JP2015053433A - Reflective mask blank and reflective mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EUV mask, the surface of which is effectively cooled (temperature-regulated) during light exposure, and a mask blank.SOLUTION: In a reflective mask blank, a multilayer reflection layer 2, a protective layer 3, and an absorber layer 4 are sequentially stacked on one surface (front side) of a base plate 1. The reflective mask blank is characterized as follows: heat conduction layers 6t, 6b and 6s are formed on the front and back sides of the base plate 1 and a side surface thereof, respectively; and the heat conduction layers are made of a material including carbon or solid metal.

Description

  The present invention relates to a reflective mask blank and a reflective mask used for EUV lithography or the like using extreme ultraviolet (Extreme Ultra Violet; hereinafter referred to as “EUV”) as a light source.

  In recent years, with the miniaturization of semiconductor devices, EUV lithography using EUV having a wavelength of around 13.5 nm as a light source has been developed. Since EUV lithography has a short light source wavelength and very high light absorption, it needs to be performed in a vacuum. Further, in the EUV wavelength region, since the refractive index of most substances is slightly smaller than 1, EUV lithography cannot use a conventionally used transmission type refractive optical system, It becomes a reflection type optical system. Therefore, a photomask for EUV lithography (hereinafter referred to as an EUV mask) as an original plate cannot be used as a conventional transmission type mask, and therefore needs to be a reflection type mask.

  In general, a reflective mask is manufactured from a reflective mask blank having a structure as shown in FIG. Specifically, on one surface (hereinafter, referred to as a surface) of a substrate 1 having low thermal expansibility, a multilayer reflective layer 2 exhibiting a high reflectivity with respect to the exposure light source wavelength, a protective layer 3 protecting the same, exposure An absorption layer 4 that absorbs a light source wavelength is sequentially laminated, and a back surface conductive film 5 for an electrostatic chuck in the exposure machine is formed on the other surface (hereinafter referred to as a back surface) of the substrate 1.

  When processing from a reflective mask blank to a reflective mask, the absorption layer is partially removed by EB lithography and etching technology. In the case of a structure having a buffer layer, the buffer layer is also removed in the same manner. A circuit pattern including a reflection portion is formed. The light image reflected by the reflection type mask thus produced is transferred onto the semiconductor substrate via the reflection optical system.

  In particular, the multilayer reflective layer used in EUV mask blanks (reflective mask blanks for EUV lithography) is formed alternately with Si (silicon) and Mo (molybdenum) at a thickness of about 4.2 nm and about 2.8 nm, respectively. In total, it consists of 40 to 50 pairs (= about 80 to 100 layers). Si and Mo are used to increase the reflectivity at the interface between Si and Mo because the absorption (extinction coefficient) with respect to EUV light is small and the refractive index difference between EUV light between Si and Mo is large. . A part of the EUV light is reflected at the first interface, but the remaining EUV light transmitted without being reflected can be reflected 40 times (in the case of 40 pairs) at the next interface, and further at the next interface. There is a chance to do. The EUV light reflected at each interface has the same phase, and the sum of them is the EUV reflectivity from the multilayer reflective layer. In EUV mask blanks (EUV mask substrates) sold by blank manufacturers, the ratio is approximately 60 to 65%.

  The EUV mask blank reflectivity (hereinafter referred to as EUV reflectivity) of the EUV mask blank directly affects the throughput (production capacity) of the semiconductor chip manufacturing, and is desired to be as high as possible, but is currently known. As the material and the combination thereof, the above-described multilayer reflection layer of Si and Mo is the best. In order to increase the essential ability to generate reflectivity, it is important that the interface between Si and Mo be formed exactly. For this reason, a method is employed in which Si and Mo are alternately formed (mainly sputtering) without breaking the vacuum in the same vacuum chamber.

In general vacuum film formation (sputtering method), since the material after film formation has a strong internal stress, the stress of the material is adjusted and stabilized by heat treatment (annealing) of the substrate. It is common. However, in the EUV mask blank, when heat treatment is performed after film formation, mixing of Si and Mo materials (diffusion) occurs, and there is a risk of reducing the reflectivity of EUV light.

  As described above, EUV mask blanks and EUV masks are vulnerable to heat, and EUV light has higher energy than conventional exposure wavelengths (ArF excimer laser, KrF excimer laser, i-line, g-line, etc.), and Since the absorption of energy into the mask material is also high, the temperature of the reflective mask is likely to rise significantly during exposure. As a result, there arises a problem that the EUV reflectance is lowered while the exposure is repeated.

