DE102005017632A1 - Method of controlling local etching or deposition in modification of surfaces with pulsed determination of a removal or deposition profile ion streams useful in the high accuracy forming of optical component surfaces involving - Google Patents

Abstract

Method of controlling local etching or deposition in modification of surfaces with pulsed ion streams involving determination of a removal m deposition profile, followed by guiding an ion or particle beam over the probe or part of it, so that local etching or material removal occurs at the ion or particle beam site corresponding to a predetermined rate thru a combination of dwell time and pulse length of an n beam from an electrically controllably shaped ion source, and a locally adapted or predetermined material removal or deposition profile is obtained.

Description

The The invention relates to a method for controlling the local etching or Separation rate in the modification of substrate surfaces with electrically pulsed ion beams.

Ion beam machining processes are getting stronger and stronger Dimensions component machining technology for producing high-precision surfaces of optical, electronic and mechanical components. By means of ion beams let yourself both material by dusting Highly accurate local ablation as well as a layer of one desired Materials re the thickness of highly accurate deposition on a substrate.

The etching or the rate of deposition must be adapted to specific requirements be. In the example of planarizing the surface of a sample, it is necessary to for each surface segment to achieve a removal according to the initial topology, so after processing one possible flat surface is produced. In the case of deposition, it may be necessary certain local structures on a substrate surface to generate corresponding locally adjustable deposition rates.

The currently the most successful and most applied technology around surfaces The above process is the computer controlled one Departure of the surface with an ion beam with Gaussian distributed Ion current density (ion beam etching) or an ion beam-generated Gaussian particle beam (Coating) line for Line at a speed proportional to the desired Removal or order. This method is called residence time method. Show it:

1 : a schematic representation of the arrangement of the substrate ( 1 ) of the ion beam ( 2 ) with a Gaussian ion current density distribution ("tool function"), and the ion source ( 3 ), and

2 : the meandering approach of a circular substrate surface.

• [1] T. Hänsel, A. Nickel, A. Schindler, H.-J. Thomas, Ion beam figuring surface finishing of x-ray and synchrotron beam line optics using stitching interferometry for the surface topology measurement, Conference on Optical Fabrication and Testing, Optical Society of America – OSA, Rochester, 10.–13.10. 2004.
• [2] A. Schindler, T. Hänsel, F. Frost, A. Nickel, R. Fechner, B. Rauschenbach, Recent achievements on ion beam techniques for microoptics fabrication, 10th Microoptics Conference MOC 04, Jena, 1.–3.09. (2004) K-7.
• [3] F. Bigl, T. Hänsel, A. Schindler, Oberflächenpräzisionsbearbeitung mit Ionenstrahlen, Vakuum in Forschung und Praxis 10 (1998) 50–56.

In order to avoid roughening of the surface, the track pitch should be a fraction of the extent (half width) of the ion beam / particle beam. Again, the size of the ion beam should be less than one-tenth the size of the surface to be machined as set forth in the following literature, inter alia:

• [1] T. Hansel, A. Nickel, A. Schindler, H.-J. Thomas, Ion beam figuring surface finishing of x-ray and synchrotron beam line optics using stitching interferometry for the surface topology measurement, Conference on Optical Fabrication and Testing, Optical Society of America - OSA, Rochester, 10-13 / 10. Of 2004.
• [2] A. Schindler, T. Hansel, F. Frost, A. Nickel, R. Fechner, B. Rauschenbach, Recent achievements on ion beam techniques for microoptics fabrication, 10th Microoptics Conference MOC 04, Jena, 1.-3.09. (2004) K-7.
• [3] F. Bigl, T. Hänsel, A. Schindler, Surface Precision Processing with Ion Beams, Vacuum in Research and Practice 10 (1998) 50-56.

Use is made of noble gas ions, preferably Ar.sup. ⁺ , As well as reactive species, in particular for the structure transfer into hard materials, in part using lacquer masks for structured surfaces.

Currently, in surface modification, ion beams with high temporal constancy of current density are used throughout the process time to achieve a given precise local substrate removal or deposition, as for example in the documents DE4108404C2 and WO02 / 095085.

The Residence time of the ion beam / particle beam on the respective surface segment The sample is controlled by mechanical positioning systems and is in the range of at least a few tenths of a millisecond. The state of the art drive and positioning systems are typically electric motor driven linear tables. These movement systems can only a certain upper limit for the occurring accelerations and with the inertia of the moved apparatus parts associated energy changes for the respective sample positions muster.

One Another problem is the dynamic range of the motion systems. Due to the insufficiently accurate setting of small speed differences For example, it comes to a not undershot minimum contrast in the machining rate between two adjacent surface segments and thus an error in the achievable quality of the ideal removal or the ideal coating.

The speed of the motion systems, which is still technically limited above, leads to a retention process which is not necessary for the corresponding process or an unnecessary coating in the residence time method and the use of a continuous wave ion beam. In the case of an etching of a substrate, the residence time method results in a so-called base removal. The base removal is by the ratio of maximum local speed and etch rate defined. The base removal means that the minimum removal on the substrate per machining operation can not be undershot. For certain substrates, post-processing is therefore not repeatable as often as desired.

Therefore would be a additional process parameters for setting the local etching or Deposition rate is an important step to find a solution for this [1].

in the Document WO02 / 095085 is in dependent claim 9, respectively Page 8, lines 25/26 in addition to the residence time for controlling the local etching rate also the variation of the current density of the continuous wave ion source as a another independent Process parameters proposed.

A change in the current density can be achieved, for example, by changing the grid geometry, the working distance, and certain operating parameters (electrical plasma power, gas flow) of the continuous wave ion beam on the sample. On the one hand, the change in the current density has a nonlinear influence on the etching or deposition rate. On the other hand, the change in the current density of the ion source also means a change in the distribution of the current density, ie the tool function ( 2 ). However, the constancy of the tool function is a prerequisite for the calculation of the residence times [2]. A change in the tool function, which must be determined before each machining by measurement, for example a so - called "footprint", means a total new calculation of the residence times and is therefore not possible in - situ Due to these difficulties, the use of the Current density of the ion beam for setting the local Ätz- or deposition rate useless and has not prevailed in practice.

The The object of the invention was thus to specify a method that it allows the previously described procedural restrictions, for example, by the mechanically specified dynamic range of Motion systems or the physical properties of the ion source, to diminish or cancel.

Innovative step

By the use of an electrically switched ion beam instead the continuous wave ion beam used so far and the combination of Pulse duration of the electrically switched ion beam with the physical Residence time of the ion beam for the respective local surface segment of Sample this object is achieved according to the invention.

It an electrically switched ion beam is used whose pulse duration on the for the respective sample position predetermined surface change according to outer predetermined Criteria is optimally attuned. A criterion for optimization may be the minimization of the total process time, or the Minimizing the total energy input or minimizing the Socket removal or a combination of these optimization criteria.

Those Make the sample, for the one less change is provided, with less residence time and at the same time shorter Pulse durations of the ion beam processed, while those places the Sample, for which provided a larger material removal is, with a correspondingly longer residence time and longer Pulse durations of the ion beam are processed.

advantages

The both process parameters (residence time of the ion beam on the surface segment and the pulse duration of the ion beam) can be set freely and independently of each other become. It can for every local surface segment the sample on external requirements calculated optimally matched value pair of these two process parameters, for the System control can be programmed and realized. Thus results a two-dimensional space for optimization compared to the earlier one-dimensional possibility the process optimization, which so far alone on the residence time of the continuous wave ion beam over the respective surface segment the sample was made. This two-dimensional freedom in optimization already means a significant leap in quality in litigation and the dynamics of the system. This new quality in the optimization of the etching process shows, for example, in terms of the total process time, and thus the utilization of the plant or the load and Wear of their mechanical components.

One important advantage is the relatively easy accessibility and easy controllability this process parameter, as opposed to changing the ion current density a continuous wave ion beam source as described in document WO02 / 095085 is proposed. The variation of the current density of the ion source has a significant impact on the distribution of current density and thus on the tool function, as well as on the etching or Deposition rate and therefore can not be used in situ.

In contrast, has the electrical circuit of the ion beam by means of the circuit the ion extraction or / and accelerating voltage has the advantage the variation of the power input with constant tool function solely by the technically relatively simple variation of the pulse duration.

One significant advantage over the previously used residence time of the ion beam on the respective surface segment the sample for adjusting the local machining rate is the improvement the minimum contrast height and the reduction of the global base debit. To generate a locally different discounts, or a locally different one Deposition, the sample or ion beam is mechanical Moving positioning. Due to the technically limited dynamics of these mechanical systems is the minimum residence time per surface segment typically at least a few tenths of a millisecond. By using a switched ion beam can now reduce the time-average ion beam intensity so that the minimum local dwell time can be increased can. Thereby can the positioning systems used better in their optimal dynamic range be used. At the same time, the base removal at the same Machining rate or the entire process time can be reduced.

The the prior art used motion systems can only a certain upper limit for the occurring accelerations and those with the inertia of the moving Apparatus parts associated energy changes for the respective sample positions muster. This problem leads It also has limitations on the minimum total Process time (cost factor) came. Through the matched simultaneous use of dwell time and pulse duration as a process parameter can that of a surface segment to the next one surface segment occurring acceleration or mechanical energy change of the positioning system can be reduced. This allows the Speed of the sample or the ion beam more uniform and the whole process is more moderate, so that a longer one Life of the components of the positioning system results.

From The advantage is the control of the intensity of the ion beams through the Use of a switched ion source also with regard to the power input and the unwanted heating of the sample. Farther The ion source (with a duty cycle of 0.0) can also be complete be switched off, for example, if the ion beam without running a Machining from one position to another position of the sample guided must be coated without coating or etching sample areas (surface treatment). By the possibility one of the tool function adapted activation by slow Pulse width variation optimizes the surface treatment. The possibility of Shutdown of the ion beam is when using ion beams with gaussian current density profile especially at the edge regions of the sample of advantage. There with a continuous wave ion beam at least at a distance of the triple half width of the position to be machined must be moved away, so that no unwanted change in the sample surface generated is reduced, an electrical shutdown of the ion beam the effective grid area and saves travel and process time and enables the implementation of the Processing the sample in a smaller device volume. A reduced Apparatus size, in particular a smaller boiler volume is economical an important advantage. Overall, this results from the use a switched ion beam instead of a continuous wave ion beam also a higher one sample number lifetime of the ion source.

By the control of the duty cycle can continue Power and current density variations of the ion source within a designated error range are compensated, as they are for Example can occur due to thermal drift. This can be the time averaged sources - emission current used as a measured variable and the duty cycle be adjusted so that the source - emission current and thus the time averaged ion current density while maintaining the other process parameters is kept constant.

The electric circuit of the ion beam has the further advantage of being significantly less inertia compared to the known mechanical switches (shutter) of ion beams. A mechanical shutter, such as the one in the document US 4,310,743 is described, would be no longer applicable for switching frequencies above 10 kHz due to the inertia of its components, so that the usual residence times in the millisecond range per sample position can no longer be met with a mechanical circuit of the ion beam. Furthermore, exposed to the ion beam components of a mechanical shutter are subject to high wear by the etching of the ions to be blocked, while the electrical circuit of the ion beam offers the advantage of wear-free circuit of the ion beam. By eliminating moving mechanical components in the high vacuum of the ion beam system, the pollution of the system is reduced by mechanical abrasion.

Furthermore, the use of an elek trically switched ion beam, the possibility of spatial control of neutralization. If one chooses a sampling frequency in such a way that the simultaneous arrival of negatively charged electrons and positively charged ions on the substrate surface is made possible, taking into account the sample distance and the different flight times of the individual particle packets, then the location of the processed surface segment is precisely the case for insulating dielectric samples necessary complete neutralization of the ions. Advantageous is the additional possibility of controlling the neutralization through the use of partial pulses of different polarity and height.

Claims (20)

Method for controlling the local etch or deposition rate in the modification of surfaces with pulsed ion beams, in which initially a removal or deposition profile is determined and then at least one ion beam or particle beam at least once over the sample or parts of the sample is guided so that at the place of the Ion beam or particle beam a local etching of the sample or a local Order on the sample according to a locally specified rate by the combination of residence time and pulse duration of an ion beam takes place from an electrically switchable designed ion source and a locally adapted or predetermined removal or deposition profile is produced. Method for controlling the local etch or deposition rate in the modification of surfaces with Pulsed ion beam according to one of the preceding claims, characterized characterized in that a noble gas or reactive gas ion beam is used. Method for controlling the local etch or deposition rate in the modification of surfaces with Pulsed ion beams according to one of the preceding claims by the use of ion energies of preferably 200 eV to 2 keV. Method for controlling the local etch or deposition rate in the modification of surfaces with Pulsed ion beams according to one of the preceding claims by the use of an ion beam or particle beam with gaussian or homogeneously distributed current density. Method for controlling the local etch or deposition rate in the modification of surfaces with Pulsed ion beam according to one of the preceding claims, characterized characterized in that the ion beam or particle beam in tracks over the Layer led and the track pitch is smaller than the half-width of the ion beam with Gaussian current density distribution or smaller than the extension of the ion beam with homogeneous current density distribution is. Method for controlling the local etch or deposition rate in the modification of surfaces with Pulsed ion beams according to one of the preceding claims through the use of a mask, for example a resist mask, which leaves only the areas of the sample to be modified open. Method for controlling the local etch or deposition rate in the modification of surfaces with Pulsed ion beams according to one of the preceding claims by the mass spectroscopic determination of the current processing rate. Method for controlling the local etch or deposition rate in the modification of surfaces with Pulsed ion beams according to one of the preceding claims through the use of electrical pulses to circuit the Ion source. Method for controlling the local etch or deposition rate in the modification of surfaces with Pulsed ion beams according to one of the preceding claims through the electrical circuit of the ion source via the circuit of the ion extraction voltage, or / and the acceleration voltage. Method for controlling the local etching or Separation rate in the modification of surfaces with pulsed ion beams according to one of the preceding claims, characterized by the use a continuously variably adjustable duty cycle from 0.0 to 1.0 for switching the ion source. Method for controlling the local etching or Separation rate in the modification of surfaces with pulsed ion beams according to one of the preceding claims, characterized by the use of the residence time adapted Tastzeiten or clock frequencies for switching the ion beam, so that in an etching or Separation process on the substrate surface in the respective residence time per surface segment at least one bar takes place. Method for controlling the local etching or deposition rate in the modification of surfaces with pulsed ion beams according to one of the preceding claims, characterized in that the substrate surface is determined by interferometric or scanning profilometric methods and the measured topology for the determination the local substrate modification is used or the processing rate is set according to a global specification. Method for controlling the local etching or Separation rate in the modification of surfaces with pulsed ion beams according to one of the preceding claims, characterized by the use a Fourier refold the given topology of the surface modification and the tool function the ion source for calculating the local combinations of residence times and duty cycles for the substrate to be processed. Method for controlling the local etching or Separation rate in the modification of surfaces with pulsed ion beams according to one of the preceding claims, characterized by the determination the tool function by measuring the topology on a test substrate to: - one punctual processing ("footprint"), - one one-dimensional editing ("digging"), or - one two-dimensional processing ("pit"). Method for controlling the local etching or Separation rate in the modification of surfaces with pulsed ion beams according to one of the preceding claims, characterized by the use a mathematically by superpositioned two-dimensional Gaussian profiles modeled tool function. Method for controlling the local etching or Separation rate in the modification of surfaces with pulsed ion beams according to one of the preceding claims, characterized by the direct Use of the measured footprint tool function for the calculation the residence time and duty cycle combinations by means of Fourier refolding. Method for controlling the local etching or Separation rate in the modification of surfaces with pulsed ion beams according to one of the preceding claims, characterized by the use the measured trench or trench topology for adapting the tool function for the Calculation of the residence time and duty cycle combinations by means of Fourier deconvolution. Method for controlling the local etching or Separation rate in the modification of surfaces with pulsed ion beams according to one of the preceding claims, characterized by line, column, meandering or spiral Leadership of Ion beam or particle beam or the sample during the Processing. Method for controlling the local etching or Separation rate in the modification of surfaces with pulsed ion beams according to one of the preceding claims, characterized by the continuous Control of the constancy of performance of the ion source via the variation of the duty cycle. Method for controlling the local etching or Separation rate in the modification of surfaces with pulsed ion beams according to one of the preceding claims, characterized by the use of subpulses of different polarity, duration and height for additional Extraction of electrons and time-compensated charge compensation on the substrate surface.