and forms an interface with air, and the second measurement beam L1 L2 is incident on a second surface 5b which forms an interface with the light-shielding pattern 2 which is the other step surface.

The measurement beam incident on each step surface is reflected on each step surface, passes through the second surface, which is the back surface of the transparent substrate 1, again, and enters the measurement system.

FIG. 2 is a diagrammatic sectional view showing the configuration of an example of the step measuring device according to the present invention. In this example, an LED that generates a coherent light beam of 470 nm as a light source
10 is used. LEDs emit light from the electrode surface,
In order to emit a linear high-intensity light beam from the side, this linear light beam is used as a measurement beam. Although the step surface is a substantially flat surface, since there are minute irregularities, when a light beam having a circular or elliptical cross section is used, there is a possibility that the step surface may be affected by the minute irregularities. On the other hand, when a linear light beam is used, there is a characteristic that it is hardly affected by minute irregularities on the step surface. Therefore, by using the linear beam from the LED 10, the influence of the step surface is reduced, and the measurement accuracy is improved. It is sufficient that the light source generates a coherent light beam, that is, a light beam having coherence, and a laser diode can be used, and a combination of a xenon lamp or a mercury lamp and a filter can also be used. . In this case, since the light beam emitted from the LED has a relatively short coherent length, there is an advantage that the light beam is hardly subjected to excessive coherence.

The coherent light beam emitted from the LED 10 is made parallel to the collimator lens 11, and this light beam is split into two ± 1 order diffracted lights by the phase diffraction grating 12. Accordingly, two light beams having coherence with each other are emitted from the diffraction grating 12. The distance between the two light beams can be set to a desired value by adjusting the grating pitch of the phase diffraction grating 12.

These light beams are incident on an objective lens 16 via a relay lens 13, a half mirror 14 for separating illumination light incident on the sample from light emitted from the sample, and a relay lens 15. The objective lens 16 is an objective lens whose thickness has been corrected with respect to the glass substrate of the phase shift mask to be measured. The two light beams are focused into a spot by the objective lens 16 and enter the phase shift mask 1 shown in FIG. The phase shift mask to be measured is mounted on an XYZ movement stage (not shown). Therefore,
The phase shift mask can be adjusted not only in the XY directions orthogonal to the optical axis but also in the Z direction which is the optical axis direction. Therefore, by adjusting the drive of the XYZ moving stage, not only the position to be measured but also the focus can be adjusted.

As shown in FIG. 1, one light beam is incident on a portion where the light shielding pattern 3 is formed, and the other light beam is incident on a surface to be etched. The reflectance at the interface between the glass substrate and air is about 4%, and the reflectance at the interface between the glass substrate and the light-shielding film of chromium or chromium oxide is 470 n.
It is about 10% for m wavelength light. Therefore, part of the light incident on the surface to be etched and part of the light incident on the light shielding film are reflected.

The two reflected beams are condensed by the objective lens 16 through the second surface of the glass substrate 1, and are passed through the relay lens 15 and the first half mirror 14 to the interference optical system 20.
Incident on. This interference optical system has a function of synthesizing two reflected beams from the phase shift mask 1 to generate an interference beam including information on a phase difference due to a step. In this example, the interference optical system is a Maffazender type sharing optical system. Constitute. The interference optical system 20 has a first half mirror 21 that divides a beam into first and second optical paths. The first optical path includes a half mirror 21, a pair of optical wedges 22 for adjusting the optical path length, a total reflection mirror 23, and a second half mirror 24. The second optical path is a half mirror 21, a total reflection mirror 2
5. Includes a pair of optical wedges 26 for adjusting the optical path length and a second half mirror 24. One reflected beam from the phase shift mask is transmitted through the first half mirror 21 and propagates in the first optical path, and the other reflected beam is transmitted to the first half mirror 2.
1 is reflected and propagates through the second optical path. The optical path lengths of the first and second optical paths are set to be the same or 2π or an integral multiple thereof by adjusting the optical wedge.

