WO2011006650A1

WO2011006650A1 - Microstructuring, polishing method and polishing device for correcting geometric deviation defects on precision surfaces

Info

Publication number: WO2011006650A1
Application number: PCT/EP2010/004294
Authority: WO
Inventors: Jan-Peter Urbach
Original assignee: Jan-Peter Urbach
Priority date: 2009-07-15
Filing date: 2010-07-14
Publication date: 2011-01-20
Also published as: DE102009033206A1

Abstract

The invention discloses a method for microstructuring for improving known polishing methods and polishing devices for correcting geometric deviation defects on precision surfaces. In order to determine the microstructure for the purpose of improving a polishing method to be applied to a workpiece surface, first a surface deviation of a workpiece surface from a desired target geometry is determined. The microstructure to be impressed on the workpiece surface is subsequently determined, wherein the surface structure of the microstructure has a shorter wavelength than the original workpiece surface and is selected such that long wavelength deviations of the workpiece surface from the target geometry are compensated for, so that after the determined microstructure has been impressed onto the workpiece surface, improved polishing results and/or shorter polishing times can be achieved in a polishing method to be carried out thereafter. The surface geometry of a workpiece surface after a polishing method can be calculated, for example, on the basis of a process model.

Description

Microstructuring, polishing and polishing device for correcting geometric deviation errors

precision surfaces

Field of the invention

The invention relates to the improvement of a polishing method and a polishing apparatus that can be used to correct geometric deviation errors on precision surfaces. In particular, the invention relates to a method for determining a macrostructure for the purpose of improving a workpiece surface

polishing method to be applied, a microstructuring method for improving a polishing method to be applied to a workpiece surface, a method for polishing and shaping workpiece surfaces, a computer program product having a program code for executing the methods of the invention, and apparatuses related to the methods.

State of the art

Many technical applications require surfaces of a well-defined shape. The degree of deviation of the actual shape from that adopted in the technical process is decisive for the applicability.

Examples of applications where the accuracy of such well-defined

Surface forms play an essential role:

Surfaces of optical elements such as lenses and mirrors:

In optical systems, the desired imaging properties are achieved by using the electromagnetic field of the light used by refraction (lenses). and the reflection (mirror) at well-defined interfaces of materials

different optical properties is influenced in the desired manner. The tolerable deviations from the ideal surface shape are in the range of fractions of the wavelength. The smaller the deviation, the greater the quality of the optical image. Especially for optical systems with high numerical apertures, as used for example in the projection systems for semiconductor lithography, it is aggravating that the shape of the optical interfaces can no longer be approximated by a simple spherical surface, but aspherical geometries are necessary.

Planarity of surfaces to be structured in semiconductor and microsystem production: In semiconductor manufacturing, the electronic components are built up on silicon substrates by means of lithographic patterning methods. Because of

Efficiency is trying to make the dimensions of the components (in particular the transistors) smaller and smaller in order to increase the number of components per silicon area unit. The optical imaging techniques used thereby also become more sensitive to defocus errors with increasing resolving power, i.

In particular, deviations from the surface to be structured by the

Focus plane of the optical system. Therefore, it is necessary to structure the

To get surfaces as planar as possible. This applies to both the surface of the

Starting substrates as well as for the surface of intermediate layers. For example, the surfaces of dielectric layers that insulate the electronic components from the overlying metallization level or successive metallization levels must be very flat.

Planarity of mask substrates in EUV (extreme ultraviolet) lithography:

To the above mentioned trend to ever smaller structure sizes in the

To pursue semiconductor manufacturing further, it is necessary to use smaller wavelengths than the currently used. A common approach is to use soft

X-radiation with a vacuum wavelength of about 13.5nm to use. For this radiation, no sufficiently transparent material is known for use in refractive optical elements. Therefore, optical systems are constructed exclusively of reflective elements. In order to separate the incident from the reflected beam spatially, is used with angles of incidence, which differ slightly from the vertical incidence (typically 6 degrees). For the photomask, which carries the circuit pattern to be imaged, this results again a very strict requirement for the planarity of the surface. As shown in Figure 1, each local vertical deviation translates into a lateral offset of the imaging rays. An incident beam (2) is reflected by the ideal planar surface (3) (beam (6)). A surface (4) deviating from the ideal surface reflects a beam (1) incident at the same point at a different height. As a result, in the reflected beam (5) an offset from that of the ideal planar

Surface reflected beam (6) generated.

Hard drive disks:

In today's popular magnetic mass storage, the so-called

Hard disk drives, the binary information is stored as a polarization direction of a small magnetic domain. The domains are formed by a magnetic layer deposited on a rapidly rotating disk. For read access, a magnetic sensor must be guided over the magnetic layer at a very short distance in order to be able to measure the polarization direction of the domains without any doubt. In order to allow for the necessary small distances between the read head and magnetic layer at the required high reading speeds, the magnetic layer must be applied to a very flat substrate.

Typically, in the applications described above, the deviations from the target or target geometry may be only a few nanometers.

For simplification, in the following the term "workpiece surface" refers only to that part of the surface of the workpiece for which the requirements with respect to shape deviation and roughness are to apply.

It is customary in technical optics to divide curved surfaces, which deviate from the spherical geometry, into so-called aspheres and free-form surfaces, the first term designating those surfaces which still have a rotational symmetry. Since this distinction is not essential to the application of the method disclosed herein, the terms "free-form surface" and "aspheric" surface or "asphere" in the following are used as synonymous terms for a curved surface deviating from the spherical shape.

In order to meet the surface shape deviation requirements described above, prior art polishing techniques are used. The need For the use of such polishing process arises from the fact that the previous process steps have left an intolerable surface roughness.

For optical components and also wafer substrates, these are mechanical processing methods such as sawing, grinding or milling, with which the workpiece surface is brought into the desired shape.

In the case of semiconductor fabrication and in the fabrication of microsystems, the roughness arises from the fact that an integrated circuit or a microsystem is built up of several layers of locally delineated components of finite height. The components are usually fabricated using lithographic techniques that have a finite depth of image. The component height in a layer intrinsically creates one

Surface roughness, which adversely affects the lithographic patterning of

subsequent component level.

Polishing processes have the task of reducing the surface roughness left over from the preceding process steps to the required level, but without changing the surface shape beyond the tolerable level. The following is a brief overview of various existing polishing methods are given.

Surface polishing process

Surface polishing processes use moldings of non-deformable materials whose shape is the negative impression of the workpiece surface, also referred to below as the polishing pad carrier. On these moldings polishing pad made of elastic materials are attached.

The resulting polishing head is pressed by a suitable mechanical device under a defined pressure on the workpiece surface. At the same time the workpiece and the polishing head are set in motion such that their surfaces perform a relative movement to each other.

In the gap between polishing pad and workpiece a so-called polishing agent is given, this is typically a suspension of very small polishing particles of a sufficiently hard material. Furthermore, suitable reagents for a chemical attack on the material to be polished are optionally dissolved in the liquid.

The polishing particles in the suspension are from the polishing pad against the workpiece surface pressed and simultaneously moved by the relative movement over the surface. This combination of pressure and movement causes a material removal similar to

macroscopic scratching.

This mechanical removal of material can be assisted by the chemical attack of the surface by the reagents contained in the abrasive change the chemical nature of the surface so that the mechanical removal is facilitated or even made possible.

In such polishing processes, the macroscopic material removal can be described by the so-called Preston equation (F.W. Preston, "The theory and design of plate glass polishing machines," J. Soc. Glass Technol., 11, 214-256 (1927)). That is, the removal rate is proportional to the product of contact pressure and relative speed between the two surfaces. The proportionality constant is the so-called preston coefficient. He is particularly dependent on the material of the workpiece surface and of the

Properties of the polishing suspension.

From the pressure dependence of the material removal results in the smoothing effect of the process. At local elevations of the surface of the elastic polishing pad is pressed more. Therefore, it provides a stronger resistance to the pressing surface. This local pressure gain causes a larger material removal according to the above-mentioned Preston equation than in the lower environment. This removes the local elevation faster. This effect continues until the compression of the polishing pad over the entire contact surface is the same. Then there is the same contact pressure everywhere, and the surface of the workpiece is only evenly removed.

It is immediately clear that in this method, the surface shape of the workpiece will gradually conform to the shape of the polishing head, and more so the longer the polishing takes. For flat workpieces, this means that the polishing pad carrier and the polishing pad itself must be worked very flat, so that the workpiece remains flat. The same applies to the polishing of spherical workpieces.

For the polishing of aspherical surfaces and free-form surfaces, this fact represents a principle-related problem. To the relative movement between polishing pad and

To realize a workpiece, both surfaces must be running within certain limits be moved against each other. The condition of a perfect match of the surface shape can, however, be ensured for aspheres in the best case only in one point. In slightly shifted positions, adjustment deviations occur.

