JP2006245225A - Stencil mask, blank therefor, and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stencil mask and a mask blank therefor by which the stencil mask with appropriate pattern position accuracy can be obtained without curving or peeling of a thin film, and to provide a method for manufacturing them. <P>SOLUTION: The mask blank for a stencil mask has a double-layer structure and is provided with a supporting substrate and a silicon thin film supported by the supporting substrate, and the stress of the silicon thin film is adjusted at ≥0 MPa and ≤100 MPa. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a mask used for manufacturing a semiconductor device, and more particularly to a mask blank for a stencil mask used for charged particle beam exposure or ion implantation, a stencil mask, and a manufacturing method thereof.

  In recent years, along with miniaturization of semiconductor integrated circuits, research and development such as electron beam lithography and ion beam lithography have been actively conducted as manufacturing techniques thereof, and among such lithography techniques, a method corresponding to semiconductor miniaturization. As a method called a cell projection exposure method or a block exposure method using an electron beam, an EPL (Electron Projection Lithography) method capable of further increasing the throughput, or a LEEPL (Low Energy E-beam Proximity Projection Lithography) method. Projection exposure methods have been developed. As a stencil mask used for EPL or LEEPL, a mask having a transfer penetrating pattern formed on a free-standing silicon thin film (membrane) having a thickness of 2 μm or less is used.

  As a stencil mask substrate used in these lithography, an SOI (Silicon On Insulator) substrate 11 as shown in FIG. 5 is used from the viewpoint of easy microfabrication. The SOI substrate 11 has a laminated structure including a silicon substrate 12, a silicon oxide thin film 13, and a silicon thin film 14.

  The silicon thin film 14 is a portion that becomes a self-supporting membrane. A single crystal silicon substrate or the like is polished to a predetermined film thickness, and a transfer pattern is formed by forming a pattern on the silicon thin film 14. In order to support the self-supporting membrane and maintain the flatness of the mask, the silicon substrate 12 as a support substrate is necessary. As the support substrate 12, a single crystal silicon substrate is used from the viewpoint of processability and availability. The silicon oxide thin film 13 as an intermediate layer is required to process the support substrate 12 or finely process the silicon thin film 14 by etching. That is, the silicon oxide thin film 13 functions as an etching stopper when the support substrate 12 or the silicon thin film 14 is etched to process the opening or the transfer pattern. This is because silicon oxide has a relatively high etching selectivity with respect to single crystal silicon, and therefore the thickness of the silicon oxide thin film itself can be reduced.

  However, the general SOI substrate 11 has a problem that a transfer pattern formed on the single crystal silicon thin film 14 is warped in the manufacturing process of the stencil mask, and a crack is caused by stress concentration depending on the pattern.

In such an SOI substrate 11, the single crystal silicon thin film 14 has a small tensile stress (preferably not less than 0 MPa and not more than 20 MPa), that is, phosphorus having a smaller atomic radius than silicon so that the self-supporting membrane is stretched without slack. It has been dealt with by a method of adjusting stress such as doping with boron or boron, a method of adjusting the stress to a low level by changing the silicon oxide thin film 13 as an etching stopper layer to another material (see, for example, Patent Document 1). ).
JP 2003-338449 A

  However, even if the single crystal silicon thin film 14 is doped with phosphorus or boron, the silicon oxide thin film 13 as an intermediate layer still has high stress, and the silicon oxide thin film 13 is replaced with another material. Even if the stress is adjusted to be low, the upper layer is also affected by the stress of the lower layer, so it is necessary to adjust the stress of the upper single-crystal silicon thin film 14, making it difficult to adjust the stress, and different materials in the mask blank. Existence causes warpage and partial peeling due to thermal stress, and the former particularly affects the positional accuracy after patterning.

  Further, since the silicon oxide layer 13 does not have conductivity, the mask is charged when exposed using the produced stencil mask, the charged particle beam is deflected, and the membrane is destroyed when the sample substrate is replaced depending on the degree of charging. Such a problem also occurs. Furthermore, when irradiating a charged particle beam having high energy such as being used as an ion implantation mask, it is not preferable that silicon oxide having a low thermal conductivity exists because of the necessity of avoiding an increase in the temperature of the mask.

  In addition, a technology to form a silicon thin film by stopping etching halfway using only a silicon substrate was also developed, but due to the in-plane distribution of the etching rate, etching could not be stopped halfway through the substrate. This can be ignored as the size of the substrate increases.

  The present invention has been made in view of such a conventional problem. A mask blank for a stencil mask capable of obtaining a stencil mask having good pattern position accuracy without causing warping or peeling of a thin film, An object of the present invention is to provide a stencil mask and a method for manufacturing the same.

