Mask storage device for mask haze prevention and methods thereof

A mask storage device and a method of preventing defect formation on a mask are provided. The method includes providing a mask storage device comprising a first and second shell configured to form a sealed space in a closed state and a desiccant positioned within the mask storage device. The method further includes placing a mask inside the mask storage device and sealing the mask storage device with the mask and desiccant inside the sealed space.

BACKGROUND

The disclosure relates generally to the prevention of damage to masks used in semiconductor manufacturing and, more particularly, to prevention of haze formation on mask surfaces.

Semiconductor manufacturing processes require the creation and maintenance of masks that are substantially free of scratches, particle deposition, and pellicle frames so that each mask is in condition for use in lithography. The presence of defects results in reduced silicon wafer yield during lithography. As such, attention to the prevention and discovery of mask defects is required to prevent yield loss of silicon wafers.

Some mask defects are formed after the lithography process. During the mask making process, masks are rinsed with various compositions, including a composition containing ammonium ions. Residual ammonium ions left on the mask surface react with residual sulfuric acid or sulfate ions from the strip process in a high energy environment. As such, ammonium sulfate [(NH4)2SO4] may form on the mask surface in the presence of water [H2O] under one of the following chemical reactions:
H2O+H2SO4+2NH4OH→(NH4)2SO4+H2O
2NH3+SO3+H2O→(NH4)2SO4

Under these conditions, an ammonium sulfate [(NH4)2SO4] haze forms on the mask surface, which impacts the usage life of the mask as well as the yield of silicon wafers.

Current measures known to the inventors for reducing the formation of an ammonium sulfate [(NH4)2SO4] haze on the mask surface include the use of storage cabinets which circulate clean dry air and purge the cabinet with nitrogen. Such cabinets are expensive to obtain and require monitoring.

DETAILED DESCRIPTION

It is understood that the following disclosure provides many different embodiments, or examples, for implementing different features of the disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this description will be thorough and complete, and will fully convey the present disclosure to those of ordinary skill in the art. It will be apparent, however, that one or more embodiments may be practiced without these specific details.

In the following description, numerous specific details are set forth to provide a thorough understanding of the present disclosure. However, one having ordinary skill in the art will recognize that the embodiments can be practiced without these specific details. In some instances, well-known structures and processes have not been described in detail to avoid unnecessarily obscuring the present disclosed embodiments.

One or more embodiments of a method of and device for storing masks used in the semiconductor wafer manufacturing process are useful in preventing defect formation on a mask surface.

FIG. 1is a front view of a mask storage device100having a lower shell102and an upper shell104in an open state and arranged to receive and retain therein a mask202(FIG. 2). Upper shell104and lower shell102are generally rectangular parallelepipeds having an open face. In some alternative embodiments, upper shell104and lower shell102are other shapes and sizes. In some alternative embodiments, upper shell104and/or lower shell102are multi-piece designs. Lower shell102and upper shell104comprise acrylonitrile butadiene styrene (ABS). In at least some embodiments, ABS is selected for impact resistance and/or electroinsulating properties. In other embodiments, lower shell102and upper shell104are constructed of anti-electrostatic discharge materials having low outgas and low particle discharge properties to prevent discharge of chemical contaminants that may create defects, such as haze, on a mask surface, including thermoplastics. In still further embodiments, the upper and lower shells104and102, respectively, are constructed of different materials as to each other. With reference toFIG. 1, the materials are translucent. In some other embodiments, the materials are transparent or opaque.

Lower shell102has an inner surface108. Mask receiving brackets106are molded to the inner surface108of the lower shell102for receiving mask202(FIG. 2). Each mask receiving bracket106has at least one surface for contacting and retaining the mask in place between the multiple mask receiving brackets106to prevent movement of the mask when placed inside the mask storage device100. The mask receiving bracket106is molded as part of the lower shell102. In other embodiments, mask receiving bracket106is bonded to the inner surface108. In other embodiments, the mask receiving bracket106is fastened to the inner surface108in a removable fashion.

A set of four (4) mask receiving brackets108is mounted to the inner surface108. In other embodiments, a single bracket or platform for receiving the mask substitutes for the plurality of mask receiving brackets106. In other embodiments, a greater or lesser number of mounting brackets are used.

