JP2006228767A - Mask for extreme ultraviolet ray exposure, mask blank, and exposure method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mask for extreme ultraviolet ray exposure improved in defect inspection performance by DUV exposure and prevented in position deviation from occurring when drawing electron beams, to provide a mask blank for the mask, and to provide an exposure method using such a mask. <P>SOLUTION: The mask blank for extreme ultraviolet ray exposure comprises a high-reflection section made of a multilayered film formed on a substrate, and a low-reflection layer made of an absorption film formed on the multilayered film. In the mask blank, the absorption film is made of a thin film comprising at least two layers. In the thin film on the uppermost layer, an exhaustion coefficient to an ultraviolet ray having a wavelength of 150-300 nm ranges from 0 to 1.2 and sheet resistance is 50 MΩ/square or smaller. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an extreme ultraviolet exposure mask, a mask blank, and an exposure method, and more particularly, to a reflective photomask, a mask blank, and an exposure method for performing pattern exposure using extreme ultraviolet light as exposure light.

  With the progress of miniaturization technology of semiconductor integrated circuits, the wavelength of light used in photolithography technology for miniaturization has been gradually shortened.

  That is, as a light source, the KrF excimer laser (wavelength 248 nm) that has been used so far is being switched to an ArF excimer laser (wavelength 193 nm), and the use of an F2 excimer laser (wavelength 157 nm) has been proposed and developed. Yes.

  However, even with the F2 excimer laser, it is not easy to use it as a lithography technique for manufacturing a device having a line width of 50 nm or less in the future due to exposure apparatus and resist problems. For this reason, research and development on EUV lithography using extreme ultraviolet (Extreme UV, hereinafter abbreviated as EUV) whose wavelength is one or more orders of magnitude shorter than that of excimer laser light (10 to 15 nm) is being advanced.

  EUV exposure is particularly a promising lithography candidate for producing devices having a line width of 45 nm or less, and application to device mass production from around 2010 is predicted.

  In EUV exposure, since the wavelength is short as described above, the refractive index of a substance is almost close to the value of vacuum, and the difference in light absorption between materials is also small. For this reason, in the EUV region, a conventional transmissive refractive optical system cannot be assembled, resulting in a reflective optical system, and thus the mask is also a reflective mask. A general EUV mask that has been developed so far is a highly reflective region in which a multilayer film part of, for example, about 40 pairs of two-layer films made of Mo and Si is stacked on a Si wafer or glass substrate, and a low-reflection film on the multilayer film. It has a structure in which a metal film pattern is formed as a region (absorption film).

  In such a defect inspection of the EUV mask pattern, since the line width is small, reflected light by DUV (far ultraviolet) having a short wavelength is used. In order to increase the inspection accuracy, the contrast C = (R1−R2) / (R1 + R2) × 100% when the reflectance of the multilayer film portion with respect to DUV light is R1 and the reflectance of the absorption film portion is R2 is at least 50%. % Or more is necessary.

  In addition, if the electric insulation of the absorption film, which is the base of the electron beam resist, is large during electron beam drawing in the mask manufacturing process, charge-up occurs and the drawing pattern is displaced, so the sheet resistance Rs of the absorption film is lowered. There is a need.

However, no absorption film material having a high contrast with the multilayer film and having low electrical insulation has not been found so far.
JP 2002-122981 A

  The present invention has been made in view of the above circumstances, improves the defect inspection performance by DUV exposure, and does not cause misalignment during electron beam drawing, an extreme ultraviolet exposure mask, and a mask blank therefor, and so on. An object of the present invention is to provide an exposure method using a simple mask.

  As a result of repeated studies to solve the above-mentioned problems, the present inventors can increase the contrast with the multilayer film in order to improve the defect inspection performance by DUV exposure, and at the time of electron beam drawing. The present inventors have found a material and a film structure of an absorption film having low electrical insulation so as not to cause displacement. The present invention is based on such knowledge.

