JP2009231670A - Stencil mask or apertures and their production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stencil mask or an aperture, which has an extremely small corner R value of rectangle opening pattern, thereby forming a resist pattern in a good rectangular shape, and to provide its production method. <P>SOLUTION: The stencil mask or the aperture includes a thermal oxidation film formed at a comparatively low temperature at least on its side or on its whole surface of opening pattern, thereby achieving a small corner R value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a stencil mask or aperture and a method for manufacturing the same.

  In recent years, miniaturization of LSIs and the like has progressed rapidly, and development of lithography techniques for forming further fine circuit patterns of these elements has been promoted. In particular, in pattern formation with a line width of 65 nm or less, the exposure method using a conventional ArF excimer laser as an exposure light source reaches the resolution limit, making pattern formation difficult. Therefore, as an alternative lithography technique, an immersion lithography method that fills the space between the lens and the wafer to be exposed with a medium having a higher refractive index than air and improves the effective resolution has attracted attention. According to this method, it is expected that a pattern of 65 nm or less, which has been difficult to form with a conventional ArF excimer laser, can be formed.

  However, when the immersion lithography method is used, the effective resolution can be improved, but the depth of focus becomes shallow, so that it is difficult to form a high aspect ratio hole pattern or the like. In addition, the resolution limit may be reached for a fine pattern of 45 nm node or less by the immersion lithography method.

  One of the methods for solving this problem is charged particle beam lithography. The charged particle beam lithography is a technique that uses a charged particle beam such as an electron beam or an ion beam as an exposure light source instead of an excimer laser such as ArF or KrF that has been conventionally used. In charged particle beam lithography, a charged particle beam serving as an exposure light source is irradiated onto a stencil mask or aperture in which a desired charged particle beam transmission hole is formed, and a resist on the wafer is exposed to form a fine pattern.

  Among charged particle beam lithography, a partial collective exposure method using an electron beam as an exposure light source is expected as a fine pattern forming technique of 65 nm node or less. A stencil mask used in the partial collective exposure system is formed with a rectangular pattern called a variable forming portion and various element patterns that repeatedly appear in the transfer pattern. An arbitrary rectangular shot is mainly formed using a variable shaped part formed on the stencil mask and a rectangular opening pattern formed on the aperture, and the transfer pattern is scanned and drawn. This is an exposure method that improves drawing throughput by performing batch exposure using a pattern formed on a mask.

  When partial batch exposure is performed using a stencil mask or aperture, it is important that the corner R value in the rectangular opening pattern including the variable forming portion formed on the stencil mask or aperture is small. This is because when the corner R value in the rectangular opening pattern is large, the shape accuracy of the pattern transferred onto the wafer is deteriorated. The corner R value is a radius of a circle inscribed in the corner in the rectangular opening pattern. The larger the corner R value, the more rounded the corner shape.

As a method for improving the accuracy of the corner R value in the rectangular opening pattern on the stencil mask or the aperture, for example, a method of controlling the etching conditions in producing the stencil mask has been proposed (see Patent Document 1).
JP 2001-358069 A

  However, in the actual etching process, it is difficult to allow the etching to proceed completely in the vertical direction with respect to the opening provided in the resist, oxide film, or the like serving as an etching mask. Etching proceeds to some extent toward the outside.

  In addition, as the material of the etching mask, a material having high resistance to the etching conditions to be used is used, but the etching mask itself is generally etched at a certain rate. For this reason, the etching mask is etched by a minute amount as the etching progresses, and the opening size gradually increases. As a result, the opening size of the etching pattern on the wafer surface becomes larger than the opening size of the initial etching mask.

  These phenomena are collectively referred to as side etching. Due to this influence, the corner R value in the etching pattern of the rectangular opening is increased. This is because when the corner R value of the initial rectangular opening is 0 and the side etching proceeds at a constant rate, the corner portion of the rectangular opening proceeds in a fan shape starting from the initial corner portion. Because it becomes. As a result, the corner R value increases.

  Even if the side etching is not performed at all, it is necessary to consider the shape of the first etching mask itself as a previous problem. In general, a pattern is formed on a resist by using a technique such as photolithography or electron beam lithography. However, in the rectangular portion of this pattern, it is impossible to set the corner R value to 0 in reality. It must have a corner R value of As a result, the corner R value of the final rectangular opening of the stencil mask or aperture is further increased.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a stencil mask or aperture having a small corner R value of a rectangular opening pattern, and a manufacturing method thereof.

