WO2006077515A2

WO2006077515A2 - Actuator and its manufacturing method

Info

Publication number: WO2006077515A2
Application number: PCT/IB2006/050144
Authority: WO
Inventors: Bartholomeus Van Nunen; Martin Brinkhuis
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2005-01-19
Filing date: 2006-01-16
Publication date: 2006-07-27
Also published as: WO2006077515A3

Abstract

In semiconductor equipments, actuators are, for instance, rectangular sheet metal boxes (12) where magnetic or electromagnetic radiation sources (11) such as electromagnetic coils have been inserted. The coils are positioned by filling the rectangular sheet metal box with a glue or moulding compound (13). By switching on the electromagnetic coils, a stage makes linear X- and Y-motions. However, the electromagnetic fields induced by the electromagnetic coils can disturb the object on the stage. The actuator 10 according to the invention solves this problem by using ferromagnetic particles in the glue or moulding compound to shield off the unwanted electromagnetic fields. If required, the rectangular sheet metal boxes can be removed after hardening of the glue or moulding compound.

Description

ACTUATOR AND ITS MANUFACTURING METHOD

FIELD OF THE INVENTION

The present invention relates to the manufacturing of actuators for any product which uses magnetic radiation sources and has sensitive parts which need shielding of the magnetic fields. For example, actuators are applied in stages and manipulators which are used in equipments for manufacturing semiconductor products, such as, for instance, electron microscopes, wafer steppers, electron beam generators.

The continuous drive for development of such equipments requires new and novel approaches to manufacture the actuators which are embedded therein. An actuators uses magnetic radiation sources such as static magnets or electromagnetic coils to induce movements that are then used in stages and manipulators. The use of the magnetic radiation sources creates magnetic fields which, in some applications, are disturbing the electron beam or influence electric parts of the equipment. Therefore, shielding of these magnetic fields is required. Magnetic fields cannot be blocked or reflected, but only redirected. To realize this, special shielding alloys with high permeability are required.

BACKGROUND OF THE INVENTION

Magnetic shielding, also known as magnetic shields, magnetic screens and EMI (ElectroMagnetic Interference) shielding, prevents magnetic fields from reaching areas where they would cause magnetic interference. Magnetic shielding is used either around the source of interference, to prevent electromagnetic radiation from leaving a device, or, more typically, around a sensitive device, to prevent the electromagnetic interference from disrupting normal operation of said device. The present invention falls into the first category.

Currently, designers shield off the parts that are sensitive to the magnetic fields with sheets of so-called μ-metal. This refers to special shielding alloys with high magnetic permeability (μ). Magnetic permeability refers to a material's ability to attract and conduct magnetic lines of flux. The more conductive a material is to magnetic fields, the higher its magnetic permeability. These alloys work by diverting the magnetic flux to themselves. As illustrated in the document US 2002/0096640 Al, welding and bending techniques are used to shape the sheets of μ-metal around the actuator manufactured in this way. Then, the final processing step is to anneal the end product. When manufacturing actuators by this way, the magnetic field is greatly reduced by the magnetic shielding.

However, a number of problems arise. In particular, only rectangular shapes can be made. Besides, no overall shielding of the magnetic fields can be obtained by using only rectangular shapes. The use of ferromagnetic particles in a fluid, so-called "ferrofluids", is already known but not for shielding off magnetic fields, and not in the manufacturing of actuators.

SUMMARY OF THE INVENTION

A first object of the present invention is to improve and simplify the manufacturing of magnetic shielding.

This object is achieved, according to a first aspect of the present invention, thanks to a method of manufacturing an actuator comprising the steps of :

- inserting at least one magnetic or electromagnetic source into a box of any form ;

- pouring into said box a glue or a moulding compound filled with particles of ferromagnetic material, so that said magnetic source is partially surrounded by said glue or moulding compound.

Hence, the shielding effect is provided by the ferromagnetic particles, instead of μ-metal plates or sheets.

