METHOD FOR FABRICATING A DAMASCENE SELF-ALIGNED FERROELECTRIC RANDOM ACCESS MEMORY (F-RAM) DEVICE STRUCTURE EMPLOYING REDUCED PROCESSING STEPS

The present application claims priority from U.S. Provisional Patent Application Ser. No. 61/522,953 filed Aug. 12, 2011, the disclosure of which is herein specifically incorporated by this reference in its entirety. The present invention is also related to the subject matter disclosed in U.S. patent application Serial Nos. [RAM 627] for “Method for Fabricating a Damascene Self-Aligned Ferroelectric Random Access Memory (F-RAM) with Simultaneous Formation of Sidewall Ferroelectric Capacitors” and [RAM 628] for “Method for Fabricating a Damascene Self-Aligned Ferroelectric Random Access Memory (F-RAM) Having a Ferroelectric Capacitor Aligned with a Three Dimensional Transistor structure”, both filed on even date herewith and assigned to Ramtron International Corporation, the disclosures of which are also herein specifically incorporated by this reference in their entirety.

The present invention relates, in general, to the field of integrated circuit (IC) memory devices. More particularly, the present invention relates to the field of non-volatile, ferroelectric random access memory (F-RAM) devices and a method for fabricating a damascene self-aligned F-RAM device structure on a planar surface using a reduced number of masks and etching steps.

According to World Semiconductor Trade Statistics (WSTS), the semiconductor market reached an important milestone in 2010, posting worldwide revenues of more than $300 billion (in United States dollars) for the first time in the industry's history. In particular, the memory chip segment exhibited the highest growth rate during 2010, increasing from $45 billion in 2009 to $71 billion in 2010, representing a 57% year-over-year growth rate. Embedded memory devices represented more than 23% of the overall semiconductor market in 2010.

Within this context, the increasing demand for higher processing power is driving the semiconductor industry to develop memory devices with higher operational speeds in order to support the capabilities of modern electronic devices. F-RAM has emerged as a promising option for the industry, particularly in the market areas of mobile computing, smart meters, radio frequency identification (RFID) devices, office equipment and other applications requiring non-volatile data storage.

Standard dynamic random access memory (DRAM) and static random access memory (SRAM) devices, while providing relatively fast access times, are considered to be volatile memory devices inasmuch as data stored in such memories is lost when power is interrupted. In contrast, non-volatile memory devices are those that function to retain data despite any loss of power.

F-RAM devices are inherently non-volatile, meaning that these memory devices are able to retain stored data while the device is not powered. In comparison to electrically erasable programmable read only memory (EEPROM) FLASH memory devices, which are currently the most popular type of non-volatile memory, F-RAM devices have several advantages including lower power requirements (operational voltages of just 5V needed during read-write operations), higher read-write speeds (less than 70 nanoseconds), and virtually unlimited write endurance capability (more than 10,000,000,000 write cycles).

F-RAM memory devices may be fabricated based on the use of lead zirconium titanate (PZT) ferroelectric storage capacitors as memory elements integrated with complementary metal oxide semiconductor (CMOS) addressing, selection, and control logic. PLZT is a lanthanum-doped form of PZT wherein some of the lead is replaced with Lanthanum.

It is also known that PZT may also be doped with strontium and calcium to improve its ferroelectric dielectric properties. Ferroelectric storage capacitors having a strontium bismuth tantalate (SBT); barium strontium titanate (BST); and strontium titanate oxide (STO) dielectrics are also known in the art.

As used in the present application, the term “PZT” shall also be considered to include PLZT, SBT, BST, STO and other comparable ferroelectric dielectric materials. Further, it should be noted that the techniques of the present invention disclosed herein are applicable to all known ferroelectric dielectrics including Perovskites and layered Perovskites (whether doped or undoped) including PZT, PLZT, BST, SBT, STO and others while simultaneously allowing for a potentially broader choice of electrode materials and the use of a forming gas anneal process step on the completed IC structure.

Regardless of the ferroelectric dielectric material employed, in operation F-RAM devices function through their ability to be polarized in one direction or another in order to store a binary value representative of a logic level “one” or “zero”. The ferroelectric effect allows for the retention of a stable polarization state in the absence of an applied electric field due to the alignment of internal dipoles within the Perovskite crystals in the dielectric material. This alignment may be selectively achieved by application of an electric field which exceeds the coercive field of the material. Conversely, reversal of the applied field reverses the internal dipoles.

