Patent Publication Number: US-7220677-B2

Title: WAT process to avoid wiring defects

Description:
FIELD OF THE INVENTION 
   This invention generally relates to metrology methods in micro-integrated circuit manufacturing, and more particularly to an improved metrology method for carrying out a wafer acceptance testing (WAT) process to avoid conductive hump defects and improve formation of an overlying metallization level including avoiding etch stop phenomenon. 
   BACKGROUND OF THE INVENTION 
   Since the introduction of semiconductor devices, the size of semiconductor devices has been continuously shrinking, resulting in smaller semiconductor chip size and increased device density. One of the difficult factors in the continuing evolution toward smaller device size and higher density has been the ability to consistently form reliable integrated circuit wiring at smaller critical dimensions. For example, the reliability and electrical continuity of integrated circuitry wiring is determined by electrical continuity measurement methods following formation of a metallization level of circuitry wiring, also referred to as acceptance testing (WAT), to quickly determine and correct processing variables that may be causing circuitry defects. 
   In addition, a recurring problem in etching high aspect ratio openings in dielectric layers in a damascene formation process relates to a failure of the etching process to completely etch through the dielectric layer, also referred to as etch stop behavior. Etch stop behavior has been associated with the build-up of polymer residues at the bottom of an etched opening which overcomes the steady state anisotropic etching process, prematurely stopping the etching depth of the opening. Subsequently formed damascene wiring interconnects are therefore defective and result in open electrical conductive pathways that can no longer be used, thereby detrimentally affecting yield and performance of a multi-level semiconductor device. 
   There is a continuing need in the semiconductor device manufacturing art for improved wafer acceptance testing (WAT) methods as well as improved damascene formation processes to improve the yield and performance of multi-level semiconductor devices. 
   It is therefore an object of the invention to provide an improved wafer acceptance testing (WAT) method as well as an improved damascene formation process to improve the yield and performance of multi-level semiconductor devices, 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 multi-level semiconductor device to eliminate conductive interconnect protrusions following a WAT test. 
   In a first embodiment, the method includes forming a first metallization layer; carrying out a wafer acceptance testing (WAT) process; and, then carrying out a chemical mechanical polish (CMP) on the metallization layer. 
   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 
       FIG. 1A–1C  are cross sectional views of an exemplary damascene formation process according to an embodiment of the present invention. 
       FIGS. 2A and 2B  illustrate the exemplary formation of a conductive hump on a contact pad during and following WAT probing. 
       FIG. 3  is a process flow diagram including several aspects of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Although the method and apparatus of the present invention is explained and is particularly advantageous for avoiding the formation of conductive wiring defects and improving the formation of an overlying metallization (wiring) layer in a single damascene formation process, it will be appreciated that the method may be applied any type of damascene formation process including single damascene and dual damascene formation processes. 
   Referring to  FIG. 1A  is shown a cross sectional view of a portion of an exemplary multi-level device including dielectric layer  10 . The dielectric layer  10 , for example, includes conductive regions  11 A and  11 B, for example to form a first metallization (e.g., M 1 ) layer. It will be appreciated that the conductive regions  11 A and  11 B in the first metallization layer may be a contact hole (via) in electrical communication with underlying conductive areas or CMOS devices (not shown). An etch stop layer  12 A, may be formed over the underlying dielectric layer  10 . The etch stop layer  12 A may be formed of conventional etch stop materials, including materials such as SiN, SiON, SiC, or SiOC, and formed by conventional process e.g., chemical vapor deposition (CVD), low pressure (LP), plasma enhanced (PE) CVD. 
   Still referring to  FIG. 1A , a dielectric insulating layer  14 A is formed on the etch stop layer  12 A, followed by conventional damascene formation processes such as photolithographic patterning to form a resist etching mask (not shown) which is then followed by plasma assisted anisotropic etching to form wiring interconnect openings overlying and in communication with the conductive regions  11 A and  112 . Conventional damascene formation processes are then carried out to backfill the interconnect openings with a conductive material to form a metallization layer (e.g., M 2 ) including conductive interconnects, e.g.,  16 A and  16 B. The interconnects may be trench lines, contact pads, or vias (holes), including dual damascenes. The conductive material may include any conductor, but preferably is a relatively ductile metal such as copper, aluminum, or alloys thereof. 
   The dielectric insulating layer  14 A may be any insulating dielectric layer but is preferably a low-K organic or inorganic dielectric material, including a porous dielectric material. The term “low-K” as used herein means a dielectric constant of less than about 3.4. Exemplary low-K dielectrics may include carbon doped silicon oxide (e.g., Black Diamond™ or the like), organo-silicate glass (OSG), or fluorinated silicate glass (FSG) . The low-K dielectric layer  14 A may be formed by conventional processes such as PECVD, spin-on processes, and the like. It will be appreciated that an organic or inorganic bottom anti-reflectance coating (BARC) layer may be formed over the dielectric insulating layer  14 A prior to photoresist patterning and interconnect opening etching. 