  To achieve the above object, a first aspect of the present invention is a mask blank for a stencil mask having a two-layer structure including a support substrate and a silicon thin film supported by the support substrate, A mask blank characterized in that the stress is adjusted to 0 MPa or more and 100 MPa or less.

  According to such a mask blank, since the stress of the silicon thin film is adjusted to a predetermined value, the silicon thin film is not loosened, and the transfer pattern formed on the silicon thin film is warped or cracked. Phenomenon is suppressed. Furthermore, since it has a simple structure of a two-layer structure, the above effect can be obtained by an easy method of adjusting the stress of only the silicon thin film. Furthermore, by using a silicon thin film, there is an advantage that the technology cultivated in SOI can be applied as it is for patterning and subsequent cleaning.

  In the mask blank according to the first aspect of the present invention, the support substrate may have conductivity. In this manner, by using a conductive support substrate, it is possible to remove charges accumulated on the support substrate side when the charged particle beam is irradiated.

  Further, the silicon thin film can be conductive. As described above, since the silicon thin film has conductivity, it is possible to remove charges accumulated on the silicon thin film side when the charged particle beam is irradiated.

  Furthermore, a silicon wafer can be used as the support substrate. Thus, by using a silicon wafer as the support substrate, the lower limit of the difference in thermal expansion coefficient between the support substrate and the silicon thin film can be reduced to 0, and the positional accuracy deviation due to the influence of thermal stress can be kept low. Can do. Moreover, since it becomes possible to use the same gas and etching equipment as in the case of etching the silicon thin film when etching the support substrate, the cost for equipment investment can be kept low. Further, even when a stencil mask obtained from such a mask blank is used as an ion implantation mask, heat is easily released, so that there is an advantage that a fine pattern is not easily deformed or displaced due to thermal expansion.

  A second aspect of the present invention is a method for manufacturing a mask blank for a stencil mask comprising a support substrate and a silicon thin film supported by the support substrate, the step of forming an etching stopper layer on the support substrate; A step of patterning the back surface of the support substrate to form an opening; a step of forming an opening support layer on the back surface of the support substrate in which the opening is formed; a step of removing the etching stopper layer; Provided is a mask blank manufacturing method comprising a step of forming a silicon thin film on a support substrate surface and a step of removing the opening support layer.

  According to such a mask blank manufacturing method, since the etching stopper layer is removed in the middle of the process and is not included in the final mask blank, a mask blank having a simple structure of a two-layer structure can be manufactured. It becomes possible.

  In the mask blank manufacturing method according to the second aspect of the present invention, the etching stopper layer contains at least one component selected from the group consisting of indium oxide, ITO, chromium, chromium nitride, copper, aluminum, and nickel. It can be taken. By using an etching stopper layer made of such a material, an extremely high selection ratio can be secured when silicon is used as the material of the support substrate, and the etching stopper layer is hardly etched. A silicon thin film having a good surface morphology can be obtained.

  According to a third aspect of the present invention, there is provided a charged particle beam stencil mask characterized in that a transfer pattern is formed on the silicon thin film of the mask blank described above.

  Since such a stencil mask is formed using a mask blank in which the stress of the silicon thin film is adjusted to a predetermined value, the substrate does not warp and the positional accuracy when forming the transfer pattern is good. is there.

  According to a fourth aspect of the present invention, there is provided a method for producing a charged particle beam stencil, further comprising a step of forming a transfer pattern on a silicon thin film after each step in the method for producing a mask blank. .

  According to such a stencil manufacturing method, since a mask blank in which the stress of the silicon thin film is adjusted to a predetermined value is used, it is possible to manufacture a good stencil mask without warping.

  According to the mask blank for a stencil mask and the stencil mask of the present invention, the stress of the silicon thin film is adjusted to a predetermined value, and the stress is adjusted between the transfer pattern and the support substrate. It is possible to prevent the occurrence of deformation and displacement of the fine pattern.

  In addition, according to the mask blank for stencil mask and the method for manufacturing a stencil mask of the present invention, it is possible to obtain a mask blank and a stencil mask that have a simple structure that does not leave an etching stopper layer and that is simple and easy to adjust stress. I can do it.

  Hereinafter, with reference to FIG. 1 and 2, the manufacturing method of the mask blank which concerns on one Embodiment of this invention is demonstrated.

