Patent Publication Number: US-11651952-B2

Title: Using sacrificial polymer materials in semiconductor processing

Description:
PRIORITY INFORMATION 
     This application is a Continuation of U.S. application Ser. No. 16/676,881, filed on Nov. 7, 2019, which is a Continuation of U.S. application Ser. No. 15/904,777, filed on Feb. 26, 2018, issued U.S. Pat. No. 10,497,558 on Dec. 3, 2019, the contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to semiconductor processing, and, more particularly, to using sacrificial polymer materials in semiconductor processing. 
     BACKGROUND 
     Semiconductor processing (e.g., fabrication) can be used to form semiconductor devices, such as integrated circuits, memory devices, microelectromechanical devices (MEMS), etc. 
     Examples of memory devices that can be formed by semiconductor processing include, but are not limited to, volatile memory (e.g., that can require power to maintain its data), such as random-access memory (RAM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), among others, and non-volatile memory (e.g., that can provide persistent data by retaining stored data when not powered), such as NAND flash memory, NOR flash memory, read only memory (ROM), electrically erasable programmable ROM (EEPROM), erasable programmable ROM (EPROM, among others. 
     Semiconductor processing can involve forming features (e.g., patterns) on and/or in a substrate, such as a semiconductor substrate (e.g., of silicon), that may be referred to as a wafer. In some examples, one or more materials, such as silicon-based materials (e.g., silicon oxide (SiO), silicon nitride (SiN), tetraethyl orthosilicate (TEOS), and/or polysilicon), conductors, etc. may be formed on the semiconductor. For instance, a deposition process, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), electrochemical deposition and/or molecular beam epitaxy, among others may be used to form the materials on the semiconductor. 
     Subsequently, portions of the one or more materials, and in some instances, portions of the semiconductor, may be removed, such as by wet and/or dry etching, to form the features. In some examples, the features may have high aspect ratios (e.g., ratios of height to width or diameter) and may be referred to as high-aspect-ratio (HAR) features. For example, the features might be separated from each other by HAR openings. 
     During processing, the substrate and the features may be subjected to wet processing, such as wet cleaning, and subsequent drying. For example, wet cleaning can be helpful to remove residue left behind, such as by the removal process or other processing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    presents various examples of feature toppling. 
         FIG.  2    is a block diagram illustration of a processing apparatus used in conjunction with the processing steps associated with forming a semiconductor device, in accordance with a number of embodiments of the present disclosure. 
         FIGS.  3 A- 3 G  illustrate cross-sectional views of processing steps associated with forming a semiconductor device, in accordance with a number of embodiments of the present disclosure. 
         FIG.  4    is a block diagram illustration of an apparatus formed, at least in part, in accordance with a number of embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure includes processing methods, such as semiconductor processing methods, associated with forming semiconductor devices, such as integrated circuits, memory devices, MEMS, among others. For example, one such method may perform a wet cleaning process to clean a structure having features and openings between the features while preventing drying of the structure. After performing the wet cleaning process, the method may deposit a polymer solution in the openings while continuing to prevent any drying of the structure. The method may then form a sacrificial polymer material in the openings from the polymer solution. The structure may be used in semiconductor devices, such as integrated circuits, memory devices, MEMS, among others. 
     Embodiments of the present disclosure provide technical advantages, such as reducing the likelihood of feature toppling (e.g. collapse) during processing, compared to previous approaches. For example, in some previous approaches, capillary forces in the openings, resulting from drying the features after wet cleaning, can cause the features to topple (e.g., collapse) into each other. For example,  FIG.  1    illustrates a feature  101  toppling into an adjacent feature and a pair of adjacent features  102  toppling into each other (e.g. in what is sometimes referred to as bridging) because of such capillary forces. This can lead to defects in the semiconductor device, and can even render the semiconductor device inoperable. 
     The embodiments disclosed herein solve the problem of feature toppling, resulting from drying occurring after wet cleaning. After wet cleaning, the features and the structure in which the features are formed are maintained in a fully (e.g., completely) wet state and a polymer solution is deposited in the openings between the features while preventing any drying from occurring. Subsequently, the polymer solution is baked to form a sacrificial polymer in the openings. This process prevents drying from occurring in the openings that can lead to feature toppling. 
