JP3259293B2 - Projection optical system inspection method, projection optical system inspection apparatus, and exposure apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to inspection of a projection optical system, and more particularly to measurement of aberration of a projection optical system of a projection type exposure apparatus used for manufacturing semiconductor devices and the like.

[0002]

2. Description of the Related Art The minimum line width of a circuit pattern of a semiconductor device or the like is becoming finer year by year, and the resolution line width required for a projection type exposure apparatus for resolving this pattern is now less than about 0.5 .mu.m. . Accordingly, the projection optical system of these exposure apparatuses is required to have various aberrations.

Conventionally, the amount of asymmetric aberration (the amount including the coma of the projection optical system and the amount of coma due to the eccentricity between the mechanical center of the projection optical system and the optical axis) of the projection optical system of the projection type exposure apparatus has been known. The following method was used for measurement. In other words, a pattern having a predetermined shape (for example, a line and space pattern) is transferred to a resist-coated substrate, and the line widths of the patterns at both ends in the pitch direction of the image of the transferred pattern are measured. It is to ask for. Alternatively, the shape of the cross section of the transferred pattern may be observed to determine the symmetry of the cross section. To measure this aberration, a pattern measuring device having a resolution of about 0.01 μm is required, and currently, only a scanning electron microscope (SEM) has the ability to match it.

[0004]

However, the SEM
The resolution varies depending on the state of optical axis alignment of the electron optical system, the internal gas pressure (degree of vacuum), and the like. That is, a difference occurs in resolution depending on individual differences between workers, the state of the apparatus, and the like. If the resolution required for an apparatus used for measuring aberrations is reduced, the difference in resolution has a large effect on the amount of aberration to be measured.

[0005] The present invention provides a high-speed,
Another object of the present invention is to measure the aberration amount of the projection optical system with high accuracy.

[0006]

According to the first aspect of the present invention, an image of a pattern on a mask illuminated by a light beam (IL) from an illumination optical system is projected on a substrate. A first edge (A) and a second edge (B) extending substantially parallel to a predetermined direction via the projection optical system (8). Exposing a pattern (7a) having the following to a predetermined surface, an image intensity corresponding to the first edge (A) projected on the predetermined surface, and an image corresponding to the second edge (B). The method includes a step of comparing intensity and a step of calculating an aberration of the projection optical system (8) based on the result of the comparison. According to a third aspect of the present invention, in the method for inspecting a projection optical system (8) for projecting an image of a pattern on a mask illuminated with a light beam (IL) from an illumination optical system onto a substrate, A first edge (A) extending substantially parallel to a predetermined direction via the projection optical system;
Projecting a pattern (7a) having an edge and a second edge (B) on a predetermined surface; an exposure amount when an image corresponding to the first edge (A) appears on the predetermined surface; The projection optical system (8) based on an exposure amount when an image corresponding to the second edge (B) appears on the predetermined surface.
And a step of obtaining the aberration. Further, according to the present invention, the light flux (I) from the illumination optical system is used.
Projection optical system (8) for exposing the image of the pattern on the mask illuminated in L) onto the substrate surface provided with the resist
A first edge (A) extending substantially parallel to a predetermined direction via the projection optical system (8).
Projecting a pattern having an edge and a second edge (B) onto the surface of the substrate; exposing the resist at a position corresponding to the first edge (A) to an exposure time;
Determining the aberration of the projection optical system (8) based on the exposure time at which the resist at the position corresponding to the edge (B) is exposed.

Further, according to the present invention described in claim 10,
A projection optical system (8) for projecting an image of a pattern on a mask illuminated by a light beam (IL) from an illumination optical system onto a substrate
A pattern (7a) having a first edge (A) and a second edge (B) extending in a predetermined direction is projected onto a predetermined surface via the projection optical system (8). At the time, the exposure amount control means (2, 4, 1
3) and calculating the aberration of the projection optical system based on the image intensity corresponding to the first edge (A) and the image intensity corresponding to the second edge (B) on the predetermined surface. And an arithmetic means (12). According to the twelfth aspect of the present invention, the luminous flux (I
An apparatus for inspecting a projection optical system (8) for projecting an image of a pattern on a mask illuminated in L) onto a substrate,
Via the projection optical system (8), a
When exposing a pattern having one edge (A) and a second edge (B) to a predetermined surface, an exposure amount control means (2, 4, 13) for controlling an exposure amount; Detecting means (11) for detecting the presence or absence of an image corresponding to the first edge and an image corresponding to the second edge, an exposure amount when an image corresponding to the first edge appears, A calculating means (12) for obtaining an aberration of the projection optical system based on an exposure amount when an image corresponding to the second edge appears.

