JP3006260B2 - Photomask inspection method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask inspection apparatus used as an original when transferring a circuit pattern such as a semiconductor, and more particularly, a phase member for changing the phase of transmitted light is added to a specific portion. The present invention relates to a photomask inspection apparatus suitable for use in measuring the amount of phase change and the presence or absence of a defect in a phase shift photomask.

[0002]

2. Description of the Related Art A photomask used as an original when a semiconductor circuit is projected and exposed on a wafer and transferred thereon generally has a structure in which a light-shielding pattern made of a metal such as chrome (Cr) is formed on a glass substrate. No. But,
The photomask having such a structure has a problem that when the circuit pattern is miniaturized, a high-contrast projected image cannot be obtained due to light diffraction and interference. Therefore, in recent years, various phase change photomasks (phase shift photomasks) have been proposed in which a phase member is added to a specific portion of the photomask surface to partially change the phase of transmitted light, thereby enhancing image contrast. . For example, Japanese Patent Publication No. 62-50811 discloses a technique related to a spatial frequency modulation type photomask.

In such a phase change photomask, it is important to accurately control the phase. Therefore, it is necessary to inspect the amount of phase change by the phase member in addition to the presence or absence of a defect in the light shielding pattern. Conventionally, the amount of phase change has been determined using an ellipsometer or the like that measures the thickness and refractive index of the thin film using multiple reflection between the thin film surface and the substrate or the thin film interface. That is, for example, the phase change amount φ by the phase member made of a silicon oxide (SiO ₂ ) film or the like is equal to the thickness d of the phase member.
And the refractive index n of the phase member at the exposure wavelength λ when the photomask is used in an actual lithography process, and then calculated by the following equation (1). φ = 2π · (n−1) d / λ (1)

[0004]

However, conventionally,
The ellipsometer used for the inspection of the phase change photomask measures the film thickness and the refractive index using the reflection at the interface of the substrate or the thin film as described above, so that the refractive index difference between the substrate and the thin film is small. In such a case, the measurement is very difficult, and if the refractive indices of the two are equal, the measurement becomes impossible because the intensity of the reflected light at the interface becomes zero.

On the other hand, light sources in photolithography have been shortened in wavelength with miniaturization of semiconductor circuit patterns, and it is expected that far ultraviolet rays will become the main light source in the future. There are few materials having high transmittance to ultraviolet rays, and it is considered that both the phase member and the substrate of the photomask are formed of quartz glass. In this case, the refractive indexes of the two become equal, and it is impossible to measure the amount of phase change using an ellipsometer as described above.

Further, the phase member in the phase shift photomask has a phase change φ represented by the above equation (1) of π.
The refractive index n and the thickness d of the phase member are controlled so that the following conditions are satisfied. Conditions for forming the phase member on the photomask (for example, conditions for forming the phase member, temperature, pressure, composition, etc.) As a result, the refractive index n slightly changes, and the thickness d of the phase member also varies in the actual manufacturing process. For example, when the exposure wavelength λ is 365 nm,
Assuming that the refractive index n of the phase member is 1.5 and an error in the amount of phase change is allowed up to 10 °, the error in the thickness d is ± 20 nm.
However, it is very difficult to control the film thickness within this error range. Therefore, there is a strong demand for efficiently detecting a portion where the error of the phase change amount φ (that is, the deviation amount of φ from π) is large.

However, when the amount of phase change is determined from the film thickness and the refractive index of the phase member as in the prior art, not only the film thickness d of the phase member but also the refractive index n that changes depending on the film forming conditions.
Must be measured each time, and the measurement requires a long time. In view of the above, the present invention can accurately detect a portion having a large phase change error regardless of the refractive index difference between a phase member and a substrate, and can accurately detect a phase change amount error at an actual exposure wavelength. It is an object of the present invention to provide a photomask inspection method and apparatus capable of easily and quickly detecting a portion having a large value.

