Abstract:
A method of removing organic anti-reflective coating (ARC) by ashing in an integrated circuit fabrication process can include providing an oxide-nitride-oxide (ONO) stack over a silicon substrate, providing a poly layer over the ONO stack, and patterning spaces in the poly layer using a patterned carbon bilayer ARC layer and a patterned hardmask layer. The patterned carbon bilayer ARC layer is ashed away before patterning spaces in the poly layer. Ashing the carbon bilayer ARC layer helps prevent damage to the ONO stack, improving the quality of the fabricated device.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to integrated circuits and methods of manufacturing integrated circuits. More particularly, the present invention relates to definition of the subresolution trench features between polysilicon wordlines using the CVD deposited bilayer ARC as a hard mask. 
     BACKGROUND OF THE INVENTION 
     Semiconductor devices or integrated circuits (Ics) can include millions of devices, such as, transistors. Ultra-large scale integrated (ULSI) circuits can include complementary metal oxide semiconductor (CMOS) field effect transistors (FET). Despite the ability of conventional systems and processes to fabricate millions of devices on an IC, there is still a need to decrease the size of IC device features, and, thus, increase the number of devices on an IC. 
     One limitation to the smallness of IC critical dimensions is conventional lithography. In general, projection lithography refers to processes for pattern transfer between various media. According to conventional projection lithography, a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film or coating, the photoresist. An exposing source of radiation illuminates selected areas of the surface through an intervening master template, the mask, for a particular pattern. The radiation can be light, such as ultra-violet light, vacuum ultra-violet (VUV) light and deep ultraviolet light. The radiation can also be x-ray radiation, e-beam radiation, etc. 
     The lithographic photoresist coating is generally a radiation-sensitive coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive image of the subject pattern. 
     Exposure of the lithographic coating through a photomask or reticle causes the image area to become selectively either more or less soluble (depending on the negative or positive photoresist coating) in a particular developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer. 
     The photoresist material or layer associated with conventional lithographic technologies is often utilized to selectively form various IC structures, regions, and layers. Generally, the patterned photoresist material can be utilized to define structures associated with an integrated circuit (IC). A conventional lithographic system is generally utilized to pattern photoresist material to form gate stacks or structures. As the features in semiconductor patterning become smaller and smaller, the photoresist thickness needs to be reduced in order to sustain reasonable aspect ratio. A thinner resist may not be suitable for etch application due to premature resist erosion. This limitation provides a need for the use of hard mask processes. 
     According to one conventional process, a high temperature oxide (HTO) hard mask is provided above polysilicon/oxide layers to pattern the small trenches between gate stacks. The hard mask must be thin enough so that it can be etched without eroding the patterned photoresist above it. The hard mask must also be thick enough to withstand an etch process that can completely remove uncovered portions of the polysilicon layer. Accordingly, the hard mask must have a precise thickness to appropriately pattern the gate stacks. The removal of the hard mask material after the gate stack is defined is also problematic due to the potential for damage to the exposed underlying material. 
     An anti-reflective coating (ARC) has been conventionally provided underneath the photoresist material or on top of the hard mask to reduce reflectivity and thereby, reduce resist notching and lifting and variation of critical dimension of the obtained pattern. Generally, the ARC (organic or inorganic) layer is a relatively thin layer which cannot be used as a hard mask because of the limited thickness flexibility due to optical design constrains. 
     Thus, there is a need to pattern IC devices using non-conventional techniques. Further, there is a need for a process of forming a small subnominal trench in the gate stack that does not require a conventional hard mask step. Yet further, there is a need for a hard mask layer that can function as an anti-reflective coating with enough thickness flexibility to be used as a masking material for trench definition and can be removed from the defined polygate structures without any damage to underlying materials. Even further still, there is a need for a gate mask process that effectively balances optical and etching efficiencies. 
     Conventionally, a carbon bilayer ARC, such as SiON or SiRN having a thickness of 100 to 600 Angstroms can be used over a high temperature oxide (HTO) hardmask to act as anti-reflective material needed for control of the critical dimensions during lithographic exposures. The ARC materials allow controlled patterning of an underlining HTO hardmask using conventional deep ultraviolet (DUV) photolithographic and dry etch techniques. The DUV photoresist is applied, exposed and developed on top of the ARC layer forming a narrow trench structures in the resist film. 