[0008]

FIG. 1A is a diagram showing an example of a spatial image intensity distribution of a pattern on a photomask. This is, for example, an image intensity distribution of a light-shielding pattern having a width of 4 μm on a photomask. A 'and B' in the figure respectively correspond to the first and second edges A and B of one of the light-shielding patterns 7a as shown in FIG. The left side of the edge A (left side of A ') and the right side of the second edge B (right side of B') have strength because of the light transmitting portion. This pattern is defined as the coherency (σ
FIG. 1B shows a spatial image intensity distribution when an exposure apparatus having a projection optical system having a numerical aperture of 0.35 and a light beam having a wavelength of 365 nm is projected on an object to be transferred. It becomes as shown in. However, the asymmetric aberration amount (Δy) of the above-mentioned projection optical system
Are two types of 0 μm and 0.3 μm. In this case, peaks a and b, which are not seen in the aerial image intensity distribution on the mask, occur near the positions corresponding to the first and second edges A and B of the pattern, respectively.

FIG. 2 is a diagram showing the intensity ratio of two peaks a and b to the amount of asymmetric aberration of the projection optical system due to the difference in σ value of the illumination optical system. As can be seen from this figure, the intensity ratio of the peak formed at the position of the aerial image corresponding to the edge of the light-shielding pattern increases in proportion to the amount of coma, and the rate of change increases as the σ value decreases. .

The amount of exposure of the photoresist irradiated with the light beam depends on the exposure energy if the material of the resist, the film thickness, and the material of the substrate as the base are all the same. The exposure energy E can be expressed as E = W × T with respect to the exposure power W and the exposure time T. Further, locally, the exposure power W is the product of the intensity I of the image and the illuminance P of the exposure light, so that E = I × P × T (1). That is, for each position on the resist corresponding to the first and second edges of the pattern, the exposure time T at which the exposure energy E reaches the energy for exposing the resist by a certain amount is obtained, thereby obtaining the intensity I.
Can be determined.

FIG. 3 shows an aerial image intensity distribution when a pattern as shown in FIG. 1A is projected and exposed through a projection optical system, and the exposure time of this pattern is t1 to t5 (t5).
FIG. 4 is a diagram illustrating a state of exposure of a positive resist when exposure is performed while changing the exposure to 1 <t5). FIG. 3 (a)
FIG. 3B shows that the projection optical system has no asymmetric aberration.
FIG. 3C shows that when the asymmetric aberration is relatively small,
Shows an example where the asymmetric aberration is relatively large.

As can be seen from FIG. 3, as the asymmetric aberration increases, the difference between the intensity peaks of the images at the positions corresponding to the two edges of the pattern increases. That is, as the asymmetric aberration increases, the exposure time T1 at which the resist starts to be exposed at a position corresponding to one edge of the pattern becomes shorter, and the exposure time T2 at which the resist starts to be exposed at a position corresponding to the other edge becomes longer. As described above, when the illuminance P is constant, the exposure time T1 is determined by the image intensity I1 of the edge on the side where the image intensity is increased due to the effect of the asymmetric aberration, and the exposure time T2 is determined by the edge of the edge on the side where the image intensity is reduced. It is determined by the image intensity I2, and from equation (1), I1 × T1 = I2 × T2. The pitch and line width of the pattern on the mask to be used,
If the numerical aperture of the projection optical system, the σ value of the illumination optical system, and the wavelength of the exposure light are known, the ratio I1 / of the intensity of the image corresponding to the edge of the pattern due to the asymmetric aberration amount of the projection optical system.
I2 can be obtained by calculation. Therefore, by measuring each exposure time T1, T2, the intensity ratio I1 / I2
Is determined, the amount of asymmetric aberration can be determined.