[0008]

A first photomask inspection apparatus according to the present invention, as shown in FIG. 1, for example, has an illumination optical system (1, 2, 2) for illuminating a photomask (8) to be inspected.
4, 7), and a light beam separating means (11) for separating the light from the photomask (8) into a first light beam LA and a second light beam LB according to the polarization state. First
A light beam combining means (18) which is arranged at a position where the optical path length of the light beam and the optical path length of the separated second light beam are substantially equal, and combines the first light beam and the second light beam; Observation means for observing the intensity distribution of the combined light beam (19,
20) and the first light beam arranged in the optical path of the first light beam.
A first variable-angle optical member (13) for laterally shifting the light beam in one direction, and a second optical member (13) arranged in the optical path of the second light beam for shifting the second light beam in the direction opposite to the one direction.
And an optical member (14) having a variable inclination angle.

A second photomask inspection apparatus according to the present invention, as shown in FIG. 5, for example, includes an illumination optical system for illuminating a photomask (8) to be inspected, and light from the photomask (8). Light beam separating means (31) for separating the light beam into a first light beam LA and a second light beam LB according to the polarization state;
The separated first light beam LA is polarized and guided to the light beam separating means (31) via a first closed optical path, and the separated second light beam LB is polarized to be first closed light beam. Beam polarizing means (32a, 33a, 3) guided to the light beam separating means (31) through a second closed light path which coincides with the reflected light path.
3b) and the first polarized light polarized by the light beam polarizing means.
Observing means (19, 20) for observing the intensity distribution of light obtained by combining the light beam LA and the second light beam LB via the light beam separating means (31), and the first and second closing means As shown in FIG. 6, for example, as shown in FIG. 6, the optical system has a variable inclination optical member (34) that causes a lateral displacement between the first closed optical path and the second closed optical path. . In addition, as shown in FIGS. 1 and 3, for example, a third photomask inspection apparatus according to the present invention includes a light source (1 to 5) for emitting illumination light having a narrow wavelength width, a phase shifter unit (PS), and a light transmitting unit. A mask stage (9A, 9B) for supporting a photomask (8) including: a first light beam LA passing through a first optical path and a second light beam passing through a second optical path; A light beam separating means (11) for branching into a light beam LB, and a light beam synthesizing means (18) for superimposing the first light beam and the second light beam to generate interference light.
And a photoelectric conversion element (2
0). Then, based on this configuration, the light beam separating means (11) and the light beam combining means (1)
Means (15) for adjusting the relative relationship between the length of the first optical path and the length of the second optical path.
And means (13, 14) for laterally shifting the first light beam and the second light beam on the photoelectric conversion element (20). In addition, the photoma
The mask inspection method includes a phase shifter section and a light transmitting section.
In the inspection method of the photomask (8), the photomask
Is illuminated with illumination light with a narrow wavelength band, and
The illuminated light passed through the first light path LA
And a second light beam LB passing through the second light path,
The first light beam and the second light beam are overlapped to form an interference light
Then, the interference light is photoelectrically converted by the photoelectric conversion element (20).
Inspection of the photomask based on the signal obtained
The length of the first optical path and the length of the second optical path
The length is relatively adjustable and its photoelectric conversion element
Adjust the lateral shift between the first light beam and the second light beam on the child
What is possible.

[0010]

According to the first photomask inspection apparatus of the present invention,
Third photomask inspection device or photomask inspection method
According to the method , illumination light of a wavelength range similar to actual exposure light is used as illumination light of the illumination optical system. Then, the first light beam LA and the second light beam LB are combined in the light beam combining means (18) in a state where they are laterally shifted from each other. Therefore, when the pattern of the photomask (8) to be inspected includes, for example, a portion of only the substrate and a phase member (phase shifter) having a phase different by π, the amount of lateral displacement is adjusted to adjust the image of the portion of only the substrate. And the image of the phase member. And
When the intensity distribution after synthesis is observed by the observation means (19, 20) or the photoelectric conversion element (20), the part where the normal part and the phase member overlap each other becomes dark. In this case, if there is a defect in the phase member whose phase difference deviates from π,
Only the portion corresponding to the defective portion in the dark area becomes bright. Therefore, even when the substrate and the phase member have the same refractive index, a defective portion of the phase member can be accurately detected.