     Dry etching the ARC and the underlying HTO hardmask layer transfers narrow space features to the HTO hard mask. After the hardmask is patterned, the remaining resist and the ARC material must be removed to allow the formation of the spacer material which allows further reduction of the narrow space between two structures formed during HTO etch. In conventional processes, the stripping of carbon bilayer ARC by dry etching or conventional wet stripping techniques damages the sensitive underlying, oxide-nitride-oxide (ONO) stack and degrades the quality of the device. The combined HTO and spacer hardmask is used to etch the exposed polysilicon with the intention to form submicron spaces between adjacent poly lines in the core. 
     Thus, there is a need for a carbon/nitride CVD-bilayer ARC that acts as an anti-reflective coating, hard mask and can be easily stripped without damage to the underlying layer. Further, there is a need to consume the thin resist during the, top nitride etch, and consume the nitride and the some of the carbon layers during HTO hard mask etch such that the remaining carbon ARC can be stripped by plasma ashing, which does not damage the ONO stack. Further, there is a need to use bilayer CVD ARC as it is superior to more conventional organic spin-on ARC because bilayer CVD ARC is conformal, providing a uniform reflectivity everywhere. Even further, there is a need for simultaneous printing of peripheral poly circuitry. 
     SUMMARY OF THE INVENTION 
     An exemplary embodiment is related to a method of providing a carbon/nitride CVD bilayer ARC that acts as an anti-reflective coating hard mask and can be easily stripped without damage to the underlying layer. This method can include providing a first layer (e.g., carbon) and a second layer (e.g., nitride) as a CVD bilayer ARC above a desired substrate and patterning spaces in the first layer using a DUV resist and patterning the second carbon layer of the ARC using the first layer as a mask. This method also includes patterning HTO hardmask layer using patterned bilayer ARC as a mask. The remaining carbon ARC layer is ashed away after complete patterning of narrow spaces in the HTO hardmask layer. 
     Another exemplary embodiment is related to a method of using low energy ashing to reduce damage effects on an oxide-nitride-oxide stack. This method can include providing a photoresist layer above a bilayer anti-reflective coating (ARC) above a hardmask layer above a polysilicon layer above an oxide-nitride-oxide stack above a substrate, patterning trenches in the photoresist layer, patterning the bilayer ARC and the hardmask layer using the patterned photoresist layer and the bilayer ARC as a mask, plasma ashing to remove the remaining bilayer ARC layer, providing spacer material over the patterned hardmask layer, removing portions of the spacer material, and defining spaces in the polysilicon layer using the spacer material and patterned hardmask layer. 
     Another exemplary embodiment is related to a method of forming spaces in poly wordlines. This method can include providing a carbon-nitride bilayer coating (ARC) over a hardmask layer, patterning the bilayer ARC and the hardmask layer using a photoresist pattern, using the photoresist pattern to etch a top layer in the bilayer ARC, using the top etched layer to transfer a desired pattern into a bottom layer in the bilayer ARC using the bottom layer to transfer the desired pattern into a poly layer and removing the remaining bilayer ARC by ashing, thus providing a method of using the patterned hardmask to form spaces in a poly layer below the patterned hardmask layer. 