A part of the reflected beam reflected on the first step surface forming the interface with the air passes through the half mirror 21,
The component reflected by the half mirror 21 is shielded. Therefore,
The reflected beam reflected on the first step surface propagates through the first optical path. Half mirror 21 of a reflected beam reflected on a second step surface forming an interface with light shielding pattern 2
The component transmitted through is shielded from light. Therefore, the component of the reflected beam reflected by the second step surface reflected by the half mirror 21 propagates through the second optical path. Then, the reflected beams propagating through the first and second optical paths are combined by the half mirror 24 and emitted from the interference optical system 20 as one interference beam.

The optical wedge 26 in the second optical path is a first wedge 26a.
And a second wedge 26b. An actuator 27 and a position detector 28 are connected to the second optical wedge 26b. A drive circuit 29 is connected to the actuator 27. The actuator 27 moves the optical wedge 26b at a constant speed in a direction orthogonal to the optical path according to a control signal from a signal processing circuit described later to change the optical path length of the second optical path at a constant speed, thereby detecting the position. The detector 28 detects the position of the wedge 26b. Accordingly, the reflected beam propagating through the second optical path is added with a phase shift amount corresponding to a change in the optical path length corresponding to the movement of the wedge 26b, that is, a movement shift amount that changes continuously with time. . Therefore, the interference beam emitted from the interference optical system 20 includes the phase information caused by the constant speed movement of the optical wedge in addition to the phase information caused by the step of the phase shift mask.

The interference beam emitted from the interference optical system 20 enters the pinhole mirror 31 via the imaging lens 30. The pinhole mirror 31 is a mirror in which an opening is formed at a portion where the beam enters, and the shape of the opening corresponds to the cross-sectional shape of the linear beam emitted from the light source, that is, the LED 10. As a result, stray light is shielded by the pinhole mirror 31, so that a confocal optical system is formed and noise can be significantly reduced. An imaging lens 32 and an imaging camera 33 are provided in order to make the interference beam accurately enter the pinhole of the pinhole mirror 31, and an image is taken near the opening. The interference beam from the interference optical system 20 passes through the aperture of the pinhole mirror 31, enters the photodetector 34, and is converted into an electric signal.

The front side of the phase shift mask 1, that is, the first
An imaging optical system for capturing an image near the step to be measured is arranged on the side of the surface 1a. The imaging optical system includes a light source 40 that emits illumination light. The illumination light from the light source 40 is made incident on a half mirror 43 through an optical fiber 41 and a condenser lens 42, and a phase shift mask is passed through an objective lens 44. Project toward 1. The reflected light from the phase shift mask 1 again enters the imaging camera 46 via the objective lens 44, the half mirror 43, and the imaging lens 45, and an image near the step to be measured of the phase shift mask is captured. The imaging camera takes an image of the measurement beam incident from the back surface 1b side in addition to the image near the step of the phase shift mask 1, so that the measurement beam is accurately incident on the step surface to be measured. You can confirm whether or not.

A PSD (Phase Sens
active device) 35 and connect the output of this PSD to A /
It is connected to a signal processing circuit 36 via a D converter (not shown). The LED 10 is connected to the signal processing circuit 35 and modulates at a high frequency by a drive signal from the signal processing circuit. Then, the PSD extracts the signal component of the modulation frequency of the LED 10 and supplies the signal component to the signal processing circuit 35. As a result, double heterodyne detection is performed, and noise can be further reduced.

