JP2009088166A - Reflective mask blank and reflective mask - Google Patents

Abstract

A reflective mask blank having at least a substrate, a multilayer reflective film that reflects exposure light, and an absorber that absorbs exposure light, the thickness of the absorber being reduced, and a pattern peripheral portion during exposure The present invention provides a reflective mask blank and a reflective mask that prevent a reduction in resolution.
The absorber includes at least In, Ga, Zn, or at least In, Ga, Sn, and O elements, and a sheet resistance value of the absorber is at least 1 MΩ / □ or less.
[Selection] Figure 2

Description

  The present invention relates to a reflective mask blank for EUV light, a reflective mask applicable to photolithography using EUV (Extreme Ultraviolet) light, and a manufacturing method thereof, which are used in the manufacturing process of a semiconductor device.

  Photolithography using visible light (g-line, h-line) or ultraviolet light (i-line, KrF, ArF) is widely used for patterning of wiring and semiconductors such as semiconductor integrated circuits and display devices. In recent years, along with miniaturization of semiconductor integrated circuits, research and development relating to immersion ArF, EUV lithography, nanoimprint lithography, and the like have been actively conducted as a manufacturing technique in addition to electron beam lithography.

  Among these, EUV lithography is one of the candidates for transfer technology used for devices of 32 nm and beyond, and is on the extension of the current photolithography technology using light, and therefore has attracted a great deal of attention. Light with a wavelength of 0.2 to 100 nm called EUV light is much shorter than the wavelength of visible light and close to the X-ray wavelength range. Since EUV light has a characteristic of being absorbed by almost all materials, a conventional system using a transparent mask on which transmitted light is a prerequisite and a refractive optical member such as an optical lens cannot be used. . Therefore, a reflective optical system is usually used. For this reason, a reflective type is also used for the mask. As shown in FIG. 1, the EUV mask has a multilayer reflective film 102 (ML: Multi layer) that efficiently reflects EUV light on a low thermal expansion coefficient glass substrate 101, and is patterned to absorb EUV light thereon. The absorbent body 104 is arranged. There may be an etching stopper layer (not shown) for the absorber, a protective film 103 that protects the multilayer film, a thin film 105 for inspection, and the like.

  In the EUV mask, this absorber (including the inspection thin film if there is an upper layer) is patterned to create an EUV light absorbing portion (reflectance Ra) and a reflecting portion (reflectance Rm) to obtain contrast. ing.

  The EUV light at the time of exposure becomes so-called oblique incidence that is incident on the EUV mask at a slight angle rather than perpendicularly. This is because it is difficult to extract reflected light while suppressing light intensity loss at normal incidence.

Known documents are described below.
JP 2006-229239 A

However, the resolution at the periphery of the pattern is reduced by this oblique incidence. Since it is an influence of only the peripheral part of the pattern, there is no problem when the pattern size is relatively large as in the prior art. However, as the integration path and the like become finer, the pattern on the mask needs to be made finer, and the above-described reduction in resolution at the periphery of the pattern makes it difficult to make the pattern finer. One of the methods for dealing with this is a method of making the incident angle of EUV light close to vertical, but at present, the incident angle has already approached a state of nearly 5 to 6 ° with respect to the normal of the mask surface. Therefore, if the incident angle is further reduced, it becomes difficult to extract reflected light.

  Another method for avoiding a decrease in resolution at the periphery of the pattern is to reduce the film thickness of the upper part of the mask structure, that is, the absorber (including an inspection thin film if it is laminated). There is a way to do it. However, when the thickness of the absorber is reduced, there is a problem that the absorbance (optical density) with respect to EUV light unique to the absorber is lowered, and the contrast during exposure when used as a reflective mask is lowered.

  In order to solve the above problems, the present invention has the following configuration.

  A reflective mask blank having at least a substrate, a multilayer reflective film that reflects exposure light, and an absorber that absorbs exposure light, wherein the absorber contains at least elements of In, Ga, Zn, and O This is a reflective mask blank.

  By setting it as such a structure, the absorber can make the film thickness thin, maintaining the light absorbency.

  Another configuration of the present invention is a reflective mask blank having at least a substrate, a multilayer reflective film that reflects exposure light, and an absorber that absorbs exposure light, wherein the absorber includes at least In, Ga, It is a reflective mask blank characterized by containing Sn and O elements.

  With such a configuration, the film thickness can be further reduced while maintaining the absorbance.

  Another configuration of the present invention is the reflective mask blank, wherein the absorber has a sheet resistance value of at least 1 MΩ / □.

  By making the absorber conductive, it is possible to avoid charge-up when the absorber is drawn and patterned by an electron beam (EB) using an electron beam resist, and the absorber can be easily patterned. .

  Another configuration of the present invention is the reflective mask blank, wherein the absorber is non-polycrystalline.