     Other principle features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The exemplary embodiments will hereafter be described with reference to the accompanying drawings, wherein like numerals denote like elements, and: 
     FIG. 1 is a schematic cross-sectional view of a portion of an integrated circuit, showing a poly layer formed over an oxide-nitride-oxide (ONO) stack; 
     FIG. 2 is a schematic cross-sectional view of a portion of an integrated circuit, showing a high temperature oxide (HTO) silicon oxide (SiO 2 ) hardmask formed over a poly layer; 
     FIG. 3 is a schematic cross-sectional view of a portion of an integrated circuit, showing an chemical vapor deposition (CVD) bilayer anti-reflective coating (ARC) formed over a hardmask; 
     FIG. 4 is a schematic cross-sectional view of a portion of an integrated circuit, showing a photoresist deposited and imaged to form narrow trenches; 
     FIG. 5 is a schematic cross-sectional view of a portion of an integrated circuit, showing resist used as mask for etching of a bilayer CVD ARC and HTO hardmask in which a top layer of the bilayer ARC is eroded away during a HTO hardmask etch leaving remaining carbon layer exposed; 
     FIG. 6 is a schematic cross-sectional view of a portion of an integrated circuit, showing that a carbon layer on top of the HTO hardmask is ashed away to leave a patterned hardmask without damage to doped polylayer and ONO stack; 
     FIG. 7A is a schematic cross-sectional view of a portion of an integrated circuit, showing an oxide-based spacer or hardmask material deposited over a patterned hardmask; and 
     FIG. 7B is a schematic cross-sectional view of a portion of an integrated circuit, showing spaces formed in a poly layer in accordance with an exemplary embodiment. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     FIG. 1 illustrates a schematic cross-sectional view representation of a portion  100  of an integrated circuit, including a silicon substrate  110 , an oxide-nitride-oxide (ONO) stack  120 , and a poly layer  130 . Portion  100  is preferably part of an ultra-large-scale integrated (ULSI) circuit having millions or more transistors. Portion  100  is manufactured as part of the integrated circuit on a semiconductor wafer, such as a silicon wafer. 
     As described below, an advantageous process can use an amorphous carbon layer in conjunction with a silicon rich nitride (SiRN) film applied by chemical vapor deposition (CVD). The carbon layer and SiRN layer can be used as anti-reflective coating (ARC) material as well as masking material needed for the patterning of a high temperature oxide (HTO) hardmask used for the definition of spaces in polysilicon word lines. 
     ONO stack  120  can be multiple layers of dielectric materials, such as silicon oxide and silicon nitride. In an exemplary embodiment, ONO stack  120  has a thickness of 30-100 Angstroms for each oxide nitride oxide layer. ONO stack  120  can include 1-5 layers. ONO stack  120  can be located above silicon substrate  110  and below poly layer  130 . ONO stack  120  can be deposited by any of a variety of deposition processes. In an exemplary embodiment, poly layer  130  has a thickness of 500-1000 Angstroms and is deposited by conventional deposition techniques. Poly layer  130  can be polysilicon. 
     FIG. 2 illustrates portion  100  described with reference to FIG. 1 with the addition of a high temperature oxide (HTO) SiO 2  hardmask layer  140  formed over poly layer  130 . In an exemplary embodiment, SiO 2  hardmask layer  140  has a nominal thickness of 300 to 1000 Angstroms. SiO 2  hardmask layer  140  can be deposited over poly layer  130  by conventional deposition techniques. 
     FIG. 3 illustrates portion  100  described with reference to FIGS. 1-2 with the addition of an carbon-nitride bilayer chemical vapor deposition (CVD) anti-reflective coating (ARC)  150  provided over SiO 2  hardmask layer  140 . In an exemplary embodiment, bilayer CVD ARC  150  can have a thickness of 300-1000 Angstroms of carbon ARC and 100-500 Angstroms of nitride and is deposited by a CVD deposition technique. 
     Bilayer CVD ARC  150  can have selectively chosen thickness designed for optical properties needed to provide good critical dimension (CD) control. Further, thickness can be selected based on the erosion rates during etch of the hard mask. For example, in an exemplary embodiment, the top nitride layer of bilayer ARC  150  should be thin enough to withstand the carbon layer patterning and to erode away during HTO hard mask etch, thus allowing the remaining carbon ARC to be stripped with oxygen plasma which does not damage the underlying poly layer  130  and ONO stack  120 . 
     FIG. 4 illustrates portion  100  described with reference to FIGS. 1-3 with the addition of a photoresist layer  160  provided over bilayer CVD ARC  150  and patterned to form trenches  162  and  164 . Trenches  162  and  164  can have widths of 140-100 nm. Photoresist layer  130  can be deposited by conventional spin application methods and imaged by KRF (DUV) or ARF radiation of the photoresist material. 