     In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown, by way of illustration, specific examples. In the drawings, like numerals describe substantially similar components throughout the several views. Other examples may be utilized and structural and electrical changes may be made without departing from the scope of the present disclosure. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present disclosure is defined only by the appended claims and equivalents thereof. 
     The term semiconductor can refer to, for example, a material, a wafer, or a substrate, and includes any base semiconductor structure. “Semiconductor” is to be understood as including silicon-on-sapphire (SOS) technology, silicon-on-insulator (SOI) technology, thin-film-transistor (TFT) technology, doped and undoped semiconductors, epitaxial silicon supported by a base semiconductor structure, as well as other semiconductor structures. Furthermore, when reference is made to a semiconductor in the following description, previous process steps may have been utilized to form regions/junctions in the base semiconductor structure, and the term semiconductor can include the underlying materials containing such regions/junctions. 
     The figures herein follow a numbering convention in which the first digit or digits correspond to the drawing figure number and the remaining digits identify an element or component in the drawing. Similar elements or components between different figures may be identified by the use of similar digits. As will be appreciated, elements shown in the various embodiments herein can be added, exchanged, and/or eliminated so as to provide a number of additional embodiments of the present disclosure. In addition, as will be appreciated, the proportion and the relative scale of the elements provided in the figures are intended to illustrate the embodiments of the present disclosure, and should not be taken in a limiting sense. 
       FIG.  2    is a block diagram illustration of a processing apparatus  203 , such as a semiconductor processing apparatus, that can be used in conjunction with the processing steps associated with forming a semiconductor device, in accordance with a number of embodiments of the present disclosure. Apparatus  203  includes a dry-removal component  204 , such as a dry-removal chamber (e.g., a dry-etch tool), that can be used to form features. Apparatus  203  includes a wet cleaning component  205 , such as a wet cleaning chamber (e.g., a wet cleaning tool), that can be used to perform wet cleaning operations to remove residues resulting from forming the features using dry-removal component  204 . In some examples, a polymer solution may be deposited at wet cleaning component  205  after performing wet cleaning operations, in accordance with a number of embodiments of the present disclosure. 
     Apparatus  203  includes a baking component  206 , such as a baking chamber, that can be used to bake the polymer solution to form a sacrificial polymer material, in accordance with a number of embodiments of the present disclosure. In some examples, baking component  206  and wet cleaning component  205  may be in different chambers of apparatus  203 . Baking component  206  and wet cleaning component  205  may be in different tools or part of the same tool. 
     A temperature controller  207  can be used to set and control the temperature of baking component  206 . For example, temperature controller  207  can be used to set the baking temperature at which the polymer solution is baked. A pressure controller  208  can be used to set and control the pressure of baking component  206 . 
     Apparatus  203  includes a polymer-removal component  209 , such as a polymer-removal chamber (e.g., a polymer-removal tool), that can be used to remove the sacrificial polymer material, in accordance with a number of embodiments of the present disclosure. For example, polymer-removal component  209  may use plasma process, such as plasma ashing (e.g., plasma stripping) to remove the sacrificial polymer. A pump  210 , such as a vacuum pump, may be used to increase or decrease the pressure in the polymer removal component  209  in which the removal process may be performed and, for example, for removing ash that may be formed during the removal process. A temperature controller  211  can be used to set and control the temperature of polymer-removal component  209 . For example, temperature controller  211  can be used to set the temperature at which the sacrificial polymer material is removed. For example, the temperature of the sacrificial polymer material may be allowed equilibrate to the temperature of polymer-removal component  209  before the sacrificial polymer material is removed, so that the sacrificial polymer material can be removed while at that temperature. 
     Apparatus  203  includes a deposition component  213 , such as a deposition chamber (e.g., a deposition tool), that can be used to deposit materials after the sacrificial polymer material is removed. A temperature controller  214  can be used to set and control the temperature of deposition component  213 . A pressure controller  215  can be used to set and control the pressure of deposition component  213 . 
       FIGS.  3 A- 3 G  illustrate cross-sectional views of processing steps, such as of a semiconductor processing method, associated with forming a semiconductor device, such as a portion of an integrated circuit, a memory device, a MEMS, among others, in accordance with a number of embodiments of the present disclosure. For example, the processing steps may be associated with forming (e.g., a memory array of) a DRAM memory device, a NAND flash memory device, a NOR flash memory device, capacitors, among others. 
