Abstract:
A composition for removing photoresist and bottom anti-reflective coating from a semiconductor substrate is disclosed. The composition may comprise a nontoxic solvent, the nontoxic solvent having a flash point above 80 degrees Celsius and being capable of dissolving acrylic polymer and phenolic polymer. The composition may further comprise Tetramethylammonium Hydroxide (TMAH) mixed with the nontoxic solvent.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Noon This application is a divisional and claims priority to U.S. patent application Ser. No. 12/970,421, filed 16 Dec. 2010, which is entirely incorporated by reference herein for all purposes. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to the field of resist-removing solutions and particularly to a composition and method for removing photoresist and bottom anti-reflective coating for a semiconductor substrate. 
       BACKGROUND 
       [0003]    Semiconductor device fabrication is the process used to create integrated circuits that are present in electrical and electronic devices. The fabrication process includes a sequence of photographic and chemical processing steps during which electronic circuits are gradually created on a substrate made of semiconductor materials. A typical substrate is made out of silicon, and is sliced and polished to obtain a regular and flat surface. 
         [0004]    Once the substrate is prepared, many process steps are necessary to produce the desired semiconductor integrated circuit. Such steps can be grouped into two major parts: Front End of Line (FEOL) processing and Back End of Line (BEOL) processing. FEOL processing refers to the formation of the transistors directly in the silicon. In FEOL processing, a semiconductor substrate is developed by the growth of an ultrapure, virtually defect-free silicon layer through epitaxy. Additional steps performed in the FEOL process include: growth of the gate dielectric (traditionally silicon dioxide), patterning of the gate, patterning of the source and drain regions, and subsequent implantation or diffusion of dopants to obtain the desired complementary electrical properties. 
         [0005]    Patterning refers to a series of steps that form or alter the existing shape of the deposited materials on the substrate. During patterning, the substrate is coated with a layer of photoresist. The photoresist is then exposed to a pattern of intense light, and the areas of the photoresist that are exposed to the intense light become soluble in a developer solution. A layer of anti-reflective coating may be utilized to reduce reflections during the exposure. The anti-reflective coating may be located at the bottom of the photoresist, and may be referred to as the bottom anti-reflective coating (BARC) layer. After the exposure, the developer solution is utilized to remove the exposed photoresist, and the remaining photoresist is solidified to form a protection for the underlying substrate during etching. 
         [0006]    Etching refers to a step of utilizing chemical agents to remove the uppermost layer of the substrate in the areas that are not protected by the remaining photoresist. Upon completion of the etching process, the remaining photoresist and anti-reflective coating are no longer needed and must be removed from the substrate. The photoresist may be removed utilizing plasma ashing, in which a plasma containing oxygen is used to oxidize the photoresist. Deionized (DI) water may be used subsequently for DI water cleaning. However, plasma ashing processes may damage refractory gate metals such as TiN, TaN and high-k dielectrics such as HfO 2  or HfSiO x . Furthermore, removal of the photoresist may be difficult in areas that have been exposed to electron beam (ebeam) bombardment as a result of polymer cross-linking (e.g., if the substrate has been exposed to a post-lithography critical dimension scanning electron microscopy (CDSEM) metrology step and has been exposed to localized areas of ebeam dosing). 
         [0007]    Alternatively, a liquid photoresist removing solvent may be utilized to chemically alter the photoresist so that it no longer adheres to the substrate. Such removal processes are referred to as wet processes. However, a requirement for a reduction in the environmental safety and health (ESH) impact of such solvents has changed. For instance, N-methyl-pyrrolidone (NMP), solvent used in photoresist and BARC removal, could be classified as reprotoxic. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The numerous advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying figures in which: 
           [0009]      FIG. 1  is a flow diagram illustrating a method for removing photoresist and BARC in a front end of line process; and 
           [0010]      FIG. 2  is a block diagram illustrating a composition including an organic and nontoxic solvent and Tetramethylammonium Hydroxide (TMAH). 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
         [0012]    The present disclosure is directed to a composition and method for removing photoresist and BARC in a front end of line process. A nontoxic composition and a wet process is disclosed that is capable of removing both photoresist and BARC from a semiconductor substrate without damaging the refractory gate metals such as TiN, TaN and high-k dielectrics. In addition, the composition and the wet process are capable of removing both photoresist and BARC on the substrate in a relatively short amount of time. 
         [0013]      FIG. 1  shows a flow diagram illustrating steps performed by a method  100  for removing photoresist and BARC from a semiconductor substrate in a front end of line process. Step  102  may receive the substrate with photoresist and/or BARC that need to be removed. Step  104  may apply a composition to the substrate to dissolve the photoresist and BARC within approximately 1 minute or less. The substrate may be removed from the composition in step  106  once the photoresist and BARC are removed. 