[0013]

FIG. 4 is a diagram showing a schematic configuration of an exposure apparatus suitable for applying an inspection method according to an embodiment of the present invention. The illumination light beam from the light source 1 is shaped into a predetermined light beam by an illumination optical system IL including an optical member (not shown), and is irradiated onto the reticle 7. In the illumination optical system IL, a fly-eye lens 3 is disposed as an optical integrator for equalizing the illumination light flux, and uniformly illuminates the reticle 7 via the lens system 5 and the condenser lens 6. Further, a dimming filter 2 is provided at a position where the illumination light flux is substantially parallel to the illumination light path, and is provided near the exit surface of the fly-eye lens 3 to make the numerical aperture of the illumination optical system variable. Aperture stop 4 is provided. The dimming filter 2 and the aperture stop 4 are controlled by an exposure amount control unit 13, and the dimming filter 2 enters the illumination optical path or the aperture stop 4.
By adjusting the numerical aperture of the illumination optical system, the illuminance of the illumination light beam on the reticle 7 can be reduced. With such a configuration, the exposure time required to obtain the same exposure amount can be lengthened, and even when the exposure amount is minutely controlled, the influence of a control error such as a shutter can be reduced.

The luminous flux transmitted through the reticle 7 is transmitted via a projection optical system 8 to a stage device 10 movable in X and Y directions.
An image of a pattern on the reticle 7 is projected and exposed on the resist on the surface of the photosensitive substrate (wafer) 9 mounted thereon. Further, in the vicinity of the projection optical system 8, there is provided an image processing type observation optical system 11 (for example, a bright field imaging type alignment optical system) having an optical axis different from the optical axis AX of the projection optical system. , The resist image formed on the wafer 9 is detected. The calculation unit 12 previously obtains and stores the relationship between the intensity ratio of the two peaks a and b of the image intensity distribution as shown in FIG. 1 and the amount of asymmetric aberration of the projection optical system. Observation optical system 1
In accordance with the presence / absence of a resist image corresponding to the first and second edges detected by No. 1 and the amount of exposure when the image was exposed, the resist was detected at a position corresponding to the first edge and the second edge of the pattern. Is determined as the intensity of the two peaks a and b of the image intensity distribution, and the ratio of the exposure amounts (ie, the ratio of the two peak intensities of the image intensity distribution) to the amount of asymmetric aberration of the projection optical system. Ask for. In the above configuration, the light source 1, the aperture stop 4, and the pupil of the projection optical system 8 are conjugate to each other, and the pattern surface of the reticle 7 and the imaging surface on the wafer 9 are conjugate to each other.

Next, an inspection method according to an embodiment of the present invention will be described. The inspection of the projection optical system 8 is performed by exposing the pattern of the reticle 7 on the wafer 9 and observing the presence or absence of an image corresponding to the edge of the pattern with the observation optical system 11 such as image processing. That is, the exposure time T1, at which the resist at the position corresponding to the two edges of the pattern begins to be exposed,
T2 is determined, and the ratio T2 / T1 is defined as the ratio I1 / I2 of the maximum values (peaks) of the two image intensities, and the asymmetry amount of the image intensity due to the coma aberration of the projection optical system is calculated from the ratio. Obtained as the amount of aberration.

First, a reticle 7 on which a line and space pattern 7a extending in one specific direction as shown in FIG. 5A is positioned at a predetermined position, and then the reticle 7 is moved to the best focus position of the projection optical system 8. The pattern 7a is exposed on the placed wafer 9. At this time, exposure is performed at different positions on the wafer 9 while changing the exposure amount in fine steps, centering on an extremely small exposure amount with respect to the exposure time that the resist on the wafer 9 is completely exposed in the film thickness direction. .

The exposed wafer 9 is developed,
After that, the resist image at each exposure time is observed by an observation optical system (a bright-field imaging type alignment device or the like) 11. At this time, as shown in FIG. 5B or FIG. 5C, the shortest exposure time of the pattern 7a in which only the resist image corresponding to one edge A of the pattern 7a is detected, and FIG.
As shown in (d), the one with the shortest exposure time is obtained from the detected resist image corresponding to the other edge B, and stored as the above-described exposure times T1 and T2, respectively. Then, the ratio T2 / T1 of the exposure times T1 and T2 is obtained, and the intensity ratio I of the left and right peaks a and b of the above-mentioned image intensity distribution is obtained.
1 / I2. Further, the amount of asymmetric aberration of the projection optical system is obtained based on the relationship between the peak intensity ratio and the amount of asymmetric aberration stored in the storage operation unit 12. Note that such inspection is preferably performed on a plurality of locations within the projection field of view of the projection optical system, and a vector map of the amount of asymmetric aberration is preferably created. Further, it is preferable to include an arithmetic unit for this and a display for displaying a vector map.

