RU2785012C1 - X-ray mask - Google Patents

Abstract

FIELD: medical equipment.

SUBSTANCE: area of application: for creating microstructures. Substance of the invention consists in the X-ray mask consisting of a substrate, a thinned membrane, a topological pattern applied to the thinned membrane, and alignment marks, wherein the substrate, the thinned membrane, and the alignment marks are made of the same material - leucosapphire and constitute a monolithic structure, a thin metal conductive layer is applied to the membrane, and a layer capable of converting the absorbed heat of X-ray radiation into infrared radiation is applied to the back surface of the membrane.

EFFECT: possibility of aligning layers in the optical and infrared spectral bands using alignment marks and possibility of hybrid lithography, as well as expanded possibility of using the claimed X-ray mask in the hard and soft X-ray radiation bands, minimised topology distortion, and reduced mechanical distortion of the membrane.

9 cl, 2 dwg

Description

The invention relates to the field of engineering and manufacturing technology of microsystems and can be used to create microstructures in a wide range of sizes and various materials - polymeric, ceramic, semiconductor materials, metals, as well as new materials such as composite.

A large number of modern micro-products are formed using lithographic methods. Such methods of microlithography are based on the use of beams: electrons, protons, ultraviolet and X-ray quanta, which locally change the properties in the microvolume of the material. In particular, the modification of the properties of materials in a wide range of sizes is provided by the use of short-wavelength X-rays. The basic tool for implementing X-ray lithography operations is an X-ray mask, the topology of which is transferred to the X-ray sensitive layer of the technological material - X-ray resist by X-rays passing through a thin, X-ray-transparent area of the X-ray mask - the membrane. The membrane of the X-ray mask is usually fixed around the perimeter on a rigid frame, which provides mechanical rigidity to the entire structure.

The membrane of the X-ray mask in the mode of using the broadband transmission spectrum should be:

• thin, in order to scatter a relatively small fraction of the radiation that has passed through the membrane;

• made of low atomic number material to ensure high X-ray transmission;

• made of radiation-resistant material so as not to deform during irradiation;

• transparent in the optical range of the spectrum for possible combination of layers;

• made of technological materials to ensure mass production of masks;

• mechanically strong;

• made of cheap materials.

The prior art known x-ray masks made on a thin (several micrometers thick) membrane of materials with low atomic number, namely aluminum, silicon, silicon nitride, silicon carbide and described in [Aristov V.V., Kopetsky I.V. , Kokhanchik G.I., Kudryashov V.A. Prospects for the use of soft X-rays in submicron lithography. – Surface. Physics, Chemistry, Mechanics, 1983, No. 11. - P. 5-15., Valiev K.A. Physics of submicron lithography. - M.: "Nauka", 1990. - 528 p., Spiller E., Feder R, 1977, X-ray lithography in Topics in Applied Physics, v.22, ed.H.J.Queisser,. - Р.35-92., Feder R., Spiller E., Topalian J. X-ray Lithography. - Polymer engineering and science, June, 1977, V.17, No. 6. - Р.385-389., Kirilenko A.G., Krivospitsky A.D., Semin Yu.F. X-ray lithography in microelectronics // Foreign Radioelectronics, 1980, V.17, No. 1. S.36-56.]. The disadvantages of the known masks are, firstly, the fragility and impracticality of thin membranes, and secondly, they have a relatively low transparency in the visible range of the spectrum, which does not allow for layer alignment and other operations.

An X-ray mask is also known (JPH03155120 A, IPC G03F1 / 22, G03F1 / 24, G03F1 / 54, H01L21 / 027, published on 07/03/1991), which is a single-crystal film of molybdenum, tungsten, gold, lead, etc., formed in the form of a membrane on a single crystal substrate such as quartz or sapphire. The disadvantage of this mask is the use of reflection geometry, in which X-rays are reflected at a fixed angle (according to the Bragg law in the angle range of ~10 ^-4 rad), which proportionally reduces the radiation power incident on the substrate and the productivity of the X-ray lithography method. Losses of the same order (with an initial wide spectral range of incident radiation) can occur in the case of using an X-ray mask made on the basis of a single-crystal surface (patent RU 2598153 IPC G03F 7/00, published on September 20, 2016). For the most complete realization of the possibilities of the X-ray lithography method, it is more efficient to use an X-ray mask in a wide spectral range in the “transmission” geometry of X-rays.