   Following formation of the conductive interconnects, which may include a planarization process such as chemical mechanical polishing (CMP), selected conductive interconnects (e.g., contact pads) are probed according to a first conventional Wafer Acceptance Testing (WAT) process, also referred to as a Wafer Electrical Testing (WET), to test electrical properties e.g., DC resistance or resistivity of the interconnect wiring in the underlying metallization layers (e.g., M 1  and M 2 ) which are then related to acceptable interconnect formation, e.g., acceptable interconnect electrical resistance. For example, the WAT process to test the electrical properties of the wiring interconnects preferably includes contacting selected conductive interconnects including probing of the interconnects by a conventional probe e.g., a probe tip, to contact and apply a DC voltage to selected conductive interconnects exposed at the wafer process surface, for example contact pads in electrical communication with other conductive interconnects in M 1  and/or M 2  metallization layers. For example, process control monitor (PCM) features, similar to those being formed in device circuitry portions of a process wafer, are typically formed over selected portions of the process wafer to allow an in-line parametric test (e.g., WET) to take place following interconnect formation processes. It will be appreciated that the method according to the present invention may be applied in connection with any in-line parametric process of any metallization layer (e.g., M 1 ) which includes contacting one or more conductive interconnects, preferably prior to formation of an overlying metallization layer (e.g., M 2 ). 
   Referring to  FIG. 2A , is shown an exemplary conductive contact pad  22  being probed by probe tip  24 . For example, in a typical WAT process, probe tips are automatically positioned with respect to the process wafer to contact the contact pad. During the alignment and contact process, a scrub mark e.g.,  26  is formed on the contact pad  22 . Referring to  FIG. 2B  is shown an exemplary cross section of damascene contact pad  22  formed in dielectric layer  22 B, where a conductive metallic hump portion e.g.,  22 C on the edge of a scrub mark (probe mark) is formed extending above the planarized surface of the conductive contact. It has been found according to the present invention, that the hump portion  22 C may adversely affect subsequent damascene formation processes during formation of an overlying metallization layer, further discussed below. 
   In one aspect of the invention, an optional thermal and/or plasma treatment is carried out on exposed conductive interconnects prior to carrying out the WAT process. For example, the process wafer surface including the exposed conductive interconnects are subjected to a plasma or thermal treatment including a hydrogen containing and/or an inert gas containing source (e.g., ambient thermal treatment source or plasma treatment source gas). For example, the hydrogen containing source gas may include one or more of H 2  and NH 3  source gases. The inert gas containing source may be formed of one or more of Ar, He, Xe, and the like. The source gas may include both hydrogen and inert gas. It will be appreciated that both a thermal and plasma treatment may also be performed. 
   Following the optional plasma or thermal treatment, and the WAT process, the wafer process surface including the exposed conductive interconnects, is subjected to a CMP step to planarize e.g., re-planarize the process surface. For example, the CMP process preferably includes a conventional metal polishing or buffing solution as is known in the art for copper, aluminum, or alloys thereof. 
   Referring to  FIG. 1B , following the CMP process, an overlying metallization layer formation process is undertaken including forming an overlying etch stop layer  12 B, and an overlying dielectric layer  14 B, preferably formed of the same or different preferred low-K materials outlined for dielectric layer  14 A. 
   Referring to  FIG. 1C , a similar process is then followed as previously outlined to form conductive interconnect features e.g.,  18 A,  18 B,  18 C which may be offset from, or overlie, conductive interconnects e.g.,  16 A and  16 B. For example, an overlying dielectric layer using the same or different preferred low-K dielectric as previously outlined for layer  14 A is first formed followed by photolithographic patterning and plasma etching e.g., reactive ion etching (RIE). Conventional metal filling processes and planarization, if necessary, are then carried out. For example, features  18 A,  18 B, and  18 C are vias, where feature  18 B, which is offset from underlying interconnects, is referred to as an isolated via. A second electrical wafer acceptance testing (WAT) process is then carried out, similar to the first WAT process, including repeating the above optional pre-WAT process thermal and/or plasma treatment and a post-WAT process CMP process in formation of a multi-level semiconductor device. 
   It has been unexpectedly found, that by carrying out pre and/or post WAT processes according to the present invention, that the yield of isolated vias e.g.,  18 B is significantly improved. For example, acceptable formation (yield) of isolated vias was significantly improved after carrying out the pre-WAT optional thermal or plasma treatment, and carrying out post-WAT CMP process. Experimental results have show that the yield of isolated vias e.g., R c  (critical resistance) was significantly improved from about 30% to about 75%, resulting in a total yield of about 98% of isolated vias. 
   The improved yield of isolated vias has been found to be related to the formation of metal (e.g., copper) protrusions (humps) existing over the interconnects (e.g., contact pads) following a WAT process. It is believed that the WAT probing process acts to displace conductive material in probed interconnects to produce the humps as explained above. Subsequently, during plasma etching an overlying interconnect opening including an isolated via opening in an overlying dielectric layer, it is believed that plasma formed current leakage paths are formed from the opening to the metal humps, thereby causing premature termination of the anisotropic etching process resulting in defectively formed (etched) interconnects including isolated vias. 
   By carrying out at least a post-WAT CMP process as outlined above, and more preferably a pre-WAT thermal or plasma treatment, according to preferred embodiments, the formation of metal humps over probe contacted interconnects is reduced or eliminated, thereby improving etching and therefore yield of isolated vias in overlying levels. 
   Referring to  FIG. 3 , is shown a process flow diagram including several embodiments of the present invention. In process  301 , a first metallization layer is formed by conventional processes including conductive interconnects. In process  303 , an optional thermal and/or plasma treatment with a hydrogen and/or inert gas containing source is performed including on exposed conductive interconnects. In process  305 , a first electrical WAT process is performed including probing conductive interconnects. In process  307 , a CMP process is carried out to remove conductive humps formed in the WAT process. In process  309 , an overlying metallization layer is formed including conductive interconnects and the above processes repeated as indicated by directional arrow  311 . 
   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.