Abstract:
A method for forming a copper dual damascene with improved copper migration resistance and improved electrical resistivity including providing a semiconductor wafer including upper and lower dielectric insulating layers separated by a middle etch stop layer; forming a dual damascene opening extending through a thickness of the upper and lower dielectric insulating layers wherein an upper trench line portion extends through the upper dielectric insulating layer thickness and partially through the middle etch stop layer; blanket depositing a barrier layer including at least one of a refractory metal and refractory metal nitride to line the dual damascene opening; carrying out a remote plasma etch treatment of the dual damascene opening to remove a bottom portion of the barrier layer to reveal an underlying conductive area; and, filling the dual damascene opening with copper to provide a substantially planar surface.

Description:
FIELD OF THE INVENTION 
   This invention generally relates to semiconductor device manufacturing methods and more particularly to a method for forming copper damascenes with reduced electrical resistivity and improved reliability. 
   BACKGROUND OF THE INVENTION 
   In forming damascene structures in integrated circuit manufacturing processes, barrier layer uniformity is critical for achieving acceptable copper diffusion resistance and for achieving electrical resistances within required IC performance standard constraints. A damascene opening, for example a dual damascene opening is formed in an inter-metal dielectric insulating layer by a series of photolithographic patterning and etching processes, followed by formation of a barrier layer and a metal filling process. 
   Increasingly, low-K layers are required to reduce signal delay and power loss effects as integrated circuit devices are scaled down. One way this has been accomplished has been to introduce porosity or dopants into the dielectric insulating layer, also referred to as an inter-metal dielectric (IMD) layer. 
   One problem with using porous low-k materials together with using copper as the metal filling in a copper damascene process is the susceptibility of the low-k materials to copper diffusion into the IMD layers, which has the effect of altering the dielectric constant of the IMD layer and degrading damascene electrical resistivity. Prior art processes have proposed different barrier layer materials for use with copper and porous low-k materials including refractory metals and refractory metal nitrides have been used to both form a robust barrier layer while achieving reduced copper damascene electrical resistivities. 
   As device characteristic dimensions have decreased below about 0.25 microns and lower including less than about 0.17 microns, adequate step coverage of damascene openings with barrier layer deposition methods has become a challenge. Prior art processes have attempted to use various physical vapor deposition (PVD) processes to achieve adequate step coverage. However, PVD processes are inherently limited in depositing thin layers of materials in smaller openings due to the physical nature of sputter deposition processes. For example, PVD processes tend to form a higher coverage at the bottom of the opening compared with the sidewall portions. In addition, with respect to a dual damascene process, barrier layer coverage tends to be thinned at corner portions, e.g., bottom via corner and via/trench transition portions of the dual damascene, making copper diffusion into the IMD layer more likely. In addition, barrier layer coverage over the via bottom portion and sidewall portions in the upper trench portion is generally formed with a relatively increased thickness thereby undesirably increasing electrical resistances. 
   There is therefore a need in the semiconductor processing art for a method for forming copper damascenes with improved barrier layer coverage uniformity while reducing a contribution to electrical resistivity thereby improving performance and reliability of an integrated circuit. 
   It is therefore among the objects of the present invention to provide a method for forming copper damascenes with improved barrier layer coverage uniformity while reducing a contribution to electrical resistivity thereby improving performance and reliability of an integrated circuit, in addition to overcoming other shortcomings of the prior art. 
   SUMMARY OF THE INVENTION 
   To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a method for forming a copper dual damascene with improved copper migration resistance and improved electrical resistivity. 
   In a first embodiment, the method includes providing a semiconductor wafer including upper and lower dielectric insulating layers separated by a middle etch stop layer; forming a dual damascene opening extending through a thickness of the upper and lower dielectric insulating layers wherein an upper trench line portion extends through the upper dielectric insulating layer thickness and partially through the middle etch stop layer; blanket depositing a barrier layer including at least one of a refractory metal and refractory metal nitride to line the dual damascene opening; carrying out a remote plasma etch treatment of the dual damascene opening to remove a bottom portion of the barrier layer to reveal an underlying conductive area; and, filling the dual damascene opening with copper to provide a substantially planar surface. 