  First, a support substrate 1 as shown in FIG. 1 is prepared. The material used for the support substrate 1 is preferably a material that has a high adhesive force with the silicon thin film 7 to be formed later and has a thermal expansion coefficient that is similar or equal, such as single crystal silicon, polycrystalline silicon, Examples include amorphous silicon. In order to increase the conductivity, it is preferable that these materials are doped with phosphorus, boron or the like to reduce the specific resistance.

  Next, as shown in FIG. 1B, an etching stopper layer 2 for etching the support substrate is formed on the support substrate 1. The material used for the etching stopper layer 2 is desirably a material having an extremely high etching selectivity with respect to the support substrate 1. That is, since the surface form of the bottom surface of the etching affects the surface form of the silicon thin film 7 to be formed later, it is preferable that the surface form is hardly etched.

  Examples of such a material include indium oxide, ITO, chromium, chromium nitride, copper, aluminum, nickel, or a composite thereof.

  As a method for etching the support substrate 1, dry etching is desirable because the support (strut) width between the openings can be narrowed, but wet etching may be used. The material of the etching stopper layer 2 is appropriately changed depending on the etching method.

  The method of forming the etching stopper layer 2 is preferably a sputtering method that can uniformly coat the support substrate 1 and has high adhesion, but any method such as a CVD method, a plating method, or the like may be used and is not limited.

  It is desirable that the stress of the etching stopper layer 2 is set to 0 MPa or more so that the etching stopper layer 2 remaining in the opening 5 after the etching does not loosen.

  As a method of adjusting the stress, a known technique can be applied. That is, a method using thermal stress with the substrate, a method of baking after film formation, and the like. When the etching stopper layer 2 is formed using a material having a thermal expansion coefficient larger than that of the support substrate in a state where the support substrate 1 is heated, a film having a tensile stress during cooling is obtained. It is possible to adjust the stress by appropriately selecting a material having a necessary coefficient of thermal expansion or a heating temperature.

  Further, firing after film formation reduces defects in the film and causes volume shrinkage. This phenomenon can be used to make the film tensile stress, and the stress can be adjusted by appropriately selecting the material of the film, the firing temperature, the time, and the like. In addition, when the sputtering method is used for film formation, a method of controlling the total pressure during film formation can also be applied. These may be used singly or a plurality of methods may be combined, and the stress adjustment method is not limited.

  As a method for measuring the stress of the film, in addition to a method of obtaining from the amount of deformation of the substrate, a so-called bulge method for estimating from the pressure applied to the free-standing membrane and the amount of deformation is known.

  Next, an etching mask material layer 3 is formed on the back surface of the support substrate 1 (the surface opposite to the etching stopper layer 2) (FIG. 1C), and the etching mask material layer 3 is patterned to form an etching mask 4 Then, the back surface of the support substrate 1 is etched using the etching mask 4 as a mask to form an opening 5 (FIG. 1E).

  Here, the method of forming the opening 5 on the back surface of the support substrate 1 is not limited to dry etching, and wet etching may be used. The etching mask material layer 3 is appropriately selected according to the etching method, and a photoresist, a silicon oxide film, a silicon nitride film, a metal film, a metal oxide film, a metal nitride film, or the like can be used.

When a silicon wafer is used as the support substrate 1 and dry etching is used as an etching method for forming the opening 5, a mixed gas mainly composed of a fluorine-based gas (CF ₄ , C ₄ F ₈ , SF _6, etc.) is used. The etching mask material layer 3 can be used in consideration of the etching resistance.

  Examples of the dry etching apparatus include those using a known discharge method such as RIE, ECR, ICP, microwave, helicon wave, and NLD. When dry etching is performed to form the opening 5, when aluminum is used as the etching stopper layer 2, a high selectivity of 30700 with respect to silicon can be expected. Similarly, when chromium is used as the etching stopper layer 2, the selection ratio is 50000.

  Subsequently, after removing the etching mask 4 (FIG. 2A), an opening support layer 6 is formed on the back surface of the support substrate 1 (FIG. 2B). The material of the opening support layer 6 is not particularly limited, and glass, resin, etc. can be used in addition to metal, metal oxide, metal nitride, metal silicide, metal boride and the like.

  After that, since the step of removing the etching stopper layer 2 while leaving the opening support layer 6 is passed, it is desirable to select the material of the opening support layer 6 in consideration of this. For example, when aluminum is selected as the etching stopper layer 2, by selecting nickel or iron for the opening support layer 6, the etching stopper layer 2 is later made of an alkaline solution, and later the opening support layer 6 is made of an acid. Can be removed. When chromium is selected as the etching stopper layer 2, by selecting glass as the opening support layer 6, the etching stopper layer 2 can be removed with sulfuric acid and the opening support layer 6 with hydrofluoric acid. .

