Abstract:
In accordance with the objectives of the invention a new method is provided for the creation of an interconnect pattern. The invention provides for a layer of Photo-Active Dielectric (PAD) to be used for the insulation material in which the interconnect pattern is created, this without the use of an overlying exposure mask of photoresist.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     (1) Field of the Invention  
         [0002]     The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of creating a pattern for conductive interconnects in a layer of photo-active dielectric material without using a separate layer of photoresist for the exposure and patterning of the layer of photo-active dielectric material.  
         [0003]     (2) Description of the Prior Art  
         [0004]     In the formation of semiconductor integrated circuits, it is common practice to form interconnect metal line structures on a number of different levels within the structure and interconnecting the various levels of wiring with contact or via openings.  
         [0005]     The first or lowest level of interconnect wires is typically formed as a first step in the process after which a second or overlying level of interconnect wires is deposited over the first level.  
         [0006]     The first level of interconnect wires is typically in contact with active regions in a semiconductor substrate but is not limited to such contact. The first level of interconnect can for instance also be in contact with a conductor that leads to other devices that form part of a larger, multi-chip structure. The two levels of metal wires are connected by openings between the two layers that are filled with metal where the openings between the two layers are lined up with and match contact points in one or both of the levels of metal lines.  
         [0007]     Previously used techniques to form multi-levels of wiring apply the technique of first forming the interconnect level metal in a first plane followed by forming the overlying level of interconnect wire in a second plane. This structure typically starts with the surface of a semiconductor substrate into which active devices have been created.  
         [0008]     The surface into which the pattern of interconnect lines of the first plane is formed may also be an insulation layer deposited over the surface of the substrate or a layer of oxide may first have been formed on the surface of the substrate. After the layer, into which the pattern of interconnecting wires has to be created, has been defined, the interconnecting pattern itself needs to be defined. This is done using conventional photolithographic techniques whereby the openings are made (in the layer) above the points that need to be contacted in the substrate.  
         [0009]     The openings, once created, may by lined with layers of material to enhance metal adhesion (to the sidewalls of the opening), the glue layer, or to prevent diffusion of materials into and from the substrate in subsequent processing steps, the barrier layer.  
         [0010]     The final phase in creating the first level of interconnect lines is to fill the created openings with metal, typically aluminum, tungsten or copper, dependent on the particular application and the requirements and restrictions that are imposed by such parameters as line width, aspect ratio of the opening, required planarity of the surface of the deposited metal and others. This process of line formation in overlying layers of metal can be repeated in essentially the same manner as highlighted for the first layer of interconnecting wires.  
         [0011]     Applying conventional methods of creating conductive interconnect patterns typically results in the consumption of large amounts of chemicals that are related to photolithographic exposure of the interconnect pattern and to the Reactive Ion Etching (RIE) process that is thereby applied. Due to this consumption of chemicals, the cost of creating conductive interconnect patterns continues to increase, more so in the era of new technology in which more stringent design requirements are imposed.  
         [0012]     The increasing use of low-k dielectrics for the insulation of the conductive interconnects further presents additional challenges in the creation of conductive interconnects, such as the potential contamination of the low-k dielectric material during the removal of the exposed photoresist mask after the interconnect pattern has been transferred to the low-k dielectric. A further problem is presented by damage to the low-k dielectric as a result of long exposure times required as part of the applied RIE.  
         [0013]     The invention addresses these concerns and provides for the use of a dielectric material into which an interconnect pattern can be directly exposed without the use of an overlying exposure photoresist mask.  
         [0014]     U.S. Pat. No. 6,506,979 (Shelnut et al.), U.S. Pat. No. 5,334,488 (Shipley, Jr.) and U.S. Pat. No. 6,521,328 (Lauffer et al.) describe the use of photo-active dielectrics in printed circuit board manufacture.  
         [0015]     U.S. Pat. No. 6,349,456 (Dunn et al.) teaches forming a resistor using a photo-active dielectric (PAD).  
       SUMMARY OF THE INVENTION  
       [0016]     A principal objective of the invention is to provide a method of creating interconnect patterns that does not require the creation of an overlying photoresist exposure mask.  
         [0017]     Another objective of the invention is to reduce the cost of creating an interconnect pattern in a layer of dielectric.  
         [0018]     Yet another objective of the invention is to significantly reduce the materials required for the creation of an interconnect pattern.  
         [0019]     A still further objective of the invention is to provide a method for the creation of an interconnect pattern that is particularly suited to the use of a low-w dielectric as insulating material.  
