Patent Publication Number: US-7723199-B2

Title: Method for cleaning post-etch noble metal residues

Description:
CROSS-REFERENCES 
     This application claims the benefit of U.S. Provisional Application No. 60/805,406 entitled “METHOD FOR CLEANING POST-ETCH MOBLE METAL RESIDUES” to Obeng, et al., filed on Jun. 21, 2006, which is incorporated herein by reference as if reproduced herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The invention is directed, in general to semiconductor devices, and more specifically, to methods for cleaning etched capacitor structures in the fabrication of semiconductor devices. 
     BACKGROUND 
     Noble metals are being increasingly used in the fabrication of various MEMS and IC semiconductor devices. E.g., noble metals are often used in the construction of components of capacitors used in ferroelectric memory cells (FRAM). Unfortunately, the patterning of such noble metal can be problematic. E.g., the etching of noble metals can leave behind a conductive by-product which short-circuits a device component. Consequently, capacitors that comprise components formed from patterned noble metals may not retain their charge because conductive by-products formed on sidewalls of the capacitor provide a route for current leakage. 
     Accordingly, what is needed is a method for manufacturing semiconductor devices that includes noble metals and that addresses the drawbacks of the prior art methods and devices. 
     SUMMARY 
     Various embodiments of a method of manufacturing a semiconductor device are provided herein. In one embodiment, the method comprises forming conductive and ferroelectric material layers on a semiconductor substrate. The material layers are patterned to form electrodes and a ferroelectric layer of a ferroelectric capacitor, wherein a conductive noble metal-containing polymer is generated on sidewalls of the ferroelectric capacitor. The method also comprises converting the conductive noble metal-containing polymer into a non-conducting metal oxide. Converting includes forming a water-soluble metal salt from the conductive noble metal-containing polymer, and reacting the water-soluble metal salt with an aqueous acidic solution to form a metal hydroxide. Converting also includes oxidizing the metal hydroxide to form the non-conducting metal oxide. 
     Another embodiment comprises a method of manufacturing an integrated circuit. The method comprises forming one or more transistors on a semiconductor substrate and depositing a pre-metal dielectric layer over the transistors. The method also comprises fabricating a ferroelectric capacitor on the semiconductor substrate. The ferroelectric capacitor is electrically coupled to at least one of the transistors. Fabricating the ferroelectric capacitor includes forming conductive and ferroelectric material layers on the pre-metal dielectric layer, and patterning the material layers to form electrodes and a ferroelectric layer of the ferroelectric capacitor. A conductive noble metal-containing polymer is generated on sidewalls of the ferroelectric capacitor. Fabricating the ferroelectric capacitor includes converting the conductive noble metal-containing polymer into a non-conducting metal oxide, as described above. 
     Still another embodiment comprises an integrated circuit. The integrated circuit comprises one or more memory cells. At least one of the memory cells includes one or more transistors on or in a semiconductor substrate, a pre-metal dielectric layer over the transistor and a ferroelectric capacitor on the pre-metal dielectric layer. The ferroelectric capacitor is electrically coupled to at least one of the transistors and includes sidewalls having a non-conducting metal oxide thereon. The non-conducting metal oxide thereon is converted from a conductive noble metal-containing polymer by the processes described above. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow diagram illustrating a method for fabricating semiconductor devices in which one or more aspects of the disclosure can be applied; and 
         FIGS. 2 to 8  present cross-sectional views of selected steps in example implementation of a method of fabricating a semiconductor device comprising an integrated circuit according to the principles of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Previous efforts to remove or clean-away conductive by-products resulting from the etching of noble metals have not been entirely successful, leading to lower-than-desired yields of devices. Embodiments of this disclosure take an alternative approach. Rather than removing conductive by-products, the conductive by-products are converted into non-conducting metal oxides. Thus, even though they remain on the device components, the non-conducting metal oxides do not short-out or cause current leakage. 