The box may be removed after hardening of the glue or moulding compound. In this case, the box is used as a moulding box only. In a particularly advantageous way of carrying out the method, however, the box may be a magnetic source holder and the glue or moulding compound may be used to fix the magnetic source within said magnetic source holder. The magnetic source and its holder may subsequently be installed in one equipment.

A second object of the present invention is to increase the freedom in the design of magnetic shielding, so as to overcome the aforementioned problems.

This is achieved, according to a second aspect of the present invention, thanks to an actuator comprising at least one magnetic or electromagnetic radiation source to induce movement, wherein said magnetic or electromagnetic radiation source is partially surrounded by a glue or moulding material filled with particles of ferromagnetic material.

The present invention gives freedom in engineering and enables the design of highly complex actuators.

An additional advantage of the ferromagnetic particles is the increase in thermal conductivity of these types of actuators. This makes better cooling of the actuators possible.

A third object of the present invention is to propose semiconductor equipment such as, for instance, an electron microscope, a wafer stepper, or an electron beam generator, in which unwanted magnetic fields generated by magnetic or electromagnetic radiation sources of actuators are shielded off.

This object is achieved thanks to an equipment which comprises at least one stage and at least one actuator for driving movement of said stage, said actuator being of the type according to the second aspect of the invention.

To summarize the invention, the basic idea of underlying present invention is to use a free formed mass shielding of the magnetic fields around the magnetic or electromagnetic source of the actuator. The invention is realizing this by pouring small particles, such as ferromagnetic nanoballs or μ-metal particles, into the glue or moulding compound to fix the magnetic or electromagnetic source of the actuator.

The above summary of the present invention is not intended to represent each disclosed embodiment, or every aspect, of the present invention.

Other aspects and example embodiments are provided in the figures and the detailed description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:

- Figs 1 to 5 illustrate steps of a method of manufacturing an actuator according to one aspect of the present invention ; - Fig. 6 is a schematic view of a substrate stage of a semiconductor equipment according to another aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION An actuator for semiconductor equipment uses magnetic radiation sources such as static magnets or electromagnetic radiation sources such as electromagnetic coils to induce movements. In some applications, the magnetic fields created by the use of said sources disturb the electron beam or influence electrical parts of the equipment. Shielding of the magnetic field is thus required. Unlike some waves, magnetic fields do not travel in straight lines, but are in loops, starting from the magnetic or electromagnetic radiation source and eventually returning there.

In Figs 1 through 5, a simplified representation of an actuator is shown, at different steps of its manufacturing process, according to embodiments of the second and first aspects, respectively, of the present invention. In a first step represented in Fig.1 , a magnetic or electromagnetic radiation source 11 for inducing movements, such as a static magnet or electromagnetic coil, is inserted into a box 12. The configuration depicted in Fig.2 is thus obtained. The box 12 can form a magnetic source holder, intended for being installed in the equipment. It can be manufactured in any desired shape or form (it is here represented by a rectangular box) and can be a sheet metal box. In one embodiment, however, the holder is made of a non-magnetic material, since shielding effect is provided by other means which shall now be explained. Such non-magnetic material, e.g., polycarbonate, makes it easier to design the base with more complicated shape.

The next step is illustrated in Fig.3. A glue or a moulding compound 13 is poured in the free space between the box 12 and the radiation source 11, for positioning the magnet and/or fixing the same. The radiation source 11 becomes partially surrounded by the material consisting of the glue or the moulding compound. To provide magnetic shielding of the actuator (to prevent unwanted magnetic fields disturbing or influencing devices or electron beams in the vicinity of the actuator), the glue or the moulding compound is filled with particles of ferromagnetic material, such as so-called ferromagnetic nanoballs or μ-metal particles. The magnetic shielding thus obtained can be of any desired shape. There is no limitation to rectangular shapes, as in the prior art. The shape is defined by the shape of the box. As an additional advantage, the ferromagnetic particles increase the thermal conductivity of the actuator. After hardening of the glue or of the moulding compound, the actuator is ready for use. An actuator 10 of this type is depicted in Fig. 4.