That is, the first aspect of the present invention is an extreme ultraviolet exposure mask blank comprising a high reflection layer comprising a multilayer film formed on a substrate and a low reflection layer comprising an absorption film formed on the multilayer film. The absorption film is composed of two or more thin films, and the uppermost thin film has an extinction coefficient in the range of 0 to 1.2 with respect to ultraviolet light having a wavelength of 150 nm to 300 nm, and a sheet resistance of 50 MΩ / □ or less. An extreme ultraviolet exposure mask blank is provided.

  In the extreme ultraviolet exposure mask blank configured as described above, the uppermost thin film of the absorption film has an extinction coefficient in the range of 0.1 to 1.0 for ultraviolet light having a wavelength of 150 nm to 300 nm. I can do it. In addition, the uppermost thin film of the absorption film may have a refractive index in the range of 1.5 to 2.5 with respect to ultraviolet rays having a wavelength of 150 nm to 300 nm.

  Further, the uppermost thin film of the absorption film can contain metal, silicon, and oxygen as main constituent elements. In addition, the uppermost thin film of the absorption film can contain metal, silicon, oxygen, and nitrogen as main constituent elements.

According to a second aspect of the present invention, there is provided an extreme ultraviolet exposure mask, wherein the absorption layer of the above-described extreme ultraviolet exposure mask blank is formed into an absorption layer pattern.

  According to a third aspect of the present invention, there is provided an exposure method characterized by irradiating the above-mentioned extreme ultraviolet exposure mask with extreme ultraviolet light and irradiating the object with the reflected light.

  According to the present invention, the absorption film is composed of two or more thin films, and the uppermost thin film has an extinction coefficient in the range of 0 to 1.2 with respect to ultraviolet light having a wavelength of 150 nm to 300 nm, and a sheet resistance of 50 MΩ / By making the following, it is possible to improve the defect inspection performance by DUV exposure and to obtain a mask blank for an extreme ultraviolet exposure mask that does not cause misalignment during electron beam drawing.

  The best mode for carrying out the invention will be described below.

  FIG. 1 is a sectional view showing an extreme ultraviolet exposure mask according to an embodiment of the present invention. As shown in FIG. 1, an extreme ultraviolet exposure mask 1 includes a low thermal expansion glass substrate 2, a high reflection portion 3 formed on the low thermal expansion glass substrate 2, and a cap formed on the high reflection portion 3. The layer 4 and the low reflection part 5 formed on a part of the cap layer 4 are provided.

  As the highly reflective portion 3, for example, a laminated body in which, for example, 40 pairs of molybdenum layers and silicon layers are alternately formed can be used. The total thickness of this laminate is, for example, 2.5 to 3.0 μm.

  As the cap layer 4, for example, a silicon film having a thickness of 11 nm can be used.

  The low reflection portion 5 is an absorption film made up of two or more thin films, and FIG. 1 shows a case of two layers made up of an upper absorption film 5a and a lower absorption film 5b. In addition, although the buffer film 6 is provided between the cap layer 4 and the lower layer absorption film 5b, this is not necessarily provided.

  The lower absorption film 5b is a film that mainly absorbs EUV light. For example, a TaSi film containing a large amount of Ta component having a large absorption capacity is employed, and a thick film of about 700 A is used to absorb sufficient EUV light. Thickness is adopted. At the same time, the TaSi film has a large absorbability for DUV light used for defect inspection.

  Since the lower absorption film 5b is also a thick film, most of the DUV light incident on the lower absorption film 5b is absorbed in the lower absorption film 5b. For this reason, the following examination results are hardly influenced by the buffer film below the lower absorption film 5b.

  On the other hand, the upper-layer absorption film 5a is a film mainly responsible for an antireflection effect for reducing the reflectivity (R2) with respect to DUV light by the thin film interference effect. Therefore, the upper-layer absorption film 5a needs to be a film that is transparent to some extent with respect to DUV light, and a film thickness of 50 to 300A, for example, about 200A at most is suitable for the antireflection effect.

  In order to obtain an optimum upper-layer absorption film 5a in which the high contrast between the high-reflection portion and the low-reflection portion is obtained and the sheet resistance of the surface of the low-reflection portion is low, the present inventors Various calculations were performed on the relationship between the constant and the reflectance contrast.

  Note that the contrast C of the upper film of the absorbing film was defined by the following equation.

