Patent Description:
Charged particle beam arrangements are widely used in a plurality of industrial fields, including, but not limited to, inspection of semiconductor devices and electronic circuits during manufacturing, exposure systems for lithography, detecting devices, defect inspection tools, and testing systems for integrated circuits. Semiconductor technologies have created a high demand for structuring and probing specimens in the nanometer or even in the sub-nanometer scale. Process control, inspection and/or structuring is often based on the use of charged particle arrangements providing charged particle beams, e.g. electron beams, which are generated and focused in charged particle beam arrangements, such as electron microscopes or electron beam pattern generators.

High performance inspection devices using charged particle beams such as scanning electron microscopes (SEM) offer superior spatial resolution compared to, e.g. photon beam arrangements because their probing wavelengths are shorter than the wavelengths of light beams. For instance in case of an SEM, the primary electron (PE) beam generates particles like secondary electrons (SE) and/or backscattered electrons (BSE) that can be used to image and analyze a specimen. In particular, a scanning electron microscope, SEM, can be used for high throughput, high resolution imaging process defects on wafers.

Prior art SEM columns may provide high-resolution of specimen structures. Wafer inspection SEM can be used for high throughput, high resolution imaging of process defects on a specimen such as a wafer. Many instruments use either electrostatic or compound electric-magnetic lenses to focus the primary beam onto the specimen. There is a need for inspection devices operating at a spatial resolution in the nanometer and sub-nanometer range at low landing energies.

As the features on a wafer become smaller the requirements of the resolution and throughput increase. For high resolution imaging devices based on electron optics systems, e.g. high resolution versus high probe current, and large image field versus small pixel size, respectively, are contradicting considerations. An electron optical system of a scanning electron microscope, SEM, which can fulfill these contradicting requirements, is beneficial.

In light of the above, a charged particle beam arrangement according to the present invention is defined in claim <NUM>. Furthermore, a method of operating a charged particle beam arrangement according to the present invention is defined in claim <NUM>. Furthermore, an inspection scanning electron device having a charged particle beam arrangement according to the present invention is defined in claim <NUM>.

Further features and details are evident from the dependent claims, the description and the drawings.

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, can be had by reference to embodiments. The accompanying drawings relate to embodiments of the invention and are described in the following:.

It is contemplated that elements of one embodiment can be advantageously utilized in other embodiments without further recitation, as long as they fall under the scope of the appended claims.

Reference will now be made in detail to the various embodiments of the invention, one or more examples of which are illustrated in the figures. Within the following description of the drawings, the same reference numbers refer to same components. Generally, only the differences with respect to individual embodiments are described. Each example is provided by way of explanation of the invention and is not meant as a limitation of the invention. Further, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment, as long as it falls under the scope of the appended claims.

In the following a charged particle beam arrangement according to some embodiments or components thereof will described. Embodiments described herein relate to a charged particle beam arrangement which includes a charged particle source adapted for generating charged particles. Furthermore, and extraction electrode is provided, which is adapted for extracting the charged particles from the charged particle source and for forming a charged particle beam. The charged particle beam is collimated by the condenser lens and then the collimated charged particle beam is focused onto a surface of a specimen, e.g. a wafer, by means of an objective lens. The objective lens includes an inner pole piece and an outer pole piece, wherein the inner pole piece is designed such to have a maximum distance between the inner pole piece and the surface of the specimen. It has been found that the contradicting requirements of beam current and resolution can be beneficially be provided with such an arrangement of the inner pole piece. Further, for example, the objective lens can have the inner pole piece being designed such that an inner diameter of the inner pole piece is equal to or larger than a distance between the inner pole piece and the surface of the specimen. It has been found that the contradicting requirements of scanning field of view and resolution can be beneficially be provided with such an arrangement of the inner pole piece.

In addition to the embodiments described herein relate to a method of operating a charged particle beam arrangement. The method includes generating charged particles in a charged particle source. In an acceleration section of the charged particle beam arrangement the charged particle beam is formed and the charged particles are accelerated. Then the charged particle beam is focused onto a surface of a specimen by means of the objective lens having an inner pole piece and an outer pole piece.