In some applications, it may be necessary or desirable to remove the rectangular box 12, after hardening of the moulding compound, for using the actuator in the equipment. An actuator 20 illustrated in Fig.5 is thus obtained. In such applications, the ferromagnetic particles are provided in a moulding compound (not in a glue). In this way, the box only acts as a moulding base.

The magnetic shielding material serves as a path for the magnetic field lines, attracting the magnetic energy into the thickness of the material, and keeping it from going where it is not wanted. It is preferable that the magnetic shielding offers a complete path for the field lines, so that they do not exit the material in a place where they will cause unintended interference.

The main constraint for obtaining a satisfactory shielding effect is the homogeneous distribution of the ferromagnetic particles in the glue or moulding compound. In order to ensure such homogeneous distribution, any mixing process, e.g. mechanical and/or electromechanical mixing process, may be carried out while filling the particles within the glue or the moulding compound.

Attenuation is a ratio used to measure the effectiveness of a given shield. Permeability refers to a material's ability to attract and conduct magnetic lines of flux. The more conductive a material is to magnetic fields, the higher its permeability. Saturation is the limiting point of a material to conduct additional magnetic lines of flux. The saturation and permeability characteristics of a material are inversely related, therefore the higher a material's permeability, the lower its saturation point.

Materials with high magnetic permeability provide high attenuation in a magnetic shield. For applications involving very strong magnetic fields, materials with relatively high saturation induction rating shall be preferred, although providing more modest attenuation factors.

If very high attenuation ratios must be achieved in a very strong field, sometimes two alloys must be used. The alloy with relatively high saturation induction rating and relatively lower attenuation factor is used closest to the source of the field to protect the other alloy from saturation.

In one exemplary embodiment, ferromagnetic materials suitable for the particles include nickel iron (NiFe), nickel iron cobalt (NiFeCo), cobalt iron (CoFe), other magnetically soft alloys of NiFe and Co, doped amorphous ferromagnetic alloys, and other ferromagnetic materials. Selection of a desirable ferromagnetic material is based on the strength of the magnetic field to be shielded, the required shield performance, operational factors, and the like.

Some embodiments of the invention also make provisions for applications in vacuum. If the actuator and the stage of the equipment are positioned in a vacuum chamber, the glue used for positioning the magnetic radiation source needs to be vacuum compatible. There are two main characteristics for vacuum compatible glue. First, it must be a single or dual component, 100% solid, heat-curing epoxy designed for high temperature applications. Additionally, it must be a material with low outgassing properties (dependent on vacuum requirements). Examples of vacuum compatible glues are, in particular, Epotek 353 ND™ (trademark of Epoxy Technology), Trabond 2248™ and Trabond 2254™ (trademarks of Tra-Con, Inc.). By using such a vacuum compatible glue, the actuator can also be used in a vacuum environment. Fig.6 shows an exemplary embodiment of a part of a semiconductor equipment according to the third aspect of the present invention. The equipment may be an electron microscope, a wafer stepper, an electron beam generator, other microlithography apparatus or, more generally, any kind of equipment for manufacturing semiconductor products (e.g., an electronic chip or the like). The part of the equipment which is shown in Fig.6 is a substrate stage 30. Such a stage is configured to hold a substrate (e.g., a semiconductor wafer) during a step (e.g., microlithography exposure) of a process of manufacturing a semiconductor product.