       FIG.  3 A  depicts a structure (e.g., to be used in a semiconductor device) after several processing steps have occurred. The structure may include a base structure, such as a substrate  320  (e.g., a semiconductor). In some examples, one or more materials  324 , such as silicon-based materials, conductive materials (e.g., metals), among others, may be formed on (e.g., over) a surface  322 , such as an upper surface, of substrate  320 , using, for example, a deposition process, such as PVD, CVD, ALD, electrochemical deposition and/or molecular beam epitaxy, among others. 
     Features  326 , such as nanofeatures (e.g., having a width or diameter of about 0.1 nanometer to about 100 nanometers) are formed by removing portions of the structure, such as portions of the one or more materials  324  and portions of substrate  320 . The removal process forms openings  328 , such as spaces (e.g., trenches), through the one or more materials  324 , stopping above, on, or in (e.g., as shown in  FIG.  3 A ) substrate  320 . For example, an opening  328  may be between adjacent features  326 . In some examples, each of the respective features  326  includes the one or more materials  324  and a portion of substrate  320 . 
     In some examples, portions of the openings  328  in substrate  320  (e.g., below surface  322 ) may correspond to isolation regions, such as shallow trench isolation (STI) regions. In an example, a feature  326  may be entirely of substrate  320 , and openings  328  may correspond to STI regions. In another example, features  326  include a conductive material, such as a metal, conductively doped silicon, among others. For example, features  326  may be access lines, such as word lines, data lines, such as bit lines, in a memory array, or capacitor plates, among others. In some examples, features  326  may be memory cells, such asnon-volatile memory cells, and may include a tunnel dielectric on surface  322 , a charge storage structure, such as a charge trapping structure, a floating gate, or the like, on the tunnel dielectric, and a control gate (e.g., that may be coupled to or form a portion of an access line) on the charge storage structure. Features  326  may be HAR features, and openings  328  may be HAR openings. For example, a HAR may have an aspect ratio of greater than 10 to 1. 
     In some examples, openings  328 , and thus the structure in  FIG.  3 A , may be formed using a dry removal process, such as a dry etch. A mask (not shown), such as imaging resist (e.g., photo-resist), may be formed over the one or more materials  324  and patterned to expose regions of the one or more materials  324 . The exposed regions may be subsequently removed, such as by the dry etch process, to form openings  328  that may terminate on or in substrate  320 . 
     After the dry processing, a wet cleaning process may be performed on the structure of  3 A to remove residues that can form on exposed surfaces of substrate  320  and features  326 , such as in openings  328 . For example, the wet cleaning process may be performed while maintaining the entire structure in  FIG.  3 A  in a fully wet state, without allowing any drying of the structure to occur (e.g., while preventing any drying of the structure). For example, the various liquids applied during the wet clean may be applied continuously with no stopping so as to avoid any drying. 
     In some examples, the wet cleaning process may include an aqueous wet clean that may include hydrofluoric acid (HF). In an example, an aqueous wet clean may include a standard clean-1 (SC-1) that may include deionized (DI) water, aqueous ammonium hydroxide, and aqueous hydrogen peroxide. For example, the standard clean-1 may be performed before and after applying the HF. In some instances, a standard clean-2 (SC-2) that may include deionized (DI) water, aqueous hydrochloric acid, and aqueous hydrogen peroxide may be performed after the standard clean-1 as part of the aqueous wet clean. The wet cleaning process may further include the aqueous wet clean followed by a liquid DI water rinse. 
       FIG.  3 B  illustrates a DI rinse in which the structure of  FIG.  3 A  is fully wetted with DI water  332  and openings  328  are overfilled with liquid DI water  332 . For example, the structure is completely covered with DI water  332  in  FIG.  3 B . In some examples, the various components (e.g., liquids) of the wet cleaning process may be spin coated onto the structure while the structure is spinning. 
