Patent ID: 12207381

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

The advanced lithography process, method, and materials described in the current disclosure can be used in many applications, including fin-type field effect transistors (FinFETs). For example, the fins may be patterned to produce a relatively close spacing between features, for which the above disclosure is well suited. In addition, spacers used in forming fins of FinFETs can be processed according to the above disclosure.

The present disclosure is related to various embodiments of an EUV lithography system with a heated tin vane bucket having a heated cover. The heated tin vane bucket may be part of an EUV light source or radiation source of the EUV lithography system that is used to collect tin debris that remains after tin droplets are struck by a laser to produce a plasma. The tin debris may be in liquid form, but solidify as it comes into contact with cooler parts of a housing or shell of an extreme ultraviolet (EUV) light source.

For example, due to the wettability of tin droplets, the tin droplets may take a concave shape when falling along a drip pin towards the heated tin vane bucket and cover. However, the surface tension of the tin droplet may pull the tin droplets and cause the tin droplets to fall at an angle rather than straight down through an opening of the cover and into the heated tin vane bucket.

When the tin droplets fall at an angle, the tin droplets may land on a surface of the cover around the opening of the cover. The cooler temperature of the surface may cause the tin droplets to solidify. Over time, many tin droplets may fall and form a stalagmite of tin. The stalagmite of tin may continue to grow upwards towards the drip pin. Eventually, the stalagmite of tin may form inside of the drip pin and clog the drip pin. When the drip pin is clogged, the tin may begin to overflow out of the gutter and towards a collector of the EUV light source.

Hydrogen gas can be provided into the EUV light source to reduce contamination in a laser or radiation source. For example, the hydrogen gas can be heated to convert the hydrogen gas into free radicals that can remove contamination from the laser source.

However, when tin droplets overflow from the gutter towards the collector, the hydrogen radicals may enter the tin droplets. The hydrogen radicals may form a bubble inside of the tin droplets from the high temperatures near the collector when the plasma is formed. The bubbles may eventually burst causing tin spitting onto a heat shield located near the collector. The tin near the heat shield may spill over into the collector causing contamination of the collector.

The collector may be a reflective component (e.g., a mirror) that reflects the EUV radiation generated by the tin plasma to be redirected towards a scanner. However, when tin or other debris, contaminates the collector, the EUV radiation may not be reflected correctly causing the EUV light source to malfunction or operate inefficiently.

Thus, the cover of the heated tin vane bucket of the present disclosure may include a heater. The heater may heat the cover to a melting point temperature of the tin. Thus, the stalagmite of tin may be melted such that it falls through the opening of the cover into the heated tin vane bucket. As a result, the heated cover may prevent the drip pin from being clogged from the tin stalagmites that can form from the surface of the cover towards the drip pin. In addition, eliminating the stalagmites may prevent tin spitting on the heat shield, which could potentially contaminate the collector.

FIG.1illustrates a schematic view of a lithography system10, constructed in accordance with some embodiments. The lithography system10may also be generically referred to as a scanner that is operable to perform lithography exposure processes. In the present embodiment, the lithography system10is an extreme ultraviolet (EUV) lithography system designed to expose a resist layer by EUV light (or EUV radiation). The resist layer is a material sensitive to the EUV light. The EUV lithography system10employs a radiation source12to generate EUV light40, such as EUV light having a wavelength ranging between about 1 nm and about 100 nm. In one particular example, the EUV light40has a wavelength centered at about 13.5 nm. Accordingly, the radiation source12is also referred to as EUV radiation source12. The EUV radiation source12may utilize a mechanism of laser-produced plasma (LPP) to generate the EUV radiation, which will be further described later.

The lithography system10also employs an illuminator14. In some embodiments, the illuminator14includes various reflective optics such as a single mirror or a mirror system having multiple mirrors in order to direct the light40from the radiation source12onto a mask stage16, particularly to a mask18secured on the mask stage16.

The lithography system10also includes the mask stage16configured to secure the mask18. In some embodiments, the mask stage16includes an electrostatic chuck (e-chuck) to secure the mask18. In the present disclosure, the terms mask, photomask, and reticle are used interchangeably. In the present embodiment, the lithography system10is a EUV lithography system, and the mask18is a reflective mask. One exemplary structure of the mask18includes a substrate with a low thermal expansion material (LTEM). For example, the LTEM may include TiO2doped SiO2or other suitable materials with low thermal expansion. The mask18includes a reflective multi-layer (ML) deposited on the substrate. The ML includes a plurality of film pairs, such as molybdenum-silicon (Mo/Si) film pairs (e.g., a layer of molybdenum above or below a layer of silicon in each film pair). Alternatively, the ML may include molybdenum-beryllium (Mo/Be) film pairs, or other suitable materials that are configurable to highly reflect the EUV light40. The mask18may further include a capping layer, such as ruthenium (Ru), disposed on the ML for protection. The mask18further includes an absorption layer, such as a tantalum boron nitride (TaBN) layer, deposited over the ML. The absorption layer is patterned to define a layer of an integrated circuit (IC). The mask18may have other structures or configurations in various embodiments.

