JPH01150037A - Vibro-isolating mechanism - Google Patents

Abstract

PURPOSE:To promote the improvement of high accurate positioning performance stably obtaining the vibration characteristic of a device total unit by controlling the spring rigidity in a horizontal direction by the shearing rigidity of an elastic unit and the spring rigidity in a vertical direction by the elastic deformation of a ball group. CONSTITUTION:A unit, constituted of a ball group 2 of steel or the like held by a holding fixture 3 and a ball group supporting bed 4 serving as the surface for the ball group 2 to roll, is suitably built in layers. The ball group supporting bed 4 of the mutually different layer built unit is connected by an elastic unit 5 of rubber or the like. A mechanism controls the spring rigidity in a horizontal direction by the shearing rigidity of the elastic unit 5 and supports the spring rigidity in a vertical direction by the elastic deformation of the ball group 2. Thus stably obtaining the vibration characteristic of a device structure, the improvement of high accurate positioning performance is promoted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a vibration isolating mechanism, and more particularly to a vibration isolating mechanism suitable for reducing vibration of an apparatus structure that receives a horizontal driving force, such as a reduction projection exposure apparatus. It is something.

[Conventional technology]

A known air spring type vibration isolator currently in practical use is Catalog 5WT-1708 of Showa Cable and Wire Co., Ltd.
There is a ``Showa era vibration isolation table, surface plate.'' An example thereof is outlined in FIG. The container body 11 and the support stand 12 are connected via a diaphragm 13, and the inside of the container body 11 is composed of an air chamber 14 and an oil tank 15.
An intake valve 16 and an exhaust valve 17 are provided,
In response to mechanical operation commands from the pressure regulating device, air is sucked and exhausted so that the air pressure in the air chamber 14 can be maintained within a constant band. With this basic configuration, it is possible to create a vibration isolator that has a splash characteristic in which the stiffness of the air chamber 14 dominates in the vertical direction, and a bounce characteristic in which the rigidity in the horizontal plane of the diaphragm 13 dominates in the horizontal direction. It has been realized. Support stand 1
The attenuator 18 attached to the lower end of the paper 2 is intended to attenuate, for example, rotation around an axis perpendicular to the plane of the paper. This type of vibration isolator has a structure in which the spring stiffness in the vertical direction is smaller than that in the horizontal direction, leading to a rigid body rocking vibration mode.

[Problem that the invention seeks to solve]

With the above conventional technology, the spring stiffness in the vertical and horizontal directions changes due to the average air pressure supplied and time fluctuations in the air pressure, making it difficult to maintain the stability of optimal vibration isolation characteristics, and causing variations in the vibration characteristics of the entire device system. occurs. In a reduction projection exposure apparatus, the stage is driven in steps at certain time intervals to repeat an exposure sequence. Therefore, as ideal vibration characteristics, it is desirable that the initial state of each exposure cycle is always constant. By the way, in the conventional air spring system, the intake and exhaust valves operate in response to a mechanical operation command from a separately provided pressure regulator. In this case, the unavoidable dead zone of the pressure regulator causes variations in the response characteristics of the intake and exhaust valves, making it impossible to maintain a constant initial state for each exposure cycle.

In addition, in the conventional air spring method, the spring stiffness in the vertical direction is almost determined by the air pressure, and the practical value is 3 to 6 kg/mm, whereas the stiffness in the horizontal plane of the diaphragm is The spring in the dominant horizontal plane is 10-20 kg/rm.

This method is characterized by the fact that the spring stiffness in the horizontal direction is greater than the spring stiffness in the vertical direction due to structural constraints, and that the spring stiffness in the vertical direction is considerably smaller than other methods. The functions of a vibration isolator for a reduction projection exposure apparatus include (1) cutting off transmission of installation floor vibration to the apparatus, and (2) reducing vibration of the apparatus in response to stage step driving force. The conventional air spring method.

Function (1) above is satisfied, but function (2) is problematic. Figure 5 shows an example of the residual vibration mode when a stage step driving force acts on the entire structure of the apparatus supported by conventional air springs, where 20 is the stage, 21 is the column body, and the upper and lower parts of the apparatus are the exposure optical axis. 22 will be subjected to forcing forces that will cause displacements in opposite phases to each other.