     In  FIG.  3 C , DI water  332  in  FIG.  3 B  is completely displaced by a liquid solvent  334 . For example, solvent  334  may be deposited in openings  328  so that openings are overfilled with solvent  334  while preventing any drying of the structure from occurring, such as while maintaining the structure in a fully wetted state. For example, the transition between depositing DI water  332  and solvent  334  may occur continuously without any breaks between the flow of DI water  332  and the flow of solvent  334  so as to avoid any drying, and thus avoiding any drying-induced toppling of features  326 . For example, solvent  334  may be spin coated onto the structure while the structure is spinning. In some examples, solvent  334  may be isopropanol, acetone, methanol, cyclohexanone, among others. 
     In  FIG.  3 D , the solvent  334  in  FIG.  3 C  is completely displaced by a liquid polymer solution  336 . For example, polymer solution  336  may be deposited in openings  328  so that openings are overfilled with polymer solution  336  while preventing any drying of the structure from occurring, such as while maintaining the structure in a fully wetted state. For example, the transition between depositing the solvent  334  and polymer solution  336  may occur continuously without any breaks between the flow of solvent  334  and the flow polymer solution  336  so as to avoid any drying, and thus avoiding any drying-induced toppling of features  326 . For example, polymer solution  336  may be spin coated onto the structure while the structure is spinning. 
     In some examples, polymer solution  336  may include a polymer resin, such as polymethylmethacrylate, polymethacrylate, polyhydroxystyrene, among others, dissolved in a solvent, such as propylene glycol monomethyl ether acetate, isopropanol, among others. In some examples, solvent  334  is miscible in polymer solution  336 , such as in the solvent of polymer solution  336 . For example, at least some of solvent  334  may be dissolved in the solvent of polymer solution  336  as polymer solution  336  is being deposited. 
     The structure of  FIG.  3 D  may be subsequently baked to form the sacrificial polymer material  340  (e.g., a polymer matrix) in  FIG.  3 E . For example, sacrificial polymer material  340  overfills openings  328 . In some examples, the structure of  FIG.  3 D  is moved to a baking chamber while preventing any drying from occurring, such as by keeping the structure covered with polymer solution  336 , as shown in  FIG.  3 D . 
     In some examples, the temperature of the baking chamber may be set to a temperature that is less than a decomposition temperature of sacrificial polymer material  340 . Baking may continue until the temperature of the structure, and thus sacrificial polymer material  340 , is brought to a bake temperature, that, in some examples, may be equal to the temperature of the baking chamber. In some examples, sacrificial polymer material  340  may be a pseudo-solid, such as a gel. In some instances, some solvent may remain in sacrificial polymer material  340  at the end of baking when sacrificial polymer material  340  is at the bake temperature. For example, sacrificial polymer material  340  may include the polymer resin and some of the solvent. 
     Subsequently, the structure may be moved to a polymer-removal chamber in which sacrificial polymer material  340  is removed to re-expose (e.g., reopen) the openings  328  between features  326 , as shown in  FIG.  3 F . Sacrificial polymer material  340  may be removed using a plasma process, such as a plasma ashing process (e.g., a plasma stripping process). For example, sacrificial polymer material  340  is completely removed in  FIG.  3 F . Note that the structure in  FIG.  3 F  is completely cleaned as a result of the wet cleaning process, and is ready for subsequent processing. For example, the processing steps of displacing DI water  332  with solvent  334  in  FIG.  3 C , displacing solvent  334  with polymer solution  336  in  FIG.  3 D , baking polymer solution  336  to form sacrificial polymer material  340  in  FIG.  3 E , and removing sacrificial polymer material  340  in  FIG.  3 F , does not introduce any additional contaminants and prevents any drying-induced toppling of features  326 . 
     In some examples, a difference between the temperature of the sacrificial polymer material  340  at the end of baking (e.g., the bake temperature) and the temperature of the sacrificial polymer material  340  while removing sacrificial polymer material  340  (e.g., the removal temperature) may act to prevent features  326  from toppling (e.g., into each other) during the removal process. For example, the removal temperature may be set to a temperature so that such a temperature difference is attained. For example, the temperature of a chuck of a tool that holds the structure, such as the chuck of an ash tool, may be modified to change the temperature of the structure of  FIG.  3 E  to the removal temperature. Sacrificial polymer material  340  may then be removed while the temperature of the structure of  FIG.  3 E  is at the removal temperature. 