     One embodiment of the disclosure is a method of manufacturing a semiconductor device.  FIG. 1  is a flow diagram illustrating a method  100  for fabricating semiconductor devices in which one or more aspects of the disclosure can be applied. The method can include fabricating a capacitor (e.g., a ferroelectric capacitor) (step  102 ). As part of fabricating the capacitor, the method  100  can comprise forming conductive (step  105 ,  107 ) and ferroelectric material layers (step  110 ) on a semiconductor substrate. As depicted in  FIG. 1 , the layers can be formed in the sequence: form first conductive material layer ( 105 ), form ferroelectric material layers (step  110 ), and then form first conductive material layer (step  107 ). The material layers are patterned (step  115 ) to form electrodes and a ferroelectric layer of a ferroelectric capacitor. As a by-product of the patterning step  115 , a conductive noble metal-containing polymer is generated (step  120 ) on the sidewalls of the ferroelectric capacitor. 
     The term conductive layer, as used herein, refers to a metal containing layer that comprises one or more noble metals. E.g., the conductive layers can comprise one or more pure or oxides of noble metals. There can be barrier layers between the substrate and a conductive layer, or between a conductive layer and the ferroelectric layer, or overlying the insulating layer. The term ferroelectric layer, as used herein, refers to any material layer having a permanent electric dipole moment and whose polarization can be changed by application of an electric field. 
     The method  100  also comprises converting (step  125 ) the conductive noble metal-containing polymer into a non-conducting metal oxide. Converting (step  125 ), the conductive noble metal-containing polymer includes forming, in step  130 , a water-soluble metal salt from the conductive noble metal-containing polymer. In some cases forming (step  130 ) the water-soluble metal salt includes hydrolyzing the conductive noble metal-containing polymer in step  132 . In other cases forming (step  130 ) the water-soluble metal salt includes halogenating the conductive noble metal-containing polymer in step  135 . 
     Converting (step  125 ) the conductive noble metal-containing polymer further includes reacting, in step  140 , the water-soluble metal salt with an aqueous acidic solution to form a hydrated metal salt via metal hydroxide intermediates. In some cases reacting (step  140 ) the water-soluble metal salt with the aqueous acidic solution include a step  145  of exposing the water-soluble metal salt to the aqueous acidic solution at a temperature of between about 40 and 100° C., and in some cases from about 60 to 99° C., and in still other cases from about 70 to 99° C. The use of an aqueous acidic solution adjusted to such elevated temperature ranges ensures that there is sufficient activation energy to cause rapid conversion of the water-soluble metal salt into a metal hydroxide. 
     Converting (step  125 ), the conductive noble metal-containing polymer also includes a step  150  of oxidizing the metal hydroxide to form the non-conducting metal oxide. In some cases oxidizing (step  150 ) includes exposing the metal hydroxide to a plasma comprising oxygen as a feed gas (step  155 ). 
     After the converting step  125 , there can be several additional steps to complete the construction of the ferroelectric capacitor. E.g., one or more diffusion barriers can be formed on the sidewalls of the capacitor (step  160 ). The diffusion barrier can be deposited on the non-conducting metal oxide produced in the converting step  125 . 
     After fabricating the capacitor, there can be several additional steps to complete the manufacture of the semiconductor device. Example manufacturing steps include depositing an inter-level dielectric (step  170 ), forming openings in the inter-level dielectric (step  172 ), and filling the openings with a conductive material (step  175 ) to form contacts configured to electrically couple the ferroelectric capacitor to other components of the semiconductor device. 
     Similarly, the method  100  can further include several device manufacturing steps prior to forming the capacitor in step  102 . Non-limiting examples include implanting dopants to form wells in the semiconductor substrate (step  180 ), forming isolation structures (step  182 ), such as shallow trench isolation or field oxide structures, in the substrates, and forming transistors (step  184 ) in or on the substrate. Additional manufacturing steps can include depositing a pre-metal dielectric (PMD) layer over the transistors (step  190 ), forming openings in the PMD layer (step  192 ) and filling the openings with a conductive material (step  194 ) to form contacts configured to electrically couple the transistor to each other or the capacitors of the device. 
       FIGS. 2-8  illustrate selected steps in one embodiment of the method of manufacturing a semiconductor device in accordance with  FIG. 1 . The method steps of  FIGS. 2-8  are presented in the context of manufacturing an integrated circuit (IC)  200 . However, one skilled in the art would understand how the method could be applied to the manufacture of any semiconductor device. 