         [0020]     A still further objective of the invention is to reduce effects of contamination of the layer of insulation in which an interconnect pattern is created.  
         [0021]     A still further objective of the invention is to reduce surface damage to the layer of insulation in which an interconnect pattern is created.  
         [0022]     In accordance with the objectives of the invention a new method is provided for the creation of an interconnect pattern. The invention provides for a layer of Photo-Active Dielectric (PAD) to be used for the insulation material in which the interconnect pattern is created, this without the use of an overlying exposure mask of photoresist. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIGS. 1 through 4  show the application of PAD for the creation of a damascene pattern.  
         [0024]      FIGS. 5 through 10  show a first application of PAD for the creation of a dual damascene pattern.  
         [0025]      FIGS. 11 through 17  show a second application of PAD for the creation of a dual damascene pattern. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     Two widely used approaches in creating metal interconnects is the use of the damascene and the dual damascene structures. The application of the damascene process continues to gain wider acceptance, most notably in the process of copper metalization due to the difficulty of copper dry etch where the damascene plug penetrates deep in very small, sub-half micron, Ultra Large Scale integrated devices. Recent applications have successfully used copper as a conducting metal line, most notably in the construct of CMOS 6-layer copper metal devices.  
         [0027]     In the formation of a damascene structure, a metal plug is first formed in a surface, this surface in most instances is the surface of a semiconductor substrate. A layer of Intra Level Dielectric (ILD) is deposited (using for instance Plasma Enhanced CVD technology with SiO 2  as a dielectric) over the surface into which trenches for metal lines are formed (using for instance Reactive Ion Etching technology).  
         [0028]     The trenches overlay a metal interconnect and are filled with metal (using for instance either the CVD or a metal flow process). Planarization of this metal to the top surface of the layer of ILD completes the damascene structure. Some early damascene structures have been achieved using Reactive Ion Etching (RIE) for the process of planarization but Chemical Mechanical Planarization (CMP) is used exclusively today.  
         [0029]     An extension of the damascene process is the dual damascene process whereby an insulating or dielectric material, such as silicon oxide, is patterned with several thousand openings for the conductive lines and vias, which are filled at the same time with metal.  
         [0030]     Damascene is an interconnection fabrication process in which grooves are formed in an insulating layer and filled with metal to form the conductive lines. Dual damascene is a multi-level interconnection process in which, in-addition to forming the grooves of single damascene, conductive via openings also are formed.  
         [0031]     One of the dual damascene approaches uses a dielectric layer that is formed by three consecutive depositions whereby the central layer functions as an etch stop layer. This etch stop layer can be SiN, the top and bottom layer of this three layer configuration can be SiO 2 .  
         [0032]     This triple layer dielectric allows first forming the vias by resist patterning the vias and etching through the three layers of dielectric. The conductive trench pattern can then be formed in the top layer of dielectric whereby the central layer of SiN forms the stop layer for the etch of the conductive trench pattern.  
         [0033]     Another approach, still using the three-layer dielectric formed on the substrate surface, is to first form the pattern for the conducting lines in the top layer of the dielectric whereby the SiN layer again serves as etch stop. The vias can then be formed by aligning the via pattern with the pattern of the conducting lines and patterning and etching the vias through the etch stop layer of SiN and the first layer of dielectric.  
         [0034]     Yet another approach is to deposit the three layer dielectric in two steps, first depositing the first layer of SiO 2  and the etch stop layer of SiN. At this point the via pattern can be exposed and etched. The top layer of SiO 2  dielectric is then deposited, the conducting lines are now patterned and etched. The SiN layer will stop the etching except where the via openings have already been etched.  
         [0035]     Dual damascene is an improvement over single damascene because it permits the filling of both the conductive grooves and vias with metal at the same time, thereby eliminating processing steps.  
         [0036]     The invention will now be described in detail, the first embodiment of the invention will be explained using  FIGS. 1 through 4 , the second embodiment of the invention will be described using  FIGS. 5 through 10  while the third embodiment of the invention will be described using  FIGS. 11 through 17 .  
         [0037]     Referring now specifically to  FIG. 1 , there is shown a cross section of a layer  10  of conductive material, typically comprising a metal such as copper, over which a layer  12  of Anti Reflective Coating (ARC) has been deposited. A layer  14  of Photo-Active Dielectric (PAD) has been deposited over the layer  12  of ARC.  