     FIG. 5 illustrates portion  100  described with reference to FIGS. 1-4 in which patterned photoresist layer  160  is used as a mask for an etch of bilayer CVD ARC  150  and SiO 2  hardmask layer  140 . The etch of bilayer CVD ARC  150  and SiO 2  hardmask layer  140  removes material below trenches  162  and  164 . Thus, removed portions of bilayer CVD ARC  150  and SiO 2  hardmask layer  140  can have a width of approximately 100-40 nm where trenches  162  and  164  have widths of 100-140 nm. 
     FIG. 6 illustrates portion  100  described with reference to FIGS. 1-5 in which photoresist layer  160  and the top layer of the bilayer CVD ARC are eroded during the SO 2  hardmask etch and remaining second layer of the bilayer ARC  150  is ashed away. Ashing is a procedure by which the carbon layer of the bilayer CVD ARC  150  can be removed or stripped without damaging the underlying poly or the ONO stack  120 . Ashing can involve introduction of a plasma of O 2  ions. After the plasma ashing procedure, a patterned SiO 2  hardmask layer  140  remains over poly layer  130 . 
     In an exemplary embodiment, ashing can be performed in a non-oxygen gas or trace oxygen forming gas plasma process. Portion  100  is exposed to an O 2  plasma that selectively removes photoresist layer  160  without damaging polysilicon and ONO stack  120 . In a preferred embodiment, the plasma used is non-oxygen forming gas plasma. For example, in a preferred embodiment a non-oxygen forming gas plasma may be used that contains up to 20% of combined hydrogen gas (H 2 ) and nitrogen gas (N 2 ). 
     FIG. 7A illustrates portion  100  described with reference to FIGS. 1-6 in which an oxide-based spacer hardmask material  200  is deposited over SiO 2  hardmask layer  140 . Spacer hardmask material  200  is to conformally cover the SiO 2  hardmask layer  140 , as well as lateral side walls and the bottoms of trenches  210  formed in the patterning of SiO 2  hardmask layer  140 . In an exemplary embodiment, spacer hardmask material  200  can have a thickness of 20-100 Angstroms. Spacer hardmask material  200  can include materials, such as SiO 2 . 
     FIG. 7B illustrates portion  100  described with reference to FIGS. 1-7A with the addition of trenches  230  formed in poly layer  130 . In an exemplary embodiment, trenches  230  have a width of 50 to 70 Angstroms. Trenches  230  are defined in part using a high temperature oxide (HTO) and a spacer hardmask material  200 . The purpose of trenches  230  is to form a subresolution spaces between two adjacent poly wordlines. 
     After etching of the poly layer  130  using layer  140 , hardmask layer  140  and spacer hardmask material  200  are removed from the polysilicon using acid bath dips. 
     Advantageously, a carbon/nitride CVD bilayer ARC in this exemplary embodiment acts as a anti-reflective coating hard mask and can be easily stripped without damage to the underlying layers. The stripping of the CVD bilayer ARC is possible because the thin resist is consumed during the top nitride etch, the nitride and the some of the carbon layers are consumed during HTO hard mask etch, and the remaining carbon ARC is stripped by plasma ashing which does not damage the underlying poly and an ONO stack. Further, the use of the bilayer CVD ARC is superior to more conventional organic spin-on ARC because bilayer CVD ARC is conformal, providing a uniform reflectivity control that in turn provides tight CD control of the described method. Further, the method described with references to FIGS. 1-7B includes the ability to remove the remaining ARC material using ashing process as opposed to a conventional SiON ARC dry etch which causes damage to the underlying layers. Use of low-energy ashing does not damage the polysilicon or the ONO layers used to store charge in flash memory devices. As such, the reliability of dual-bit flash devices can be improved. 
     While the exemplary embodiments illustrated in the FIGURES and described above are presently preferred, it should be understood that these embodiments are offered by way of example only. Other embodiments may include, for example, different material layers as well as additional or combined steps in the process. The invention is not limited to a particular embodiment, but extends to various modifications, combinations, and permutations that nevertheless fall within the scope and spirit of the appended claims.