The upper shell104has an inner surface110. Retention brackets112are attached to surface110similarly, as described above, with regard to attachment of brackets106to surface108. A plurality of retention brackets112are attached to the inner surface110. In at least some embodiments, inner surface110does not have retention brackets112. In at least some embodiments, a single platform or bracket is attached to the surface110. In some embodiments, upper shell104is a copy of lower shell102.

Affixed to the lower shell102is at least one retainer for holding a desiccant or desiccant packet therein, e.g., a humidity reducing material or other component. Each desiccant container114is a retainer that is affixed to the lower shell102along the perimeter of the lower shell that holds desiccant therein. In other embodiments, desiccant containers114are affixed to the upper shell. In some embodiments, desiccant containers are affixed to both the upper and lower shells104and102, respectively.

Desiccant container114is a rectangular box with one or more air vents116. In some other embodiments, the desiccant container114has a single air vent. In some embodiments, the desiccant container114has one or more membranes which are permeable to allow air to penetrate through the membranes into the desiccant container114.

A set of four (4) desiccant containers114is removably attached to the lower shell102. In at least some other embodiments, a single desiccant container114is affixed to the storage device100. In some other embodiments, a greater or lesser number of desiccant containers114are used. In at least some other embodiments, the set of desiccant containers114is removably or fixedly attached to the upper shell104and/or the lower shell102.

Each desiccant container114is a parallelepiped having a removable lid134generally defining an upper surface of the desiccant container. The lid134is removable. When removed, the inner surfaces of the desiccant container define an inner space130(FIG. 8). A desiccant or desiccant packet118(broken line) is placed within space130and the lid is secured to the desiccant container114to secure the desiccant therein. As such, the desiccant container114retains a desiccant therein for reducing humidity level in the space130. Types of desiccant include clay, calcium oxide, silica gel and a molecular sieve, or any other suitable desiccants to remove humidity from an air supply. The lid134has a plurality of air vents116located therein to allow the flow of air within the mask storage device100to contact the desiccant. In other embodiments, other surfaces of the desiccant container114comprise the air vent or air vents.

In some other embodiments, desiccant container114is an integrated structure formed as part of lower shell102. In some other embodiments, desiccant container114is an integrated structure formed as part of upper shell104. In some other embodiments of the mask storage device100, the retainer is a clamp formed as part of the lower shell. The clamp is a clip that retains a desiccant packet. In some other embodiments, the clamp is a flexible member sized to retain the desiccant packet.

Lower shell102has a lower shell mating surface120along the outer perimeter of the lower shell102. A gasket122is positioned along the lower shell mating surface120.

In one embodiment, the gasket122is an anti-electrostatic, low outgas block glue, including but not limited to ABS.

The upper shell104has an upper shell mating surface124that contacts the gasket122when the mask storage device100is in a closed state, thereby sealing the mask202(FIG. 2) within the mask storage device.

In at least some embodiments, lower shell102and upper shell104are connected via a pair of hinges132. In other embodiments, the lower shell102and upper shell104are connected by a single hinge132or more than two hinges. Hinge132allows pivoting of the upper shell104with respect to the lower shell102, thereby alternating the mask storage device100between open and closed states. In some embodiments, hinge132is replaced by one or more latch mechanism, such as one similar to the latch mechanism126and128, so that the upper shell104and lower shell102are removed from each other and reattached by contacting the lower shell mating surface120and/or upper shell mating surface124to the gasket122, and secured in the closed state by latch mechanisms126and128.

Mask storage device100also has a latch mechanism126and128on corresponding outer surfaces of upper shell104and lower shell102to secure the mask storage device in a closed state.

In some embodiments, the mask storage device includes at least an upper shell104and a lower shell102, where the lower shell defines a storage space for masks, and the upper shell is a door for accessing the storage space. In some embodiments, the mask storage device100includes two or more shells that define an airtight sealed storage space.

FIG. 2is a view of mask storage device100(broken line) in a closed state and containing mask202within the mask storage device. Mask202is supported within the mask storage device100between the retention brackets112and receiving brackets106. In one embodiment, a single mask202is placed and secured within the mask storage device100. In other embodiments, multiple masks are placed and secured within the mask storage device100. In some embodiments, multiple masks stored within the mask storage device100are separated from each other by a spacer.