         [0038]     It must be understood in the cross section shown in  FIG. 1  that layer  10 , of for instance copper, may be deposited over a semiconductor surface  90 , preferably but not limited to the surface of a semiconductor substrate.  
         [0039]     The semiconductor surface  90  can be a printed circuit board, a flex circuit, a metallized substrate, a glass substrate and a semiconductor device mounting support.  
         [0040]     The semiconductor substrate can be a ceramic substrate, a glass substrate, a gallium arsenide substrate, a silicon substrate comprising a single layer of material, such as a silicon wafer or comprising silicon on insulator (SOI) technology and silicon on sapphire (SOS) technology, a doped or undoped semiconductor, an epitaxial layer of silicon supported by a base semiconductor, a sapphire substrate or a substrate used for flat panel displays.  
         [0041]     Conventional methods can be applied for the creation of the three layers  10 ,  12  and  14 .  
         [0042]     Layer  12  of ARC is deposited to minimize the effect that reflected light has on image creation. A layer of ARC is frequently applied as a blanket deposition over a surface that causes light to be reflected such as a layer of metal, comprising for instance copper.  
         [0043]     Layer  12  of ARC can for instance be deposited through a spin coating process followed by a thermal cure at a temperature of about 120 degrees C. for a time period of about 90 seconds to yield a blanket focusing layer when cured of a thickness of about 1,500 Angstrom.  
         [0044]     Layer  14 , of critical importance to the invention, comprises Photo Active Dielectric (PAD), which is a dielectric material that is sensitive to the exposure of photo-electric energy. This sensitivity to the exposure of photo-electric energy results in changing the chemical composition of the layer of PAD upon exposure by light energy.  
         [0045]     Layer  14  preferable comprises a material that is, as stated, sensitive to exposure to photo energy in addition to being thermally compatible with other processes that are used for the creation of semiconductor devices.  
         [0046]     Layer  14  for this purpose preferably comprises, without being limited thereto, such materials as contained in the polymer family of polyimide materials. Due to these characteristics of photo-active and thermal compatibility, layer  14  allows, using this layer  14  and of critical importance to the invention, for the pattern definition, the pattern transfer and the pattern freeze all in this layer  14  of PAD.  
         [0047]     For layer  14  can for instance be used a low-k polymer material including polyimides, fluorinated polyimides, polysilsequioxane, benzocyclobutene (BCB), parlene F, parlene N and amorphous polytetrafluorothylene.  
         [0048]     A polymer film can be spun onto the wafer and can contain polycarbonate (PC), polystyrene (PS), polyoxides (PO), polymethylmethacrylate (PPMA) and poly-polyoxides (PPO).  
         [0049]     It is important to use a material for the polymer film that can be applied by spin coating and that can, at a later date, be easily removed by dipping the coated semiconductor package in a solvent. Solvents that can be used for this purpose include acetone, THF and trichloro-methane.  
         [0050]     The preferred thickness for layer  14  of PAD is between about 5,000 and 15,000 Angstrom.  
         [0051]     Relating to layer  14  of PAD the following comments apply: 
        layer  14  allows for, due to its photosensitivity, the elimination of an additional layer of photoresist that is conventionally required for interconnect pattern definition     the layer  14  minimizes the need for RIE application, and     by defining the chemical composition of layer  14 , low-k dielectric characteristics can be obtained in layer  14 .        
 
         [0055]     By now interposing, as shown in the cross section of  FIG. 2 , a mask  16  between a light source  18 / 20  and the substrate over which the structure that is shown in cross section in  FIG. 1  has been created, light  20  of light source  18 / 20  penetrates the mask  16  and exposes the surface of layer  14  of PAD, converting the chemical composition of layer  14  where light  20  impacts and penetrates layer  14 .  
         [0056]     The newly created composition of layer  14  is highlighted as layers  22  in the cross section of  FIG. 2 , the layer  20  remains unchanged in the not exposed to photo energy regions  14 , also as highlighted in the cross section of  FIG. 2 .  
         [0057]     For light source  18 / 20 , an UV or DUV light source may be used to project the image of a mask onto a target surface. Any other source of photo-electric energy is equally suitable for the exposure  18 / 20  such as E-beam lithography, X-ray lithography and ion beam lithography, which are applied by more advanced methods of creating small device features.  
         [0058]      FIG. 3  shows a cross section of the structure after development of the exposed layer  14  of PAD, removing the exposed PAD regions  22  and thereby creating damascene openings  20 ′ through the layer  14  of PAD.  