In operation, the substrate stage is situated downstream of a (non represented) illumination-optical and projection-optical system (typically a deep-ultraviolet beam generator), a charged particle beam generating device, or the like. The stage is movable, and is actuated by respective actuators, each comprising at least one controllable magnetic radiation source (e.g. an electromagnetic coil). The substrate stage can be regarded as extending in a respective X-Y plane that is perpendicular to a Z-axis. The Z-axis is parallel to the optical axis of the illumination-optical and projection-optical systems. To this end, a stage device 32 is driven in each of the X- and Y-axis direction by a pair of actuators 33,33' and 34,34' respectively. More specifically, the stage device 32 is slidably mounted (through non represented rail-guides) between the pairs of actuators 33,33' and 34,34', which are facing two-by-two along the X-axis and the Y-axis, respectively. By switching on the electromagnetic coils, the stage makes linear X- and Y-motions.

Other stages and other actuators may be present in the equipment, such as, for instance, actuators used to drive motion of a (movable) reticle stage in a microlithography apparatus (e.g., an electron beam generator or the like).

In conventional equipments, such stages and their respective actuators are enclosed in a respective chamber of substantially rectangular shape that is made of a ferromagnetic material to shield off magnetic fields. In embodiments of the present invention, however, at least some of the actuators are of one of the hereinabove described types. Stated otherwise, they are sealed by hardened glue or compound material filled with ferromagnetic particles which provide magnetic shielding effect.

While there has been illustrated and described what are presently considered to be the preferred embodiments of the present invention, it will be understood by those skilled in the art that various other modifications may be made, and equivalents may be substituted, without departing from the true scope of the present invention. Additionally, many modifications may be made to adapt a particular situation to the teachings of the present invention without departing from the central inventive concept described herein. Furthermore, an embodiment of the present invention may not include all of the features described above. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed, but that the invention include all embodiments falling within the scope of the appended claims.

Claims

1. Method of manufacturing an actuator characterized in that it comprises the steps of :

- inserting at least one magnetic or electromagnetic radiation source into a box of any form; - pouring into said box a glue or a moulding compound filled with particles of ferromagnetic material, so that said magnetic source is partially surrounded by said glue or moulding compound.

2. Method according to claim 1, wherein the box is removed after hardening of the glue or moulding compound.

3. Method according to claim 1, wherein the glue or moulding compound is vacuum compatible.

4. Method according to claim 3, wherein the glue or moulding compound is selected in the group consisting of Epotek 353 ND™, Trabond 2248™ and Trabond 2254.

5. Method according to any one of the preceding claims wherein the ferromagnetic material is selected in the group consisting of NiFe, NiFeCo, CoFe, other magnetically soft alloys of NiFe and Co, and doped amorphous ferromagnetic alloys.

6. Actuator comprising at least one magnetic or electromagnetic radiation source to induce movement, characterized in that said magnetic or electromagnetic radiation source is partially surrounded by a glue or moulding compound filled with particles of ferromagnetic material.

7. Actuator according to claim 6, further comprising a magnetic or electromagnetic radiation source holder for holding the magnetic or electromagnetic radiation source, and wherein said magnetic or electromagnetic radiation source is fixed within said magnetic or electromagnetic radiation source holder by the glue or moulding compound.

8. Actuator according to claim 6 or 7 wherein the glue or moulding compound is vacuum compatible.

9. Actuator according to claim 8, wherein the glue or moulding compound is selected in the group consisting of Epotek 353 ND™, Trabond 2248™ and Trabond 2254™.

10. Actuator according to any one of claims 6 through 9, wherein the ferromagnetic material is selected in the group consisting of NiFe, NiFeCo, CoFe, other magnetically soft alloys of NiFe and Co, and doped amorphous ferromagnetic alloys.

11. Actuator according to any one of claims 6 through 10, wherein the magnetic or electromagnetic radiation source comprises a static magnet or an electromagnetic coil.

12. Actuator according to any one of claims 6 through 11 , wherein the box is made of a non-magnetic material.

13. Semiconductor equipment, comprising at least one stage and at least one actuator for driving movement of said stage, characterized in that said actuator is of the type defined in any one of claims 6 through 12.