According to the first aspect of the present invention, in the stencil mask or aperture having a rectangular opening pattern on at least the substrate, at least an oxide film is provided on at least a side surface of the rectangular opening pattern, so that the corner R of the rectangular opening pattern is obtained. A stencil mask or aperture having a reduced value.
According to a second aspect of the present invention, at least a side surface or an entire surface of the rectangular opening pattern is provided with at least an oxide film, and at least a surface of the oxide film is provided with a conductive film, whereby the corner R of the rectangular opening pattern is provided. The stencil mask or aperture according to claim 1, wherein the stencil mask or aperture is formed by reducing the value and imparting conductivity to the surface.
Invention of Claim 3 is a manufacturing method of the stencil mask or aperture of Claim 1,
Forming an opening pattern on the substrate;
Forming an oxide film by thermally oxidizing at least a side surface or the entire surface of the opening pattern at a relatively low temperature;
A method for producing a stencil mask or aperture.
Invention of Claim 4 is a manufacturing method of the stencil mask or aperture of Claim 2,
Forming an opening pattern on the substrate;
Forming an oxide film by thermally oxidizing at least a side surface or an entire surface of the opening pattern at a relatively low temperature;
Forming a conductive film on the entire surface of the oxide film;
A method for manufacturing a stencil mask or an aperture.

  Hereinafter, the reason why the corner R value in the rectangular opening of the stencil mask or the aperture becomes small and the effect thereof according to the present invention will be described.

  When silicon is oxidized, if there are irregularities or openings on the surface, a phenomenon is known in which the thickness of the oxide film formed locally changes depending on the shape (see Patent Document 1).

Furthermore, an attempt has been made to use this phenomenon as a near-field light device by providing a fine opening in a probe used in a scanning probe microscope or the like. (See the following non-patent literature).
Non-Patent Document 1: J. Electrochem. Soc., Vol. 129, 1278 (1982)
Non-Patent Document 2: Appl. Phys. Lett., Vol.75, 4076 (1999)

  According to the contents described in Non-Patent Documents 1 and 2, when the thermal oxide film is formed at a relatively low temperature (for example, about 950 ° C.), the oxide film thickness at the concave and convex corners is flat. It is thinner than that in the place. This is because compressive stress is generated in the corner due to volume expansion during oxidation. The thing which illustrated this phenomenon is FIG.

  As shown in FIG. 1, the oxide film 102 after thermal oxidation is formed on both the inside and outside of the initial silicon surface 101. This is because oxygen atoms enter the inside from the silicon surface 101 and this reaction causes the reaction. This is because the volume expands. As a result, in the corner of the concave shape (the angle formed by the two sides forming the corner is smaller than 180 °), the angle of the corner 103 formed by the oxide film surface after oxidation is smaller than that formed by the initial silicon, Presents a notch shape.

  On the other hand, if the angle formed by the convex corners, that is, the two sides forming the corner is larger than 180 °, the angle of the corner 104 formed by the oxide film surface after oxidation becomes larger than that formed by the initial silicon, The corner becomes dull.

  Consider applying this phenomenon to a typical rectangular opening in a stencil mask or aperture. When the opening 201 before oxidation has a strictly geometric rectangular shape, in other words, when the angle formed by the two sides forming the corner is 90 ° and the corner R value is 0, the opening 202 after oxidation is formed. As shown in FIG. 2 (a), the shape is such that four corners have notches. This is clear from the above description.

  On the other hand, FIG. 2B shows a case where the rectangular opening shape of the stencil mask or aperture is deformed by the influence of lithography or etching and has a corner R value larger than zero. In this case, if thermal oxidation is performed on the opening 203 before oxidation, the compressive stress generated in the corner portion is completely ignored, and the oxide film surface is grown isotropically toward the inside of the rectangle. Even in this case, it is clear from geometrical consideration that the corner R value decreases with growth.

  Actually, the degree of the initial corner R value is lower than that when the initial corner R value is 0 (because the compressive stress generated in the corner portion is small), but the growth rate of the oxide film also decreases in the vicinity of the corner. The thickness is thinner than the flat part. As a result, the oxidized oxide film surface has a slightly blunt notch shape at the corner as shown in FIG. 2B, but the oxidized rectangular surface is smaller than the corner R value of the initial rectangular opening 203. The corner R value of 204 becomes small.

  Based on the above principle, in the stencil mask or aperture of the present invention, it is possible to reduce the corner R value of the rectangular opening pattern enlarged by side etching by oxidizing the side surface or the entire surface of the rectangular opening pattern. Beam exposure can be performed.