In the present invention, it is desirable to use a positive resist as the resist. This is because, when a negative resist is used, if the resist layer is not completely exposed (up to the base such as a substrate), the resist is completely removed by a development process, and it is difficult to determine an exposure amount at which the resist starts to be exposed. This is because The pattern for measurement is not limited to the pattern shown in FIG. 5, but may be any line and space pattern extending in a predetermined direction. Further, the number of patterns may be one or more, but in particular, in the case of three or more, the measurement is performed on each of two opposing edges of each of the remaining patterns excluding the patterns at both ends in the pitch direction of the patterns. Is desirable.
This is to eliminate the influence of the wraparound of the illumination light beam.

The object to be measured is not limited to the projection optical system, but may be a reflection optical system. Further, it is not necessary to share the configuration in the exposure apparatus with the inspection apparatus, and a dedicated inspection apparatus may be used.

[0020]

As described above, according to the present invention, it is not necessary to use a scanning electron microscope when obtaining the aberration (particularly the amount of asymmetry) of the projection optical system, and thus the trouble in setting the apparatus is eliminated. It is possible to inspect the aberration of the projection optical system at high speed and with high accuracy. Further, if the exposure apparatus actually operating on the production line is inspected, the optical element of the projection optical system can be finely moved immediately on the spot.

[Brief description of the drawings]

FIG. 1A is a diagram showing an aerial image intensity distribution of a pattern on a photomask. FIG. 1B is a diagram showing an aerial image intensity distribution when a pattern on the photomask is projected via a projection optical system.

FIG. 2 is a diagram showing an intensity ratio of two peaks to a coma amount of a projection optical system due to a difference in σ value of an illumination optical system.

FIGS. 3A and 3B show a spatial image intensity distribution when a pattern as shown in FIG. 1A is projected through a projection optical system and a state of exposure of a positive resist image when exposure is performed by changing an exposure time, respectively. Diagram shown

FIG. 4 is a diagram showing a schematic configuration of an exposure apparatus suitable for applying the inspection method according to the embodiment of the present invention;

5A is a diagram showing an example of a measurement pattern used in the inspection method according to the embodiment of the present invention. FIGS. 5B, 5C, and 5D show patterns as shown in FIG. 5A. A diagram showing a state of a resist image projected by changing an exposure time.

[Explanation of symbols]

 2 Attenuating filter 4 Aperture stop 7a Measurement pattern 11 Observation optical system 12 Storage operation unit 13 Exposure amount control unit A First edge B Second edge

Claims (14)

