JP2708050B2 - Pattern exposure apparatus and mask inspection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] Regarding an exposure apparatus for a fine pattern in a semiconductor element, etc., it is possible to easily and quickly inspect for defects in a mask plate having a specific pattern for forming a charged particle beam. In a pattern exposure apparatus, a charged particle beam is formed by passing a charged particle beam through a transmission hole of a mask plate having a transmission hole of a specific pattern, and then irradiating a predetermined position on a wafer for exposure. Beam scanning means for scanning on the mask plate, provided near the mask plate,
A radiation detecting means for detecting a radiation emitted from the mask plate by irradiation of the charged particle beam by the beam scanning, and an image of a transmission hole of the mask plate based on an output of the radiation detection means. And an image generating means for generating the image.

[Industrial applications]

The present invention relates to a pattern exposure apparatus for forming a fine pattern formed on a semiconductor element or the like, and more particularly, to a technique for inspecting a defect or a defect of a beam forming transmission mask used for pattern formation. is there.

[Conventional technology]

In recent years, with the increase in the density of integrated circuits, a new exposure method using an electron beam has been studied instead of photolithography, which has been the mainstream of a fine pattern forming method for many years, and has been actually used.

Such an electron beam exposure apparatus is generally called a variable rectangular type, and uses a mask having two rectangular holes for a charged particle beam, and at least one of the masks has an appropriate deflecting means or scanning means. By displacing by
The beam is formed to be freely movable along a two-dimensional plane, and the cross section of the beam is formed into an arbitrary rectangular shape, and the beam is exposed on, for example, a silicon wafer. This is based on the idea that all the patterns to be formed are collections of rectangles, and all the desired patterns are divided into appropriate rectangles, and a beam cross section that matches the size and shape is created at each location according to the above operation and exposed. Things. However, such an electron beam exposure apparatus is based on a huge amount of pattern data,
It is a drawing device that deflects an electron beam and draws a pattern on a sample wafer. Such a device is a device that has a pattern generation function to create hardware called a pattern from soft pattern data. Since exposure is so-called one-stroke writing, there is a problem that high throughput cannot be obtained.

By the way, most semiconductor devices which require a recent ultrafine pattern are, for example, 16M-DRAMs, although they are fine, most of the exposed area is a repetitive pattern in many cases.
Therefore, in a semiconductor device formed of an ultrafine pattern, paying attention to the fact that this repeated portion occupies most of the entire desired exposure pattern, only the repeated pattern portion is extracted from the desired entire pattern, and the pattern of the repeated portion is extracted. The basic cell unit that is the basis of the repetitive pattern is formed on a mask in advance, and in the area where the cell is formed, the basic unit is irradiated and exposed to the electron beam, and the other parts are the same as before. A so-called stencil transfer exposure method in which exposure is performed in a variable rectangle has been proposed.

 FIG. 2 shows an example of the stencil transfer exposure method.

An electron beam emitted from the electron gun 1 is shaped into a rectangle by a first rectangular shaping aperture 2, passes through a lens 3, and an arbitrary basic pattern portion (basic cell portion) 6 on a stencil mask 5 by an aperture selecting deflector 4.
Alternatively, the light is applied to the aperture 7 for variable deformation. Thereafter, the patterned electrons are reduced by a reduction lens 9 which reduces the size by about 1/100, and further a lens 10 constituting a deflection system.
Then, the wafer 12 is deflected and exposed by the coil 11. An aperture 8 for a variable rectangle (a patternless slit) is also provided on the mask for a non-repeated pattern.

FIG. 3 shows a cross-sectional shape of a stencil mask used in the present apparatus. That is, a portion 14 of the stencil portion 13 made of Si or an appropriate metal, on which a pattern is to be formed, is thinned, and an arbitrary pattern is formed by an appropriate drilling means such as an etching method and a cutting method. The pattern to be formed is not limited to one cell, but may be a pattern in which several cells are formed as one group.

The pattern portion 14 may be formed at any position on the mask as long as the portion can be irradiated with electrons by the aperture selecting deflector 4.

However, in such a stencil type exposure apparatus, the quality of the pattern used is particularly important, and even if defects are found in the pattern after the wafer is exposed and inspected, a huge number of products have already been manufactured. The economic losses are large because they have been lost. However, in the existing method,
To perform strict pattern detection, it is necessary to inspect the actual pattern itself exposed on the wafer. However, in recent years, the pattern size has become finer, and it has become difficult to perform inspection using conventional optical means.