A hysteresis curve, wherein the abscissa and ordinate represent the applied voltage (“V”) and resulting polarization (“Q”) states respectively, may be plotted to represent the response of the polarization of a ferroelectric capacitor to the applied voltage. A more complete description of this characteristic hysteresis curve is disclosed, for example, in U.S. Pat. Nos. 4,914,627 and 4,888,733 assigned to Ramtron International Corporation, assignee of the present invention, the disclosures of which are herein specifically incorporated by this reference.

Representative of the current state of the art in F-RAM device fabrication is that disclosed in U.S. Pat. No. 6,150,184 for: “Method of Fabricating Partially or Completely Encapsulated Top Electrode of a Ferroelectric Capacitor,” also assigned to Ramtron International Corporation. Therein described is the structure of a ferroelectric capacitor that includes a bottom electrode, a top electrode, and a ferroelectric layer located between the top and bottom electrodes that extends to completely encapsulate the top electrode, except for a contact hole to allow metallization of the top electrode. The total encapsulation of the top electrode reduces the sensitivity of the ferroelectric capacitor to hydrogen and thus improves electrical switching performance. The encapsulation technique can also be used to improve the performance of ferroelectric integrated circuits and other devices.

Further representative of the state of the art in the fabrication of F-RAM devices is that disclosed in U.S. Pat. No. 6,613,586 for: “Hydrogen Barrier Encapsulation Techniques for the Control of Hydrogen Induced Degradation of Ferroelectric Capacitors in Conjunction with Multilevel Metal Processing for Non-Volatile Integrated Circuit Memory Devices,” also assigned to Ramtron International Corporation. Therein described is a device structure which ameliorates the hydrogen induced degradation of ferroelectric capacitors by completely encapsulating the capacitor within a suitable hydrogen barrier material, such as chemical vapor deposition (“CVD”) or sputtered silicon nitride (Si₃N₄), thus ensuring process compatibility with industry standard process steps. Although the deposition process for CVD Si₃N₄itself contains hydrogen, the deposition time may be kept relatively short thereby allowing the titanium nitride (TiN) local interconnect layer to act as a “short term” hydrogen barrier.

The disclosures of U.S. Pat. Nos. 6,150,184 and 6,613,586 are herein specifically incorporated by this reference in their entirety.

Despite the aforementioned advantages over volatile memory devices and other non-volatile technologies, F-RAMs currently account for a relatively small share of the non-volatile memory device market. Competitively, the main limitation of the F-RAM technology has been its lower storage density compared to FLASH devices coupled with higher manufacturing costs. These limitations stem primarily from the generally complex structure of current F-RAM devices which results in a manufacturing process that requires a high number of processing masks and etching steps. As such, in order to be more competitive in the current memory device marketplace and be usable in a wider range of modern electronic devices, F-RAM devices need to be more highly integrated, implying increased storage densities and reduced manufacturing costs.

As such, it would be highly advantageous to reduce the number of layers and etching steps required during F-RAM fabrication in order to reduce manufacturing costs. Still further, it would be highly advantageous to simplify the structure of F-RAM devices with the purpose of improving storage density capabilities.

Disclosed herein is a method for forming a damascene self-aligned ferroelectric RAM (F-RAM) device on a planar surface comprising the steps of forming, on a planar surface of a semiconductor substrate, a thick oxide layer which is etched based on the pattern established by a non-erodible mask, forming an opening for the F-RAM construction, followed by the application and etching of a CVD aluminum oxide conformal layer to form spacers, deposition of a titanium aluminum nitride layer, followed by the application and O₂plasma ash etching of a photoresist material, deposition and planarization of an oxide material using chemical mechanical polishing (CMP), application of a photoresist mask to create an etching pattern on the oxide, deposition of a CVD aluminum oxide conformal layer to form a second set of spacers after the oxide is etched, deposition, planarization and etching of a ferroelectric layer ideally doped with lead zirconium titanate (PZT), followed by a similar process on top electrode and nitride layers, and the etching of the oxide and nitride layers for the formation of CVD tungsten, titanium/titanium nitride studs on a planar surface of the F-RAM structure.