  In addition, an increase in the temperature of the mask during exposure also causes thermal expansion of the mask, thereby reducing the positional accuracy of the mask pattern, and as a result, reducing the overlay accuracy (referred to as overlay accuracy) of the wafer pattern. For this reason, the low thermal expansion substrate described above is used for the reflective mask blank so that the mask position accuracy does not deteriorate even with a slight temperature change. However, since the EUV mask blank has a multilayer reflective layer made of Si and Mo and an absorption layer made of Ta material on the surface side of the substrate, even if only the substrate has low thermal expansion, the heat of those materials other than the substrate can be reduced. The expansion is unavoidable, and the mask is also deformed, resulting in a problem that the mask pattern position accuracy and the wafer overlay accuracy are lowered.

  In order to solve such problems, the mask chuck of the EUV exposure apparatus uses a radiation cooling method, a method using a Peltier element (Patent Document 1), or a method using a refrigerant in order to keep the mask temperature constant. (Patent Document 2) has been proposed. In an actual EUV exposure machine, the mask chuck is of an electrostatic chuck type, and a cooling coolant is allowed to flow through the mask chuck to keep the mask chuck temperature constant, thereby keeping the mask temperature constant. A way to keep is taken.

JP 09-92613 A Japanese Patent Laid-Open No. 09-306834

  However, in the current exposure apparatus mask cooling method, since only the back surface of the EUV mask is cooled, a temperature gradient in the thickness direction due to the thickness of the 6.35 mm substrate itself is likely to occur, and EUV light is directly irradiated. The mask surface (pattern surface) to be formed is not sufficiently cooled, resulting in a problem that the temperature becomes high. As a result, mixing occurs in the multilayer reflective layer on the mask surface side and the reflectivity decreases, and the quality of the mask pattern position decreases due to thermal expansion of the material on the mask surface, and the overlay accuracy also decreases. The problem of degradation occurs.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an EUV mask and a mask blank in which the EUV mask surface is effectively cooled (temperature adjustment) during exposure.

  The invention of claim 1 according to the present invention is a reflective mask blank formed by sequentially laminating a multilayer reflective layer, a protective layer, and an absorption layer on one surface of a substrate, wherein the substrate has a heat conductive layer on both sides. The reflective mask blank is formed.

  According to a second aspect of the present invention, in the reflective mask blank according to the first aspect, a heat conductive layer is formed on the front and back sides and side surfaces of the substrate.

  According to a third aspect of the present invention, in the reflective mask blank according to the first or second aspect, the heat conductive layer is made of a material containing carbon or a solid metal.

  According to a fourth aspect of the present invention, the solid metal is selected from at least one of Ag, Cu, Au, Al, Si, Ni, Fe, Pt, W, Cr, Ti, Ru, Ta, and Mo. The reflective mask blank according to claim 3.

  The invention according to claim 5 is the reflective mask blank according to any one of claims 1 to 4, wherein the thermal conductivity of the thermal conductive layer is 50 W / (m · K) or more. is there.

  The invention according to claim 6 is the reflective mask blank according to any one of claims 1 to 5, wherein the film thickness of the heat conductive layer is 0.5 μm or more.

  A seventh aspect of the present invention is a reflective mask produced using the reflective mask blank according to any one of the first to sixth aspects.

According to the present invention, the substrate of the reflective mask formed by sequentially laminating a multilayer reflective layer, a protective layer, and an absorption layer is formed on one surface of the substrate, and a heat conductive layer is formed on the front and back surfaces, and further on the side surfaces. By
The mask surface can be efficiently cooled during EUV exposure. As a result, a decrease in EUV reflectivity and mask deformation caused by heat generation during EUV exposure can be suppressed, and a high-quality semiconductor device can be manufactured for a long time while maintaining the quality of the EUV mask. .

The schematic sectional drawing of the conventional reflective mask blank. The schematic sectional drawing of the structure of the reflective mask blank of this invention. The schematic sectional drawing of the structure of the reflective mask of this invention. The schematic sectional drawing which shows the manufacturing process of the reflective mask blank and reflective mask of an Example. The schematic sectional drawing which concerns on the heating experiment of the mask surface produced in the Example. The mask surface temperature measurement result in the Example by FIG.

  The reflective mask blank according to the present invention and the reflective mask based thereon are characterized in that a heat conductive layer is provided on the front and back surfaces of the substrate having low thermal expansibility, and further on the side surfaces of the substrate.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 2 shows an embodiment of a reflective mask blank according to the present invention. In the reflective mask blank 201 shown in FIG. 2A, a heat conductive layer 6t, a multilayer reflective layer 2, a protective layer 3, and an absorption layer 4 are sequentially laminated on the surface of the substrate 1, and the heat conductive layer is formed on the back surface of the substrate 1. 6b and the conductive film 5 are sequentially laminated.

  Although not shown in FIG. 2, there is also a structure having a buffer layer between the multilayer reflective layer 2 and the absorption layer 4. The buffer layer is a layer provided so as not to damage the underlying protective layer 3 when the mask pattern of the absorption layer 4 is corrected (such as ion beam, mechanical grinding with a fine probe).