FIG. 3 shows a signal processing circuit 35 from a photodetector 34.
3 shows an example of a signal waveform output to the first embodiment. In FIG. 3, the horizontal axis indicates the amount of phase shift introduced into one reflected beam by the movement of the optical system wedge 26a or the time when the wedge moves at a constant speed, and the vertical axis indicates light received by the photodetector 34. 3 shows the amplitude of the interference beam. Curve A shows the first output signal of the photodetector when the phase difference occurs due to the step, that is, the change in the amplitude of the interference beam with respect to the phase shift amount, and curve B shows the phase shift amount when another phase difference occurs. 5 shows the change in the amplitude of the interference beam with respect to. Since the optical wedge 26a moves at a constant speed in a direction orthogonal to the optical axis, the interference optical system 2
The optical path length of the second optical path 0 increases with time over the optical path length of the first optical path, and the phase difference between the reflected beams propagating through the two optical paths of the interference optical system 20 increases with time.
On the other hand, the interference beam received by the photodetector 34 includes both the phase difference between the two reflected beams reflected on the step surface of the phase shift mask 1 and the phase shift introduced by the movement of the optical wedge 26a. , The output signal of the photodetector 34 can be described as a general expression as follows. I =
Acos (θ−2πωt) where I is the intensity of the signal output from the photodetector 34, that is, the amplitude of the interference beam, A is a constant, θ is the phase difference between the two reflected beams, ω is an angular velocity corresponding to the moving speed of the wedge, and t
Is time.

The output signal from the photodetector 34 is a sine wave signal containing phase difference information. Therefore, if the output signal in a certain step state and the output signal in another step state are compared and the phase difference Δθ between them is obtained, this phase difference becomes phase difference information caused by the step. In this case, if one output signal is the output signal in a state where the phase difference θ is zero, for example, the phase difference information in a state before the step is formed by etching is the reference phase difference information, the phase difference between the two is compared. Then, by obtaining the phase difference Δθ, the value of the step can be determined based on the equation (1).

The output signal from the photodetector 34 includes a phase difference due to phase inversion due to reflection on the step surface and a phase difference due to reflection at various optical elements, and these phase differences may be regarded as constants. For example, if the output signal from the photodetector 34 before the step is formed by the etching is used as the reference phase information, and the output measured after the step is formed by the etching is used as the measurement phase information, the difference between these phase information can be obtained. Is only the phase difference Δθ caused by the step. Therefore,
If the phase difference Δθ between the two pieces of measured phase information is detected, the step difference based on the equation (1) can be obtained without being affected by the phase difference generated by the various optical elements and the phase difference due to the phase inversion due to reflection. Can be determined. With this configuration, even when two step surfaces having different optical characteristics at the interface are formed, the step amount or the etching amount can be accurately detected without being affected by the interface.

Next, the operation of the signal processing circuit 35 will be described. The measurement is performed by setting the phase difference between the first and second optical paths of the interference optical system 20 to zero or 2nπ (n is a positive integer). First, a first reference measurement is started. The actuator 27 moves by at least a distance corresponding to one cycle, and increases the optical path length of the second optical path by an optical distance corresponding to one cycle at the measurement wavelength. Then, the signal processing circuit 35 sequentially stores the output data from the photodetector 34 corresponding to one cycle, that is, the amplitude change of the interference beam with respect to the introduced phase shift amount in the memory via the A / D converter. The first state can be, for example, a state in which a step before etching in which a resist pattern is formed is not formed. Next, etching is performed to form a step having a predetermined depth, and this state is referred to as a second state. Then, in the second state, the same measurement is performed, and the signal processing circuit 35 stores the data of the amplitude change of the interference beam with respect to the phase shift amount over one period. Then, these two data are compared, the amount of phase displacement between them is obtained, and the step is determined.

There are various methods for obtaining the amount of phase displacement. For example, a Fourier transform phase shift method is used. In this case, first, Fourier transform is performed on the data for one cycle stored in the memory in the first state.
Next, the tangent of the real part to the imaginary part is obtained to obtain a phase angle θ1, which represents the phase difference between the two reflected beams in the first state. Next, the second
The same processing is performed on the data in the state (1) to obtain the phase angle θ2 in the second state. Next, the amount of phase displacement is obtained by subtracting the phase angle θ2 in the second state from the phase angle θ1 in the first state. Then, the depth of the step or the depth d of the concave portion is obtained based on Expression (1).