On the other hand, in such an exposure method, the mask surface having the pattern is directly irradiated by the beam, so that the pattern may be changed or a defect may occur on the mask surface. Also, there is a possibility that the pattern portion generates heat due to the heat of the beam and is melted and lost. However, in the conventional apparatus, it is difficult to find such a defect unless the pattern actually transferred onto the sample (wafer) is inspected.

Therefore, it takes a long time for the inspection, and when the mask is taken out and inspected, the operation must be performed by breaking the vacuum state each time, and the number of operation steps is increased, so that the cost required for the inspection is extremely high. Also, because it takes time to find mask defects, the yield is greatly reduced,
There was also the problem of increasing production costs.

[Problems to be solved by the invention]

The present invention improves the above-mentioned prior art, especially the exposure apparatus for forming a pattern by the stencil method, in which a complicated means has to be adopted for inspecting the defect of the mask pattern and it takes a long time to improve the defect. By adopting a detection means that is easy to operate, the defect of the mask pattern can be easily detected in a very short time, and the cost of the inspection process can be greatly reduced, and at the same time, the productivity of the semiconductor device can be improved. An object of the present invention is to provide a pattern exposure apparatus and a mask inspection method.

[Means for solving the problem]

In order to solve the above-mentioned problems of the prior art, according to the basic mode of the present invention, a charged particle beam is formed by passing through a transmission hole of a mask plate having a transmission hole of a specific pattern, and then forming a predetermined beam on a wafer. In a pattern exposure apparatus that irradiates a position to perform exposure, a beam scanning means for scanning the charged particle beam on the mask plate, and is provided near the mask plate, and the charged particle beam is scanned by the beam scanning. A radiation detecting means for detecting a radiation emitted from the mask plate by irradiation, and an image generating means for generating an image of a transmission hole of the mask plate based on an output of the radiation detecting means. There is provided a pattern exposure apparatus characterized by having:

According to another embodiment of the present invention, a charged particle beam is formed by passing through a transmission hole of a mask plate having a transmission hole of a specific pattern, and then is irradiated to a predetermined position on a wafer to perform exposure. A method for inspecting the mask plate in a pattern exposure apparatus, wherein the charged particle beam is scanned on the mask plate in the pattern exposure apparatus, and the charged particle beam is emitted from the mask plate by the irradiation of the charged particle beam by the scanning. Detecting a radiation object, generating an image of the transmission hole of the mask plate based on the detected result, and inspecting a pattern of the transmission hole of the mask plate based on the generated image. A mask inspection method is provided.

That is, the present invention relates to a means for detecting such radiated substances by using a stencil mask or the like that emits radiated substances such as secondary electrons, reflected electrons, or wide radiation when irradiated with a charged particle beam. By providing the mask in the vacuum chamber of the exposure apparatus, the state of the pattern on the mask can be inspected on-machine.

More specifically, the exposure operation of the exposure apparatus is temporarily interrupted, and for example, a charged particle beam emitted from an electron gun is irradiated with a beam diameter by a beam diameter changing means or the like. Not less than or equal to the diameter, i.e. the beam diameter can be moved through the pattern aperture without any obstruction, and the beam is scanned over the pattern using a separate beam polarizing means. At that time, the amount of the radiated substance is detected by the detector by utilizing the fact that the radiated substance radiated from the mask is different between when the beam is irradiated on the mask part and when the beam passes through the hole part of the pattern. Then, by displaying the result as an SEM image on an appropriate display means, for example, a cathode ray tube of a television which operates in synchronization with the scanning of the beam deflecting means, the defect of the pattern can be inspected.

(Operation)

In the present invention, as described above, the amount of radiation emitted from the mask by beam irradiation differs between when the beam is irradiated on the mask portion and when the beam passes through the transmission hole of the pattern provided in the mask. By using this, the radiant is detected while scanning the mask pattern by the beam scanning means, and this is displayed on the display means as an SEM image, so that the pattern inspection can be performed without opening the exposure apparatus. Can be performed, and the inspection can be performed on-machine and during the exposure process, so that the inspection can be performed early and easily, which is advantageous in process management.

〔Example〕

 Hereinafter, the present invention will be described in more detail by way of examples.

