JP2008198788A - Method of forming resist pattern - Google Patents

Abstract

The effect of light having a wavelength different from that of pattern light in EUV exposure can be reduced, and the pattern transfer accuracy can be improved.
A resist pattern forming method for transferring a pattern formed on a mask to a resist film on a substrate using an EUV exposure apparatus, the step of forming a resist film on the substrate, and a resist film An auxiliary film 102 having a light transmittance different from that of the pattern light in the EUV exposure apparatus and having a light transmittance for exposing the resist film 101 is lower than that of the EUV exposure apparatus with respect to the pattern exposure light. A step of irradiating the resist film 101 with EUV light from a mask using an EUV exposure apparatus, a step of removing the auxiliary film 102 after pattern exposure of the resist film 101, and a resist film after removing the auxiliary film 102 101, and developing using a developing solution.
[Selection] Figure 2

Description

  The present invention relates to a resist pattern forming method for transferring a mask pattern onto a resist film on a substrate, and more particularly to a resist pattern forming method using an EUV exposure apparatus.

  In optical lithography up to DUV (Deep Ultra Violet) light, flare light having the same wavelength as pattern exposure light is regarded as a problem, and a mask pattern correction method based on a point spread function is also found. It has been.

  However, in EUV (Extreme Ultra Violet) lithography, flare light (EUV exposure) having the same wavelength as EUV light, which is pattern exposure light (pattern light) generated by the surface topology and phase difference of the reflecting mirror constituting the optical system of the exposure apparatus. Even if the device is an early mass production device, it is expected that flare of several to tens of percent will remain.) In addition, the substrate is irradiated with light having a wavelength different from EUV light as pattern light. There is.

  In the EUV exposure apparatus, spectroscopy is performed using a plurality of reflecting mirrors having a maximum reflectance with respect to EUV light as pattern light from continuous light emitted from a plasma light source. However, since the reflection mirror exhibits a certain degree of reflection characteristic even for light having a wavelength different from the exposure wavelength (typically 13.5 nm) of the EUV light, unintentional light (Out of Band light having a wavelength different from EUV light). : OoB light) may be irradiated onto the substrate (for example, see Non-Patent Document 1). Non-Patent Document 1 reports that OoB light is exposed to a resist film that is supposed to be used in EUV exposure. In the spectral distribution of the plasma light, the EUV light intensity is weaker than the DUV light, and the relative sensitivities of the EUV light and the DUV light are substantially equal. Therefore, when the intensity of the OoB light having the DUV wavelength is sufficiently strong, It is assumed that the imaging characteristics by EUV light are affected. In DUV lithography, a change in pattern dimensions due to flare light of several percent, and in some cases, a fraction of one percent may be a problem.

  Further, since the EUV light has high energy, it is assumed that the constituent materials of the reflecting mirror and the reflective mask positioned on the optical path are excited to emit various luminescences. In addition, the flare light having the same wavelength as the pattern light and the secondary excitation light by the luminescence may excite the members constituting the EUV exposure apparatus and emit luminescence. Such luminescence is emitted almost isotropically from the excitation source. In particular, when a continuum such as a metal is excited, luminescence is not a characteristic line but may be continuous light (see, for example, Patent Document 1). Hereinafter, OoB light and luminescence are combined and described in this application as OoB light.

As described above, in EUV lithography, unlike normal optical lithography, there is a possibility that light (OoB light) having a wavelength different from that of pattern light may be irradiated onto the resist film.
Patent No. 383626 F. Goodwin, et al., “Baselining the performance of a EUVL full field scanner through rigorous modeling”, 2006 EUVL Symposium, IET05, 2006

  The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a resist that can reduce the influence of light having a wavelength different from that of pattern light in EUV exposure and can improve pattern transfer accuracy. It is to provide a pattern forming method.