The lithography system10also includes a projection optics module (or projection optics box (POB))20for imaging the pattern of the mask18onto a semiconductor substrate22secured on a substrate stage (or wafer stage)24of the lithography system10. The POB20includes reflective optics in the present embodiment. The light40directed from the mask18, carrying the image of the pattern defined on the mask18, is collected by the POB20. The illuminator14and the POB20may be collectively referred to as an optical module of the lithography system10.

In the present embodiment, the semiconductor substrate22is a semiconductor wafer, such as a silicon wafer or other type of wafer to be patterned. The semiconductor substrate22is coated with a resist layer sensitive to the EUV light40in the present embodiment. Various components including those described above are integrated together and are operable to perform lithography exposing processes.

In one embodiment, the radiation source12(also referred to hereinafter as an EUV light source) may include a heated tin vane bucket that is used to collect tin debris, as noted above. However, the tin debris may solidify and form stalagmites that continue to grow upwards towards the drip pin creating a clog in the drip pin. This may cause tin to overflow out of the gutter and towards a collector of the EUV light source. The present disclosure provides a heated cover for the heated tin vane bucket of the EUV light source to prevent the tin from solidifying and clogging the drip pin.FIG.2illustrates an example of the EUV light source having a heated tin vane bucket with a heated cover of the present disclosure.

FIG.2illustrates an example of an EUV light source100. The EUV light source100may be device that is operable to perform lithography exposure processes. For example, the EUV light source100may be part of an EUV lithography system to expose a resist layer (that is sensitive to the EUV light) by EUV light. In one embodiment, the EUV light source100may be enclosed in a vessel that is maintained in a vacuum environment (not shown).

In one embodiment, the EUV light source100may generate EUV light via laser produced plasma (LPP). For example, the EUV light source100may include a laser source102. The laser source102may include a single light source or multiple light sources that can generate at least one laser beam122. In one embodiment, the laser source102may be a carbon dioxide (CO2) laser source, or any other type of lasers source that can create two laser beams. For example, the laser source102may also include a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser source. In one embodiment, the laser beam122may be emitted through an aperture132of a collector104.

In one embodiment, the EUV light source100may include a tin droplet generator110. The tin droplet generator110may generate tin droplets126that fall down through the EUV light source100in front of the laser source102. A droplet catcher106may be located on a side of the EUV light source100that is opposite the tin droplet generator110. The droplet catcher106may catch the tin droplets126that are not struck by the laser beam122.

Although theFIG.2illustrates a tin droplet generator110, other types of materials may also be used. For example, the droplets may be a tin containing liquid material such as a eutectic alloy containing tin, lithium, and xenon.

In one embodiment, the tin droplets126may be generated to have a diameter of approximately 30 microns. The tin droplet generator110may generate the tin droplets126at a rate of approximately 50 kilohertz. The tin droplet generator110may drop the tin droplets126at a rate of approximately 70 meters per second.

In one embodiment, the laser beam122may strike the tin droplets126to form a plasma. As noted above, the laser beam122may include two laser beams that are pulsed. A first laser beam (or an adopted pre-pulse laser) may hit the tin droplet126to shape the tin droplet126. For example, the tin droplet126may be flatten to a “pancake” like shape, which may be referred to as a precursor target.

A second laser beam (or a main-pulse laser) may be used to almost instantaneously vaporize and ionize the tin droplet126into a plasma. The second laser beam may be emitted at a higher power than the first laser beam. The second laser beam may be emitted for an appropriate duration and at a certain angle to hit the tin droplets126that are shaped to generate the plasma. The plasma may emit an EUV light in a spectrum having a wavelength of approximately 4-20 nm. In one embodiment, the EUV light emitted by the plasma may be approximately 13.5 nm.

In one embodiment, the activation of the laser beam122and the generation of the tin droplets126by the tin droplet generator110may be synchronized or controlled. The tin droplet generator110may be controlled such that the tin droplets126consistently receive peak powers from the laser source102.

In one embodiment, the collector104may be configured to collect, reflect, and focus the EUV light towards a scanner118. The collector104may have a reflective or mirrored side having an ellipsoidal geometry. For example, the collector104may be fabricated from a reflective material or coated with a reflective or mirrored material. For example, the coating material may be a number of molybdenum and silicon film pairs with a capping layer such as ruthenium.