In this case, the first photomask inspection apparatus
Respond to the polarization state using, for example, a polarizing beam splitter.
First, the first light beam LA and the second light beam LB are separated.
Since the light is synthesized after the
A bright observation image is obtained. However, for example, use a half mirror
Observation that can be finally obtained even if it is split into two light beams
The intensity of the image is reduced by half, but observation is possible. This
As described above, the use efficiency of illumination light decreases,
The third photomask inspection device can use ordinary light
is there. Furthermore, in the first photomask inspection apparatus, the first tiltable optical member (13) and the second tiltable optical member (14) laterally shift light beams in directions opposite to each other. When the light beam is laterally shifted in the opposite direction as described above, the optical members (13, 14) may be inclined in the opposite directions as shown in FIG. 2, for example. When the light beams are inclined in opposite directions, the first light beam LA and the second light beam LB
And the change in the optical path length is almost the same. Therefore, even if the lateral shift amount between the light beam LA and the light beam LB is increased, the first
Beam synthesizing means (18) for the light beam LA and the second light beam LB
Since the difference in the optical path length is small, it is possible to observe the intensity distribution of the combined interference image with a good contrast even when the coherency of the illumination light is relatively poor.

According to the second photomask inspection apparatus, the optical path length of the first closed optical path through which the first light beam LA passes and the optical path length of the second closed optical path through which the second light beam LB passes The length is the same. Further, since the first light beam LA and the second light beam LB are traveling in opposite directions, when the tiltable optical member (34) is tilted by a predetermined angle, the first closed light path and the second closed light path are closed. In the opposite direction to the optical path. Therefore, with an extremely simple and compact configuration, it is possible to observe the intensity distribution of the interference image in a state where the first light beam LA and the second light beam LB are laterally shifted and superimposed. Further, since the difference in the optical path length between the first light beam LA and the second light beam LB is so small that it can be ignored, the contrast of the obtained intensity distribution is extremely good.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a photomask inspection apparatus according to the present invention will be described below with reference to FIGS. FIG. 1 shows a configuration of an inspection apparatus according to the present embodiment.
Reference numeral 1 denotes a mercury lamp. Illumination light emitted from the mercury lamp 1 enters a wavelength selection filter 5 through a condenser lens 2, a field stop 3, and a collimator lens 4. The illumination light whose wavelength width has been narrowed by the wavelength selection filter 5 and has improved coherence passes through the aperture stop 6 and is then condensed by the condenser lens 7 to illuminate the mask 8 to be inspected. The illumination range of the test mask 8 is adjusted by the field stop 3, and the brightness of the illumination light on the test mask 8 is adjusted by the aperture stop 6. The test mask 8 is placed on a mask stage 9A,
The mask stage 9A is connected to the stage 2 via the stage driving means 9B.
By moving the mask 8 in the two-dimensional plane, the entire surface of the test mask 8 can be inspected.

The illumination light transmitted through the test mask 8 is focused by the objective lens 10 and enters one end of the first prism 12. The first prism 12 is connected to the objective lens 10
In order from the side, a prism having a triangular cross section parallel to the paper of FIG. 1 and a prism having a parallelogram parallel to the paper of FIG. 1 are bonded together. The polarization beam splitter surface 11 is inclined by 45 ° with respect to the optical axis of the objective lens 10. Prism 1
The first light beam LA of the P-polarized light with respect to the polarization beam splitter surface 11 of the illumination light incident on the polarization beam splitter 2 is transmitted through the polarization beam splitter surface 11 and then totally reflected at the other end of the prism 12 to the outside. Injected into. Also, the prism 12
, The second light beam LB of S-polarized light with respect to the polarization beam splitter surface 11 is reflected by the polarization beam splitter surface 11 and emitted to the outside.