As another method for obtaining the amount of phase displacement, FIG.
As shown in (1), each peak value is obtained from the relationship between the phase shift amount in the two states and the amplitude of the interference beam, and the first value is obtained.
The amount of phase displacement can also be determined from the difference between the peak value in the state (1) and the peak value in the second state.

FIG. 4 is a diagram showing the configuration of another embodiment of the level difference measuring device according to the present invention. The same components as those used in FIG. 2 will be described with the same reference numerals. LED
The light beam emitted from 10 is made incident on the polarization beam splitter 50 via the collimator lens 11, and only the light beam on a specific polarization plane is reflected. Polarizing beam splitter 5
The light beam reflected at 0 enters the Nomarski prism 52 via the λ / 4 plate 51. The Nomarski prism 52 emits two light beams having coherence with each other, and the distance between these beams can be set to a desired distance by changing the inclination angle or the like of the Nomarski prism. The two light beams emitted from the Nomarski prism 52 are converged into a minute spot by the objective lens 16 and are incident on the phase shift mask 1. One light is incident on one step surface and the other light beam is on the other step surface. Incident on the surface. The beams incident on these step surfaces are reflected on the respective step surfaces, again enter the Nomarski prism 52 via the objective lens, and are combined into one interference beam. The actuator 27 is connected to the Nomarski prism 52,
By changing the amount of insertion of the Nomarski prism into the optical path continuously over time, the relative phase continuously changing over time between the two beams emitted from the Nomarski prism and reflected by the phase shift mask 1 A shift can be introduced. Therefore, an interference beam including the phase difference information caused by the step of the phase shift mask 1 and the phase shift amount caused by the optical path length difference introduced by the Nomarski prism is emitted from the Nomarski prism 52.

The interference beam emitted from the Nomarski prism 52 enters the polarization beam splitter 50 via the λ / 4 plate 51. Since this interference beam has passed through the λ / 4 plate twice, its polarization plane has been rotated by 90 ° and transmitted through the polarization beam splitter 50. Further, this interference beam enters the photodetector 34 via the imaging lens 30 and the pinhole mirror 31. The light detector 34 outputs a change in the amplitude of the interference beam with respect to the amount of phase shift introduced by the movement of the Nomarski prism, as in the embodiment shown in FIG.

Next, an object which can be measured by the present invention will be described. 5A to 5C show examples of measuring various objects that can be measured according to the present invention. FIG. 5A shows a step measurement and a film thickness measurement when another layer 61 is formed on a transparent substrate 60 on which a step is formed. The two interfaces 62 and 63 constituting the step are both formed of a transparent substrate and another layer. In this case, the light beams L1 and L2 are reflected at the interfaces 62 and 63, respectively. , The step d can be measured. That is, even when the two interfaces forming the step are both formed of the same medium, the step can be measured based on the present invention. In this case, as the first measurement, the interface 62 or 6
3, two light beams are made incident on one of the interfaces to measure the phase information between the reflected beams from the same interface, and then the second measurement is performed by projecting the illustrated light beams L1 and L2. By measuring the second phase information and obtaining the amount of phase displacement from the phase information, the step d can be measured.

When the other film 61 is an optically transparent transparent layer, the light beams L1 'and L2' are projected and the transparent substrate 60
The thickness of the transparent layer formed on the substrate can also be measured by using the reflected beams reflected at the interface 63 between the transparent layer 61 and the transparent layer 61 and the interface 64 between the transparent layer 61 and the air. That is, the present invention can also function as an apparatus for measuring the thickness of a transparent layer formed on a transparent substrate.

FIG. 5B shows another transparent layer 65 on a transparent substrate 60.
An example in which an opaque layer 66 is formed and a step d1 formed in another transparent layer 65 is measured will be described. As described above, the level difference of the transparent layer formed on the transparent substrate without being directly formed on the surface of the transparent substrate can be measured. It is particularly useful when a semiconductor device is manufactured by forming various semiconductor layers on a glass substrate, and when a waveguide and various optical components are formed on a glass substrate. Further, the light beams L1 'and L
By projecting 2 ', the thickness d2 of the transparent layer 65 formed on the transparent substrate can also be measured.

