JP2962752B2 - Pattern inspection equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an assertion state inspection apparatus, and more particularly to a semiconductor manufacturing process using a light exposure method, other than a circuit pattern attached to a substrate such as a reticle or a photomask. The present invention relates to a surface condition inspection apparatus suitable for detecting foreign matter, for example, impermeable dust.

[Prior Art] In general, in an IC manufacturing process, a circuit pattern for exposure formed on a substrate such as a reticle or a photomask is printed by a semiconductor printing apparatus (stepper or mask aniler).
Is transferred onto a wafer surface coated with a resist.

At this time, when foreign matter such as dust is present on the substrate surface, the foreign matter is also transferred at the time of transfer, which causes a decrease in the yield of IC manufacturing.

In particular, when a reticle is used and a circuit pattern is repeatedly printed on the wafer surface by the step-and-repeat method, one foreign matter on the reticle surface is burned over the entire wafer surface, which significantly reduces the yield of IC manufacturing. It is becoming.

Therefore, in the IC manufacturing process, it is essential to detect the presence of a foreign substance on a substrate, and various inspection methods have been conventionally proposed. For example, FIG. 2 shows an example of a method utilizing the property that foreign matter isotropically scatters light. In the same figure, a laser is transmitted through a scanning mirror 11 and a lens 12.
The luminous flux from 10 is directed upward or downward by moving the mirror 13 in and out, and is incident on the front and back surfaces of the substrate 15 by the two mirrors 14 and 45, respectively. Scanning. A plurality of light receiving units 16, 17, 18 are provided at positions distant from the optical paths of the direct reflected light and the transmitted light from the substrate 15, and the substrate 15 is output using the output signals from the plurality of light receiving units 16, 17, 18. The presence of the foreign matter above is detected.

That is, since the diffracted light from the circuit pattern has a strong directivity, the output value from each light receiving section is different, but when the light flux enters a foreign substance, the incident light flux is scattered isotropically, so that the output values from a plurality of light receiving sections are obtained. Become equal to each other. Therefore, the presence of the foreign matter is detected by comparing the output values at this time.

FIG. 3 shows an example of a method utilizing the property that foreign matter disturbs the polarization characteristics of an incident light beam. In the same figure, a light beam from the laser 10 is turned into a light beam of a predetermined polarization state via the polarizer 19, the scanning mirror 11, and the lens 12, and is directed upward or downward by entering and exiting the mirror 13 by two mirrors 14, 45. The light is incident on the front surface and the back surface of the substrate 15, respectively, and is scanned on the substrate 15 by the scanning mirror 11. The polarizers 20 and 2 are located at positions away from the optical paths of the direct reflected light and the transmitted light from the substrate 15, respectively.
Two light receiving sections 21 and 23 having 2 disposed in front are provided. The difference in the amount of received light resulting from the difference in the polarization ratio between the diffracted light from the circuit pattern and the scattered light from the foreign object is calculated by the two light receiving units 2.
The circuit pattern on the substrate 15 is discriminated from the foreign matter by the detection from the reference numerals 1 and 23.

[Problems to be solved by the invention] However, these conventional examples have the following disadvantages in common. That is, since light other than exposure light, that is, He-Ne laser having a wavelength of 633 nm, is mainly used as inspection light, depending on dust, even if light is transparent at this wavelength, the burning wavelength is different from the inspection light wavelength. Since the light is ultraviolet light, it absorbs light and the like. As a result, even if it is determined that the reticle is free of dust during foreign matter inspection, a common defect occurs on the wafer during actual exposure. is there.

The present invention has been made in view of the above-described drawbacks of the related art, and provides an exposure apparatus that reliably detects a light-transmitting foreign substance or the like and increases the reliability of determining the presence or absence of a foreign substance that affects the actual exposure. Aim.

[Means and Actions for Solving the Problems] In order to achieve the above object, according to the present invention, an illuminating means for illuminating a reticle, and a pattern formed on the reticle is transferred to a substrate by the illuminating means. An exposure optical system for forming a pattern latent image and a latent image inspection means capable of inspecting a latent image formed on the substrate and inspecting other than a circuit pattern are provided.

Embodiment FIG. 1 is a configuration diagram of a first embodiment of the present invention.

Reference numeral 1 denotes a printing (exposure) light source, such as an ultrahigh-pressure mercury lamp or an excimer laser.

Reference numeral 2 denotes an illumination system which uniformly illuminates the luminous flux emitted from the light source 1 over a substantially entire surface of the reticle 3 at a predetermined opening angle. The reticle 3 is sent from the reticle changer 7 onto the object plane of the printing lens 4 (exposure stage).

