Patent Description:
Evolution of the semiconductor manufacturing industry is placing greater demands on yield management and, in particular, on metrology and inspection systems. Critical dimensions continue to shrink, yet the industry needs to decrease time for achieving high-yield, high-value production. Minimizing the total time from detecting a yield problem to fixing it determines the return-on-investment for a semiconductor manufacturer.

Fabricating semiconductor devices, such as logic and memory devices, typically includes processing a semiconductor wafer using a large number of fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that involves transferring a pattern from a reticle to a photoresist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing (CMP), etch, deposition, and ion implantation. An arrangement of multiple semiconductor devices fabricated on a single semiconductor wafer may be separated into individual semiconductor devices.

The continued shrinking of design geometries in integrated circuit devices generates a continual need for improved optical inspection and metrology tools. For example, light sources for photolithography systems have historically evolved to smaller and smaller wavelengths, thereby allowing the construction of smaller and smaller structures. For instance, the use of visible wavelength light (e.g., <NUM>) gave way to near ultraviolet light (e.g., <NUM>), which then gave way to deep ultraviolet (DUV) light (e.g., <NUM>). Then, more recently, DUV light sources have given way to extreme ultraviolet (EUV) sources (e.g., <NUM>).

With feature sizes in semiconductor technologies getting increasingly smaller, the wavelength of light has become a limiting factor in optical processes used in semiconductor processes, including lithography and wafer and mask inspection and metrology. Advanced optical technologies use EUV light (for example, wavelengths in the range of <NUM> to <NUM> and more specifically wavelengths of <NUM>) to address issues resulting from increasingly smaller features sizes, and a bright EUV light source free of debris is invaluable in the pursuit of next generation semiconductor processes. One challenging aspect of developing a bright EUV light source is to mitigate debris from the plasma generation process while minimizing the loss of EUV light produced by the plasma.

One disadvantage of inspection tools operating in the EUV regime is that a particle protection device, such as a pellicle, which is commonly used in tools at longer wavelengths, cannot be used in EUV settings because the protection device is opaque at EUV wavelengths. Furthermore, the critical dimensions of the reticles intended to be inspected on a EUV tool may be so small that nearly any particle present on the reticle surface will cause unacceptable problems. By way of example, the contaminant particles may emanate from nearby optics used to direct inspection light to the reticle. In addition, the reticle stage used to move the reticle during inspection also may be a source of contaminant particles.

Furthermore, some of the optics in an EUV or other vacuum environment inspection system will need to be actuated for alignment reasons. This requires precise (e.g., sub-nanometer) accurate movement for one or more degree of freedom. In addition, some optics are large (e.g., several kilograms) and require actuation force to move. These optics are moved in vacuum. The exposed optic surface is sensitive to contamination, both from volatile organic compounds (VOCs) and from particles. The VOCs can be contaminants. The actuators required to move the optics can outgas volatile hydrocarbons. This actuation can generate particles that could land on critical surfaces within the system.

Presently, particle control in light-based reticle inspection systems is carried out with flowing air, which pushes the particles in a known direction. In vacuum systems, such as in electron beam inspect systems, particle control is done with slight amounts of positive pressure and particle reduction methods designed to reduce the number of particles in general. The previous methods have several disadvantages. For example, they have not shown a capability to eliminate particles down to <NUM> in diameter. In addition, previous methods have only been used in processes that allow reticle cleaning after inspection. However, the EUV reticle inspection tool must contend with smaller particles since no cleaning is allowed after inspection.

Differential pumping can be used to separate the vacuum environment containing an outgassing part. A differentially pumped vacuum region requires connection to pumping system. This can be difficult to achieve for a vacuum chamber within a larger assembly. In addition, the vacuum pump can create vibrations that are detrimental to precision aligned optics.

Cleaning processes can reduce the outgassing rate from components. Most actuators contain lubricants or other materials that outgas and can never be fully mitigated. In addition, during movement additional molecular and particle contaminants are generated that cannot be totally removed with cleaning.

Therefore, improved systems and methods of particle mitigation are needed.