Such a vibration mode adversely affects the high precision positioning of the exposure optical system, which is a condition for realizing fine IC pattern exposure. That is, the reference points of the reticle 23 and the wafer 24 held on the stage 20, which must form the same exposure optical axis 22, are deformed by the vibrational force, resulting in relative positional deviation.

As shown in the figure, the reticle 23 and the wafer 24 are mounted on different structures, and therefore a certain degree of relative displacement must be allowed. It is important to keep the amount to a very small amount. This is because the support spring rigidity in the horizontal direction, which coincides with the plane of action of the stage step driving force, is greater than the support spring rigidity in the vertical direction, and is an unavoidable phenomenon in the air spring system.

The purpose of the present invention is to solve the problems of the prior art described above,
We have developed a vibration isolation mechanism that has constant spring stiffness and good responsiveness, can stabilize the vibration characteristics of the entire device, and also enables high-precision positioning even against the action of stage step driving force. It is about providing.

[Means for solving problems]

The above purpose is to provide a spring rigid member having relatively small elasticity and moderate viscosity in the horizontal direction, and a spring rigid member having considerably greater spring rigidity than the horizontal spring rigid member in the vertical direction. The structure is achieved by combining the rigid member and the spring rigid member.

In the operation cycle of a stepper, the time required for one step of the stage to move is currently 0.5 seconds or less due to throughput constraints.
When referring to a)), the stage driving force generated thereby acts on the device structure as a horizontal external force. Looking at the spectrum analysis results of the driving force due to speed control (see the solid line in Figure 2 (b)), it is found that f 3-5 Hz region, f 49
There is a relatively large excitation force component in the ~11Hz region, etc.
A minimum region exists in the frequency region between these. Particularly for device structures, the excitation force component of 3 to 5 Hz is a problem, and it is essential to suppress the vibration displacement due to this component as small as possible. Conventional air spring type vibration isolation tables are not flexible enough to achieve such characteristics, and for example, the resonance point is indicated by the Δ mark in Fig. 2(b), and the resonance point is indicated by the broken line in Fig. 2(c). Therefore, optimum characteristics cannot be obtained.

Therefore, in the present invention, it is possible to set the resonance point in the minimum excitation force region, which is impossible in the conventional type, as shown by the circle mark in Fig. 2 (b), and as a result, as shown in Fig. 2 (Q). The vibration displacement can be minimized as shown by the solid line.

[Effect]

The support spring characteristics in the horizontal and vertical directions are superior in response characteristics compared to air springs by using a solid elastic body such as a rubber material.

Since it exhibits stable spring characteristics, the vibration characteristics of the entire device supported by it are stabilized, and vibration isolation performance can be improved.

In addition, by using a vibration isolation mechanism in which the stiffness of the support spring in the horizontal direction is relatively small and the stiffness of the support spring in the vertical direction is considerably large, the residual vibration component when the stage step driving force is applied is reduced to f. It can be set in the < I Hz region and the region where the excitation force is minimal. By adopting the spring rigidity structure of the present invention, it is possible to leave the horizontal translating rigid body vibration mode, and it is possible to minimize the vibration displacement of the device structure, contributing to high precision positioning.

〔Example〕

The present invention will be described in detail below with reference to the embodiment shown in FIG. 1 and FIG. 3.

FIG. 1 is a longitudinal sectional view showing an embodiment of the vibration isolation mechanism of the present invention. In Fig. 1, 1 is an installation floor, 2 is a steel ball, 3 is a holder, 4 is a steel ball support, 5 is a rubber material, 6 is a load holder,
A steel ball support base that is connected to the inner circumference of the holder 3 of a steel ball ring portion, which is composed of a group of steel balls 2 arranged at appropriate pitches in the same plane and a holder 3 for holding them together. 4 are piled up an appropriate number of times as shown in the figure, a rubber material 5 having appropriate elasticity is interposed between each layer, and the upper and lower surfaces of the rubber material 5 are covered with different layers of steel ball supports. 4 and is integrally joined by adhesive or the like.