Moreover, it is not possible for reasons of economy, for each

Free form surface to provide a dedicated polishing head. Instead, you hold

Usually a more or less large set of polishing heads of different curvature forms before and selects depending on the application of the most appropriate. This approximate adaptation of the surface geometry additionally increases the shape error.

To solve this problem, methods and devices have become known in which the shape of the polishing head can be adapted directly to the tool to be ground, such as by sliding metal pins or thermally deformable materials. In these methods, the problem described above persists that the adjustment can be made exactly in one point only. Because of the relative movement required for mechanical removal, a surface deviation in the other points can not be avoided. In addition, one can through the previous one

Work steps caused form deviation no longer correct, since they are yes in the

Polishing tool is impressed.

Local polishing process

To avoid these problems when using large-area polishing heads or to correct the errors generated by the planar polishing process, local polishing methods are used, which allow local corrections of the

To attach surface shape while the roughness does not exceed a tolerable level.

A group of such methods is characterized in that the polishing tool is designed so that the polishing pad either only has a small extent per se (eg in the case of the so-called polishing pins) or is shaped and guided in such a way that only a small area is created at any one time is in contact with the workpiece.

Just as with the planar polishing method, a relative movement between the workpiece and the polishing head surface is produced by a suitable movement of the polishing tool. This relative movement generates a limited to the contact surface with the addition of a polishing suspension and under application of a suitable pressure Material removal.

The eroded height is e.g. Controlled by how long the polishing head lingers at a certain point on the workpiece surface polishing. For correcting surface deviations from the target or target geometry, which are known from previous measurements, the corresponding local polishing times are determined.

A disadvantage of these methods is the small contact surface between the polishing head and the workpiece, which leads to long process times and thus to high wear of the polishing head compared to the surface polishing method.

Another disadvantage is that the correction of target deviations is limited to those deviations whose lateral dimensions are at least as large as the contact surface. These are typically in the range of a few millimeters.

Another group of local polishing methods are the so-called magneto-rheological methods. These are characterized in that the polishing suspension in addition to the polishing granules also contains magnetizable particles. The polishing suspension is applied to a support body and can then be solidified by means of a strong magnetic field. The shape of the support body and the magnetic lines can in turn be a small contact surface between the workpiece and polishing head (here the support body with the magnetically solidified suspension) set.

The further polishing process is analogous to the method described above.

A disadvantage of the magneto-rheological method is that only relatively low removal rates can be achieved. This is due to the fact that the polishing suspension can not be very strongly solidified by the magnetic field.

Another method, which is used according to the prior art for local post-processing, is to press the particles dissolved in the polishing suspension not by a solid body on the workpiece, but solely by a fast-flowing liquid flow. Such a method is described, for example, in DE 101 13 599 A1. Here, the liquid flow flows through an annular gap, which is formed between an outlet nozzle and the workpiece surface.

Due to the lack of direct mechanical contact pressure of the polishing particles, the achievable removal rates are very low. In addition, at least in the case of DE 101 13 599 Al described device that the dimension of the outlet nozzle the lateral

Extension of correctable deviations limited downwards.

Description of the invention

The present invention is therefore based on the object to overcome the described disadvantages of existing polishing methods. In particular, the invention makes it possible to correct shape deviations whose lateral extent is smaller than the range which can be polished by the existing methods (i.e., usually a few millimeters). In addition, the required polishing times are shortened, which helps on the one hand, the

Surface fidelity (i.e., the accuracy with which the desired surface shape is achieved) and, second, to reduce the consumption of process agents. It is possible to obtain from the process parameters the most accurate and simple mathematical modeling of the surface geometry after polishing. Such a modeling makes it possible to predict the geometry of any remaining deviations after polishing and thus to estimate their influence on subsequent process steps and also in the end application and, if appropriate, corresponding ones

To apply countermeasures.

The object is solved by the subject matter of the independent claims.

Dependent claims are directed to advantageous embodiments of the invention.

As described above, the smoothing effect of polishing with elastic polishing pads is caused by the different contact pressures of the polishing particles on the workpiece surface. These differences result from a local elevation of the workpiece surface relative to the undeformed surface of the polishing pad

Deformation in the polishing pad causes. This local deformation causes an elastic counterforce in the elastic medium with which the polishing pad surface presses the polishing particles onto the workpiece surface.

For deformations that are much smaller than the extension of the polishing pad in the direction of deformation, the elastic force is proportional to the deformation itself. The proportionality constant is the so-called spring hardness. Is the spring hardness on the

Extension of the pad, we obtain a characteristic material property, the so-called modulus of elasticity (also called Young's modulus). The smoother effect of the polishing principle described above is the faster, the harder the material of the polishing pad used is. A hard material (ie with a high modulus of elasticity) will oppose a given indentation by a local unevenness of the workpiece surface a greater force than a soft material. As a result, the local abrasion at the local unevenness is greater, and the unevenness is leveled faster.

In many elastic materials, especially in polymers, the modulus of elasticity depends on whether the deformation is of a static or dynamic nature, that is to say more precisely at which speed a certain deformation is achieved. This behavior is usually described by a frequency-dependent, complex-valued one

Modulus of elasticity. A force that varies sinusoidally over time will also cause an equally varying deformation. The maximum amplitude of the deformation is proportional to the maximum amplitude of the applied force, the

Proportionality constant is now the amount of the (complex) Young's modulus. The phase of the modulus of elasticity describes a possible time delay between the force and the deformation.

In many polymers, the modulus of elasticity increases with increasing frequency. This increase has its cause in a so-called glass transition or more generally in one

viscoelastic transition and is particularly close to a so-called

Glass transition frequency especially strong, while for very small and very large

Frequencies has a saturation. The elastic modulus above and below the glass transition frequency may differ by a factor of 10 or more. A typical frequency dependence is shown in Figure 2 which shows the glass transition of a polyurethane (PTMG2000 / MDI 3 / BDO / DMPD). The values for the shear modulus (curve (8) marked by o) and for the loss factor (curve (7) denoted by D) at room temperature are plotted against the decadic logarithm of the frequency on the x-axis (9). The curve for the shear modulus refers to the left y-axis (10) in FIG

Units of Pascal, while the curve for the loss factor refers to the right-hand y-axis (11) in dimensionless units. (From: JV Duffy, GF Lee, JD Lee, and B. Hartmann, in RD Corsaro, and LH Sperling, eds., Sound and Vibration Damping with Polymers, (ACS Symposium Series 424), ACS Press, Washington, DC, 1990 , pp. 281-300).

In addition to the glass transition, many transitions at higher frequencies are observed in many polymers. In polyurethanes, for example, in addition to the glass transition (also α-transition) also a ß and a γ transition known. For simplicity, such secondary transitions are to be understood in the present application as "glass transitions", since the relevant properties for these transitions are similar.

The shear modulus shown in FIG. 2 is identical to the factor 2 (1-μ)

Modulus of elasticity. Here μ denotes the Poisson number, which is independent of the frequency at about 0.5 for most polymers. The frequency dependence of

Glass transitions, in particular of polymers, can be described to a good approximation by the following function:

E (") = E _{o H} e" -E _o ) _-T (FD

\ + ω l ω _tr

E _{0 is} the static modulus of elasticity and E _{00 is} the elastic modulus in the limit of infinite frequencies. ω _tr is the glass transition frequency. A more detailed description of the glass transition succeeds with the Havriliak-Negami Model. In both models is the

Frequency dependence is a function of the ratio between the frequency ω and the glass transition frequency ω _tr .

The increase in the frequency-dependent Young's modulus results in slow changes in deformation requiring less force than fast ones.

In fact, the deformation of a polishing pad during a polishing process is dynamic. The relative movement between the workpiece surface and the polishing pad guides each point of the polishing pad a certain distance over the workpiece surface. Considering the distance a particular point of the polishing pad surface travels on the workpiece surface, any unevenness in the workpiece surface along that path will cause a time varying local deformation of the polishing pad at the point of interest.

The time course of the deformation is determined by the lateral shape of the unevenness for a given relative movement between the polishing pad and the workpiece surface. A wide unevenness gives a slower height at identical height

Deformation in the polishing pad as a little extended rub. Due to the dynamic dependence of the modulus of elasticity, however, the elastic force in the case of the widely extended unevenness is then always at points of identical height of both unevenness smaller than in the corresponding points of less extensive rub. This difference results from the increase in modulus of elasticity (more precisely, its magnitude) with the rate of deformation. In particular, in the case of a dormant

Polishing pad for both unevenness the elastic force in points of the same height identical, since in the static case, only the local extent of the elastic deformation determines the elastic force. Because of the overall smaller forces in the case of extended unevenness, the difference between the force at the foot and at the top of the unevenness is smaller than in the case of the less extensive one. Therefore, the latter is leveled faster.

