DE10233828A1 - Optical component used in an illuminating system for microlithography comprises a material having a temperature-dependent thermal longitudinal expansion coefficient - Google Patents

Abstract

Optical component comprises a material having a temperature-dependent thermal longitudinal expansion coefficient alpha(T). The thermal longitudinal expansion coefficient or the derivation of the thermal longitudinal expansion coefficient alpha(T)/dT according to the temperature close to a temperature T0 changes the sign from positive to negative or from negative to positive with increasing temperature. The temperature T0 corresponds to the maximum temperature Tmax, to which the optical component is heated. Independent claims are also included for the following: (1) Illuminating system containing the optical component; (2) projection lens containing the optical component; (3) projection illuminating device for microlithography comprising the above illuminating system, a projection lens and a light-sensitive substrate; and (4) process for the production of microelectronics components.

Description

The invention relates to an optical component which heats up to a maximum temperature T _max as a result of electromagnetic radiation from a light source impinging on the optical component, the optical component comprising a material which has a temperature-dependent thermal coefficient of longitudinal expansion α (T).

Such optical components are especially in the field of X-ray lithography of special interest. This applies in particular to lithography with soft x-rays, the so-called EUV lithography in the wavelength range 10–30 nm. Mirrors are also used as optical components in the field of X-ray lithography a high reflectivity in the x-ray range Use. Such mirrors can are operated near the vertical incidence as so-called normal incidence mirrors, or in grazing incidence as a so-called grazing incidence mirror. A grazing-incidence mirror is a mirror in which the rays of a bundle of rays falling on the mirror below Angles α> 70 ° relative to the surface normal incident.

X-ray mirrors with a high reflectivity in X-ray range, which as a normal incidence Operated mirrors include a substrate material and thereon built a multiple layer system, for example a Mo / Si multiple system or a Mo / Be multiple system or a MoRu / Be multiple layer system. With such systems can Peak reflectivities in the EUV area of over 50 and even over 60% can be achieved.

Depending on the wavelength of the light to be reflected can but also layer systems made of other materials can be used.

In addition to the X-ray mirrors, which act as normal incidence mirrors are also operated mirrors that graze in incidence operated, so-called grazing incidence mirrors, conceivable. such Mirrors also include a substrate material. On the substrate material however, a simpler layer system is applied. The angry one Layer can for example be a ruthenium, palladium or rhodium layer his.

For X-ray mirrors, those in the field of EUV lithography, especially in projection lenses Find use, it is desirable if high image quality can be achieved.

Since the X-rays, as shown earlier, neither under normal incidence nor under grazing Grazing incidence is fully reflected entered into the mirror energy, so that the mirror or the respective optical components warm up. The temperature warming of the respective optical components in turn leads to the fact that due to thermal Extend the picture quality affected becomes.

The minimization of thermal effects with optical components that are used in EUV projection systems is the subject of EP 0 955 565 ,

To suppress the thermal effects, those from the EP 0 955 565 known mirror as a substrate material on a metallic substrate. Due to the good thermal conductivity of the metals, the heat introduced into the mirrors is efficiently dissipated via the back of the metal substrates, preferably by a cooling device. This heat dissipation minimizes the imaging errors due to mirror deformations.

A disadvantage of the solution according to the EP 0 955 565 is that the minimization of the image errors introduced due to heat occurs by actively dissipating the heat input into the optical component, for example by the cooling device. This involves a lot of effort. Furthermore, additional components are always a risk of failure.

Another disadvantage of using it of metals as substrate material can be seen in the fact that it is necessary is to get one if possible smooth surface too reach the metal substrate with a thin film of an amorphous substance to be coated as an intermediate layer. This intermediate layer is polished to to achieve sufficiently low roughness. Only on this layer the optical layers of the EUV component, for example the multiple layer systems for the normal incidence mirror or the optical coatings for the grazing incidence mirror, applied.

The object of the invention is that To overcome disadvantages of the prior art, in particular one possibility specify with the image error due to the heating of the respective optical component be minimized, this goal with the lowest possible technical Effort should be achieved.