In some embodiments, the collector104may include a grating structure to scatter the laser beam122. For example, a silicon nitride layer may be coated onto the collector104and patterned to have a grating structure.

In one embodiment, the aperture132may be located at an approximate center of the collector104. In one embodiment, the aperture132may be located off center of the collector104. Regardless of where the aperture132is located, the aperture132may be located such that the laser beam122may be emitted through the aperture132to hit the tin droplets126to generate the plasma.

In one embodiment, the EUV light source100may include a gas distributor120. The gas distributor120may distribute a cleaning gas into the EUV light source100. The gas distributor120may be positioned around a circumference of the collector104. The gas distributor120may include other components that are not shown, such as, a regulator to control the flow of the cleaning gas out of the gas distributor120.

In one embodiment, the cleaning gas may be hydrogen gas. A heater (e.g., a radio frequency energy source that I not shown) may heat the hydrogen gas before exiting the gas distributor120. The hydrogen gas may be heated to a predefined temperature that converts the hydrogen gas into free radicals. In other words, the predefined temperature may be a temperature that can break a bond in the hydrogen gas, or any other cleaning gas, to create free radicals. The free radicals may help remove contamination from the laser source102and/or the laser beam122.

In one embodiment, the EUV light source100may also include a plurality of vanes112. The vanes112are arranged around an optical axis of the collector104(e.g., the optical axis may be represented by a line drawn from the aperture132to the scanner118). The vanes112may be thin and elongated plates that are aligned so that their longitudinal axes are parallel to the optical axis. The vanes112may be fabricated such as stainless steel, coper, aluminum, ceramics, and the like.

The surface of the vanes112may be coated with a catalytic layer including ruthenium, tin, tin oxide, titanium oxide, or any combination thereof. The vanes112may collect any tin debris created from the plasma that is generated and prevent the tin debris from falling directly on the surface of the collector104. For example, the surface of the vanes112may be coated with ruthenium that may reduce SnH4(generated by the tin and hydrogen cleaning gas) to tin and trap the tin thereon.

In one embodiment, the vanes112may also have a temperature control to cycle between a warm and hot cycle. For example, the temperature of the vanes112may be controlled to be from about 100 degrees Celsius (° C.) to 350° C. In one embodiment, the hot cycle may melt the tin debris at a temperature that avoids bubbling of the tin. For example, the hot cycle may be at a temperature between approximately 232° C. to 350° C.

The warm cycle may be a temperature that maintains the tin debris in liquid form and allows the melted tin debris to slide and roll smoothly along the vanes112towards a gutter114. In one embodiment, the warm cycle may be at a temperature between approximately 100° C. to 232° C.

In one embodiment, the tin debris may fall as liquid and flow into the gutter114and through a drip pin116towards a bucket108. In one embodiment, although the EUV light source100is illustrated as being horizontal, the EUV light source100may be angled or tilted to allow the tin debris to slide down the vanes112into the gutter114via gravity.

In addition, it should be noted that the EUV light source100has been simplified for ease of explanation. The EUV light source100of the present disclosure may include additional components that are not illustrated. For example, the EUV light source100may include a radio frequency (RF) generator to heat the cleaning gas, an exhaust module to collect any additional waste gas or debris, a controller to control operation of the various components and the like.

FIG.3illustrates a more detailed cross-sectional view of a portion130of the EUV light source100. In one embodiment, the bucket108may include a volume or heated tin vane bucket202and a cover204. The cover204may include at least one opening208.

As described above, tin debris218may slide or roll down the vanes112that are located inside of a shell or vessel wall220of the EUV light source100. The tin debris218may roll down as a liquid or liquid droplets into the gutter114. The gutter114may then guide the tin debris218towards the drip pin116.

In one embodiment, the tin debris218may fall directly through the opening208of the cover into the heated tin vane bucket202as shown by an arrow212. However, as the tin debris218reaches the end of the drip pin116, the tin debris218may form a droplet. Due to the tin wettability of the pin, the tin debris218may take a concave shape. The surface tension pulls on the tin droplet causing the droplets of tin debris218to fall at an angle216relative to the line212, as shown by a line214.

However, when the tin debris218contacts a cooler surface (e.g., a surface of a heat shield206, or a surface210around the opening208of the cover204, the tin debris218that drops as a liquid may solidify. Over time, the solid tin debris may form a stalagmite and clog the drip pin116causing the tin debris218to overflow out of the gutter114towards the collector104. As noted above, the overflowing tin debris218may react with the hydrogen radicals and cause tin spitting on the heat shield, which is located adjacent to the collector104. The tin spitting may then contaminate the collector104.