         [0014]    Referring to  FIG. 2 , an illustration depicting the composition  200  of the present disclosure is shown. The composition  200  includes a blend of organic solvents  202  that has an appropriate concentration of a strong base  204  and/or an oxidant. The solvent blend may dissolve photoresist and BARC within approximately 1 minute or less without attacking refractory metal or a high-k oxide of a semiconductor. Furthermore, a solvent blend with short process time also means that a single wafer wet tool may be utilized for resists removals. 
         [0015]    The composition  200  is also capable of removing electron beam (ebeam) hardened resist for areas of the semiconductor that may have been exposed to ebeams as a result of polymer cross-linking. For example, the semiconductor substrate may be exposed to a post-lithography critical dimension scanning electron microscopy (CDSEM) metrology, which may expose the substrate to localized areas of electron beams and harden the photoresist that remains on the substrate. The ebeam hardened photoresist may be difficult to remove utilizing plasma ashing. However, the composition  200  of the present disclosure is capable of removing ebeam hardened photoresist efficiently. 
         [0016]    In one embodiment, the materials (chemical formulations) of solvent  202  may be selected based on their Hansen Solubility parameters. The selected materials may be nontoxic (e.g., based on ESH criteria), having high flash points (e.g., above 80 degrees Celsius) and capable of dissolving both acrylic polymer and phenolic polymer. In addition, the selected materials for solvent  202  may be selected based on their efficiencies in dissolving photoresist materials such as ultraviolet photoresist. Furthermore, the selected materials for solvent  202  may have high polarity and may be required to mix well with water. For instance, a suitable material for solvent  202  may be N-(2-Hydroxyethyl)-2-Pyrrolidone (NHEP), Diethylene Glycol Monomethyl Ether (DEGME), or Dimethyl Sulfoxide (DMSO). 
         [0017]    Base  204  may be added to the solvent  202  for BARC removal. The mixture of the solvent  202  and the base  204  may produce a composition  200  having a pH less than approximately 9. In one embodiment, Tetramethylammonium Hydroxide (TMAH) is utilized as the base  204 . The concentration of TMAH in the composition  200  is specifically blended so that the composition  200  does not attack the refractory metal such as TiN and TaN or the high k material such as HfO x  or HfSiO x  during the resist-removal process. 
         [0018]    TMAH is a quaternary ammonium salt with the molecular formula (CH 3 ) 4 NOH. It is a phase transfer catalysis that facilitates acceleration of the reaction from one phase into another phase where reaction occurs. In the presence of TMAH, ionic reactants are easily soluble in the organic solvent  202 . The amount and concentration of TMAH may be optimized to selectively etch BARC layer but not over-etch the gate metals such as TiN, TaN and high-k dielectrics such as HfO x  or HfSiO x . 
         [0019]    For instance, if NHEP is utilized as the solvent  202 , then the addition of TMAH to NHEP produces a composition  200  (having a concentration of approximately 2.5% of TMAH by volume) that may allow the composition  200  to dissolve both photoresist and BARC on the semiconductor within 1 minute or less. In another example, if DEGME is utilized as the organic solvent, then the addition of TMAH to DEGME produces another composition  200  (having a concentration of no more than approximately 2.5% of TMAH by volume) that may dissolve both photoresist and BARC on the semiconductor within 1 minute or less at the temperature of approximately 50 degrees Celsius. In still another example, if DMSO is utilized as the organic solvent, then the addition of TMAH to DMSO produces still another composition  200  (having a concentration of no more than approximately 2.5% of TMAH by volume) that may dissolve both photoresist and BARC on the semiconductor within approximately 1 minute or less at the temperature of approximately 60 degrees Celsius. 
         [0020]    The effectiveness and the optimal chemical formulations of the composition of the present disclosure may be tested and determined utilizing a high throughput approach. To reduce the number of substrates used for testing and product development, the etch rates of all the films of interest may be tested on blanket substrates by varying the process condition. This may include testing the etch rates on photoresist, BARC, the underlying refractory material, and the high-k. The composition being tested may include various types of solvent and formulations mixed with different concentrations of base (TMAH). In addition, the tests may be conducted under different testing conditions, such as varying temperatures and varying agitation to the composition fluid (e.g. stirrer speed). In one embodiment, a high productivity combinatorial (HPC) system may be utilized to quickly generate a set of libraries for the various compositions being tested. An exemplary HPC system is disclosed in: Combinatorial Process System, U.S. patent application Ser. No. 12/027,980, which is herein incorporated by reference in its entirety. Furthermore, the effectiveness of removing ebeam or CDSEM hardened photoresist utilizing the composition of the present disclosure is also tested. For example, the CDSEM hardened photoresist may be reproduced for testing purposes utilizing a flood gun dose that matches the CDSEM dose on a real product substrate. 
         [0021]    It is believed that the present invention and many of its attendant advantages will be understood by the foregoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely an explanatory embodiment thereof, it is the intention of the following claims to encompass and include such changes.