C = (R1-R2) / (R1 + R2) × 100%
R1: Reflectivity of the high reflection portion R2: Reflectance of the low reflection portion The calculation results regarding the relationship between the optical constant of the upper-layer absorption film 5a and the reflectance contrast are shown in FIGS. Note that the lower absorption film 5b is a TaSi film having a thickness of 700A, and in the figure, the optical constants (refractive index: n, extinction coefficient: k) of the upper absorption film 5a are set as the horizontal axis and the vertical axis, respectively, and the contrast C is set. It is represented by contour lines.

  The film thickness of the upper absorption film 5b is three types of 150A, 200A, and 250A, and the inspection wavelength (DUV light) is represented by two types of 257 nm and 193 nm.

  That is, FIG. 2 shows the case where the film thickness of the upper absorption film 5b is 200 A and the inspection wavelength is 257 nm, FIG. 3 shows the case where the film thickness of the upper absorption film 5 b is 200 A and the inspection wavelength is 193 nm, and FIG. When the film thickness of the film 5b is 150A and the inspection wavelength is 193 nm, FIG. 5 shows the case where the film thickness of the upper absorption film 5b is 250A and the inspection wavelength is 193 nm.

  The following can be seen from FIGS.

  That is, when the inspection wavelength is shortened, the optimum range of n and k (the range where the contrast C is high) moves in a direction where n becomes smaller and k becomes larger. Similarly, when the thickness of the upper absorption film 5b increases, the optimum range moves in a direction in which n decreases.

  However, in any case, it can be seen that the preferable range of k of the upper absorption film 5a is around 0 to 1.2. The optimum value of k is around 0.3. Similarly, a preferred range for n is around 1.5 to 2.5.

  As described above, the upper absorption film 5a needs to be a relatively transparent film with 0 <k <1.2. Accordingly, a simple metal film cannot be used as the material of the upper absorption film 5a, and a compound film containing oxygen or nitrogen is better. These oxide films and nitride films can be produced, for example, by reactive sputtering in which a reactive gas such as oxygen or nitrogen is mixed with a normal inert gas.

  By the way, a transparent film has a higher electrical insulating property, and if electron beam drawing is performed on such a film, the pattern is displaced and the position of the pattern is shifted. Therefore, the transparent film is not suitable for electron beam drawing. is there. Therefore, when an electron beam is drawn on a highly insulating film, a conductive polymer having a sheet resistance of usually about 50 MΩ / □ is applied on the electron beam resist in order to prevent charge-up. However, the use of a conductive polymer is undesirable because it increases the number of processes and defects.

Therefore, it is necessary to obtain the optimum upper-layer absorption film 5a so as to satisfy two contradictory characteristics such as optical transparency and electrical conductivity as necessary characteristics for the upper-layer absorption film 5a.
By the way, when performing reactive sputtering using a metal target, a metallic light-shielding film can be obtained while the mixing ratio of the reactive gas to the inert gas is small. It becomes a transparent film. Accordingly, it is difficult to obtain a film having both transparency and conductivity as described above by this method.

  In order to mitigate a rapid change from light shielding properties to transparency, reactive sputtering may be performed using a compound target including a metal and silicon (Si), which is a semiconductor, instead of a metal target.

  In this case, if the composition ratio of Si with respect to the metal is too large, a transparent film tends to be formed, but it becomes difficult to satisfy the sheet resistance <50 MΩ / □, and eventually a film having both transparency and conductivity is obtained. It becomes difficult.

Table 1 below shows the results of measuring the optical constants (n, k) and sheet resistance of TaSixOy films prepared by reactive sputtering using TaSi ₂ as a target and a mixed gas of Ar and O ₂ as a sputtering gas. Show.

Table 2 below shows optical constants (n, k) and sheet resistance measured for TaSixOyNz films prepared by reactive sputtering using TaSi ₂ as the target and a mixed gas of Ar, N ₂ and O ₂ as the sputtering gas. The results are shown.

