Method for forming an integrated barrier/plug for a stacked capacitor

A dynamic random access memory (DRAM) cell is implemented using a number of memory cells formed as part of a large array in a semiconductor chip. The memory cells typically comprise a storage capacitor in combination with an access transistor. A stacked DRAM cell is formed by a stacked capacitor structure which lies on the surface of a semiconductor. An underlying drain/source region from an access transistor is coupled to the stacked transistor's bottom electrode by a conductive plug which extends from the bottom electrode to an underlying drain/source region of the access transistor.

Typically, the conductive plug is separated from the bottom electrode by a diffusion barrier. For instance, U.S. Pat. No. 5,825,609 (hereinafter referred to as '609) to Andricacos et al. discloses such a structure at column 6, lines 58-60. This patent also describes a number of layered electrode structures generally connected together by conductive sidewall coatings. Andriacacos further discloses that the conductive plug structure can be entirely filled with one or more barrier materials. However, the complexity of the layered and conductive sidewall-coated structures generally are not well suited for small capacitors which are associated with 1 gigabit or higher memories.

FIGS. 1 through 7 are cross-sectional drawings illustrating the process of forming a stacked capacitor cell according to the invention as described below. Reference numerals are carried forward.

The invention provides a method whereby an improved stacked capacitor results therefrom. With reference to FIG. 1, dielectric 2 such as an oxide is formed on a single crystalline substrate such as single crystalline silicon 4 .

As shown in the resulting structure of FIG. 2, which illustrates a cross-sectional view of the in-process memory cell, dielectric 2 is patterned and etched using conventional etchants and lithographic methods to form contact plug area 6 through dielectric 2 down to substrate 4 . Conductive material 7 such as titanium nitride (TiN), tungsten nitride, titanium aluminum nitride, tantalum silicon nitride (Ta 1−x Si x N y , with O<x<1 and y>1), or other materials having the property of being a barrier to oxygen diffusion as well as to adjacent material, is used to fill contact plug area 6 thereby providing a conductive plug and a diffusion barrier between materials from substrate 4 and adjacent areas including stacked layers adjacent the plug/diffusion barrier. An integrated plug and barrier 8 (referred to hereinafter as barrier/plug 8 ) is thereby provided in a single step. Preferably, this conductive material is deposited using a chemical vapor deposition (CVD) process.

With reference to FIG. 3, which illustrates a cross-section of the capacitor cell undergoing processing, the barrier/plug material is planarized by a method of CMP or other conventional planarization methods.

Material 10 for a bottom electrode is placed over barrier/plug 8 , preferably by a method of deposition as shown in the cross-sectional drawing of FIG. 4 . The bottom electrode is preferably formed of Platinum (Pt). However, other materials can be used for material 10 such as those selected for the groups consisting of noble metals (e.g. Au, Pt, PD, Ir, and Rh), alloys of noble metals with noble or non-noble metals, metals whose oxides are conducting (such as Ru and Mo) electrically conducting oxides (e.g. RuO 2 , IrO 2 , and Re 2 O 3 , etc.), electrically conductive, oxidation-resistant nitrides (e.g. TaN, TaSiN) and electrically conductive materials whose oxides can be insulating such as Ti, Al, TiN, W, WN, doped polysilicon, etc.

With reference to FIG. 5, which illustrates a cross-section of the processedmemory cell, the electrode material is patterned and etched by conventional methods to form bottom electrode 12 as shown.

With reference to FIG. 6, dielectric 14 , which serves as the capacitor cell dielectric, is preferably BSTO (barium strontium titanate oxide) and alternatively selected from materials such as, paraelectrics, perovskites, pyrochlores, relaxors, layered perovskites,ferroelectrics, or other dielectric material having a high (e.g.>18) dielectric constant. Dielectric 14 is deposited over all as illustrated in the cross-sectional drawing of FIG. 6 . Other suitable dielectrics include, TA 2 O 5 , (Ba,SR)TiO 3 , barium strontium titanate (BST), BaTiO 3 , SrTiO 3 , PbZr 1−x , Ti 2 , 0 3 (PZT), PbZrO 3 , Pb l−x La x TiO 3 (PLT), Pb 1−x La x (Zr y Ti 1−y ) 1−x/z O 3 (PLZT), and SrBi 2 Ta 2 O 9 (SBT). Top electrode 16 , which can be formed of the same material as bottom electrode 12 , is deposited over dielectric 14 as illustrated in the cross-sectional drawing of FIG. 7, thereby forming the structure of a capacitor comprising two electrically conductive surfaces in spaced apart relation separated by an insulator.

A primary advantage of the invention lies in the fact that the reduced complexity of the process, in relation to prior art processes, is better suited for obtaining improved functionality and process yield for highly integrated, dimensionally smaller devices.

A further advantage of the invention is that the single material plug structure is a better diffusion barrier as compared with structures wherein a barrier abuts a conductor such as polysilicon. Diffusion barrier effectiveness is governed to an extent by thickness and the barrier to diffusion provided by the invention's conductive barrier material is more effective than a non-conductive barrier and conductor which occupy comparable space.

Another advantage of the invention is provided through plug material which is much more conductive than polysilicon; a material typically used for plugs. Consequently, the foregoing invention provides a method which results in decreased contact plug resistance as compared with conventional methods leading to for instance, a poly plug.

The foregoing invention is especially well suited for use in forming the storage capacitor of a memory cell in a dynamic random access memory (DRAM).

Although the invention has been described in detail herein with reference to the preferred embodiments and certain described alternatives, it is to be understood that this description is by way of example only, and it is not to be construed in a limiting sense. It is to be further understood that numerous changes in the details of the embodiments of the invention and additional embodiments of the invention, will be apparent to, and may be made by, persons of ordinary skill in the art having reference to this description. For instance, the substrate on which the capacitor is formed may be silicon or any other known semiconductor such as, gallium arsenide, indium, germanium, or diamond. It is contemplated that all such changes and additional embodiments are within the spirit and true scope of the invention as claimed below.