According to the invention, this object is achieved in that the optical component comprises a material which has a temperature-dependent thermal expansion coefficient α (T), the temperature-dependent thermal expansion coefficient α (T) or the derivative of the temperature-dependent thermal expansion coefficient dα (T) / dT after Temperature near a temperature T _{0 changes} the sign from positive to negative or from negative to positive and the temperature T ₀ approximately corresponds to the maximum temperature T _max to which the optical component is heated by the incident radiation speaks.

If the material of the mirror, in particular the substrate material, is selected as described above, there is no complex cooling as in the prior art, for example the EP 0 955 565 , more necessary to keep image errors due to the heating of the optical component by the energy input low.

A material with an approximately linear temperature dependence α (T) = m * (T-T ₀ ) of the temperature-dependent thermal coefficient of longitudinal expansion in a temperature range near the temperature T _{0 is} particularly preferably used as the material, in particular as the substrate material. Here, m denotes the slope of the temperature-dependent coefficient of thermal expansion.

Substrate materials with such a course of the temperature-dependent thermal expansion coefficient are, for example, glass ceramics or Ti-doped quartz glasses. glass ceramics or Ti-doped quartz glass as the substrate material have the advantage that on this substrate material layer systems without an amorphous Intermediate layer in contrast to, for example, metallic substrate materials can be applied. Another advantage of such substrate materials is the low one Thermal expansion.

For a Ti-doped quartz glass in "Ultra low expansion glasses and their structure in the SiO ₂ -TiO ₂ system" from PCSchultz, the course of the temperature-dependent thermal coefficient of longitudinal expansion as a function of the temperature and the possibility of influencing it by changing the material properties, HTSmyth, Amorphous Materials, September 1970, pages 453-461 and in the patent US 2326056 described. The disclosure content of these documents is fully included in the disclosure content of the present application.

As known from these writings is changing for such Materials of temperature-dependent thermal Coefficient of longitudinal expansion α (T) in the for the EUV lithography interesting temperature range from about 20 ° C to 70 ° C, with increasing temperature the sign. This behavior is in other temperature intervals different. Even the slope can change the sign here.

The temperature-dependent thermal coefficient of longitudinal expansion is defined according to "Ultra low expansion glasses and their structure in the SiO ₂ -TiO ₂ system" by PCSchultz, HTSmyth, Amorphous Materials, September 1970, pages 453-461 as the change in the longitudinal expansion of a body in relation to ΔL a reference length L at a temperature T, the temperature T = 25 ° C. in "Ultra low expansion glasses and their structure in the SiO ₂ -TiO ₂ system" by PCSchultz, HTSmyth, Amorphous Materials, September 1970, pages 453-461 is. According to PCSchultz, HTSmyth, Amorphous Materials, September 1970, pages 453–461, the dependence α (T) = ∂ΔL / ∂L applies.

The temperature-dependent thermal coefficient of linear expansion therefore has a value α (T ₀ ) = 0 at a temperature T ₀ , the so-called zero expansion point or the zero crossing point. The temperature T _{0 of} the zerocrossing point depends on the TiO ₂ content.

The temperature-dependent thermal linear expansion coefficient α (T) of glass ceramics shows a sign change from positive to negative for certain compositions for rising temperatures in the temperature range from 20 ° C to 70 ° C, which is of interest for EUV lithography, i.e. this material also shows one Temperature T ₀ a value α (T ₀ ) = 0. This point is referred to as the so-called zero expansion point or zero crossing point.

This behavior results from the fact that the glass ceramics comprise microcrystallites with negative thermal expansion, which are embedded in an amorphous material with positive thermal expansion. The negative thermal expansion of the crystallites cancels the positive thermal expansion of the glass at temperature T ₀ at the zero crossing point and vice versa.

On the basis of the roughness values of the glass ceramic or the TiO ₂ -doped glass, a layer system comprising a large number of layers which, for example, form a multi-layer system for a normal incidence mirror, can be built up on the surface of such a glass or such a glass ceramic become. It is also possible to apply a coating for a grazing incidence EUV mirror to a glass ceramic or a glass as the substrate material. An intermediate layer that is used to achieve the optical surface quality as in the EP 0955565 described between the substrate material and the coating is not necessary.