The first light beam LA emitted to the outside is
Are transmitted through an optical wedge 15 formed of a glass plate having a trapezoidal cross section and incident on the side surface on one end side of the second prism 17. The second prism 17 has the same configuration as that obtained by rotating the first prism 12 by 180 °.
The first prism 12 and the second plum 17 constitute a Mach-Zehnder interferometer. The second prism 17 is formed by bonding a prism having a triangular cross section parallel to the paper of FIG. 1 and a prism having a parallelogram parallel to the paper of FIG. It is a polarizing beam splitter surface 18 inclined by 45 ° with respect to the optical axis of the first light beam LA on which the joining surface is incident. Since the first light beam LA is also P-polarized light with respect to the polarization beam splitter surface 18, the first light beam LA is transmitted through the polarization beam splitter surface 18 and emitted to the outside.

On the other hand, the second light beam LB emitted from the first prism 12 passes through the second plane-parallel plate 14 and the optical path length compensating plate 16 and then the other side surface of the second prism 17. Incident on the part. The first parallel plane plate 13 and the second parallel plane plate 14 have the same shape, and the optical path length (glass path length) of the optical path length compensating plate 16 is substantially equal to the average optical path length of the optical wedge 15. The second light beam LB is totally reflected at the other end of the second prism 17 and travels to the polarization beam splitter surface 18.
Since the second light beam LB is also S-polarized light with respect to the polarization beam splitter surface 18, it is reflected by the polarization beam splitter surface 18 and emitted to the outside.

The first light beam LA and the second light beam LB emitted from the second prism 17 are superimposed and
Through 9, an image is formed on a light receiving surface of a photoelectric conversion element 20 such as a two-dimensional charge-coupled image sensor (CCD). The analyzer 19 causes the first light beam LA and the second light beam LB to have the same polarization direction and become coherent, and the light receiving surface of the photoelectric conversion element 20 has a pattern of the test mask 8 and a pattern obtained by laterally displacing the pattern. Is formed. The imaging signal output from the photoelectric conversion element 20 is sent to the arithmetic means 22 via a signal processing circuit 21 for performing analog / digital conversion or the like.
The calculating means 22 includes an input means 2 such as a data file.
4 supplies the design data of the pattern of the mask 8 to be inspected. The calculating means 22 detects a phase difference defect or the like of the pattern of the mask 8 to be inspected from the actual measurement result and the design data, and displays the defective portion on the display means 23.

At the time of actual measurement, first, one glass plate of the optical wedge 15 shown in FIG.
The difference between the optical path lengths of the first and second light beams LB to the polarization beam splitter surface 18 is set to be substantially zero. next,
As shown in FIG. 2, the first parallel flat plate 13 is inclined, for example, counterclockwise by an angle θ (0 <θ <π / 2), and the second parallel flat plate 14 is tilted clockwise by an angle θ. Incline. In this case, when the longitudinal direction of the prisms 12 and 17 is defined as the Z direction in a plane parallel to the paper surface of FIG. The second light beam LB is formed by the parallel plane plate 14.
Shifts laterally by −δz in the Z direction.

Therefore, by adjusting the inclination angle θ of the parallel plane plates 13 and 14, the amount of lateral displacement between the first light beam LA and the second light beam LB can be easily set to an arbitrary value. . Moreover, since the optical path length (glass path length) in the first parallel plane plate 13 and the optical path length in the second parallel plane plate 14 are the same, even if the inclination angle θ is greatly changed, the first The optical path length difference between the light beam LA and the second light beam LB does not change, and an interference image with good contrast is always formed on the light receiving surface of the photoelectric conversion element 20 in FIG.