The circuit pattern on the reticle 3 is reduced and transferred onto the wafer 5 by the printing lens 4. The wafer 5 is coated with a resist for forming a latent image. In the present embodiment, the pattern of the reticle 3 is transferred and exposed onto the wafer 5 at least once. Thereafter, the stage 6 is moved to send the wafer 5 to the latent image inspection unit A.

 Next, the latent image inspection unit A will be described.

The inspection light source 20 has a wavelength at which a latent image on the wafer can be observed,
Further, it emits a light beam in a wavelength band that does not erase the latent image. As the light source 20, a laser, a halogen lamp (with a color filter), or the like can be used. This optical system illuminates a latent image area (a reticle pattern transfer area) on the wafer via a condenser lens 21, a beam splitter 22, and an inspection objective lens 23. The reflected light is the objective lens
23, return through beam splitter 22, relay lens
The light is condensed on the light receiver 25 by the action of 24. The wafer surface and the light receiving surface are set in an optically conjugate relationship. The light receiver 25 is a position sensor such as a two-dimensional CCD array or a picture tube, and by the above system configuration, after the circuit pattern on the reticle is transferred onto a single wafer, including foreign matter,
The image is displayed on the light receiving surface of the inspection unit.

The output of the light receiver 25 is processed by the electric processing system 26 to detect foreign matter. FIG. 4 shows an example of a circuit of the electric processing system 26.

The output of the position sensor (photodetector) 25 is taken in under the control of the controller 46 which controls the setting of inspection conditions, for example, the controller 46 which instructs start and end of the wafer positioning inspection, and receives timing management. Then, after being amplified by the amplifier 41, it is A / D converted by the A / D converter 42, and further binarized by the binarization circuit 43. on the other hand,
The controller 46 reads out the reticle pattern design data stored in the device in advance, and compares the two with the comparison circuit.
Compare with 44. If the outputs do not match, it is determined that there is a foreign substance on the reticle, and the position, size, and the like are stored in the memory 45.

In FIG. 1, B is an alignment unit for positioning the wafer and sending it to a predetermined exposure position. There are roughly two methods for finally positioning the wafer with respect to the reticle.

One is TTL, which is aligned through a printing lens
In this method, the unit B plays a role of wafer pre-alignment.

The other is an off-actress system in which positioning of the wafer is completed outside the exposure position by increasing the precision with which the stage is fed, and the wafer is fed as it is for exposure. For this scheme, unit B serves for final alignment of the wafer.

The basic configuration of any of the systems includes a light source 10, an objective lens 14, a light receiver 15, and an electric processing system 16.
Therefore, considering the apparatus configuration of the entire stepper, the alignment unit B includes the latent image inspection unit A of the present invention.
Function may be provided.

Another embodiment of the present invention is shown in FIG. The difference from the embodiment of FIG. 1 is that a spatial filter is used in the inspection unit. The advantages of inserting the spatial filter (31) will be described below.

Generally, a circuit pattern on a wafer has many vertical and horizontal lines. When a laser beam is applied to this, Fig. 6 (a)
As shown in (b), the diffracted light skips in the direction perpendicular to the pattern. Therefore, a spatial filter (FIG. 7 (a)) that blocks these diffracted lights is connected to the inspection objective lens 23 (5
If it is provided at the position of the exit pupil in the figure, vertical and horizontal lines will not be imaged on the re-imaging plane (light receiving plane) of the light receiver 25. On the other hand, since the shape of the foreign matter is almost circular, the scattered light passes through the spatial filter and re-images.

By the above operation, only the foreign matter can be electrically detected in a state where the main circuit pattern on the wafer has been erased. Therefore, in the circuit of FIG. 4, a circuit for comparison with the design data is not required, so that the configuration of the electric system is greatly simplified.

FIG. 7 (b) shows a spatial filter for optically eliminating vertical and horizontal lines on a circuit pattern and lines obliquely at 45 °.

Actually, there is a disadvantage that foreign matter adhering to the wafer after exposure is detected in the same manner as the foreign image of the foreign matter transferred from the reticle. In order to distinguish this, the reticle pattern is repeatedly exposed and transferred onto the wafer twice (steps), and the above inspection is performed for each chip. And 2
It is sufficient to check whether or not foreign matter is detected at the same position on one chip. If the foreign matter adheres to the reticle, the foreign matter is detected at the same position on all the chips to be exposed. On the other hand, in the case of foreign matter adhering to the wafer, there is almost no probability that foreign matter of the same size adheres to the same position of adjacent chips.

FIG. 7 (c) shows a third example of the spatial filter 31 similarly located at the exit pupil position of the light receiving objective lens, which is a phase plate used in a phase contrast microscope system.

Its periphery P ₁ whereas a mere parallel flat plate, the central part P ₀ is an optical thin film is deposited to give a phase difference between the peripheral portion [pi / 2. By using such a phase plate, a phase difference between an exposed portion and an unexposed portion of a latent image can be detected as a difference in intensity on the light receiving surface with high contrast.

