The invention relates generally to a photolithography method for making a semiconductor device, for example, a diode containing nonvolatile memory array.
One prior art process using a hard mask stack shown in
One embodiment of the invention provides a method of making a device, comprising forming a first photoresist layer over an underlying layer, patterning the first photoresist layer to form a first photoresist pattern, rendering the first photoresist pattern insoluble to a solvent, forming a second photoresist layer over the first photoresist pattern, patterning the second photoresist layer to form a second photoresist pattern over the underlying layer, and etching the underlying layer using both the first and the second photoresist patterns as a mask.
Another embodiment of the invention provides a method of making a device, comprising forming a device layer, forming an organic hard mask layer over the device layer, forming a DARC layer over the organic hard mask layer, forming a BARC layer over the DARC layer, forming a first photoresist layer over the BARC layer, patterning the first photoresist layer to form a first photoresist pattern, forming a barrier layer on the first photoresist pattern, forming a second photoresist layer over the first photoresist pattern, patterning the second photoresist layer to form a second photoresist pattern over the device layer patterning the DARC layer using the combination of the first and the second photoresist patterns as a mask, patterning the organic hard mask layer using at least the patterned DARC layer as a mask, and patterning the device layer using at least the organic hard mask layer as a mask.
One embodiment of the invention provides a method of making a device, comprising forming a first photoresist layer over an underlying layer, as shown in
A second photoresist layer 201 is formed over the first photoresist pattern 111, as shown in
The barrier layer 115 comprises a thin polymer film (such as a monolayer film) having a thickness of less than 10 nm, preferably about 1-2 nm, which is disposed on a surface of the first photoresist pattern 111. The increase in critical dimension of the first photoresist pattern before and after forming barrier layer 115 may or may not be observable. The underlying layer 109 is exposed in first openings 112 in the first photoresist pattern. The barrier layer protects the first photoresist pattern from being dissolved by a solvent during the step of patterning the second photoresist layer.
The first and second photoresist materials may be any suitable photoresist material(s), preferably acrylate materials, such as poly(methyl acrylate) or poly(methyl methacrylate). The first and second photoresist materials may be same or different materials. In some embodiments, the barrier layer 115 is formed by reacting the first photoresist pattern with a reactive material 113 to form the monolayer thick polymeric barrier layer. This barrier layer can be formed by causing cross-linking on the surface of the pattern 111 or by any other suitable methods. In some embodiments, when the first photoresist is an acrylic material, the freezing reagent may be the same acrylic material with an active functional group on the side chain. The reactive material 113 can be a chemical shrink material, such as CSX004, FZX F112, FZX F114 which comprises a poly(methyl)acrylate derivative, melamine resin, and other ingredients including water, methyl isobutyl carbinol, n-butyl alcohol, or combinations thereof. For example, FZX F114 comprises a poly(methyl)acrylate derivative, and a solvent containing methyl isobutyl carbinol and n-butyl alcohol having a volume ratio of 70:30 to 90:10, such as a volume ratio of 80:20. CSX004, FZX F112, and FZX F114 are all available from JSR Micro (http://www.jsrmicro.com). Another chemical shrink material, RELACS® available from AZ Electronic Materials or other reactive reagents which are used in the prior art to reduce the dimensions of openings between adjacent resist patterns (i.e., which are used to widen small resist patterns), may also be used. The cross-linking may be achieved by heating material 113 for 1-2 minutes at a temperature between 130° C. and 180° C. The removal of material 113 may be achieved by development in suitable developer solution followed by a second heating step. For example, the methods described in U.S. patent application Ser. No. 11/864,205, which is incorporated by reference in their entirety, may be used.
Other freezing methods may also be used to protect the first photoresist pattern from being dissolved by a solvent(s) used (i.e. to render the first photoresist pattern insoluble) in the step of patterning the second photoresist layer. For example, a protective agent may selectively replace some functional groups of the first photoresist polymer, which in turn renders the first photoresist insoluble to the solvent(s). Alternatively, the first photoresist may crosslink with a compatible chemistry under a desired condition, such as an application of heat (e.g. a high temperature bake), or other desired treatments, to “freeze” the first photoresist pattern.
