DE2333902A1 - METHOD OF ALIGNMENT OF MASKS FOR SOFT X-RAY RADIATION - Google Patents

Description

DipL-big. Richard MüHer-Börnef

Dtt-kq. Hons-Iienridi Wey 68

Berlin, June 29, 1973

Massachusetts Institute
of Technology

Method for aligning masks for soft X-ray radiation

The subject of this invention is an alignment system which ensures that each individual soft X-ray mask is within a set of such masks is in proper register with a substrate to be exposed and that each pattern on these masks is opposite to the corresponding patterns on the other masks of the Sentence is arranged exactly.

Recently, the lithography with soft X-rays

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as a method of duplicating flat images using a sub-micron resolution has been proposed been; see patent application serial number 217 * 902 of 1 * 1. January 1972 by Snith et al. With the title "Device and Process for Soft X-Ray Lithography ". Soft X-ray masks are included with one Transducers made at an electrode spacing of 1.3 microns for surface acoustic wave images and has been reproduced with good success. Thus, the soft X-ray lithography has shown a resolving power higher than that of the ordinary one Light lithography achievable and that is roughly comparable to that of the process that involves scanning work an electron beam. The simplicity and low cost of soft X-ray lithography suggest that they will have a significant impact on device manufacturing in the future ultra high resolution is likely to have. However, multiple masking operations can be used in many manufacturing processes to be required. The images generated by the various masks must be superimposed in register will. In the meantime, a much higher level of accuracy is required than before, since the previous mask reproduction methods did not reproduce images containing submicron elements; at the Electrode beam scanning method, according to which images with im £ r, b-

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ORIGINAL

elements lying in the raikron area have been created so far, each image is scanned individually and the masks are not duplicated, so that a register content of the individual Masks are not required. On the other hand, the image on each mask must be in a set of masks that are used for manufacturing a complete circuit or an entire device on a subetrat is required, with submicron accuracy registers with the corresponding images of each of the other masks of the set as otherwise the images will not be in register with the image or images in spite of the exact alignment between mask and substrate which have previously been reproduced on the same image area.

It is therefore an object of this invention to provide an alignment system for a soft X-ray lithography process whose submicron accuracy is that of lithography for soft X-rays and that is moreover simple and cheap and the white ones X-rays takes advantage of the soft X-rays available from the operations of lithography stand.

Another object of this invention is to provide such an alignment system that is capable of accurate registration of the individual masks within a mask set with respect to a substrate to be exposed.

Another object of the invention is to obtain such an alignment system which ensures that

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ORIGINAL INSPECTED

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the images on the individual masks of a mask set are correctly arranged with respect to the corresponding images of the other masks.

The invention is based on the knowledge that for an efficient application of lithography for soft X-rays An alignment system is absolutely necessary that continues to be due to the high accuracy, i.e. the very small picture elements in the micron range, which is possible with this method, through this alignment system high accuracy must be marked unc 'that as The more important finding a system of this type is best made use of the soft X-rays that from the operations of lithography for soft X-rays are available.

A feature of the invention is an alignment system for a lithography process for soft X-rays for aligning a mask with respect to a substrate to be printed with an image, for which purpose first register devices are located on the mask and second register devices are located on the substrate. One of the register devices is a first device having a specific shape for absorbing soft X-rays, and the other of the register means is a second device for absorbing soft X-rays which contains a space with the same specific shape therein. One of the register means is one for We _-: toe X-rays

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ORIGINAL INSPECTED

transparent register window on the mask and the other register means over a register window permeable to soft X-rays on the Substrate.

Further objects, characteristics and advantages will emerge from the following description of a preferred exemplary embodiment with reference to the accompanying drawings. Included demonstrate:

Fig. 1 is a schematic plan view of a master mask with Register devices and work table marking devices according to the alignment system according to the invention, FIG. 2 is a schematic cross-sectional side view taken along line 2-2 of FIG. 1;

3 is a schematic cross-sectional view showing the exposure of the electron-sensitive cover material with a scanning electron microscope for generating the register devices and work table marking devices shows on the master mask

Figure k is a schematic side view of the master mask of Figure 3 after development of the exposed masking material; Figure 5 is a schematic cross-sectional side view of the Maxter mask after a soft X-ray absorbing material has been applied to the exposed areas and after the remaining electron-sensitive masking material has been dissolved away ,