  One aspect of the present invention is a resist pattern forming method for transferring a pattern formed on a mask to a resist on a substrate using an EUV exposure apparatus, the step of forming the resist film on the substrate; On the resist film, an auxiliary film having a wavelength longer than that of the pattern light generated in the EUV exposure apparatus and a transmittance of light for exposing the resist film is lower than the transmittance of the EUV exposure apparatus for the pattern light A pattern exposure step of irradiating the resist film with EUV light from the mask using the EUV exposure apparatus, a step of removing the auxiliary film after pattern exposure of the resist film, and the auxiliary And a step of developing the resist film using a predetermined developer after removing the film.

  According to the present invention, by forming an auxiliary film on the resist film, the transmittance for the EUV light that is the pattern exposure light is higher than the transmittance for the OoB light that has a wavelength different from that of the EUV light and sensitizes the resist film, The influence of OoB light in EUV exposure can be reduced, and the pattern transfer accuracy can be improved.

  The details of the present invention will be described below with reference to the illustrated embodiments.

  FIG. 1 is a schematic block diagram showing an EUV exposure apparatus used in an embodiment of the present invention. As an example, a step-and-scan reduction projection exposure apparatus is shown.

  This exposure apparatus includes a light source unit 10 that emits EUV light, an illumination optical system 20 that propagates EUV light emitted from the light source unit 10, and a mask that is irradiated with light propagated by the illumination optical system 20 (reflection type reticle). 30 and a mask stage 31 for holding the mask 30. Furthermore, a projection optical system 40 that propagates the light reflected by the mask 30, a wafer 50 coated with a resist film that is exposed by the light propagated by the projection optical system 40, and a wafer stage 51 that holds the wafer 50 are provided. .

  The light source unit 10 includes a light source 11, a condenser lens 12, an elliptical mirror 14, and a parabolic mirror 15. The light source 11 emits laser light having a wavelength from the infrared region to the visible region. For example, a yttrium, aluminum, garnet (YAG) laser, a CO 2 laser, an excimer laser, etc. emitted from a semiconductor laser is emitted from the light source 11. A condenser lens 12 is disposed adjacent to the light source 11. The condensing lens 12 condenses the laser light emitted from the light source 11 at the focal point 13. The focal point 13 is supplied with xenon (Xe) gas. Xe gas becomes a high temperature when irradiated with laser light. When Xe is excited to a plasma state and transitions to a low potential state, EUV light in a soft X-ray region having a wavelength of 12 nm to 14 nm is emitted. The emitted EUV light is collected by the elliptical mirror 14 and reflected by the parabolic mirror 15.

  The illumination optical system 20 through which EUV light reflected by the parabolic mirror 15 is propagated includes reflecting mirrors 21 and 22, a condenser mirror 23, and an optical path bending mirror 24. The EUV light is reflected by the reflecting mirrors 21 and 22 and further reflected and collected by the condenser mirror 23. The EUV light reflected and collected by the condenser mirror 23 is reflected by the optical path bending mirror 24 and reaches the mask 30 fixed to the mask stage 31 by electrostatic attraction force.

  A projection optical system 40 is disposed below the mask 30. Below the projection optical system 40, a wafer stage 51 for holding the wafer 50 is disposed. The projection optical system 40 includes a condenser mirror 41, optical path bending mirrors 42 and 43, a condenser mirror 44, an optical path bending mirror 45, and a condenser mirror 46. The EUV light reflected by the mask 30 is reflected and collected by the condenser mirror 41 and reflected by the optical path bending mirrors 42 and 43. Further, the EUV light is reflected and collected by the condenser mirror 44 and reflected by the optical path folding mirror 45. The EUV light reflected by the optical path folding mirror 45 is condensed and reflected by the condenser mirror 46 and focused on the resist film applied to the surface of the wafer 50. The magnification of the projection optical system 40 is 1/4, for example. Since EUV light is absorbed by air, the environment of the illumination optical system 20 and the projection optical system 40 is preferably kept in a vacuum.

  In such a configuration, since the EUV light is irradiated onto the mask 30 by the illumination optical system 20 and the reflected light is irradiated onto the wafer 50 by the projection optical system 40, the pattern of the mask 30 is reduced by the projection optical system 40. And transferred onto the wafer 50. At this time, the mask stage 31 and the wafer stage 51 are synchronously scanned according to the reduction ratio of the projection optical system 40, respectively.

