Patent Application
20070257396
The present invention relates to a process of making nanostructure devices and more particularly to nanoimprint lithography.
Nanoimprint lithography (NIL) may generally be described as a lithographic method designed to create ultra-fine patterns of sub-micron features in a thin film coated on a surface. The process involves a master mold having a desired pattern of nanostructures being mechanically pressed into a thin film of resist material applied over a target layer. The mechanical pressing by the master mold creates a negative pattern on the resist material. The pattern in the resist material is transferred into the target layer using a technique such as reactive ion etching (RIE) or plasma etching.
NIL for forming nanostructures such as semiconductor integrated electrical circuits is well known in the art. One example of NIL is described in U.S. Pat. No. 4,512,848 ('848 patent), issued to Deckman, incorporated herein by reference.
One exemplary method of forming nanostructures using NIL is shown in
A target structure 18 to which the pattern in the master mold is transferred includes a target layer 20 and a substrate 22 that carries the target layer. A resist layer 24 having a low viscosity is deposited or formed on the target layer 20. Typically, the thickness of the resist layer 24 is about the same as or somewhat higher than the depth of the features to be replicated. For example, to pattern a feature having a depth of about 50 nm, the resist should be about 100 nm thick. A possible thickness range for the resist layer 24 is 50 nm-300 nm.
Once the resist layer 24 is applied, the master mold 10 is lightly pressed into the resist layer 24 as shown in
Thereafter, the master mold 10 is removed from the target structure 18 as shown in
The resist layer 24 is then used as a mask for etching the target layer 20. Specifically, the residual layer 26 and then the target layer 20 are etched using any of the well-known etching techniques such as Reactive Ion Etching (RIE). Depending on the etching characteristics of the residual layer 26 and target layer 20, different etching agent may need to be used for each layer. The final nanostructure device 18 is shown in
In manufacturing nanostructures, particles and contaminations play a large role in yield efficiency. As feature size to be replicated becomes smaller and smaller, e.g., on the order of 100 nm or smaller, particles become an even bigger problem because even an extremely small particle on the order of 50 nm can cause imprint defects generally known as particle-associated defects (PAD's). As shown in
Moreover, as shown in
Therefore, it would be desirable to have a device and method for increasing the life of the master mold and increasing the manufacturing yield of the nanostructure devices, thereby reducing the overall manufacturing cost.
According to the principles of the present invention, a novel method of forming a nanostructure device is provided. A master having a nanostructure pattern is formed. The master is used to make an intermediate replica of the master. The intermediate replica includes a relatively thick buffer layer and a pattern layer overlying the buffer layer. The depth of the buffer layer is at least ten times greater than the depth of the pattern layer. The intermediate replica, rather than the master, is then used to make the final nanostructure device.
According to another aspect of the invention, an intermediate mold for use in forming a nanostructure device is provided. The intermediate mold is a replica of a master mold and has a pattern layer having a pattern to be transferred to the nanostructure device and a relatively thick buffer layer underlying the pattern layer. The depth of the buffer layer is at least ten times the depth of the pattern layer of the intermediate mold.
According to the invention, a master mold holding a nanostructure pattern is replicated to an intermediate mold having a thick buffer layer such that any particles that are trapped between the master mold and the intermediate mold during the replication process are pushed down into the buffer layer. The intermediate mold is then used to fabricate the final nanostructure device. As compared to the master mold whose cost is in the range of $1,000 to $1,000,000, the cost of an intermediate mold is usually about $100 or less. As a result the present invention increases the life of the master mold and increases the manufacturing yield.
As shown in
The pattern layer 32, which is a type of composition that is capable of transformation, with or without a physical treatment, into a polymer unit is provided. According to an aspect of the invention, the pattern layer 32 has a polymerizable composite so that it may be polymerized to retain the mold shape. Thus, in this aspect, it may be necessary to use a polymerizable compound or precursor of a polymer as part of the polymerizable composite of a liquid layer composition. For example, polymerizable monomers or oligomers, or a combination thereof, can be used as building blocks so that a homopolymer or a copolymer is obtained. There are a great number of polymerizable compounds known to one skilled in the art. These include, for example, organic materials (or composites) such as epoxy, methyl acrylate, acrylamide, acrylic acid, vinyl, ketene acetyl groups containing monomers, oligomers and inorganic composites such as silicon, aluminum and other metallic or semi-metallic composites. A suitable polymerizable composite may include at least one polymerizable compound or precursor and optionally a diluent and/or a solvent. A diluent is not the same as a solvent for purposes of this invention. Diluent as used herein refers to one of the reactive components which is one of the components and forms part of the final film. Solvent is not intended to be part of the final film. The solvent may be used to control the viscosity of the liquid layer composition and the use of a solvent in the final composition is optional depending on the coating process. For example, solvent may be needed to modulate the viscosity of a composition used for spin coating a substrate. Typical solvents that may be use include toluene, dimethyl formamide, chlorobenzene, xylene, dimethyl sulfoxide (DMSO), dimethyl formamide, dimethyl acetamide, dioxane, tetrahydrofuran (THF), methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, lower alkyl ethers such diethyl ether and methyl ethyl ether, hexane, cyclohexane, benzene, acetone, ethyl acetate, and the like. The boiling a solvent or solvent mixture can be, for example, below 200 C. Selection of suitable solvents for a given system will be within the skill in the art and/or in view of the present disclosure.
Forming the intermediate mold 30 is similar to the steps as shown in
According to the invention, the depth of the buffer layer 34 is at least ten times as high as the depth of the pattern layer 32. For example, the depth of the buffer layer can be 500 nm or higher while that of the pattern layer can be 50 nm. This is to ensure that any dust particles that settle on the liquid resist layer are pushed down into the buffer layer 34 so as not to interfere with forming accurate features in the pattern layer 32. Preferably, the ratio of the depth of the buffer layer 34 to the depth of the pattern layer 32 is at least 200:1 and is between 200:1 and 1000:1. Depending on the type of resist materials used for the pattern layer 32 and buffer layer 34, to initially hold the liquid or semi-liquid resist layer 32 and buffer layer 34, a container having vertical sidewalls may be used to hold the liquid in its place over the substrate 22 if the depth ratio is very high.
In
As shown in
The liquid resist layer 24 is applied on the target layer 20 overlying the substrate 22. Once the resist layer 24 is applied, the intermediate mold 30 is lightly pressed into the resist layer 24 to create a negative impression of the pattern in the resist layer while leaving a residual layer 26. After being pressed, the resist material is cured in order to change its state from liquid to solid. As discussed above, different curing methods are used depending on the resist material being used.
Thereafter, the intermediate mold 30 is removed from the target structure 18 as shown in
The resist layer 24 is then used as a mask for etching the target layer 20. Specifically, the residual layer 26 and then the target layer 20 are etched using any of the well-known etching techniques. The final product is shown in
Typically, either the source pattern layer or target layer or both are treated with a mold release agent, to reduce sticking forces between the source layer and the cured target layer, to ease separation. Suitable treatments may include siloxane or fluorinated release agents. Such treatments may be additionally applied within or to the target layer. By way of specific non-limiting example, the source layer 14 of
By manufacturing nanostructures using an intermediate mold having a thick buffer layer, the present invention, substantially reduces defects in the nanostructures, decreases manufacturing costs and increases the life of the master mold.
The foregoing specific embodiments represent just some of the ways of practicing the present invention. Many other embodiments are possible within the spirit of the invention. Accordingly, the scope of the invention is not limited to the foregoing specification, but instead is given by the appended claims along with their full range of equivalents.