This difference does not derive from the fact that with a further extended unevenness more material must be removed, in order to obtain a flat surface, but represents an independent effect. The simplest one does this on the basis of two

Sinewave surface topographies of different spatial frequency clearly. In this case, the amount of material that must be removed for complete planarization is the same in both cases, as the volume of the trenches and elevations is exactly equal. A point of the polishing pad, which is guided perpendicular to the wave crests on one of the two surfaces, in this case undergoes a sinusoidally varying deformation over time. Because of the elastic behavior described above, the resulting force difference between wave crest and trench bottom is larger in the case of the short-wave surface topography than in the long-wave case. Thus, the erosion difference in the short-wave case is greater with the result that the unevenness is removed faster.

For further discussion, the Fourier decomposition of a given surface topography is appropriate. The surface topography is described as a linear combination of plane waves in two dimensions of different directions and wavelengths. In the following, we denote the reciprocal of the wavelength as a spatial frequency.

The inventive concept for the present invention is based on those discussed above

Material Property of Some Elastic Surfaces: For the elastic surface in polishing processes, a material is used whose modulus of elasticity has a dynamic dependence in a certain frequency range such that the force necessary to produce a time-varying deformation in the material , is greater for rapid deformations than for slow deformations. A typical example of such a deformation behavior are viscoelastic materials, in particular polymers. For each glass transition occurring in these materials (including the mentioned secondary transitions) the modulus of elasticity is below the Glass transition frequency significantly smaller than above.

The property of the dynamic behavior of the modulus of elasticity of the polishing pad is used according to the invention in that during polishing processes the deviations of the workpiece surface from the target geometry can be corrected by imposing a suitable short-waved surface structure (the so-called microstructuring) so that the long-wave deviations ( with a small spatial

Frequency) are suppressed as much as possible and advantageously after the

Microstructuring only short-wave deviations remain, which then in

subsequent polishing step are removed much faster than the original long-wave deviations.

An essential aspect of the invention thus lies in the determination of a suitable

Microstructure that can serve to improve a polishing process to be applied to a workpiece surface. The method according to the invention for determining such a microstructure comprises at least two method steps: First, determining a surface deviation of a workpiece surface from a desired one

Target geometry, and on the other hand, the determination of a on the workpiece surface

microstructure to be applied, wherein the microstructure has a shorter wavelength

Having surface structure than the original workpiece surface and is chosen so that long-wave deviations of the workpiece surface are compensated or suppressed by the target geometry, so that after an imprinting of the determined microstructure on the workpiece surface in a subsequently feasible polishing process better

(in particular smaller nominal geometry deviations and / or shorter polishing times)

Polishing results are achievable.

The chosen term "microstructuring" or "microstructure" is intended to indicate that the structure to be applied is of shorter wavelength than the starting structure. The term is thus used to a certain extent as a synonym for "small" or "shortwave" (similar to the term "miro- and macrocosm") .The term, however, does not mean an exclusive definition of structures in the micrometer range Wavelengths in the

Micrometer range can be generated.

According to a preferred embodiment of the invention takes place to determine the

Microstructure an association between a height structure of the workpiece surface and a local microstructure. The height structure of a workpiece surface is known for example from measurements, but can also be determined theoretically by simulation. A local microstructure is understood to mean a microstructure which is to be applied to the workpiece surface only in a spatially limited area. For example, in the above-mentioned assignment, the workpiece surface is divided into various small areas, each of the areas is examined for the height profile therein, and each area is assigned a local microstructure based on the classification.

According to a preferred embodiment of the invention, the method for

Determining a microstructure further comprises the following step: Providing a process model for predicting the surface geometry of a workpiece surface after a polishing process. Such a process model may already exist or else be designed and / or optimized in the context of the method according to the invention. Parameters of such a process model may include: temperature, polishing speed, polishing pressure, material, roughness and elastic modulus of an elastic polishing surface. The modulus of elasticity is frequency-dependent, so it is not a classical constant parameter, but a frequency-dependent function.

According to a preferred embodiment of the invention, the process model is used to determine the microstructure to be imprinted.

According to a preferred embodiment of the method according to the invention for

Determining a microstructure is predicted from the process model

Surface geometry uses to compensate for an aberration caused by a deviation of the workpiece surface from the target geometry by adjusting the geometry of components to be applied to the workpiece, which can be patterned by a subsequent lithography process.

According to a further preferred embodiment, the surface geometry predicted from the process model is used, an aberration resulting from a deviation of the workpiece surface from the target geometry by a

To correct the shape of the workpiece itself or by the use of other optical elements.

According to a preferred embodiment of the invention, the microstructure is through Optimization processes determined. In particular, iterative methods can be used for this purpose.

To determine a suitable short-wave surface structure can from the

described elastic properties of the polishing pad in combination with the other process conditions so a mathematical model are derived, which the

Changes in a given surface topography by the polishing process at least approximately describes.

The property used according to the invention of the dynamic behavior of the

Modulus of elasticity is synonymous with the fact that such a mathematical process model has the character of a low-pass for the spatial frequencies. The quantitative

Properties of such a process model depend exclusively on the process conditions and materials used, but in particular not on the shape of the

Workpiece surface.

Polyurethane polishing pads, which are typically used during polishing, do not lie completely on the workpiece surface in the typical contact pressures used during polishing. Instead, because of their rough surface, they only have contact with the workpiece surface with the most prominent tips. The effective contact area makes up only a fraction in the single-digit percentage range of the nominal

(See CL Elmufdi and GP Muldowney, "A novel optical technique to measure pad-wafer contact area in chemical mechanical planarization," in Mater. Res. Soc. Symp. Proc, TY Tsui, Y. -C.Joo, L Michaelson, M. Lane, and AA Volinsky, Eds., Vol. 914, 2006, pp. Paper 0914-Fl 2-06.).

Under certain assumptions (in particular, that the frequency of the polishing pad tips decreases exponentially with their height, the tips in the contact area are spherical and Hertzian contact is present), it can be shown that the elastic contact can be described by an effective exponential spring law, wherein the prefactor the modulus of elasticity of the polishing pad material is linear (see J. Vlassak, "A model for chemical-mechanical polishing of a material surface based on contact mechanics," Journal of the Mechanics and Physics of Solids, vol. 52, pp. 847-873, 2004) ).

For small deformations one can approximate the exponential law by the linear term of Taylor evolution. In this case, it follows from Preston's equation that the Leveling of a sinoidal surface topography during polishing is exponential with time, the time constant being proportional to the value of the elastic modulus at the resulting frequency, which is determined by the relative velocity and by the spatial frequency. This behavior is equivalent to a convolution in space with a convolution function which is bell-shaped due to the frequency dependence of the elastic modulus and whose characteristic width increases with the polishing time.

For larger deformations, a linear approximation of the effective spring law is no longer sufficient. The Taylor development must then be extended to higher terms. This complicates the mathematical description of the process, because convolution in space is then no longer sufficient. The mathematical description is advantageously carried out in the Fourier space of the spatial domain. The quadratic term of

Taylor development can then be calculated, for example, by the autocorrelation function of the surface profile.

The basic behavior of a polishing process, according to which, with the above-described course of the dynamic modulus of elasticity, short-wave surface structures are leveled out faster than long-wavelength, higher orders remain even when added. This property is the basis of the methods and devices according to the invention.

It is obvious that a process model can only ever be a statistical approximation of the sum of the individual abrasions caused by the individual polishing pad tips in the course of the polishing process. Therefore, it is advantageous for the use of a polishing method according to the invention to ensure that all areas of the

Workpiece surface whose shape is to be processed in the polishing process, come into contact with a sufficiently large number of polishing pad tips. This also has the advantage that the desired shape is achieved sufficiently quickly, even in the low-lying areas of the workpiece surface.

This can be, for example, by a sufficiently large roughness of

Reaching the polishing pad surface. This ensures that even in the lower areas of the workpiece surface a large number of polishing pad tips rests.

Against this background, the use of foamed materials for the Polishing pad advantageous because the roughness of the polishing pad can be influenced by adjusting the pore size. According to the state of the art, polishing pads are roughened (conditioned) with suitable diamond tools before the polishing process. The surface is removed so far that creates an open pore structure on the surface. The pore walls then form the tips with which the polishing pad rests on the workpiece surface during the polishing process. Larger pores give greater roughness after thawing.

It is also advantageous between the polishing pad, which directly on the

Rests workpiece surface, and the polishing pad carrier an additional intermediate layer of softer viscous, softer elastic or softer visco-elastic material, in particular of pitch or resin or a polymer to apply. By a suitable choice of the moduli of elasticity and the layer thicknesses of the two layers can be

advantageously achieve that long - range height differences in the

Workpiece surface are compensated by the softer intermediate layer. For this softer layer is also a material with a high viscosity, such as certain pitches or resins. Such materials offer the advantage that their static modulus of elasticity is zero. Therefore, the dynamic elastic modulus at low frequencies is very small. Therefore, the leveling of long-wave deviations between polishing head surface and workpiece surface, as they occur when using only approximately matched polishing head surfaces, very slowly.