In addition to the optical components the invention also a lighting system and a projection lens and a projection exposure system available, which at least one includes optical component.

The invention is based on the following of the embodiments be described in detail.

Show it:

1a the schematic course of the thermal coefficient of longitudinal expansion α (T) as a function of the temperature for a TiO ₂ - doped glass in the temperature range of about 20 ° C. to 70 ° C. which is interesting for EUV lithography

1b : the schematic course of the thermal expansion coefficient α (T) as a function of the temperature for a glass ceramic in the temperature range of about 20 ° C. to 70 ° C. which is of interest for EUV lithography

1c the schematic course of the thermal expansion coefficient α (T) as a function of the temperature for a material in which the slope dα / dT changes the sign in the temperature course in the temperature range of about 20 ° C. to 70 ° C. which is interesting for EUV lithography

characters 2a and 2 B the deformation of the mirror surface of the mirror substrate for the and first mirror of a microlithography projection objective with six mirrors in accordance with 3 with a maximum temperature T _max = 30 ° C, where T _o = 20 ° C ( 2a ) and T _o = 30 ° C ( 2 B ) was chosen for the substrate material

characters 2c and 2d the deformation of the mirror surface of the mirror substrate for the second mirror of a microlithography projection objective with six mirrors in accordance with 3 with a maximum temperature T _max = 27 ° C, where T _o = 23 ° C ( 2c ) and T _o = 27 ° C ( 2d ) was chosen for the substrate material.

3 a projection lens with 6 mirrors, of which at least one mirror is an optical component according to the invention

4 an EUV projection exposure system with a light source, a lighting system and a projection lens. The temperature-dependent thermal expansion coefficient of a substrate material is a temperature-dependent function α (T).

For the materials used in the optical components according to the invention, there is more than one option for the course of α (T). These are in the figures 1a to 1c shown.

At the in 1a material shown, the temperature-dependent coefficient of longitudinal expansion changes in the temperature range of about 20 ° C to 70 ° C, which is interesting for EUV lithography, the sign from negative to positive with increasing temperature. The temperature-dependent thermal coefficient of longitudinal expansion thus has a zero crossing at a temperature T ₀ . If the temperature T is greater than T ₀ , the temperature-dependent thermal coefficient of longitudinal expansion is positive, ie the material expands when the temperature rises. For temperatures T less than T ₀ , the temperature-dependent coefficient of thermal expansion is negative, ie the material contracts when the temperature rises. At the in 1a The material shown can be, for example, Ti-alloyed quartz glass. In the area of the zero crossing at the temperature T ₀ , the temperature-dependent course of the coefficient of longitudinal expansion can be determined by the linear relationship α (T) = m · (T – T ₀ ) - as in 1a shown, described. The slope m is in the range 1.5 · 10 ^–9 –K ^–2 ≤ m ≤ 1 · 10 ^{- 7} K ^–2 , depending on the composition of the glass. What is decisive for the invention is not the absolute value of the slope, but the zero crossing of the coefficient of thermal expansion at temperature T ₀ and the adjustability of T ₀ in a temperature range ΔT of, for example, ΔT = 50 K through the material composition. A material composition is preferred, as a further property having a slight slope of, for example, m = 1.5 · 10 ⁻⁹ K ⁻² .

A reverse course for α (T) is obtained for the glass ceramic material Zerodur® (Zerodur®, brand from Schott-Glas, Mainz). For Zerodur®, the course can be approximated by α (T) = m · (T - T ₀ ) in the area of the zero crossing. The slope α for the Zerodur ® material is negative and lies in the range –0.5 · 10 ^–9 K ^–2 ≤ m ≤ –1.0 · 10 ^–8 K ^–2 . The material preferably has a low gradient m of, for example, −1.5 × 10 ⁻⁹ K ⁻² . For temperatures greater than T ₀ , the temperature-dependent thermal expansion coefficient in the temperature range of about 20 ° C to 70 ° C, which is of interest for EUV lithography, is negative, i.e. the material contracts, for temperatures T less than T ₀ , the temperature-dependent thermal expansion coefficient is positive, ie the material expands when the temperature rises. By a suitable choice of the material composition of the glass ceramic, the zero crossing or the zero crossing point can be shifted in a temperature range of ΔT of, for example, ΔT = 50 K.