Also further disclosed herein is a method for forming an integrated circuit device on a substrate comprising forming a first insulating layer on the substrate and removing a portion of the first insulating layer to produce an opening to an exposed surface of the substrate therein. First spacers are formed on sidewalls of the opening and a first conductive layer is formed on the exposed surface of the substrate separated from the first spacers on the sidewalls of the opening by a gap therebetween. A bottom electrode of a ferroelectric capacitor is formed over the first conductive layer and in the gap laterally of the first conductive layer. A second insulating layer is formed adjoining the spacers in the opening and second spacers are formed on the second insulating layer in the opening. A ferroelectric dielectric layer is formed on the bottom electrode between the second spacers and a top electrode is formed on the ferroelectric dielectric. A bottom electrode contact opening is formed through a portion of the second insulating layer to the bottom electrode and a first electrical contact is formed to the top electrode and a second electrical contact is formed to the bottom electrode through the bottom electrode contact opening.

Still further disclosed herein is a method for forming a ferroelectric device on a planar surface of a semiconductor substrate comprising forming a relatively thick oxide layer on the planar surface and selectively etching an opening through the oxide layer in a pattern established by a non-erodible mask. A first aluminum oxide conformal layer is applied and selectively etched to form first spacers on sidewalls of the opening and a titanium aluminum nitride layer is deposited in a lower portion of the opening and separated from the first spacers. A bottom electrode of a ferroelectric capacitor is formed over the aluminum oxide layer in contact with the spacers and laterally of the aluminum oxide layer. An oxide material is deposited, planarized and selectively removed to form an additional oxide layer adjoining the first spacers in the opening. A second aluminum oxide layer is deposited and selectively etched to form second spacers on the additional oxide layer. A ferroelectric layer is deposited and etched on the bottom electrode between the second spacers. A top electrode is formed on the ferroelectric layer and a Ti/TiN and W contact is formed to the bottom electrode through the oxide material and a Ti/TiN and W contact is also substantially concurrently formed to the top electrode.

Additionally disclosed herein is a ferroelectric device which comprises a contact stud formed upon a semiconductor substrate and a first conductive layer overlying the substrate and adjoining the contact stud. A bottom electrode layer overlies the first conductive layer and first spacers are disposed laterally of the bottom electrode layer extending distally of the substrate. Second spacers are disposed on the bottom electrode layer extending distally therefrom substantially parallel to the first spacers and an insulating layer is disposed between the first and second spacers. A ferroelectric dielectric layer overlies the bottom electrode layer between the second spacers and a top electrode layer overlies the ferroelectric dielectric layer. A top electrode contact adjoins the top electrode layer and a bottom electrode contact adjoins the bottom electrode layer extending through the insulating layer.

Also further disclosed herein is a method for forming an integrated circuit device on a substrate including at least one contact stud. The method comprises forming a first insulating layer on the substrate and removing a portion of the first insulating layer to produce an opening to an exposed surface of said substrate therein. First spacers are formed on the sidewalls of the opening and a first conductive layer is formed in contact with the contact stud on the exposed surface of the substrate separated from the first spacers on the sidewalls of the opening by a gap therebetween. A bottom electrode of a ferroelectric capacitor is formed over the first conductive layer and in the gap laterally of the first conductive layer. A second insulating layer is formed adjoining the spacers in the opening and second spacers are formed on the second insulating layer in the opening. A ferroelectric dielectric is formed on the bottom electrode between the second spacers and a top electrode is formed on the ferroelectric dielectric. An electrical contact is then formed to the top electrode.

Also further disclosed herein is a ferroelectric device which comprises a semiconductor substrate and a first conductive layer overlying the semiconductor substrate. A bottom electrode layer overlies the first conductive layer and first spacers are disposed laterally of the bottom electrode layer and extend distally of the substrate. Second spacers are disposed on the bottom electrode layer and extend distally therefrom substantially parallel to the first spacers. An insulating layer is disposed between the first and second spacers and a ferroelectric dielectric layer overlies the bottom electrode layer between the second spacers. A top electrode layer overlies the ferroelectric dielectric layer, a top electrode contact adjoins the top electrode layer and a bottom electrode contact adjoins the bottom electrode layer extending through the insulating layer.

The present invention presents a novel, non-volatile, ferroelectric random access memory (F-RAM) device and a method for fabricating a damascene self-aligned F-RAM device structure on a planar surface using a reduced number of masks and etching steps.