     With continuing reference to  FIG. 1 ,  FIG. 2  shows the IC  200  after forming one or more transistors  210  (e.g., nMOS, pMOS, CMOS transistors) on a semiconductor substrate  220  in accordance with step  184 . Any conventional materials and methods can be used to form the transistor  210 , e.g., such as discussed in U.S. patent application Ser. No. 11/016,400 by Summerfelt et al. (“Summerfelt”) or in U.S. Pat. No. 6,500,678 to Aggarwal et al. (“Aggarwal”), which are incorporated herein by reference in their entirety. E.g.,  FIG. 2  also shows the IC  200  after forming doped wells  230 , doped source and drain structures  235 , shallow trench isolation structures  240 , and transistor gate structures  245  in or on the substrate  220 , in accordance with steps  180 - 184 . Further examples of such steps are presented in Summerfelt or Aggarwal. 
       FIG. 2  also shows the IC  200  after depositing a pre-metal dielectric layer  250  over the substrate  220  and over the transistors  210  in accordance with step  190 .  FIG. 2  further shows the IC  200  after forming openings  260  in the pre-metal dielectric layer  250  and filling the openings  260  with a conductive material  265  to form a contact  270 , in accordance with steps  192  and  194 , respectively. Any suitable dielectric material and conductive material may be used for the pre-metal dielectric layer  250  (e.g., silicon dioxide), and contacts  270  (e.g., tungsten), respectively. Additional examples of suitable materials are presented in Summerfelt or Aggarwal. 
       FIGS. 3 and 4  show steps in the fabricating a ferroelectric capacitor  300  on the semiconductor substrate  220 .  FIG. 3  shows the IC  200  after forming lower and upper conductive material layers  305 ,  310  and ferroelectric material layer  315  on the pre-metal dielectric layer  250 , in accordance with steps  105 ,  107  and step  110 , respectively. Forming the lower conductive material layer  305  can include depositing (e.g., chemical vapor deposition, CVD or physical vapor deposition, PVD) a lower diffusion barrier layer  320  (e.g., TiN, TaSiN, TiSiN, TiN, TaN, HfN, ZrN, HfAlN, CrN, TaAlN, CrAlN, or multilayer combinations thereof) on the pre-metal dielectric layer  250 , followed by depositing the lower noble metal-containing material layer  305  (e.g., Ir, IrO x , Pt, Pd, PdO x , Au, Ru, RuO x , Rh, RhO x , LaSrCoO 3 , (Ba,Sr)RuO 3 , LaNiO 3 , YBa 2 Cu 3 O 7-x , AgO x , or multilayered combinations thereof, x≧1) on the lower diffusion barrier layer  320 . Forming the ferroelectric layer  315  on the lower conductive layers  305  can include depositing (e.g., metal organic CVD) lead zirconate titanate (PZT), strontium bismuth tantalate (SBT), or other suitable materials well know to those skilled in the art. Forming the upper conductive material layer  310  on the ferroelectric layer  315  can include depositing an upper noble metal-containing material layer  310  and upper diffusion barrier layer  330 . The upper noble metal-containing material layer  310  and upper diffusion barrier layer  330  can comprise similar materials as used for the lower diffusion barrier layer  320  and lower noble metal-containing material layer  305 . Examples of additional suitable materials and deposition methods for forming the conductive and ferroelectric material layers  305 ,  310 ,  315  are presented in Summerfelt or Aggarwal. 
       FIG. 4  shows the IC  200  after patterning the material layers  305 ,  310 ,  315  ( FIG. 3 ) in accordance with step  115 , to form lower and upper electrodes  405 ,  410  and a ferroelectric layer  415  of the ferroelectric capacitor  300 . E.g., as discussed in Summerfelt or Aggarwal, a hard mask (e.g., TiN, TiAlN, SiO 2  or other suitable material) in single, or multilayered combinations, can be deposited and patterned to cover portions of the underlying material layers  305 ,  310 ,  315  to thereby form an etch hard mask for subsequent etching processes to form the capacitor  300 . The upper and lower noble metal-containing material layers  305 ,  310  and ferroelectric material layer  315  can be etched (using e.g., reactive ion etching, RIE, processes) in separate etch processes and using separate hard masks, or they can be etched using a single process and single hard mask. The RIE processes to remove uncovered portions of the material layers  305 ,  310 ,  315  can include dry plasma etching etch using feed gases of halogens (e.g., Cl 2 ), alone, or in combination with other feed gases (e.g., O 2 , N 2 , CO, fluorocarbons). Different components of the stack require different etch chemistries. An example RIE etch process for PZT comprises Cl 2 :CHF 3 :O 2  in sccm ratios of about 140:12:45 and RF power of about 1200 Watts and substrate bias of about 450 Watts, and a chuck temperature of about 150° C. One skilled in the art would understand the range of different etchant chemistries may be used depending on the composition of the material layers. 