         [0059]     As a final step under the first embodiment of the invention, the layer  12  of ARC is removed from the bottom surface of openings  20 ′, the result of which is shown in the cross section of  FIG. 4 . The layer  10  of metal, preferably comprising copper, is now exposed, enabling the creation of single damascene interconnects by filling openings  20 ′ with a conductive material, such as copper, which will be in direct contact with the layer  10  of for instance copper.  
         [0060]     As an example of layer  12  can be cited a layer of Bottom Anti Reflective Coating (BARC), comprising either SiON or organic BARC, which can be removed from opening  20 ′ with a recipe comprising O 2  at a flow rate between 10 and 100 sccm, N 2  at a flow rate between 10 and 100 sccm, applied for a time period between about 30 and 60 seconds.  
         [0061]     The second embodiment of the invention will now be explained using  FIGS. 5 through 10  for this purpose.  
         [0062]     The cross section shown in  FIG. 5  will be recognized as the cross section of  FIG. 1  with the addition of a second layer  26  of PAD that has been deposited over the first layer  24  of PAD. The first layer  24  of PAD is similar to the layer  14  of PAD that has been shown in the cross section of  FIG. 1 .  
         [0063]     Comments that have been made with respect to layers  10 ,  12  and  14  of  FIG. 1  equally apply to layers  10 ,  12 ,  24  (a first layer of PAD) and  26  (a second layer of PAD) shown in cross section in  FIG. 5  and are enclosed at this time by reference.  
         [0064]     It must further be pointed out that layer  24 , the first PAD layer, and layer  26 , the second PAD layer, preferably comprise different types of PAD materials, as these PAD materials have previously been defined, and are exposed and subsequently developed using different types of lithographic exposures, thus allowing for the creation of openings having different width or cross sections in the two layers  24  and  26  as is basic to and required for the creation of a dual damascene structure.  
         [0065]     As a next step in the process of creating a dual damascene structure, the second PAD layer  26  is first exposed with a first photolithographic exposure  30 / 32  and developed, similar to the sequence of exposure and development that has previously been described using  FIGS. 2 and 3 .  
         [0066]     The exposure mask  28 , as shown in the cross section of  FIG. 6 , is for this purpose interposed between the source  30 / 32  of photo energy and the structure shown in cross section in  FIG. 5 . The openings created through the exposure mask  28  have the dimensions of a desired trench that forms the upper part of a dual damascene structure, allowing the photo energy  32  to penetrate through the mask  28  and impart photo energy to the second layer  26  of PAD, thereby changing the chemical composition of layer  26  in the highlighted and bounded regions  34  of layer  26 .  
         [0067]     By now developing the exposed portions  34  of the first PAD layer  26 , that is removing the second PAD layer from regions  34  highlighted in the cross section of  FIG. 6 , the cross section of  FIG. 7  is obtained wherein first openings  32 ′ have been created through the first layer  26  of PAD. These opening  32 ′ will at a later time be recognized as being the trenches of a dual damascene structure.  
         [0068]     The invention continues, as shown in the cross section of  FIG. 8 , with a second photolithographic exposure by interposing a second exposure mask  34  between the source  36 / 38  of light energy and the structure shown in cross section in  FIG. 7 . The light exposure highlighted as exposure  36  is blocked by the second exposure mask  34  and therefore has no effect on the second layer  26  of PAD or the first layer  24  of PAD. The openings created through the second exposure mask  34 , through which light energy  38  is allowed to pass, have the dimensions of a via interconnect that forms part of a dual damascene structure.  
         [0069]     The photo electric energy highlighted as  38  in the cross section of  FIG. 8  passes through the openings created in the second exposure mask  34 , creating a pattern of light exposure in the first layer  24  of PAD that has been highlighted as bounded pattern  40 , in which the chemical composition of the first layer  24  of PAD is changed so that this layer can be developed, thus creating the via interconnects of a dual damascene structure.  
         [0070]     The result, after developing the exposed sections  40  of the first layer  24  of PAD, that is after removing of these exposed portions  40 , is shown in the cross section of  FIG. 9 , wherein the openings  32 ′ will be recognized as being the upper or trench portion of a dual damascene structure while openings  40 ′ will be recognized as being the lower or via interconnect portion of a dual damascene structure.  
         [0071]     As a final step, the results of which are shown in the cross section of  FIG. 10 , the layer of ARC is removed from the bottom of openings  32 ′/ 40 ′, preventing electrical opening between the bottom metal layer  10  and the dual damascene circuits.  