  On the other hand, when an oxide film as an insulator is formed on the entire surface, there is a concern that the mask itself will be charged (charge up), particularly when using an electron beam or ion beam. The present invention provides means for solving the problem by oxidizing only the side surface of the opening pattern or by forming a thin conductive film on the entire surface after oxidizing the side surface or the entire surface of the opening pattern.

Hereinafter, the stencil mask or aperture of the present invention will be described.
The stencil mask or aperture of the present invention is characterized in that in the stencil mask or aperture having an opening pattern on the substrate, a thermal oxide film is provided on the side surface or the entire surface of the opening pattern.

  As for the opening pattern, the opening pattern may be formed on the substrate according to the desired design pattern, and a known method may be used as appropriate. For example, you may manufacture using well-known lithography, an etching technique, etc.

  The stencil mask or aperture of the present invention is characterized in that after an opening pattern is appropriately formed using a known method, at least the side surface of the opening pattern is thermally oxidized. At this time, not only the side surface of the opening pattern but also the entire surface of the stencil mask or the aperture may be oxidized. At least the corner R value of the opening pattern can be improved by thermally oxidizing the film on the side surface of the opening pattern.

  In order to determine the process conditions of the thermal oxidation process, for example, the oxidation temperature, the processing time, etc., it is necessary to measure the corner R value of the opening pattern with a measuring device such as a CD-SEM before processing and to determine it according to the result. . Further, it is desirable to try various conditions in advance as to what thermal oxidation conditions are applied according to the value of the initial corner R value. The “thermal oxidation at a relatively low temperature” in the present invention is carried out by heating in the presence of oxygen at, for example, 800 to 1050 ° C. (more specifically, around 950 ° C.).

  From the viewpoint of simply improving the corner R value, it can be said that the method of performing thermal oxidation on the entire surface is desirable because the number of steps is minimized. On the other hand, since the oxide film is an insulator, when it is used as a stencil mask or aperture for charged particle beam exposure, the surface may be charged, which may cause a problem of bending the traveling direction of the charged particle beam. As a solution to this problem, a method of forming a thin conductive film on the entire surface of the opening pattern surface on which the thermal oxide film is formed has been shown.

  Hereinafter, specific steps of the embodiment of the present invention will be described.

  First, a silicon substrate is prepared. This substrate has a three-layer structure including a stencil layer made of silicon having a thickness of about several hundreds of nanometers to several tens of microns, a supporting layer having a thickness of several hundreds of microns, and a boundary layer thereof. In view of the characteristics required for the substrate, it is considered most effective to use the SOI substrate. However, as long as necessary characteristics can be satisfied, other types of substrates may be used, and any two or more of the above three layers may be used.

  The step of forming the opening pattern on the substrate by etching may use a pattern forming method using a known etching technique as appropriate. For example, a resist resin may be applied to the substrate, pattern exposure may be performed, and etching may be performed.

  Next, a thermal oxide film is formed at a relatively low temperature of about 950 ° C. on at least the side surface of the opening pattern. Actually, a thermal oxide film may be formed on the entire surface of the substrate on which the opening pattern is formed.

  Hereinafter, the stencil mask or aperture manufacturing method of the present invention will be described with a specific example. The stencil mask or aperture manufacturing method of the present invention is not limited to the following examples, and includes other manufacturing methods that can be analogized. For example, although the following example shows a manufacturing method for processing the support layer after processing the thin film layer, a manufacturing method for processing the thin film layer after processing the support layer may be used. Alternatively, a manufacturing method may be used in which a support layer is formed on a substrate other than the SOI substrate and then processed. Further, the stencil mask or aperture of the present invention is not limited to the configuration of the stencil mask or aperture manufactured in the following embodiment.

  First, an etching stopper layer 320 made of a 1.0 μm thick silicon oxide film is formed on the upper surface of a 100 mmφ support layer 310 made of 500 μm thick single crystal silicon, and further, a 5 μm thick single crystal silicon is made on the upper surface of the etching stopper layer 320. A substrate (SOI substrate) having a thin film layer 330 formed thereon was prepared (FIG. 3A).

  Next, an electron beam resist 340 is applied to the upper surface of the thin film layer 330 by a spinner to form a photosensitive layer having a thickness of 0.5 μm, and a resist opening pattern 341 is formed by performing patterning processing such as electron beam drawing and development. (FIG. 1 (b)). At this time, in the resist opening pattern 341, the corner R value in the rectangular opening pattern was 100 nm (FIG. 1 (b ′)).