As in the current state of the art, it is assumed that the deviations from the desired surface shape at a sufficiently large number of points on the workpiece surface is known.

For the production of optical elements, this information is typically with

gained interferometric measurement.

In the manufacture of semiconductor devices or microsystems, the

Surface shape usually from the placement data of the components (i.e.

Layout data) in the previous levels and the process conditions are derived.

Furthermore, it is assumed that for the polishing process used and its

Process conditions a process model has been determined which, as stated above, due to the described property of the elastic modulus of the elastic surface has a low-pass character for the surface geometry. This can be done either by empirical measurements on the basis of suitable test structures or directly from the

Process conditions and material properties or a combination of both methods derived.

The workpiece surface can now by suitable methods (so-called.

Microstructuring method, see below) a short-wave surface structure are imprinted. This surface structure is selected with the aid of the process model in such a way that, in combination with the existing surface geometry (ie in particular with the known deviations), it corresponds as well as possible to the desired target surface after the polishing process. The aim is to correct the long-wave deviations using shortwave structures.

The lateral dimensions of the impressed surface structure should be as small as possible in order to keep the leveling time for the embossed surface structure in the subsequent polishing step as short as possible. Here is the possible

Resolution limits of the structuring process used.

The thus prepared workpiece can now be polished with the polishing process on which the process model is based. According to the effect described above, the impressed short-wave surface structure is leveled much faster than the long-wave deviations of the untreated surface. The method for impressing the surface structure must make it possible to impart the required structure with a sufficient lateral and vertical resolution. The experiments leading to the described invention show that advantageously minimum feature sizes in the range of about 10 μm are sufficient to be sufficient in combination with commercially available polishing pads and typical polishing rates (e.g., 0.5 m / s)

To provide correction options.

Such structure sizes can be produced, for example, with the aid of laser-based lithographic processes, as are customary in the production of photomasks for semiconductor production, without technical difficulties on flat substrates. Lithographic structuring is also possible on curved substrates (see, for example, "Laser Lithography on Nonplanar Surfaces" by D. Radtke and UD Zeitner in Optics Express, Vol. 15, Issue 3, pp. 1167-1174). With this method, the required surface structure can be individually adjusted for each workpiece. It is therefore very suitable for the correction of individual pieces and

Small series, as well as for the correction of unsystematic deviations, i. Deviations that differ from workpiece to workpiece.

To correct systematic errors, especially in the production of larger quantities, the use of a photomask seems useful, with the help of which one can expose an identical surface structure on a variety of workpieces. The exposure can then take place either as a contact exposure or with the aid of a projection optics.

A combination of both methods is also advantageous in order to correct for both systematic and random deviations.

Furthermore, the resist mask can also by high-resolution printing techniques on the

Workpiece surface are applied. Advantageous are so-called

Ink jet printing similar or ink jet method, which by taking advantage of

piezoelectric or thermal processes very small amounts of liquid

can apply predefined positions of the workpiece surface. Such methods are well known for printing images in electronic form on paper.

Accordingly, with such procedures, which are necessary for the correction

Apply resist mask structures to the workpiece surface and then etch into the workpiece surface analogously to photolithography.

Analogous to the photomask one can also with the printing technology-based

Resist masking using a printmask (or print matrix) to

to correct systematic deviations on a large number of workpieces easier. This method is well known in the offset printing art. Here you use

Printing plates, which are imaged with the image and text data and with which then in a kind of stamping process, a large number of prints can be made.

According to an advantageous embodiment of the invention

Microstructuring method is the structuring of the workpiece surface by means of a photolithographic process using a computer-controlled

Laser beam made.

For the microstructuring according to the invention are also other Patterning process conceivable, such as micro-engraving, laser ablation or microetching. Such methods have the advantage over microlithography that not only the lateral dimensions but also the local structuring depth for correcting the surface deviation can be varied within one process step. In addition, the material removal takes place directly (ie without detour via a masked etching). The simpler process management facilitates direct integration into a polishing device. As a result, structuring and polishing can take place directly in the same workpiece holder.

In addition to the described material-removing Strukturierverfahren can also

material-applying method can be used. So, for example

layer-separating processes using a correspondingly structured

Shadow mask are applied. Even high-resolution printing techniques can be used with a suitable choice of process parameters. Such an application appears

especially advantageous for the use of the inventive method in reflective optical elements. In this case, the optical properties of the substrate are unimportant, since the reflection takes place on a subsequently deposited thin layer.

In the case of the material-applying structuring methods, it may be unavoidable that the polishing process removes the material applied for structuring more quickly or more slowly than the material of the workpiece surface. This difference can be taken into account in the process model by introducing a location-dependent Preston coefficient.

Alternatively, a sufficiently thick homogeneous intermediate layer can be deposited after the material-applying patterning process, which then forms the new workpiece surface, which can be processed in the subsequent polishing step.

Of course, it is also possible to use material-removing and -aufbringende procedures

combine. This may be particularly advantageous if the height deviations extend only over a small proportion of the entire workpiece surface, but point both into the surface and out of the surface. In this case, the different deviations can be corrected by the respective complementary structuring method, so that the area to be structured remains limited to the deviations themselves.

In order to achieve a high dynamic modulus of elasticity for the impressed microstructure, despite a limited resolving power of a structuring method used an elastic material can be selected whose glass transition frequency is matched to the resolution of the structuring method used.

The elastic properties of many polymers can be deduced from the contributions of the individual monomers via so-called group contribution or fragment methods. This is especially true for the frequency dependence of the modulus of elasticity. Davis and Szabo were able to determine the frequency dependence of 14 polyurethanes very precisely

Determine monomer contributions. Noteworthy in this context is that the

Glass transition frequency in the materials studied varied by about 10 orders of magnitude (see WM Davis and JP Szabo, "Group Contribution Analysis applied to the Havriliak-Negami model for polyurethanes", Comp.And Theor.Polymer Science, 11 (2001), pp 9-15 This means that the glass transition frequency of the used

Polierkissenmaterials by suitable material synthesis in a wide range on the

Resolution and the relative speed used can be adjusted.

The sizes of the low-frequency and the high-frequency elastic modulus can be optimized by a suitable composition of the material used for the inventive method. In order to minimize the influence of long-range deviation errors between the polishing head and the target geometry, the corresponding low-frequency elastic modulus should be as small as possible. At the same time, the high-frequency

Young's modulus should be as large as possible so that the embossed surface structure can be leveled as quickly as possible.

In addition, two process parameters can be chosen suitably in order to optimize within certain limits the coordination between the glass transition frequency and the resolution limits of the structuring method.

On the one hand, an increase in the relative speed between the workpiece surface and the polishing pad surface shifts the time profile of the deformation caused by a given microstructure to higher frequencies, thereby increasing the effect

Modulus of elasticity.

On the other hand, the frequency dependence of the modulus of elasticity is temperature-dependent. At lower temperatures, the glass transition frequency shifts to smaller values. With a decrease in temperature, therefore, for a given microstructure, higher values for the effective modulus of elasticity are also achieved. It is obvious that the process cycle in accordance with the invention, including determination of the surface deviation, determination and imprinting of the correction pattern and subsequent polishing, can also be carried out several times in succession. This is particularly advantageous if the achievable

Structuring depths of the selected structuring processes are not sufficient to correct the existing deviations in a single process cycle. Also with repeated application in the different steps different

Structuring widths, polishing pad materials and process conditions are used to correct deviations on different length and height scales.

In accordance with what has been generally stated above, another aspect of the invention relates to a method of polishing and shaping workpiece surfaces. This includes at least the following steps: providing a microstructured one

Workpiece surface whose microstructure has been produced by means of one of the microstructuring methods described above; Placing an elastic surface on the workpiece surface; and polishing the workpiece surface by generating a pressure between the elastic surface and the workpiece surface and moving the elastic surface and the workpiece surface relative to each other using a material for the elastic surface whose modulus of elasticity has a dynamic dependence in a certain frequency range such that the force necessary to produce a time-varying deformation in the material is greater for rapid deformations than for slow deformations. In this way, in particular the polishing time for polishing a workpiece surface can be significantly shortened. According to the polishing method according to the invention is a microstructured

Workpiece surface provided. This provision may be such that the microstructuring required prior to the polishing step has been performed temporally and / or spatially separated from the polishing step. But it is also possible that the

Microstructuring promptly to the polishing step and in particular spatially close - for example, in the same company - or even with the help of a single device having a microstructuring unit and a polishing unit is made.

According to a preferred embodiment of the invention, the polishing method according to the invention comprises the following method step: selecting process conditions so that the required polishing time becomes as short as possible. This can in particular the temperature and / or the amount of relative speed between the workpiece surface and the elastic surface, taking advantage of the above-described functional relationships between the parameters.