6 is a schematic cross-sectional side view from FIG

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ORIGINAL KNSPECTED

~ ⁶ ~ ■ 23 ^, - 02

the use of soft X-rays to generate an image mask with the master mask is evident, FIG. 7 shows a schematic cross-sectional side view of the image mask from FIG. 6 after the exposed portions have been developed the covering material,

Figure 8 is a schematic cross-sectional side view of the image mask of Figure 7 after application of a soft x-ray absorbent material on the developed portions and after covering the remaining against soft X-rays Material has been dissolved away,

FIG. 9 is a schematic plan view of the image mask of FIG Fig. 8,

10 shows a schematic cross-sectional side view of the image mask along line 10-10 of Fig. 9, after images have been created thereon,

Fig. 11 is a cross-sectional side view of the image mask of Fig. 10 after under the tabs and under windows have been etched in the images, FIG. 12 is a schematic cross-sectional side view the use of soft X-rays and the image mask to create registers on a substrate it appears

13 is a schematic cross-sectional side view of the Substrate of Fig. 12 after the exposed portion developed and absorbed by a soft X-ray Material has been replaced after the unexposed material has been removed,

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ORIGINAL JNSPHCTED

2332902

Fig. L4 is a view of the substrate of FIG. 13 after have been etched under the register means window, Fig. 15 is a plan view of the substrate of FIG. Ik, Fig. L6 is a schematic cross-sectional side view of a lithography system for soft X-rays using an inventive alignment method, in order to obtain registration between an image mask and a substrate to be printed, and FIG. 17 shows a schematic, axonometric view of an image mask with several image zones, in which register devices and work table marking devices according to the alignment system according to the invention are used.

In practicing the invention, a master mask can be used which carries alignment devices, the at least two register devices and a work table marking device for each image to be formed on a substrate. The registry facilities and the work table markers are placed on the master mask using a scanning electron microscope - and each of the alignment devices has a specific shape created by a soft X-ray absorbing Material is delimited, which is located on a permeable portion of the master mask. Likewise has Each of the worktable marking devices has a very specific shape made by absorbing soft X-rays Material is delineated, which is based on for soft

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OFHGINAL INSPECTED

X-ray transparent parts of the master mask are located. According to the rays in lithography for soft X ¹ usual method, a whole set of image masks is produced by exposure to soft X-rays by the master mask. Each of the image masks obtained in this way has one or more register devices which are similar to the register devices on the master mask. These register devices can be a positive or negative of the very specific shape that the register devices have on the master mask. Each of the image masks also contains a plurality of work table marking devices which correspond to the work table marking devices on the master mask and which can also be a positive or negative of the corresponding work table marking devices on the master mask. Each of these work table marking devices on the image mask is assigned an image zone. An image is generated in all these zones of all image masks using the methods customary in scanning electron microscopy. Using the work table marking devices as a starting point, the scanning electron microscope can produce exactly one image on one mask and compatible images at the same relative position on all other image masks of the mask set. Thus, each of the images to be printed on an image area of a substrate to obtain the frame is accurate

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in register with all other images on all other image masks that are placed one after the other on the substrate have to. The register devices generated on the substrate have exactly the same shape as those on the master mask and on all image masks, however, represent the inverse of the register facilities on the image mask The result is that in the event of register accuracy between the register devices on any one of the image masks on the one hand and the register devices on the substrate, on the other hand, no soft X-ray radiation this zone of image mask and Can penetrate the substrate. Thus, sensors for soft X-rays can be used to through the Detect soft X-rays passing through register devices and use a zero indicator connected to the sensor devices to determine when exact registration is available. A servomechanism comprising one or more piezoelectric drive units can be used to move the substrate and image masks towards one another in order to obtain a zero display, the exact registration corresponds. If this registration is present, the image will be of all image zones printed on the image mask aligned with the substrate using soft X-rays on the substrate. After printing with the first image mask, this mask is removed and replaced by a second image mask that is inserted into the correct registration with the substrate and the second set of images on the image zones on the substrate

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- .. *. INSPECTED

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strat applied. This continues until all of the images on each of the image masks have been applied to all of the corresponding zones on the substrate and a full image has been created in each of the image zones on the substrate. The details of lithography for soft X-rays can be obtained from the co-pending patent application "Lithography device for soft X-rays", which is available under serial number 217.902 by Henry I. Smith, David L. Spears and Ernest Stern at Ik. January 1972 has been registered.