<CIT> discloses an actuation mechanism comprising a moving part and a static part, the moving part including a magnet that is driven to move across a working range by magnetic fields generated by the static part; and a shield surrounding the working range of the magnet to reduce propagation of magnetic fields, the shield being formed of a ferromagnetic material and having therein at least one interruption.

A system is provided in a first embodiment. The system includes a vacuum chamber; an optic mount disposed in the vacuum chamber; an optical component disposed on the optic mount in the vacuum chamber; a base; a bellows disposed between the base and the optic mount; an actuator disposed in the actuator compartment; and a filter assembly disposed in fluid communication between the actuator compartment and an interior of the vacuum chamber. The bellows, the base, and the optic mount define an actuator compartment therebetween. The bellows provides a seal between the base and the optic mount. The actuator is configured to move the optic mount relative to the base. The filter assembly includes a first particle filter, a second particle filter, and a purifier medium disposed between the first particle filter and the second particle filter.

The filter assembly can be disposed in the base.

In an instance, the system further includes a gas pathway disposed on the base. The gas pathway is in fluid communication between the actuator compartment and the vacuum chamber. The filter assembly is disposed in the gas pathway.

The bellows can be fabricated of stainless steel or other materials.

At least one of the first particle filter and the second particle filter can be a mesh of metal or a sintered metal. The purifier medium can include at least one of activated carbon, a zeolite, a silica gel, or a polymer. In an instance, the first particle filter and the second particle filter are a mesh of metal and the purifier medium includes activated carbon.

The system can include a plurality of baffles disposed on the optic mount on a side of the bellows opposite the actuator compartment. The baffles extend toward the base.

The filter assembly can capture more than <NUM>% of particles that have a diameter of <NUM> or larger.

The optical component can be configured for use at extreme ultraviolet wavelengths.

An extreme ultraviolet semiconductor inspection tool can include the system of the first embodiment.

A method is provided in a second embodiment. An optical component is provided on an optic mount in a vacuum chamber. An actuator disposed between the optic mount and a base is provided. A bellows is disposed between the base and the optic mount. The bellows, the base, and the optic mount define an actuator compartment therebetween. The bellows provides a seal between the base and the optic mount.

A pressure is reduced in the vacuum chamber and in the actuator compartment with a vacuum pump. Gas evacuated from the actuator compartment passes through a filter assembly between the actuator compartment and the vacuum chamber. The filter assembly includes a first particle filter, a purifier medium, and a second particle filter.

The filter assembly can be disposed in the base or in a gas pathway disposed on the base.

The first particle filter and/or the second particle filter can be a mesh made of metal. The purifier medium can include at least one of activated carbon, a zeolite, a silica gel, or a polymer. In an instance, the first particle filter and the second particle filter are a mesh made of metal and the purifier medium includes activated carbon.

The method can further include moving the optic mount relative to the base using the actuator.

The method can further include directing a beam of extreme ultraviolet light through the vacuum chamber at the optical component.

The pressure can be less than <NUM>-<NUM> Torr.

Although claimed subject matter will be described in terms of certain embodiments, other embodiments, including embodiments that do not provide all of the benefits and features set forth herein, are also within the scope of this disclosure. Various structural, logical, process step, and electronic changes may be made without departing from the scope of the disclosure. Accordingly, the scope of the disclosure is defined only by reference to the appended claims.

Aspects of the present disclosure are directed to mitigating damage due to debris in the optical path of a plasma-produced light source, particularly EUV light generated by laser-produced plasma and discharge-produced plasma used in next generation semiconductor fabrication processes, including wafer and mask inspection, metrology, and lithography. A sealed actuator compartment has a connection to a greater vacuum environment that is permeable to gas but impermeable to particles and VOC. This reduces particle count and eliminates extra pumps that otherwise cause vibration.

To mitigate these issues with in-situ optic actuation, the entire active actuation assembly is positioned in a gas-sealed environment. The walls of the enclosure are a flexible vacuum material, such as a stainless steel bellows. To pump out atmospheric gas from the enclosed region and to prevent large pressure gradients between the regions, the enclosure can allow flow into the outside vacuum through a series of particle and molecular contaminate filters.