     As further illustrated in  FIG. 4 , and in accordance with step  120 , as a consequence of etching the material layers  305 ,  310 ,  315  (and diffusion barrier layers  320 ,  330 , when present) a conductive noble metal-containing polymer  420  is generated on sidewalls  425  of the ferroelectric capacitor  300 , as a by-product of the patterning process. The polymer  420  can cover all or a portion of the sidewalls  425 , and can have variable or uniform thickness. 
       FIGS. 5-7  shows the IC  200  at different stages in converting the conductive noble metal-containing polymer  420  ( FIG. 4 ) into a non-conducting metal oxide  710  ( FIG. 7 ), in accordance with step  125 .  FIG. 5  depicts the IC  200  after forming a water-soluble metal salt  510  from the conductive noble metal-containing polymer  420  ( FIG. 4 ), as per step  130 . In some cases the metal salt  510  comprises a metal hydroxide salt, while in other cases, the metal salt  510  comprises a metal halide salt. In some cases, the metal hydroxide or metal halide salts  510  are non-conducting (e.g., a sheet resistance of about 250 Ohms/square). 
     With continuing reference to  FIGS. 1 and 4 , in some embodiments, forming the water-soluble metal salt  510  includes hydrolyzing the conductive noble metal-containing polymer  420  as per step  132 . Hydrolyzing can include exposing the conductive noble metal-containing polymer  420  to a plasma generated using water (H 2 O) as a feed gas. In some cases, e.g., the conductive noble metal-containing polymer  420  is exposed to an RF plasma generated using a O 2 :N 2 :H 2 O seem ratios of about 20:2:3 to about 40:2:5 as a feed gas, a plasma power of about 1000 to 2000 Watts, and a chuck temperature of about 50 to 350° C. In other cases, the hydrolyzing plasma can include an RF plasma generated using a feed gas of O 2 :N 2 :H 2 O in seem ratios ranging from about 3500:200:300 to about 3500:200:500, a plasma power of 1400 Watts and a chuck temperature of about 300° C for about 60 seconds. In still other cases, the hydrolyzing plasma can include an RF plasma power of about 1200 to 1600 Watts, a pressure of about 2,000 mTorr for about 0.5 to 3 minutes with feed gas comprising O 2 :N2:H2O in seem ratios of about 3500:200:300 and a chuck temperature of about 50 to 300° C. Excessive amounts of H 2 O in the feed gas (e.g., ≧about 500 seem) is to be avoided as this is correlated with high capacitor leakage. 
     In other embodiments forming the water-soluble metal salt  510  includes halogenating the conductive noble metal-containing polymer  420  as per step  135 . Halogenating can include exposing the conductive noble metal-containing polymer  420  to a plasma generated using a halogen as a feed gas. E.g., the halogenating plasma can include an RF plasma power of about 800 to 1200 Watts, a pressure of about 6 to 10 mTorr for about 0.25 to 2 minutes with feed gas comprising halogens (e.g., Cl 2 , Br 2  or I 2  plus an inert gas, such as Ar, at seem ratios of halogen:inert gas equal to about 70:50) and a chuck temperature of about 40 to 75° C. at a bias power of 100 to 200 watts. 