The etching process used to produce relatively transparent parts or windows is described in the patent application "Mask carrier substrate for soft X-rays "described on the same day by David L. Spears, Henry I. Smith and Ernest Stern has been submitted.

Fig. 1 shows a master mask 10 with alignment devices, consisting of two register devices 12 and Ik and two work table marking devices 16 and 18. Typically, each mask has two register devices and a work table marking device is associated with each image zone. Since FIG. 1 shows a master mask 10 with two image zones 20, 22, it also has two work table marking devices 16 and 18. Each of the register devices 1 a and 14 comprises a layer 2 k of soft material which absorbs X-rays and which contains an open space 26 which has the shape 28 of the register mark 25

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ORIGINAL INSPECTED

specifies. In the case shown, the form 28 has the register markings the shape of an object with four protruding points.

The work table marking devices 16 and 18 also each include a layer 30 of soft X-ray absorbing material. The work table marking 32 consists of four rooms 34 in the form 36 of a Greek Orthodox cross without a central part. The register devices 12 and Ik and the work table marking devices l6 and l8 are located on transparent parts of the master mask, 10, in each case above the windows
40 and 42 or 44 and 46 (Fig. 2). The membrane 48, 50,
52 and 54 in the windows 40 or 42 or 44 or 46 is quite thin and thus permeable to soft X-ray radiation, while the remaining zones of the master mask 10, the much
are thicker, are relatively opaque to soft X-rays.

To produce the master mask 10, one can start from a plate 60 (FIG. 3) made of silicon, which has been doped with boron to a depth of a few microns in order to form a boron diffusion layer 62. Then that will
Plate 60 on one side with a protective layer 64
made of e.g. silicon dioxide and coated on the other
Side with a layer 66 of polymethyl methacrylate, which is sensitive to electrons, the wafer 60 is then treated in a scanning electron microscope 68 which has the

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Images generated on layer 66 depicting tabs 12 and 14 and work table markers. The wafer 60 comes in a developer
from, for example, 40 % methyl isobutyl ketone and 60 % isopropyl alcohol for development in order to remove the exposed zones 67 from the
Remove layer 66, which now delimits register devices 12 and 1 ^ t and work table marking devices 18.

Then the various holes 70 (FIG. 4) remaining in the layer 66 are filled with a soft X-ray absorbing material, for example by vapor deposition with gold. The remaining portions of layer 66 are then
removed by dissolving with a trichlorethylene solution. The now remaining portions of soft X-ray absorbing material 24 (Fig. 5) now define the
Register mark 25 of register devices 12 and 14, and the soft X-ray absorbing material 30 defines work table marking 32 of the work table marking devices. Using a caustic such as buffered hydrofluoric acid, which removes the silicon dioxide from the
If layer 64 attacks but not the silicon of die 60, openings 72, 74, 76 and 78 are etched into layer 64. The plate 10 is now prepared to such an extent that the windows 40, 42, 44 and 46 (FIG. 2) are etched into it. An etchant can be used which does not attack the remaining portions of the silicon layer 62, though

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but the open areas of the silicon wafer 60 in the Openings 72, 74, 76 and 78 This is achieved by using a 115 ° C solution of 68 ml of ethylenediamine, 12 g pyrocatechol and 32 ml water, which are left to act for about 1 1/2 hours. This etchant etches the silicon wafer 60 good, but does not attack the boron diffusion layer 62. In this way, as shown in Fig. 2, windows% 0, 42, 44 and 46 produced in thin membranes 48, 50, 52 and 54, that cover them · This method is detailed in the patent application "Mask Backing Substrate for Soft X-ray Radiation" by David L. Spears, Henry I. Smith, and Ernest Asterisk, which was filed at the same time as the present one.

