Patent Application
20210185793
Embodiments of the present disclosure generally relate to methods and apparatus for an adhesive layer removal process from a photomask. Particularly, embodiments of the present disclosure provide methods and apparatus for an adhesive layer removal process after a pellicle removal process on a photomask using a dielectric barrier discharge plasma process.
In the manufacture of integrated circuits (IC), or chips, patterns representing different layers of the chip are created by a chip designer. A series of reusable masks, or photomasks, are created from these patterns in order to transfer the design of each chip layer onto a semiconductor substrate during the manufacturing process. Mask pattern generation systems use precision lasers or electron beams to image the design of each layer of the chip onto a respective mask. The masks are then used much like photographic negatives to transfer the circuit patterns for each layer onto a semiconductor substrate. These layers are built up using a sequence of processes and translate into the tiny transistors and electrical circuits that comprise each completed chip. Thus, any defects in the mask may be transferred to the chip, potentially adversely affecting performance. Defects that are severe enough may render the mask completely useless. Typically, a set of 15 to 30 masks is used to construct a chip and can be used repeatedly.
The increasing circuit densities have placed additional demands on processes used to fabricate semiconductor devices. For example, as circuit densities increase, the widths of vias, contacts and other features, as well as the dielectric materials between them, decrease to sub-micron dimensions, whereas the thickness of the dielectric layers remains substantially constant, with the result that the aspect ratios for the features, i.e., their height divided by width, increases. Reliable formation of high aspect ratio features is important to the success of sub-micron technology and to the continued effort to increase circuit density and quality of individual substrates.
Photolithography is a technique used to form precise patterns and structures on the substrate surface and then the patterned substrate surface is etched to form the desired device or features. The photolithographic technique utilizes a photolithographic substrate, such as a reticle, which has corresponding configures of features desired to be transferred to a target substrate, such as a semiconductor wafer. A light source emitting ultraviolet (UV) light or deep ultraviolet (DUV) light is transmitted through the photomask substrate to expose photoresist disposed on the substrate. Generally, the exposed resist material is removed by a chemical process to expose the underlying substrate material. The exposed underlying substrate material is then etched to form the features in the substrate surface while the retained resist material remains as a protective coating for the unexposed underlying substrate material.
Typically, one photomask, e.g., a reticle, may be repeatedly used to reproducibly print thousands of substrates. Typically, a photomask, e.g., a reticle, is typically a glass or a quartz substrate giving a film stack having multiple layers, including a light-absorbing layer and an opaque layer disposed thereon. While performing the photolithography process, a pellicle is used to protect the reticle from particle contamination. Pellicle is a thin transparent membrane which allows lights and radiation to pass therethrough to the reticle. Pellicles provide a functional and economic solution to particulate contamination by mechanically separating particles from the mask surface. After the photomask has been used for a number of cycles and the pellicle has become damaged or too dirty to use, the photomask is removed and the pellicle replaced.
Pellicles are typically supported and held on the reticle by an adhesive material, such as glue. However, when replacing the pellicle and the attachment feature from the photomask, residual adhesive material is often difficult to be removed from the reticle. Aggressive mechanical cleaning often results in reticle damage, surface roughness, or film stack and/or structure damage of the photomask.
Therefore, there is a need for apparatus and methods for removing or cleaning adhesive material from the attachment feature on the reticle after periodic use.
Embodiments of the present disclosure generally provide apparatus and methods for removing an attachment feature, particularly for adhesive materials in the attachment feature, from a photomask. In one embodiment, an apparatus for processing a photomask includes an enclosure, a substrate support assembly disposed in the enclosure, and a dielectric barrier discharge (DBD) plasma generator disposed above the substrate support assembly, wherein the dielectric barrier discharge plasma generator further comprises a first electrode, a second electrode, wherein the first and the second electrodes are vertically aligned and in parallel, a dielectric barrier positioned between the first electrode and the second electrode, and a discharge space defined between the dielectric barrier and the second electrode.
In another embodiment, a method for processing a photomask includes removing an adhesive material from a photomask by a plasma generated from a dielectric barrier discharge plasma generator.
In yet another embodiment, a method for processing a photomask includes applying a power in a dielectric barrier discharge plasma generator disposed in an enclosure, directing a discharge gas in a discharge space defined in the dielectric barrier plasma generator to a surface of a photomask disposed in a substrate support assembly in the enclosure, generating a plasma in the discharge space toward the surface of the photomask, and removing an adhesive material on the photomask.
So that the manner in which the above recited features of embodiments of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.