The method includes arranging the objective lens such that the inner diameter of the inner pole piece of the objective lens e.g. <NUM> or below, such as <NUM> or below, particularly <NUM> or below. Further, it may be equal to or larger than a distance between the inner pole piece of the objective lens and the surface of the specimen. In a deceleration section which is located downstream along a beam propagation path and an axis of the charged particle beam the charged particles are decelerated to a predefined landing energy at the surface of the specimen.

Furthermore, embodiments described herein relate to a scanning electron device comprising the charged particle beam arrangement, the scanning electron device being adapted for carrying out wafer review, critical dimensioning, or specimen inspection procedures.

As described herein, some discussions and descriptions relating to the generation of a charged particle beam are exemplarily described with respect to electrons in electron microscopes. However, other types of charged particles, e.g. positive ions, could be provided by the arrangement in a variety of different instruments. According to embodiments described herein, which can be combined with other embodiments, a charged particle beam is referred to as an electron beam.

A "specimen" as referred to herein includes, but is not limited to, semiconductor wafers, semiconductor workpieces, and other workpieces such as memory disks and the like. Generally, when referring to a "surface of the specimen", it is understood that this surface is the wafer surface where the interaction with the focused charged particle beam takes place. As such the specimen includes a surface to be structured or a surface on which layers are deposited. A "specimen holder" as referred to herein includes, but is not limited to, a mechanically fixed or movable arrangement such as a specimen stage.

According to some embodiments, which can be combined with other embodiments described herein, the apparatus and methods can be configured for or can be applied for electron beam inspection, for critical dimensioning processes and defect review monitoring. Generally, when referring to a "beam current", it is understood that the beam of charged particles carries a predetermined charge. The charged particle beam device can be in particular used for high speed scanning and detection, for example for electron beam inspection systems (EBI).

<FIG> shows schematically the principle setup of a charged particle beam arrangement <NUM> according to an embodiment. A charged particle source <NUM> is provided for generating charged particles. A beam path <NUM> of the charged particles is defined by an optical axis <NUM> of a charged particle beam. The charged particle beam is collimated by a condenser lens <NUM> which is located in the vicinity of the charged particle source <NUM>. Downstream along the optical axis <NUM> an objective lens at <NUM> is arranged. The objective lens <NUM> is located in the vicinity of the specimen <NUM>. The specimen <NUM> is held by a specimen holder <NUM>. A surface of the specimen <NUM> facing the objective lens <NUM> is located at a predetermined distance with respect to the objective lens <NUM>. According to embodiments described herein, the objective lens <NUM> includes an inner pole piece <NUM> and an outer pole piece <NUM>, wherein in inner diameter of the inner pole piece <NUM> is equal to or larger than a distance between the inner pole piece <NUM> and the surface <NUM> of the specimen <NUM>.

According to the embodiments, the magnetic objective lens, and also the magnetic condenser lens is an axial gap lens. An axial distance between the inner pole piece of the magnetic objective lens and a surface of a specimen is larger than axial distance between the outer pole piece of the magnetic objective lens and the specimen. For example, the gap between the inner pole piece and the outer pole piece can extend along the optical axis of the objective lens. For example, according to the embodiments of the present disclosure, an axial distance between the inner pole piece of the magnetic objective lens and a surface of a specimen amounts to less than approximately <NUM>.

According to the embodiments of the present invention, the charged particle source <NUM> includes a cold field emitter. According to yet another modification thereof, the cold field emitter can include a tungsten single crystal <NUM> which can have a tip <NUM>, such as a sharp tip, the tip being configured for field emission by tunneling. The advantage of the cold field emission source is that a charged particle beam with high density can be obtained. A virtual source size of such a source is small. In order to be able to benefit from the high beam density the subsequent optical system is carefully designed.

<FIG> illustrates an electron energy profile <NUM> provided by the charged particle beam arrangement <NUM> shown in <FIG>. A reference numeral <NUM> denotes a beam path of the charged particles from the charged particle source <NUM> to the surface <NUM> of the specimen <NUM>. According to the embodiments described herein, the charged particle beam arrangement <NUM> includes at least one acceleration section <NUM> adapted for accelerating the charged particles to a predetermined energy and at least one deceleration section <NUM> adapted for decelerating the charged particles to a predetermined landing energy. If electrons are considered, the acceleration section <NUM> can provide an acceleration of the charged particles to an energy of at least <NUM> keV, particularly at least <NUM> keV, and in particular to an energy of at least <NUM> keV.