  The exposure apparatus performs exposure by repeating step-and-scan. When exposure is completed on the entire surface of the wafer 50, the exposure apparatus moves to the next wafer. Further, when the exposure on all the wafers is completed, the mask 30 is replaced, and the exposure is repeated again in the same procedure. The wafer 50 has its surface position measured by a height position detection sensor (Z sensor) for alignment in the Z direction (optical axis direction of the projection optical system), and the height position is determined according to this measurement information. Be controlled.

  Next, the resist pattern forming method of this embodiment using the above apparatus will be described with reference to a comparative example.

(Comparative example)
Before describing the embodiment, as a reference example, a general resist pattern forming method using EUV light will be described.

  First, a resist film is formed on a substrate such as a semiconductor wafer. In a typical method, a heating process (PAB process: Post Apply Bake process) under a predetermined condition is performed as necessary after performing the coating process by the spin coating method.

  A pattern exposure process using an EUV exposure apparatus is performed on the resist film formed on the substrate. As shown in FIG. 1, the EUV exposure apparatus differs from conventional photolithography in that the optical system is formed by a reflective mirror, and the photomask is also formed by a reflective mask.

  When the resist film is a chemical amplification type or the like, a heating process (PEB process: Post Exposure Bake process) under a predetermined condition is performed on the resist film subjected to pattern exposure, if necessary.

  The resist film on which the latent image is formed by the pattern exposure process or the PEB process is subjected to a developing process under predetermined conditions, and a developer rinsing process is performed as necessary. A typical example of a developing solution is 2.38% TMAH, and a typical example of a rinsing solution is pure water. The developer and rinse solution may contain a surfactant. In some resist films, development may be performed in an organic solvent.

  Flare light and OoB light generated in the EUV exposure apparatus sensitize the resist film used for EUV exposure, which causes a decrease in pattern transfer accuracy. It is estimated that flare light can be modeled and mask corrected by Point Spread Function in the same way as photolithography knowledge.

  On the other hand, with respect to OoB light, there is a possibility that a technique for grasping the photosensitive characteristics of the resist pattern for all wavelengths of the generated OoB light or a set of predetermined wavelength sections and correcting it in the same manner as in photolithography. . However, it is necessary to quantify the influence of the OoB light in advance in addition to the assumed work amount for obtaining the photosensitive wavelength, and further, it is assumed that the influence of the OoB light in the shot has the same distribution. Become. For this reason, correction is considered extremely difficult.

(Embodiment)
Next, a description will be given of this embodiment as a countermeasure against the method described in the comparative example.

  In this embodiment, first, as shown in FIG. 2A, a resist film 101 is formed on a substrate 100 by a spin coating method or the like, as in the comparative example described above, and heating under predetermined conditions is performed as necessary. Perform the process (PAB process: Post Apply Bake process). The substrate 100 may be a semiconductor wafer itself, or may be one in which various films are formed on a semiconductor wafer and a film to be processed is formed on the uppermost surface. As the resist film 101, it is possible to use various resist films that have been used in conventional UV, DUV, and EB lithography. However, in the resist in EUV lithography, the performance of the conventional resist may be insufficient from the combined viewpoint of OUTGAS, LWR, sensitivity, and resolution. Good. For example, as a commercial product of EUV resist in the invention stage, (MET-2D manufactured by ROHM & HAAS) can be mentioned. It is also conceivable to use non-polymer type or molecular resists such as polynuclear phenol type resists and starburst type resists. The purpose of these resists is to improve LWR and resolution by reducing the size of the resist material. On the other hand, a conventional resist mainly composed of a polymer or an oligomer is improved by changing a substituent of the polymer or oligomer that is separated by an acid generated in an exposed portion, or a basic structure of these resists Apart from this improvement, it is also possible to use a photoacid generator whose sensitivity and acid diffusion length are reduced by improving the photoacid generator. In addition, in a conventional chemically amplified resist, it is possible to use a resist having a structure in which a photoacid generator as an additive to a polymer or oligomer that is a resist main component is combined with the resist main component. I can think. Further, the film thickness of the resist film 101 is desirably 150 nm.