T ₀ can therefore be set as required. The inventors have now found that an optical component has a minimal aberration when the zero crossing of the temperature-dependent thermal expansion coefficient α (T ₀ ) = 0 is chosen such that T ₀ corresponds to the maximum temperature T _{max of} the respective optical element. The zero crossing at the in 1a and 1b The materials shown are at temperature T ₀ at which the temperature-dependent coefficient of thermal expansion changes the sign from positive to negative with increasing temperature or vice versa from negative to positive. The maximum temperature T _{Max of} the respective optical component, which is preferably a substrate material for a mirror, is the temperature to which the optical component heats up due to absorbed heat radiation. The heating can be caused, for example, by EUV radiation incident on the optical component, which radiation is emitted by a light source, or by actuators or sensors arranged on the substrate material. Due to this heat radiation, the optical component heats up to a temperature T _max . The optimal temperature T _{0 of} the zero crossing of the temperature-dependent thermal coefficient of longitudinal expansion α (T), at which the smallest image errors occur, for example when used as substrate material for mirrors, is T ₀ = T _max . In the case of a mirror, the maximum temperature T _max usually occurs in the middle of the mirror. The mirror surface relevant in this application is the surface on which electromagnetic radiation, for example EUV radiation, strikes and is partially reflected.

Minimal image defects are also found when using materials that do not have a zero crossing of the temperature-dependent thermal expansion coefficient, but a minimum in the course of the temperature-dependent thermal expansion coefficient α (T) at a temperature T ₀ as in 1c shown. In the case of such a material, the derivative of the coefficient of thermal expansion according to the temperature dα (T) / dT has a zero crossing or a change of sign. If T ₀ of such a material can be set, there are minimal image errors when used as substrate material for a mirror if T ₀ is chosen such that the zero crossing of the derivative dα (T) / dT at the maximum temperature T _max is due to the heating the optical component, for example the mirror surface of a substrate material.

The following are special exemplary embodiments can be specified.

2a shows the deformation of a substrate surface for a material with a zero crossing T ₀ = 20 ° C of the temperature-dependent thermal expansion coefficient and 2 B the deformation of a substrate surface, in which the zero crossing of the temperature-dependent thermal coefficient of longitudinal expansion α (T) of the substrate material was chosen to be T ₀ = 30 ° C. The maximum temperature T _max at which the substrate surface, for example the surface of the first mirror of a projection object, for example according to the US 6,353,470 can be heated due to absorbed heat radiation is 30 ° C. As from the 2a and 2 B it can be seen that the deformation due to heating is greater for the mirror with the substrate material with T ₀ = 20 ° C. than for the mirror with the substrate material T ₀ = 30 ° C. The variation of the deformation occurring on the mirrors is shown in FIGS 2a and 2 B represented by contour lines. The variation is the peak-to-valley (PV) value on the mirror surface. The peak-to-valley (pV) value is the difference between maximum deformation and minimum deformation. The peak-to-valley value (pV) value due to thermal expansion at thermal load is for the exemplary embodiment according to 2a 1.7 nm and according 2 B 0.16 nm. The peak-to-valley (pV) value for the material whose zero crossing of the temperature-dependent thermal expansion coefficient corresponds to the maximum temperature T ₀ = T _max is thus significantly lower than for the material with T ₀ <T _max , The image errors due to such deformations induced by heating can be significantly reduced by a suitable choice of, for example, the substrate material with a zero crossing of the temperature-dependent thermal expansion coefficient at the maximum mirror temperature. In the exemplary embodiment according to 2a and 2 B for example, these are reduced by a factor of 10. According to the embodiment 2a and 2 B was based on Ti-doped quartz glass, with α (T) = 1.5 ppb / K ² (T - T ₀ ). As the energy input that leads to the heating of the substrate surface were in the embodiment according to 2a and 2 B 0.8 W assumed. If one assumes a uniform energy input into the optical surface of the mirror substrate, the mirror substrate heats up to the aforementioned maximum temperature of T _max = 30 ° C. The maximum temperature T _max = 30 ° C occurs in the middle of the mirror.