Embodiments of the present disclosure generally provide apparatus and methods for removing an adhesive material in an attachment feature utilized to hold a pellicle from a photomask. The attachment feature is utilized to hold and/or support a pellicle to the photomask. The attachment feature includes an adhesive material attached between the pellicle and the photomask. An adhesive material removal apparatus is utilized to remove the adhesive material from the photomask. In one example, an adhesive material removal apparatus includes a dielectric barrier discharge (DBD) plasma generator that may generate plasma to react with the adhesive material, thus enabling removal of the adhesive material from the photomask. In one example, the dielectric barrier discharge (DBD) plasma may be performed in suitable pressure range, including under an atmospheric pressure (AP).
Furthermore, after a number of process has been performed and the pellicle 214 and the attachment fixture 216 is removed from the photomask 202, some residual adhesive compounds may remain on the periphery region 217 of the photomask 202 where the attachment fixture 216 was supported, which often requires additional cleaning or adhesive removal process to remove the adhesive materials or compounds from the photomask 202.
The film stack 204 includes features 207 formed therein. The film stack 204 is formed in a center region 205 and a periphery region 217. It is noted that the features 207 and the film stack 204 depicted in
In the periphery region 217 of the photomask 202, the attachment fixture 216 is formed thereon to support the pellicle 214, as shown in
Prior to the adhesive material removal process depicted in
The adhesive material removal process 400 starts at operation 402 by providing the photomask 202 in an adhesive material removal apparatus, such as the adhesive material removal apparatus 550 depicted in
At operation 404, a power is applied to the dielectric barrier discharge (DBD) plasma generator 503 disposed in the adhesive material removal apparatus 550 to generate a plasma. In one embodiment, the dielectric barrier discharge (DBD) plasma generator 503 includes a pair of electrodes 504, such as a first electrode 504a and a second electrode 504b disposed in parallel and vertically aligned and a dielectric barrier 506 disposed against the first electrode 504a. The first electrode 504a may be grounded. The electrodes 504 are attached to but insulated from the enclosure 551 (insulation not shown in the Figures). The dielectric barrier 506 is disposed between the first electrode 504a and the second electrode 504b defining an opening 508 (e.g., a discharge space) between the first and the second electrodes 504a, 504b. The dielectric barrier 506 also maintains the first electrode 504a and the second electrode 504b in a spaced-apart relation. Though the example depicted in
In one example, the first and the second electrodes 504a, 504b are an electrical conductive material that may generate electronic field when applying a power thereto. Suitable materials of the first and the second electrodes 504a, 504b include, but not limited to, aluminum, stainless steel, tungsten, copper, molybdenum, nickel, and other metal material.
Furthermore, in one embodiment, the first electrode 504a may be a conductive material as described above and coated with a dielectric layer to form the dielectric barrier 506. Suitable materials of the dielectric layer include, but not limited to MgO, SiO2, Y2O3, La2O3, CeO2, SrO, CaO, MgF2, LiF2, and CaF2, among others. The conductive material could be indium tin oxide (ITO), SnO2, W, Mo, Cu, aluminum, alloys thereof, or another metal.
The dielectric barrier 506 acts as a current limiter during plasma generation process so as to assist generating plasma in a discharge gas supplied into the opening 508. In one embodiment, the dielectric barrier 506 is a transparent dielectric material such as glass, quartz, ceramics, polymer materials or other suitable materials.
The opening 508 defined between the first and the second electrodes 504a, 504b is a discharge space that allows the discharge gas to be supplied thereto. A gas outlet 510 is coupled to a gas source 530 configured to supply the discharge gas into the opening 508. The gas outlet 510 is disposed at a predetermined angle so as to inject the discharge gas predominately in the opening 508 defined between the first and the second electrodes 504a, 504b. As a result, the center region 205 where the phase shift mask layer 203 is disposed on the photomask 202 would not be affected, reacted, or damaged by the discharge gas supplied into the adhesive material removal apparatus 550 during the adhesive material removal process. The gas outlet 510 is configured to continuously supply gas into the opening 508 so as to allow the plasma generated in the opening 508 to align with a location where the adhesive material 210 is formed on the photomask 202. Similarly, the configuration of the electrodes 504 is also selected so as to confine the first and the second electrodes 504a, 504b in a manner that allows the plasma as generated to be flown in a direction toward the adhesive material 210 on the photomask, rather than the center region 205 of the film stack 204 on the photomask 202, so as to dominantly react with the adhesive material 210 on the photomask without damaging other areas of the photomask 202, including the absorber layer 208 disposed underneath the adhesive material 210.