FIG. 5C shows three transparent layers 6 on a transparent substrate 60.
An example in which the thickness of each transparent layer is measured when 7, 68 and 69 are sequentially formed will be described. Also in this case, the thickness of each transparent layer can be measured by measuring the phase difference between the reflected lights at each interface. In this example, there is an advantage that the thickness of the intermediate transparent layer can be measured by using the reflected light at the interfaces on both sides of the intermediate layer 68. That is, it is particularly useful when a transparent layer is continuously formed on a substrate.

Next, an etching apparatus and an etching method using the step measurement method according to the present invention will be described.
FIG. 6 is a diagram showing a configuration of an example of the plasma etching apparatus according to the present invention. Referring to FIG. 6, the etching apparatus according to the present invention includes an etching chamber 70 for performing an etching process and a preliminary chamber 71 for measuring an etching amount. The etching chamber 70 has an upper electrode 72 and a lower electrode 73, and an RF power supply 74 for applying a predetermined voltage is connected between these electrodes. The phase shift mask 1 to be etched is arranged on the lower electrode 73. Various conduits for supplying an etching gas, conduits for exhausting gas, and the like are connected to the etching chamber 70.

The etching chamber 70 and the preliminary chamber 71 communicate with each other by a valve. The preparatory chamber 71 is provided with an optical system unit 75 in which the optical system of the above-described step measurement device is unitized.
This optical system unit is connected to a signal processing circuit 76 arranged outside the spare room, performs various signal processing from outside the spare room 71, and extracts phase difference data. A conduit for supplying nitrogen gas and a conduit for exhaust are connected to the preliminary chamber 71, and are connected to outside air via a valve.

The phase shift mask 1 in which the resist pattern disposed in the etching chamber 70 is formed is transferred to the preliminary chamber 71 by a loader (not shown) and is placed on the susceptor 77. An opening is formed in the central portion of the susceptor 77, and the light beam projected from the optical system unit 75 is incident on the back side of the phase shift mask 1 to be measured through the opening of the susceptor 77, and a resist pattern is formed. The light is reflected by the surface 1 and again enters the optical system unit.
The output from the photodetector is supplied to a signal processing circuit 76 disposed outside, and the signal processing circuit generates measurement data. A display device is connected to the signal processing circuit 76 to display data such as an etching amount and an etching rate.

FIG. 7 shows an algorithm of the etching method according to the present invention. Prior to the etching process in step 1, a phase shift mask on which a resist pattern is formed is placed in a preliminary chamber, phase measurement before the etching process is performed, and the interference beam with respect to the phase shift amount of the phase shift mask before the etching process is measured. The change in the amplitude is stored in the memory of the signal processing circuit 76 as first phase information.

Next, in step 2, a first etching process is performed. The throughput of this first etching process is:
The etching amount can be set to be less than the target etching amount, for example, 80% of the target etching amount. Also, the first
Can be set as an etching time.

After the first etching process is completed, in step 3, the phase shift mask is carried into the preliminary chamber by the loader, and the second phase measurement is performed. In the second phase measurement,
Under the same conditions as in the first phase measurement, the change in the amplitude of the interference beam with respect to the phase shift amount of the etched phase shift mask is measured and stored in the memory of the signal processing circuit 66 as second phase information.

Next, in step 4, the signal processing circuit 66
Calculates the phase difference Δθ by comparing the first phase information before the etching with the second phase information after the first etching. Next, the etching rate is determined from the relationship between the etching time in the first etching process and the phase difference Δθ. Further, a difference between a phase difference corresponding to the target etching amount and a phase difference generated by the first etching process is obtained, and an additional etching amount is determined. Further, an etching time to be further performed is obtained from the obtained etching rate and the additional etching amount, and this etching time is set as an etching time to be subjected to the second etching process. With this configuration, the second phase can be obtained simply by using the phase difference as a factor.
Of the etching process can be determined.
Note that the actual etching depth can be determined from the phase difference Δθ, and the second etching processing time can be defined based on the information on the etching depth.