Next, a case will be described in which the inspection apparatus of FIG. 1 inspects a target mask on which a phase member is formed as the target mask 8. FIG. 3A shows a cross section of an example of a test mask on which a phase member is formed. In FIG.
A phase shifter PS for shifting the phase by π is formed at a constant pitch in a lattice pattern on a mask blank MB as a substrate, and a defect D occurs on the central phase shifter PS. After passing through the mask to be inspected, the wavefront of the light beam emitted from the polarization beam splitter surface 18 as the first light beam LA in FIG. 2 becomes the wavefront WA in FIG. 3B, and the second light beam LB in FIG. The wavefront of the light beam that exits the polarization beam splitter surface 18 is the wavefront WB in FIG.

When these two wavefronts WA and WB are superimposed, the wavefront passing through the phase shifter PS and the wavefront passing only through the mask blank MB overlap, but the phase shifts by π in the normal portion. Therefore, the amplitudes cancel each other and a dark interference image is obtained. However, defect D
In the part where the phase shift is not π corresponding to the above, the amplitude is rather strengthened when the two wavefronts are superimposed, so that only the part corresponding to the defect D becomes a bright image. FIG. 3D shows a waveform obtained by taking the intensity I of the interference image on the vertical axis and the position of the pattern of the test mask on the horizontal axis. This allows
The defect D can be detected easily and quickly.

Further, the use of the optical wedge 15 shown in FIG. 1 makes it possible to measure the amount of phase change by the phase shifter formed on the mask 8 to be inspected. An example of the measuring method will be described. In this case, the phase of the phase shifter formed on the test mask 8 changes by π with respect to the mask blank (ie,
The phase change amount is π), and the phase change amount of the defective portion is π / 2. In addition, in FIG.
The difference φ in the optical path length between the light beam LA and the second light beam LB in FIG.
As shown on the horizontal axis of FIG. 4A, the position of the interference image of the first light beam LA and the second light beam LB shifted laterally from each other is shown on the vertical axis of FIG. Plot the intensity I at.

First, in FIG. 4A, the first light beam LA
Represents a change in intensity I at a portion where the second light beam LB has passed through the mask blank after passing through the phase shifter (a portion corresponding to the region 25 in FIG. 3B) by a curve IPS, and the first light beam LA passes through the defective portion of the phase shifter and passes through the second light beam LB.
Shows the change in the intensity I of the portion passing through the mask blank (the portion corresponding to the region 26 in FIG. 3B) by a curve ID, and the first light beam LA passes through the phase shifter or the mask blank and the first light beam LA passes through the mask blank. A curve ICR shows a change in the intensity I of a portion where the second light beam LB is in a light shielding portion such as chrome. By operating the optical wedge 15 in this way to change the optical path length difference φ continuously or stepwise, and by examining the change in the intensity I of each region,
It is possible to determine the phase shifter, a defective portion of the phase shifter, a light shielding portion, and the like.

Similarly, when the phase shifter formed on the test mask 8 changes the phase by π / 2 with respect to the mask blank (ie, the phase change amount is π / 2), the optical wedge in FIG. 15, the first light beam LA and the second light beam L
The difference φ in the optical path length from B is gradually increased as shown on the horizontal axis in FIG. Then, the intensity I at a certain position of the interference image of the first light beam LA and the second light beam LB laterally displaced from each other is plotted on the vertical axis of FIG. 4B.

In FIG. 4B, the first light beam LA
Shows a change in intensity I at a portion where the second light beam LB has passed through the mask blank after passing through the phase shifter (a portion corresponding to the region 25 in FIG. 3B) by a curve IA, and the first light beam A curve IB indicates a change in intensity I at a portion where LA passes through the mask blank and the second light beam LB passes through the phase shifter, and both the first light beam LA and the second light beam LB pass through the mask blank. The change in the intensity I at the portion indicated by a curve is indicated by a curve IG. Thus, by operating the optical wedge 15 to continuously or stepwise change the optical path length difference φ and examining the change in the intensity I in each region, the amount of phase change by the phase shifter can be measured. .