  Next, as shown in FIG. 2B, an auxiliary film 102 for reducing the influence of OoB light is formed on the resist film 101. The auxiliary film 102 has a higher transmittance for EUV light than that for OoB light, for example, DUV light. Conversely, the absorption rate for OoB light is higher than the absorption rate for EUV light. Further, the auxiliary film 102 is preferably thinner than the resist film 101 in order to reduce image deterioration in the focus direction.

  As described in the comparative example, OoB light having a longer wavelength than EUV light, which is regarded as a problem in EUV exposure, can be broadly divided into infrared light, visible light, UV light, and DUV light. Generally, the photosensitive wavelength of a resist film used for EUV exposure is light shorter than UV light regardless of whether it is chemically amplified or non-chemically amplified. Therefore, when an auxiliary film with Tp> Ti is present on the resist film at the unit transmittance Tp of the wavelength λp that is pattern exposure light and the unit transmittance Ti of the OoB light wavelength λi shorter than the UV light, OoB It is possible to reduce the influence of light on the resist film.

  Next, the pattern of the reflective mask is transferred to the resist film 101 using the EUV exposure apparatus shown in FIG. At this time, the pattern light from the exposure apparatus is applied to the resist film 101 through the auxiliary film 102. For this reason, the EUV light is also attenuated by the auxiliary film 102, but the OoB light is greatly attenuated more than that. If the resist film 101 is a chemical amplification type or the like, a heating process (PEB process: Post Exposure Bake process) under a predetermined condition is performed on the resist film 101 to which the pattern has been transferred, if necessary.

  Next, after the auxiliary film 102 is removed, a development process is performed on the resist film 101 under a predetermined condition to form a pattern on the resist film 101 as shown in FIG. That is, a resist pattern corresponding to the mask pattern is formed. Here, a developer rinsing step is performed as necessary. A typical example of a developing solution is 2.38% TMAH, and a typical example of a rinsing solution is pure water. The developer and the rinsing solution may contain a surfactant. In some resist films, development may be performed with an organic solvent.

  With such a method, the influence of OoB light can be reduced compared with the case where EUV exposure is performed without the auxiliary film 102 as in the comparative example, and the dimensional accuracy of the finally obtained resist pattern is reduced. Will improve.

  In pattern exposure by photolithography using DUV light etc., TARC (Top Anti-reflection Coating) as an auxiliary film formed on the resist film, mainly a base etc. proposed mainly in the early stage of chemically amplified resist Examples include a protective film (Cover material) against chemical species of the above, a protective film (Immersion Top Coating Film) against an immersion liquid (Liquid Immersion Fluid) in immersion exposure, and the like. As a basic characteristic of such an auxiliary film on the resist film, it is known that it is almost transparent to the pattern light.

  However, it is essential that the auxiliary film 102 formed on the resist film 101 in the present embodiment, which is EUV lithography, absorbs EUV light having a pattern exposure wavelength λp to a certain extent. This is because the absorption of EUV light, which is a soft X-ray region, is determined by the element density and film thickness in the substance. This point greatly differs from DUV light to visible light whose absorption is determined by the molecular bond structure. Further, in the method of the present embodiment, in order to receive the EUV light absorption by the auxiliary film 102, it is necessary to increase the irradiation amount of the EUV light on the exposure apparatus side.

  The material of the auxiliary film 102 for effectively obtaining the effect of this embodiment will be described. In the auxiliary film 102 used in this embodiment, the most convenient method for absorbing UV light from DUV light is a method in which the auxiliary film 102 includes an aromatic ring and a derivative thereof. As a method including an aromatic and a derivative thereof, there are a method in which the main substance forming the auxiliary film 102 includes aromatic as a constituent factor and a method in which the main material includes an additive. Furthermore, you may use both together. In addition, since aromatics cause some variation in absorption wavelength due to functional groups, they may include aromatics having a plurality of different structures.