(57) [Claims] 1. A method for inspecting a projection optical system for projecting an image of a pattern on a mask illuminated by a light beam from an illumination optical system onto a substrate, comprising: Projecting a pattern having a first edge and a second edge extending in parallel on a predetermined surface; an image intensity corresponding to the first edge projected on the predetermined surface; and the second edge A method for inspecting a projection optical system, comprising: a step of comparing the image intensity with the image intensity corresponding to the following; and a step of calculating an aberration of the projection optical system based on the comparison result. 2. The projection optical system according to claim 1, wherein the aberration of the projection optical system is obtained based on a ratio between a peak of an image intensity corresponding to the first edge and a peak of an image intensity corresponding to the second edge. The method for inspecting a projection optical system according to claim 1. 3. A method for inspecting a projection optical system for projecting an image of a pattern on a mask illuminated by a light beam from an illumination optical system onto a substrate, comprising: Projecting a pattern having a first edge and a second edge extending in parallel on a predetermined surface while controlling the exposure amount; and when an image corresponding to the first edge appears on the predetermined surface. Determining the aberration of the projection optical system on the basis of the exposure amount and the exposure amount when the image corresponding to the second edge appears on the predetermined surface. System inspection method. 4. The method according to claim 1, wherein the predetermined surface is a substrate surface provided with a resist, and the projecting step includes sequentially projecting the pattern onto each of a plurality of different positions on the substrate surface while changing the exposure amount. The step of obtaining aberration includes, among a plurality of resist images appearing at respective positions on the substrate surface, an exposure amount when an image corresponding to the first edge appears, and an exposure amount when the second surface appears on the predetermined surface. 4. The method according to claim 3, wherein the aberration of the projection optical system is obtained based on a ratio to an exposure amount when an image corresponding to the edge appears. 5. The exposure amount when an image corresponding to the first edge appears is an exposure amount at which the resist starts to be exposed at a position corresponding to the first edge. The method according to claim 4, wherein the exposure amount when the corresponding image appears is an exposure amount at which the resist starts to be exposed at a position corresponding to the second edge. 6. The apparatus according to claim 3, wherein the exposure amount is smaller than an appropriate exposure amount for projecting the pattern on the mask onto the substrate. Inspection method of projection optical system. 7. A method for inspecting a projection optical system for projecting an image of a pattern on a mask illuminated by a light beam from an illumination optical system onto a substrate surface provided with a resist, comprising: Projecting a pattern having a first edge and a second edge extending substantially parallel to a predetermined direction on the substrate surface; and exposing the resist at a position corresponding to the first edge to an exposure time. And a step of obtaining an aberration of the projection optical system based on an exposure time at which the resist at a position corresponding to the second edge is exposed, the inspection method of the projection optical system. 8. The step of projecting includes sequentially projecting the pattern at each of a plurality of different positions on the surface of the substrate while changing the amount of exposure, and the step of obtaining the aberration includes the step of appearing at each position on the surface of the substrate. Of the plurality of resist images, the exposure time at which the resist at the position corresponding to the first edge is exposed, and the exposure time at which the resist at the position corresponding to the second edge is exposed, 8. The method according to claim 7, wherein an aberration of the projection optical system is obtained. 9. An apparatus for inspecting a projection optical system for projecting an image of a pattern on a mask illuminated with a light beam from an illumination optical system onto a substrate, wherein the inspection optical system extends in a predetermined direction via the projection optical system. When projecting a pattern having a first edge and a second edge onto a predetermined surface, an exposure amount control means for controlling an exposure amount, and an image of an image corresponding to the first edge projected on the predetermined surface. An inspection apparatus for a projection optical system, comprising: calculation means for calculating aberration of the projection optical system based on intensity and intensity of an image corresponding to the second edge. 10. The predetermined surface is a surface of a substrate on which a resist is provided. The arithmetic means includes: an exposure time at which the resist at a position corresponding to the first edge starts to be exposed; The ratio of the exposure time at which the resist corresponding to the position starts to be exposed is defined as the ratio between the intensity of the image corresponding to the first edge and the intensity of the image corresponding to the second edge, and based on the ratio. The inspection apparatus for a projection optical system according to claim 9, wherein an aberration of the projection optical system is obtained. 11. An apparatus for inspecting a projection optical system for projecting an image of a pattern on a mask illuminated with a light beam from an illumination optical system onto a substrate, wherein the inspection optical system extends in a predetermined direction via the projection optical system. When projecting a pattern having a first edge and a second edge onto a predetermined surface, an exposure amount control means for controlling an exposure amount, and an image corresponding to the first edge projected on the predetermined surface and Detecting means for detecting the presence or absence of an image corresponding to the second edge; and an exposure amount when an image corresponding to the first edge appears, and an exposure amount when an image corresponding to the second edge appears. A projection optical system inspection apparatus, comprising: an arithmetic unit that calculates an aberration of the projection optical system based on an exposure amount. 12. The method according to claim 11, wherein the predetermined surface is a substrate surface on which a resist is provided, and the exposure amount control means projects the pattern onto each of a plurality of different positions on the substrate surface, and 12. The projection optical system inspection apparatus according to claim 11, wherein when projecting the respective images, the exposure amount is changed at each position. 13. The projection optical system according to claim 9, wherein said inspection apparatus is provided in an exposure apparatus for projecting a circuit pattern onto a semiconductor substrate. Inspection equipment. 14. An exposure apparatus comprising the inspection apparatus according to claim 9. Description: