DE102016015822B3 - Method for ion implantation - Google Patents

Abstract

A method comprising: implanting ions into a wafer by irradiating the wafer with an ion beam via an implantation device having a filter frame and a filter held by the filter frame, the filter being adapted to be irradiated by the ion beam, wherein Collimator structure is disposed on the wafer and the ions are implanted by the collimator structure in the wafer.

Description

The invention relates to an implantation arrangement with an energy filter (implantation filter) for ion implantation and its use and an implantation method.

By ion implantation doping or the generation of defect profiles in any materials, such as semiconductors (silicon, silicon carbide, gallium nitride) or optical materials (LiNbO3) can be achieved with predefined depth profiles in the depth range from a few nanometers to several 100 micrometers. In particular, it is desirable to produce depth profiles characterized by a greater depth distribution width than the width of a doping concentration peak or defect concentration peak producible by monoenergetic ion radiation, or to produce doping or defect depth profiles which can not be produced by one or a few simple monoenergetic implants ,

1 shows a known from [7] method for generating a depth profile. In this case, an implantation takes place through a structured energy filter in an installation for ion implantation for the purpose of wafer processing. Shown is the implantation method and the resulting from the implantation of dopant distribution or defect distribution in the wafer after processing.

1 shows the basic principle of the energy filter. A monoenergetic ion beam is modified in its energy as it passes through the microstructured energy filter component, depending on the point of entry. The resulting energy distribution of the ions leads to a modification of the depth profile of the implanted substance in the substrate matrix.

2 shows a plant for ion implantation. This system includes an implantation chamber in which multiple wafers can be placed on a wafer wheel. The wafer wheel rotates during implantation, so that the individual wafers repeatedly pass through a beam opening in which the energy filter is arranged and through which the ion beam passes into the implantation chamber, and thus into the wafers.

2 shows on the left a wafer wheel on which the substrates to be implanted are fixed. During processing / implantation, the wheel is tilted by 90 ° and rotated. The wheel is thus "described" in concentric circles by the ion beam indicated in green with ions. In order to irradiate the entire wafer surface, the wheel is moved vertically during processing. Right shows 2 a mounted energy filter in the area of the beam exit.

In the 3 shown layouts or three-dimensional structures of filters show the basic possibilities using energy filters to produce a variety of Dotierstofftiefenprofilen. The filter profiles can in principle be combined with each other to obtain new filter profiles and thus doping depth profiles. Shown are respective cross-sections of the energy filter (in the figures at the left), plan views of the energy filters and gradients of the doping concentration reached across the depth of the wafer. The "depth" of the wafer is a direction perpendicular to the surface of the wafer being implanted.

3 is a schematic representation of various doping profiles (doping concentration as a function of depth in the substrate) for differently shaped energy filter microstructures (each shown in side view and top view). (a) Triangular prismatic structures produce a rectangular doping profile. (c) Trapezium prismatic structures produce a rectangular doping profile with a peak at the beginning of the profile; (d) Pyramidal structures produce a triangular doping profile rising into the depth of the substrate.

Heretofore known energy filters (implantation filters) and energy filter elements are not suitable for high throughputs for many reasons. many wafers per hour to reach. It is desirable in particular, high wafer throughputs per hour, ease of handling, ease of manufacture and the realization of any profile shapes.

From the literature static or movably mounted filters are known, which are monolithic, i. are made of a block of material and are individually mounted to the ion beam [2], [3], [4], [5], [6], [7], [8], [9], [10].

In contrast to silicon, doped regions in SiC wafers i.a. can not be changed in shape by outdiffusion of doping profiles [2], [4], [5], [6]. The reason lies in the even at high temperatures very low diffusion constant of the common dopants (dopants), such as Al, B, N, P. These are many orders of magnitude below the comparative values of, for example, silicon.

Due to this fact, it has not been possible to date to provide doping regions, especially those with high aspect ratios, i. small ratio of floor area to depth, economical to realize.

Dopant depth profiles in semiconductor wafers can be made by in-situ doping during epitaxial deposition or by (masked) monoenergetic ion implantation. With in-situ doping, high inaccuracies can occur. Even with homogeneous doping profiles, significant deviations from the target doping can be expected on the wafer, ie from center to edge. For gradient depth profiles, this inaccuracy also extends to the vertical direction of the doping region, since now the local dopant concentration depends on a large number of process parameters such as temperature, local doping gas concentration, topology, width of the Prandtl boundary layer, growth rate, etc. The use of monoenergetic ion beams means that many individual implants have to be performed to obtain doping profiles with acceptable vertical ripples. This approach is only partially scalable, it is very economically unprofitable very quickly.

Examples of the invention relate to the design of an energy filter element for ion implantation systems, so that it corresponds to the requirements resulting from the application of the energy filter element in the industrial production of semiconductor devices, in particular for devices based on SiC semiconductor material. Production conditions are defined with regard to the use of energy filter elements, for example by the following aspects:

Technically simple filter change

In a productive environment, i.e. in a factory, production is also carried out on ion implanters by professional operators ("operators"), who in most cases have not undergone engineering training.

The energy filter is a highly fragile microstructured membrane whose nondestructive handling is difficult. For economical use of the filter technology, it should be ensured that after a brief briefing, non-specialists (in the sense of non-engineers) must be able to replace the filter after wear or as part of a tool change at the Implanteranlage.

Any vertical profile shapes

Novel semiconductor devices such as e.g. Superjunction devices or optimized diode structures cause a non-uniform doping process. However, the simple energy filters described in [2] and [4 - 6] only produce constant profiles. More complicated filter structures such as e.g. Structures described in Rüb [8] are technically very complex and difficult to realize according to the state of the art for productive tasks. The object is to provide complicated vertical profile shapes with uncomplicated, i. to realize easily fabricated filter structures.

High throughput cooling systems in combination with filter movement

For example, production conditions mean that ion implanters (typical terminal voltage at tandem accelerators> 1MV to 6MV) should produce more than typically 20-30 wafers with 6 "diameter and surface doses per wafer of approximately 2E13cm-2 per hour To be able to produce a number of wafers, ion currents of more than 1pμA up to a few 10pμA have to be used or there are powers of more than a few watts, eg 6W / cm-2 on the filter (typical area 1 -2cm ² ). This leads to heating of the filter. It turns the task to cool the filter by appropriate measures.

Simple, cost-effective production of the filter structures in the case of homogeneous, constant depth profiles

Filter structures can be made by anisotropic wet chemical etching. In the simplest embodiment, the filter structures consist of appropriately sized triangular long lamellae (e.g., 6μm high, 8.4μm spacing, a few millimeters long) periodically arrayed on a thin membrane as possible. In this case, the production of pointed triangular lamellae is cost-intensive, since the wet-chemical anisotropic etching must be precisely adjusted. Peak, i. Non-trapezoidal lamellae are expensive, since etching rates and etching times must be precisely matched to one another for pointed lamellae. In practice, this leads to high process control effort during the etch and results in loss of yield due to the expected uneven processing (etch rates of wet chemical processes are never perfectly reproducible and are never homogeneous over larger areas) on a chip with many hundreds of slats. not perfectly structured filter elements. The object is to realize a simple and cost-effective energy filter production.

High lateral homogeneity of the generated doping or defect region

The energy filters for ion implantation described in the cited references [2], [3], [4], [5], [6], [7], [8], [9], [10] have an internal 3-dimensional Structure that leads to path length differences of the ions in transmission through the filter. These path length differences generate, depending on Braking power of the filter material, a modification of the kinetic energy of the transmitted ions. A monoenergetic ion beam is thus converted into a beam of ions of different kinetic energy. The energy distribution is determined by the geometry and the materials of the filter, ie the filter structure is transferred into the substrate by means of ion lithography.

Monitoring of the "End of Life" for the energy filter

Due to the nuclear interaction of the ion beams with the filter material and due to the thermal stress, a typical lifetime of the filter is specific to each ion implantation process with energy filters. For an energy filter made of silicon, with approx. 2μm support layer, 8μm regular serrations and an implantation process of 12MeV nitrogen with currents around 0.1pμA, an approximate maximum production of approx. 100 wafers ( 6 " ).

For the operator and to safeguard the filter manufacturer, the total number of wafers processed with a specific filter should be monitored.

Restriction of the angular distribution of the transmitted ions

For the preparation of masked, i. In their lateral spatial extension restricted doping regions, in particular in cases of high aspect ratios, the angular spectrum of the transmitted ions must be limited in order to avoid a "subimplantation" of the masking layer.

Low filter wear due to sputtering effects

Avoidance of channeling effects (grid guidance effects) due to the arrangement of the filter to the ion beam

Realization of complex dopant depth profiles by simple filter geometry

Electron suppression when using the filter

It is known that in the transmission of ions through a solid, the ions assume a state of equilibrium with respect to their electrical charge. Electrons of the primary beam can be emitted or absorbed in the solid, i. the transmitted ions have on average a higher or lower charge state, depending on the properties of the filter material and the primary energy after passing through the filter [26]. This can lead to positive or negative charging of the filter.

At the same time, ion bombardment on both the front and the back of the filter can generate secondary electrons with high kinetic energy.

At high current densities, as required in industrial production, the energy filter will heat up, see 34 , Due to thermionic electron emission (Richardson-Dushman law) thermal electrons are generated depending on the temperature and the work function of the filter material.

The distance (in high vacuum) of the ion accelerator between filter and substrate is typically only a few centimeters or less. That by diffusion of thermal electrons (from thermionic emission) and by the action of fast electrons (from ion bombardment), the measurement of the ion current at the substrate, for example by a Faraday Cup attached there, is falsified.

Alternative manufacturing methods by injection molding, casting or sintering

In the publications [ 2 ] and [4 - 12] micro-technical methods are proposed for the production of the energy filter. In particular, it is described that lithographic processes in combination with wet-chemical or dry-chemical etching processes are used to produce the filters. For the filter production, the anisotropic wet-chemical etching process by means of alkaline etching media (eg KOH or TMAH) in silicon is preferably used.

For filters made by the latter method, the functional filter layer is made of single crystal silicon. Thus, when bombarded with high-energy ions, it must always be assumed that, in principle, channeling effects influence the effective energy loss in the filter layer in a manner which is difficult to control.

Arrangement for irradiating a static substrate

An irradiation arrangement is to be used which allows to irradiate a static substrate with high lateral homogeneity over the entire substrate surface in an energy-filtered manner. Reason: End stations of irradiation facilities often do not have a full mechanical scan of the wafer (Waferwheel) using a punctiform or nearly point-shaped beam spot, but many systems have an electrostatically expanded beam (= line in the x-direction), which is scanned, for example, electrostatically over the wafer (y-direction). Partly also partially mechanical scanners are in use, ie widening of the beam in the x-direction and mechanical (slow) movement of the wafer in the y-direction.

Arrangement for utilizing a large filter surface

It is necessary to use an irradiation arrangement which allows a static or movable substrate to be irradiated energy-filtered with high lateral homogeneity over the entire substrate surface and to use a large filter surface. As a result, thermal effects and degradation effects in the filter can be reduced.

Modification of the doping profile in the substrate by means of a sacrificial layer

The energy filter is a tool for manipulating the doping profile in the substrate. Under certain conditions, manipulation of the producible doping profile in the substrate AFTER the energy filter is desirable. In particular, a "pushing out" of the near-surface beginning of the doping profile from the substrate is desirable. This may be particularly advantageous if the beginning of the doping profile in the substrate through the filter for various reasons (in particular loss of ions by scattering) can not be adjusted correctly. Such a dopant profile manipulation after the energy filter can be done by implantation in a sacrificial layer on the substrate.

Lateral modification of the doping profile in the substrate by sacrificial layer

For some applications, a laterally variable doping profile in the substrate is desirable. In particular, the change in the implantation depth of a homogeneous doping profile for edge terminations in semiconductor components could be advantageously used. Such a lateral adjustment of the doping profile can take place by means of a laterally variable thickness sacrificial layer on the substrate.

Adaptation of a profile transition of several implantation profiles

For certain applications it is desirable that 2 or more profiles have to be connected at a certain depth at a "seam", otherwise there will be insulation between the layers. In particular, this problem occurs in a layer system when the lower end of an upper doping profile or the upper end of a lower doping profile have a slowly expiring concentration tail.

Special arrangement of the multifilter concept with coupled pendulum motion

If a multifilter is attached to the moving part of a movable substrate chamber which moves in front of the beam with a linear pendulum motion (eg in the case of a rotating wafer disk with vertical scanning device), movement of the multifilter relative to the beam can be easily achieved by the Movement of the substrate chamber can be achieved. By means of a magnetic or static scanning device in front of the filter in one direction, a very large multifilter surface can be used, which results, for example, as a product of vertical pendulum distance and horizontal scan distance. The movement of wafer and filter are coupled in this arrangement, which can lead to problems with regard to lateral doping homogeneity. Due to the rotation of the wafer wheel, the ion beam "writes" lines on the wafers. As a consequence of said arrangement, the position of, for example, a horizontal irradiated line on the wafer is coupled to a particular vertical position on the multifilter. For example, a gap between individual filter elements would result in an inhomogeneously doped line on the wafer. Therefore, an arrangement of the filter components in the multifilter must be chosen so that the lateral homogeneity is ensured despite the coupling of the linear movements of filter and substrate.

Examples of energy filters, implantation devices, or parts of implantation devices that satisfy the aforementioned production conditions are explained below. It should be mentioned that the measures and concepts explained below can be combined with one another as desired, but can also be applied individually in each case.

Ad 1. Technically simple filter change

It is proposed on the respective implantation filter, which is referred to below as a filter chip to provide a frame that allows easy handling of the filter chip. install. This frame can, as in the 4 to 6 is shown to be designed so that it can be used on the ion implantation in a pre-installed there, suitable frame holder. The frame protects the energy filter, allows easy handling and ensures electrical and thermal dissipation or electrical insulation (see 36 ). The frame can be equipped with the filter chip in a dust-free environment by the manufacturer of the filter elements and delivered in a dust-free packaging to the ion implantation system.

In the 4 and 5 only one embodiment for the geometric and mechanical design of a filter frame is shown. According to one embodiment, the filter holder and / or the filter frame is provided with a coating which prevents material removal from the filter frame and filter holder.

Filter frames and filter holders can be made of metals, preferably stainless steel or similar. produced. During the implantation process sputtering effects in the local environment of the energy filter must be expected due to scattered ions, i. it must be expected with near-surface removal of frame and filter holder material. Metal contamination on the substrate wafer could be the undesirable consequence. The coating prevents such contamination, the coating being of a non-contaminating material. Which substances are non-contaminating depends on the properties of the target substrate used. Examples of suitable materials include silicon or silicon carbide.

4 shows a cross section of a filter frame for receiving an energy filter chip.

5 shows a plan view of a filter frame for receiving an energy filter element with closure element and mounted energy filter

6 shows a typical installation of a frame for receiving an energy filter element in the beam path of an ion implanter. In the example, the filter holder is disposed on one side of the chamber wall. In the example, this side is the inside of the chamber wall, that is, the side that faces the wafer (not shown) during implantation. The inserted into the filter holder frame with the filter chip covers the opening of the chamber wall through which occurs during implantation of the ion beam.

The frame can be made of the same material as the filter. In this case, the frame can be made monolithic with the filter and referred to as a monolithic frame. As explained above, the frame can also be made of a different material, such as the filter, such as a metal. In this case, the filter can be inserted into the frame. As another example, the frame includes a monolithic frame and at least one other frame of a different material than the filter attached to the monolithic frame. This further frame is for example a metal frame.

The frame may completely surround the filter as explained and shown above and as shown to the right in the figure below 7 is shown. According to further examples, the frame does not adjoin all (four) sides (edges) of the filter, but adjoins only three, two (opposite) or only one of the edges of the filter. Under frame is in the context of this description, therefore, a full frame that completely surrounds the filter on the sides (edges), but also a sub-frame that surrounds the filter only partially on the sides to understand. Examples of such subframes are in 7 also shown.

7 shows a subframe (left in the figure) and full frame (far right in the figure), each of which may consist of the same (eg monolithic) and / or of a different material than the energy filter.

The energy filter or any other scattering element can be fastened by its frame, which can be realized according to one of the examples explained above, in various ways in the beam path of the Implanter. The above-mentioned insertion of the frame into a filter holder is just one of several possibilities. Other options are explained below.

According to an example that is in 8th is shown, the frame can be secured by at least one web on the chamber wall. In this case, the at least one web serves as a filter holder.

According to another example, in 9 is shown, the frame can also be attached by suspensions or suspension elements on the chamber wall. These suspension elements are, for example, flexible and can be stretched between the frame and chamber wall such that the frame is held firmly. The suspension elements act as filter holders in this example.

According to another example, in 10 is shown, the frame is held with the filter by magnets floating (non-contact). For this purpose, magnets are fixed to a front and a back of the frame and the chamber wall such that in each case a magnet on the chamber wall or a holder attached to the chamber wall opposite a magnet on the frame, in each case opposite poles of the opposite magnets facing each other. Due to the magnetic forces, the frame is held suspended between the magnets attached to the chamber wall and the holder, respectively. The magnets on the frame of the filter can be realized, for example, by thermal evaporation or any other layering method.

8th shows an attachment of the filter frame with filter or any other passive scattering element by one or more webs.

9 illustrates a mounting of the filter frame with filter or any other scattering element by a single or multiple suspension.

10 shows a mounting of the filter frame with filter or any other scattering element by magnetic fields.

Ad 2. Any vertical profile shapes

In principle, the implementation of any desired doping profile in a semiconductor material can be achieved by the geometric design of an energy filter for ion implantation systems. For complex profiles, this means that it is necessary to produce geometrically very demanding three-dimensional etched structures of different sizes, possibly of different heights, such as pyramids, trenches with defined wall inclination, inverted pyramids etc. on the same filter chip.

It is proposed to approximate any profile by rectangular profile shapes, as can be generated with simple triangular structures (multifilter). Optionally, non-triangular structures (e.g., pyramids) may also be used as the basis for approximation.

This means that it is proposed to disassemble any doping profile, for example into box sections, and to produce a triangular filter structure for each box section. Subsequently, the individual filter chips, for example, in the in 4 shown frame mounted such that the areal weighting of the respective corresponding to the box profile element doping concentration, see 11 ,

The decomposition of a doping depth profile is not limited to the triangular structures shown here, but it may be further structures, which contain in the most general case bevels or convex or concave rising edges. The flanks do not necessarily have to be monotonically increasing, but may also contain valleys and depressions.

Binary structures with flank angles of 90 ° are also conceivable.

In embodiment, the filter elements are cut out "obliquely" and arranged directly next to one another. The oblique cutting has the advantage that no adhesive connection between the filters is required to block off ions at the filter edge. In addition, the irradiated area can be optimally used in this way. For the same overall filter dimensions and ion current, this increases wafer throughput.

11 illustrates a simple implementation of a multifilter. Three differently shaped filter elements are combined in a frame for filter holder to a whole energy filter. The ion beam sweeps all individual filter elements evenly. In the present example (left), the dopant depth profile shown on the right thus arises. This profile contains three subprofiles numbered 1, 2, and 3. Each of these sub-profiles results from one of the three sub-filters shown on the left, from the sub-filter provided with the corresponding number.

12 shows a detailed representation of the multifilter concept. On the left three filter elements are shown as examples. Four elements are numerically described. Each filter element results in a dopant depth profile for a given ion species and primary energy. The weighting, ie the resulting concentration is adjustable by the dimensioning of the surfaces of the individual filter elements. For the example, it was assumed that the filter and substrate have the same energy-dependent deceleration capability. In general, however, this is not the case.

13 shows that once everyone in 12 described filter elements combined with suitable weighting to form a total filter and evenly overshadowed by an ion beam suitable primary energy, the sum profile shown results.

14 shows an exemplary arrangement of single filter elements in a multifilter. The individual elements F1 . F2 . F3 etc. are sawn at an angle and mounted directly on each other.

Ad 3. High throughput cooling systems in combination with filter movement

High throughputs of wafers can only be achieved with high target ionizations for given target dopings. Since between about 20% to about 99% of the primary energy of the ion beam in the filter membrane, i. are deposited in the irradiated part of the implantation filter, the use of a cooling method is proposed, thereby preventing an excessive increase in the temperature of the filter even at high ion currents.

Such cooling can be achieved, for example, by one or more of the following under a. to c. The measures described are:

Coolant flow in the filter holder.

As a result, the heated filter chip is cooled by dissipation of the heat.

15 illustrates a filter assembly incorporated into an ion implantation system. In the filter holder, which accommodates the filter frame, cooling lines are integrated, which are supplied by an external cooling unit with coolant. The cooling lines could also be arranged on the surface of the filter holder (not shown).

Movement of the filter or ion beam

It is proposed when using a rotating, for example, with 10-15 wafers loaded wafer wheel to make the filter or the holder of the filter such that it rotates or oscillates with a linear movement. Alternatively, the ion beam can be electrostatically moved across the filter while the filter is stationary.

In these embodiments, the filter is irradiated only partially by the ion beam per unit time. As a result, the currently unirradiated part of the filter can be cooled by radiation cooling, see 16 and 17 cooling down. Thus, in continuous operation averaged higher current densities can be realized with a given filter.

16 shows an energy filter with a large area, which is only partially irradiated per unit time. Thus, the non-irradiated areas can cool by radiation cooling. This embodiment is also configurable as a multifilter as described above. That is, as a filter having a plurality of different filter elements. In the illustrated example, the frame oscillates with the filter in a direction perpendicular to the beam direction of the ion beam. The area of the filter covered by the ion beam is less than the total area of the filter, so that only part of the filter is irradiated per unit of time. This part is constantly changing due to the pendulum movement.

17 shows a further embodiment of an arrangement of energy filters, which rotate about a central axis. Also, only partially irradiated per unit time and the unirradiated elements can cool. This embodiment can also be designed as a multifilter.

Ad 4. Simplified filter design

The production of serrated structures with exact height and perfect tip is technically demanding and accordingly expensive.

For simple doping processes (for example homogeneous doping) which start from the substrate surface and which only require a simple prong structure, a simplified design and consequently a simplified production are proposed here.

It is proposed instead of a tip to design the microstructured membrane (eg serrated structure) with a plateau on the teeth and to dimension the thickness of the support layer of the membrane so that the resulting low-energy dopant peak is pushed into the support layer of the filter and thus not into the substrate is implanted.

18 illustrates a schematic representation of the invention "displacement of the peak". By implanting ions into the energy filter, a rectangular profile can be produced in the substrate with the aid of a trapezium-prism-shaped structure. The initial peak is implanted in the energy filter. The implant profile has the advantageous property that it starts directly on the substrate surface, which is of crucial importance for the application of the energy filter.

Plateau on the spikes: This significantly simplifies the process technology implementation of the filter. It is known to produce triangular structures in silicon, for example by wet-chemical etching using KOH or TMAH. This requires the lithographic coverage of the triangle vertices. If perfect tips are to be produced, this leads to the problem of undercutting the paint or hard mask structure. Without the idea proposed here, this problem can only be solved by perfect (and thus costly) processing. The idea proposed here thus considerably simplifies the production of the filter structures.

This also applies analogously to modern plasma-assisted etching processes, such as RIBE or CAI-BE.

Ad 5. High lateral homogeneity of the generated doping or defect region

The aspect of lateral homogeneity is crucial in static implantation situations. In the case of using a rotating wafer disc (wafer wheel) with, for example, 11 wafers and fixed ion beam, the homogeneity through the Rotation and translational movement of the wafer disc relative to the ion beam determined.

Filter-Substrate Distance: The angular distribution of the transmitted ions is energy-dependent. If the filters and the energy of the ions are so matched to one another that, inter alia, very low-energy ions (nuclear deceleration regime) leave the filter, the width of the angular distribution is large since large-angle scattering events frequently occur. If the filters and the energy of the ions are coordinated so that only high-energy ions (only in the electronic regime, dE / _dxelectron > dE / dx _nuclear ) leave the filter, the angular distribution is very narrow.

Minimum distance: is characterized in that the structure of the filter is not transferred to the substrate, i. e.g. for a given scattering angle distribution of the transmitted ions, they cover at least one lateral distance comparable to the period of the lattice constant of the ion filter.

Maximum distance: For a given scattering angle distribution, the maximum distance is determined by the loss to be tolerated by the application (semiconductor component) due to scattered ions, in particular at the edge of the semiconductor wafer.

The 19 Figure 4 shows the result of an experiment in which ions were implanted through an energy filter during static implantation into a PMMA (polymethylacrylate) substrate. The ions destroy the molecular structure of the PMMA, so that a subsequent development process, the energy distribution of the ions exposed so that areas of high energy deposition are resolved. Areas less or without energy deposition by ions are not dissolved in the developer solution.

The idea proposed here is to produce a high lateral doping homogeneity with correct selection of the filter-substrate distance for both dynamic and static implantation arrangements.

19 shows that ions are implanted through an energy filter during a static implantation into a PMMA substrate. The ions destroy the molecular structure of the PMMA. A subsequent development process exposes the energy distribution of the ions. Areas of high energy deposition are removed. Areas less or without energy deposition by ions are not dissolved in the developer solution.

Ad 6. Monitoring the End of Life for the Energy Filter

Due to the nuclear interaction and the high temperature changes (heating of the filter typically to some 100 ° C), energy filters degrade as a function of the accumulated implanted ion dose.

From a critical ion dose, the filter is changed in its chemical composition, its density and its geometry so that the effects on the target profile to be realized can no longer be neglected. The critical ion dose depends on the filter material used, the implanted ion type, the energy, the geometry and the allowed fluctuation range (= specification) of the target profile.

Therefore, for each given energy, ion type, profile etc. filter implantation process, a specification including a maximum temperature during implantation and a maximum allowable accumulated ion dose may be defined. According to one example, it is envisaged to monitor the use of the energy filter such that it can not be used outside the specification, even without the supervision of an engineer. For this purpose, it is proposed to detect each filter with an electronically readable signature as soon as the filter is inserted into the filter holder on the Implanter and read out this signature, for example by a control computer. The signature is stored for this purpose, for example, in an electronically readable, arranged on the filter memory. A database stores, for example, the signatures of the filter which can be used on a particular implanter and their properties, for example for which process (ion type, energy) the filter is suitable and which accumulated dose and which maximum temperature can be achieved. By matching the read signature with the database, the control computer can thus determine whether the filter is suitable for a planned implantation process.

20 shows a control system to identify the filter and monitor compliance with the filter specification (maximum temperature, maximum accumulated ion dose).

Once the filter has been identified, the built-in sensors (charge integrator and temperature sensor) permanently measure, for example, the accumulated ion dose and the temperature of the filter. The implantation process is terminated when one of the specified parameters is reached or exceeded, for example when the filter becomes too hot or when the maximum permissible dose is exceeded Filter was implanted. That is, if the specification is violated, a signal is sent to the control computer, which terminates the implantation process.

Ad 7. Restriction of the angular distribution of the transmitted ions

For applications which require recessed areas on the target substrate, masking may be applied to the target substrate.

In order to avoid a lateral "softening" of the structures by a filter-induced too broad ion distribution, it is proposed to collimate the ion beam transmitted through the filter. The collimation can be done by striated, tubular, latticed or hexagonal structures with high aspect ratios, which are placed in the transmitted beam after the energy filter. The aspect ratio of these structures defines the allowed maximum angle.

Embodiments are in the 21 - 25 shown.

21 shows a collimator structure which is fixed to the filter holder.

The aspect ratio determines the maximum angle a. Should the available distance to the implantation substrate not be sufficient, then the collimator may also consist of a plurality of co-juxtaposed collimator units with a smaller opening. These may e.g. be arranged honeycomb

Alternatively, the collimator structure can also be arranged directly on the filter element. The preparation of such an element can be monolithic or by microbonding.

22 illustrates a collimator structure which is constructed directly on the filter.

The aspect ratio determines the maximum angle a. Here the filter is placed in back sides to front side configuration in ion beam. The collimator acts in an advantageous embodiment mechanically stabilizing on the filter and improves cooling due to the increased surface of the Fiterchips by radiation.

23 shows a collimator structure, which is constructed directly on the filter. The aspect ratio determines the maximum angle a. Here, the filter is placed in front to backside configuration in the ion beam.

24 illustrates a collimator structure which is constructed directly on the filter. The collimator structure can be lamellar, strip-shaped, tubular or honeycomb-shaped - depending on the layout of the filter and the required maximum angular distribution.

For masked implants, a mask can be applied to the target wafer. A condition for this masking may be that the slowing down of the masking must be at least equal to the mean range of the transmitted ion beam in the target substrate material. In order additionally to provide the required restriction of the angular distribution by the masking, the aspect ratio of the masking can be adjusted accordingly. The aspect ratio is the ratio of height (h in 25 ) to width (b in 25 ) of the collimator structure.

25 represents a collimator structure that is built directly on the target substrate. The collimator structure can be lamellar, strip-shaped, tubular or honeycomb-shaped - depending on the layout of the substrate structure and the required maximum angular distribution.

Ad 8. Low filter wear due to sputtering effects

Implantation arrangement of the filter to the substrate, once spikes to the substrate, once spikes away from the substrate (→ sputtering, scattering on impact)

26 shows a schematic representation of the invention "turning the filter". (a) The filter is used in a regular arrangement, ie the microstructures point away from the beam. (b) The filter can be reversed, ie the microstructures face the beam. This has beneficial effects on sputtering effects in the filter.

Ad 9. Prevention of channeling effects due to the arrangement of the filter to the ion beam

Tilting the filter and / or the substrate

If the filter and / or substrate are made of crystalline material, unwanted channeling effects may occur. That Ions can achieve an increased range along certain crystal directions. The size of the effects and the acceptance angle are temperature and energy dependent. The implantation angle, as well as the crystallographic surface orientation of the starting material used for filter and substrate play a crucial role. In general, the channeling effect can not be reliably reproduced over a wafer, as the above mentioned. Parameters from wafer to wafer and from implantation plant to implantation plant.

Channeling should therefore be avoided. Tilting the filter and substrate can prevent channeling. Channeling in the filter or in the substrate can each have completely different effects on the depth profile of the implanted dopant, in particular if filter and substrate consist of different materials.

27 illustrates a schematic representation of the invention "tilting the filter". If the energy filter is made of anisotropic materials, it can lead to the channeling effect. This can be prevented by tilting the energy filter.

Ad 10. Realization of complex dopant depth profiles with simple filter geometry

As explained above, more complex dopant depth profiles can be realized by adapted geometric design of the filter element. For simplicity in the following explanations scattering effects of all kinds are neglected.

In the case of the same ability to decelerate ions (stopping power (dE / dx)) in the filter and in the substrate material, e.g. the following situations:

28 shows a schematic representation of various doping profiles (doping concentration as a function of depth in the substrate) for differently shaped energy filter microstructures (each shown in side view and top view). (a) Triangular prismatic structures produce a rectangular doping profile, (b) Smaller triangular prismatic structures produce a less depth distributed doping profile. (c) Trapezium prismatic structures produce a rectangular doping profile with a peak at the beginning of the profile. (d) Pyramidal structures produce a triangular doping profile rising into the depth of the substrate.

For example, when using silicon as the substrate material, which is to be doped with boron, for example, the dopant depth profiles in the substrate are changed in the design of the energy filter with different materials, depending on the density and the course of dE / dx as a function of the current kinetic ion energy. A perfectly homogenous, ie constant course of the doping in the depth is only with identical materials for filter and substrate (here in 29 Silicon).

29 illustrates different target profile shapes with the same primary ion and the same primary energy, due to different target materials. Filter material is silicon.

30 shows a curve of the deceleration capacity as a function of energy [4] (SRIM simulation)

It is now proposed, for a given surface geometry, the energy-dependent course of the deceleration power, e.g. by adapting the filter as a multilayer system.

It is proposed to model the course of the deceleration capacity as a function of the ion energy (ie for a given ion species and primary energy as a function of the vertical position in a filter spike) so that in total (ie from the entry of the ion into the filter to the end position in the irradiated Substrate) results in a total loss of kinetic energy dependent on the entry position on the filter (more specifically on the actual path of the ion through the filter and substrate). The energy loss in the filter is thus no longer determined only by the irradiated length of the filter material, but by the location-dependent course of the deceleration.

Thus, with appropriate modeling and, for example, fixed geometry increasing or decreasing in depth doping can be produced. The deceleration capacity thus becomes a function of the lateral position y (FIG. 32 )

Embodiments of the filter proposed here are in the 31 to 33 shown.

31 shows a starting material of a simple multi-layer filter. Filter materials with suitable deceleration capability are sequentially stacked by suitable deposition techniques.

32 shows that, with a suitable design of the layer stack of materials with different deceleration, complex dopant depth profiles can be realized even with simple filter geometry (here: strip-shaped triangles).

In a generalized form of the energy filter, the geometries of the individual filter structures and / or the layer composition of the filter body are different from each other, see 33 , As materials for the individual layers are, for example, but not limited to such materials, silicon, silicon compounds or metals. Silicon compounds are, for example, silicon carbide (SiC), silicon oxide (SiO ₂ ) or silicon nitride (SiN). Suitable metals are, for example, copper, gold, platinum, nickel or aluminum. According to one example, at least one layer of a silicon compound is grown on a silicon layer and on the at least a layer of a silicon compound, a metal layer is evaporated. A metal layer can also be vapor-deposited directly onto a silicon layer. It is also possible to produce different metal layers on top of each other by vapor deposition, to thereby obtain different layers of the filter.

33 shows a generalized structure of an energy filter, from the materials 1 - 6 and with different geometries of the individual filter structures.

Ad 11. Electron suppression

It is known that in the transmission of ions through a solid, electrons of the primary beam remain in the solid or are absorbed by the ion, ie the transmitted ions have a higher or lower average, depending on the properties of the filter material and the primary energy after passing through the filter Charge state [ 26 ], electrons are released or absorbed to the filter.

34 shows equilibrium charge states of an ion (black line: Thomas Fermi estimation, blue line: Monte Carlo simulations, red line: experimental results) as a function of the kinetic energy of the ion when irradiating a thin membrane. Ion: sulfur, membrane: carbon. [ 27 ]

At the same time, ion bombardment on both the front and the back of the filter can generate secondary electrons with high kinetic energy. At high current densities, as required in industrial production, the energy filter will heat up, see 35 , Due to thermionic electron emission (Richardson-Dushman law) thermal electrons are generated depending on the temperature and the work function of the filter material.

35 shows heating of an energy filter by ion bombardment; 6MeV C ions in energy filters that are not transparent for these conditions [ 2 ].

The distance (in high vacuum) of the ion accelerator between filter and substrate is typically only a few centimeters or less. That by diffusion of thermal electrons (from thermionic emission) and by the action of fast electrons (from ion bombardment), the measurement of the ion current at the substrate, for example by a Faraday Cup attached there, is falsified.

As described, from the viewpoint of the filter, there are processes that supply electrons (stripping of the primary ions) and there are processes that emit electrons. Thus, the potential of an electrically isolated mounted filter is not well defined but will vary depending on ion current, vacuum conditions, temperature, etc. during the implantation process. A net negative charge will promote the emission of electrons, a net positive charge will tend to suppress the emission of electrons. Various ways to prevent such charging are explained below.

Energy filter element at defined (positive) potential

It is proposed to design and assemble the energy filter in such a way that the filter is always at a defined potential during ion bombardment, cf. 36 ,

36 Figure 1 illustrates an embodiment of a filter arrangement in which the filter in the filter frame is held at a defined (positive) potential with respect to the filter holder for the purpose of suppressing secondary electrons.

It is further suggested that this potential should be regulated, i. It is proposed, regardless of the charge balance resulting from the implantation process, to set a constant potential with respect to the potential of the substrates to be implanted or the ground potential during the implantation. For this purpose, the regulated supply of positive or negative charge by a power source is proposed.

The potential to be set can in particular be chosen such that, for example, the emission of electrons from the filter is completely suppressed, and thus only the (positive) charge of the transmitted ion current is measured in the Faraday cup next to or on the substrate. Typical values for such a (positive) potential are between a few 10V and a few 1000V.

In the event that the energy filter is very high-impedance due to its material nature, it is proposed to cover the filter with a thin highly conductive layer with a thickness of a few nanometers to a few tens of nanometers on one or both sides. The stopping power of this layer must be included in the design of the filter in the overall balance of Stoppingpower. It is important to ensure that the applied layer (even when applied to the side facing away from the substrate) in principle causes no harmful contamination in the substrate material to be implanted. The layer may consist of carbon, for example, for processing SiC substrates.

Energy filter is coated with material of high work function

In order to reduce strong thermionic emission, it is proposed to use the energy filter with a material of high electron work function, see 37 with sufficient thickness on one or both sides to occupy and thus at a given temperature to cause the lowest possible thermionic emission.

The stopping power of this layer must be included in the design of the filter in the overall balance of Stoppingpower. It is important to ensure that the applied layer (even when applied to the side facing away from the substrate) in principle causes no harmful contamination in the substrate material to be implanted.

37 shows work functions of some elements. [25] Materials Science-Poland, Vol. 24, no. 4, 2006

Ad 12. Alternative manufacturing methods by injection molding, casting or sintering

1. a. Bei einem Beispiel ist vorgesehen, bei Gestaltung des Herstellprozesses als typischer mikrotechnischer Prozess, an Stelle von nasschemischen anisotropen Ätzverfahren, welche einkristallines Material erfordern, auf trockenchemische Ätzprozesse zu setzen und polykristallines oder amorphes Ausgangsmaterial für die Filtermembran zu verwenden. Der resultierende Filter hat strukturell, aufgrund seiner Materialstruktur, hinsichtlich Channeling verbesserte Eigenschaften.
2. b. Bei einem anderen Beispiel ist vorgesehen, den Filter nicht mit einer typischen mikrotechnischen Prozessabfolge herzustellen, sondern Imprint-, Spritzguss- ,Guss- und Sinterverfahren zum Einsatz zu bringen. Kerngedanke ist es die genannten Prozesse derart anzuwenden, dass eine Form bzw. ein Formeinsatz die finale Form der Energiefiltermembran vorgibt. Das gewählte Filtermaterial wird nun in bekannter Weise für das jeweilige Verfahren verarbeitet d.h. in weichem Zustand (Imprint), flüssigem Zustand (Spritzguss- und Guss) bzw. granularem Zustand (Sinterprozesse) durch die vorgegebene Gussform, den Formeinsatz, den Stempel etc. in die geforderte Geometrie gebracht.

Implantation filters can be made by microfabrication techniques, such as lithography techniques in combination with wet chemical or dry chemical etching techniques. In particular, anisotropic wet-chemical etching processes by means of alkaline etching media (eg KOH or TMAH) in silicon can be used for the filter production. In such filters, the functional filter layer is made of monocrystalline silicon. When bombarded with high-energy ions, channeling effects can influence the effective energy loss in the filter layer in a way that is difficult to control. Examples of how such effects can be avoided are explained below.

1. a. In one example, when designing the manufacturing process as a typical microtechnical process, instead of wet-chemical anisotropic etch processes requiring single crystalline material, it is intended to rely on dry chemical etch processes and to use polycrystalline or amorphous feedstock for the filter membrane. The resulting filter structurally has improved properties in terms of channeling due to its material structure.
2. b. In another example, it is intended not to produce the filter with a typical microtechnical process sequence, but to use imprinting, injection molding, casting and sintering methods. The core idea is to apply the processes mentioned in such a way that a mold or a mold insert defines the final shape of the energy filter membrane. The selected filter material is now processed in a known manner for the respective process ie in soft state (imprint), liquid state (injection molding and casting) or granular state (sintering processes) by the given mold, the mold insert, the stamp, etc. in the required geometry brought.

The advantages of using the methods mentioned are that, on the one hand, typically no monocrystalline filter membranes are formed and thus channeling is suppressed. Another advantage is that the available range of filter membrane materials is very large. For example, the use of sintered SiC filter membranes is particularly advantageous for producing homogeneous doping profiles in SiC substrates.

A further advantage is that the use of the aforementioned molding methods can greatly reduce the cost of producing a large number of filter elements compared to microtechnical production.

Ad 13 irradiation of a static substrate

Homogeneous, energy-filtered irradiation of a static substrate can be achieved by wobbling the ion beam in front of the filter, placing the filter between the sweep unit (= ion beam deflection system) and the static substrate and choosing the deflection angle and distance d between the filter and the substrate (usually a few cm to m), see 38 ,

38 illustrates an arrangement of an energy filter implantation, in which the complete irradiation of a static substrate is achieved by means of ion deflection system in front of the filter and suitable distance between the filter and substrate (typically in the range of a few cm to a few m).

Ad 14. Arrangement for utilizing a large filter surface

Arrangement with completely active filter surface

In 39 the arrangement of an energy filter implantation is shown in which the jet area has been increased by suitable measures and the irradiated filter area is larger than the substrate surface. The substrate may be static or mobile. By this arrangement, a utilization of a large filter area (= reduction of degradation effects and thermal effects in the filter) and a complete irradiation of the substrate guaranteed. The use of such an arrangement is particularly advantageous if the required filter structures are "large". When doping high-blocking Si-IGBTs or Si power diodes with protons, penetration depths> 100 μm are required. For this application, filter structures with "serrated heights"of> 100μm are needed. Such filter structures can be produced with sufficient mechanical stability very easily, even for large substrates (eg 6 "or 8").

In the arrangement described here, a minimum distance between substrate and filter must be maintained, which ensures that there is sufficient lateral homogenization of the implanted ions by scattering effects.

39 shows an arrangement of an energy filter implantation, in which the entire surface of the energy filter compared to the substrate, a complete irradiation of the substrate can be achieved and a large filter area is used. The irradiated filter area diameter is larger than the substrate diameter.

Arrangement with not completely active filter surface

Firstly, the same arrangement as in FIG. 14 a) is used: The arrangement of an energy filter implantation in which the beam surface has been enlarged by suitable measures and the irradiated filter surface is larger than the substrate surface. However, here is not the entire filter surface active, but only a certain proportion. This means that the filter consists of an arrangement of a number of, for example, strip-shaped filter elements. These filter elements can e.g. be prepared monolithically from a substrate by suitable manufacturing processes. The other (non-active) part of the filter surface is used to stabilize the filter membrane. This part shadows the ion beam. Therefore, either the substrate or the filter must be moved in this arrangement to compensate for the shading effects. By this arrangement, a utilization of a large filter surface (= reduction of degradation effects and thermal effects in the filter) and a complete irradiation of the substrate is ensured.

40 shows a partially active filter with mechanical scan in one direction.

Ad 15. Modification of the doping profile in the substrate by sacrificial layer

A sacrificial layer is applied to the substrate, the thickness and stopping power of which is selected in a suitable manner, so that the implant profile is displaced in its depth in the substrate in the desired manner. Such a sacrificial layer can be used for masked ion implantation (as in 40 ) or for unmasked ion implantation. In particular, by this method, an undesired beginning of a doping profile can be "pushed out" of the substrate into the sacrificial layer by implanting the beginning of the profile in the sacrificial layer.

41 shows a modification of the doping profile in the substrate by means of sacrificial layer in the case of a masked, energy-filtered implantation. In the example shown here, the beginning of the implantation profile is pushed into the sacrificial layer. This principle can be used analogously for unmasked, energy-filtered ion implantation.

Ad 16. Lateral modification of the doping profile in the substrate by means of a sacrificial layer

A sacrificial layer is deposited on the substrate, the stopping power and thickness of which are selected over the wafer surface in a suitable manner, so that the implant profile is displaced in its depth in the substrate as a function of the lateral position on the wafer in the desired manner. Such a sacrificial layer can be used for masked ion implantation or even for unmasked ion implantation (as in FIG 42 ) be used. In particular, the change in the implantation depth of a homogeneous doping profile can be advantageously used for edge terminations in semiconductor components.

42 illustrates a lateral modification of the doping profile in the substrate by sacrificial layer in the case of an unmasked, energy-filtered ion implantation. The lateral depth modification is due to the laterally different thickness of the sacrificial layer. The principle can be used analogously for masked, energy-filtered implantations.

Ad 17. Adaptation of a profile transition of several implantation profiles

2 or more doping profiles can be skilfully overlapped so that a desired Gesamtdotierprofil arises especially in the region of the overlap. This technique is particularly advantageous in growing and doping multiple layers. A representative example is the growth of several SiC epi layers and respective energy-filtered doping. Here, a good contact between the layers must be guaranteed. In 58 a process flow is indicated, which in particular shows the overlap and the respective setting of the respective underlying doping tail.

Ad 18. Special arrangement of the multifilter concept with coupled pendulum motion

A clever arrangement can be used, so that despite coupled oscillating movement of filter and substrate, that is, no relative vertical movement between filter and substrate, a lateral homogeneity of the distribution of the ions is achieved. Such an arrangement is in 43 shown. The wafers are guided by the rotation of the wafer wheel in the x-direction behind the substrate along. The ion beam (not shown) is, for example, widened in the x direction and is scanned by the vertical oscillating movement of the implantation chamber over the complete multifilter surface. The surface consists of active filter areas and inactive mounting areas. Arrangement A) is an unfavorable arrangement. Considering for y1 and y2 the irradiated filter surface, so be at y1 3 filters irradiated while at y2 no filter is irradiated. As a result, a laterally inhomogeneous fringe pattern is obtained on the wafer. Arrangement B) shows a possible example of a better arrangement. As well as y1 and y2 each 2 filters are irradiated. This is true for all y. As a result, a laterally homogeneous doping over the wafer surface is achieved.

43 shows the vertical movements in y-direction of filter and substrate are coupled. The wafers are guided by the rotation of the wafer wheel in the x-direction behind the substrate along. The ion beam (not shown) is, for example, widened in the x direction and is scanned by the vertical oscillating movement of the implantation chamber over the complete multifilter surface. The surface consists of active filter areas and inactive mounting areas. Arrangement A) is an unfavorable arrangement. Considering for y1 and y2 the irradiated filter surface, so be at y1 3 filters irradiated while at y2 no filter is irradiated. As a result, a laterally inhomogeneous fringe pattern is obtained on the wafer. Arrangement B) shows a possible example of a better arrangement. As well as y1 and y2 each 2 filters are irradiated. This is true for all y. As a result, a laterally homogeneous doping over the wafer surface is achieved.

Ad 19. Monitoring

Another aspect is to solve the problem of monitoring (monitoring) important parameters of the ion implantation modified by an energy filter. Such parameters are, for example, the minimum or maximum projected range, the depth concentration distribution set by the filter geometry and the (energy-dependent) angular distribution. The monitoring of other parameters, such as implanted ion species, etc., could also be useful. A monitoring should be possible in particular on the wafers to be implanted or on (parallel multiple) structures which are arranged in the vicinity of the wafer. According to one aspect, the monitoring should be carried out without further processing of the monitoring structures or the wafers.

The monitoring can be performed by measuring optical parameters such as spectral absorption, spectral transmission, spectral reflectance, refractive index changes, global absorption (wavelength range of meter dependent) and global transmission, as well as reflection (wavelength range of meter dependent).

According to one aspect, it is provided to use arrangements of masks and substrate materials for monitoring said implantation parameters, which ( 1 ) are arranged at a suitable location on the surface to be implanted, eg wafer wheel, and ( 2 ) by ion implantation their eg optical properties "as implanted", ie change without further post-processing so that, for example, the change is proportional to the implanted ion dose for a given ion species. Such under ( 2 ) materials are, for example, PMMA (plexiglass), PMMA, SiC, LiNbO3, KTiOPO4 or the like.

44 shows a wafer wheel with an array of wafers to be irradiated, as well as monitoring structures between the wafers.

In case the optically ion-sensitive material is simultaneously the material of the target substrate, the target substrate (e.g., a SiC wafer) may be used directly for optical monitoring.

In addition to changes in optical properties, it is known that materials such as e.g. PMMA change their solubility to certain acids and solvents after irradiation by ions. Thus, the depth (or etch rate or resulting etch geometry, etc.) of an ion beam modified structure can be considered as a measure of the implanted ion dose.

Monitoring of further changes of physical parameters by ion irradiation is conceivable. Such changes may be, for example, mechanical properties of the monitor material, electrical properties of the monitor material, or else the nuclear physical activation of the monitor material by high-energy ion irradiation.

According to one aspect, the detection is to take place via the change of optical properties. Such an implementation will be described below. For the common case, that the monitoring does not take place on the target substrates to be implanted, the implementation of separate monitoring structures is proposed. A monitoring structure consists of the arrangement of a suitable substrate material with one or more mask structures, see 45 and 46 ,

45 1 illustrates a monitoring mask with an exemplary arrangement of different ion beam transparent or partially transparent mask structures Ma1 to Ma. 46 shows a cross section through the arrangement of a monitoring mask and a suitable monitoring material.

The monitoring structure or structures (monitoring chips) become, as in 44 represented at a suitable location, for example, on the Waferwheel arranged. The readout of the monitoring chips takes place after the implantation, for example without further post-processing. If necessary. the mask for the readout measurement must be separated from the monitoring substrate. In one aspect, the mask is reusable.

Mask material and substrate material of the monitoring chip can be made of different materials. The criteria for selecting the mask material is, for example, compatibility with the material of the target substrates (to exclude contamination by sputtering effects) and a high energy ion deceleration capability such that high aspect ratio mask structures can be made.

It is also possible that mask material and substrate material of the monitoring chip are made of the same material. Mask and substrate can also be made monolithic. In this case, neither a reuse of the mask nor the substrate is usually possible.

1. 1. Durchführung der energiefiltermodifizierten Ionenimplantation
2. 2. Entfernung der Maske, ggfs. nicht unbedingt notwendig, da die Auslesemessung auch reflektierend von der Rückseite des Substrates erfolgen kann.
3. 3. Optische Messung
   1. a. Absorptionsspektrum, wellenlängenaufgelöst
   2. b. Transmissionsspektrum, wellenlängenaufgelöst
   3. c. Reflektivität, wellenlängenaufgelöst
   4. d. einfache globale Absorption, d.h. nicht wellenlängenaufgelöst
   5. e. einfache globale Transmission, d.h. nicht wellenlängenaufgelöst
   6. f. Messung Änderung des Brechungsindexes
   7. g. Änderungen der Polarisation
4. 4. Vergleich mit Eichkurve oder Vergleichsstandard und somit Feststellung, ob der Implantprozess wie erwartet abgelaufen ist.

Execution and evaluation of the masked structure after ion implantation:

1. 1. Performance of the energy filter-modified ion implantation
2. 2. Removal of the mask, if necessary. Not absolutely necessary, since the reading measurement can also be done from the back of the substrate reflective.
3. 3. Optical measurement
   1. a. Absorption spectrum, wavelength resolved
   2. b. Transmission spectrum, wavelength resolved
   3. c. Reflectivity, wavelength resolved
   4. d. simple global absorption, ie not wavelength resolved
   5. e. simple global transmission, ie not wavelength resolved
   6. f. Measurement change in the refractive index
   7. G. Changes in polarization
4. 4. Comparison with calibration curve or comparison standard and thus determination of whether the implant process has expired as expected.

1. A. Tiefenabhängige Dosis, somit Test auf Degradation des Filters und Test auf korrekt maschinenseitig eingestellte Implantdosis
2. B. Maximaler/minimaler Projected Range, somit Test auf Anwendung der korrekten Implantenergie; Test auf Degradation des Filters und korrekt hergestellte Filterstrukturen.
3. C. Winkelverteilung der implantierten Ionen, somit Test auf Degradation des Filters, Test auf korrekte Ausbildung des Filters, Test auf korrekte geometrische Anordnung in der Implantationskammer.

By applying the described monitoring structures, the following implant parameters can be tested:

1. A. Depth-dependent dose, thus test for degradation of the filter and test for correct implant dose set on the machine side
2. B. Maximum / Minimum Projected Range, thus testing for the application of the correct implant energy; Test for degradation of the filter and correctly produced filter structures.
3. C. Angular distribution of the implanted ions, thus test for degradation of the filter, test for correct formation of the filter, test for correct geometric arrangement in the implantation chamber.

Monitoring the depth distribution of the implanted ions

Ad A. Depth-dependent dose

• - Die Veränderung der optischen Eigenschaften ist nur durch die lokal implantierte Ionendosis und die dadurch verursachten Eigendefekte erzeugt.
• - Ionen welche beispielsweise das Tiefengebiet III mit der Ionenkonzentration C1 (49) nur durchqueren (um in den Konzentrationsbereich C2 zu gelangen) führen zu keiner weiteren Veränderung der optischen Eigenschaften.
• - Denkbar wäre, dass genau eine solche Veränderung der optischen Eigenschaften z.B. in PMMA durch elektronisches Abbremsen zu beobachten wäre.
• - Dies ist für die prinzipielle Auswertbarkeit kein Problem, soll aber im Beispiel der 49 und 50 aus Gründen der Vereinfachung ausgeschlossen sein.

In the following 47 . 48 . 49 . 50 By way of example, the monitoring of the depth distribution of the implanted ion dose set by the energy filter is explained. In this example, the following simplifying assumptions apply:

• - The change in the optical properties is only generated by the locally implanted ion dose and the resulting self-defects.
• - ions which, for example, the depth region III with the ion concentration C1 ( 49 ) only traverse (to the concentration range C2 to arrive) lead to no further change in the optical properties.
• - It would be conceivable that exactly such a change in the optical properties, for example in PMMA, would be observed by electronic braking.
• - This is not a problem for the basic evaluability, but in the example of the 49 and 50 be excluded for reasons of simplification.

47 shows an exemplary concentration depth profile generated by an energy filter was produced. 48 illustrates an example of a mask structure for monitoring the depth-dependent dose distribution.

In the 48 Depending on the desired depth resolution, the mask structures described are staggered in their thickness and number, or designed as an "inclined plane" or continuous ramp.

For the largest thickness, the following applies: "thickness of the mask"> Rp, max.

The lateral dimensions of the individual structures can be large, depending on the requirements of the read-out apparatus, from square micrometers over square millimeters to square centimeters.

Ad B. Monitoring the maximum projected range

In 51 a structure is shown, which is suitable to monitor the maximum projected range.

Analogous structures, using evaluation procedures as described under A., are also used to measure or monitor the minimum projected range.

Ad C. Monitoring the angular distribution of the implanted ions

It is known that the ion implantation energy filter produces an energy-dependent spectrum of ion angles after passing through the filter.

In principle it holds true that with vertical monoenergetic ion incidence on the filter after the filter the resulting low-energy ions are scattered more strongly than the high-energy ones.

The resulting angular distribution is thus a function of the filter geometry, the change in the geometry during the life of the filter, the occurrence of channeling effects, the type of ion used, the primary energy, the resulting maximum and minimum energy of the transmitted ions and the geometric arrangement in the implantation chamber. All these parameters can be monitored by monitoring the angular distribution.

For the monitoring of individual parameters, different mask structures, which may be arranged in a monitoring chip, are proposed, see 52 . 53 . 54 . 55 . 56 and 57 ,

It should be noted that for the evaluation of the angular distribution often only the aspect ratio of the mask structure is decisive.

Thus, the aperture sizes of the mask structures for thin masks, which are only slightly thicker than the maximum projected range in the mask material, can be in the micrometer or sub-micron range.

Such monitoring structures are preferably arranged as arrays, which consist of many individual structures in order to be able to carry out a global (ie on an area of several mm ² or cm ² ) optical evaluation.

In contrast, with equal aspect ratios and e.g. Mask thicknesses in the millimeter range, the opening sizes are in the millimeter or centimeter range. In these cases, the evaluation of individual structures that are not arranged in an array without excessive technical effort is possible.

1. 1. Feste Maskendicke, Maskenöffnungen verschiedener Geometrie → Variation des Aspektverhältnisses
2. 2. Variable Maskendicke, feste Geometrie der Maskenöffnung → Variation des Aspektverhältnisses
3. 3. Mischungen aus 1 und 2
4. 4. Durch die Anordnung mehrerer Arrays (oder von Einzelstrukturen) aus jeweils 1, 2 oder 3 in zueinander verschiedenen Winkeln kann die Richtungsabhängigkeit der Winkelverteilung überwacht werden.

Kreisförmige Anordnungen sind auch denkbar.Suggested mask structures:

1. 1. Fixed mask thickness, mask openings of different geometry → Variation of the aspect ratio
2. 2. Variable mask thickness, fixed geometry of the mask opening → Variation of the aspect ratio
3. 3. Mixtures of 1 and 2
4. 4. By arranging a plurality of arrays (or individual structures) of 1, 2 or 3 at different angles, the directional dependence of the angular distribution can be monitored.

Circular arrangements are also conceivable.

52 shows a mask structure. 53 shows a structure array after implant. 54 illustrates a mask structure with variable mask thickness and fixed aperture size. 55 shows a mask structure with fixed mask thickness, a non-perpendicular flank angle and a positive profile and retrograde.

56 shows a mask structure for monitoring asymmetric angular distributions.

As in 57 shown, in addition to the nested circular rings, individual circles and rings of different dimensions particularly advantageous in monitoring the angular distribution of the transmitted through the energy filter ions.

The core of the last-mentioned aspects is to apply the (essentially) dose-dependent modification of the (preferred) optical parameters of a material for the as implanted monitoring of the energy filter implantation process. As a result, the resulting implantation result in its most important parameters can be monitored as completely as possible by means of (for example) optical measurement, without the need for elaborate post-processing (eg annealing and application of metallic contacts).

This results in the possibility of detecting defective implantation quickly and, if necessary, being able to sort out affected wafers.

58 shows an adaptation of a profile transition of two implantation profiles A and B in a clever manner, so that the resulting total concentration profile, for example, can produce a desired homogeneous profile. This can (but does not have to be) especially for layer systems 2 Layers as in the picture shown here may be advantageous. Proposal for a realization with the following process sequence: 1 ) Doping the lower layer (Implant B). 2) growing the upper layer. 3 ) Doping of the upper layer. In the design of the high-energy tail of the implant A remain limited possibilities, however, the low-energy tail of Implant B can be influenced in particular by the introduction of a sacrificial layer, as described in "15: Modification of the doping profile in the substrate by sacrificial layer". Proposal for a realization with the following process sequence: 1 ) Growing sacrificial shift. 2 ) Doping the lower layer (Implant B). 3) removing the sacrificial layer 4 ) Growing the upper layer. 5) doping of the upper layer.

The concepts discussed above enable production-ready implantation methods for the semiconductor industry, i. an economical application of implantation methods in an industrial production process. In addition to the homogenous dopings to be realized by simple triangular filter structures, the illustrated concepts allow, in particular, a very flexible (multifilter concept) realization of complex vertical doping concentration courses with a low angular distribution of the implanted ions. In particular, all types of doping concentration curves can be approximated through the use of triangular filter structures in conjunction with collimator structures. Another important aspect concerns the suppression of artifacts, which distort the ion current measurement on the substrate.

Finally, it should again be noted that the above under Ad 1 , until Ad 19 , explained measures can be used each alone, but also in any combination with each other. For example, the illustrated "end-of-life" detection may be applied to a frame held filter, but may be applied to an otherwise held filter.

Furthermore, the above-explained wafer may be a semiconductor wafer, but may also be made of another material to be implanted, such as PMMA.

references

• [0] Energy filters for ion implantation plants; M.Rüb, Research Report of the Ernst-Abbe-Hochschule Jena 2013/2014
• [2] Constantin Csato, Florian Krippendorf, Shavkat Akhmadaliev, Johannes von Borany, Weiqi Han, Thomas Siefke, Andre Zowalla, Michael Rüb, Energy filter for tailoring depth profiles in semiconductor doping application, Nucl. Instr. Meth. B (2015), http://dx.doi.org/10.1016/j.nimb.2015.07.102
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Claims (16)

A method comprising: Implanting ions into a wafer by irradiating the wafer with an ion beam via an implantation device having a filter frame and a filter held by the filter frame, the filter being adapted to be irradiated by the ion beam; wherein a collimator structure is disposed on the wafer and the ions are implanted into the wafer through the collimator structure. Method according to Claim 1 in which the frame surrounds the filter completely or only partially along edges of the filter. Method according to one of Claims 1 to 2 in which the frame is made of a different material than the filter. Method according to Claim 1 in which the filter frame is inserted into a filter holder on a chamber wall of an implantation chamber. Method according to one of the preceding claims, wherein the filter has at least two differently structured and juxtaposed filter elements. Method according to Claim 5 in which the filter elements in the filter frame are spaced from one another. Method according to Claim 5 in which the filter elements in the filter frame directly adjoin one another. Method according to Claim 5 in which the filter elements have chamfered side surfaces and adjoin one another on the chamfered side surfaces. Method according to one of the preceding claims, in which the filter frame is coated. Method according to one of the preceding claims, in which the filter has, at least in sections, a structure which is trapezoidal in cross-section. A method according to any one of the preceding claims, wherein the collimator structure comprises at least one tube having a length and a width, wherein a width to length ratio is less than 1, less than 2, less than 5 or less than 10. Method according to one of the preceding claims, wherein an electronically readable memory is provided with an information stored in the memory via the filter in the implantation device. Method according to Claim 12 in which the information comprises at least one of the following: a signature; a maximum allowable temperature of the filter; and a maximum allowable transmission dose. Method according to one of the preceding claims, wherein the filter has a layer structure with at least two different material layers, which are arranged one above the other in a transmission direction. Method according to one of the preceding claims, further comprising: arranging a monitoring structure on the wafer and implanting in the monitoring structure. The method of any one of the preceding claims, further comprising: Moving the wafer under the ion beam.

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