A representative method in accordance with the present invention comprises the processing steps disclosed in FIGS. 1 through 31 inclusive.

With reference now to FIG. 1, the structure of F-RAM substrate 100 is shown, and provides a depiction of the first-level F-RAM substrate with contact stud 108 and contact stud 110. In FIG. 1, a layer of BSPG 102 (boron phosphorus silicon glass) is deposited and planarized onto a silicon or other substrate (not shown in FIG. 1). Any oxide, nitride, or other appropriate dielectric can be substituted for the BPSG 102 layer. Formed in the BPSG 102 layer are contact stud 108 and contact stud 110 which are formed by Ti/TiN 104 (titanium/titanium nitride) liners and a chemical vapor deposition (CVD) of CVD tungsten (W) 106.

With reference additionally now to FIG. 2, the structure of F-RAM substrate 200 is illustrated depicting a thick oxide 202 layer of one to two microns thick, deposited over the F-RAM substrate 100. The thick oxide 202 layer is planar as it is deposited over the planarized surface, BPSG 102.

With reference additionally now to FIG. 3, the structure of a photoresist non-erodible mask 300 is shown. Following the process in FIG. 3, the first contact stud 110 is masked over using a photoresist mask 302. Masking may be performed through a standard process of spin applying photoresist, imaging it and developing it leaving an opening 303

With reference additionally now to FIG. 4, an F-RAM opening structure 400 is shown. In FIG. 4, the exposed portion of the thick oxide 202 layer surface is then etched away with a reactive-ion etching process using standard etch gases such as, but not limited, to CF₄and H₂in oxygen. This etching technique creates the F-RAM opening 402 where the F-RAM will be constructed. It should be noted that the BPSG layer 102 may be over etched and recessed (not shown).

With reference additionally now to FIG. 5, the F-RAM opening structure 500 is shown with the photoresist mask removed from F-RAM opening structure 400. In FIG. 5, the photoresist mask 302 may be removed employing a standard O₂plasma ash.

With reference additionally now to FIG. 6, the conformal CVD structure 600 is shown. In FIG. 6, a layer of between 2000 to 4000 angstroms of CVD aluminum oxide (Al₂0₃) is subsequently deposited over the F-RAM opening structure 500, forming a conformal CVD 602 layer of aluminum oxide on the top, sides and bottom of the thick oxide 202 layer.

With reference additionally now to FIG. 7, the removal of a portion of the CVD Al₂O₃material layer to create F-RAM structure with AL₂O₃spacers 700 is depicted. In FIG. 7, the conformal CVD 602 layer is removed from the top and bottom using a reactive ion directional etch using Cl₂/BCl₃/CCF₄/Ar on the planar surfaces leaving Al₂O₃spacers 702. With reference additionally now to FIG. 8, the F-RAM structure with AL₂O₃spacers 700 is shown with the addition of a conformal layer of about 1000 angstroms of titanium aluminum nitride film by a chemical vapor deposition (CVD) system. Titanium tetrachloride (TiCl₄), dimethylethylamine alane (DMEAA) and ammonia gas may be used as source gases. This forms titanium aluminum nitride structure 800. In FIG. 8, a layer of titanium aluminum nitride 802 is formed over the top of the F-RAM structure with AL₂O₃spacers 700. Note that the titanium aluminum nitride 802 layer covers the sides and bottom of the F-RAM opening 402.

With reference additionally now to FIG. 9, the application of a photoresist material on top of the titanium aluminum nitride structure 800 (titanium aluminum nitride) is shown, forming photoresist application structure 900. In FIG. 9, a photoresist 902 material is spun applied over the top of the titanium aluminum nitride structure 800 (titanium aluminum nitride).

With reference additionally now to FIG. 10, the etching of the photoresist material in photoresist application structure 900 is shown to create etched photoresist structure 1000. In FIG. 10, the photoresist 902 material is etched back using an oxygen (O₂) plasma ash in order to shape a structure below the surface of the titanium aluminum nitride 802 layer, leaving the photoresist 902 materials in the F-RAM opening 402.