In one embodiment, the cover204may include a heater224. The heater224may heat the cover to melt any tin debris218that has solidified. In one embodiment, a sensor222may be located in or near the drip pin116. The sensor222may detect the presence of tin debris218that has solidified or the formation of a tin stalagmite. In one example, the sensor222may be a resistive sensor, a contact sensor, and the like.

In one embodiment, a controller226may be in communication with the sensor222and the heater224. In one embodiment, the sensor222may send an indication or a signal to the controller226when solid tin debris is detected. In response, the controller226may activate the heater224to heat the cover204and melt the solid tin debris. In one embodiment, the controller226may activate the heater224when a plasma generation process is deactivated or inactive (e.g., between EUV light generation).

In one embodiment, the controller226may receive an indication based on a manual observation. For example, a technician may observe tin spitting on the heat shield and provide an input on a user interface (not shown) of the EUV light source100. In response, the controller226may activate the heater224to heat the cover204and melt the solid tin debris.

FIG.4illustrates a top view of the cover204. The cover204may include at least one opening208. In some embodiments, the cover204may include two openings208.FIG.3illustrates how the tin debris218has solidified into solid tin debris302on the surface210around the opening208of the cover204. The solid tin debris302begins to block the opening208(e.g., the actual size of the opening208is illustrated in dashed lines below the solid tin debris302). The heater224may heat the cover204to melt the solid tin debris302and allow the tin debris to fall through the opening208and into the heated tin vane bucket204.

FIG.5illustrates a side view of the cover204. In one embodiment, the heater224may be deployed as a heating coil402. The heating coil402may be an inductive heat source that is coupled to a side of the cover204. In one embodiment, the heating coil402may cover at least 50% of the surface area of a side of the cover204. The heating coil402may generate enough heat to heat the cover204to a temperature that is above the melting point of the solid tin debris302. It should be noted that the heating coil402is one example of the heater224. The heater224may also be deployed as a radiant heat source, heat generated from an external heat source and directed towards the surface of the cover204, and the like.

FIGS.6A-6Dillustrate a plurality of partial cross-sectional views illustrating one embodiment of the heated cover of the heated tin vane bucket in operation in accordance with at least one embodiment of the present disclosure. Referring toFIG.6A, tin debris218that is generated during plasma generation may be collected by the plurality of vanes112. For example, after tin droplets are struck by a laser beam the tin may be ionized into plasma and emit a EUV light that is collected and redirected towards a scanner.

In one embodiment, tin debris218from the ionization of the tin droplets may be collected by the vanes112. The vanes112may be heated to allow the tin debris218to roll or slide down the vanes112towards the gutter114. As noted above, when the tin debris218reaches an end of the dip pin116, the tin debris218may form a droplet that has a concave shape. The surface tension of the droplet and the concave shape may cause the droplets to fall at an angle away from an opening208of the cover204. When the droplets contact a cool surface (e.g., the heat shield206or a surface210around the opening208of the cover204), the droplets may solidify.

InFIG.6B, over time the droplets of tin debris218may solidify to form a stalagmite230of tin. The stalagmite230may grow and eventually plug or clog the opening of the drip pin116.

InFIG.6C, subsequent tin debris218that slides off of the vanes112may be unable to fall through the drip pin116. As a result, the tin debris218may begin to over flow out of the gutter114towards the heat shield206, which may extend inwards (e.g., away from the vessel wall220) towards the out circumference of a collector (shown inFIG.1).

As noted above, cleaning gas such as hydrogen may be fed into the EUV light source. The hydrogen gas may be heated (e.g., via an RF energy source) to generate hydrogen radicals. The hydrogen radicals may enter the droplets of tin debris218that overflow out of the gutter114. The hydrogen radicals may form a bubble inside of the droplets of tin debris218. As the pressure builds the bubble may burst causing tin spitting on portions of the heat shield206that are near the collector. Tin that collects on the heat shield206near the collector may then fall onto the collector and cause contamination of the collector. When the collector is contaminated, the EUV light emitted by the ionized tin droplets may not be properly collected and reflected.

InFIG.6D, a heater224may be activated in response to the detection of the drip pin116being clogged by the stalagmite230. In one embodiment, a sensor may be located in, on, or near the drip pin116to detect the solid tin formed in the stalagmite230. The sensor may then send an indication to a controller. In response, the controller may activate the heater224. The heater224may heat the cover204to a temperature at or above a melting temperature of the tin.