  As a method for forming the opening support layer 6, a plating method or a vapor deposition method is preferable because the shape of the back surface of the support substrate 1 is not flat, but a sputtering method, a CVD method, or the like can also be used. In that case, it is preferable to rotate the substrate holder with an inclination. Since the silicon thin film 7 is then formed on the surface of the support substrate 1, the stress of the opening support layer 6 is set to 0 MPa or more so that the opening support layer 6 does not loosen. The stress adjustment method is as described above.

  Next, the etching stopper layer 2 is removed (FIG. 2C). The removal method is not particularly limited, but it may be simple by wet etching.

  Thereafter, a silicon thin film 7 is formed on the surface of the support substrate 1 from which the etching stopper layer 2 has been removed (FIG. 2D). The silicon thin film 7 may be either an amorphous silicon film or a crystalline silicon film. However, when a stencil mask is used as an ion implantation mask, it is necessary to increase the thermal conductivity, and therefore it is desirable to use a crystalline silicon film.

  As a method for forming the silicon thin film 7, a sputtering method that allows uniform coating and high adhesion is preferable, but not limited to the PVD method, a CVD method or the like can be used, and the film forming method is not particular. Depending on the film formation conditions, the stress may act due to the influence of the impurities incorporated into the film or the shape, and the support substrate 1 may be warped. However, by supporting the stress by controlling the stress to form the silicon thin film, Warpage of the substrate 1 can be suppressed. Specifically, the stress control is adjusted so that the stress of the silicon thin film at this time becomes 0 MPa or more and 100 MPa or less. If the pressure is less than 0 MPa, the substrate warps or the membrane becomes slack as shown in FIG. On the other hand, if it exceeds 20 MPa, as shown in FIG. 4B, the substrate is warped, the membrane is cracked, or when the transfer pattern is formed on the membrane, the pattern position is shifted depending on the shape of the pattern. When the stress exceeds 100 MPa, this effect becomes significant, and it can no longer be used as a charged particle beam mask.

  Finally, the opening support layer 6 is removed to complete a mask blank (FIG. 2 (e)).

  According to the mask blank manufacturing method as described above, since the etching stopper layer 2 is removed in the middle of the process and is not included in the final mask blank, a simple mask blank having a two-layer structure is manufactured. I can do it. Further, since the stress of the silicon thin film is adjusted to 0 MPa or more and 100 MPa or less in the mask blank obtained by the above method, the substrate 1 is not warped or the silicon thin film 7 is not loosened.

  Next, a process for manufacturing a transfer mask from the mask blank manufactured as described above will be described with reference to FIG.

  First, a charged particle beam resist 8 is formed on the surface of the silicon thin film 7 (FIG. 3A), and this is patterned by ordinary photolithography or charged particle beam lithography to be used as a mask for patterning the silicon thin film 7. A particle beam resist pattern 9 is formed (FIG. 3B).

Next, using the resist pattern 9 as a mask, the silicon thin film 7 is patterned by dry etching to form a charged beam transmission hole transfer pattern 10 (FIG. 3C). In this case, the dry etching conditions and the like are not particularly limited. Examples of the gas used for this etching include fluorine-based gases such as CH ₄ , C ₄ F ₈ , and SF ₆ , or a mixed gas thereof. Examples of the dry etching apparatus include a dry etching apparatus using a discharge method such as RIE, magnetron RIE, ECR, ICP, microwave, helicon wave, and NLD.

  Finally, the charged particle beam resist pattern 9 is removed to complete a stencil mask having the charged beam transmission hole pattern 10 (FIG. 3D).

  Since the stencil mask manufactured as described above is formed using a mask blank in which the stress of the silicon thin film 7 is adjusted to 0 MPa or more and 100 MPa or less, the substrate 1 is not warped and formed. The positional accuracy of the charged beam transmission hole pattern is good.

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

  First, a blank for a charged particle beam exposure mask was manufactured by the process shown in FIGS.

  First, a boron-doped single crystal silicon wafer having a low resistivity is used as the support substrate 1 (FIG. 1A), and an aluminum film is formed thereon by sputtering and baked to form an etching stopper layer 2. (FIG. 1B). The sputtering of the aluminum film was performed with a DC magnetron sputtering apparatus using an aluminum target and argon as a sputtering gas at an input power of 300 W.

  Next, a resist film 3 was applied to the back surface of the support substrate 1 using a spin coater and baked (FIG. 1C). Subsequently, the resist film 3 was contact-exposed using a photomask for producing the opening 5 and developed with an alkali developer to form a resist pattern 4 (FIG. 1D).