With reference additionally now to FIG. 11, the removal of the exposed regions of the titanium aluminum nitride 802 layer in the etched photoresist structure 1000 is shown to create etched titanium aluminum nitride structure 1100 (etched titanium aluminum nitride). The titanium aluminum nitride is wet etched. In FIG. 11, the titanium aluminum nitride 802 layer is etched away exposing the base of the thick oxide 202 layer and also forming thin etched openings 1102 between the photoresist 902 material and the Al₂O₃spacers 702.

An enhanced view of section 1104 is shown (above-right) to detail the structure formed after the etching away of the titanium aluminum nitride 802 layer. Section 1104 illustrates how the titanium aluminum nitride 802 coating is etched back to the base of the thick oxide 202 layer, leaving a layer of titanium aluminum nitride 802 only below the remaining photoresist 902 material.

With reference additionally now to FIG. 12, the removal of the remainder of the photoresist material in the etched titanium aluminum nitride structure 1100 (etched titanium aluminum nitride) is shown, forming F-RAM titanium aluminum nitride structure 1200. In FIG. 12, the photoresist 902 material is completely removed by the same O₂plasma ash process described above. Note that a titanium aluminum nitride 802 layer remains on the base of the thick oxide 202 in the F-RAM opening 402.

With reference additionally now to FIG. 13, a layer of CVD platinum deposited over the top of the F-RAM titanium aluminum nitride structure 1200 is shown, forming F-RAM platinum structure 1300. In FIG. 13, a conformal platinum 1302 layer of 500 to 1000 angstroms is deposited by chemical vapor deposition over the top of the F-RAM titanium aluminum nitride structure 1200.

This platinum 1302 layer covers the top and bottom of the thick oxide 202, the top of the titanium aluminum nitride 802 layer and sidewalls of the Al₂O₃spacers 702.

With reference additionally now to FIG. 14, an application of photoresist material on top of the F-RAM platinum structure 1300 is shown, forming the second photoresist application structure 1400. In FIG. 14, a photoresist 1402 material is applied for the second time (as in FIG. 9) over the top of the F-RAM platinum structure 1300.

With reference additionally now to FIG. 15, the removal of a portion of the photoresist material in the second photoresist application structure 1400 is shown, forming etched photoresist structure 1500. In FIG. 15, the photoresist 1402 material is etched back using an oxygen (O₂) plasma ash in order to shape a structure below the surface of the conformal platinum 1302 layer. This etching process leaves the photoresist 1402 material only in the F-RAM opening 402.

With reference additionally now to FIG. 16, the removal of a portion of the platinum layer in the etched photoresist structure 1500 is depicted, creating etched platinum structure 1600. In FIG. 16, the conformal platinum 1302 layer is etched away from the top of the thick oxide 202 and the sides of the Al₂O₃spacers 702, forming a second etched opening 1602 between the photoresist 1402 material and the Al₂O₃. Note that in this process step the platinum 1302 layer is not etched all the way back to base of the thick oxide 202 layer in the F-RAM opening 402. Platinum is typically etched using a wet etch in an argon or chlorine atmosphere, although other gases may be used. Ion milling can be used as well as an alternative etching technique. As illustrated in FIG. 16, the photoresist 1402 material is left on top of the platinum 1302 layer in the F-RAM opening 402.

With reference additionally now to FIG. 17, the removal of the remainder of the photoresist material from the etched platinum structure 1600 is depicted, creating F-RAM platinum titanium aluminum nitride structure 1700 (titanium aluminum nitride). In FIG. 17, just the photoresist 1402 material is etched away using an O₂plasma ash etching technique and removed with a vacuum pump. Note that in this process step, the titanium aluminum nitride 802 layer remains at the base of the thick oxide 202 layer, with the platinum 1302 layer positioned above the titanium aluminum nitride 802 layer and is also in contact with the base of the thick oxide 202 layer.

With reference additionally now to FIG. 18, the deposition of an oxide layer over the top of the F-RAM platinum titanium aluminum nitride structure 1700 (titanium aluminum nitride) is shown, creating oxide deposition structure 1800. In FIG. 18, an oxide 1802 layer thick enough to completely fill the F-RAM opening 402 is formed.

With reference additionally now to FIG. 19, the removal of the oxide material in the oxide deposition structure 1800 is shown to form CMP oxide structure 1900. In FIG. 19, CMP is used once more to polish away the oxide 1802 material all the way back to the level of the thick oxide 202 to form a planar surface 1902 on top of the thick oxide 202. Notice that the oxide 1802 remains embedded in F-RAM opening 402 and is planar to the top surface of the thick oxide 202.