         [0072]     After the cross section that is shown in  FIG. 10  has been obtained, the surface of the structure is subjected to a thorough surface clean and a thermal treatment to enhance the quality of the created dual damascene structures.  
         [0073]     The cleaning steps may involve wafer scrubbing to remove loose particulate contaminants. Subsequent to a cleaning process, treatment with organic solvents, such as trichloroethylene, acetone, p-xylene, methanol and ethanol, is performed to remove organic impurities such as hydrocarbons and greases, which may remain. A final cleaning may include treatment with various inorganic chemicals to remove heavy metals, for example. These inorganic chemical mixtures are strong oxidants, which form a thin oxide layer at the wafer surface. This oxide layer is stripped, removing impurities absorbed into the oxide layer.  
         [0074]     Chemical cleaning for removing chemically bonded film from wafer surface is one in a cleaning process. Conventional chemical cleaning includes a series of acid and rinse baths.  
         [0075]     Chemical solutions have been used extensively for the manufacture of semiconductor devices. Wet chemical processing baths have been used for cleaning semiconductor wafers, as well as for etching deposited films on these wafers. For example, the use of hydrogen peroxide (H 2 O 2 ) containing solutions for cleaning silicon semiconductor wafers is well known. In addition to wafer cleaning, hydrogen peroxide is utilized in combination with sulfuric acid for photoresist removal and in combination with phosphoric acid, sulfuric acid or ammonium hydroxide for selective titanium etching.  
         [0076]     The thermal treatment that is applied to the structure that is shown in cross section of  FIG. 10  may be performed at a temperature of about 500 degrees C. for a time period of about 10 to 20 minutes.  
         [0077]     The third embodiment of the invention starts with the structure that has been shown in the cross section of  FIG. 2 . This cross section is again shown in the cross section of FIG.  11 , the exposure mask  16  and the source  18 / 20  of light energy, which are shown in  FIG. 2 , are omitted from the cross section shown in  FIG. 11 . The steps that are required to create the cross section that is shown in  FIG. 1  therefore are assumed to precede the cross section shown in  FIG. 11 .  
         [0078]     It must be noted in  FIG. 11  that the layer  12  of ARC remains in place underneath the exposed regions  22  of the first layer  14  of PAD.  
         [0079]      FIG. 12  shows a cross section after a second layer  42  of ARC has been deposited, for the conventional reasons as highlighted previously for the deposition of a layer of ARC, over which a second layer  44  of PAD has been deposited.  
         [0080]     The second layer  44 , as shown in the cross section of  FIG. 13 , is now exposed using exposure mask  46 . The openings contained in exposure mask  46  are aligned with regions  22  of the first layer  14  of PAD, the openings in mask  46  have the dimensions of a trench pattern for a dual damascene structure.  
         [0081]     The photo energy exposure  48  is blocked by exposure mask  46  and therefore does not affect the second layer  44  of PAD. The photo energy exposure  50  passes through the exposure mask  46  and therefore changes the chemical composition of the second layer  44  of PAD, preparing the second layer  44  of PAD for development thereof in the regions highlighted as regions  52 . After layer  44  has been developed, the cross section that is shown in  FIG. 14  is obtained, wherein now trench opening  52 ′ for a dual damascene structure have been created overlying the layer  42  of ARC.  
         [0082]     The exposed layer  42  of ARC, overlying the first layer  14  of PAD, is removed from the bottom of openings  52 ′, as shown in the cross section of  FIG. 15 , after which the exposed layers  22  of the first layer  14  of PAD are removed, as shown in the cross section of  FIG. 16 .  
         [0083]     It is clear from the cross section that is shown in  FIG. 16  that the openings  22 ′ and  52 ′ from a dual damascene structure, wherein openings  52 ′ form the upper or trench portion of the dual damascene structure and openings  22 ′ form the lower of via interconnect portions of the dual damascene structure.  
         [0084]     By as a final step removing the exposed first layer  12  of ARC from the bottom of openings  22 ′/ 52 ′, the completed dual damascene structure is obtained as shown in the cross section of  FIG. 17 .  
         [0085]     Although the invention has been described and illustrated with reference to specific illustrative embodiments thereof, it is not intended that the invention be limited to those illustrative embodiments. Those skilled in the art will recognize that variations and modifications can be made without departing from the spirit of the invention. It is therefore intended to include within the invention all such variations and modifications which fall within the scope of the appended claims and equivalents thereof.