The finished master mask 10 (FIG. 2) can now, as shown in FIG. 6, be used to produce a set of image masks one of which, namely the image mask 80, consists of a chip of silicon 82 which contains a boron diffusion layer 84 such as that described above. Tile 82 carried a layer 86 of a soft X-ray sensitive material such as polymethyl methacrylate, on one side and a protective layer 88 of material such as silicon dioxide on the other side. Layer 86 becomes through the windows 40, 42, 44 and 46 in the master mask 10, exposed, specifically with soft X-ray radiation 91 from a source of wecjiche X-ray radiation 90, so that on the layer 86 the register devices 12 and 14 and

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the work table markers 16 and 18 are defined. The exposed portions 92 of layer 86 are then exposed to a developer such as a solution of 40% methyl isobutyl ketone and 60% isopropyl alcohol to leaving behind holes 9 ^l i of these fractions (Fig. 7), the exposed portions 92 instead of the layer 86 to remove. The holes 91 are filled with a soft X-ray absorbing material such as gold and then the remaining portions of layer 86 are removed by dissolving it with a trichlorethylene solution, leaving one layer of soft X-ray absorbing material 96 (FIG. 8) and the second Set of registers 12 * and 1% 'represents, which are the same as the original register devices 12 and Ik on the master mask 10 (Fig. 1).

The register devices 12 * and IV (FIG. 9) on the image mask 80 have the same shape 28 'as the register devices 12 and Ik, only that in this case the register marking 25' is delimited by the soft X-ray absorbing material 2k ^% itself and not like in the case of the register devices 12 and 14 by the space 26 which is surrounded by the soft X-ray absorbing layer 2k . The worktable marking devices 16 'and 18' also comprise worktable markings 32 ', the shape of which is defined by the soft X-ray absorbing layer 3 °' which actually defines the spaces Jk '

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in order to define the shape j6 · of the work table ^{marking 32 1} , while in the work table marking 32 the shape j6 was defined by the soft X-ray absorbing layer 30 surrounding the spaces Jk. In FIGS. 1-9 it is shown that there is a variant of the register and work table markings in the master mask 10, which are arbitrarily designated as positives, and that the image mask 80 has register and work table markings that are called negatives may be referred to, ie that the markings 25 ', 32' are the negatives or the inversions of the markings 25 and 32, but this is not necessarily a delimitation of the invention, namely if, for example, a negative cover was used instead of the polymethyl methacrylate layer 86, so marks 25 'and 32' would be the positives of marks 25 and 32.

The image zones 20 'and 22' on the image mask 80 can now be printed with the images 100 and 102 (FIG. 10) in the same manner as this using a scanning electron microscope guided through the work table marking devices 16 'and 18' described with reference to FIGS. 3-5 and as described in detail in co-pending patent application "method and apparatus for lithography soft X-ray ^11, January Ser. No. 217,902, filed on Ik. 1972 I. by Henry Smith, David L. Spears and Ernest Stern, is indicated. Well, in the

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Silicon dioxide layer 88 made holes 104, 106, 108 and 110 ^ as described above for layer 64 became. Then, as indicated above, windows 112, 114, 116 and 118 (Fig. 11) are etched into the die 82, membranes 120, 122, 124 and 126 which are transparent to soft X-rays remain behind.

A substrate 130 (FIG. 12) on which an image is to be built up is made of a silicon wafer 132 with a layer 134 of soft X-ray sensitive material, namely of polymethyl methacrylate on one side and a protective layer 136 such as silicon nitride the other side. The layer 134 is then exposed to soft X-ray radiation 91 '(FIG. 12) through an image mask. In this operation, the image zones 100 and 102 are not exposed, since only alignment devices have to be produced on the substrate I30. Any means, such as soft X-ray opaque elements I38, 140, can be used to cover windows II6 and II8 in image mask 80 to prevent images 100 and 102 from being imaged on layer I34. However, soft X-rays from the soft X-ray source 90 'pass through the windows 112 and 114 through the register devices 12' and 14 'and expose the portions 142 of the layer 134. The exposed portions 142 are made by dissolving with 40 % methyl isobutyl ketone and 60 % Isopropyl alcohol removed and put through soft X-rays