In order to improve the effect of such a phase difference detection method,
In the light emitting section, a laser is used as the light source 20. Then, similarly to the spatial filter 31, a stop 32 as shown in FIG. 7D is provided at the exit pupil position of the objective lens 23 on the light path incident on the beam splitter 22. The aperture 32 is opened at the center (P ₂ ), and the size of the opening is equal to the size of the center (P ₀ ) of the spatial filter 31 in the arrangement shown in FIG. This is for the following reason.

Generally, since the stop 32 and the spatial filter 31 are in an optically-imaged relationship, a light beam emitted from a point on the stop 32 is reflected on the latent image surface via the beam splitter 22 and the objective lens 23, Similarly, the light returns through the objective lens 23 and the beam splitter 22 to form an image at a corresponding point at the center of the spatial filter 31. In the phase difference method, this is referred to as a zero dimension, but it is necessary to give a strict phase difference to the zero dimension in order to obtain high contrast.

FIG. 8 shows the configuration of the third embodiment of the present invention. First
The difference from the embodiment of the figure is that two sets of inspection optical systems are provided in parallel in the latent image inspection unit. The distance between the optical axes of the two objective lenses 23 and 23 'is made equal to the pitch (p) between the chips when the reticle pattern is transferred onto the wafer a plurality of times. The configuration of the electric processing system 30 is different from that of FIG. 4, and there is no need to read out the design data, and the outputs of the two detectors may be simply compared (the ninth embodiment)
Figure).

Such a method is very effective when a plurality of chips (three chips in the following description) are arranged on one reticle. The advantages are as follows.

FIG. 10 shows the reticle pattern repeatedly transferred onto the wafer 12 times (12 chips C1 to C12). In each chip, the same pattern area is repeated three times (A, B, C).

First, one of the two inspection objective lenses is set in the area A of the C1 chip, and the other is set in the area B of the C2 chip. Then, the corresponding positions of the two regions are sequentially compared. If the two outputs are different, store the position (P _R ).

Next, move the wafer and use one of the objective lenses to
Examining the C region P _R points of the chip. Or C of C1 chip
The _PR point in the area may be used. The output of the _PR point in these three regions is 3
In comparison, it can be seen that only one point is different in output. For example that point, and it P _R points A region. Finally, checking the C2 chip A region P _R points, if it was the same output as C1 chips that of (outlier), P _R points A region in all chips particle on a reticle is repeatedly transferred It will be.

Conversely, if, C2 when the output of the chip A region P _R points different from that of C1 chip (anomalies), C1 chips A region
Only the _PR point is considered abnormal. In this case, it is determined that the foreign matter has adhered only to the position on the wafer.

By performing the chip comparison as described above, the processing is greatly simplified in terms of electrical processing, and there is no time loss for reading out the design data, so that the processing can be sped up.

FIG. 11 is a diagram showing a case where the inspection method is applied to one chip / one reticle. In this case, three reticles of the same pattern are required. Then, each reticle is shifted and printed on one latent image forming wafer (R _A , R
_B , _RC ).

The three regions A, B, and C in the example of FIG. 10 correspond to R _A , R _B , and R _C in this case, and two of these regions are used in the same manner as in the previous example.
Each object lens is compared and inspected.

FIG. 12 shows a fourth embodiment of the present invention. The difference from the embodiment of FIG. 1 is that a different inspection system is used in the latent image inspection unit. That is, a laser beam is obliquely incident on the wafer and beam-scanned in one direction (a direction orthogonal to the paper surface) to detect the scattered light of the foreign matter. Then, in synchronism with the beam scan, the wafer is moved in a direction substantially perpendicular to the beam scan (S ₁ S ₂ ), and the entire inspection area is inspected without omission.

The beam emitted from the laser 80 is spread by a beam expander 81 and is incident on a polygon mirror 82. The polygon mirror 82 rotates in a plane perpendicular to the plane of the drawing, whereby a focused beam is formed on the wafer via the scanning lens 83 and is scanned in a direction perpendicular to the plane of the drawing.

The light receiving optical system is set so as to anticipate the beam scanning line formed on the wafer and not to pick up the directly reflected light on the wafer surface (in FIG. 12, it picks up the backscattered light). The scattered light emitted by the foreign matter on the wafer spreads in almost all directions, and the light beam captured by the light receiving objective lens 84 becomes a parallel light beam after passing through the lens. At the exit pupil position of the light receiving objective lens 84, there is an aperture stop 85, which determines the diameter of a light beam to be captured. The scattered light beam passing through the stop 85 is refocused by the action of the re-imaging lens 86, and a position optically conjugate with the beam scanning line on the wafer is created here. At this position, a field stop 87 (slit shape) is provided to block unnecessary flare light and the like from other than scanning lines on the wafer. The scattered light beam diverges when passing through the field stop, is made parallel by the condenser lens 88, and is received by the photomultiplier 89.