FIG. 1 is a view showing one embodiment of a fine pattern exposure apparatus according to the present invention, in which an electron gun 1, a beam diameter changing deflector 26, a beam A focusing means 17, a beam shaping aperture 2, a minute aperture 2 ', etc. are provided. Further, a scanning deflection means (coil) for scanning a pattern transmission hole formed in a stencil mask 5 provided below the beam with a beam. ) 18
Is provided. Further, below the stencil mask 5, a converging lens 17 'for converging the beam passing through the pattern transmission hole onto a wafer (not shown) is provided. The beam is deflected into the minute aperture 2 'by the beam diameter changing deflector 26 so that the stencil mask 5
The upper beam diameter is adjusted so that the pattern width area provided on the mask to be inspected is equal to or smaller than the diameter.

As the beam diameter changing means in the present embodiment, a minute aperture 2 ′ arranged side by side with the beam shaping aperture 2,
And a beam deflector 26 for introducing a beam into the minute aperture 2 '. The beam diameter changing means adjusts the sectional area of the beam so that the width of the pattern provided on the mask 5 whose beam diameter is to be inspected is equal to or smaller than the diameter. In other words, the beam diameter should be smaller than the width or diameter of the minimum portion of the pattern transmission hole to be inspected, so that the beam irradiates the mask body when scanning the pattern with the beam and when the beam passes through the pattern. So that there is a difference in the radiation state of the radiation from the mask,
In particular, since the difference becomes large at the boundary, the pattern can be recognized. A method of focusing an electron beam exposure apparatus by converging an electron beam on a first beam shaping aperture by an electron lens and scanning the electron beam has already been applied for a patent (1973-3974).
9) Has been. In this method, there is a problem that the current density of the beam spot after convergence becomes very large, and the aperture substrate is melted. However, according to this method, a minute beam for scanning on the stencil mask can be formed without changing the current density, and the problem of mask substrate melting does not occur. Another reason for making the beam diameter smaller than the size of the transmission hole is to try to view the shape of the transmission hole as an SEM image, which is the point of the present invention, so that the beam diameter is about the same as the size of the transmission hole or If the size is larger than the size of the transmission hole, the influence of the beam cross-sectional shape appears on the SEM image, and the shape of the transmission hole that one really wants to see does not appear.

Next, as shown in FIG. 4, for example, the scanning deflecting means 18 in this embodiment operates so that the beam 16 having a reduced diameter scans the transmission holes 20 of the pattern. An AC current is caused to flow along the scanning locus 21 by passing an alternating current through the coil according to a predetermined control program.

At this time, the scanning of the beam may be performed by scanning only one predetermined pattern, or may be performed by scanning a plurality of identical or different patterns collectively.

If the scanning range is narrowed, that portion will be enlarged when displaying an image described later. Needless to say, the deflecting means can operate as a deflector for deflecting only the selected pattern 6 in the same manner as the aperture selecting deflector in FIG. 2 when the inspection step is not performed.

Next, in the present embodiment, a radiation detector is provided near the stencil mask 5 in the mask chamber 19. This radiant detector detects either reflected or secondary electrons emitted from the mask when the charged particle beam collides with the mask and thermal radiation is also emitted from the mask as described above. Any device having the ability may be used.

The above-mentioned reflected electrons and secondary electrons are generally classified according to the degree of energy, and those having an energy of 2 to 5 eV are called secondary electrons, and those having an energy of 20 to 30 keV are called reflected electrons. When attempting to detect backscattered electrons, the backscattered electrons have strong directivity, and it is therefore desirable to arrange a detector at a specific position. The portion indicated by B in FIG. 1 indicates a preferable position of the detector for detecting the reflected electrons. On the other hand, when secondary electrons are to be detected, the position of the detector is not particularly specified because the secondary electrons generally have a property of filling the inside of the vacuum chamber 19, and may be anywhere near the mask 5. The position of the backscattered electron detector may be used, or it may be provided at a location indicated by A in FIG. The secondary electron detector is mainly composed of, for example, a photomultiplier 24, and a fluorescent substance surface is provided on the front surface thereof.
It is preferable that a sink electrode 25 to which 23 and a voltage of about 10 kV are applied is provided in parallel. By adopting such a configuration, the radiation is constantly detected while the beam is scanned on the mask.When the beam hits the boundary of the pattern, the amount of the radiation changes greatly. Is converted as, for example, a voltage change of a detector and supplied to a television screen scanned in synchronization with the deflecting means, an SEM image of the pattern is displayed. Therefore this S
By visually inspecting the EM image, it is possible to easily identify the defect and the quality of the pattern. As described above, since the SEM image of the pattern is enlarged and displayed on the television screen by narrowing the beam scanning range, it is effective for detailed inspection.