<FIG> is a cross-sectional diagram of a system <NUM>. The system <NUM> includes a vacuum chamber <NUM>. In an instance, the vacuum chamber <NUM> is part of an EUV semiconductor inspection tool. The optical component <NUM> is inside the vacuum chamber. Walls of the vacuum chamber <NUM> define an interior <NUM>, which can be pumped to low or vacuum pressures. The vacuum pressure may be as low as <NUM>-<NUM> Torr. Partial pressure for hydrocarbons may be as low as <NUM>-<NUM> Torr.

In an instance, the vacuum chamber <NUM> can operate in ultra-high vacuum (UHV). The total pressure in the vacuum chamber <NUM> can be UHV (e.g., <<NUM>-<NUM> Torr), but the majority of that is water vapor. The partial pressure due to hydrocarbons can be lower (e.g., <<NUM>-<NUM> Torr).

The optical component <NUM> can be held by an optic mount <NUM>. The optic mount <NUM> includes supports <NUM>. The supports <NUM> can hold the optical component <NUM>.

The optical component <NUM> can be, for example, a lens, mirror, aperture, sensor, filter, attenuator, or shutter. The optical component <NUM> can be configured for use at EUV wavelengths. In another instance, the optical component <NUM> is a mask. The mask may not include a pellicle, so even one particle on the mask can mean failure during operation. The optical component <NUM> can be other components that are actuated remotely in vacuum.

EUV light or light at other wavelengths can be directed through the optical component <NUM>. There may be a light source in the vacuum chamber <NUM>.

The optic mount <NUM> is connected to a base <NUM>. A bellows <NUM> is positioned between the base <NUM> and the optic mount <NUM>. The bellows <NUM> provides a seal between the base <NUM> and the optic mount <NUM>. This seal may provide several orders of magnitude of protection with molecules. For example, the seal may provide a protection factor of approximately <NUM><NUM>. Nearly all particles with a size of <NUM> or larger can be contained using the bellows <NUM>.

The base <NUM> may be on feet or other supports (not illustrated) so that at least part of the exterior of the base <NUM> is exposed to the vacuum chamber <NUM>. This can allow gas flow to the actuator compartment <NUM>.

The bellows <NUM>, the base <NUM>, and the optic mount <NUM> define an actuator compartment <NUM> therebetween. <FIG> is a cross-sectional view, so the bellows <NUM> may extend around an entirety of the base <NUM> and optic mount <NUM> to seal the actuator compartment <NUM>. The bellows <NUM> may be connected to the base <NUM> and optic mount <NUM> using welding, brazing, soldering, or other techniques.

In an instance, the bellows <NUM> are fabricated of stainless steel. This includes <NUM>, <NUM>, <NUM>, or <NUM> stainless steel. The bellows <NUM> also can be fabricated of Ivar, Super Invar, aluminum, Hastelloy C-<NUM>, Hastelloy C-<NUM>, Hastelloy X, Monel <NUM>, nickel <NUM>, Inconel <NUM>, or other materials. The bellows <NUM> can be any flexible material that is vacuum compatible and can prevent the majority of contaminant passage.

An actuator <NUM> is positioned in the actuator compartment. The actuator <NUM> is configured to move the optic mount <NUM> relative to the base <NUM>. The actuator <NUM> typically has lubricant for operation, and any movement by the actuator <NUM> can generate particles and VOCs. The particles are typically made of the materials in or around the vacuum chamber <NUM> or the materials in the filter assembly <NUM>. For example, two components in the vacuum chamber <NUM> may rub together and form particles. VOCs can be lubricants, cleaning agents, residues from a machine shop, or the materials in the vacuum chamber <NUM>.

Thus, particles can occur due to shedding of material caused by some disturbance. The particles generally are made of the same material as the actuator (e.g., metals, plastics, and lubricants). These can be shredded material from two materials rubbing together or dislodgement of loosely-adhered material (e.g., deposited particles, lubricants, etc.) caused by movement and vibration. Generally, anything that moves (e.g., actuator <NUM>) can generate particles. In addition, even static items can generate VOCs either as the material degrades or as adhered volatile compounds evaporate through outgassing.