Next, in step 5, a second etching process is performed for a set time.

Next, in step 6, the resist pattern is removed, and in step 7, it is confirmed whether or not a step having a final desired depth is formed. This confirmation measurement can be confirmed by transmitted light measurement from the surface side.

The present invention is not limited to the embodiment described above, and various modifications and changes are possible. For example, in the above-described embodiment, the etching amount was measured in the preliminary chamber adjacent to the etching chamber. However, an opening was provided in a part of the lower electrode in the etching chamber, and a step according to the present invention was provided below this opening. An optical system unit containing the optical system of the measuring device can be arranged to continuously measure the phase shift amount during the etching process. In this case, a signal from the imaging camera for performing alignment is supplied to a display device arranged outside the etching chamber, and operations such as alignment can be performed from outside the chamber.

Further, in the above embodiment, the case where the etching shift is performed on the phase shift mask has been described.
The present invention can be applied to all cases where an optically transparent substrate is subjected to etching treatment, and can be applied to, for example, the manufacture of an optical integrated circuit such as an optical waveguide.

[Brief description of the drawings]

FIG. 1 is a diagrammatic cross-sectional view showing a configuration of an example of a phase shift mask for explaining the principle of step measurement according to the present invention.

FIG. 2 is a diagram showing a configuration of an example of a level difference measuring device according to the present invention.

FIG. 3 is a graph showing a relationship between a moving time of a wedge and a photodetector output.

FIG. 4 is a diagram showing the configuration of another embodiment of the level difference measuring device according to the present invention.

FIG. 5 is a diagram showing a configuration of an example of an etching apparatus according to the present invention.

FIG. 6 is a diagram showing various objects to be measured by the step measurement method according to the present invention.

FIG. 7 shows an algorithm of an etching method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Phase shift mask 2 Transparent substrate 3 Light-shielding pattern 4 Resist pattern 10 Light source 12 Phase diffraction grating 16 Objective lens 20 Interference optical system 21, 24 Half mirror 23, 25 Total reflection mirror 22, 26 Optical wedge pair 27 Actuator 28 Position detector 31 pinhole mirror 34 photodetector 35 signal processing circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H01L 21/3065 H01L 21/302 EF term (Reference) 2F065 AA25 AA54 BB13 CC20 DD04 FF01 FF07 FF53 GG03 GG06 GG07 HH05 JJ16 LL02 LL09 LL12 LL36 LL42 LL47 NN05 NN08 QQ04 QQ16 QQ23 QQ25 QQ34 RR05 UU07 2G051 AA56 AB02 BA10 CA03 CA04 CB01 CC11 EA30 2H095 BB03 BB14 BC28 BD04 BD13 BD15 BD19 AH30A HA25A25A004A

Claims (20)