In the present invention, as described above, since the pattern exposure step on the actual wafer and the pattern inspection step can be used simultaneously, a subroutine for appropriately executing the pattern inspection step is inserted into the program for executing the exposure step. By doing so, for example, when one pattern is to be exposed, the pattern can be inspected immediately before the start of the exposure step or at an appropriate interval during the exposure step to check whether there is a defect in the pattern. Inspection is easy, can be performed accurately in a short time, and the number of steps required for the inspection can be extremely reduced. Therefore, the quality of the obtained semiconductor can be improved and the production cost can be reduced.

(Effect)

In the present invention, the inspection of the pattern can be performed easily and accurately in a short time. In addition, as described above, the inspection can be performed without placing the pattern in the exposure apparatus and without subjecting the exposure apparatus to a vacuum state. And the reliability of the device is greatly improved. Furthermore, in the present invention, since the inspection target is a mask pattern that is about 100 times larger than the exposure pattern on the wafer, and is a relatively simple pattern that is the basis of the repeated portion, it is much easier to judge the quality of the inspection result. However, if the defect-freeness of this portion is guaranteed, the transfer result does not cause a defect due to the abnormality of the basic pattern.

[Brief description of the drawings]

FIG. 1 is an enlarged view of an example of a pattern inspection section of a fine pattern exposure apparatus according to the present invention. FIG. 2 is a schematic view showing an example of a conventional pattern exposure apparatus. FIG. 3 is a sectional view of a stencil mask used in a conventional pattern exposure apparatus. FIG. 4 is a view for explaining a beam scanning method in the pattern exposure apparatus according to the present invention. 1 ... Electron gun, 2 ... Beam shaping aperture, 2 '... Micro aperture 3,3' lens (focusing lens), 4 ... Deflector for aperture selection, 5 ... Stencil mask, 6 ... Basic pattern, 7 ...... Aperture for variable rectangle, 8 ... Mark pattern for aperture selection deflector adjustment, 9 ... Reduction lens, 10 ... Projection lens, 11 ... Deflection coil, 12 ... Wafer, 13 ... Stencil part, 14 ... Pattern forming unit, 16: Mask scanning beam, 16 ': Exposure beam, 17: Beam focusing means, 17': Focusing lens, 18: Deflection means (coil), 19: Vacuum chamber (mask) Chamber), 20 pattern opening, 21 scanning locus, 23 phosphor screen, 24 photomultiplier, 25 sink electrode, 26 beam deflector for changing beam diameter.

Claims (4)

(57) [Claims] After a charged particle beam is formed by passing through a transmission hole of a mask plate having transmission holes of a specific pattern,
In a pattern exposure apparatus for performing exposure by irradiating a predetermined position on a wafer, a beam scanning means for scanning the charged particle beam on the mask plate, provided near the mask plate, Radiant detecting means for detecting a radiant emitted from the mask plate by irradiation of the charged particle beam, and an image for generating an image of a transmission hole of the mask plate based on an output of the radiant detecting means A pattern exposure apparatus comprising: a generating unit. 2. A pattern exposure apparatus according to claim 1, further comprising a beam diameter changing means for narrowing a beam diameter of the charged particle beam scanned on said mask plate to a value smaller than a minimum width of said transmission hole. . 3. The image generating means generates an image of a transmission hole of the mask plate by synchronizing an output signal of the radiation detecting means with a signal applied to the beam scanning means. Item 3. The pattern exposure apparatus according to Item 1 or 2. 4. After forming the charged particle beam by passing through the transmission holes of a mask plate having transmission holes of a specific pattern,
A method of inspecting a mask plate in a pattern exposure apparatus that performs exposure by irradiating a predetermined position on a wafer, wherein the charged particle beam is scanned on the mask plate in the pattern exposure apparatus, and the charging is performed by the scanning. A radiation emitted from the mask plate by the irradiation of the particle beam is detected, an image of a transmission hole of the mask plate is generated based on the detected result, and an image of the mask plate is generated based on the generated image. A mask inspection method characterized by inspecting a pattern of a transmission hole.