Abstract:
A structure including a TiW oxygen plasma mask, a photoresist mask above and in contact with the TiW oxygen plasma mask, a 2000 angstrom thick oxygen plasma vaporizable RuO 0.8  electrode layer partially under and in contact with the TiW oxygen plasma mask, the RuO 0.8  electrode layer not being completely covered by a pattern of the TiW oxygen plasma mask, a first side of a PZT ferroelectric layer in contact with the RuO 0.8  electrode layer and a second RuO 0.8  electrode layer in contact with a second side of the PZT ferroelectric layer.

Description:
A prior art method for forming a ruthenium oxide (RuOx) layer into an RuOx electrode involved wet chemical etching of the RuOx layer. The wet chemical etching method involved use of wet chemicals, such as chlorine or fluorine. Due to a lack of easy use of the wet chemical, the wet chemical etching method was not satisfactory. In an RuOx layer, x can have a decimal value such as 0.8, 
     Another prior art method for forming a ruthenium oxide (RuOx) layer into an RuOx involved ion milling the RuOx layer. The ion milling method was not an efficient manufacturing method. The ion milling method provided only a low throughput of RuOx electrodes. The ion milling method did not provide selectivity of underlying RuOx layers, such as in a sandwich structure that had a buried RuOx layer or multiple level RuOx layers. 
     The present method involves forming an RuOx electrode by forming a titanium-tungsten (TiW) alloy mask on an RuOx layer The masked RuOx layer is formed into an RuOx electrode by oxygen plasma etching the masked RuOx layer, thus forming the RuOx electrode. 
     The method of the present invention involves placement of a TiW layer on the RuOx layer and formation of the TiW layer into a TiW mask. The TiW masked RuOx layer is then etched by an oxygen plasma. A TiW mask is used in the oxygen plasma, since a TiW mask is highly resistant to oxygen plasma. 
     After an RuOx electrode is formed, the TiW mask and RuOx electrode can remain permanently attached together. Alternately, the TiW mask can be removed from the RuOx electrode. The disclosed method also allows for an efficiently manufacturing of multi-layer RuOx electrodes. 
     An oxygen plasma of a reactive ion etch (RIE) method, is used in order to pattern a TiW masked RuOx layer into an RuOx electrode. The TiW mask is used to mask portions of the RuOx layer. Unmasked portions of the RuOx layer are then vaporized by the oxygen plasma. The disclosed method allows for a high throughput of RuOx electrodes. 
     The present method also involves oxygen plasma vaporization of unmasked portions of multilevel TiW masked RuOx layers. Multilevel RuOx electrodes are thus formed. Multilevel RuOx electrodes are formed as electrodes of a ferroelectric capacitor. 
     Ferroelectric capacitors can be successfully fabricated by means of the disclosed TiW masking and oxygen plasma etching method. The resultant capacitors have a performance level that meets industry standards. 
     SUMMARY OF THE INVENTION 
     A method for forming an RuOx layer into an RuOx electrode comprising, depositing a TiW layer on the RuOx layer, forming a photo-resist mask on the TiW layer, in order to form a masked TiW layer, exposing the masked TiW layer to CF4, a TiW mask being formed on the RuOx layer, and vaporizing unmasked portion of the RuOx layer with an oxygen plasma, the RuOx layer being patterned into an RuOx electrode. 
    
    
     
       DESCRIPTION OF THE DRAWING 
         FIG. 1  is a sectional view of a sandwich structure having an uppermost first RuOx layer, a PZT ferroelectric layer, a second RuOx layer, a Ti adhesion layer, a silicon oxide insulator layer and a silicon layer. 
         FIG. 2  is a sectional view of the sandwich structure  FIG. 1 , plus a sectional view of additional sandwich structure having a TiW layer in contact with the first RuOx layer, a photo-resist film and a photographic mask. 
         FIG. 3  is a sectional view of the sandwich structure of  FIG. 1 , plus a sectional view of additional sandwich structure having a TiW layer in contact with the first RuOx layer and a photo-resist mask. 