       FIG. 6  depicts the IC  200  after reacting the water-soluble metal salt  510  ( FIG. 5 ) with an aqueous acidic solution to form a metal hydroxide  610 , as per step  140 . In some cases reacting comprises exposing the water-soluble metal salt  510  to the aqueous acidic solution at a temperature of between about 60 and 100° C. (step  145 ). This temperature range ensures sufficient activation energy to cause rapid conversion of the water-soluble metal salt  510  into a metal hydroxide  610 . In some cases heating to about 60° C. only gives a marginal product, and therefore, heating to temperature of 65° C. or higher is used. Other temperatures can be used, e.g., greater than room temperature (e.g., about 25° C. or higher) but less than the boiling point of water. Reacting can be conducted in a tank or using a tank-less process, e.g., a spin washing process that comprises pouring the acid aqueous acidic solution onto the surface of a spinning substrate wafer  220  having the patterned material layers  305 ,  310 ,  315  thereon. 
     In some cases, reacting in step  140  includes exposing the water-soluble metal salt  510  to an acid aqueous acidic solution having about 50 wt % phosphoric acid. E.g., in some cases the water-soluble metal salt  510  can be exposed to an acid aqueous acidic solution of 1:1 H 2 O:H 3 PO 4  at about 65° C. for about about 1 to 1.5 minutes. In some cases the temperature of the solution ranges from about 45 to 80° C. and the time ranges from about 0.5 to 5 minutes, while in other cases, the temperature ranges from about 50 to 60° C. 
     In other cases, reacting in step  140  includes exposing the water-soluble metal salt  510  to an aqueous acidic solution having hydrochloric acid and hydrogen peroxide. e.g., 1:1:4 H 2 O:HCl:H 2 O 2  for about 0.5 to 10 minutes. In some cases aqueous acidic solution has a temperature ranging from 20 to 80° C., while in other cases, the temperature ranges from 50 to 65° C. In some cases, the duration of exposure ranges from 0.5 to 15 minutes. E.g., the water-soluble metal salt  510  can be exposed to the above H 2 O:HCl:H 2 O 2  solution at about 60° C. for about 1 to 3 minutes. 
     In still other cases, reacting in step  140  includes exposing the water-soluble metal salt  510  to an aqueous acidic solution having a carboxylic acid. Example carboxylic acids include EDTA, acetylacetonate, acetic acid, and oxalic acid. The aqueous acidic solution having a carboxylic acid is at a temperature ranging from about 45 to 80° C. In some instances the temperature ranges from 50 to 65° C. E.g., in some cases the water-soluble metal salt  510  is exposed to the aqueous acidic solution at about 65° C. to about 1 to 1.5 minutes. A temperature of less than about 45° C. can result in the water-soluble metal salt  510  having a nonuniform complexation of metal salt and carboxylic acid. A temperature of greater than about 80° C. can result in the complex disproportionating to undesirable by-products. 
     In some case, reacting in step  140  includes exchanging one or more halides of the water-soluble metal salt  510  to with one or more anionic ligands of the aqueous acidic solution. E.g., when the water-soluble metal salt  510  comprises IrCl 2 (OH)3H 2 O, and the acid comprises phosphoric acid or sulfuric acid, then at least one of the Cl atoms can be exchanged with a phosphate (e.g., PO 4   −2 ) or a sulfate (e.g., SO 4   −2 ), respectively. 
       FIG. 7  depicts the IC  200  after oxidizing the metal hydroxide  610  ( FIG. 6 ) to form the non-conducting metal oxide  710 , as per step  150 . In some cases oxidizing includes exposing the metal hydroxide  610  to a plasma comprising oxygen as a feed gas, as per step  155 . E.g., an RF plasma with at least about 66% oxygen as a feed gas, and a power of least about 700 Watts. E.g., oxidizing can include an RF plasma power of about 100 to 5000 Watts, a pressure of about 50 to 5000 mTorr for about 1 to 5 minutes with a feed gas comprising O 2  (e.g., O 2  and an inert gas such as N 2  at sccm ratios of O 2 : inert gas equal to about 100:1000 to 1000:1000) and a chuck temperature of about 20 to 300° C. In some cases oxidizing the metal hydroxide  610  comprises an RF plasma power of about 700 Watts with about 70% oxygen as a feed gas. 