Lubricants generate outgas, but outgassing can come from the material itself as it breaks down. For example, plastics can outgas. Outgassing also can come from molecular contaminates adhered to otherwise clean surfaces like metal. Contaminates generally comes from residual contamination during manufacture.

A size of the particles can depend on which parts move, materials, or surface finishes. Particles may be <NUM> or larger in diameter, such as <NUM> or larger in diameter.

A filter assembly <NUM> is in fluid communication between the actuator compartment <NUM> and an interior <NUM> of the vacuum chamber <NUM>. in an instance, the filter assembly <NUM> in in the bottom <NUM>. The filter assembly <NUM> allows gas flow between the actuator compartment <NUM> and interior <NUM> of the vacuum chamber <NUM>. Thus, pressure in the actuator compartment <NUM> can be reduced using the same pump <NUM> as the interior <NUM> of the vacuum chamber <NUM>. The pressure in the actuator compartment <NUM> can be the same as the interior <NUM> of the vacuum chamber <NUM> after pumpdown.

To remove trapped gas within the actuator compartment <NUM> during system pumpdown, light atmospheric gases (e.g., hydrogen, nitrogen, oxygen, or water) can escape the actuator compartment <NUM> through the filter assembly <NUM>. The filter assembly <NUM> captures particles and VOCs, which prevents particles and VOCs from reaching the optical component <NUM> or other sensitive components in the system <NUM>. In an instance, the filter assembly <NUM> can capture particles and VOCs with a diameter of <NUM> or larger. For example, approximately <NUM>% of particles that have a diameter <NUM> or larger are captured. More than <NUM>%, more than <NUM>%, more than <NUM>%, more than <NUM>%, or more than <NUM>% of particles that have a diameter of <NUM> or larger are captured.

The filter assembly <NUM> is positioned in the base <NUM> instead of in the optic mount <NUM>. Thus, any particles or contaminants not captured by the filter assembly <NUM> are expelled on a side opposite from the optical component <NUM>, which lessens the probability of a particle or contaminant impacting the optical component <NUM>. Of course, the filter assembly <NUM> also can be positioned in the optic mount <NUM> if the particle or contaminant capture levels are acceptable or if smaller particles are less of a concern.

The filter assembly <NUM> includes a first particle filter <NUM>, a second particle filter <NUM>, and a purifier medium <NUM> disposed between the first particle filter <NUM> and the second particle filter <NUM>.

The first particle filter <NUM> can be a particle blocking material, such as a sintered metal (e.g. Mott material) or a fine wire mesh that will capture particles. The sintered material, mesh, or combination thereof can have a porosity or mesh type to filter sizes of particles that are contained in the actuator compartment <NUM> (i.e., away from the optical component <NUM>). The purifier medium <NUM> can be a chemically-active adsorber substance that can adsorb VOCs. An adsorber substance can adsorb VOC or other chemical species on the surface (mostly the internal surface) of a granule, bead, or crystal of adsorbent material. The adsorber substance can be activated carbon, zeolites, silica gels, or polymers. A second particle filter <NUM> is an additional particle filter that can prevent the purifier medium <NUM> from generating particles.

The first particle filter <NUM> and second particle filter <NUM> may have different specifications. Thus, the material or other parameters of the first particle filter <NUM> and second particle filter <NUM> can be different.

In an instance, the first particle filter <NUM> and second particle filter <NUM> may be a mesh made of metal.

For example, the first particle filter <NUM> and/or second particle filter <NUM> can have a stainless steel (e.g., <NUM>) thickness from <NUM> inch to <NUM> inch. This thickness also can apply to <NUM> stainless steel, <NUM> stainless steel, Hastelloy C-<NUM>, Hastelloy C-<NUM>, Hastelloy X, Monel <NUM>, nickel <NUM>, Inconel <NUM>. To capture VOCs, the minimum thickness of the first particle filter <NUM> and/or second particle filter <NUM> may be greater than <NUM> inch. The maximum thickness may be governed by space constraints. , but may be less than <NUM> inch.

The purifier medium <NUM> can include at least one of activated carbon, a zeolite, a silica gel, or a polymer. The purifier medium <NUM> can be tailored to the outgassing species that to be adsorbed. For example, a bed of purifier medium <NUM> with a desired grain or pore size or with a chemically active surface can be selected.