         FIG. 4  is a sectional view of the sandwich structure of  FIG. 1 , plus sectional view of additional sandwich structure having a TiW mask in contact with the first RuOx layer and a photo-resist mask. 
         FIG. 4A  is a sectional view of an RIE machine  40  plus the sandwich structure of  FIG. 4   
         FIG. 5  is a sectional view of a sandwich structure having an uppermost a first TiW mask, a first RuOx electrode, a PZT ferroelectric layer, a second RuOx layer, a Ti adhesion layer, a silicon oxide insulator layer and a silicon layer. 
         FIG. 6  is a sectional view of a sandwich structure of  FIG. 5  plus a second TiW mask  50  in contact with the PZT ferroelectric layer, first TiW mask and first RuOx electrode. 
         FIG. 7  is a sectional view of a sandwich structure having a third TiW mask in contact with each of the second TiW mask  50  and PZT ferroelectric plate and second RuOx layer, a Ti adhesion layer, a silicon oxide insulator layer and a silicon layer. 
         FIG. 8  is a sectional view of the sandwich structure of  FIG. 7 , plus a sectional view of additional sandwich structure having a fourth TiW layer in contact with the third TiW mask, a photo-resist layer and a photographic mask. 
         FIG. 9  is a sectional view of a completed ferroelectric capacitor. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present oxygen plasma method is used in patterning ruthenium oxide (RuOx) layers of a sandwich structure  10  of  FIG. 1 . The sandwich structure  10  has an uppermost first RuOx layer  12 . The sandwich structure  10  also has a PZT ferroelectric layer  14  in contact with the first RuOx layer  12 . The sandwich structure  10  further has a second RuOx layer  16  in contact with the PZT layer  14 . Still further the sandwich structure  10  has a titanium (Ti) adhesion layer  18  in contact with the second RuOx layer  16 . The sandwich structure  10  has a silicon oxide insulator layer  19  in contact with the Ti adhesion layer  18 . Finally the sandwich structure  10  has a silicon layer  20  in contact with the silicon oxide insulator layer  19   
     PZT is an alloy that has the general chemical formula PbxZryO3. PZT is a ternary alloy of lead oxide, zirconium oxide and titanium oxide. 
     The RuOx layer  12 , the PZT layer  14  and the RuOx layer  16  are 2000 angstroms thick. The Ti adhesion layer  18  is 500 angstroms thick. The silicon oxide insulator layer  19  is 4000 angstroms thick. The silicon layer  20  is a base for the other layer of structure  10 . Silicon layer  20  can be a section of a thin silicon wafer (not shown). The Ti adhesion layer  18  is oxidized after it is deposited on the silicon oxide insulator layer  19 . 
     As shown in  FIG. 2 , a first titanium-tungsten (TiW) alloy layer  22  has been laid down on the first RuOx layer  12 , such as by use of a TiW sputtering technique. The first TiW layer  22  is 1200 angstroms thick. A photo-resist film  24  is laid down on the first TiW layer  22 . A photographic mask  26  is placed on the photo-resist film  24 . 
     The photographic mask  26  and photo-resist film  24  are exposed to ultraviolet light. Then, the exposed photo-resist film  24  is processed with a photo-resist developer. A photo-resist mask  30  is thus formed on the first TiW layer  22 , as shown in  FIG. 3 . 
       FIG. 3  shows the photo resist mask  30  on the first TiW layer  22 . The TiW layer  22  of  FIG. 3  is etched with a CF4 plasma in an RE machine, to form a first TiW mask  32 , as shown in  FIG. 4 . The CF4 plasma forms the first TiW mask  32 . During the etching with a CF4 plasma, the photo-resist mask  30  remains in place, as shown in  FIG. 4 . 
     Conventional photo-resist image processing techniques are used to transfer the desired photographic pattern of photographic mask  26  into the photo-resist layer  24  that has been deposited on the TiW layer  22 . A photoresist mask  30  is formed on TiW layer  22  as shown in  FIG. 3 . 