2c and 2d show the deformations due to the heating of the substrate surface of the second mirror of an EUV projection lens, for example according to the US 6,353,470 occur for materials with different zero crossing of the temperature-dependent thermal expansion coefficient. The energy input in the second mirror of a microlithography projection lens is generally less than in the first mirror and is assumed to be 0.5 W over the entire optical surface of the substrate. If Ti-alloyed quartz glass is again used as the substrate material, the temperature rises to a maximum temperature T _Max = 27.5 ° C. When using a substrate material with a zero crossing of the temperature-dependent thermal expansion coefficient with T ₀ = 23 ° C, the peak-to is -valley- (pV) -value 0.34 nm ( 2c ) and when using a substrate material with a zero crossing of the temperature-dependent thermal expansion coefficient at T ₀ = T _max = 27 ° C 0.11 nm ( 2d ). The peak-to-valley (pV) value is the same as for the 2a and 2 B described, defined. In this application the optical surface of the substrate is the substrate surface which forms the mirror surface or in the case of which it has a coating on which the electromagnetic radiation, for example the EUV radiation, strikes and is reflected. The optical surface of the substrate therefore corresponds in its geometric shape to the mirror surface.

As in the 2a and 2 B the first mirror is shown as an elliptical mirror, the long axis of the ellipse being 160 mm long and the short axis of the ellipse being 120 mm long. The second mirror according to 2c and 2d is a circular mirror with a radius of 165 mm.

In 3 is an EUV projection lens like from the US 6,353,470 known known. The EUV projection lens comprises a total of six mirrors. A first mirror S1, a second mirror S2, a third mirror S3, a fourth mirror S4, a fifth mirror S5 and a sixth mirror S6. An object in an object area ne 2 is through the 6-mirror projection lens into a reduced image in one image plane 4 displayed. The aperture B of the projection object is formed on the second mirror S2. The system is centered around the optical axis HA and has an intermediate image Z in the light path from the fourth mirror S4 to the fifth mirror S5.

The mirrors S1, S2, S3, S4, S5 and S6 of the projection objective are designed as normal incidence mirrors with a substrate material and a multi-layer system of Mo / Si alternating layers applied thereon. The substrate material of at least one mirror or a plurality of mirrors S1, S2, S3, S4, S5, S6 is an inventive substrate material whose temperature-dependent thermal expansion coefficient α (T) has a zero crossing at a temperature T ₀ = T _max .

In addition to the substrate material, the idea according to the invention of setting the zero crossing of the temperature-dependent thermal coefficient of longitudinal expansion to the maximum temperature which occurs due to the heating of the optical component can also be applied to the coatings. The only condition for this is that the temperature-dependent thermal expansion coefficient α (T) or its derivative after the temperature dα (T) / dT of the coating material has a zero crossing or a change of sign at a temperature T ₀ , which is in a temperature range that is due to the Heating of the optical component is reached to the maximum.

In 4 An EUV projection exposure system is shown, comprising a light source 100 as well as a lighting system 101 for illuminating a field on one level 102 , in which a structure-bearing mask is arranged and a projection lens 104 , comprising six mirrors, to represent the structure-bearing mask in the plane 102 on a photosensitive substrate in one plane 106 , Regarding the EUV lighting system, the EP-A-1 123 195 , referenced, the disclosure content of which is fully incorporated in the present application. Concerning the 6-mirror lens is on the US 6,353,470 directed.

Each of the optical components of the EUV projection exposure system, ie the optical components of the lighting system or the mirrors of the projection objective or also the reticle or the reflection mask, can be constructed according to the invention, ie have a substrate material or also a coating whose temperature-dependent thermal expansion coefficient α (T) or its derivative after the temperature dα (T) / dT has a zero crossing or a change of sign at a temperature T ₀ , the materials being selected such that the zero crossing of the temperature-dependent thermal expansion coefficient α (T) or its derivative after the temperature dα (T) / dT is chosen so that the temperature T ₀ corresponds to the maximum temperature T _max occurring on the respective component due to heating.

