Abstract:
An improved method of etching very small contact holes through dielectric layers used to separate conducting layers in multilevel integrated circuits formed on semiconductor substrates has been developed. The method uses bi-level ARC coatings in the resist structure and a unique combination of gaseous components in a plasma etching process which is used to dry develop the bi-level resist mask as well as etch through a silicon oxide dielectric layer. The gaseous components comprise a mixture of a fluorine containing gas, such as C 4 F 8 , C 5 F 8 , C 4 F 6 , CHF 3  or similar species, an inert gas, such as helium or argon, an optional weak oxidant, such as CO or O 2  or similar species, and a nitrogen source, such as N 2 , N 2 O, or NH 3 or similar species. The patterned masking layer can be used to reliably etch contact holes in silicon oxide layers on semiconductor substrates, where the holes have diameters of about 0.1 micron or less.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    (1) Field of the Invention  
           [0002]    This invention relates to a method of fabricating integrated circuits and other electronic devices on semiconductor substrates. More particularly, the invention relates to an improved process for forming contact holes on semiconductor substrates.  
           [0003]    (2) Description of Related Art  
           [0004]    In the fabrication of semiconductor integrated circuits multilevel integration structures are used to connect the various devices in the circuits. As circuit density increases very large scale integration (VLSI) and ultra-large scale integration (ULSI) are used to interconnect the devices in integrated circuits fabricated on semiconductor substrates and the feature sizes of device components have decreased to 0.1 micron and less. This is particularly true for the contact holes required to connect devices between levels in multilevel structures. Therefore, fabrication processes for achieving VLSI and ULSI levels of integration must be capable of reliably forming contact holes between successive levels, where the contact holes have dimensions of the order of 0.1 micron or less in diameter.  
           [0005]    An important challenge in the fabrication of multilevel integrated circuits on semiconductor substrates is to develop masking and etching technologies which allow reliable formation of semiconductor devices, interconnection conducting patterns, and interlevel contact holes which have dimensions of 0.1 micron on less. The masking technologies and the etching technologies must be compatible and result in high fabrication process yield and minimum process cost. In order to minimize cost, fabrication tool throughput must be maximized. Therefore, sequential processing in the same fabrication tool, without necessity to transfer to additional tools, is desirable and leads to reduced product cost.  
           [0006]    As device feature size is reduced to 0.1 micron and less, the ability to achieve good image resolution in high density, small pitch patterns requires that the photo resist exposure and imaging processes be performed on a thin photo resist imaging layer. However, when etching features in thick layers, such as ILD (Inter-Level Dielectric) layers, thin photo resist masks are inadequate and schemes to provide more robust masking layers are required.  
           [0007]    Numerous patents disclose bi-level resist masking structures in order to achieve greater dimensional fidelity in the desired integration pattern. For example, U.S. Pat. No. 5,227,280 entitled “Resists With Enhanced Sensitivity And Contrast” granted Jul. 13, 1993 to James A. Jubinsky et al. describes a bi-level resist structure and method of fabrication. The method forms a bi-level resist structure for use in lift-off processes wherein the underlayer comprises a photo resist layer with an admixture of cyclic anhydrides and the top layer comprises a photo resist layer.  
           [0008]    Also, U.S. Pat. No. 5,286,607 entitled “Bi-Layer Resist Process For Semiconductor Processing” granted Feb. 15, 1994 to Andrew V. Brown shows a method of forming a resist mask on a substrate in which a planarizing polymer layer is first formed on the substrate. Then the planarizing polymer layer is exposed to a silicon containing medium, so as to cause silicon from the medium to penetrate the top portion of the planarizing polymer layer. Next a resist layer is formed over the first layer, exposed and developed to form a pattern and then RIE is used to remove the exposed areas of the first layer including the silicon that penetrated the first layer. Finally RIE in an oxygen plasma removes the resist layer while etching through the planarizing polymer in the exposed areas.  
           [0009]    And, U.S. Pat. No. 5,545,512 entitled “Method Of Forming A Pattern Of Silylated Planarizing Photoresist” granted Aug. 13, 1996 to Tatsuo Nakato describes a multilayer photo resist process, wherein a mask pattern of silicon dioxide is formed on the surface of a layer of photo resist. The steps in the method include irradiating the surface of a photo resist layer to create a unpatterned silicon-reactive region adjacent to the surface of the photo resist. The next step is to soft bake the irradiated photo resist in a silicon containing environment to convert the silicon-reactive region to a silicon-enriched region adjacent to the surface of the photo resist. A patterned layer of photo resist is then formed overlying the silicon-enriched region and an etching step transfers the mask pattern to the silicon-enriched region of the photo resist. The remaining areas of the silicon-enriched layer are exposed to an oxygen plasma which converts the silicon-enriched areas to silicon dioxide.  
           [0010]    Also, U.S. Pat. No. 5,427,649 entitled “Method For Forming A Pattern By Silylation” granted Jun. 27, 1995 to Cheol-hong Kim et al. describes a method for forming a mask pattern by forming a first photo resist layer having a silylated surface. Then, a second photo resist layer is formed on the silylation layer, which is then exposed and developed to form a pattern in the second photo resist layer. The pattern in the second photo resist layer is used to etch a pattern in the silylated first photo resist layer. The silylation pattern is then oxidized. Next, the first photo resist layer is etched using the oxidized silylation pattern as a mask.  