   These and other embodiments, aspects and features of the invention will be better understood from a detailed description of the preferred embodiments of the invention which are further described below in conjunction with the accompanying Figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A to 1F  are cross sectional views of a dual damascene structure at stages of manufacture according to an embodiment of the invention. 
       FIG. 2  is a schematic diagram of an exemplary remote plasma etch system for carrying out embodiments of the method of the present invention. 
       FIG. 3  is a process flow diagram including several embodiments of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Although the present invention is explained by reference to an exemplary dual damascene formation process, it will be appreciated that the method of the present invention applies generally to the formation of damascenes including dual damascenes whereby stacked multi-layer inter-metal dielectric (IMD) layers, also referred to as an inter-layer dielectric (ILD), may be formed with an intervening etch stop layer to improve barrier layer coverage, resistance to copper electro-migration, and improved electrical performance and reliability. Although the method of the present invention is particularly advantageous in forming copper damascenes with characteristic dimensions of less than about 0.17 microns, and aspect ratios (depth to diameter/width) of greater than about 6 to 1, it will be appreciated that the method of the present invention may be adapted to larger characteristic dimension damascene processes. 
   By the term damascene is meant any metal filled opening formed in a dielectric insulating layer e.g., both single and dual damascenes. Further, although the method is particularly applicable and advantageously applied to copper filled damascenes, it will be appreciated that the metal used to fill the damascene opening may include other metals such as tungsten, aluminum, and copper alloys. The method of the present invention is particularly advantageously used in the formation of copper damascene features such as vias and trench lines with linewidths/diameters less than about 0.25 microns, more preferably less than about 0.17 microns, e.g., 0.13 microns and lower. In addition, the method is particularly advantageously used with silicon oxide based low-K dielectric insulating layers having an interconnecting porous structure and having a dielectric constant of less than about 3.0 including less than about 2.5, for example from about 2.2 to about 3.0. Further, the term ‘copper’ will be understood to include copper and alloys thereof. 
   For example, in an exemplary embodiment, referring to  FIGS. 1A–1F , are shown cross sectional views of a portion of a multi-level semiconductor device at stages in an integrated circuit manufacturing process. 
   Referring to  FIG. 1A , a conductive region  11 , for example a conductive metal interconnect, e.g., a copper damascene, is formed in a dielectric insulating layer  10  by conventional processes known in the micro-electronic integrated circuit manufacturing process followed by deposition of an overlying first etch stop layer  12 A, preferably including at least one of silicon nitride (e.g., SiN, Si 3 N 4 ), silicon oxynitride (e.g., SiON), and silicon carbide (e.g., SiC) to a thickness of about 300 Angstroms to about 700 Angstroms by a conventional CVD method, for example LPCVD or PECVD. Most preferably, the first etch stop layer  12 A is formed of silicon nitride. 
   Still referring to  FIG. 1A , formed over first etch stop layer  12 A is first dielectric insulating (IMD) layer  14 A, preferably formed of a silicon oxide based low-K material having a porous structure, for example including interconnecting pores. The dielectric insulating layer  14 A is preferably formed by a PECVD process including organo-silane precursors such as methylsilanes, for example, tetramethylsilane and trimethylsilane. In addition, organo-siloxane precursors such as cyclo-tetra-siloxanes may be used as well to form the IMD layer portion  14 A. The dielectric insulating layer  14 A may additionally be formed of fluorinated silicate glass (FSG). Preferably the lower IMD layer portion  14 A is formed at a thickness sufficient to encompass a via portion of a subsequently formed dual damascene structure, for example from about 1000 Angstroms to about 2700 Angstroms in thickness. 
