Semiconductors & Integrated Circuits : Lithography

Semiconductors & Integrated Circuits Portfolios


Block Copolymers for Sub-10 Nanometer Lithography

UW–Madison researchers have developed BCPs characterized by high Flory-Huggins interaction parameters (χ). They can self-assemble into domains having very small dimensions, and therefore are extremely useful in lithography.

The new BCPS may be polymerized from PHS monomers or from tert-butyl styrene and 2-vinylpyridine monomers. Overall degree of polymerization (N) can be experimentally controlled so that it’s high enough to form a desired phase (e.g., cylinders, spheres, lamellae, etc.) but low enough to produce very small dimensions.

Patterned Graphene for Field Effect Transistors

UW–Madison researchers have developed a simpler method for making and patterning GNRs using block copolymer etch masks.

In the process, a graphoepitaxy channel is created over a graphene substrate. Nonpreferential layers are first deposited followed by a secondary layer of block copolymer films over the channels. Under suitable conditions, the spatial confinement of the channel causes the block copolymer to align its self-assembled domains into an array of parallel cylinders or perpendicular lamellae. When one of the polymer blocks is etched away, the periodic pattern is transferred to the underlying graphene, producing patterned GNRs.

A field effect transistor can be formed by incorporating electrodes and using the patterned array as a conducting channel region.

Degradable Neutral Layer for BCP Lithography

UW–Madison researchers have developed easier-to-cleave neutral layers using a new type of polymer film. Linkages both within the film, as well as between the film and its substrate, may be cleaved apart using only a mild acid or light (‘photocleaving’).

The film is made of random copolymer chains having crosslinkable functional groups. The film can be coated on a BCP substrate and then selectively removed.

Achieving Non-Regular Nanostructures Using Block Copolymer Melt

A UW–Madison researcher and others have developed block copolymers for better replication of non-regular structures. The method combines covalently and non-covalently bonded (supramolecular) blocks in melt form.

Nanostructures like films can be formed by depositing a layer of the block copolymer onto a patterned substrate and applying conditions that cause it to assemble and replicate the pattern. The desired shape can be irregular because the bonding between the non-covalent subunits is highly sensitive and responsive to designed conditions like temperature and solvent type.

Bottom-Up Patterning of Smooth Graphene Microstructures and Nanostructures

UW–Madison researchers have developed methods for growing patterned, single-crystalline graphene microstructures and nanostructures. Desired features and dimensions are shaped using a growth barrier ‘mask.’

First, a mask of suitable material (such as metal or metal oxide) is deposited in a desired pattern onto a substrate via any lithographic method. Graphene then is grown around the boundaries of the mask by chemical vapor deposition. The method can be used to produce a single layer or multilayer graphite.

Improved Block Copolymer Engineering for Directed Self-Assembly of Thin Films

UW–Madison researchers have developed novel BCP material that can be used in directed self-assembly and allows structures smaller than 10 nanometers. Methods also have been developed to modify or synthesize material to have stronger interactive parameters without increasing the energy differences working between constituent blocks.

The thin-film BCP can be a poly(styrene-b-isoprene) (PS-PI) chemically modified to increase the first block’s interaction property. The material is deposited on a patterning substrate with microphase-separated domains where it assembles accordingly.

Improved Nansocale Patterning by Directed Assembly of Triblock Copolymers

UW–Madison researchers have developed fabrication methods that involve directing the assembly of ABA triblock copolymers to form desired, complex features. In the process, a layer or thin film of the copolymer material is deposited on a nanopatterned surface and induced to separate, thus replicating the pattern in the layer. Chemical patterns with periods much different than the natural period of the ABA triblock copolymer may be used to direct the assembly process. The triblock includes a component from a polymer group that includes polystyrene (PS) and polyethylene oxide (PEO).

Improved Method for Forming Nanoscale Structures Using Solvent Annealing of Block Copolymers

UW–Madison researchers now have developed methods of fabricating block copolymer thin film structures by solvent annealing, which can be performed at temperatures lower than the thermal annealing used in the previous method and may be useful for block copolymers that are not amenable to thermal annealing. One method includes providing a substrate pattern, depositing a block copolymer material on the substrate pattern and inducing the formation of microphase-separated domains in the block copolymer material by solvent annealing. Another method comprises providing a block copolymer film on a substrate pattern, exposing the block copolymer film on the substrate pattern to a solvent to direct the assembly of the block copolymer film and then evaporating the solvent.