           [0011]    Also, U.S. Pat. No. 6,218,292 B1 entitled “Dual Layer Bottom Anti-Reflective Coating” granted Apr. 17, 2001 to David K. Foote describes a method of manufacturing a semiconductor device wherein a first anti-reflective coating is deposited on a substrate followed by depositing a second anti-reflective coating on the first anti-reflective coating.  
           [0012]    Also, U.S. Pat. No. 6,057,587 entitled “Semiconductor Device With Anti-Reflective Structure” granted May 2, 2000 to Kouros Ghandehari et al. reveals an anti-reflective structure for use in patterning metal layers on semiconductor substrates.  
           [0013]    Also, U.S. Pat. No. 6,037,276 entitled “Method For Improving Patterning Of A Conductive Layer In An Integrated Circuit” granted Mar. 14, 2000 to HuaTai Lin et al. shows a lithographic patterning process on a conductive layer wherein an oxynitride layer is formed on the conductive layer, a nitride layer is formed on the oxynitride layer, and a photoresist layer is formed on the nitride layer.  
           [0014]    Further, U.S. Pat. No. 6,147,007 entitled “Method For Forming A Contact Hole on a Semiconductor Wafer” granted Nov. 14, 2000 to Chan-Lon Yang et al. describes a process for etching a contact hole in silicon oxide using a patterned photo resist layer as a mask. A silicon nitride layer is used as an etch stop when etching through a silicon oxide layer.  
           [0015]    When circuit density requires that contact holes be of the order of 0.1 micron or less in diameter, resist masking schemes which use a single organic ARC (anti-reflection coating) layer or a single inorganic ARC layer are not adequate. Such single layer ARC schemes result in irregularly shaped etched holes having severe striations which can then contribute to shorting between adjacent contact holes.  
           [0016]    Also, when using a bi-level resist structure, comprising a top imaging layer and a bottom dry developed organic layer, as the mask for plasma etching holes in silicon oxide using conventional gaseous mixtures of C x F y , argon, and O 2  the top imaging layer is not removed by the silicon oxide etch process and a residue forms on the top of the top imaging layer during the etching of the silicon oxide. This residue further impacts the successful removal of the top imaging layer by subsequent O 2  ashing processes and degrades the fabrication process yield.  
           [0017]    The present invention is directed to an improved method of etching very small contact holes through dielectric layers used to separate patterned conducting layers in multilevel integrated circuits formed on semiconductor substrates. The method uses bi-level ARC coatings in the resist structure and a unique combination of gaseous components in a plasma etching process which can be used to dry develop the bi-level resist mask as well as etch through a silicon oxide dielectric layer. Contact holes formed using this improved method may be used to make contact to active devices formed within the semiconductor substrate or the contact holes may be used to make contact between successive layers in multilevel integrated circuit structures.  
         SUMMARY OF THE INVENTION  
         [0018]    It is a general object of the present invention to provide an improved method for forming a patterned masking layer on the top surface of a semiconductor substrate using a multilevel resist structure.  
           [0019]    A more specific object of the present invention is to provide an improved method of forming contact holes through dielectric layers on a semiconductor substrate, where the contact holes have a diameter of about 0.1 micron or less.  
           [0020]    Another object of the present invention is to provide an improved, high yield method of forming contact holes through a dielectric layer on a semiconductor substrate, where the contact holes have a diameter of about 0.1 micron.  
           [0021]    And, yet another object of the present invention is to provide an improved method of forming contact holes through a dielectric layer on a semiconductor substrate where the fabrication process uses the same plasma etching tool to dry develop the image in the resist mask and to sequentially etch the holes in the dielectric layer.  
           [0022]    In accordance with the present invention, the above and other objectives are realized by using a method of forming a patterned masking layer having the desired pattern of areas on the top surface of a semiconductor substrate using a multilevel resist structure comprising the steps of: forming on the top surface of the semiconductor substrate an inorganic ARC layer; forming an organic ARC layer over the inorganic ARC layer; forming a resist layer over the organic ARC layer, exposing the resist layer to the desired pattern, and developing the resist layer to expose areas of the organic ARC layer; and exposing the semiconductor substrate to a plasma etching environment generated by RF or microwave power in a gaseous mixture of a fluorine containing gas, such as C 4 F 8 , C 5 F 8 , C 4 F 6 , CHF 3  or similar species, an inert gas, such as helium or argon, an optional weak oxidant, such as CO or O 2  or similar species, and a nitrogen source, such as N 2 , N 2 O, or NH 3  or similar species, for a time sufficient to etch through the organic ARC layer and the inorganic ARC layer.  