  In the case where the absorber is polycrystalline, irregularities seen as crystal grain boundaries may be observed at the pattern edge portion after patterning, and LER (Line edge roughness) may be deteriorated. By making the absorber non-polycrystalline, it is possible to avoid such deterioration of LER.

  Another configuration of the present invention is the reflective mask blank, wherein an absolute value of stress of the absorber is 200 MPa or less.

  By keeping the stress of the film low, the positional accuracy (IP: Image Placement) of each pattern after patterning can be increased. If the absolute value of the stress exceeds 200 MPa, when the absorber is patterned, distortion of a level that affects transfer occurs in the pattern.

  Another configuration of the present invention is the reflective mask blank, wherein the absorber is formed at room temperature.

Heating at the time of film formation or baking after film formation leads to an increase in cost and a decrease in throughput.

  Another configuration of the present invention is the reflective mask blank, wherein the absorber is formed by a sputtering method.

  By using the sputtering method, a thin film can be easily formed, and stress adjustment and conductivity adjustment can be easily performed.

  Another configuration of the present invention is a reflective mask manufactured using the reflective mask blank.

  The reflective mask manufactured in the above-described configuration can be arranged as a fine pattern and can be applied as a next generation EUV mask due to the thin film thickness of the absorber. Transcription) results can be expected.

FIG. 2 shows the measurement of reflectance in EUV light for each absorber according to the present invention, and the absorbance is calculated by fitting based on the obtained result. When InGaZnO ₄ is used, the conventional Ta-based absorption film has a thickness of 2.5, which is an optical density (OD: Optical density) 2.5 equivalent to that of the conventional Ta-based absorption film. 47 nm. Similarly, when InGaSnO ₅ is used, a film thickness of 40 nm is sufficient. However, although it has been confirmed that the conductivity of InGaSnO ₅ is somewhat inferior to that of InGaZnO ₄ , the charge-up during EB writing can be completely suppressed by appropriately adjusting the O content. . Further, the absorber having this structure can easily obtain an amorphous structure by room temperature film formation. By using a sputtering method for the film formation method, the absorber having a stress of 200 MPa or less can be easily produced by appropriately controlling the film formation conditions such as the gas pressure and the target-substrate distance during film formation. can do.

  From the above, according to the present invention, the mask blank has an effect that the thickness of the absorber can be reduced by using the configuration. Therefore, it is expected that a fine pattern can be transferred with high resolution by exposure using the produced mask.

  Hereinafter, the present invention will be described in detail by embodiments.

  The reflective mask blank of the present invention includes at least a multilayer reflective film that reflects exposure light formed on a substrate and an absorber that absorbs exposure light formed on the multilayer reflective film. More preferably, a flat substrate having a very low thermal expansion coefficient is used as the substrate, a multilayer reflective film that reflects exposure light is provided on the substrate, and a protective film that protects the multilayer reflective film on the multilayer reflective film; , A role as an etching stopper layer of the absorber and a buffer layer used as a multilayer film protection at the time of pattern correction, an absorber that absorbs exposure light, a low reflection layer for the inspection wavelength to obtain a contrast at the inspection wavelength, Is a reflective mask blank.

With regard to the material of the absorber, for example, EUV light is absorbed even with a configuration of only In and O, or only Sn and O, but it is difficult to obtain non-polycrystalline material. As described above, it is desirable that the In, Ga, Zn, and O systems include at least the four elements, and the In, Ga, Sn, and O systems include at least the four elements. More preferably, InGaZnO _x (3 ≦ x ≦ 4) or InGaSnO _x (4 ≦ x ≦ 5) is used as the absorber material.

It is convenient to use a sputtering method for the film formation of the absorber, but PLD (plus las
er deposition) or other methods. Hereinafter, a reflective mask blank having an absorber having a composition of InGaZnO _x (3 ≦ x ≦ 4) and a manufacturing method using a sputtering method will be described, but the case where the absorber is InGaSnO _x (4 ≦ x ≦ 5). Is the same.

Although it is convenient to use an oxide target, that is, InGaZnO ₄ as the target, a conductive InGaZnO _4-x target that is a lower oxide may be used. By forming a film at room temperature using this, an absorber thin film having an amorphous structure can be easily obtained. In the case where the film is made conductive, an absorbing film having conductivity can be obtained by introducing oxygen gas in addition to the sputtering gas and appropriately controlling the flow rate at the time of film formation. Since the appropriate amount of oxygen gas introduced varies depending on the film forming apparatus, the target material, the gas pressure at the time of film formation, and the like, it is not appropriate to set the amount of oxygen introduced unconditionally. By appropriately controlling the gas pressure at the time of film formation, an absorber thin film having a stress of 200 MPa or less in absolute value can be obtained. As for the optimum gas pressure and the like, the specific part of the apparatus has a great influence, so it is necessary to determine the conditions for each apparatus to be used, and it is not appropriate to set a value in general.