According to another preferred embodiment of the invention

Polishing process individual process steps are performed several times in succession. These process steps can be identical or changed

Process parameters are executed.

According to a further aspect of the invention, this relates to a

Computer program product with a program code for executing the

inventive method. Typically this is on a

Disk stored software, such a separate disk is not mandatory. The program code can be written in all known programming languages.

As already stated above, according to a first aspect, the invention is implemented by the described method for determining a microstructure. The invention thus encompasses various theoretical aspects or method steps, which are likely to be realized with the aid of computer programs. It is also possible to separate the method for determining a microstructure from the

Mikrostrukturierungs- or polishing process itself: The microstructure can be temporally, spatially and personally independent of the implementation of the actual

Mikrostrukturierungsverfahrens or carried out by performing a polishing process. Also can be called reason a corresponding

Distribute computer program product separately to determine a microstructure.

Of course, it is also possible to combine the method for determining the microstructure with the actual microstructuring method and optionally also with the subsequent polishing method. All processes can be computer-controlled, with the help of an appropriate software on the one hand the necessary

On the other hand, the microstructuring process and, if appropriate, the subsequent polishing process are computer-controlled.

According to a further aspect of the invention, this relates to an apparatus for carrying out the method according to the invention for polishing and shaping work piece surfaces. Such a device has a microstructuring unit for Microstructuring a workpiece surface as described above and a polishing unit for polishing the workpiece surface. It is possible, for example, already existing polishing units or polishing devices to a corresponding

To complement or combine microstructuring unit.

According to a preferred embodiment of the device according to the invention, this has a support for carrying a workpiece and a polishing pad and a

Polishing pad support for supporting the same, the apparatus being arranged to polish a workpiece surface by generating a pressure of the polishing pad on the workpiece surface and by moving the polishing pad and the

Workpiece surface is relative to each other.

Advantageously, while the polishing pad on a foamed material. Particularly preferred are visco-elastic polymer foams such as in particular

Polyurethane foam.

According to another preferred embodiment of the invention is between the

Polishing pad, which rests directly on the workpiece surface, and the Polierkissenträger an intermediate layer of softer viscous, softer elastic or softer viscoelastic material, in particular of pitch or resin or even suitable polymers provided.

According to a further aspect of the invention, this relates to a use of a microstructuring unit for improving a method for polishing and shaping workpiece surfaces. As stated above in detail, are

Methods and devices for structuring workpiece surfaces are already well known, with the aid of the known methods and devices

In particular, it is also possible to apply the structure designated as microstructure in the context of the invention to a workpiece surface. By contrast, the use of such structuring units for the purpose intended according to the invention, namely for improving already known polishing methods and methods for shaping workpiece surfaces, is completely unknown.

In the following, the advantages of the concept of the invention will be discussed explicitly:

The actual correction of long-wave deviations of workpiece surfaces from A target geometry is no longer achieved by polishing, but by

Micropatterning. Microstructuring methods are orders of magnitude better (ie higher) spatial resolution than the local polishing methods of the prior art. For a much more accurate correction of the deviations is possible, especially if the lateral extent is small. By utilizing the dynamic characteristics of suitable elastic materials for the polishing pad, a surface topography impressed according to the invention can be leveled much faster than the original deviations. This reduces the required

Polishing times over the prior art. The shortening of the process also reduces the consumption of process agents (in particular less energy and energy)

Abrasives consumption) as well as the wear of the polishing tools.

In addition, a shortened polishing time also offers a principal advantage. It is relatively expensive and even impossible for aspherical surfaces to adapt the surface of the polishing pad exactly to the desired surface. For planar and spherical surfaces, the polishing pad carrier and the polishing pad itself must be worked very precisely. For aspherical surfaces, an exact adaptation is generally possible in principle only in one point. By the necessary for the polishing process

Relative movement results at almost all times deviations from the ideal adjustment because of the relative displacement of the polishing head from the ideal position. With otherwise identical process conditions, such adaptation errors are transmitted to the workpiece the more the longer the polishing time. A shorter polishing time, as can be achieved by the process according to the invention, therefore allows a greater dimensional accuracy of the polishing process.

Furthermore, the adjustment deviations of the polishing head from the desired workpiece surface described in the previous section can also be corrected by the described microstructuring correction.

In particular, for the aforementioned local polishing methods with polishing pins and similar small polishing heads, the described correction of the fitting deviations allows the use of larger polishing pin surfaces. This additionally reduces the polishing time for a given workpiece.

Furthermore, a polishing method according to the invention requires only one additional

Process step, namely the microstructuring, to make it into existing manufacturing processes integrate. In particular, it can be applied to surface polishing processes and already allows in this process step the more accurate correction of local deviations.

In addition, in the case of aspherical surfaces, the reduced process duration reduces the geometry deviations caused by the principle-related mismatching. This eliminates the need for subsequent local Korrekturpolierschritte in the best case, but at least the necessary corrections are greatly reduced. In addition, these advantages allow aspheric surfaces to produce the same surface fidelity with a reduced set of polishing head shapes. This also saves process costs.

Further advantages result from the use in semiconductor production or the production of microsystems. There, the components are produced by layered structure, wherein in each layer the necessary microstructuring is carried out by lithographic processes. The lithografi used methods usually have a planar

Focal plane and a small imaging depth (also called depth of field). Any unevenness in the surface to be exposed causes a local focus error and thus an error in the width of the imaged structure. In order to minimize this error, the intermediate surfaces with the above-described chemical-mechanical

Polishing procedure polished flat.

The planarization mechanism according to the invention is essentially based on the property of the modulus of elasticity of the elastic surface, which has already been mentioned several times. The elastic modulus has a dynamic range in a certain frequency range

Dependency such that the force necessary to produce a time-varying deformation in the material is greater for rapid deformations than for slow deformations. This makes it possible to change the time of the

Surface structure with relatively simple mathematical means very precise

predict. Since known process and material properties are incorporated into the process model, this model can be set up for any process conditions. This eliminates or reduces the hitherto complex process characterization with the aid of topographical measurements on defined test structures, as described, for example, in DE 100 65 380 B4.

It is customary in the prior art to choose the arrangement of the structures required for the function of the integrated circuit so that the surface is as flat as possible after polishing. It is also common to additional structures (so-called Filling structures) or to choose the shape of the functionally necessary structures so that the surface is as flat as possible after polishing. The rules by which these changes and insertions are made are empirical and less accurate.

A common approach is to limit the local layout density (that is, the proportion of the structured area in a location, averaged within a certain environment) to a specific range of values. The size of the averaging range is determined by empirical measurements and considered to be a characteristic length of the CMP process. Typical values for this planarization length are in the range of several 100 μm up to a few millimeters. It is immediately clear that such an approach does not take into account the influence of small-scale layout density variations. However, it has been shown that these small-scale layout density variations cause a substantial part of the height variation after polishing, which in particular can not be corrected by automatic tracking of the focal plane during the exposure.

In addition, such empirical process models need to be changed every time

Process conditions are re-determined.

By applying a method according to the invention, these rules can be determined without renewed empirical characterization, since the process model depends in a defined manner on material properties and process parameters. In addition, the predictive power of a process model determined by a method of the present invention is much more accurate because the influence of the small-scale layout density variations is modeled correctly.

For the same reason, it is possible according to the invention to predict the surface geometry very accurately after the polishing process. This prediction makes it possible to compensate for the influence of any non-correctable geometry deviations by suitable measures. Thus, it is possible, for example, an existing defocus error by a suitable Strukturbreitenvorhalt in the levels to be exposed on it

compensate. Furthermore, it is possible, for example, the influence of a local

Deviation of the dielectric layer thickness between two metal planes from the nominal value simulatively to examine whether the deviation at this point is critical to the function of the circuit, and to compensate for their influence, if necessary by a suitable design of the electronic components. With lens elements, knowing the systematic deviations from the desired geometry, it is possible to alleviate the negative effects by suitably designing other or additional optical elements.

The present invention will be better understood with reference to the accompanying drawings:

Fig. 1: illustrates a lateral offset of imaging rays in the presence of a

Deviation from an ideal planar surface;

Fig. 2: shows a typical frequency dependence of the modulus of elasticity of a polymer with a glass transition;

Fig. 3: shows a schematic representation of a chemical-mechanical polishing machine for

Wafer substrates;

Fig. 4: shows a result of empirical studies for smoothing a

Surface topography as a function of spatial frequency;

Fig. 5: shows an interpolated height profile;

Fig. 6: illustrates one according to a polishing method according to the prior art

remaining residual topography;

FIG. 7 shows a profile of height on which a microstructure has been impressed, FIG.