  Next, using the resist opening pattern 341 as an etching mask, the thin film layer 330 is etched by dry etching using fluorocarbon mixed gas plasma, and then the electron beam resist 340 is removed by oxygen plasma ashing. A thin film layer opening pattern 331 was formed (FIG. 1C). The corner R value of the opening pattern 331 in the rectangular opening pattern was 150 nm, which was larger than the resist opening pattern 341 (FIG. 1 (c ′)).

  Next, a photoresist is applied to the lower surface of the support layer 310 with a spinner to form a backside resist layer 350 having a thickness of 20 μm, and patterning processing such as exposure and development so that the position coincides with the thin film layer opening pattern 331. To form a back resist pattern 351 (FIG. 1D).

  Next, the support layer 310 is etched by dry etching using a fluorocarbon-based mixed gas plasma with the backside resist pattern 351 as an etching mask, and further wet etching using 5% concentration hydrofluoric acid, The etching stopper layer 320 was removed, and a support layer opening 311 and an etching stopper layer opening 321 were formed. Thereby, a membrane composed of the thin film layer 330 was formed. Further, the unnecessary back resist layer 350 was removed by oxygen plasma ashing (FIG. 1 (e)).

  Next, thermal oxidation was performed at a temperature of 950 ° C. to form a thermal oxide film 360 having a thickness of 50 nm on the entire surface (FIG. 3F). As a result, the corner R value of the opening pattern 361 in which the thermal oxide film was formed on the side surface became 100 nm or less, which was improved to a value smaller than that of the thin film layer opening pattern 331 (FIG. 3 (f ′)).

  By the above steps, a stencil mask or aperture having a rectangular opening with a small corner R value, which is an object of the present invention, can be produced. This stencil mask or aperture can be used as it is for charged particle beam lithography.

  However, when the problem of charging the stencil mask or aperture occurs during use, it is necessary to impart conductivity to the surface of the stencil mask or aperture. Therefore, a metal thin film such as Ta or Mo is formed by sputtering. A stencil mask or aperture having a surface provided with conductivity was prepared by forming 370 on the entire surface of the stencil mask or aperture with a thickness of about 10 to 100 nm and having an opening pattern 371 having a metal thin film formed on the side surface (see FIG. 3 (g)).

It is the figure which showed how the shape of the silicon surface changes by the thermal oxidation at comparatively low temperature. It is the figure which showed that the corner R value of a rectangular opening changes by the thermal oxidation at comparatively low temperature. It is the figure which showed the manufacturing method of the stencil mask or aperture which concerns on this invention.

Explanation of symbols

101, 201, 203... Silicon surface 102, 202, 204 before thermal oxidation ... Convex shape of concave corner portion 104 ... 102 of thermal oxide film 103 ... 102 formed at relatively low temperature Corner portion 310... Opening portion 320 formed in support layer 311... 311... Opening portion 330 formed in etching stopper layer 321. ... 340... Opening 350 patterned with electron beam resist layer 341... 340... Opening 360 patterned with back resist layer 351... 350. Opening 370 in which 360 is formed on the side surface of the thermal oxide film 361... 331... Opening in which 370 is formed on the side surface of the conductive thin film 371.

Claims (4)

  In a stencil mask or aperture having a rectangular opening pattern at least on a substrate, at least an oxide film is provided on at least a side surface of the rectangular opening pattern, thereby reducing the corner R value of the rectangular opening pattern. A stencil mask or aperture.   By providing at least an oxide film on at least the side surface or the entire surface of the rectangular opening pattern, and further providing a conductive film on the surface of the oxide film, the corner R value of the rectangular opening pattern is reduced and the surface is electrically conductive. The stencil mask or aperture according to claim 1, wherein the stencil mask or the aperture is given. A method for producing a stencil mask or aperture according to claim 1,
Forming an opening pattern on the substrate;
Forming an oxide film by thermally oxidizing at least a side surface or the entire surface of the opening pattern at a relatively low temperature;
A method for producing a stencil mask or aperture. A method for producing a stencil mask or aperture according to claim 2,
Forming an opening pattern on the substrate;
Forming an oxide film by thermally oxidizing at least a side surface or the entire surface of the opening pattern at a relatively low temperature;
Forming a conductive film on the entire surface of the oxide film;
A method of manufacturing a stencil mask or aperture.

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