[Claims] A first surface of an optically transparent substrate having a first surface and a second surface opposite to the first surface, the second surface being a back surface facing the first surface;
And a second interface formed of two media having different refractive indexes similarly to the first interface formed of two media having different refractive indexes and formed on or above the surface. A step measuring device for optically measuring a step which is a distance in a direction orthogonal to these interfaces, comprising: a light source device for generating a light beam; and two light sources having a coherence from the light beam generated from the light source device. An optical system for generating a light beam of the type described above;
An objective lens for projecting toward the surface of the transparent substrate; and a phase shifter between the two reflected beams transmitted through the second surface of the transparent substrate and respectively reflected at the first interface and the second interface. An interference optical system that combines the two reflected beams to generate an interference beam, receives the interference beam emitted from the interference optical system, and adjusts the amplitude of the interference beam corresponding to the phase shift amount given by the interference optical system. An output photodetector; first phase information connected to the photodetector and including information on a change in the amplitude of the interference beam with respect to a phase shift amount in the first measurement of the transparent substrate; Calculates the amount of phase displacement between the second phase information including the information on the change in the amplitude of the interference beam with respect to the amount of phase shift in a different second measurement, and determines the size of the step to be measured from the obtained amount of phase displacement. You Step measurement apparatus characterized by comprising a signal processing unit. 2. The light source device according to claim 1, wherein the light source device comprises an LED, and an optical system for generating two light beams from the light beam generated from the light source device comprises a phase diffraction grating. Step measuring device. 3. The step measuring device according to claim 1, wherein the optical system for generating two light beams from the light beam generated from the light source device is constituted by a Nomarski prism. 4. The apparatus according to claim 1, wherein said interference optical system is constituted by a Mach-Zehnder type shearing optical system.
4. The step measuring device according to 4. 5. The interference optical system has two light paths and a light combining element that combines light beams propagating through these light paths, and moves an optical wedge disposed in one of the light paths in a direction orthogonal to the light paths. The step measurement device according to claim 4, wherein the phase of the two reflected beams is relatively shifted. 6. The interference optical system includes a Nomarski prism, an actuator for moving the Nomarski prism in a direction orthogonal to an optical axis, and a position detector for detecting a position of the Nomarski prism. The step measuring device according to claim 1. 7. A phase shift amount given to two reflected beams in the interference optical system is at least 2π, and the phase is relatively shifted continuously or stepwise over a period of at least 2π. 2. The step measuring device according to 1. 8. A mirror having an opening formed substantially at the center thereof is disposed on the front side of the photodetector, and light passing through the opening of the mirror is incident on the photodetector to form a confocal optical system. The step measurement device according to claim 1, wherein the step is configured so that reflected light from an interface other than the interface to be measured does not enter the photodetector. 9. The signal processing device according to claim 1, wherein the first and second signal processing devices include:
2. The step measuring device according to claim 1, wherein the phase information of each of the above is Fourier-transformed to obtain corresponding first and second phase angles, and a phase displacement is determined from a difference between these phase angles. 10. The level difference to be measured from the obtained phase displacement amount, wherein the signal processing device obtains a phase displacement amount between a peak value of the first phase information and a peak value of the second phase information. The step measurement device according to claim 1, wherein the step is determined. 11. The level difference measuring apparatus according to claim 1, wherein the medium forming the first interface and the medium forming the second interface are the same medium. 12. The step measuring device according to claim 1, wherein a medium forming the first interface is different from a medium forming the second interface. 13. The medium of one of the first and second interfaces is both the transparent substrate, the other medium of the first interface is air, and the other medium of the second interface is a light shielding pattern or an etching medium. 13. The level difference measuring device according to claim 12, wherein the resist pattern is: 14. The step measuring device according to claim 1, wherein the medium forming the first and second interfaces is formed of a film formed on the transparent substrate. 15. An optically transparent substrate having a first surface and a second surface opposite to the first surface, the optically transparent substrate being formed on or above the first surface and having mutually different refractive indices. Is a distance between a first interface formed by two media having different refractive indexes and a second interface formed by two media having different refractive indices in a direction orthogonal to these interfaces. Projecting two first and second light beams having coherence to each other toward the second surface of the transparent substrate, and measuring the second surface of the transparent substrate A step of relatively shifting the phases of two reflected beams transmitted and reflected at the first and second interfaces of the first surface, respectively, and combining the reflected beams to generate an interference beam; Generating phase information indicating a change in amplitude with respect to a phase shift amount of Determining the size of the step to be measured by comparing phase information in two different measurements of the transparent substrate. 16. An etching monitor device for detecting the progress of etching of a transparent substrate on which a resist pattern is formed, wherein the transparent substrate faces a first surface to be subjected to an etching process and the first surface. A second surface which is a back surface not subjected to an etching process, wherein the first surface has a first portion to be subjected to the etching process and a second portion on which a resist pattern is formed; A light source device that generates a light beam; an optical system that generates two light beams having coherence from each other from the light beam emitted from the light source device; and a second light source that is a back surface of the transparent substrate.