With reference additionally now to FIG. 20, the application of a photoresist mask over the CMP oxide structure 1900 is shown, creating photoresist mask structure 2000. In FIG. 20, a photoresist mask 2002 is deposited over the CMP oxide structure 1900 and then imaged and developed to form a mask opening 2004. This step leaves the oxide 1802 partially exposed in the area of the F-RAM opening 402.

With reference additionally now to FIG. 21, the etching of the exposed oxide in the photoresist mask structure 2000 is shown, forming etched oxide structure 2100. According to the pattern created by the photoresist mask 2002, the oxide 1802 material in the F-RAM opening 402 is etched down to the platinum 1302 layer. This oxide 1802 material can be removed using reactive-ion etch processing. This step creates oxide 1802 layers on each side of the F-RAM opening 402.

With reference additionally now to FIG. 22, the formation of the second conformal CVD structure 2200 is shown. In FIG. 22, the photoresist mask 2002 is subsequently removed using the same O₂plasma ash etching technique described above. A second layer of 1000 to 2000 angstroms of Al₂O₃is then deposited using chemical vapor deposition (as in FIG. 6) over the top of the thick oxide 202, the etched oxide 1802, the platinum 1302 and the sides and bottom of the F-RAM opening 402, forming a another conformal CVD oxide 2202 layer of Al₂O₃.

With reference additionally now to FIG. 23, the removal of a portion of the conformal CVD layer from the second conformal CVD structure 2200 is shown, forming an F-RAM Al₂O₃structure 2300. In FIG. 23, the conformal CVD oxide 2202 layer is etched away from the planar regions of the thick oxide 202 with a directional reactive-ion etch, forming the second set of Al₂O₃spacers 2302. Note that in this step, the conformal CVD oxide 2202 layer of Al₂O₃remains along the sides of F-RAM opening 402.

With reference additionally now to FIG. 24, the addition of a ferroelectric layer to the F-RAM Al₂O₃structure 2300 is shown, creating F-RAM PZT structure 2400. In FIG. 24, a first ferroelectric layer, ideally doped with PZT (lead zirconium titanate), PZT 2402 material is deposited, planarized and then etched back into F-RAM opening 402. The PZT 2402 material is formed of lead (Pb), zirconium (Zr), and titanate (Ti) atoms, with an atomic ratio of the Zr atoms to the Ti atoms (Zr:Ti) of less than 2:3. After the PZT 2402 material is deposited, a first anneal is performed to crystallize the PZT 2402 material. This involves a 650° C. heat treatment for about five seconds followed by another heat treatment at 850° C. for another 5 seconds. While PZT 2402 is used as the ferroelectric layer, other known ferroelectric compounds such as strontium bismuth tantalate (SBT) may also be employed.

With reference additionally now to FIG. 25, the addition of a top electrode to the F-RAM PZT structure 2400 is shown, creating an F-RAM PZT electrode structure 2500. In FIG. 25, a top electrode, TE 2502 material is deposited, planarized and etched back into the F-RAM opening 402. The etching is performed with a reactive-ion agent and the TE 2502 material lies on top of the PZT 2402 layer. Suitable materials for the TE 2502 include iridium (Ir) and iridium oxide (IrOx), platinum (Pt), palladium (Pd) and palladium oxide (PdOx), ruthenium (Ru) and ruthenium oxide (RuOx), rhodium (Rh) and rhodium oxide (RhOx), and other compatible noble metals.

With reference additionally now to FIG. 26, the addition of a layer of Ti/TiN to the F-RAM PZT electrode structure 2500 is illustrated, creating an F-RAM PZT Ti/TiN structure 2600. In FIG. 26, a layer of titanium/titanium nitride Ti/TiN 2602 is deposited onto the F-RAM PZT electrode structure 2500. The Ti/TiN 2602 is planarized to the surface of the F-RAM opening 402 and then etched with a reactive-ion reagent back in the F-RAM opening 402. In this step the Ti/TiN 2602 layer overlies the top of the TE 2502 layer.

With reference additionally now to FIG. 27, the addition of a nitride layer is shown, forming F-RAM PZT nitride structure 2700. In FIG. 27, a nitride 2702 layer is subsequently deposited and planarized on top of the Ti/TiN 2602 layer in the F-RAM PZT Ti/TiN structure 2600. Note that in this step, the nitride 2702 layer remains planar with the top surface of the thick oxide 202.