Next, using the resist pattern 4 as a mask, the back surface of the support substrate 1 was etched by a dry etching apparatus using SF ₆ gas to form an opening 5 in the support substrate 1 (FIG. 1E). Then, the resist pattern 4 was removed by an oxygen plasma ashing device (FIG. 2A).

  Thereafter, a nickel thin film (not shown) is sputter-deposited as a conductive layer for plating on the back surface of the support substrate 1, and then nickel plating is performed by an electrolytic plating method to form the opening support layer 6 ( Next, the etching stopper layer 2 was removed with an aqueous potassium hydroxide solution (FIG. 2B).

  Next, a silicon film 7 having a low specific resistance is formed on the surface of the support substrate 1 by a sputtering method using a low specific resistance silicon target, argon as a sputtering gas, and a DC magnetron sputtering apparatus with an input power of 300 W. And baked (FIG. 2D).

  Subsequently, the opening support layer 6 was removed with hydrochloric acid, and the charged particle beam exposure mask blank according to this example was completed (FIG. 2E).

  Subsequently, a transfer mask was manufactured from the mask blank manufactured as described above by the process shown in FIG.

  First, a resist film was formed on the surface of the silicon thin film 7 using a spin coater and baked to form a charged particle beam resist film 8 (FIG. 3A). Subsequently, drawing was performed on the charged particle beam resist 8 with an electron beam drawing machine, and development was performed using a dedicated alkali developer, thereby forming a resist pattern 9 serving as a semiconductor circuit pattern on the charged particle beam resist 8 ( FIG. 3 (b)).

  Next, by using the resist pattern 9 as a mask, the silicon thin film 7 was etched by a dry etching apparatus using a fluorocarbon mixed gas to form a charged beam transmission hole transfer pattern 10 (FIG. 3C).

  Finally, the remaining charged particle beam resist pattern 9 was removed with an organic solvent to complete a charged particle beam exposure mask (FIG. 3D).

  The mask manufactured as described above is a stencil mask in which in-plane pattern deformation is suppressed even after the transfer pattern is formed, and the position accuracy of the transfer pattern is good.

  The mask blank for a stencil mask of the present invention and the stencil mask obtained thereby can be widely used in various semiconductor device manufacturing processes.

It is sectional drawing which shows an example of the manufacturing process of the mask blank which concerns on one Embodiment of this invention. It is sectional drawing which shows an example of the manufacturing process of the mask blank which concerns on one Embodiment of this invention. It is sectional drawing which shows an example of the manufacturing process of the stencil mask using the mask blank which concerns on one Embodiment of this invention. It is a schematic diagram which shows the mode of the curvature of the board | substrate which formed into a film without adjusting stress. It is the schematic explaining the state of the SOI substrate generally used.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Support substrate, 2 ... Etching stopper layer, 3 ... Etching mask material layer, 4 ... Etching mask, 5 ... Opening, 6 ... Opening support layer, 7 ... Silicon thin film, 8 ... Charged particle beam resist film, 9 ... Charged particle beam resist pattern, 10 ... charge beam transmission hole transfer pattern, 11 ... SOI substrate, 12 ... silicon substrate, 13 ... silicon oxide thin film, 14 ... silicon thin film.

Claims (8)

  A mask blank for a stencil mask having a two-layer structure including a supporting substrate and a silicon thin film supported by the supporting substrate, wherein the stress of the silicon thin film is adjusted to 0 MPa or more and 100 MPa or less. Mask blank.   The mask blank according to claim 1, wherein the support substrate has conductivity.   The mask blank according to claim 1, wherein the silicon thin film has conductivity.   The mask blank according to claim 1, wherein the support substrate is a silicon wafer. A method for producing a mask blank for a stencil mask comprising a support substrate and a silicon thin film supported by the support substrate,
Forming an etching stopper layer on the support substrate;
Patterning the back surface of the support substrate to form an opening;
Forming an opening support layer on the back surface of the support substrate on which the opening is formed;
Removing the etching stopper layer;
Forming a silicon thin film on the support substrate surface;
And a step of removing the opening support layer. A method for manufacturing a mask blank, comprising:   6. The method for manufacturing a mask blank according to claim 5, wherein the etching stopper layer includes at least one selected from the group consisting of indium oxide, ITO, chromium, chromium nitride, copper, aluminum, and nickel.   A charged particle beam stencil mask, comprising a transfer pattern formed on the silicon thin film of the mask blank according to claim 1.     The method for producing a charged particle beam stencil mask according to claim 5, further comprising a step of patterning the silicon thin film to form a transfer pattern after each step in the method for producing a mask blank according to claim 5.

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