The purifier medium <NUM> can absorb VOCs, such as through physisorption due to high surface area and affinity for hydrocarbons. A thickness of the purifier meditum <NUM> can be related to capture efficiency and total absorption capacity. To capture VOCs, the minimum thickness of the purifier medium <NUM> may be greater than <NUM> inch. The maximum thickness may be governed by space constraints.

The filter assembly <NUM> can filter particles that have a size of <NUM> or greater. A majority of VOCs can be captured by the filter assembly <NUM>.

Activated carbon for the purifier medium <NUM> can be made by the pyrolysis of coal, wood, bark, coconut shells, etc. The substance is activated in a high temperature, controlled oxidation process. Activated carbon tends to have a large surface area.

Zeolites can be used to remove VOCs. For example, naturally-occurring zeolites such as alumino-silicate crystals are hydrophilic, which means these zeolites have an affinity for polar molecules, such as water. Dealtuninizing a natural zeolite can render it hydrophobic, which means the dealuminized zeolites have an affinity for non-polar substances, such as many VOCs. Hydrophobic zeolites can be synthesized in crystals from <NUM> micron to <NUM> millimeter in diameter, and can be bonded into larger granules to lower their resistance to air flow.

Polymer-based adsorbents can be manufactured with pores designed for a particular application. These pores can range from macro-porous through molecular sizes. Polymers are used as granules or beads. Some polymers have been observed to desorb faster than carbon. Like carbon, polymers are not typically considered highly-selective as to which VOC, they will adsorb, although some polymers will adsorb some VOCs better than others.

In an instance, the purifier medium <NUM> is a combination of materials disclosed herein.

In an instance, the first particle filter <NUM> and the second particle filter <NUM> are a mesh of metal and the purifier medium <NUM> includes activated carbon.

A filter assembly <NUM> may last ten years or more between replacements, but more frequent replacements are possible. There may not be a continuous flow of gas through the filter assembly <NUM>, so a long lifetime is possible.

As seen in <FIG>, the actuator <NUM> that generates molecular and particle contaminants is separated from the vacuum environment of the optical surface of the optical component <NUM>. The <NUM> bellows allows the actuator <NUM> to move, but can be connected to the optic mount <NUM> and base <NUM> with gas-impermeable welds. This allows in-situ movement of the optical component <NUM> for alignment under vacuum with lower risk of contaminating the optical component <NUM> or other optics in the system with particles or VOCs. The embodiments disclosed herein can be self-contained and may not use separate vacuum pumping beyond the pump <NUM> for the vacuum chamber <NUM>.

<FIG> is another cross-sectional diagram of part of a system <NUM>. In this embodiment, the actuator <NUM> is a hexapod, combination of linear actuators, or an actuator with rotational capability. The filter assembly <NUM> passes light gases, but blocks particles and adsorbs VOCs. The actuator compartment <NUM> is sized appropriately and the bellows are positioned to enable desired movement by the actuator <NUM>. While illustrated in the base <NUM>, the purifier medium <NUM> can extend to the edges of the base <NUM> if sealed. A final interface from the filter assembly <NUM> to the interior <NUM> of the vacuum chamber <NUM> can be the second particle filter <NUM> to prevent the purifier medium <NUM> itself from generating particles. The purifier medium <NUM> may be a fine powder.

In <FIG>, the filter assembly <NUM> is built into the base <NUM> with the first particle filter <NUM> or second particle filter <NUM> on either end. The gas flow through filter assembly <NUM> is in series through the first particle filter <NUM>, purifier medium <NUM>, and second particle filter <NUM>. When both the vacuum chamber <NUM> and actuator compartment <NUM> are at vacuum pressure there will be little total flow through the filter assembly <NUM>.

<FIG> is another cross-sectional diagram of part of a system. Baffles <NUM> are disposed on the optic mount <NUM> and the base <NUM> on a side of the bellows <NUM> outside the actuator compartment <NUM>. The baffles <NUM> on the optic mount <NUM> extend toward the base <NUM>. The baffles <NUM> on the base <NUM> extend toward the optic mount <NUM>. To mitigate particle generation from the bellows <NUM> during actuation, the baffles <NUM> can be positioned outside the bellows <NUM> to create a labyrinthine path for particles.