Further, when the OoB light shows a strong intensity in the vicinity of a wavelength of 193 nm, it is considered effective that the auxiliary film 102 contains an aromatic or carbon double bond. In addition to this, it is possible to refer to structures having absorption that have been studied in the development of resist materials for DUV exposure such as KrF, ArF, and F ₂ . For example, novolak, which has been widely used as an I-line resist composition, is an effective example for attenuating light in the vicinity of a wavelength of 248 nm. For light near a wavelength of 193 nm, a polyhydroxystyrene derivative that has been used as a KrF resist is an effective example. Moreover, it becomes possible to use these mixtures. By adding an appropriate functional group to such a structure, it is possible to impart solubility to a resist developer or a stripping solution. In addition, the absorption wavelength is shifted by adding an appropriate electron donating group or potential applying group.

  On the other hand, the auxiliary film 102 is formed on the resist film 101 formed on the substrate and needs to be removed during the process of developing the latent image of the resist film 101 formed by performing the pattern exposure with EUV light. is there. For this reason, it is necessary not to deteriorate the pattern forming performance of the resist film 101 in forming on the resist film 101, and to not deteriorate the latent image formation and development characteristics.

  As a simple method for this evaluation, there is a method in which a coating solvent for the auxiliary film 102 is dropped onto the resist film 101, and a change in the resist film thickness before and after that is examined. Alternatively, there is a method of examining a change in the resist film thickness after the auxiliary film 102 is removed (details will be described later) when the auxiliary film 102 is formed on the resist film 101 and when the auxiliary film 102 is not formed. In these methods, not only a state where the resist film 101 is not exposed (unexposed state), but also a step of irradiating the resist film 101 with an exposure amount necessary for actual patterning, and further a developing step for the resist film 101 It is even more desirable to consider by including comparisons.

  Further, in order to ensure the characteristic that the resist resolution is not affected, as a coating solution for the auxiliary film 102 when the auxiliary film 102 is formed by a chemical solution coating method such as spin coating, the resist film itself is of course used. In addition to the resin that is the main component of the resist film 101, a solution that does not dissolve additives such as an acid generator and a basic substance in the resist film 101 is desirable. As a solution having such characteristics, in addition to water, a solvent for the immersion protective film can be considered. As a solvent used for the immersion protective film, alcohols and ketones having about 3 to 10 carbon atoms are generally considered. Alternatively, halogenated hydrocarbon solvents can be considered as candidates, but attention must be paid to their release into the atmosphere.

  In investigating the influence of the resist composition on the coating solution of the auxiliary film 102, the target chemical solution on the resist film 101, in this case, the auxiliary film 102, in the same manner as the method known as elution analysis in immersion lithography. After supplying the coating solution under predetermined conditions, the chemical solution on the resist film 101 may be collected and composition analysis may be performed. A simpler method may be to confirm the resist pattern shape when the auxiliary film 102 is formed on the resist film 101 and when the auxiliary film 102 is not formed. More specifically, exposure may be performed by changing the irradiation exposure amount of the pattern exposure and, if necessary, the focus setting amount, and the shape and the shape change rate with respect to the exposure amount may be compared.

  The formation method of the auxiliary film 102 may be a method using a vacuum apparatus such as a molecular beam epitaxy method in addition to the spin coating method.

  As a method for removing the auxiliary film 102 after the latent image is formed in the resist film 101 and before development, a removal method using a solution different from the resist developer or a gas phase may be considered. However, in order to continuously remove the auxiliary film 102 and develop the resist film 101, it is preferable to remove the auxiliary film 102 with the developer for the resist film 101.

  As the auxiliary film 102 removal solution different from the developing solution for the resist film 101, when the auxiliary film 102 is an organic resin, use of a solvent that does not dissolve the resist film 101 is conceivable. When the auxiliary film 102 is made of an organic material, it may be an oxidizing solution such as ozone water or a solution containing an oxidizing acid. As the auxiliary film 102 constituting material in which the auxiliary film 102 is dissolved in the resist developer, the base resin structure is almost the same as that of the resist film 101, and a resin that is dissolved in a predetermined developer may be a main component. Specifically, a PHS structure, a (meth) acrylic structure, a siloxane oxide structure, or the like can be considered.