In one example, the opening 508 (e.g., the discharge space) has a selected discharging distance 560 (e.g., a width) creating a discharge volume to allow sufficient collisions among the electrons and the discharge gas executed in the opening 508. The discharge volume is configured to sufficiently promote the collisions of the electrons and the discharge gas so that excited species, including excimers, may be created, therefore, generating the plasma as desired. In one embodiment, the discharging distance 560 of the opening 508 (e.g., the discharge space) is selected within an adequate range to promote the collisions in the opening 508. In another embodiment, the discharging distance 560 of the opening 508 is selected between about 5 mm and about 50 mm, such as between about 10 mm and about 20 mm, for example, between about 2 mm and about 30 mm.
The collision of electrons with the discharge gas provides energy to the discharge gas creating reactive species including discharge plasma species and excimers. Such discharge plasma species and excimers reach to the adhesive material 210 disposed on the photomask 202, activating the adhesive material 210 so as to soften and react with the adhesive material 210, which may be removed from the photomask 202 in volatile state, or by further mechanical cleaning/scrubbing after the adhesive material removal process.
In one embodiment, the discharge gas may be oxygen gas (O2), a hydrogen gas (H2), or a nitrogen gas (N2). In another embodiment, the discharge gas may be a gas mixture selected from a group including noble gases, such as xenon gas (Xe), krypton gas (Kr), argon gas (Ar), neon gas (Ne), helium gas (He) and the like. In yet another embodiment, the discharge gas may be a gas mixture including at least one of oxygen gas (O2), a hydrogen gas (H2), a nitrogen gas (N2), a noble gas, a halogen containing gas, such as fluorine, bromine and chlorine gas, H2O, NH3, the combinations thereof, or the like.
A circuit arrangement 534 applies an operating voltage from a power supply 532 to the first electrode 504a and the second electrode 504b. In operation, the voltage applied to the two electrodes 504a, 504b establishes an electric field that promotes the electrons being collided in the opening 508. The electron collision generates energy to the discharge gas in the opening 508, thus energizing the discharge gas into an excited state, forming a plasma, which often includes reactive species, discharge species, or excimers. The plasma promotes reaction between the reactive species from the plasma selective to the adhesive material 210 and relatively inert to the underlying absorber layer 208, thus efficiently removing the adhesive material 210 from on the surface of the photomask 202 without damaging the underlying absorber layer 208. In one example, the voltage applied by the circuit arrangement 534 from the power supply 532 is selected so that an electric field may be established that is sufficient to generate a plasma as described above. In one embodiment, the voltage may be applied between about 100 Volts or about 20,000 Volts.
An atmosphere control system 564 is coupled to the enclosure 551. The atmosphere control system 564 includes throttle valves and pumps for controlling chamber pressure. The atmosphere control system 564 may additionally include gas sources for providing process or other gases to the interior volume of the adhesive material removal apparatus 550. In one embodiment, the atmosphere control system 564 may assist controlling the pressure at a desired range during the adhesive material removal process. In one example, the pressure during the adhesive material removal process may be controlled at atmospheric pressure, such as at ambient pressure wherein the photolithographic system 100 is located.
During the operation 404, a frequency of power supply between about 100 KHz and about 3 GHz may be applied to the dielectric barrier discharge (DBD) plasma generator 503 to generate a plasma in the opening 508 toward the adhesive material 210 for reaction.
At operation 406, after the plasma is generated and flown toward the adhesive material 210, the adhesive material 210 may be chemically reacted with the plasma, forming residuals in volatile state, pumping out of the adhesive material removal apparatus 550. Furthermore, in some embodiments, a fluid wash process (e.g., suitable liquid precursors or gas precursors) to remove undesired precipitates, side product or residual adhesive materials, if any, from the photomask 202. During the fluid wash process, an ultrasonic or megasonic energy may be applied during the process to assist dislodging the precipitates, side product or residual adhesive materials, if any, from the photomask 202.
After adhesive material removal process, the adhesive material 210 is removed from the photomask 202, as shown in
Thus, embodiments of the present disclosure generally provide apparatus and methods for removing an adhesive material of an attachment feature from a photomask. The methods and apparatus advantageously removing the adhesive material from the photomask by a dielectric barrier discharge (DBD) plasma under a desired pressure range control. Accordingly, the method and the apparatus provided herein advantageously facilitate fabrication of photomasks which is suitable for utilization in lithography applications.
While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