Baffles <NUM> also can be positioned on the optic mount <NUM> and/or base <NUM> inside the actuator compartment <NUM>. This can capture particles before they reach the filter assembly <NUM>.

<FIG> is another cross-sectional diagram of part of a system <NUM>. A gas pathway <NUM> is disposed on the base <NUM>. The gas pathway <NUM> is in fluid communication between the actuator compartment <NUM> and a vacuum chamber on the other side of the base <NUM>. The filter assembly <NUM> is disposed in the gas pathway <NUM>.

The gas pathway <NUM> can be a pipe, duct, or conduit. The gas pathway <NUM> is illustrated as terminating under the base <NUM>, but can be connected to a more remote location. For example, the gas pathway <NUM> may terminate at a vacuum pump for the vacuum chamber <NUM>, somewhere outside the vacuum chamber <NUM>, or a separate vacuum pump for the actuator compartment <NUM>.

If the gas pathway <NUM> is used, the base <NUM> may be mounted flat on a surface in the vacuum chamber <NUM>. The gas pathway <NUM> can be formed through the surface that the vacuum chamber <NUM> is mounted on.

<FIG> is a flowchart of a method <NUM>. The method <NUM> can be used in a system, such as the system <NUM>. An optical component is provided on an optic mount in a vacuum chamber at <NUM>. An actuator disposed between the optic mount and a base also is provided at <NUM>. A bellows is disposed between the base and the optic mount. The bellows, the base, and the optic mount define an actuator compartment therebetween. The bellows provides a seal between the base and the optic mount.

Pressure is reduced in the vacuum chamber, which surrounds the optical component and bellows, with a vacuum pump at <NUM>.

Pressure in the actuator compartment is reduced with the vacuum pump at <NUM>. Gas evacuated from the actuator compartment passes through a filter assembly between the actuator compartment and the vacuum chamber. The filter assembly includes a first filter, a purifier medium, and a second filter. The first filter and/or the second filter can be a mesh made of metal. The purifier medium can include at least one of activated carbon, a zeolite, a silica gel, or a polymer. In an instance, the first filter and the second filter are a mesh made of metal, and the purifier medium includes activated carbon. The filter assembly can disposed in the base or in a gas pathway disposed on the base.

The optic mount can be moved relative to the base using the actuator. A beam of EUV light can be directed through the vacuum chamber at the optical component.

While disclosed as reducing particles and contamination on the optical components, the embodiments disclosed herein also can protect the actuator from the environment outside the actuator compartment. When cleaning the area with the optical component, solvents, plasma, O<NUM>, ultraviolet light, and/or H<NUM> may be used. These cleaning techniques can damage the actuator. The bellows and filter assembly can protect the actuator from these cleaning techniques.

While the description provided throughout the present disclosure has focused on particle control around an optical component in an EUV lithography tool, EUV metrology tool, or EUV reticle inspection tool, the embodiments disclosed herein should be interpreted to apply to any critical region of an EUV optical tool or optical tool for other light wavelengths that is sensitive to the presence of particles. Embodiments disclosed herein also can be applied to other vacuum systems that are sensitive to particles, such as electron beam systems.

Claim 1:
A system comprising:
a vacuum chamber (<NUM>);
an optic mount (<NUM>) disposed in the vacuum chamber;
an optical component (<NUM>) disposed on the optic mount in the vacuum chamber;
a base (<NUM>);
a bellows (<NUM>) disposed between the base and the optic mount, wherein the bellows, the base, and the optic mount define an actuator compartment (<NUM>) therebetween, wherein the bellows provides a seal between the base and the optic mount;
an actuator (<NUM>) disposed in the actuator compartment, wherein the actuator is configured to move the optic mount relative to the base; and
a filter assembly (<NUM>) disposed in fluid communication between the actuator compartment and an interior (<NUM>) of the vacuum chamber, wherein the filter assembly includes a first particle filter (<NUM>), a second particle filter (<NUM>), and a purifier medium (<NUM>) disposed between the first particle filter and the second particle filter.