Such a mechanism is interposed between the load pedestal 6 that supports the weight of the device and the installation floor 1.

When the stage step driving force in the horizontal plane acts on this vibration isolating mechanism, the shear resistance and spring rigidity of the rubber material 5 between each layer are controlled in the horizontal direction, and the steel ball group 2 acts on the steel ball support base 4.
The rolling friction force when rolling on the surface and the viscosity of the rubber material 5 act as damping elements. If the plate thickness of the rubber material 5 in each interlayer i is t, the shear resistance area is AI, and the transverse elastic modulus is Gi, then the horizontal overall spring constant KM can be set by the following relational expression.

'Gi・A.

On the other hand, the spring rigidity in the vertical direction is controlled by the amount of elastic contact displacement between the steel ball group 2 and the steel ball support base 4, and is determined using the well-known Hertz equation. The overall spring constant Kv in the vertical direction is
The fulcrum load is P, and the radius, longitudinal elastic modulus, and Poisson's ratio of steel ball 2 are RB, respectively.

If EB, νB, the longitudinal elastic modulus and Poisson's ratio of the steel ball support 4 are Es and vs, respectively, and the amount of elastic displacement between each layer is δ2I, then Kv=-°=(4) Σ □ ' kZI , The vertical spring stiffness Kv can be set to a much larger value than the horizontal spring stiffness Kn.

When a horizontal force during stage step drive is applied to a device structure mounted on a vibration isolation mechanism having such characteristics, a vibration mode as shown in FIG. 3 remains. In the air spring support mechanism, the upper and lower parts of the device have a residual vibration mode in which the phases are opposite to each other (see Fig. 5), whereas in the vibration isolation mechanism of the present invention, the upper and lower parts of the device have the same phase. A vibration mode that is subjected to forced force remains. By making the spring stiffness in the horizontal direction relatively small and the spring tonality in the vertical direction considerably large, it is possible to provide a support vibration isolation mechanism that is effective in improving high-precision positioning performance.

〔Effect of the invention〕

As explained above, according to the present invention, since a solid elastic body is used as a spring rigid element, the response characteristics are good.
Moreover, it exhibits stable characteristics, and therefore, the vibration characteristics of the device structure supported by these mechanisms are stabilized, and it is effective in realizing low vibration. By using a support mechanism with a small spring stiffness in the horizontal direction, a residual vibration mode can be created that is advantageous for improving the performance of high-precision positioning, and is effective in reducing vibration.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an embodiment of the vibration isolation mechanism of the present invention;
Fig. 2 is a diagram for explaining the present invention in detail, Fig. 3 is a schematic diagram of the residual vibration mode during operation of the device structure mounted in the vibration isolation mechanism of the present invention, and Fig. 4 is a diagram for explaining the vibration isolation mechanism of the present invention. A vertical cross-sectional view of the spring-type vibration isolation mechanism, and FIG. 5 is a schematic diagram of the residual vibration mode during operation of the device structure mounted in the air-spring type vibration isolation mechanism. Body, 3... Holder,
4...Steel ball support stand, 5...Rubber material, 6...Load receiving stand. (1 other person) ', 1 :j, -4,'-2 $ 1 Figure 1 - 1 body 2 - autopsy 3 - holder 4 - @ ball supporter 5 - boom talent r ot - m - Load cradle No. Z mouth tea 30

Claims (1)

[Claims] 1. A unit consisting of a ball group made of steel or the like held by a holder and a ball group support base that is a surface on which the ball group rolls is appropriately stacked, and the ball group support of different laminated units is performed. In a support mechanism in which a base is coupled with an elastic body such as rubber, the spring stiffness in the horizontal direction is controlled by the shear stiffness of the elastic body, and the spring stiffness in the vertical direction is controlled by the elastic deformation of the group of balls. A vibration isolation mechanism characterized in that the spring stiffness in the horizontal direction is made small and the spring stiffness in the vertical direction is made considerably large.