In some embodiments, the first photoresist pattern 111 comprises first openings 112, the first photoresist pattern is formed by a first exposure using a first photo mask, the second photoresist pattern 211 is formed in the first openings 112 such that second openings 212 remain between adjacent portions of the first and the second photoresist patterns. The second photoresist pattern is formed by a second exposure using a second photo mask. A combination of the first and the second photoresist patterns can have a final pitch that is double a pitch of the first photoresist pattern. The photo masks used in pattering the first photoresist layer and patterning the second photoresist layer can be the same (with shifting of mask position) or different. In some embodiments, features of “frozen” first photoresist pattern may be used as alignment marks for the second exposure.
One or more photosensitive layers can be formed and patterned over the stack described above. For example, 193 nm radiation sensitive photoresist and TArF P6239 can be used. A Bottom Anti-reflective Coating (BARC) (for example, but not limited to, ARC29SR available from Brewer Science) layer, with a desired thickness, may be added to improve the performance of the photo resist by forming a sharper resist contrast after double patterning. Other photosensitive layer or layers may also be used. Immersion lithography (i.e., a lithography which utilizes a liquid at the interface) may be used to expose the photoresist, in which water or other high-index fluids may be used as an immersion medium. A regular dry lithography may also be used. A topcoat may be used on top of the photoresist to prevent diffusion of chemical by-products into water and lens during exposure. Alternatively, a top-coat free photoresist may be used. Other lithography methods, including but not limited to regular UV or X-ray methods, may also be used.
Exposure doses used to size the photoresist into the correct critical dimension (CD) in double patterning is another important factor, and may not show a linear correlation with the resulting CD. Thus, some interaction effects cannot be fully captured through simulations. For example, the photoresist CD might get bigger or smaller after the step of the first photoresist freeze (depending on the chemistries involved), and then can get either bigger or smaller again after the second photoresist patterning. Therefore, an optimized set of exposure doses to apply with a particular chemical combination may be different to simulate. Thus, a matrix of first and second exposure doses (as shown in
If the DARC layer and organic hard mask (such as APF) layers are located between the photoresist and device layer, then the DARC layer is patterned using the combination of the first and the second photoresist patterns as a mask, an the organic hard mask layer is patterned using at least the patterned DARC layer as a mask, and the device layer is patterned using at least the organic hard mask layer as a mask. Photoresist layer patterns 111 and 211 may be consumed in the step of APF 103 etching, the DARC 106 (and optional oxide hard mask) may be consumed in the step of device layer 101 etching, while at least lower portion of APF layer 103 may still remain after device layer etching. The remaining APF layer 103 can then be stripped. Multiple etching steps may be conducted in one chamber or in plural chambers of a multi-chamber apparatus without breaking the vacuum.
In one embodiment, the device layer comprises a conductive material, such as a metal or metal alloy, which is patterned into line shaped electrodes. Alternatively, the device layer may comprise an insulating layer which is patterned into a desired shape or where openings or vias are etched in the insulating layer. In another embodiment, the device layer comprises at least one semiconductor layer, and the step of patterning the device layer forms an array of semiconductor pillars, and each pillar in the array of pillars comprises a diode. The diode may be a steering element of a memory cell which also includes a storage element.
In some embodiments, the storage element comprises a resistivity switching element. The resistivity switching element can be a metal oxide antifuse dielectric layer or another element, and the diode and the metal oxide antifuse dielectric layer can be arranged in series. The memory cell can be further located in a monolithic three dimensional array of memory cells. The memory cell can be a read/write memory cell or a rewritable memory cell. The memory cell type can be selected from at least one of antifuse, fuse, polysilicon memory effect cell, metal oxide memory, switchable complex metal oxide, carbon nanotube memory, graphene, amorphous or polycrystalline carbon switchable resistance material, phase change material memory, conductive bridge element, or switchable polymer memory. U.S. application Ser. Nos. 11/864,532 and 11/819,595, U.S. Published Application Numbers US 2007/0164309 A1 and US 2007/0072360 A1, and U.S. Pat. Nos. 6,946,719, 6,952,030, 6,853,049, disclosing memory cells and methods of making and/or using thereof, are hereby incorporated by reference in their entirety.