Table 3 below shows the results of measuring optical constants (n, k) and sheet resistance for ZrSixOy films prepared by reactive sputtering using ZrSi ₂ as a target and a mixed gas of Ar and O ₂ as a sputtering gas. Show. The total flow rate of Ar and O ₂ is constant at 40 SCCM.

Table 4 below shows the results of measuring optical constants (n, k) and sheet resistance for ZrSixOyNz films prepared by reactive sputtering using ZrSi ₂ as a target and a mixed gas of Ar and N ₂ O as a sputtering gas. Indicates. The total flow rate of Ar and N ₂ O is constant at 40 SCCM.

  As is apparent from Tables 1 to 4, an upper layer that achieves both desired transparency (optical constant) and conductivity (sheet resistance) by appropriately selecting the target material and film formation conditions such as gas flow rate. An absorption film can be obtained.

  That is, by selecting a gas flow rate such that the extinction coefficient is in the range of 0 to 1.2 and the sheet resistance is 50 MΩ / □ or less, an upper-layer absorption film suitable for an extreme ultraviolet exposure mask can be formed. It is.

  The extreme ultraviolet exposure mask according to the present invention can be suitably used in a photolithography technique or the like for manufacturing a semiconductor integrated circuit, and is very useful in the field of semiconductors.

Sectional drawing which shows the mask for extreme ultraviolet exposure which concerns on one Embodiment of this invention. The characteristic view which represented the contrast C with the contour line by making the optical constant of the upper-layer absorption film used for the extreme ultraviolet exposure mask which concerns on one Embodiment of this invention into a horizontal axis and a vertical axis, respectively. The characteristic view which represented the contrast C with the contour line by making the optical constant of the upper-layer absorption film used for the extreme ultraviolet exposure mask which concerns on one Embodiment of this invention into a horizontal axis and a vertical axis, respectively. The characteristic view which represented the contrast C with the contour line by making the optical constant of the upper-layer absorption film used for the extreme ultraviolet exposure mask which concerns on one Embodiment of this invention into a horizontal axis and a vertical axis, respectively. The characteristic view which represented the contrast C with the contour line by making the optical constant of the upper-layer absorption film used for the extreme ultraviolet exposure mask which concerns on one Embodiment of this invention into a horizontal axis and a vertical axis, respectively.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Extreme ultraviolet exposure mask, 2 ... Low thermal expansion glass substrate, 3 ... High reflection part, 4 ... Cap layer, 5 ... Low reflection part, 5a ... Upper layer absorption film, 5b ... Lower layer absorption film, 6 ... Buffer film.

Claims (7)

  In an extreme ultraviolet exposure mask blank comprising a high-reflection layer made of a multilayer film formed on a substrate and a low-reflection layer made of an absorption film formed on the multilayer film, the absorption film comprises two or more layers It is made of a thin film, and the uppermost thin film has an extinction coefficient in the range of 0 to 1.2 with respect to ultraviolet rays having a wavelength of 150 nm to 300 nm, and has a sheet resistance of 50 MΩ / □ or less. Mask blank.   2. The mask blank for extreme ultraviolet exposure according to claim 1, wherein the uppermost thin film of the absorption film has an extinction coefficient with respect to ultraviolet rays having a wavelength of 150 nm to 300 nm in a range of 0.1 to 1.0.   The extreme ultraviolet exposure mask blank according to claim 1 or 2, wherein the uppermost thin film of the absorption film has a refractive index in the range of 1.5 to 2.5 for ultraviolet light having a wavelength of 150 nm to 300 nm. .   The extreme ultraviolet exposure mask blank according to any one of claims 1 to 3, wherein the uppermost thin film of the absorption film contains metal, silicon, and oxygen as main constituent elements.   The extreme ultraviolet exposure mask blank according to any one of claims 1 to 3, wherein the uppermost thin film of the absorption film contains metal, silicon, oxygen, and nitrogen as main constituent elements.  An extreme ultraviolet exposure mask comprising the absorption layer pattern of the absorption layer of the extreme ultraviolet exposure mask blank according to any one of claims 1 to 5.   7. An exposure method comprising irradiating an extreme ultraviolet ray to the extreme ultraviolet exposure mask according to claim 6 and irradiating an object to be exposed with the reflected light.

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