     In some situations, if the removal temperature is much greater than (e.g., greater than about 50° C.) the bake temperature, features  326  may topple during the removal. For example, bubbles may form in polymer material  340  (e.g., adjacent to substrate  320 ), resulting in the toppling of features  326 . For instance, toppling may occur if the bake temperature is at a temperature recommended by the polymer manufacturer for baking and the removal temperature is at temperature typically recommended for ashing. 
     In some examples, the temperature difference between the bake temperature and the removal temperature necessary to reduce (e.g., prevent) toppling (e.g., bubbling) during the removal of sacrificial polymer material  340  is having the removal temperature being less than about 50° C. above the bake temperature, the removal temperature being 0° C. to 30° C. above the bake temperature, the removal temperature being less than the bake temperature, and the removal temperature being up to about 100° C. less than the bake temperature. 
     In some examples, sacrificial polymer material  340  may be removed continuously, starting from an exposed surface of sacrificial polymer material  340  (e.g., upper surface  342  of sacrificial polymer material  340 ) and continuing (e.g., downward) into the structure of  FIG.  3 E . For example, sacrificial polymer material  340  may be removed using a continuous top-down process until sacrificial polymer material  340  is completely removed and openings  328  are re-exposed, as shown in  FIG.  3 F . 
     In an example, for aspect ratios greater than 22:1, the semiconductor process previously described in conjunction with  FIGS.  3 A- 3 F  was found to have an average of less than about 0.00015 toppling defects/square micron compared to an average of about 1.3 toppling defects/square micron for previous approaches in which surfaces of the features were treated to reduce capillary forces. 
     In some examples, as shown in  FIG.  3 G , a material  346  may be formed in the openings  328  in the structure of  FIG.  3 F  (e.g., in a deposition chamber). For example, material  346  may be formed in a gaseous phase or a plasma phase, such as by PVD, CVD, ALD, among others. For example, material  346  might be an epitaxial silicon material or a dielectric material, such as silicon oxide or silicon nitride. In some examples, material  346  may overfill openings  328  and extend over the upper surfaces  348  of features  326 . Subsequently, a portion of material  348  may be removed, such as by chemical mechanical planarization (CMP) so that upper surfaces  350  of material  346  are coplanar with upper surfaces  348 , as shown in  FIG.  3 G . 
     In some examples, portions below surface  322  may be isolation regions. In examples in which features  326  may be comprised entirely of substrate  320 , rather than a subsequently deposited material as previously described in conjunction with  FIG.  3 A , and the regions between features  326  containing material  346  may be isolation regions. 
       FIG.  4    is a block diagram of an apparatus, such as a memory device  460 . For example, memory device  460  may be a volatile memory device, such as a DRAM, a non-volatile memory device, such as NAND flash or NOR flash, among others. For example, memory device  460  may be formed, at least in part, using the processing previously described, such as in conjunction with  FIGS.  3 A- 3 G . 
     Memory device  460  includes a controller  462 , such as an application specific integrated circuit (ASIC), coupled to a memory array  464 , such as a DRAM array, a NAND array, a NOR array, among others. For example, memory array  464  might be formed, at least in part, according to the processing described previously. 
     The controller  462  can control the operations on the memory device  460 , and of the memory array  464 , including data sensing (e.g., reading) and data programming (e.g., writing), for example. Memory device  460  may be coupled to a host device (not shown in  FIG.  4   ). 
     Embodiments of the disclosure use sacrificial polymer materials to close openings in structures (e.g., to be used in semiconductor devices, such as integrated circuits, memory devices, MEMS, and the like), such as between features in the structures, during wet processing without allowing any drying to occur. This acts to prevent drying-induced toppling of the features that occurs in previous approaches. 
     Although specific examples have been illustrated and described herein, those of ordinary skill in the art will appreciate that an arrangement calculated to achieve the same results may be substituted for the specific embodiments shown. This disclosure is intended to cover adaptations or variations of one or more embodiments of the present disclosure. It is to be understood that the above description has been made in an illustrative fashion, and not a restrictive one. The scope of one or more examples of the present disclosure should be determined with reference to the appended claims, along with the full range of equivalents to which such claims are entitled.