   Still referring to  FIG. 1A , second etch stop layer  12 B is deposited, preferably formed of a composite layer including at least two different material layers, preferably one of the material layers, preferably a lowermost layer, is formed of silicon nitride (e.g., SiN, Si 3 N 4 ) or silicon oxynitride (e.g., SiON), (e.g., SiON) of about 200 to about 400 Angstroms in thickness. Another layer, preferably an uppermost layer, for example an overlying layer, is formed of silicon carbide (e.g., SiC) or silicon oxycarbide (e.g., SiOC) formed at a thickness of about 100 Angstroms to about 300 Angstroms. 
   Most preferably, the composite etch stop layer  12 B is formed of a lowermost layer of silicon nitride and an overlying (uppermost) layer of silicon carbide. The etch stop layer  12 B may be formed by conventional CVD processes, for example PECVD or LPCVD. The composite etch stop layer  12 B serves to add increased resistance to copper migration and advantageously enables etching endpoint detection using conventional methods, such as optical detection of etching plasma constituents, to enable controlled partial etching through a thickness of the composite etch stop layer  12 B as further explained below. 
   Still referring to  FIG. 1A , a second dielectric insulating layer  14 B is then deposited, for example formed of the same preferred materials and the same manner as the first dielectric insulating layer portion  14 A. The upper IMD layer  14 B is preferably deposited to a thickness sufficient to encompass a trench line portion of a subsequently formed dual damascene structure. Still referring to  FIG. 1A , an optional ARC layer  16 , organic or inorganic material, preferably formed of silicon oxynitride, is deposited overlying the upper dielectric insulating layer  14 B. 
   Referring to  FIG. 1B , conventional photolithographic patterning and dry etching processes are then carried to form a dual damascene opening  18 , for example exposing the underlying conductive area  11 . For example a via opening  18 A, is first formed by conventional photolithographic patterning and reactive ion etch (RIE) processes, preferably, but not exclusively formed having a diameter of less than about 0.25 microns, more preferably less than about 0.17 microns. In an important aspect of the invention, the trench opening portion  18 B is etched by a conventional RIE etch process to stop on the composite SiON/SiC second etch stop layer  12 B, preferably including etching through a thickness portion, preferably through the thickness of the uppermost layer, but not through the entire thickness of the second stop layer  12 B. 
   Referring to  FIG. 1C , according to an aspect of the invention, a PVD method is then carried out to blanket deposit a barrier layer  20 A, preferably including one of a refractory metal, refractory metal nitride, and silicided refractory metal nitride layer, for example Ta, Ti, W, TaN, TiN, WN, TaSiN, TiSiN, and WSiN. In a preferred embodiment, the barrier layer  20 A is formed of Ta/TaN, TaN, or TaSiN, most preferably, a Ta/TaN composite layer. Preferably, the Ta/TaN layer is deposited by an ion metal plasma (IMP) process with the barrier layer  20 A preferably deposited to a thickness of between about 100 Angstroms and about 350 Angstroms. 
   Referring to  FIG. 1D , In an important aspect of the invention, a remote plasma etch treatment including one or more inert plasma source gases such as nitrogen, helium, and argon is carried out to etch a portion of the barrier layer  20 A. Preferably the remote plasma etch treatment is carried out to remove the barrier layer  20 A covering the bottom portion  20 B of via portion  18 A of the dual damascene opening to reveal the underlying conductive portion  11 , for example a copper interconnect. It has been found that the remote plasma etch treatment carried out according to preferred embodiments, serves to make the barrier layer  20 A more uniform in thickness at the sidewalls of the trench portion  18 B and the via portion  18 A of the dual damascene opening while removing the bottom portion of via portion  18 A. Preferably, the barrier layer  20 A following the remote plasma treatment is formed having a thickness between about 50 Angstroms and about 250 Angstroms. 