Although the optical path length difference between the two light beams is changed by using the optical wedge 15 in the above-described embodiment, the light path between the two light beams may be changed by using, for example, a Babinet-Soleil compensator. The length difference can be changed. In this case, a Babinet-Soleil compensator is disposed between the polarizing beam splitter surface 18 and the analyzer 19 with the optical wedge 15 and the optical path length compensator 16 shown in FIG. Although the polarizing beam splitter surfaces 11 and 18 can be used as beam splitter surfaces and the analyzer 19 can be functioned in principle as a photomask inspection device even if the analyzer 19 is removed. Is preferred.

Next, another embodiment of the present invention will be described with reference to FIGS. 5, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.
FIG. 5 is a front view of a main part of the present embodiment. In FIG. 5, light from the test mask 8 is focused by the objective lens 10 and is incident on one end of the main prism 32. The main prism 32 is formed by laminating a prism having a triangular cross section parallel to the paper of FIG. 5 and a prism having a parallelogram parallel to the paper of FIG. 5 in order from the objective lens 10 side. The polarizing beam splitter surface 31 whose bonding surface is inclined at 45 ° with respect to the optical axis of the objective lens 10
It has become. Among the light incident on the main prism 32, the first light beam LA of the P-polarized light with respect to the polarization beam splitter surface 31 passes through the polarization beam splitter surface 31 and then the inclined surface 32 a at the other end of the main prism 32. And is emitted to the outside after being totally reflected. Also, of the light that has entered the main prism 32, the second light beam LB of S-polarized light with respect to the polarization beam splitter surface 31 is reflected by the polarization beam splitter surface 31 and emitted to the outside.

The first light beam LA emitted to the outside passes through the plane parallel plate 34, and then enters one end of a sub-prism 33 having a trapezoidal cross section in a plane parallel to the plane of FIG. The second light beam LB is incident on the other end of the sub-prism 33.
The first light beam LA is provided on an inclined surface 33 on one end side of the sub-prism 33.
After being totally reflected at a, the inclined surface 33b at the other end of the sub-prism 33 is also totally reflected, emitted outside and enters one end of the main prism 32. On the other hand, the second light beam LB is the first light beam LB.
After exiting from one end of the sub-prism 33 through the same optical path in the opposite direction to the light beam LA, the light passes through the parallel flat plate 34 and enters the other end of the main prism 32.

Since the first light beam LA incident on one end side of the main prism 32 is P-polarized light with respect to the polarization beam splitter surface 31, the polarization beam splitter surface 31 is left as it is.
And is emitted outside. On the other hand, the second light beam LB incident on the other end side of the main prism 32 is totally reflected by the inclined surface 32a on the other end side and goes to the polarization beam splitter surface 31, but the second light beam LB is S-polarized light. The second light beam LB reflected by the polarization beam splitter surface 31
Are combined with the first light flux and emitted to the outside. The two light beams LA and LB emitted outside are incident on the light receiving surface of the photoelectric conversion element 20 after their polarization directions are aligned by the analyzer 19. Other configurations are the same as those in FIG.

FIG. 6 is a plan view of the inspection apparatus of FIG.
As shown in FIG. 6, the parallel flat plate 34 is inclined clockwise by an angle θ (0 <θ <π / 2) in a state perpendicular to the paper surface of FIG. In this case, assuming that the direction parallel to the plane of FIG. 6 and perpendicular to the optical axes of the light beams LA and LB outside the parallel plane plate 34 is the Y direction, the first light beam LA is
, An interval δ determined by an angle θ in the Y direction
While the second light beam LB passes through the plane parallel plate 34 in the opposite direction, the second light beam LB shifts by −y in the Y direction, while shifting laterally by y.
Side shift by y. That is, the first light flux LA and the second light flux LB are laterally shifted in directions opposite to each other in the Y direction. Further, the light beams LA and LB do not relatively shift laterally in a direction perpendicular to the plane of FIG. Therefore, on the polarization beam splitter surface 31 in FIG. 5, the first light flux LA and the second light flux LB are combined in a state of being relatively laterally shifted in a direction perpendicular to the paper surface of FIG. .