The S / N ratio between the circuit pattern and the foreign matter can be increased by adopting the above arrangement, that is, by obliquely incident the beam and detecting the backscattered light. This is because the diffracted light of the circuit pattern is generated along with the directly reflected light (R) on the upper surface of the wafer. Then, as the angle becomes farther away from the directly reflected light (as θ in the figure becomes larger), the light intensity is reduced. Therefore,
If the arrangement shown in FIG. 12 is adopted, θ can be made large, so that the accuracy of discriminating foreign substances from the circuit pattern can be improved.

FIG. 13 is a configuration example for further increasing the S / N ratio between the pattern and the foreign matter. The beam incidence system and light receiving system can use the configuration shown in FIG. This example shows the vertical
The projection line on the wafer of the optical axis of the inspection optical system is twisted by about 15 ° (β °) with respect to the horizontal pattern direction (V ₁ V ₂ , H ₁ H ₂ directions in the figure).

The circuit pattern on the wafer is diffracted in the direction perpendicular to the pattern and skips as described with reference to FIG. The most common directions for circuit patterns are vertical and horizontal, and then ±
There are many 45 ゜ directions. ± 30 °, ± 60 ° in some cases. Therefore, when the beam is incident on the optical system by 15 ° with respect to the optical system and the light is received within the incident surface, the diffracted light of the circuit pattern can be avoided. Since foreign matter scattered light jumps in all directions, if the scattered light coming in this direction is picked up, the foreign matter detection rate can be significantly increased.

[Effects of the Invention] As described above, in the present invention, it is possible to reliably detect the presence of a foreign substance that affects the actual printing.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention, FIGS. 2 and 3 are explanatory diagrams of a conventional example, FIG. 4 is a circuit diagram of an electric processing system of the embodiment of FIG. 6A and 6B are explanatory diagrams of a circuit pattern and its diffracted light, and FIGS. 7A to 7D are diagrams of a spatial filter. FIG. 8 is an explanatory diagram of another example, FIG. 8 is a block diagram of a third embodiment of the present invention, FIG. 9 is a circuit diagram of an electric processing system of the embodiment of FIG. 8, and FIG. FIG. 11 is an explanatory view of one example of the inspection method of the embodiment, FIG. 11 is an explanatory view of another example of the inspection method of the embodiment of FIG. 8, FIG. 12 is a configuration diagram of a fourth embodiment of the present invention, FIG. 13 is an explanatory view of a modified example of the fourth embodiment of the present invention, 1: light source, 2: illumination system, 3: reticle, 5: wafer, 20: light source, 2
3: Inspection objective lens, 25: light receiver, 26: electric processing system.

Continuation of the front page (56) References JP-A-60-249327 (JP, A) JP-A-63-136541 (JP, A) JP-A-63-299122 (JP, A) JP-A 1-239437 (JP) JP-A-64-32623 (JP, A) JP-A-64-77139 (JP, A) JP-A-1-239922 (JP, A) JP-A-3-37650 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) G03F 1/00-1/16

Claims (8)

(57) [Claims] 1. An illuminating means for illuminating a reticle, an exposure optical system for transferring a pattern formed on the reticle to the substrate by the illuminating means to form a pattern latent image, and a latent image formed on the substrate And a latent image inspection means capable of inspecting for foreign matter other than the circuit pattern by inspecting the pattern. 2. The latent image inspection means includes: a light source; an illumination optical system for illuminating the substrate with light from the light source; an optical detector for receiving light reflected from the substrate; and an output of the optical detector. 2. The pattern inspection apparatus according to claim 1, further comprising an electric processing system for processing the pattern. 3. A pattern inspection apparatus according to claim 2, wherein said latent image inspection means includes a spatial filter for removing diffraction light of a pattern from light reflected from the substrate. . 4. A patent wherein the illumination optical system of the latent image inspection means illuminates the substrate obliquely, and the optical detector detects backscattered light opposite to the illumination direction of the substrate. The pattern inspection apparatus according to claim 2. 5. The pattern inspection apparatus according to claim 1, wherein said latent image inspection means is configured to also serve as a pre-alignment mechanism for positioning said substrate. 6. The electric processing system of the latent image inspection means is configured to compare previously stored pattern data with output data of the optical detector. The pattern inspection device according to the item. 7. The electric processing system of the latent image inspection means, wherein a plurality of exposures are performed by one reticle and a latent image formed by each exposure is compared. 3. The pattern inspection apparatus according to claim 2, wherein 8. An electric processing system of the latent image inspection means, wherein a plurality of exposures are performed with a plurality of reticles and a latent image formed for each reticle is compared. The pattern inspection apparatus according to claim 2.