  Thus, the reflective mask blank of the present invention is completed.

  The reflective mask blank thus obtained is patterned by using a general electron beam (EB) lithography technique or the like, thereby completing the reflective mask of the present invention.

  Hereinafter, an example of the manufacturing method of the reflective mask blank of the present invention will be described in detail with reference to FIG.

A substrate on which a multilayer film 102 for reflecting EUV light was formed on a glass substrate 101 having a high flatness and a very low coefficient of thermal expansion, and a multilayer film protective layer 103 formed thereon was prepared (FIG. 3A). The absorber 104 was formed on this substrate as follows. That is, rf magnetron sputtering was used as the film formation method, an InGaZnO ₄ oxide target was used as the target, a mixed gas of Ar and oxygen was introduced into the vacuum chamber, and film formation was performed at a discharge power of 350 W. At this time, in order to give conductivity to the absorber, the flow rate ratio of oxygen gas to Ar was adjusted and optimized. In order to make the absolute value of stress 200 MPa or less, the pressure of the introduced gas was adjusted and optimized. The conductivity of the obtained absorber thin film was 3.3 kΩ / □ in terms of sheet resistance. In consideration of patterning, in the case of a general EB drawing apparatus, the conductivity of the substrate is required to be 1 MΩ / □ or less. This result was about 3 orders of magnitude lower than that, and an absorber having sufficient conductivity was obtained. The stress of the produced absorber was −22 MPa. As a result of the evaluation of crystallinity by X-ray diffraction (XRD), this absorber was confirmed to be amorphous. Thus, the reflective mask blank of the present invention was completed (FIG. 3B).

  Hereinafter, another example of the manufacturing method of the reflective mask blank of the present invention will be described in detail.

A substrate on which a multilayer film 102 for reflecting EUV light was formed on a glass substrate 101 having a high flatness and a very low coefficient of thermal expansion, and a multilayer film protective layer 103 formed thereon was prepared (FIG. 3A). The absorber 104 was formed on this substrate as follows. That is, rf magnetron sputtering was used as the film formation method, an InGaSnO ₅ oxide target was used as the target, a mixed gas of Ar and oxygen was introduced into the vacuum chamber, and film formation was performed at a discharge power of 200 W. At this time, in order to give conductivity to the absorber, the flow rate ratio of oxygen gas to Ar was adjusted and optimized. In order to make the absolute value of stress 200 MPa or less, the pressure of the introduced gas was adjusted and optimized. The conductivity of the obtained absorber thin film was 98 kΩ / □ in terms of sheet resistance. The stress of the produced absorber was −65 MPa. As a result of crystallinity evaluation by X-ray diffraction method, this absorber was confirmed to be amorphous. Thus, the reflective mask blank of the present invention was completed (FIG. 3B).

  A resist 106 is applied on the surface of the reflective mask blank (FIG. 3B) produced as in Example 2 (FIG. 3C), and this is patterned by lithography (FIG. 3D). This was used as an etching mask. The patterned reflective mask blank with resist was put into a general dry etching apparatus, and the absorber in the exposed portion was etched using chlorine gas (FIG. 3E). After completion of the etching, the resist on the surface was removed to complete the reflective mask of the present invention (FIG. 3 (f)).

EUV mask structure An example of the absorbance of the absorber in the reflective mask of the present invention Example of manufacturing process of reflective mask blank and reflective mask of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Back surface conductive film 101 ... Substrate 102 ... Multilayer reflective film 103 ... Protective film 104 ... Absorber 105 ... Inspection thin film 106 ... Resist

Claims (8)

  A reflective mask blank having at least a substrate, a multilayer reflective film that reflects exposure light, and an absorber that absorbs exposure light, wherein the absorber contains at least elements of In, Ga, Zn, and O A reflective mask blank characterized by that.   A reflective mask blank having at least a substrate, a multilayer reflective film that reflects exposure light, and an absorber that absorbs exposure light, wherein the absorber contains at least elements of In, Ga, Sn, and O A reflective mask blank characterized by that.   The reflective mask blank according to claim 1 or 2, wherein a sheet resistance value of the absorber is at least 1 MΩ / □ or less.   The reflective mask blank according to any one of claims 1 to 3, wherein the absorber is non-polycrystalline.   The absolute value of the stress of the said absorber is 200 Mpa or less, The reflective mask blank in any one of the Claims 1 thru | or 4 characterized by the above-mentioned.   6. The reflective mask blank according to claim 1, wherein the absorber is formed at room temperature.   The reflective mask blank according to claim 1, wherein the absorber is formed by a sputtering method.   A reflective mask produced using the reflective mask blank according to claim 1.