Fig. 8: illustrates a surface profile after microstructuring and subsequent

Polishing process;

Fig. 9 shows a device by means of which both a microstructuring and a polishing process can be carried out;

Fig. 10: shows by way of example a device according to which microstructuring and polishing can take place directly in the same workpiece holder; and

FIG. 11: shows an example of a microstructuring wherein a material-carrying

Structuring method is combined with a material applying method.

FIG. 9 shows an apparatus for carrying out the microstructuring method according to the invention using a lithographic patterning method. One Robot arm (43) with a workpiece holder (44) places a photoresist painted workpiece first on the stage (41) of an exposure unit. There, the photoresist is exposed using a laser beam (40). The laser beam is focused by a suitable optics (39) on the workpiece surface. At every point of the

Workpiece surface to expose the appropriate correction pattern in the paint is the

Focusing optics (39) (or alternatively the stage (41)) in all three spatial axes movable. Subsequently, the robot arm (43) first places the exposed workpiece in one

Developer station (36) in which the varnish develops, i. Depending on the type of varnish, the exposed or unexposed varnish is advantageously removed by wet-chemical means. Subsequently, in the etching chamber (37), the areas not masked by the paint are etched, so that in the

Workpiece surface creates the desired microstructure. In a cleaning station (38), the remaining paint residues are removed. Now the workpiece is placed on the polishing station (42) and polished.

FIG. 10 shows, by way of example, a device by means of which the microstructuring and the polishing can take place directly in the same workpiece holder.

To simplify the illustration, a planar workpiece (50) is shown. The

Workpiece is mounted on a holder (49) which is rotated by the shaft (48). On the polishing pad carrier (52) the polishing pad (51) is attached. Both are also rotated by the shaft (54) and also pressed against the workpiece. The polishing suspension (58) is applied to the workpiece surface via the polishing suspension feed (58) and is distributed (indicated by (57)) there, in particular also into the intermediate space between polishing pad (51) and workpiece (50). For impressing the microstructure according to the method, a device for laser ablation is integrated into the polishing machine. A suitable optics (46) focuses a laser beam (47) on the workpiece surface. The optics can be moved in the plane parallel to the surface in order to impart the appropriate microstructure at each point of the workpiece surface. For curved surfaces, the vertical position of the laser focus can be varied by appropriate optics or by optics itself. The person skilled in the art recognizes that in this application example, in contrast to those described so far

Application examples of the polishing head is smaller than the workpiece. This embodiment appears expedient here, since in the opposite case, the workpiece surface is not readily accessible to the microstructuring, since it is completely covered by the polishing pad. The embodiment in this application example is exemplary, but not restricting to understand.

As already explained above, it is possible to combine material-removing and -methods of microstructuring with each other. This may be advantageous in particular if the height deviations extend over only a small portion of the entire workpiece surface, but point both into the surface and out of the surface. In this case, the different deviations can be corrected by the respective complementary structuring method, so that the area to be structured remains limited to the deviations themselves. An example of such a process sequence is shown in FIG. In those areas where the

Deviation of the surface of the material (60) to the outside, material is removed locally by an erosive patterning process (61). In the areas where the deviations point inwards, material (62) is applied locally by a material applying process. Then, a homogeneous layer (63) is applied, which is so thick that it can be used over the remaining polishing time during the polishing period which is necessary

Height differences einzuebenen, not completely removed. The polishing process then creates a planar surface (64) of the layer (63).

The following exemplary embodiments are explained by way of example with reference to the planar grinding of silicon wafers. This is due to the fact that for this application example a quantitative process characterization is available, by means of which the advantages according to the invention can be quantified by way of example. The other is the

Display of planar workpieces in drawings easier and clearer to achieve than for curved surfaces.

All application examples can be generalized by suitable polishing devices on curved surfaces. The main difference is to use a curved polishing pad head that has a negative impression of the

Workpiece surface is.

The main difference when polishing workpieces from other materials is an adjustment of the polishing times and possibly the use of others

Polishing suspensions. Both modifications have no influence on the essential properties of the method according to the invention.

Figure 3 shows the schematic representation of a chemical mechanical polishing machine for Wafer substrates. In this application, the wafer surface should be polished planar. The polishing pad carrier (15) is therefore designed as a disc and the polishing pad (19) as a thin polishing cloth. The polishing pad carrier (15) is rotated by a shaft (16). On the support a polishing pad (19) is attached. Through a liquid outlet (17) the polishing suspension (18) is continuously applied to the polishing pad, so that it is distributed over the polishing pad and in particular between the wafer (14) and the polishing pad (19). The wafer carrier (13) presses the wafer (14) onto the polishing pad (19) with an adjustable contact pressure. About the shaft (12) and the wafer carrier (13) and with it the wafer (14) is set in rotation.

Wafer and polishing head are each set in rotation about their respective center. The angular velocity of these rotations is adjusted so that on the whole

Wafer surface in terms of amount, the same relative speed between the wafer and polishing pad surface prevails. The direction of the relative speed rotates in

Reference frame of the wafer evenly over time. As a result, an isotropic removal is achieved, which is additionally identical in each point of the wafer.

The relative speed between wafer and polishing cloth surface was set to about 0.5m / s. The polishing pad (16) is a double-layered polyurethane cloth. The bottom layer, which is in direct contact with the wafer surface, is an approximately 1270 μm thick foamed polyurethane cloth. The pores have a typical size of about 10 μm to 80 μm. The second layer is another, thicker polishing cloth, especially with a lower modulus of elasticity. The nominal contact pressure between wafer and

Polishing pad is about 41.4kPa. The polishing suspension advantageously contains 30% polishing particles of silicon oxide, which have a mean size of 50 nm. A preferred polishing time is 90s.

Empirical investigations on the smoothing of the surface topography as a function of the spatial frequency have revealed the relationship between these process conditions in FIG. 4. The curve (21) shows the attenuation of the amplitude (plotted on the y-axis (22) in dimensionless units) of sinoidal surface topographies as a function of their wavelength (plotted on the upper x-axis (20) in μm) spatial frequency (lower x-axis (23) in μm ^"1 )

Recognize polishing process. This process model results from the curve of the dynamic modulus of elasticity approximated by formula (Fl) with a glass transition frequency of about 18000 Hz. As an example of a possible surface deviation, we assume that the otherwise ideally planar 300mm diameter wafer has a Gaussian elevation anywhere that has a height of 200nm and a half width of about 500μm. The surface geometry of the wafer is an interferometric

Measurement is known, which has a lateral resolution in the range of lOμm. FIG. 5 plots the interpolated height profile (24) of such a deviation as a function of the location (in μm on the x-axis (26)). The zero point of the elevation axis (25) is chosen so that cancel all deviations in the middle. The direction of the elevation axis points out of the wafer surface. The heights on the altitude axis are given in units of nm. Because of the very small extent of the survey, the average height of

Wafer surface almost identical to the height at long distances from the survey.

After application of the above-described polishing method according to the prior art (that is, in particular without imprinting a short-waved surface structure, that is without microstructuring), the residual topography (27) shown in FIG. 6 remains (axis definition and scaling as in FIG. 5). The assumed deviation is only reduced by a factor of about 4. The remaining maximum height difference after the polishing process is about 54nm.

For an embodiment of the method according to the invention, a suitable microstructure is now determined from the height profile in FIG. In this example, we assume that a lithography method is available which has a lateral resolution of better than 2 μm and an etching depth of d = 400 nm. Then a suitable

Find microstructure in the following way. The available etch depth is divided into 16 equidistant classes. Each of these height classes is assigned a 4x4 pixel pattern. Filled (black) pixels denote ² × ² μm ² large fields, at which etching is applied, while no etching takes place on unfilled (white) pixels on ² × ² μm ² large fields. The average height of the resulting local etching patterns are identical to the center of the associated altitude interval except for an offset of d / 2 and the factor "-1." Such a set of local etching patterns together with the associated altitude classes is listed by way of example in the following table.

Table 1: Mapping table between local height deviation and local

Korrekturätzmuster

From the interferometric height data of the workpiece surface, the

Average heights determined in flush contiguous square 8x8 μm ² large areas. According to the definition of the height scale, this is the local average height

synonymous with the difference between this local and the global one

Average height. The local average height falls into one of the 16 equidistant

Height classes. The local microstructure needed to correct this difference is then determined from Table 1.

This relatively simple method with the aid of a fixed assignment between height class and local microstructure serves at this point only to clarify the method. It is obvious that the determination of the microstructure can be significantly improved. For example, a finer height discretization can be used in combination with a larger set of local patterns. Moreover, algorithms for converting a gray image into a black-and-white rasterized image (so-called "dithering") may also be employed Such a dithering algorithm has been proposed, for example, by RW Steinberg and L. Steinberg (RW Floyd, L. Steinberg, An adaptive algorithm for spatial gray scale Proceedings of the Society of Information Display 17, 75-77 (1976)). Furthermore, in the method described by way of example, the process model for the polishing step has only been used to determine the size of the local correction etching patterns. It can be seen in FIG. 3 that the size of the local correction patterns of 8 μm falls within the structural width range in which the attenuation of the surface topography is very strong. The exact shape of the attenuation curve, however, was not exploited to determine the correction pattern. By fully computer-aided procedures that perform the optimization of the correction pattern taking into account the entire process model, therefore, an even better adaptation of the microstructuring to the existing deviations is possible.