     A mask pattern, of photo-resist mask  30 , is then transferred into the first TiW layer  22  by an CF4 plasma of a reactive ion etch (RIE) process in an RIE machine  40 ; shown in  FIG. 4A . A first TiW mask  32  is formed from TiW layer  22 , in machine  40 , shown in  FIG. 4A . The conditions used with the RIE machine  40  are: CF4 at 112 sccm, O2 at 10 sccm, 100 millitorr pressure, 200 watts of RF power. The etch rate of the TiW layer  22  is 310 angstroms per minute. The first TiW mask  32  is thusly formed on the first RuOx layer  12  in RIE machine  40  in 3.87 minutes. In  FIG. 4  the TiW mask  32  is shown as having been formed on an outer surface of the first RuOx layer  12 . 
     An oxygen plasma etching method is then used on the TiW masked RuOx layer  12 , in RIE machine  40 , shown in  FIG. 4A , to pattern the TiW masked RuOx layer  12  of  FIG. 4  into first RuOx electrode  12 A, shown in  FIG. 5 . RuOx electrode  12 A is formed as a result of the application of the oxygen plasma method to the TiW masked RuOx layer  12 , shown in  FIG. 4 . The photo-resist mask  30  is removed from the first TiW mask  32 , during application of oxygen plasma to the TiW masked RuOx layer  12 ; as shown in  FIG. 5 . 
     To obtain the structure shown in  FIG. 5 , the sandwich  10 C of  FIG. 4  is placed in a chamber  41  of a Materials Research diode type RIE machine  40 , as shown in  FIG. 4A . As shown in  FIG. 4A , oxygen  42  is ionized in the RIE machine  40 , to form an oxygen plasma  44 . The oxygen plasma  44  vaporizes unmasked portions of the RuOx layer  12  of sandwich  10 C of  FIG. 4 . The vaporization is due to an oxidation type chemical reaction of the oxygen plasma  44  with unmasked portions of the RuOx layer  12 . A first RuOx electrode  12 A, shown in  FIG. 5 , is formed from RuOx layer  12 , during the oxygen plasma oxidation process. The oxidation reaction that takes place in the chamber  41  of the RIE machine  40  is a chemical conversion of unmasked portions of RuOx layer  12  into gaseous oxide, such as RuO4. 
     The preferred system for use in performing the oxidation process is an RIE machine  40 . The RIE machine  40  is manufactured by Materials Research Corporation and is an RIE  61  type plasma machine. The machine  40  has a diode system with a 20 inch diameter chamber  41 , a 16 inch diameter anode  46  and a 12 inch diameter cathode  48 . 
     The sandwich  10 C of  FIG. 4 , whose masked RuOx layer  12  is to be processed, is placed on the bottom cathode  48 . The cathode  48  is supplied with RF power at 13.56 megahertz. Vaporization of unmasked portions of the RuOx layer  12  is accomplished by introducing oxygen, O2, at a flow rate of 50 sccm into the chamber  41  of RIE plasma machine  40 , adjusting the pumping speed with a throttle valve, to achieve a chamber pressure of 100 millitorr and by applying 300 watts of RF power to the cathode  48 . 
     For the above given parameters in using machine  40 , the etch rate for RuOx layer  12 , where x equals 0.8, is 110 angstroms per minute. The RuOx layer  12  has a thickness of 2000 angstroms. Therefore unmasked portions of RuOx layer  12  are removed from PZT layer  14  in 18.181 minutes. 
     A TiW masked Ru layer, a TiW masked RuO2 layer or a TiW masked RuOx layer can be oxygen plasma etched, that is, vaporized, in machine  40 . x can have an integer value or decimal value. 
     The first TiW mask  32  can remain in place while PZT layer  14  is patterned, and while second RuOx layer  16  is patterned. Alternately, the first TiW mask  32  can be removed from the first RuOx electrode  12 A by using a hydrogen peroxide solution at 50 degrees centigrade for 3 minutes. The underlying first RuOx electrode  12 A, PZT layer  14  and second RuOx layer  16  are unaffected by the hydrogen peroxide. 