In one embodiment, the heater224may be activated by a technician based on a manual observation. For example, the technician may see the tin spitting on the heat shield206near the collector, which may be an indication that the drip pin116is clogged by the stalagmite230. In response, the technician may provide an indication to a controller via user interface or activate the heater224via the user interface.

When the cover204is heated to a temperate at or above the melting point of tin, the stalagmite230of tin may be melted. The liquid tin debris218may fall through the opening208of the cover204and into the heated tin vane bucket202.

In one embodiment, the heater224may be activated when the plasma generation process is deactivated. For example, the heater224may be activated between processing of wafers via the EUV light source. Said another way, the heater224may be activated when the laser source and the tin droplet generator are inactive.

FIG.7illustrates a flowchart of a method700of heating a cover of a heated tin vane bucket according to at least one embodiment of the present disclosure. The method700may be performed via the controller226or another controller of the EUV light source100.

While the method700is illustrated and described below as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apparat from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases.

The method700begins at block702. At block704, the method700activates an EUV light source to pattern a resist layer on a substrate. For example, the EUV light source may be part of a lithography system illustrated inFIG.1, and discussed above.

At block706, the method700receives an indication that solid tin is detected on a surface around an opening of a cover of a heated tin vane bucket. For example, a sensor in, on, or near a drip pin may detect solid tin that may be clogging the opening of the drip pin. In response, the sensor may send an indication or an electronic signal to a controller.

In one embodiment, the indication may be a signal from a user interface provided by a technician. For example, the technician may manual observe tin spitting on a heat shield near a collector of the EUV light source. The tin spitting may indicate that the drip pin is clogged by a solid stalagmite of tin.

At block708, the method700deactivates a plasma generation process. In one embodiment, the method700may wait until a current plasma generation process is completed and temporarily deactivate the plasma generation process. In another embodiment, the method700may immediately pause the plasma generation process to prevent any further miss-processing of a wafer that may be caused by potential contamination of the collector.

At block710the method700activates a heater coupled to the cover to heat the cover to a melting temperature of the solid tin. In one embodiment, the heater may be a heating coil coupled to a surface of the cover. The heating coil may generate inductive heat that heats the cover to a temperature above a melting point of tin. The cover may be heated to melt the solid stalagmite of tin. The tin may melt and then flow through the opening of the cover and into the heated tin vane bucket.

In one embodiment, any type of heater or energy source may be applied to heat the cover. For example, a radiant heater, an RF energy source, an external heater that directs heat onto the surface of the cover, or any combination thereof may be used.

At block712, the method700reactivates the plasma generation process. After the thermal cycle of the heater on the cover is executed, the plasma generation process may be reactivated. In one embodiment, where a sensor is deployed in, on, or near the drip pin, the controller may wait until a second indication is received from the sensor. The second indication may indicate that the solid stalagmite of tin is no longer detected in the drip pin. In response, the controller may deactivate the heater and reactivate the plasma generation process. In one embodiment, the blocks706-712may be continuously repeated during operation of the EUV light source. At block714, the method700ends.

Therefore, the present disclosure relates to an EUV light source that includes a heated tin vane bucket with a heated cover. The heated cover may include an opening where liquid tin that solidifies into solid tin may form on a surface around the opening. The heated cover may include a heater that heats the cover to melt the solid tin.

In other embodiments, the present disclosure relates to an EUV light source that is part of a lithography system. The EUV light source may include a tin droplet generator to generate a plurality of liquid tin droplets. A laser source may direct a laser through an aperture of a collector to contact one of the plurality of liquid tin droplets to generate a plasma. The plasma may radiate at EUV wavelengths that are reflected by the collector towards a scanner. The EUV light source may include a plurality of tin vanes that redirect tin debris formed from the plasma that is generated. A heated tin vane bucket may collect the tin debris. The heated tin vane bucket may include a heater and a cover that includes an opening to allow the tin debris to fall into the heated tin vane bucket. The heater may heat the cover to melt any solid tin that may form on a surface around the opening of the cover.

In yet other embodiments, the present disclosure relates to a method for patterning a resist layer on a substrate using an EUV light source. The method includes activating the EUV light source to pattern the resist layer on the substrate. During operation of the EUV light source, solid tin is detected on a surface around an opening of a cover of a heated tin vane bucket of the EUV light source. The solid tin may be detected based on stalagmites that grow from the surface up into a drip pin that contains a sensor. The solid tin may also be detected based on visual observation of a collector that shows tin spitting has occurred. A plasma generation process may be deactivated and a heater coupled to the cover may be activated to heat the cover and melt the solid tin that is detected. The plasma generation process may be reactivated after the solid tin is melted.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.