And the phase of two reflected beams transmitted through the second surface of the transparent substrate and reflected at the interface between the first and second portions of the first surface, respectively. An interference optical system that shifts and combines these two interference beams to generate an interference beam, receives an interference beam emitted from the interference optical system, and corresponds to a phase shift amount given by the interference optical system. A photodetector that outputs the amplitude of the interference beam; first phase information connected to the photodetector, the first phase information including information on a change in the amplitude of the interference beam with respect to a phase shift amount in the first state of the transparent substrate; A phase shift amount between the phase shift amount in the second state where the etching process has progressed from the first state and the second phase information including information on the amplitude change of the interference beam with respect to the phase shift amount is obtained, and from the obtained phase shift amount Etching monitoring apparatus characterized by comprising a signal processing device for determining the progress of etching. 17. The etching monitor according to claim 16, wherein the first state is a state before the etching process. 18. A first optically transparent substrate having a first surface on which a resist pattern is formed and to be etched and a second surface facing the first surface and not being etched. In selectively forming a concave portion having a target depth by performing etching on the surface, two light beams having coherence with each other are projected toward the second surface of the transparent substrate, and the rear surface is formed. A reflected beam transmitted through the second surface and reflected at the interface of the first portion etched or to be etched on the first surface and reflected at the interface of the second portion not subjected to the etching process. The phase of the beam is relatively shifted, and the two reflected beams are combined to generate an interference beam.
Providing an optical device for detecting an amplitude change with respect to the phase shift amount of the interference beam; and using the optical device, a first substrate including an amplitude change with respect to the phase shift amount of the interference beam for the transparent substrate before being etched. A step of detecting phase information; a first etching step of performing an etching process on the transparent substrate on which the phase difference information has been detected to a depth less than the target depth; and a first etching process using the optical device. Detecting the second phase information for the transparent substrate on which the process has been performed; and obtaining a phase displacement amount corresponding to the depth of the concave portion formed by the first etching process from the first and second phase information, Determining an additional etching amount to be further performed based on the phase displacement amount. 19. The method according to claim 19, wherein the step of determining the amount of additional etching includes the step of determining an etching rate in a first etching step from the first and second phase information, and a step of determining a target etching amount and a first etching process. Detecting a difference between the formed etching amount and an additional etching time based on the detected etching amount difference and the etching rate. 14. The etching method according to 13. 20. An etching chamber for performing an etching process on a transparent substrate, and a concave portion formed on the transparent substrate that has been subjected to the etching process in the etching chamber by a step measurement device disposed adjacent to and inside the etching chamber. A preliminary chamber for measuring the depth, and a moving mechanism for moving the transparent substrate to be processed between the etching chamber and the preliminary chamber, wherein the level difference measuring device comprises: a light source device for generating a light beam; and An optical system for generating first and second two light beams having coherence from each other from the emitted light beam; and a first surface receiving the two light beams by subjecting the transparent substrate to an etching process. An objective lens for projecting toward an opposing second surface that is not subjected to an etching process, and an objective lens that transmits through the second surface of the transparent substrate and has a first surface. The phase of the two reflected beams respectively reflected at the interface of the first portion which is or is to be subjected to the etching process and the interface of the second portion which is not subjected to the etching process is relatively shifted, and the two reflected beams are also shifted. And an interference optical system that generates an interference beam by combining the interference optical system and an optical detection device that receives the interference beam emitted from the interference optical system and outputs an amplitude of the interference beam corresponding to the phase shift amount given by the interference optical system. A first phase information, which is connected to the photodetector and includes a change in the amplitude of the interference beam with respect to a phase shift amount in the first state of the transparent substrate, and a second phase information different from the first state. The phase shift between the phase shift amount and the second phase information including the information on the change in the amplitude of the interference beam with respect to the phase shift amount in the state is obtained, and the etching amount to be measured from the obtained phase shift Etching apparatus characterized by comprising a determination signal processor.