According to embodiments of the present disclosure, an extraction electrode <NUM> can be provided. The extraction electrode can have a positive voltage to apply an extraction field for the emission mechanism. The extraction main mechanism of a cold field emitter is a tunneling effect through the surface potential barrier of the tip surface. This can be controlled by the extraction field of the extraction electrode <NUM>. Further, according to some embodiments, the extraction electrode accelerates the electrons. The extraction electrode can provide a portion of the acceleration section <NUM>. An acceleration electrode <NUM> can be provided as a portion of the acceleration section. According to some embodiments, which can be combined with other embodiments described herein, the acceleration section can extend from the emitter the acceleration electrode <NUM>. An acceleration field strength may be about 3kV/mm or slightly above. An acceleration can be e.g. up to <NUM> kV. The electrons can travel on a high energy from the acceleration electrode <NUM> to the electrode <NUM>. The electrode can be provided as a portion of the deceleration section <NUM>. According to some embodiments, which can be combined with other embodiments described herein, the deceleration section can extend from the electrode <NUM> to the specimen or a proxi electrode. A deceleration field strength may be about 3kV/mm or slightly above. The electrons can be decelerated by a potential difference between the electrode <NUM> and a further electrode, such as a proxi electrode, or between the electrode <NUM> and the specimen. For example, a proxi electrode can be provided between the objective lens and the specimen. The deceleration section and the acceleration section may overlap with respective fields of the objective lens and the condenser lens.

According to the embodiments of the present invention, the condenser lens <NUM> is arranged such that a field of the condenser lens <NUM> overlaps, at least partially, the acceleration section <NUM> within the charged particle beam path <NUM>. According to some embodiments, an electrode, e.g. the extraction electrode, can be provided between the charged particle source <NUM> and condenser lens to provide the acceleration section.

The deceleration section <NUM> can provide a deceleration of the charged particles from a high energy to a landing energy which amounts to approximately <NUM> keV or below, and in particular amounts to approximately <NUM> keV or below.

According the embodiments of the present invention, the objective lens <NUM> is arranged such that a field of the objective lens <NUM> overlaps, at least partially, the deceleration section <NUM> within the charged particle beam path <NUM>. According to some embodiments, a further electrode can be provided between the objective lens and a specimen support to provide the deceleration section. The further electrode may act as an electrostatic lens portion of the objective lens.

Between the acceleration section <NUM> and the deceleration section <NUM> the energy of the charged particles along the beam path <NUM> of the charged particles can be approximately constant, i.e. the energy of the charged particles, in this case electrons, can be at a level of approximately <NUM> keV or higher, such as <NUM> keV or higher. In the context of the present disclosure a predetermined landing energy is an energy which is suitable for an interaction of the charged particles with the wafer structures, i.e. the structures on the surface <NUM> or on surface regions of the specimen <NUM>, before landing on the wafer surface <NUM>.

As described herein, some discussions and descriptions relating to the generation of a charged particle beam are exemplarily described with respect to electrons. In this context <FIG> exhibits an electron energy profile <NUM>. In an acceleration section <NUM> the energy of the charged particles is increased from a low level to a high level, wherein at the deceleration section <NUM> the energy of the charged particles is reduced from a high level to a landing energy of the charged particles, e.g. electrons, on the surface <NUM> of the specimen <NUM>. The acceleration and the deceleration of the charged particles takes place along the beam propagation path <NUM> which approximately coincides with an optical axis <NUM>, i.e. the axis of the charged particle beam.

As shown in <FIG>, the charged particle beam arrangement <NUM> includes at least one condenser lens <NUM> and at least one objective lens <NUM>. The combined action of the two lenses provides both the formation of an electron beam by collimating the charged particles originating from the charged particle source <NUM> and the focusing of the electron beam onto a specific location on the surface <NUM> of the specimen <NUM>. The spot of the electron beam at the specific location on the surface <NUM> can have a predefined size. Furthermore, a predefined probe current of the electron beam at the location of the surface <NUM> of the specimen <NUM> can be provided.