In preferred embodiments, the memory cell includes a cylindrical semiconductor diode located in series with the storage element. The diode and the film are disposed between two electrodes, as illustrated in
As a non-limiting example,
The memory cell may be fabricated by any suitable methods. For example, the methods described in U.S. patent application Ser. No. 11/125,939 filed on May 9, 2005 (which corresponds to US Published Application No. 2006/0250836 to Herner et al.), and U.S. patent application Ser. No. 11/395,995 filed on Mar. 31, 2006 (which corresponds to US Patent Published Application No. 2006/0250837 to Herner et al.,) which are incorporated by reference in their entirety may be used.
The above described memory cell shown in
A monolithic three dimensional memory array is one in which multiple memory levels are formed above a single substrate, such as a wafer, with no intervening substrates. The layers forming one memory level are deposited or grown directly over the layers of an existing level or levels. In contrast, stacked memories have been constructed by forming memory levels on separate substrates and adhering the memory levels atop each other, as in Leedy, U.S. Pat. No. 5,915,167, “Three dimensional structure memory.” The substrates may be thinned or removed from the memory levels before bonding, but as the memory levels are initially formed over separate substrates, such memories are not true monolithic three dimensional memory arrays.
A monolithic three dimensional memory array formed above a substrate comprises at least a first memory level formed at a first height above the substrate and a second memory level formed at a second height different from the first height. Three, four, eight, or indeed any number of memory levels can be formed above the substrate in such a multilevel array.
In following non-limiting examples, a high numerical-aperture immersion scanner, and chromium-less phase-shift masks were used to form dense pillars and spaces (openings between the pillars). A BARC layer was provided over the substrate.
First, a first TArF P6239 resist, was spin coated onto the BARC layer. The final thickness of this first photoresist was around 80 nm. Other resists that consist of high loading amount of photo-acid generators, preferably one that was not bulky, such that long acid diffusion is present during the subsequent post-exposure bake may be used. After post bake at 120° C. for 60 seconds, the first photoresist is exposed to a first radiation pattern using immersion lithography, followed by a post exposure bake at 110° C. for 60 seconds and a development step for 30 seconds.
A chemical shrink, CSX004, was then applied on the first photoresist pattern. Without wishing to be bound by a particular theory, a thin polymeric monolayer is believed to have formed around the first photoresist pattern, having a thickness of around 5 nm on each side of the original boundary of the first photoresist pattern. This barrier layer protected the first photoresist pattern from being dissolved by a solvent during the step of patterning the second photoresist layer. After a bake at a temperature ranging from 130° C. to 150° C. for 60 seconds, the CSX004 treated surface was then developed in 2.38% TMAH solution for 15 seconds, followed by a surfactant-based DI water rinse.
A second photo resist is then spin coated without the BARC layer. Before exposure, the layout of the second mask is aligned over the first photoresist pattern using a pre-defined set of alignment marks and algorithm. Alternatively, the same layout pattern for the first photoresist patterning can be shifted in a manner that a combination of the first and the second photoresist patterns have a final pitch that is double a pitch of the first photoresist pattern.
In example 1, masks having a pattern of opaque dots were used.
Alternatively, instead of CSX004, FZX F114 comprising a blend of 80% methyl isobutyl carbinol and 20% n-butyl alcohol was used as a freezing reagent applied on the first photoresist pattern to render the first photoresist pattern insoluble to a solvent, in example 2.
In example 3, masks having a pattern of lines are used. A 160 nm oxide layer was located over a substrate, and an APF film was formed over the oxide layer. A BARC layer was formed over the APF film. The same process steps were used in this example, except that the illumination conditions were adjusted based on the different shape of the resist patterns according to exposure apparatus specifications.
As described above, a BARC layer with desired thickness may improve the performance of the photoresist by forming a sharper resist contrast after double patterning. A surface reflectivity is tested on stacks with a silicon oxynitride DARC and a BARC layer having various thicknesses, to identify a desired point of operation. As shown in
The foregoing detailed description has described only a few of the many forms that this invention can take. For this reason, this detailed description is intended by way of illustration, and not by way of limitation. It is only the following claims, including all equivalents, which are intended to define the scope of this invention.
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