This above-exemplified microstructure is now impressed on the original height profile. This results in the height profile (30) shown in FIG. 7 (axis definition and scaling as in FIG. 5). It can clearly be seen that almost the entire surface is etched off at the maximum. Here, the etching lowers the local height level by 400nm. Outside the local deviation, the etch pattern is used with 50% area coverage, resulting in a local mean height reduction of only 200nm. This difference corresponds exactly to the original amount of deviation. On the flanks of the deviation, the area coverage of the correction patterns toward the center increases to compensate for the increasing altitude profile.

FIG. 8 shows the surface profile of the thus modified surface according to the polishing method adopted here (axis definition and scaling as in FIG. 5). The residual topography (33) is only about 5 nm and has thus been reduced by an order of magnitude compared to the pure polishing process. To be without the

Surface structuring to achieve a comparable planarity, the polishing time would have to be increased from the 90s assumed here to about 300s.

In this exemplary method of determining the microstructure, regions in which the workpiece surface deviates only slightly from the desired geometry are etched with a correction pattern of 50% surface coverage. This is necessary in order to also be able to correct negative height deviations (not shown in FIG. 5). A disadvantage, however, is that basically the entire workpiece surface must be etched. It may therefore be advantageous, depending on the requirement and the output topography, to appropriately shift the reference level for the height deviation and to use the entire height correction range made possible by the etching process only to correct the positive deviations. Alternatively, a combination of material-removing and -aufbringenden

Microstructuring be used.

In another application example, we use a laser ablation process for surface structuring.

Laser ablation techniques typically achieve a minimum patterning width of 10 - 50μm. Using the same method as in the preceding example for determining the correction etching pattern, this results in a maximum structure width of about 40 μm-200 μm. With this structure width, the modulus of elasticity under the above-mentioned process conditions is not yet in the high-frequency saturation.

Therefore, in this application example, a relative speed of 2.5- 12.5 m / s is used, which is higher by a factor of 5-25 than in the previous one

Example. If such relative speeds can not be achieved with a rotating polishing machine shown in FIG

Linear polishing machines are used, in which the polishing cloth only in one

translational movement is performed over the workpiece.

The increase in the relative speed has the consequence that the spatial frequency of the impressed microstructure in a higher frequency of the generated in the polishing pad

Deformation is converted. In particular, the relationship applies: ω _t = v _r ω _s (F 2) where ω _t denotes the temporal frequency of the deformation, ω _s the spatial frequency and v _r the relative velocity.

In another application example, we assume that the achievable maximum relative speed is only 2 m / s and the structuring method has a minimum resolution of 20 μm. Thus, the temporal deformation frequencies generated by the microstructuring are only by a factor 0.4 less than in the first application example.

To compensate for this factor, in this application example

Utilized temperature dependence of the glass transition.

The temperature behavior of the glass transition frequency follows in most cases an Arrhenius law for most polymers, that is to say:

where ΔH is a material-specific activation energy, R is the gas constant, T is the

Temperature and ω _{0 is} a material constant. Since the frequency dependence of

Modulus of elasticity depends only on the ratio ω / ω _tr , is a shift of

Glass transition frequency from ω _tr i to ω _{tr> 2} equivalent to a scaling of the frequency axis by the factor ω _tr> 2 / ωtr, i •

In order to reduce the glass transition frequency ω _tr by a factor of 0.4 compared to the temperature Ti from the first application example, and thus to scale the entire frequency dependence by the same factor, the following relationship arises:

0.4 = ^ ω _{tr 1} = exp, ^ K (f I ₂ -f I ₁ ), (F4)

Typical activation energies are in the range of 10-100 kJ / mol and can be adjusted by suitable methods of preparation of the polymer used.

Polishing processes such as that characterized in Figure 4 occur at room temperature and above. Due to a temperature reduction from 1OK to 30K you can therefore depending on

Activation energy Scaling the frequency dependence around the factor assumed here 0.4 and above.

Therefore, in this application example, the polishing pad carrier is cooled by means of a suitable temperature control to a temperature which is about 10K to 30K below the process temperature of the first application example. This can be made possible, for example, by liquid cooling with a suitable coolant, as indicated in FIG. A coolant flows through the inflow (55), a pipe (52) inside the polishing pad carrier and the drain (56) through the polishing pad carrier. Other cooling devices such as with Peltier elements are possible.

This is achieved despite the larger structure widths and the lower

Relative speed again, that induced by the microstructuring

Deformation frequencies are in the range in which the dynamic elastic modulus assumes the desired high values. In a further example of application, the method according to the invention is used for the production of a microlens matrix. In contrast to the previous application examples, the shape of the optically active surface is generated directly by the appropriate application of the method according to the invention.

Each individual lens should have a diameter in the range of lmm, and the arrangement should, for example, take place in a square matrix, the spacing of the lenses being identical to their diameter. The lens profile should be spherical with a

Ball radius of 500mm. This results in a lens height of 1 micron.

One starts from a planar substrate of a suitable material (e.g., quartz glass or silicon). Into this substrate a suitable microstructure is impressed by photolithographic microstructuring. The calculation of the microstructure can be carried out in a manner analogous to that in the first application example, the surface of the microlens matrix being used as the desired geometry in this example. The subsequent polishing step once again flattens the short-wave microstructure, but the long-wave components of the applied microstructure are retained and form the desired spherical microlenses.

In order to achieve smaller ball radii, larger etching depths can be used in this application, or several process cycles can optionally be carried out with it

different process parameters (in particular polishing pad roughness) can be used. In addition, it may be necessary to calculate the microstructure with

To work process models that take into account the higher orders of the effective pen law. It is also advantageous to use a softer elastic

Intermediate layer between the upper polishing pad and the polishing pad carrier to allow adjustment of the polishing pad surface to the long range height differences.

In another application example, we use this from the dynamic one

Elastic modulus and the other process parameters specific process model for

Placement of filling structures to improve the planarity of a dielectric

Insulation layer between two metal layers of an integrated circuit. We assume that the process model can be described by a simple convolution with the convolution function shown in Figure 4, that is, the height differences in the dielectric layer are small compared to the roughness of the polishing pad. First, an approximation for the surface geometry of the workpiece surface after the deposition of the dielectric layer is calculated from the strip layout of the lower metal layer. In the simplest case, this is done by assigning the height of the metal layer thickness to all surfaces on which a printed conductor is drawn, and setting all other regions to zero height. It is more advantageous at this point to use more accurate models for the deposition process. Then the surface is divided into small plots, and in each plot the average height is calculated. The

Plot size is advantageously chosen so that it is significantly smaller than the typical radius of the convolution function of the process model.

With the thus determined surface geometry and the process model, the

Surface geometry determined after the polishing process. For the case assumed here, this is advantageously done by multiplying the Fourier transform

Surface geometry with the Fourier-transformed folding function of the process model.

In order to achieve a surface geometry of the workpiece surface that is as flat as possible after polishing, one now looks for a height correction function, around which the original

Surface geometry must be corrected. Due to the low-pass behavior of the process model, such a height correction function can be found by taking into account only the long-wave components up to a certain spatial frequency from the original surface geometry and setting all shorter-wave contributions to zero. The spatial cutoff frequency is determined from the convolution function such that the area below the cutoff frequency accounts for a very large fraction (e.g., 95%) of the

Total integral of the convolution function has. The location of a suitably chosen

Cutoff frequency is indicated by way of example in FIG. 4 by (66) and designated there by ω _thr . By inverse transformation of the height correction function thus determined into the spatial space, the required height is obtained at each location by which the mean height must be changed by adding corresponding filling structures. Since the altitude correction function is different from zero only up to the spatial limit frequency ω _thr , the determined

Altitude correction for a larger area than the originally selected plot size. This accommodates the expansion of the convolution function. The larger this area is, the larger the area on which fill structures can be placed and the easier it is to achieve the height correction.

In general, this method will detect both positive and negative altitude corrections. Since usually only adding additional filling structures is allowed results This poses the problem that only positive altitude corrections (ie an increase of the mean local altitude) are possible. This problem can be solved by extending the altitude correction function by a constant offset, which is chosen so large that the negative altitude corrections are converted into positive values. Since it is a constant, that is location-independent offset, he changed the

Surface geometry after polishing not.

In the following, particularly advantageous embodiments of the invention are enumerated again.