Low-Temperature Method for Smoothing the Disordered Edges of Graphene

UW–Madison researchers have discovered a technique that reduces the required temperatures for edge restructuring of graphene. With this technique, the disordered edges of the material can be smoothed and straightened at temperatures below 1000°C. Because this technique effectively repairs the disordered edges, the current method of top-down etching can still be used to create graphene.

New Method for Direct Patterning in Block Copolymer Lithography

UW–Madison researchers have designed a polymer brush that may be used in underlying buffer or imaging layers for block copolymer lithography. These low molecular weight block copolymers (brushes) can be anchored to substrate surfaces to provide a non-preferential buffer layer for the assembly of higher molecular weight block copolymer thin films. The higher lithographic sensitivity of the brushes allows for shorter processing time and a reduction in the number of steps involved with the assembly process. It also allows for more predictable control over the contrast in chemical pattern and provides a lower defect density in the assembled BCP.

This discovery combines bottom-up and top-down approaches into a single system involving depositing a block copolymer solution on a patterned buffer or imaging layer on a substrate and then inducing the BCPs to separate into domains. The direct patterning and assembly approach presents notable simplification with regards to BCP processing. 

Directed Self-Assembly of Block Copolymers to Make Bit Patterned Media

UW–Madison researchers have developed a method to generate chevron structures suitable for servo regions in BPM by self-assembly of block copolymers. The method uses conventional or e-beam lithography to form a pattern of chemically modified polymer brush material on the master mold substrate that will result in the desired pattern of concentric rings for the data tracks and chevron pattern of slanted stripes for the servo sectors. The pattern includes interface strips between the sets of slanted stripes and at the transition regions between the concentric rings and the stripes. It is the patterned interface strips that significantly reduce defects and control the extent of the disruptive areas in the servo patterns of the resulting nano-imprinted disks.

A block copolymer material is deposited on the pattern, resulting in directed self-assembly of the block copolymer as lamellae perpendicular to the substrate are formed into alternating slanted stripes of the first and second components of the block copolymer. One component also forms on the interface strips, but as a lamella parallel to the substrate. One of the components then is removed, leaving the remaining component as a grid that acts as a mask for etching the substrate to form the master mold.

Improved Method to Create and Transfer Nanoscale Patterns Using Self-Assembling Block Copolymers

UW-Madison researchers now have developed an improved method of creating and transferring chemical or physical nanoscale patterns using block copolymers.  This method builds upon the researchers’ previous inventions by controlling the chemistry of the copolymer pattern to facilitate reactions that lead to transferring of the chemical or physical patterns.   The copolymers used in such an approach comprise two or more constituent units engineered to exhibit distinct chemical properties based on blocking of monomer units and branching thereof.  Different chemical properties among monomer units establish micro-phase separation at the polymer surface and allow ink or transfer molecules to be sequestered into specific copolymer blocks to generate distinct patterns.  The ink molecules are designed to interact with a second substrate, commonly by raising the temperature just above the glass transition temperature, to facilitate mass transfer of the ink and reproduce the copolymer template pattern.

Traditional lithography techniques can be incorporated into the new method, creating the master template to which the copolymers are adhered.  The master template also can be fabricated via chemically nanopatterned surface techniques.  The master template is regenerated after each use, but also may be replicated given specific inks that facilitate the bonding of a new copolymer surface after initial copying.  This method can be used to rapidly and easily generate chemical or physical patterns to be employed in all fields of nanotechnology, such as manufacture of integrated circuits.

Improved Method for Density Multiplication and Lithography via Directed Block Copolymer Assembly

UW–Madison researchers now have developed an improved method to create dense, uniform nanoscale patterns via integration of lithographic techniques and self-assembling block copolymer technology.  The method involves chemical patterning, for example by electron-beam lithography, to activate desired regions on a substrate.  Then a block copolymer film possessing a specific structure and composition is deposited on the patterned substrate.  Upon perturbation of the system, microphase separation of copolymer domains becomes thermodynamically favorable, which generates a second pattern comprising the constituents of the original block copolymer.

The second pattern may have greater density and resolution than the first pattern, depending on the particular block copolymer and desired pattern.  In certain applications of the improved method, density can be increased by a factor of four, resolution can be doubled and superior pattern uniformity can be achieved. 