Known masks based on a sapphire membrane several micrometers thick, transparent to X-rays, as well as in the visible range of the spectrum. For example, an X-ray mask (JPS5330277 A, IPC H01L21/027, H01L21/302, published Mar. 22, 1978) has a sapphire layer formed on a single crystal substrate bearing an X-ray absorbing pattern. Also known is the X-ray mask JPH0795512 B2 (IPC G03F1 / 22, G03F1 / 68, G03F1 / 80, H01L21 / 027, H01L21 / 30, published 10/11/1995) based on a membrane from a thin (from 2 to 4 microns) film of inorganic material. An aggravating disadvantage of using a thin membrane (which in itself does not have mechanical rigidity) is the method of its attachment to the support frame - gluing, which can introduce significant topology distortions.

The prototype can serve as an x-ray mask, claimed in the patent JPH02158121A (IPC G03F1/22, H01L21/027, H01L21/30, published 06/18/1990). The prototype consists of a thinned membrane supporting the frame and mask pattern, all made from the same material. However, the described design does not contain the alignment marks necessary for the alignment of the layers, and is also subject to the influence of an electrostatic charge and does not contain elements that contribute to the removal of the Joule heat released during the absorption of X-rays.

The purpose of the proposed technical solution is to minimize topology distortions both in the manufacture of a mask by using a non-rigid adhesive joint that causes deflection of the surface planarization, and to ensure the possibility of combining layers by making the membrane highly transparent, reducing thermal and electrostatically caused mechanical stresses during operation.

The technical result of the proposed invention is the possibility of combining layers both in the optical range of the spectrum using alignment marks, and in the ranges of ultraviolet and infrared radiation. The ability to combine layers is achieved due to the properties of the transparency of the mask material made of leucosapphire in the visible, infrared and ultraviolet ranges. The above result is also ensured through the use of alignment marks formed in the volume of the mask material without introducing distortions into the mask. Such signs can be used both when aligned under the conditions of reflection of radiation back to the detector, and under conditions of transmission of radiation through a semiconductor substrate made of materials transparent in the IR range, such as leucosapphire, silicon, germanium, polymers.

Alignment marks made of the material of the mask can be in the form of both microlenses that refract radiation and holes that transmit radiation.

Registration marks are usually used to combine complementary patterns, however, using different radiation ranges (for example, X-ray and ultraviolet), two different patterns can be transferred into one layer sequentially from the corresponding masks (X-ray and ultraviolet, respectively), which is called hybrid lithography. In this case, each type of radiation corresponds to its own resist extinction thickness, which makes it possible to obtain a two-level structure in the resist. Thus, the claimed mask can be used in two successive exposures with overlapping layers.

Another technical result of the invention is the minimization of topology distortions. As is known, X-ray radiation quanta initiate the emission of photoelectrons from the atomic shells of a material. As a result, the photoelectron current exceeding the leakage current through the contact surface of the mask causes a potential difference, which contributes to the deflection of the X-ray mask membrane. Mask deflection distorts image transmission to the greatest extent when the mask and substrate are tilted towards the X-ray beam. In practice, this angle reaches 45 degrees. In order to minimize the deflection of the membrane, a thin layer of metal is applied to the mask (in areas that do not prevent alignment), galvanically connected to the ground, due to which the electrical neutrality of the mask, disturbed by the loss of electrons, is maintained.

Another technical result of the invention is the reduction of mechanical distortions of the membrane. In order to minimize mechanical distortions of the membrane, a thin layer of material is also created on the mask, which has a degree of blackness close to one. In the case of an aluminum layer, for example, a chemical oxidation operation in oil vapor is used. Such a layer, without making a significant contribution to the absorption of the energy of X-ray quanta by the mask, will more effectively dissipate Joule heat into the environment than the polished surface of a leucosapphire membrane.