     Again, the first TiW mask  32  is formed in order to patterning the RuOx layer  12  into the first RuOx electrode  12 A. A 1200 angstrom thick TiW layer  22  is deposited on the RuOx layer  12  and the TiW layer  22  is then masked by photo-resist mask  30 , and etched, in order to form first TiW mask  32 . 
     It is noted that oxygen plasma is a very effective photo-resist mask remover. The etch rate of a photo-resist mask by an oxygen plasma is approximately 1 micrometer per minute. 
     Thereafter, PZT layer  14  is masked by a second TiW mask  50 , as shown in FIG.  6 . The second TiW mask  50  is formed in the same manner as described for the formation of first TiW mask  32  of  FIG. 4 . A second TiW layer (not shown) is used in forming second TiW mask  50 . 
     The masked PZT layer  14  of  FIG. 6  is patterned by a plasma etching method using a chloride and fluorocarbon plasma This plasma etching method is disclosed in U.S. Pat. No. 5,443,688, issued Aug. 22, 1995. The teaching of the &#39;688 patent are incorporated herein by reference. As shown in  FIG. 7 , a PZT ferroelectric plate  14 A is formed by the etching method of the &#39;688 patent. 
     A third TiW mask  60  is formed on second RuOx layer  16 , as also shown in  FIG. 7 . The third TiW mask  60  is formed, on second RuOx layer  16 , by the method described above for forming a first TiW mask  32 . The third TiW mask  60  is formed from a third TiW layer (not shown). 
     The above described oxygen plasma RIE process is applied to masked second RuOx layer  16 . An second RuOx electrode  16 A is formed, as shown in  FIG. 8 , from second RuOx layer  16 , shown in  FIG. 7 . 
     Again, the PZT layer  14  is patterned by a method such described in U.S. Pat. No. 5,443,688, to form PZT plate  14 A under first RuOx electrode  12 A. The lower RuOx layer  16  is patterned using an oxygen RIE process to form a second RuOx electrode  16 A under PZT plate  14 A. The oxygen RIE process is described for patterning the first RuOx layer  12  that is above PZT layer  14 . The second RuOx electrode  16 A, as shown in  FIG. 8 , is formed from the lower RuOx layer  16 , shown in  FIG. 7 . 
     The oxygen plasma RIE process is used to etch TiW masked RuOx layer  12  and simultaneously remove the photo resist-mask  30 . The TiW mask  32  is unaffected by the oxygen RIE process. The TiW mask  32  serves as an effective mask, in a transfer of the TiW mask pattern to the RuOx layer  12 . Since the TiW mask  32  is unaffected by the oxygen plasma, the TiW mask  32  serves effectively as a mask. 
     The underlying Ti adhesion layer  18 , shown in  FIG. 8 , is patterned by first depositing a 2800 angstrom thick fourth TiW layer  70  over exposed portions of the Ti adhesion layer  18  and over the third TiW mask  60 . A photo-resist layer  72  is placed on the fourth TiW layer  70 . A photographic mask  74  is placed on photo-resist layer  72 . A fourth TiW mask (not shown) is formed on the Ti adhesion layer  18 . The fourth TiW mask is used in plasma etching the Ti adhesion layer  18 . A plasma RIE process used to etch the Ti adhesion layer  18 . The plasma RIE process, for etching Ti adhesion layer  18 , uses CC12F2 at 107 sccm, O2 at 1 sccm, 15 millitorr pressure, 100 watts of RF power. The etch rate equals 80 angstroms per minute in the MRC system. 
     Thereafter, the TiW masks  32 ,  50 ,  60  and the fourth TiW mask, are striped away to form a nearly completed PZT ferroelectric capacitor. The stripping, is done by applying a 50 degree centigrade hydrogen peroxide solution to the TiW masks. 
     A completed PZT ferroelectric capacitor  80  is shown in  FIG. 9 . Electrical lead  82  has been attached to first RuOx electrode  12 A. Electrical lead  84  has been attached to second RuOx electrode  16 A. 
     While the present invention has been disclosed in connection with the preferred embodiment thereof, it should be understood that there are other embodiments which fall within the spirit and scope of the invention as defined by the following claims.