According to the embodiments of the present invention, focusing the electron beam onto a specific location on the surface <NUM> of the specimen <NUM> includes providing a combined action of a field of the condenser lens <NUM> and a field of the objective lens <NUM>. In particular, the condenser lens <NUM> and the objective lens <NUM> is arranged with respect to each other such that the charged particle beam is focused onto the surface of the specimen by a combined action of both a field of the condenser lens <NUM> and a field of the objective lens <NUM>.

According to the embodiments of the present invention, the condenser lens <NUM> is provided as a magnetic condenser lens. According to the embodiments of the present invention, the objective lens <NUM> is provided as a magnetic objective lens. A deceleration may act as a further electrostatic lens component to have a combined magnetic-electrostatic objective lens.

According to yet another alternative, the condenser lens <NUM> and the objective lens <NUM> can be arranged approximately symmetrically with respect to each other and the axis <NUM> of the charged particle beam. This symmetrical arrangement of the condenser lens <NUM> and the objective lens <NUM> has the advantage, that the setup of the charged particle beam arrangement <NUM> can be simplified.

For example, embodiments described herein provide a charged particle beam arrangement. The arrangement includes a charged particle source <NUM> including a cold field emitter having a tungsten tip and an extraction electrode assembly or an extraction electrode <NUM> configured to extract a charged particle beam from the charged particle source. A magnetic condenser lens <NUM> is adapted for collimating the charged particle beam. The condenser lens includes a first inner pole piece <NUM> and a first outer pole piece <NUM>, wherein a first axial distance <NUM> between the charged particle source and the first inner pole piece is equal or less than approximately <NUM> and wherein the first axial distance is larger than a second axial distance <NUM> between the charged particle beam source and the first outer pole piece. A magnetic objective lens <NUM> includes a second inner pole piece <NUM> and a second outer pole piece <NUM>. A third axial distance <NUM> between the second inner pole piece and a surface of a specimen is equal to or less than approximately <NUM>, and wherein the third axial distance is larger than a fourth axial distance <NUM> between the second outer pole piece and the surface of the specimen. The combined action of the magnetic condenser lens and the magnetic objective lens focuses the charged particle beam onto the surface of the specimen.

The first axial distance <NUM> and the third axial distance <NUM> can be substantially the same. Further, the second axial distance <NUM> and the fourth axial distance <NUM> can be substantially the same. According to yet further embodiments, which can be combined with other embodiments described herein, the condenser lens includes an inner pole piece and an outer pole piece, wherein the inner pole piece is designed such that an inner diameter of the inner pole piece is equal to or larger than a distance between the inner pole piece and the tip of the emitter.

Furthermore, embodiments described herein relate to a method of operating a charged particle beam arrangement <NUM>. The method provides generating charged particles by means of the charged particle source <NUM>. In the acceleration section <NUM>, the charged particle beam is formed and the charged particles are accelerated to a predetermined charged particle energy of approximately <NUM> keV or higher. The charged particle beam is collimated by means of the condenser lens <NUM>. The condenser lens <NUM> includes an inner pole piece <NUM> and an outer pole piece <NUM>. The charged particle beam propagates along the beam propagation path <NUM>, which can coincide with the optical axis <NUM> of the charged particle beam. At the location of the objective lens <NUM>, the charged particle beam is focused onto the surface <NUM> of the specimen <NUM> by means of the objective lens <NUM>.

The objective lens <NUM> is designed such that it includes an inner pole piece <NUM> having an inner diameter <NUM>, and an outer pole piece <NUM>, wherein the inner diameter <NUM> of the inner pole piece <NUM> is equal to or larger than a distance <NUM> between the inner pole piece <NUM> and the surface <NUM> of the specimen <NUM>. In a deceleration section <NUM> the charged particle is decelerated to a predetermined landing energy at the surface <NUM> of the specimen <NUM>, the landing energy amounting to approximately <NUM> keV or below, and in particular amounting to approximately <NUM> keV or below.