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Replaced absorbing material, after which the remaining unexposed portions 14l of layer 134 can be dissolved in trichlorethylene, so that only the register devices 12 ″ and 1V ′ (FIG. 13) remain. Windows 150 and 152 can now be created in plate 132 by etching the silicon with an etchant such as a mixture of hydrofluoric and nitric acid or a mixture of hydrofluoric, nitric and acetic acid. With these etching agents, the etching with a neutralizing bath is practically stopped shortly before the other surface. In the case of the substrate I30, a less selective etching agent can be used, since maximum transparency through the use of a very thin membrane, as will be explained below, is not absolutely necessary. The register devices 12 '* and 14 *' on the substrate I30 (FIG. 15) comprise a layer 24 "of soft X-ray absorbing material in which a space 26 * 'with the shape 28 ^{ft of} the register mark 25" is located. Since the image mask 80 is flipped over for printing on the substrate I30, the arrangement of the negative devices on the substrate I30 is a mirror image of that on the image mask 80. The register devices 12 * 'and l4 ·' are the inverse of the register devices 12 'and Ik ' and the same as the registers 12 and Ik. The last-mentioned of these special relationships is not essential for the invention. It is important, however, that the register devices 12 "and Ik · '

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are the inverse of the register devices 12 'and Ik' , regardless of whether the register devices 12 'and 14 · or 12' · and Ik ·· are the same as the original register devices 12 and Ik on the master mask 10 or their inversion . The substrate 130 (FIGS. Ik and 15) bears two image zones 20 "and 22", j # dceh no work table markings, since the final alignment only requires that each successively used image mask is correctly aligned during the exposure to the substrate 130 Previously, all images on all image zones such as zone 20 'were generated using the worktable markers as a guide for the scanning electron microscope so that all images on the image zones of each of the sequentially applicable image masks versus all images in the same location the other image masks in the sentence are aligned correctly.

In practical use, the substrate 130 is coated with a layer 160 of material sensitive to soft X-rays, such as polymethyl methacrylate, and then exposed to soft X-rays 91 ″ from a soft X-ray source 90 ″ through an image mask 80. The soft x-ray radiation 91 ″ from the source for soft x-ray radiation 90 ″ passes through the windows 112 and 114 in the image mask 80 only in the zones which are not blocked by the soft x-ray absorbing material Zk *. The soft

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X-rays that are not blocked by the soft X-ray absorbing material 24 'then pass through the substrate 130 at the locations not blocked by the soft X-ray absorbing material 24'. When the image mask 80 and substrate 130 are aligned, the soft X-ray absorbing materials 24 ″ and 24 ′ are also precisely aligned so that no soft X-rays pass through the substrate 130 and the soft X-ray sensor 170 does not detect any soft X-rays. As a result, the zero indicator 172 registers a zero point; a character for this is entered into controller 174. A doubling system with the sensor for soft X-ray radiation 170 · and the zero indicator 172 'is assigned to the register devices 14' and 14 '. The controller 174 can be used to generate signals for controlling perpendicularly oriented, piezoelectric drive devices 175, 175 ', as they can be obtained from Coherent Optics Inc. (Electro-Micrometer Model Ik) and which the substrate I30 via very small Ability to move distances in the order of magnitude of a few microns, as are required for the exact alignment of image mask 80 and substrate I3O.

In practice, the soft X-rays 91 · ', which pass through the windows II6 and II8 of the image mask 8O are blocked from the registering process. If exact

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If there is registration, the blocking is canceled and the windows 116 and 118 around the images 100 Soft X-rays passing around 102 and 102 create an exposure image in layer 160, which then can be developed and further processed by etching or according to other aspects known to the person skilled in the art. After completing this operation, the next image mask of the set is inserted in place of the image mask 80, and the next image is generated in zones 20 'and 22' ', until all for the production of the whole picture in the zones 20 ' and 22 ″ required images are reproduced on the substrate I30 have been.

The substrate produced according to the invention typically has several image zones and requires an image mask with an equally large number of image zones and work table marking devices. Thus, in Figure 17, a typical image mask 80 'includes forty-two separate image zones I80, each of which a work table marking device I82 is assigned is. It also contains two registers 184 and I86. The image mask 80 typically has the

2
Size of 1 inch; each of the forty-two image zones is approximately 65 mils.

Those skilled in the art will also be familiar with other embodiments that lie within the following claims.