FIG. 3is a side view of the closed mask storage device100ofFIG. 2. The lower shell102and upper shell104are secured in closed position by the latch mechanism126and128to reinforce the closed position. In other embodiments, a clamp is affixed around the mask storage device100to reinforce the mask storage device100in a closed state. Types of clamps include C-clamps, elastomeric bands, or other suitable closure mechanisms. Some embodiments include both the latch mechanism and the clamp.

In at least some embodiments, hinge132comprises a first member304and second member306. First member304is integrally formed as part of upper shell104. Second member306is integrally formed as part of lower shell102. In some other embodiments, hinge132is formed separately from upper shell104and lower shell102and thereafter affixed to the mask storage device100.

FIG. 4is a front view of the mask storage device100ofFIG. 2.

FIG. 5is an expanded view of a corner of the lower shell ofFIG. 2. Gasket122is affixed to the lower shell mating surface120by curing the gasket122onto the mating surface120. In at least some other embodiments, gasket122is lacquered onto the mating surface. In at least some other embodiments, the gasket122is formed independently of the mask storage device and is removably secured to the mating surface120,

Gasket122forms an airtight seal between the mating surfaces120and124to prevent the flow of air into the mask storage device100. In some embodiments, gasket122is compressible.

FIG. 6is an expanded cross-sectional view of the mask storage device100in a closed state along line X-X inFIG. 4. The upper shell mating surface124and lower shell mating surface120are formed to match each other when the mask storage device100is in a closed state. In a closed state, upper shell mating surface124contacts the gasket122. As such, an airtight seal is sufficiently formed between the lower shell102and upper shell104to prevent circulation of air from space A (outside the mask storage device) and into space B (inside the mask storage device). In some other embodiments, upper shell mating surface124and lower shell mating surface120are formed to define a gap for retaining the gasket122when the mask storage device100is in a closed state yet still form a seal with the gasket122.

FIG. 7is an expanded cross-sectional view of an alternative embodiment of the interaction of the gasket122and upper shell104, wherein the gasket122is applied directly to the upper shell mating surface124. In a differing embodiment, the gasket122may be applied to either the lower shell mating surface120or the upper shell mating surface124. In some other embodiments, separate gaskets are applied separately to both the lower shell mating surface120and the upper shell mating surface124and an air tight seal is sufficiently formed as the gaskets contact each other. In other embodiments, the gasket122is an O-ring, or other sealing or compressible member, that contacts the lower shell102and upper shell104to sufficiently create an airtight seal.

FIG. 8is a view of the lower shell102with the upper shell104removed for clarity. Each desiccant container114has a pair of ends806that are substantially identical. Each end806has an end surface906that has an elongated stud904molded (FIG. 9). Each desiccant container114is mounted between a pair of desiccant supports804aand804b.

Desiccant supports804aand804bare flanges molded as part of the inner surface108of lower shell102. Desiccant supports804aand804bare substantially mirror images of each other. In other embodiments, desiccant supports804aand804bare mounted or affixed to the lower shell102. In some other embodiments, desiccant supports804aand804bare bonded to the inner surface108. In some other embodiments, desiccant supports804aand804bare removably attached to inner surface108.

FIG. 9is an expanded view of one end806of the desiccant container114and desiccant support804b. Desiccant support804ahas an inner surface908defining a detent906therein. Stud904is configured to be fitted within the detent906. As such, placement of the stud904in the detent906secures the one end906of the desiccant container114to a desiccant support804b. Placement of the stud904on each end806into the through hole906of desiccant supports804aand804bsecured the desiccant container to the lower shell102.

FIG. 10is a view of a plurality of mask storage devices100stacked within a mask storage container1000in an open state. Mask storage container1000has an inner volume1002to allow placement of mask storage devices100therein. Mask storage container1000has mateable surfaces1004and1006that contact to create an airtight seal when the mask storage container1000is in a closed state. Mask storage container1000is made of ABS. In other embodiments, mask storage container is made of anti-electrostatic discharge materials having low outgas and low particle discharge properties, including some thermoplastics. Mask storage container1000has at least one desiccant container1008secured therein similarly to how desiccant containers114are secured to mask storage device100.