<FIG> shows an inspection scanning electron device according to another embodiment. The inspection scanning electron device includes the charged particle beam arrangement <NUM> having at least one condenser lens <NUM> and at least one objective lens <NUM>. The charged particle beam arrangement <NUM> includes a charged particle source <NUM> adapted for generating charged particles, e.g. electrons. The source of the electrons is of the cold field emission type, the cold field emission type providing field emission of electrons from an emitting surface located in the charged particle source <NUM>. The cold field emission type electron source has the advantage, that it can be operated close to or below room temperature. Herein the main emission mechanism is the tunneling effect through the surface potential barrier controlled by an applied extraction field.

According to an embodiment which can be combined with other embodiments described herein, the charged particle source <NUM> can be provided as a single crystal <NUM>. The material of the single crystal <NUM> is tungsten. Furthermore, the charged particle source <NUM> formed as a tungsten single crystal <NUM> can be provided with a sharp tip <NUM> which is adapted for emitting the charged particles. For example, the tungsten single crystal <NUM> can be etched into the form of the sharp tip <NUM>. For example, the single crystal can have a (<NUM>,<NUM>,<NUM>) orientation.

As shown in <FIG>, an extraction electrode <NUM> is provided between the condenser lens <NUM> and the objective lens <NUM>. The extraction electrode <NUM> is adapted for extracting the charged particles from the charged particle source <NUM> and for forming a charged particle beam. If electrons are considered as representing the charged particles, a positive voltage with respect to the source <NUM> is applied at the extraction electrode <NUM>, i.e. the extraction electrode has a positive electrical potential with respect to the tip <NUM> of the single crystal <NUM> in the charged particle source <NUM>.

According to an embodiment which can be combined with other embodiments described herein, the extraction electrode can include a beam-limiting aperture, the beam-limiting aperture being adapted for passing the charged particles, e.g. electrons, therethrough.

According to further embodiments, which can be combined with other embodiments described herein, and as exemplarily shown in <FIG>, an beam-limiting aperture <NUM> can be provided between the condenser lens <NUM> and the objective lens <NUM>. For example, the beam-limiting aperture <NUM> can be positioned such that the center of the beam-limiting aperture <NUM> approximately coincides with the optical axis <NUM> of the charged particle beam.

The objective lens <NUM> which is designed for focusing the charged particle beam onto the surface <NUM> of the specimen <NUM> includes an inner pole piece <NUM> and an outer pole piece <NUM>. The inner pole piece <NUM> of the objective lens <NUM> has a diameter which is denoted by a reference numeral <NUM> in <FIG>.

According to an embodiment of the lens arrangement the design of the objective lens <NUM> can be such that a ratio of the diameter <NUM> of the inner pole piece <NUM> of the objective lens <NUM> and its distance <NUM> from the surface <NUM> of the specimen <NUM>, i.e. from the wafer plane is larger than or equal to one. In other words, the inner diameter <NUM> of the inner pole piece <NUM> of the objective lens <NUM> can be equal to or larger than a distance <NUM> between the inner pole piece <NUM> and the surface <NUM> of the specimen <NUM>.

According to embodiments, which can be combined with other embodiments described herein, the lens arrangement has design of the condenser lens <NUM> can be such that a ratio of the diameter <NUM> of the inner pole piece <NUM> of the condenser lens <NUM> and its distance <NUM> from the tip <NUM> of the charged particle source <NUM> is larger than or equal to one.

The axial distance <NUM> between the inner pole piece <NUM> of the objective lens <NUM> and the surface <NUM> to of the specimen <NUM> amounts to less than <NUM>, and in particular can amount to less than approximately <NUM>. An advantage of such an arrangement of the objective lens <NUM> with respect to the surface <NUM> of the specimen <NUM> is that the focusing properties of the objective lens <NUM> can be improved. In other words, the axial distance <NUM>, i.e. a wafer-side distance of the inner pole piece <NUM> of the objective lens <NUM> with respect to the surface <NUM> of the specimen <NUM>, i.e. the wafer plane, can determine the quality of the focusing properties of the objective lens <NUM>.