With reference additionally now to FIG. 28, the application of a photoresist mask on top of the F-RAM PZT nitride structure 2700 is depicted, creating a contact photoresist mask structure 2800. In FIG. 28, a photoresist mask 2802 (similar to the step in FIG. 20) is imaged and developed on top of the F-RAM PZT nitride structure 2700 to form mask openings over three different regions: the opening 12804 over the nitride 2702, the opening 22806 over the etched oxide 1802, and the opening 32808 over the thick oxide 202.

With reference additionally now to FIG. 29, the etching of the exposed oxide in the contact photoresist mask structure 2800 is shown, creating contact oxide etching structure 2900. Continuing with the process, in FIG. 29, the exposed oxide 1802 layer and the exposed thick oxide 202 are etched away using CF₄in oxygen, forming opening 2902 and opening 2904 conforming to the pattern of the photoresist mask 2802. Note that in this process step, opening 12804 over the nitride 2702 is left undisturbed.

With reference additionally now to FIG. 30, an additional etching in the contact oxide etching structure 2900 is shown, forming contact nitride etching structure 3000. In FIG. 30, a gas etch chemistry (CF₄with 4% oxygen) is employed to etch the exposed area of the silicon nitride 2702 layer back to the Ti/TiN 2606 layer. This etching agent acts without affecting the thick oxide 202, oxide 1802, or the Ti/TiN 2602 layer below the silicon nitride 2702. This process step forms the opening 3002.

With reference additionally now to FIG. 31, the removal of the photoresist mask and the addition of three contact studs to the contact nitride etching structure 3000 is shown, creating the final F-RAM contact stud structure 3100.

The last process steps are illustrated in FIG. 31. The photoresist mask 2802 is removed from the F-RAM contact stud structure 3100 using the same O₂plasma ash etching technique as used earlier. Subsequently Ti/TiN liners 3102 are deposited onto opening 2902, opening 2904, and opening 3002 followed by an application of a CVD tungsten 3104 layer over the entire surface of the F-RAM contact stud structure 3100, followed by a CMP process to polish back and planarize the CVD tungsten 3104 back to the level of the thick oxide 202. As a result of these steps, three new contact studs (contact stud 3106, contact stud 3108 and contact stud 3110) are formed of Ti/TiN and CVD tungsten. Contact stud 3106 contacts the Ti/TiN 2602 layer and consequently the TE 2502 layer. Contact stud 3108 contacts the base of the platinum 1302 which is on the other side of the F-RAM structure and between the Al₂O₃spacers 2302 and 702 as illustrated.

As can be appreciated by reference to the drawing figures, there are provided alternative contacts to the bottom electrode (platinum 1302 layer) of the ferroelectric capacitor in the form of contact stud 108 and contact stud 3108. Although both are herein illustrated and described, either may be utilized alone or in combination. It should be noted that omitting contact stud 3108 will provide greater device density in an integrated circuit embodiment of the present invention.

While there have been described above the principles of the present invention in conjunction with specific processing steps and device structure, it is to be clearly understood that the foregoing description is made only by way of example and not as a limitation to the scope of the invention. Particularly, it is recognized that the teachings of the foregoing disclosure will suggest other modifications to those persons skilled in the relevant art. Such modifications may involve other features which are already known per se and which may be used instead of or in addition to features already described herein. Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure herein also includes any novel feature or any novel combination of features disclosed either explicitly or implicitly or any generalization or modification thereof which would be apparent to persons skilled in the relevant art, whether or not such relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as confronted by the present invention. The applicants hereby reserve the right to formulate new claims to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

As used herein, the terms “comprises”, “comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a recitation of certain elements does not necessarily include only those elements but may include other elements not expressly recited or inherent to such process, method, article or apparatus. None of the description in the present application should be read as implying that any particular element, step, or function is an essential element which must be included in the claim scope and THE SCOPE OF THE PATENTED SUBJECT MATTER IS DEFINED ONLY BY THE CLAIMS AS ALLOWED. Moreover, none of the appended claims are intended to invoke paragraph six of 35 U.S.C. Sect. 112 unless the exact phrase “means for” is employed and is followed by a participle.