Therefore, on the light receiving surface of the photoelectric conversion element 20,
An interference image is formed in a state where the pattern of the mask 8 to be inspected is laterally shifted and superimposed, and a defect or the like of the pattern of the mask 8 to be inspected can be detected from this interference image in the same manner as in FIG.

Further, in the example of FIG. 5, the mechanism for changing the optical path length difference between the first light beam LA and the second light beam LB is omitted. For example, in FIG. Instead, a plurality of normal beam splitters are arranged. After passing a plurality of light beams branched by the beam splitter through optical elements that change only a predetermined polarization phase by different amounts, the polarization directions are aligned by an analyzer, so that the light paths of the two light beams are changed. The interference image can be observed while changing the length difference.
For example, each detection light (LA, LB) emitted from the polarization beam splitter surface 31 is divided into four light beams by three beam splitters, and the four divided light beams are respectively 0, λ / 4, λ / 2, If an optical element giving an optical path length difference of 3λ / 4 is arranged, the phase difference of the mask at each point can be obtained from the intensity of each point of the four interference images.

It should be noted that the present invention is not limited to the above-described embodiment, but can take various configurations without departing from the gist of the present invention.

[0034]

According to the first photomask inspection apparatus of the present invention, by tilting the first and second variable-angle optical members, the pattern of the photomask is shifted laterally by a desired amount. An interference image with the pattern can be observed. Therefore, when a defect of the phase member is included in the pattern, even if the refractive index of the phase member is the same as that of the substrate, the defect can be easily and quickly detected only by adjusting the amount of lateral displacement. can do. Further, since the first and second tiltable optical members are tilted in opposite directions, the difference in the optical path length between the first light beam and the second light beam hardly changes. Therefore, an interference image with high contrast can always be observed. Also, use polarized light for illumination light.
The light is separated into two luminous fluxes and further combined, so that the illumination light
Use efficiency is high. Also, a third photomask of the present invention
According to the inspection device, the utilization efficiency of illumination light may decrease
Yes, the contrast of the interference image may decrease,
Regardless of the refractive index difference between the phase member (phase shifter) and the substrate
It is possible to accurately detect parts with large phase change errors.
Phase change at the same wavelength as the actual exposure wavelength.
Simple and quick detection of parts with large errors
You.

Also, in the second photomask inspection apparatus, a defective portion of the phase member included in the pattern of the photomask can be easily and quickly detected by tilting the optical member having a variable tilt angle by a predetermined amount. can do.
Furthermore, since the two split light beams pass through the optical path having the same optical path length, even if the refractive index of the light beam propagation member changes due to temperature change, or even if there is a mechanical error or vibration, 2
Since there is no difference in optical path length between the light beams, there is an advantage that an interference image with high contrast can always be observed. In addition,
According to the third photomask inspection apparatus of the present invention,
The mask inspection method can be performed as it is. same
As described above, the first or second photomask inspection apparatus of the present invention
According to the above, the optical path lengths of the two split light beams are almost equal.
Set, but substantially the photomask inspection of the present invention
The method can be implemented.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a photomask inspection apparatus according to the present invention.

FIG. 2 is a configuration diagram showing a part of an interferometer of the inspection apparatus of FIG.

3A is a cross-sectional view illustrating a test mask on which a phase member is formed, FIG. 3B is a diagram illustrating a wavefront of a first light beam that has passed through the test mask, and FIG. FIG. 9 is a diagram illustrating a wavefront of a second light beam that has passed through the detection mask, and FIG. 10D is a waveform diagram illustrating an intensity distribution of an interference image between the first light beam and the second light beam.