  The reflective mask blank 202 shown in FIG. 2 (b) has a configuration in which the conductive film 5 is removed from the reflective mask blank 201 shown in FIG. 2 (a), and the heat conductive layer 6b on the back surface of the substrate 1 is a conductive film. It also features 5 functions.

  A reflective mask blank 203 shown in FIG. 2C is characterized in that a heat conductive layer 6s is also provided on the side surface of the base 1 of the reflective mask blank 201 shown in FIG. That is, by providing the side surface of the substrate 1 with the heat conductive layer 6s, the mask surface can be more effectively cooled (temperature adjustment).

  The reflective mask blank 204 shown in FIG. 2D has a structure in which the conductive film 5 is removed from the structure of the reflective mask blank 203, and the heat conductive layer 6 b on the back surface of the substrate 1 has the function of the conductive film 5. It is also characterized by serving.

  Since the heat conductive layers 6t, 6b, 6s according to the reflective mask blank of the present invention need to be a material for efficiently releasing the heat generated on the surface of the reflective mask during exposure with an EUV exposure machine, A metal material, a carbon material, or a compound thereof having high thermal conductivity.

  In order to satisfy the purpose, the thermal conductivity of the heat conductive layers 6t, 6b, and 6s is 50 W / (m · K) or more. Incidentally, since the thermal conductivity of the low thermal expansion substrate used for a general EUV mask blank is about 1 to 1.5 W / (m · K), the thermal conductive layer used in the present invention is at least 30 times larger. It has the above thermal conductivity.

  The heat conductive layer is preferably made of a material containing C, Ag, Cu, Au, Al, Si, Ni, Fe, Pt, W, Cr, Ti, Ru, Ta, and Mo. For example, the material containing C has several structures, and typical examples include diamond and graphite. Thermal conductivity is the highest for diamond, 1000 W / (m · K) or more, and about 500 W / (m · K) for graphite. Metal materials such as Ag (420), Cu (398), Au (320), and Al (236) also have high thermal conductivity.

  The thickness of the heat conductive layer is preferably 0.5 μm or more. This is because the actual movement of heat is proportional not only to the thermal conductivity but also to the film thickness of the thermal conductive layer, so that a thicker thickness is more preferable.

  The multilayer reflective layer 2 according to the present invention preferably has a reflectance of about 60% with respect to EUV light. Specifically, the multilayer reflective layer 2 is a laminate in which 40 to 50 pairs of molybdenum (Mo) layers and silicon (Si) layers are alternately laminated. A membrane is used. Mo and Si have low absorption (extinction coefficient) for EUV light and a large refractive index difference between Mo and Si EUV light, so that the reflectance at the interface between Si and Mo can be increased. It is used.

  The protective layer 3 formed on the multilayer reflective layer 2 plays a role in protecting the multilayer reflective layer 2 in the stopper layer used for processing the absorption layer 4 laminated thereon or in mask cleaning. It consists of material which has the washing | cleaning tolerance with respect to an alkali. Generally, ruthenium (Ru) or silicon (Si) is used, and specifically, a ruthenium (Ru) layer having a thickness of 2 to 3 nm or a silicon (Si) layer having a thickness of about 10 nm. When Ru is used, the uppermost layer of the multilayer reflective layer 2 adjacent below the protective layer 3 is a Si layer.

  When Si is used for the protective layer 3, a buffer layer may be provided between the protective layer 3 and the absorbing layer 4. Similarly to the protective layer 3, the buffer layer is provided to protect the Si layer, which is the uppermost layer of the multilayer reflective layer 2 adjacent to the buffer layer, when the absorbing layer 4 is etched or the pattern is modified. The nitrogen compound (CrN).

  The absorption layer 4 according to the present invention is preferably a tantalum (Ta) nitrogen compound (TaN) having a high absorption rate with respect to EUV light. As other materials, tantalum boron nitride (TaBN), tantalum silicon (TaSi), tantalum (Ta), oxides thereof (TaBON, TaSiO, TaO), or the like can also be used.

  The absorbing layer 4 may have a two-layer structure in which an upper layer is provided with a low reflection layer having an antireflection function for ultraviolet light having a wavelength of 190 to 260 nm. At this time, the low reflection layer has an effect of increasing the contrast and improving the inspection property with respect to the inspection wavelength of the mask defect inspection machine.

  The conductive film 5 according to the present invention is generally composed of CrN. However, the conductive film 5 is not particularly limited as long as it has electrical conductivity and is made of a metal material. Further, even if the conductive film 5 is not provided, the heat conductive layer 6b shown in FIGS. 2B and 2D having a function as a conductive film may be substituted for the conductive film 5.