In at least some embodiments, the components described herein are constructed of ABS, or other material having anti-electrostatic discharge properties having low outgas and low particle discharge properties to prevent the discharge of chemical contaminants that may create defects on a mask surface. Further, the presence of a desiccant within the device or container creates a low humidity environment that prevents the formation of ammonium sulfate [(NH4)2SO4] haze on a mask surface. In this regard, the inventors have found that storage of masks in mask storage devices100and/or containers1100as described herein have increased the effective lifetime of masks used in the silicon manufacturing process by three times. In other embodiments, the mask storage device100is stored in a humidity controlled room. A system for controlling the room's environment, such as ambient humidity, is connected to the room. Further, the room is constructed of low outgas and low particle discharge materials.

FIG. 11is a flow chart describing the storage of a mask within the mask storage device to prevent defect formation on a mask surface. A mask is provided1102by the operator or user. A mask storage device having at least a gasket and a desiccant is provided, and the mask storage device is opened1104. The mask is then placed within the mask storage device1106and the mask storage device is sealed1108. Upon sealing, an electrostatic preventive environment is created1110within the mask storage device. Further, ambient humidity is reduced1112within the mask storage device.

In the event a user requires use of the mask contained within the mask storage device, the user opens the mask storage device1114, removes the mask1116, and uses the mask in the lithography1118. After lithography is complete, a user may then perform the steps to store the mask within the mask storage device. The storage of a mask includes temporary and permanent storage for purposes of maintaining the mask during periods of nonuse or processing of masks, regardless of whether lithography is performed before or after storage of the mask within the mask storage device100, such as during shipping of masks.

Additionally, the mask storage device may be placed within a mask storage container1120. The mask storage container is then sealed, an electrostatic preventive environment is created within the mask storage container and humidity is removed from the mask storage container1122. Should a user require to use a mask, the mask storage container is opened1124, a mask storage device removed1126, and the mask storage device is opened1114.

FIG. 12is a flow chart describing the storage of a mask within the mask storage device and environment controlled room. In some embodiments, mask storage device100is placed within an environment controlled room1202. The room is humidity controlled by a dehumidifying system that filters and/or removes moisture from the air within the room1204. The room is sealable and the dehumidifying system is controlled by a processor. Should a user require to use a mask, the environment controlled room is opened1206, a mask storage device removed1208, and the mask storage device is opened1114.

Provided is a method of preventing defect formation on a mask surface used in lithography. The method includes providing a mask storage device comprising an upper and lower shell configured to form a sealed space in a closed state and a desiccant positioned within the mask storage device. A mask is placed inside the mask storage device. The mask is then sealed inside the mask storage device. In at least some embodiments, the mask is used in lithography before or after placement in and sealing of the mask storage device.

Further provided is a mask storage device for storing a mask used in lithography. The mask storage device has a lower shell containing a desiccant container. The desiccant container has a desiccant placed therein. The mask storage device has an upper shell removably attached to the lower shell and arranged to form a sealed space with the lower shell in a closed state. The mask storage device also has a gasket positioned between the lower shell and the upper shell, which is configured to create a sufficiently airtight seal between the lower shell and the upper shell in the closed state.

Still further provided is a method of preventing defect formation on a mask used in lithography. The method includes providing a mask storage device having a lower shell having a desiccant container, the desiccant container comprising a desiccant. Further, the mask storage device has an upper shell removably attached to the lower shell, and a gasket configured to contact the lower shell and upper shell to create a sufficiently airtight seal between the lower shell and upper shell. The method further includes placing a mask inside the mask storage device; and sealing the mask inside the mask storage device.

In the preceding detailed description, exemplary embodiments have been described. It will, however, be evident that various modifications, structures, processes, and changes may be made thereto without departing from the broader spirit and scope of the claims. The specification and drawings are, accordingly, to be regarded as illustrative and not restrictive. It is understood that the disclosure is capable of using various other combinations and environments and is capable of changes or modifications within the scope of the concept as expressed herein.