The invention is the first optical components, in particular mirrors for EUV projection lenses specified, the minimal image errors due to appropriate material selection exhibit.

Claims (16)

Optical component which heats up to a maximum temperature T _max , the optical component comprising a material which has a temperature-dependent thermal expansion coefficient a (T), characterized in that the temperature-dependent thermal expansion coefficient α (T) or the derivative of the temperature-dependent thermal expansion coefficient dα (T) / dT after the temperature near a temperature T ₀ the sign changes from positive to negative or from negative to positive with increasing temperature and the temperature T ₀ corresponds approximately to the maximum temperature T _max to which the optical component is heated. Optical component according to claim 1, characterized in that the optical component is an optical Component for electromagnetic radiation with a wavelength λ ≤ 193 nm, especially in the range 5 nm ≤ λ ≤ 20 nm. Optical component according to claim 1 or 2, characterized in that the material has a temperature-dependent thermal expansion coefficient α (T) with an approximately linear temperature dependence α (T) = m · (T - T 0 ) in a temperature range close to the temperature T ₀ and α is the slope of the temperature-dependent coefficient of thermal expansion. Optical component according to Claim 2 or 3, characterized in that the amount of the slope m of the temperature-dependent thermal coefficient of longitudinal expansion of the material in the range | m | <1 · 1 ^-6 K ^-2 , in particular | m | <1 · ^-7 10 ^-7 K ^-2 ; preferred | m | <1 · 10 ^-8 K ^-2 , particularly preferably | m | <2 · 10 ^-9 K ^-2 . Optical component according to one of claims 1 to 4, characterized in that the optical component comprises a material which has a temperature-dependent thermal expansion coefficient α (T), the temperature-dependent thermal expansion coefficient α (T) or the derivative of the temperature-dependent thermal expansion coefficient dα (T) / dT according to the temperature near a temperature T ₀ Sign changes from positive to negative or from negative to positive with increasing temperature and the temperature T ₀ corresponds approximately to the maximum temperature T _max to which the optical component is heated, and the material is a substrate material. Optical component according to claim 5, characterized in that the optical component is a coating comprises, which is applied to the substrate material. Optical component according to claim 5 or 6, characterized in that the substrate material of a of the following materials is: a glass ceramic Ti-alloyed quartz glass Optical component according to one of claims 1 to 7, characterized in that the optical component Reticle mask for is EUV lithography. Optical component according to one of claims 5 to 7, characterized in that the optical component Mirror with a substrate material and a coating, the at least one Layer is. Optical component according to claim 9, characterized in that the at least one layer is a ruthenium, palladium or Rhodium Schichtumfasst. Optical component according to claim 9, characterized in that the Coating comprises a multiplicity of layers, which form a multilayer system, where the layer pairs are one of the following materials Mo / Si Mo / Be MoRu / Be includes. Lighting system for Wavelengths ≤ 193 nm, in particular for the EUV lithography for illuminating a level with a field, characterized in that that at least an optical component of the lighting system an optical component according to one of claims 1 to 11. Projection lens for Wavelengths ≤ 193 nm for Illustration of an object in an object plane in an image in a Image plane, characterized in that at least one optical Component of the projection lens an optical component according to a of claims 1 to 11. Projection lens according to claim 12, characterized in that the Projection lens has a plurality of mirrors and at least one mirror an optical component according to one of the Expectations 1 to 11. Projection exposure system for microlithography with a radiation source a lighting system that matches that of radiation generated by the source partially collects and illuminates forward a level with a ring field of a structure wearing mask on a support system, this mask lies in the plane of the ring field a projection lens, which masks the illuminated part of the structure Depicts image field a light-sensitive substrate on a carrier system, wherein the light-sensitive substrate in the plane of the image field of the projection device lies, characterized in that at least one optical Component of the EUV projection exposure system an optical component according to one of claims 1 to 11 comprises. Process for the production of microelectronic components, in particular semiconductor chips, with a projection exposure system according to claim 15.