When employed with other chemical etching techniques, the improved patterning method can be used to fabricate a substrate possessing one to seven trillion features per square inch with a deviation less than one nanometer from ideal placement.  The features patterned on the substrate may include cylinders parallel or perpendicular to the surface, hemispheres or rows.  These techniques could be used to manufacture hard drives or similar disk storage systems that could hold much more information per unit area than surfaces prepared by traditional lithographic methods.

Synthesis of Low-Cost, High-Density DNA Microarrays

UW-Madison researchers have developed a system and method for synthesizing DNA microarrays using a device that includes a reduction optics assembly and a target assembly. These new components incorporate image reduction and precision stage motion into the synthesis process, increasing the density of the DNA chip to 25 times the density of a traditional microarray while maintaining the cost per feature. As a result, the system offers a significant reduction in the cost of DNA microarrays by increasing the amount of information contained within the microarray while keeping the consumables necessary for the process constant when compared to similar technologies.

Using Block Copolymer Materials to Form Patterns with Isolated or Discrete Features

The UW–Madison researchers have expanded their previous work to include methods for directing the self-assembly of block copolymers to form patterns with isolated structures such as those used in the fabrication of integrated circuits. They start with a chemically patterned or otherwise activated surface. These surfaces direct the morphology of the overlying block copolymer films to be oriented parallel to the surface in unpatterned regions or in regions with relatively large patterned features and oriented perpendicular to the surface in regions with the smallest patterned features. This allows block copolymers to form complex circuit designs from patterns with isolated features as small as a few nanometers.

Silicon Nanomembrane Thermoelectric Materials and Devices

UW-Madison researchers have developed methods for fabricating nanowires and nanoribbons that form the core of improved thermoelectric materials and thermoelectric devices. A lithography-based approach is used to construct nanowires and nanoribbons from semiconductor nanomembranes, such as silicon nanomembranes (SiNMs), which are single-crystal membranes from five to 200 nanometers thick. Epitaxial growth of nanostructures on free-standing wires leads to a periodic strain in the ribbon that is the equivalent of superlattice nanowires, but more easily produced in large quantities. Alternatively, the nanowires may be formed from alternating bands of different semiconductor materials.

Because the nanowires periodically vary in composition and/or strain along their length, minibands are formed that restrict the energies of charge carriers to a narrow range, optimizing the thermopower. In addition, the small size of the nanowires and these periodic variations lower the thermal conduction and increase the value of ZT, a dimensionless metric used to rate the efficiency of thermoelectrics.

Directed Assembly of Triblock Copolymers

UW-Madison researchers have developed a method for the complex three-dimensional fabrication of nanoscale structures based on a two-dimensional chemical substrate. A triblock or greater order copolymer is deposited on a chemically patterned substrate that is symmetrical in two dimensions. The substrate has several different chemically active regions. As long as the number of distinct regions is one fewer than the order of the copolymer, the surface pattern can be directed to assemble into a three-dimensional structure by annealing the block copolymer above its glass transition temperature. This process provides conditions that energetically favor the desired three-dimensional morphology.

Fabrication of Complex 3-D Structures Based on Directed Assembly of Self-Assembling Materials

UW-Madison researchers have developed methods of fabricating a thermodynamically stable three-dimensional structure that varies perpendicularly to its substrate. They mismatched the symmetry of the substrate pattern to the block copolymer. When the copolymer is heated above its glass transition temperature, ordering of the material is induced. The interaction of the ordered copolymer with the mismatched substrate alters the energy balance so that three-dimensional structures are the most energetically favorable. As the copolymer materials self-assemble in the upward direction, they transition from following the exact pattern of the substrate to exhibiting a complex three-dimensional morphology.

Materials and Methods for Creating Nanoscale Patterned Features with Atomically Smooth Surfaces

The methods developed by UW-Madison researchers can now produce “Manhattan-style” patterned features less than 50 nm in size, with tall vertical sidewalls, high aspect ratios and atomically smooth surfaces. These patterned features are called “polymer brushes.” To make them, polymers such as styrenes, acrylates, and silanes are grown and covalently bonded to a substrate at an initiation, or grafting, site. The principal innovation is that surface tension between the polymer and air, or between the polymer and a solvent, is exploited to produce atomically smooth surfaces on features as small as 25 nm. The researchers also showed that by varying the polymers’ grafting density and molecular weight, they could control polymer brush height and aspect ratio.