  FIG. 3 shows a schematic sectional view of a reflective mask produced using the reflective mask blank (see FIG. 2) according to the present invention described above. In addition, the normal mask preparation method can be used for the method of producing a mask by drawing or an etching process using the reflective mask blank of this invention.

  Hereinafter, the present invention will be described in more detail with reference to the embodiment shown in FIG.

  The low thermal expansion glass substrate shown in FIG. 4A was used as the substrate 1, and Cu was formed with a film thickness of 500 μm by electroless plating as the heat conductive layers 6t, 6b, 6s shown in FIG.

  Next, as shown in FIG. 4C, on the heat conductive layer 6t (surface) formed as described above, the multilayer reflective layer 2 made of Si and Mo, the protective layer 3 made of Ru, and the absorption layer 4 made of TaSi. Were sequentially laminated, and the conductive film 5 made of CrN was formed on the heat conductive layer 6b (back surface) to produce a reflective mask blank 203.

  Next, as shown in FIG. 4D, a positive chemically amplified resist (FEP171: manufactured by FUJIFILM Electronics Materials) is applied on the absorption layer 4 to a film thickness of 300 nm, and an electron beam drawing machine (JBX9000: Japan). The pattern was drawn in a predetermined pattern. Thereafter, a resist pattern 7 was formed by heat treatment at 110 ° C. for 10 minutes and spray development (SFG3000: manufactured by Sigma Meltech Co., Ltd.).

  Next, as shown in FIG. 4E, the absorption layer 4 was etched by dry etching with CF4 plasma and Cl2 plasma using the resist pattern 7 as a mask. Thereafter, the remaining resist was peeled and washed to produce a reflective mask 303 as shown in FIG.

<Comparative Example 1>
Without forming the heat conductive layers 6t, 6b, 6s on the substrate 1, the multilayer reflective layer 2 made of Si and Mo, the protective layer 3 made of Ru, and the absorption layer 4 made of TaSi are sequentially laminated directly on the surface of the substrate 1. In addition, a reflective mask was produced in the same manner as in Example 1 except that the conductive film 5 made of CrN was directly formed on the back surface of the substrate 1.

<Evaluation>
Using the reflective masks obtained in Example 1 and Comparative Example 1, in order to evaluate the heat dissipation of the heat on the surface of each mask, the same situation as the inside of the exposure machine was simulated and experiments were conducted. It was. Specifically, as shown in FIG. 5, each mask is placed so that the back surface of the mask is in contact with a cool plate 10 maintained at 23 degrees Celsius, and heated by an infrared heater 11 disposed at a distance of about 30 cm from the mask surface. The mask surface temperature was measured with the infrared radiation thermometer 12 at that time. The measurement results are shown in FIG.

<Comparison result>
The product of the present invention according to Example 1 showed almost no increase in temperature with respect to the elapsed time, and was kept constant at the surface temperature at the start of the experiment, indicating excellent temperature control results. On the other hand, the comparative example product (conventional product) according to Comparative Example 1 increases in surface temperature with the passage of time, reaches 50 degrees after about 10 minutes, exceeds 140 degrees after about 70 minutes, It was found that the temperature rise continued.

  INDUSTRIAL APPLICABILITY The present invention is useful for a reflective mask blank and a reflective mask that use EUV light, and can suppress a decrease in EUV reflectivity and mask deformation caused by heat generation during exposure, and can manufacture a high-quality semiconductor device. .

  DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Multilayer reflection layer, 3 ... Protective layer, 4 ... Absorption layer, 5 ... Conductive film, 6t ... Thermal conduction layer on the surface side, 6b ... Thermal conduction layer on the back side, 6s ... Thermal conduction on the side side Layers 7, resist patterns 10, cool plates 11, infrared heaters 12, radiation thermometers 101, conventional reflective mask blanks 201, 202, 203, 204, reflective mask blanks 301 according to the present invention 301, 302, 303, 304 ... reflective mask of the present invention

Claims (7)

  A reflective mask blank comprising a multilayer reflective layer, a protective layer, and an absorbing layer sequentially laminated on one surface of a substrate, wherein the substrate has a heat conductive layer formed on both sides thereof Mask blank.   The reflective mask blank according to claim 1, wherein the substrate has heat conductive layers formed on the front and back sides and side surfaces.   The reflective mask blank according to claim 1, wherein the heat conductive layer is made of a material containing carbon or a solid metal.   4. The solid metal according to claim 3, wherein the solid metal is selected from at least one of Ag, Cu, Au, Al, Si, Ni, Fe, Pt, W, Cr, Ti, Ru, Ta, and Mo. Reflective mask blank.   The reflective mask blank according to claim 1, wherein the thermal conductivity of the thermal conductive layer is 50 W / (m · K) or more.   The reflective mask blank according to claim 1, wherein the thickness of the heat conductive layer is 0.5 μm or more.   A reflective mask produced using the reflective mask blank according to claim 1.