   Advantageously, according to the present invention, the barrier layer  20 A is made more uniform in thickness following the remote plasma etch process along the sidewalls and corner portions, e.g., at the trench/via transition portion e.g.,  23  extending through a thickness portion of the SiON/SiC composite etch stop layer  12 B. Advantageously, the barrier layer  20 A may be made thinner with increased thickness uniformity along the sidewalls including corner portions to reduce an electrical resistivity contribution of the barrier layer  20 A while assuring sufficient coverage to avoid copper diffusion and migration into the IMD layers. 
   Referring to  FIG. 2  is shown a conventional remote plasma etcher configuration suitable for use with the method of the present invention. Remote plasma source  34  generally comprises a chamber coupled to one or more plasma gas sources e.g.,  36  via gas lines e.g.,  36 A. Remote plasma source  34  is positioned upstream of process chamber e.g.,  38  and fluidly coupled by a conduit e.g.,  34 A to process chamber  38  through a gas diffusion (distribution) manifold  30 . The plasma generated by the remote plasma source  34  enters the process chamber  38  through the gas diffusion manifold  30  and is directed downward to impact process wafer  32 A supported on wafer pedestal  32 B. The wafer pedestal  32 B may be connected to a DC or an RF bias source (not shown). A gas pumping port, e.g.,  36  maintains a desired operating pressure in the process chamber, for example between about 1 mTorr and about 100 mTorr. The remote plasma source  34  may include an RF generator and electrodes (not shown) and may include deflectors (not shown) to direct the flow of gas in a spiral flow pattern. The remote plasma source  34 , for example, may operate at between about 1000 and about 5000 Watts of RF power, at a frequency between about 1 MHz and about 100 MHz. The remote plasma source  34  may alternately include a remote microwave plasma source including a microwave cavity coupled to a microwave generator operating between about 1500 and 2500 watts, at a frequency of between about 1 and 5 GHz. 
   Referring back to  FIG. 1E , conventional copper deposition processes, preferably electrochemical deposition (ECD) of copper preceded by deposition of a copper seed layer (not shown) is then carried out to fill the dual damascene opening with copper layer  22 . Advantageously, the copper seed layer is advantageously able to be formed more reliably over the more uniform step coverage of remote plasma etched barrier layer  20 A. For example, the copper seed layer is preferably deposited to a thickness of between about 50 Angstroms and about 150 Angstroms. 
   Referring to  FIG. 1F , a conventional planarization process, for example a chemical mechanical polish (CMP) process is then carried out to remove the excess portion of copper layer  22  above the damascene opening level, preferably including barrier layer  20 A, and the ARC layer  16  to complete the formation of the copper dual damascene. 
   Referring to  FIG. 3  is shown a process flow diagram including several embodiments of the present invention. In process  301 , a semiconductor wafer process surface is provided including metal interconnects formed in a dielectric insulating layer. In process  303 , a first etch stop layer is formed over the process surface according to preferred embodiments. In process  305  a first IMD layer is formed over the first etch stop layer according to preferred embodiments. In process  307 , a composite etch stop layer is formed over the first IMD layer according to preferred embodiments. In process  309 , a second IMD layer is formed over the composite etch stop layer. In process  311 , a via opening followed by formation of an overlying trench opening is formed stopping on the composite etch stop layer, e.g., extending through a thickness portion of the composite etch stop layer to form a dual damascene opening. In process  313 , a barrier layer is blanket deposited to line the dual damascene opening according to a PVD process. In process  315 , a remote plasma etch treatment is carried out to remove a portion of the barrier layer including the bottom portion of the via portion to reveal an underlying metal interconnect portion. In process  317 , the dual damascene is completed by conventional processes including filling with copper and planarization. 
   The preferred embodiments, aspects, and features of the invention having been described, it will be apparent to those skilled in the art that numerous variations, modifications, and substitutions may be made without departing from the spirit of the invention as disclosed and further claimed below.