       FIG. 8  shows the IC  200  after the converting step  125 , and after forming a diffusion barrier  810  on the sidewalls  425  of the capacitor  300 , in accordance with step  160 . In addition to protecting the capacitor  300  from the diffusion of substances (e.g., a hydrogen or lead diffusion barrier) into or out of the capacitor  300 , the diffusion barrier permits the misalignment of an overlying interconnect without shorting out the capacitor  300 . In some cases, the diffusion barrier  810  is deposited over the entire capacitor  300 , including on the non-conducting metal oxide  710 . The diffusion barrier  810  can comprise a single layer or multiple layers of, e.g., AlO x  (x≧1), Ta 2 O 5 , AlN, TiO 2 , ZrO 2 , HfO 2 , SiN. The diffusion barrier  810  can be deposited using atomic layer deposition (ALD) plasma enhanced chemical vapor deposition (PECVD) or other deposition techniques. Further examples are presented in are presented in Summerfelt or Aggarwal. 
       FIG. 8  also shows the IC  200  after depositing one or more inter-level dielectric layers (ILD)  820  on the substrate  220 . As shown in  FIG. 8 , the ILD  820  can be on the capacitor  300  and pre-metal dielectric layer  250 , in accordance with step  170 . Each the ILD  820  can comprise single or multi-layered combinations of insulating materials such as silicon oxide (e.g., SiO 2 ), fluorosilicate glass (FSG), phosphosilicate glass (PSG), or other low dielectric constant materials (e.g., dielectric constant of 4 or less). The ILD  820  can be deposited using CVD, PVD, ALD or other conventional methods. Additional example materials and deposition processes are presented in Summerfelt or Aggarwal. 
       FIG. 8  further shows forming openings  830  in the inter-level dielectric (step  172 ), and filling the openings  830  with a conductive material  840  (step  175 ) to form contacts  850 . Conventional patterning and etch methods can be used to form single or dual damascene openings  830 . Suitable conductive material  840  includes Al, W or Cu, and can further include a metal diffusion barrier  855  (e.g., silicon carbide or silicon nitride) lining the opening  830 . Other suitable contact material and methods of forming openings and forming contacts are presented in Summerfelt or Aggarwal. 
     The contacts  850  can be configured to electrically couple the ferroelectric capacitor  300  to other components of the IC  200 . E.g., the ferroelectric capacitor  300  can be electrically coupled to at least one of the transistors  210  through one or more contacts  850 . In some embodiments, one or more transistor  210  and the ferroelectric capacitor  300  are interconnected to form a memory cell  860 . 
     Another embodiment of the disclosure is depicted in  FIG. 8 , an IC  200 . The IC  200  comprises one or more memory cells  860 , wherein at least one of the memory cells  860 , includes one or more transistors  210  on or in a semiconductor substrate  220  and the one or more capacitor  300 . The IC  200  further comprises a pre-metal dielectric layer  250  over or on the one or more transistors  210  and ferroelectric capacitor  300 . The ferroelectric capacitor  300  is electrically coupled to at least one of the transistors  210  and includes sidewalls  425  having a non-conducting metal oxide  710  thereon. 
     Embodiments of the IC  200  can be fabricated by any of the methods discussed above. E.g., the non-conducting metal oxide  710  can be generated from converting a conductive noble metal-containing polymer  420  ( FIG. 4 ), formed on the sidewalls as a by-product of patterning materials layers  305 ,  310 ,  315  ( FIG. 3 ) done as part of fabricating the ferroelectric capacitor  300 . 
     The conversion can include any of the processes described in the context of steps 125-155 ( FIG. 1 ). E.g., in one embodiment of the IC 200, e.g., forming a water-soluble metal salt  510  ( FIG. 5 ) includes hydrolyzing the conductive noble metal-containing polymer  420  ( FIG. 4 ) by exposing the conductive noble metal-containing polymer  420  to an RF plasma generated using a O 2 :N 2 :H 2 O seem ratio of about 3500:200:300 as a feed gas, a plasma power of about 1400 Watts, and a chuck temperature of about 150° C. Reacting the water-soluble metal salt  510  comprises exposing it to an acid aqueous acidic solution comprising about 50 wt % phosphoric acid at about 65° C. Oxidizing the resulting metal hydroxide  610  includes an RF plasma with about 70% oxygen as a feed gas and a power of about 700 Watts. 
     Those skilled in the art to which the invention relates will appreciate that other and further additions, deletions, substitutions and modifications may be made to the described example embodiments, without departing from the invention.