Methods and Compositions for Forming Aperiodic Patterned Copolymer Films

UW-Madison researchers have developed methods of using block copolymers to replicate patterns with irregular features. Block copolymer materials are deposited onto patterned substrates, and then components in the copolymer material are ordered to replicate the pattern. The ordering may be facilitated through the use of blends of the copolymer material and/or by configuring substrate patterns so that regions of the substrate pattern interact in a highly preferential manner with at least one of the components in the copolymer material.

Organoelement Resists for EUV Lithography

UW-Madison researchers have developed organoelement resist materials that are robust to processing with both UV and EUV. Unlike current resist materials, these materials contain an oxygen and fluorine content of 14 percent or less, and are primarily composed of low-absorbing elements, such as hydrogen, carbon, silicon and boron. The incorporation of silicon- and boron-containing polymers into a resist material can reduce ion reactive etch rates and improve transmission characteristics, both of which are needed during EUV lithography. The invention also includes methods for synthesizing silicon- and boron-containing materials for use in resist compositions.

Defect Inspection of Extreme Ultraviolet Lithography Mask Blanks

UW-Madison researchers have developed a method for inspecting EUV lithography mask blanks for defects.  A multi-layer EUV mask blank is coated with a layer of photoresist that has been mixed with a fluorescent dye.  The mask blank then is exposed to a source of radiation such that the photoresist is fully exposed by the combination of direct and reflected radiation from the mask blank in areas of the mask blank in which there are no defects. 

Using this method, photoresist will remain after development only in areas where defects are present.  Because the remaining photoresist contains fluorescent dye, defects can be detected easily by illuminating the mask blank with the excitation wavelength of the dye and then observing the mask blank under a dark field microscope.

Method of Forming a Microstructure by Using Maskless Lithography

A UW-Madison researcher has developed a method of using maskless lithography to fabricate microfluidic channels and systems. To create a microfluidic device, a first layer is laid down in relation to a base layer so as to create a construction cavity between them. The construction cavity is filled with a polymerizable material and a desired mask pattern is drawn on a computer. Using the mask as a guide, the computer uses mirrors to direct a polymerizing agent, such as UV light, toward the regions of the device that will be polymerized.

Parts of the device not subjected to the polymerizing agent (including the inside of the channels) are not polymerized. Flushing the non-polymerized material from the construction cavity leaves the desired channel network.

Additional layers may be placed on top of the first layer to create additional construction cavities between them. The additional construction cavities are filled with material, a portion of which is polymerized to define additional channels in the microstructure.

Atomic Lithography of Two-Dimensional Nanostructures

A UW-Madison researcher has developed a method for precisely depositing atomic species in arbitrary patterns on a substrate without the need for mechanical motion. Specifically, the method uses spatial light modulators to control the mask of light over the full substrate plane, allowing precise positioning of atomic species during deposition. By eliminating the need for mechanical control, this new atomic lithographic technique expands the range of possible lithographic patterns well beyond simple stripes or arrays.

Guided Self-Assembly of Block Copolymer Films on Interferometrically Nanopatterned Substrates

UW-Madison researchers have developed a new strategy for controlling the ordering of micro-phase separated domains in thin films of self-assembling block copolymers. Using advanced interferometric lithographic techniques, the researchers have created chemically patterned surfaces that act as templates for the self-assembly of block co-polymer films. Extreme ultraviolet interferometric lithography is ideal for this purpose because it produces the periodic surface pattern in the underlying substrate that is needed to guide self-assembly of the periodic domain structure in the overlying block copolymer film.

Enhanced Phase-Shifting Mask for Gate Widths and Vias

UW–Madison researchers have developed a clear, phase-shifting mask that can be used for 1-D features such as device gate widths and 2-D patterns such as contact holes (or vias). Specifically, the device positions two, adjacent, phase-shifting edges such that constructive interference occurs between the bright-peaks associated with the individual edges to minimize diffraction and enhance intensity.

Inspection of Lithography Masks with X-ray and Extreme Ultraviolet Radiation

UW-Madison researchers have developed a method for detecting imperfections in X-ray lithography masks by passing X-rays through them in the same manner as when the system is used for fabrication. The method involves the use of a photo-emitting cathode, which is placed in the same position as the photoresist during fabrication. When X-rays pass through the mask and strike the cathode, the cathode emits electrons whose intensities are directly proportional to the local intensities of the X-rays. The emitted electrons are then magnified by an electron microscope, producing a mask image that exactly matches the photoresist pattern that will be imprinted during production.