The use of one material expands the scope of the claimed X-ray mask, the different thickness of the membrane which corresponds to the corresponding spectrum of the applied X-ray radiation. The method owes small topology distortions during size transfer to the relatively low X-ray scattering cross section of the membrane material, leucosapphire, which has a low atomic number. In addition, a mask with a durable membrane can be used in the manufacture of micro-products both on flat substrates (planar technology) and on curved surfaces.

The invention is illustrated by drawings. In FIG. 1 shows a schematic representation of an x-ray mask with alignment marks in the form of microlenses; in fig. 2 shows a schematic representation of an X-ray mask with alignment marks in the form of pinholes in the substrate.

The X-ray mask includes a substrate (1), a membrane (2) with topological structures from a sublayer (for adhesion of the topological structures of the absorber) material (3) and absorber structures (4) on it, a conductive layer (5), alignment marks ( 6) in the form of microlenses (figure 1) or in the form of microholes (8) in the substrate (figure 2) and a layer that generates infrared radiation (7).

The mask is made of a solid leucosapphire substrate of such an initial thickness that, on the one hand, provides sufficient mechanical rigidity of the entire structure, and, on the other hand, transmits at least 50% of the X-ray radiation incident on it. The region of the substrate with the applied topological pattern (3, 4) is thinned and is a transparent membrane not only for X-rays, but also for visible, ultraviolet and infrared radiation. The membrane thickness ranges from tens to hundreds of microns.

To match the layers, the matching marks are used, which are located on the substrate from the planar side or from the non-planar side, or from both sides, depending on what area the topological pattern occupies. The substrate, the thinned membrane, and the alignment marks are made of the same leucosapphire material and represent a monolithic structure.

Alignment marks are formed by a surface protruding above the level of a planar (or non-planar) plane (or recessed below the level of a planar (or non-planar) plane). Such a surface deflects the incident rays, creating a contrasting image of the surface of the registration marks. If the entire surface of the substrate in the area where the alignment marks should be located is covered with layers to remove the charge or generate thermal radiation, the alignment marks are made in the form of holes in the leucosapphire substrate.

A thin metal conductive layer (5) is deposited on the membrane surface to compensate for the loss of electric charge carried away by photoelectrons. On the back surface of the membrane, a thin layer of material (7) is applied, processed to a high degree of blackness, which converts the absorbed heat of X-ray radiation into infrared radiation. This layer can be either dielectric or conductive. Both solutions can be implemented by applying a thin layer of aluminum to the mask and then oxidizing it in hot oil vapor.

Claims (9)

1. An X-ray mask consisting of a substrate, a thinned membrane, a topological pattern applied to the thinned membrane, and alignment marks, characterized in that the substrate, the thinned membrane, and alignment marks are made of the same leucosapphire material and represent a monolithic structure; a metal conductive layer, a layer is applied to the back surface of the membrane, which converts the absorbed heat of x-ray radiation into infrared radiation. 2. X-ray mask according to claim 1, characterized in that the thickness of the membrane is from tens to hundreds of microns. 3. X-ray mask according to claim 1, characterized in that the alignment marks are in the form of microlenses. 4. X-ray mask according to claim 3, characterized in that the alignment marks are located on the substrate on a planar surface. 5. X-ray mask according to claim 3, characterized in that the alignment marks are located on the substrate on a non-planar surface. 6. X-ray mask according to claim 3, characterized in that the alignment marks are located on the substrate on planar and non-planar surfaces. 7. X-ray mask according to claim 1, characterized in that the alignment marks are made in the form of micro-holes in the substrate. 8. X-ray mask according to claim 1, characterized in that the layer that converts the absorbed heat of X-ray radiation into infrared radiation is a dielectric layer. 9. X-ray mask according to claim 1, characterized in that the layer that converts the absorbed heat of X-ray radiation into infrared radiation is processed to a high degree of blackness.

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