4A is a diagram illustrating an example of a change in the intensity I of an interference image when the optical path length difference φ is changed, and FIG. 4B is a diagram illustrating an optical path length difference φ;
FIG. 10 is a diagram showing another example of a change in the intensity I of the interference image when the value is changed.

FIG. 5 is a front view showing a configuration of a main part of another embodiment of the present invention.

FIG. 6 is a plan view for explaining the operation of the plane-parallel plate of FIG. 5;

[Explanation of symbols]

7 condenser lens 8 test mask 10 objective lens 11 polarization beam splitter surface 12 first prism 13 first parallel flat plate 14 and the second parallel flat plate 15 wedge 16 optical path length compensating plate 17 and the second prism 18 polarized The light beam splitter surface 19 analyzer 20 photoelectric conversion element 31 polarization beam splitter surface 32 main prism 33 secondary prism 34 parallel plate

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-181805 (JP, A) JP-A-1-128538 (JP, A) JP-A-3-270213 (JP, A) JP-A-4- 127150 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03F 1/08-1/16 H01L 21/027

Claims (4)

(57) [Claims] An illumination optical system that illuminates a photomask to be inspected; a light beam separation unit that separates light from the photomask into a first light beam and a second light beam according to a polarization state; The optical path length of the separated first light beam and the separated second light beam
A light beam combining unit that is arranged at a position where the optical path lengths of the light beams are substantially equal to each other and combines the first light beam and the second light beam; and an observation unit that observes the intensity distribution of the combined light beam; A first tiltable optical member that is arranged in the optical path of the first light beam and shifts the first light beam in one direction; and the second light beam that is arranged in the optical path of the second light beam. A second tiltable optical member that shifts laterally in a direction opposite to the one direction. 2. An illumination optical system for illuminating a photomask to be inspected, a light beam separating means for separating light from the photomask into a first light beam and a second light beam in accordance with a polarization state; The polarized first light beam is guided to the light beam separating means via a first closed optical path, and the second light beam after the separation is polarized.
A light beam polarizing unit that polarizes the light beam and guides the light beam to the light beam separating unit via a second closed light path that matches the first closed light path; and the first light beam polarized by the light beam polarizing unit and the light beam. An observation unit for observing an intensity distribution of light obtained by combining a second light beam through the light beam separation unit; and an observation unit arranged in the first and second closed optical paths,
A photomask inspection apparatus, comprising: an optical member having a variable tilt angle that causes a lateral shift between the closed optical path and the second closed optical path. 3. A light source that emits illumination light having a narrow wavelength width, a mask stage for supporting a photomask including a phase shifter and a light transmitting unit, and a first optical path that transmits the illumination light transmitted through the photomask. Beam splitting means for splitting a first light beam passing through the first light beam and a second light beam passing through the second light path; and a light beam combining means for overlapping the first light beam and the second light beam to generate interference light And a photoelectric conversion element for photoelectrically converting the combined light beam, wherein a relative distance between the length of the first light path and the length of the second light path is between the light beam separating means and the light beam combining means. A photomask inspection apparatus, comprising: means for adjusting the relationship; and means for laterally displacing the first light flux and the second light flux on the photoelectric conversion element. 4. A method of inspecting a photomask including a phase shifter portion and a light transmission portion, and illuminating the photomask with illumination light of a narrow wavelength width, the illumination light passing through the photomask, the first optical path A first light beam passing through the first light beam and a second light beam passing through the second light path. The first light beam and the second light beam are superimposed to form interference light, and the interference light is photoelectrically converted by a photoelectric conversion element. When inspecting the photomask based on the signal obtained by the conversion, the length of the first optical path and the length of the second optical path can be relatively adjusted, and the length of the first optical path and the length of the second optical path can be adjusted on the photoelectric conversion element. A method for inspecting a photomask, wherein an amount of lateral shift between one light beam and the second light beam is adjustable.