The condenser lens <NUM> includes an inner pole piece <NUM> and an outer pole piece <NUM>. According to yet another modification thereof, an axial distance <NUM> between the charged particle source <NUM>, or the tip <NUM> of the single crystal <NUM> of the charged particle source <NUM>, respectively, and the inner pole piece <NUM> of the condenser lens <NUM> can amount to less than approximately <NUM>, and in particular can amount to less than approximately <NUM>. An advantage of such an arrangement of the condenser lens <NUM> with respect to the emitter tip <NUM> of the charged particle source <NUM> is that the collimation properties of the condenser lens <NUM> can be improved. In other words, the axial distance <NUM>, i.e. a source-side distance of the inner pole piece <NUM> of the condenser lens <NUM> with respect to the tip <NUM> of the charged particle source <NUM> can determine the quality of the collimation properties of the condenser lens <NUM>.

As shown in <FIG>, in the inspection scanning electron device, the charged particle beam arrangement <NUM> is provided with a scanning deflector unit <NUM>. The scanning deflector unit <NUM> is adapted for scanning the charged particle beam propagating along the optical axis <NUM> across the surface <NUM> of the specimen <NUM>. The scanning deflector unit <NUM> can be provided, e.g. as a scanning coil or a pair of deflector plates. Thereby, the charged particle beam can be scanned across the surface <NUM>, e.g. in a raster fashion over a rectangular area of the specimen surface <NUM>.

According to an embodiment which can be combined with other embodiments described herein, the scanning deflector unit can be positioned between the extraction electrode <NUM> and the objective lens <NUM>. According to another modification thereof, the scanning deflector unit <NUM> can be positioned in the vicinity of a field of the objective lens <NUM>. According to an embodiment which can be combined with other embodiments described herein, a size of an achievable scanning field provided by the scanning deflector unit <NUM> is determined by the ratio of the diameter <NUM> of the inner pole piece <NUM> of the objective lens <NUM> and its distance <NUM> from the wafer plane <NUM>. According to another modification thereof, the ratio of the diameter <NUM> and the distance <NUM> indicated in <FIG> is at least one, in particular at least two.

According to embodiments, which can be combined with other embodiments described herein, the apparatus and methods can be configured for or can be applied for electron beam inspection systems, for critical dimensioning applications and defect review applications. In particular, the charged particle beam device according to embodiments described herein can be used as a charged particle beam inspection device which can be designed e.g. for defect review applications, for testing integrated circuits, for critical dimensioning analysis, for high speed scanning, etc. In particular, if electrons are used as the charged particles, the charged particle beam inspection device can be designed as an electron beam inspection (EBI) device.

Claim 1:
A charged particle beam arrangement (<NUM>), comprising:
a charged particle source (<NUM>) including a cold field emitter having a tungsten tip;
an extraction electrode assembly (<NUM>) configured to extract a charged particle beam from the charged particle source;
a beam limiting aperture (<NUM>) between the charged particle source (<NUM>) and a magnetic condenser lens (<NUM>);
the magnetic condenser lens (<NUM>) adapted for collimating the charged particle beam and comprising a first inner pole piece (<NUM>) and a first outer pole piece (<NUM>), wherein a first axial distance (<NUM>) between the charged particle source (<NUM>) and the first inner pole piece (<NUM>) is equal or less than approximately <NUM> and wherein the first axial distance (<NUM>) is larger than a second axial distance (<NUM>) between the charged particle source (<NUM>) and the first outer pole piece (<NUM>);
an acceleration section (<NUM>) for accelerating the charged particle beam to an energy of <NUM> keV or more, a field of the magnetic condenser lens (<NUM>) overlaps, at least partially, with the acceleration section (<NUM>);
a magnetic objective lens (<NUM>) comprising a second inner pole piece (<NUM>) and a second outer pole piece (<NUM>), a third axial distance (<NUM>) between the second inner pole piece (<NUM>) and a surface of a specimen (<NUM>) is equal to or less than approximately <NUM>, and wherein the third axial distance (<NUM>) is larger than a fourth axial distance (<NUM>) between the second outer pole piece (<NUM>) and the surface of the specimen, a combined action of the magnetic condenser lens (<NUM>) and the magnetic objective lens (<NUM>) focuses the charged particle beam onto the surface of the specimen (<NUM>); and
a deceleration section (<NUM>) for decelerating the charged particle beam from the energy of <NUM> keV or more to a landing energy of <NUM> keV or below, a field of the magnetic objective lens (<NUM>) overlaps, at least partially, with the deceleration section (<NUM>).