  As described above, according to the present embodiment, when pattern exposure is performed by the EUV exposure apparatus, the transmittance of the EUV light on the resist film 101 is longer than that of the EUV light, and the OoB light that exposes the resist film is exposed. By forming the auxiliary film 102 having a higher transmittance than that and performing EUV exposure in this state, it is possible to prevent degradation of resist resolution due to DUV light that is secondarily generated by EUV light, and to improve the process margin. Can be measured. That is, the influence of OoB light in EUV exposure can be reduced, and the pattern transfer accuracy can be improved. In addition, there is an advantage that can be realized by a simple process of forming the auxiliary film 102 on the resist 101 film.

(Modification)
In addition, this invention is not limited to embodiment mentioned above. The EUV exposure apparatus is not limited to the configuration shown in FIG. 1 as long as it can irradiate the substrate with EUV light including mask pattern information. For example, the mask is not necessarily limited to the reflective type, and may be a transmissive type. Furthermore, the configuration of the optical system can be changed as appropriate.

Further, the auxiliary film is not limited to novolak, polyhydroxystyrene, or a mixture thereof, and the OoB light generated in the EUV exposure apparatus and the transmittance with respect to the light that sensitizes the resist film has a pattern exposure of the EUV exposure apparatus. What is necessary is just to be lower than the transmittance for light. Therefore, it is also possible to use a mixture of the above-mentioned novolak and polyhydroxystyrene, or other aromatic derivative resins and resin films containing aromatic derivatives for various resins such as polyvinyl alcohol derivatives and (alkyl) acrylic acid derivatives. It is. Moreover, it is not limited to organic substances such as aromatics, and may be a resin containing a transition metal oxide such as TiO ₂ as long as it does not affect the characteristics of the semiconductor element to be manufactured.

  In addition, various modifications can be made without departing from the scope of the present invention.

1 is a schematic block diagram showing an EUV exposure apparatus used in an embodiment of the present invention. Sectional drawing which shows the resist pattern formation process concerning one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Light source part 11 ... Laser light source 12 ... Condensing lens 13 ... Focus 14 ... Elliptical mirror 15 ... Parabolic mirror 20 ... Illumination optical system 21, 22 ... Reflection mirror 23, 41, 44, 46 ... Condenser mirror 24, 42 , 43, 45 ... Optical path folding mirror 30 ... Mask (reflective reticle)
31 ... Mask stage 40 ... Projection optical system 50 ... Wafer (substrate)
51 ... Wafer stage 100 ... Semiconductor wafer (substrate)
101 ... resist film 102 ... auxiliary film

Claims (5)

A resist pattern forming method for transferring a pattern formed on a mask to a resist film on a substrate by pattern light of a predetermined EUV wavelength using an EUV exposure apparatus,
Forming the resist film on the substrate;
On the resist film, an auxiliary film having a wavelength longer than that of the pattern light generated in the EUV exposure apparatus and a transmittance of light for sensitizing the resist film is lower than the transmittance of the EUV exposure apparatus for the pattern light. Forming, and
A pattern exposure step of irradiating the resist film with EUV light from the mask using the EUV exposure apparatus;
Removing the auxiliary film after pattern exposure of the resist film;
A step of developing the resist film with a predetermined developer after removing the auxiliary film;
A resist pattern forming method comprising:   2. The resist pattern forming method according to claim 1, wherein light having a longer wavelength than pattern light generated in the EUV exposure apparatus has a shorter wavelength than UV light.   2. The resist pattern forming method according to claim 1, wherein the auxiliary film is dissolved by a developing solution for the resist film.   The resist pattern forming method according to claim 1, wherein the auxiliary film has an aromatic in the composition.   2. The resist pattern forming method according to claim 1, wherein the auxiliary film is formed by applying a chemical solution, and the solvent of the auxiliary film coating chemical solution does not dissolve the resist film.

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