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Claims (1)

PATENT CLAIMS IJ alignment system for a lithography system for soft X-rays including a register system for the production of registration between a mask and a substrate to be printed with a picture, characterized in that it consists of a first register means on this mask, and second register means consists
on this substrate, / wherein one of the register devices is a first soft X-ray absorbing device of a very specific shape and the other of the register devices is a second, soft X-ray absorbing device that contains a space of a very specific shape, one of the register devices having a for soft X-ray permeable register window is guided on the mask, while the other register device is guided over a register window permeable to soft X-ray radiation on the substrate and one of the register devices is the inverse of the other. 2. Alignment system according to claim 1, characterized in that that the very definite shape includes four protruding parts. 3. Alignment system according to claim 2, characterized in that these protruding parts on transverse axes at a distance mutually attached pairs are arranged. * i. Alignment system according to claim 1, characterized in that that there is a detector for soft X-ray radiation 309883/1367 Establishing around the first adsorption facilities for soft x-ray around and through the space in the second soft x-ray adsorbent comprises passing through, soft X-ray radiation and a first zero display device for determining a The point in time when the first adsorption devices block the space in the second adsorption devices, from which it can be seen that the mask and substrate are in register with one another. 5. Alignment system according to claim 4, characterized in that that there is a piezoelectric positioning device comprises, which moves the mask and substrate relative to one another as a function of the first zero display device in order to to obtain correct registration of the first register device. 6. Alignment system according to claim 1, characterized in that at least two sets of first and second register devices are present on every mask or substrate. 7. alignment system according to claim 1, characterized in that that it includes a work table marking system to oppose each image on each mask of a mask set correctly position the corresponding images on the other masks of the set, this work table marking system a very specific work table marking Form includes. 309883/1367 8. Alignment system according to claim 7i, characterized in that that the work table marking of a very specific shape comprises four protruding parts. 9. Alignment system according to claim 8, characterized-characterized, that the protruding parts are arranged on transverse axes in spaced-apart pairs 10. Alignment system according to claim 7, characterized in that that this very specific shape is delimited by a space surrounded by a first material. 11. Alignment system for a lithography system for soft X-rays, characterized in that it consists of: A master mask with at least one first register device of a first shape in a soft X-ray radiation absorbent material located on a part of the master mask that is permeable to soft X-rays, a plurality of image masks, each of which has a second register device on a part permeable to soft X-rays for each of the first register means, the second register means being one of the first Shape same second shape made of soft X-ray absorbing material Material include, and a substrate to be exposed through the image mask, which has a third register device for each of the second Has register facilities, the third register facilities comprise a third form of soft X-ray absorbing material which is the inverse of the 309883/1367 ORIGINAL WSPECTED second form is. 12. Alignment system according to claim 11, characterized in that, that it comprises a soft X-ray detector to determine whether soft X-ray radiation passes around the second and third register means, and a null indicator for determining when the first and second register means make passage soft block x-rays, which shows that the mask and substrate are in register. 13. Alignment system according to claim 11, characterized in that it comprises a work table marking system to each image on each mask of a set of hats opposite the corresponding images on the other masks of the Set correctly to position, whereby this work ti s.ch marking system comprises several first work table marking devices - one for each image to be exposed, which are based on one for soft X-ray radiation permeable part are located on the master mask, and several second work table marking devices - one each for each image to be exposed, which are located on each of the image masks. 1 * 1. Method for producing an alignment system for soft x-rays for aligning a soft x-ray mask and substrate, characterized in that it consists of: The production of a first register device of a first shape in soft X-ray absorbing material 309883/1367 a part of a that is transparent to soft X-rays Master mask, the production of a second register device a the first form is similar to the second form in soft X-ray absorbing material on one for soft X-ray transparent part, on each of several image masks, and the manufacture of third register means which are the inverse of the second shape and for registering with corresponding ones of the second shapes on successive ones of the Image masks are used on a substrate. 15 · A method of manufacturing a soft X-ray alignment system, a soft X-ray mask and substrate, characterized in that it ordered from: Manufacture of a first resist device of a first shape in soft X-ray absorbing material on a part of a master mask that is transparent to soft X-rays, the manufacture of a first work table marker of a second shape in soft X-ray absorbing material on a soft X-ray permeable part of a master mask, the production of second register devices of a third, the first same form in soft X-ray absorbing material on a soft X-ray through 309883/1367 casual part on each of several image masks, and making second work table markers of a fourth, the second same shape on each from multiple image masks. 309883/1367 Blank page