A method of polishing and shaping workpiece surfaces comprising the steps of:

- Determining the deviations from the desired geometry

- placing an elastic surface on the workpiece surface

Polishing the workpiece surface by generating a pressure of the elastic surface on the workpiece surface and moving the elastic surface and the workpiece surface relative to each other

the use of a material for the elastic surface whose modulus of elasticity has a dynamic dependence in a certain frequency range such that the force necessary to produce a time varying deformation in the material is greater for rapid deformations than for slow ones

Deformations.

B polishing method according to Example 1, with the step

Patterning the workpiece surface by means of a microstructuring method before the polishing step, such that long-wave deviations from the desired geometry are reduced, accepting a defined short-wave surface topography.

C polishing method according to one of Examples A to B with the step

Selecting the process conditions, especially the temperature and the amount of Relative speed between the workpiece surface and the elastic surface, so that generated by the microstructure short-wave

Deviations are leveled much faster than uncorrected long-wave deviations.

D polishing method according to one of Examples A to C,

wherein the method steps are carried out several times in succession.

E polishing method according to one of examples B to D,

characterized,

the structuring of the workpiece surface is carried out by means of a photolithographic method with the aid of a photomask.

F polishing method according to one of Examples B to D,

characterized,

in that the structuring of the workpiece surface is carried out by means of a photolithographic method using a computer-controlled laser beam.

G polishing method according to one of Examples B to D,

characterized,

the structuring of the workpiece surface with the aid of lithographic processes known from printing technology for structuring a resist mask and a subsequent etching step for molding the resist mask geometry into the mask

Workpiece surface is made.

H polishing method according to one of Examples B to D,

characterized,

that the structuring of the workpiece surface is carried out by means of a computer-controlled laser ablation method.

I polishing method according to one of examples B to D,

characterized,

that the structuring of the workpiece surface is carried out by means of a computer-controlled mechanical removal method, for example by mechanical scribing with suitably hard tips. J polishing method according to one of examples B to D,

characterized,

that the microstructure is already generated by a suitable process control of shaping preliminary processes.

K polishing method according to one of examples A to C,

characterized,

that the surface structure, which is generated by a placement of components and the manufacturing processes, is influenced by a placement of other non-functional components so that long-wave deviations from the desired geometry are reduced, taking into account short-wave deviations.

L polishing method according to one of the examples A to K,

characterized,

that a process model for the prediction of the surface geometry after the polishing process is derived from the process and material properties.

M polishing method according to example L,

characterized,

that the surface geometry predicted from the process model is used to correct the aberration caused by a deviation from the desired geometry by shaping the workpiece itself or other optical elements.

N polishing method according to Example L,

characterized,

that the surface geometry predicted from the process model is used to compensate for the aberration resulting from a deviation from the desired geometry by adapting the geometry of components which are patterned by a subsequent lithography process.

An apparatus for carrying out a polishing method according to any one of Examples A to J, comprising a wafer carrier (13) for supporting the workpiece and a polishing pad carrier (15) for supporting the elastic surface, the polishing of

Workpiece surface by generating a pressure of the elastic surface on the Workpiece surface and moving the elastic surface and the

Workpiece surface is done relative to each other by a suitable mechanism and a device that can produce microstructures by any of the methods described in Example E to H.

Claims

claims

A method of determining a microstructure to improve a polishing process to be applied to a workpiece surface, comprising the steps of: determining a surface deviation of a workpiece surface from a desired target geometry; and

determine a microstructure to be applied to the workpiece surface, wherein the microstructure has a shorter-waved surface structure than the original one

Workpiece surface and is chosen so that long-wave deviations of

Workpiece surface can be compensated by the target geometry, so that after a

Imprinting of the determined microstructure on the workpiece surface in a subsequently feasible polishing process better polishing results and / or shorter polishing times can be achieved.

2. Method according to the preceding claim, wherein for determining the

Microstructure takes place an assignment between a height structure of the workpiece surface and a local microstructure.

A method according to any one of the preceding claims, further comprising the step of:

providing a process model for predicting the surface geometry of a workpiece surface after a polishing process.

4. The method of claim 3, wherein the process model is used to determine the microstructure to be imprinted.

5. The method according to claim 3, wherein the process model comprises at least one of the following parameters: temperature, polishing speed, polishing pressure, material, roughness and frequency-dependent elastic modulus of an elastic

Polishing surface.

6. The method according to any one of claims 3 to 5, wherein the predicted from the process model surface geometry is used, an aberration caused by a Deviation of the workpiece surface from the target geometry arises to compensate by adjusting the geometry of applied to the workpiece components, which can be structured with a subsequent lithographic process.

7. The method of claim 3, wherein the surface geometry predicted from the process model is used to correct an aberration resulting from a deviation of the workpiece surface from the target geometry by shaping the workpiece itself or by using further optical elements.

8. The method according to any one of the preceding claims, wherein the determined

Microstructure is determined by optimization processes.

9. A microstructuring method for improving a polishing method to be applied to a workpiece surface, comprising the following step:

Imprinting a determined by means of the method according to one of claims 1 to 8 microstructure on a workpiece surface.

10. The microstructuring method according to claim 9, wherein the microstructure is impressed by means of a material-removing structuring method.

11. The microstructuring method according to claim 9, wherein the microstructure is impressed by means of a material-applying patterning process.

12. The microstructuring method according to claim 9, wherein the microstructure is impressed by means of a material-removing structuring method and a material-applying structuring method.

13. The microstructuring method according to claim 9, wherein the structuring of the workpiece surface is carried out by means of a lithographic method for patterning a resist mask and with the aid of a subsequent etching step for molding the lacquer mask

Lackmaskengeometrie is made in the workpiece surface.

The microstructuring method according to claim 13, wherein the resist mask is directly formed (printed) by means of an ink jet printing-like process.

The microstructuring method according to claim 13, wherein the resist mask is directly generated by means of a pressure matrix.

16. The microstructuring method according to claim 9, wherein the structuring of the workpiece surface is carried out by means of a photolithographic method with the aid of a photomask.

17. Microstructuring method according to claim 9, wherein structuring the

Workpiece surface is made by means of a photolithographic process using a computer-controlled laser beam.

18. A microstructuring method according to claim 9, wherein the structuring of the workpiece surface is performed by means of a computer-controlled laser ablation method.

19. The microstructuring method according to claim 9, wherein the structuring of the workpiece surface is carried out by means of a computer-controlled mechanical removal method, in particular by mechanical scribing with suitably hard tips.

20. The microstructuring method according to claim 9, wherein a surface structure, which is generated by a placement of components on the workpiece and the manufacturing processes used therein, is influenced by a placement of further non-functional components such that long-wave deviations from the target geometry at the expense of Generation of short-wave deviations can be reduced.

21. The microstructuring method according to claim 9, wherein the microstructure is already produced by a tailored process control of shaping preliminary processes.

22. A method of polishing and shaping workpiece surfaces, comprising the steps of:

providing a microstructured workpiece surface whose microstructure has been produced by the microstructuring method according to any one of claims 9 to 21; placing an elastic surface on the workpiece surface; and polishing the workpiece surface by creating a pressure between the elastic surface and the workpiece surface and by moving the elastic surface and the workpiece surface relative to each other,

wherein a material for the elastic surface is used, the

Young's modulus in a certain frequency range has a dynamic dependence such that the force necessary to produce a time-varying deformation in the material is greater for rapid deformations than for slow ones

Deformations.

The polishing method according to claim 22, further comprising the step of: selecting process conditions, particularly temperature and / or temperature

Amount of the relative speed between the workpiece surface and the elastic surface, so that the polishing time is as short as possible.

24. Polishing method according to one of claims 22 to 23, wherein the method steps are carried out several times in succession.

25. Computer program product with a program code for carrying out the method according to one of claims 1 to 24.

26. A device for carrying out the method according to one of claims 22 to 25, which has the following:

a microstructuring unit for microstructuring a workpiece surface according to one of claims 9 to 21; and

a polishing unit for polishing the workpiece surface.

27. Device according to the preceding claim with:

a carrier for supporting a workpiece; and

a polishing pad and a polishing pad carrier for carrying the same;

wherein the apparatus is arranged to polish a workpiece surface by generating a pressure of the polishing pad on the workpiece surface and moving the polishing pad and the workpiece surface relative to each other.

28. The device of claim 26, wherein the polishing pad comprises a foamed material.

29. The device according to claim 26, wherein the polishing pad has a rough surface.

30. The apparatus of claim 26, wherein the polishing pad is in contact with the workpiece surface only at individual polishing pad tips.

31. The device according to one of claims 26 to 30, wherein between the polishing pad, which rests directly on the workpiece surface, and the polishing pad carrier a

Intermediate layer of softer viscous, softer elastic or softer visco-elastic material, in particular of pitch or resin or a polymer, is provided.

32. Use of a microstructuring unit for improving a method for polishing and shaping workpiece surfaces.