           [0023]    In a second embodiment of the present invention, the above and other objectives are realized by using a method of forming a contact hole on a semiconductor substrate comprising the steps of: providing a semiconductor substrate having formed thereon a layer of first material and a second layer of dielectric material formed on the top surface of the layer of first material; providing a first ARC layer comprising an inorganic material on the top surface of the second layer of dielectric material; providing a second ARC layer comprising an organic material on the top surface of the first ARC layer; providing a patterned mask layer on the top surface of the second ARC layer, wherein the patterned mask layer has holes therein, said holes being open to the top surface of the second ARC layer; performing a first anisotropic etching process in an RF or microwave generated plasma to remove the second ARC layer comprising an organic material and the first ARC layer comprising an inorganic material at the sites of the holes in said patterned mask layer; continuing said first anisotropic etching process in an RF or microwave generated plasma to remove the second layer of dielectric material at the sites of the holes in the patterned mask layer; performing a second anisotropic etching process in an RF or microwave generated plasma to remove the layer of first material at the sites of etched holes in said second layer of dielectric material; and performing a plasma stripping process to remove the remaining patterned mask layer and the remaining second ARC layer comprising an organic material.  
           [0024]    In a third embodiment of the present invention, the above and other objectives are realized by using a method of forming a contact hole on a semiconductor substrate comprising the steps of: providing a semiconductor substrate having formed thereon a layer of first material and a layer of dielectric material formed on the top surface of the layer of first material; providing a bottom ARC layer comprising a non-silicon containing organic material on the top surface of the layer of dielectric material; providing a top ARC layer comprising a silicon containing organic material on the top surface of the bottom ARC layer comprising a non-silicon containing organic material; providing a patterned mask layer on the top surface of the top ARC layer, wherein the patterned mask layer has holes therein, said holes being open to the top surface of the top ARC layer; performing a first anisotropic etching process in an RF or microwave generated plasma to remove the top ARC layer comprising a non-silicon containing organic material at the sites of the holes in said patterned mask layer; continuing said first anisotropic etching process in an RF or microwave generated plasma to remove the bottom ARC layer of non-silicon containing organic material at the sites of the holes in said patterned mask layer; and further comprising the steps of: continuing the first anisotropic etching process in an RF or microwave generated plasma to remove said layer of dielectric material at the sites of the holes in said patterned mask layer, said first anisotropic etching process simultaneously removing the patterned mask layer on the top surface of the top ARC layer; performing a second anisotropic etching process in an RF or microwave generated plasma to remove the layer of first material at the sites of etched holes in said layer of dielectric material; and performing a plasma stripping process to remove the remaining patterned mask layer and the remaining top ARC layer comprising a silicon containing organic material and bottom ARC layer comprising a non-silicon containing organic material. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    The object and other advantages of this invention are best described in the preferred embodiments with reference to the attached drawings that include:  
         [0026]    [0026]FIGS. 1A and 1B, which in cross-sectional representation illustrate the method of one embodiment of the present invention.  
         [0027]    FIGS.  2 A- 2 E, which in cross-sectional representation illustrate the method of a second embodiment of the present invention.  
         [0028]    FIGS.  3 A- 3 D, which in cross-sectional representation illustrate the method of a third embodiment of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    The new and improved method of forming a patterned masking layer on the top surface of a semiconductor substrate using a multilevel resist structure and the method of forming contact holes through dielectric layers on a semiconductor substrate, where the contact holes have a diameter of about 0.1 micron or less will now be described in detail.  
         [0030]    Please refer to FIGS. 1A and 1B, which in cross-sectional representation illustrate the method of one embodiment of the present invention. Referring to FIG. 1A, a semiconductor substrate  10  is provided and the semiconductor substrate  10  comprises isolation areas  11 , which may contain an active area  12  and a dielectric layer  13 . The isolation areas  11  may be silicon oxide or other dielectrics. The active area  12  may comprise titanium silicide or other silicides. The dielectric layer  13  may be silicon oxide or other suitable insulating materials. Formed on the top surface of the semiconductor substrate is an inorganic ARC layer  14 . Inorganic ARC layer  14  comprises SiON and has a thickness between about 100 and 1000 Angstroms. Next, an organic ARC layer  15  is formed over the inorganic ARC layer  14 . The organic ARC layer  15  has a thickness between about 100 and 1000 Angstroms. Layer  16  is a patterned resist layer formed over the organic ARC layer  15 . Conventional exposure and development processes are used to form the desired pattern in the resist layer and to form holes in the resist layer at sites where contacts are to be made on the semiconductor substrate. Illustrated is one such hole  17 , which exposes the underlying organic ARC layer  15 .  
         [0031]    Now referring to FIG. 1B, the semiconductor substrate having thereon the structure illustrated in FIG. 1A is loaded into a plasma etch tool and exposed to a plasma etching environment generated by RF or microwave power in a gaseous mixture of a fluorine containing gas, such as C 4 F 8 , C 5 F 8 , C 4 F 6 , CHF 3  or similar species, an inert gas, such as helium or argon, an optional weak oxidant, such as CO or O 2  or similar species, and a nitrogen source, such as N 2 , N 2 O, or NH 3  or similar species, for a time sufficient to etch through the organic ARC layer  15  and the inorganic ARC layer  14 . A plasma generated in a gaseous mixture comprising C 4 F 6 , CF 4 , CHF 3 , O 2  and argon, where the volume ratios of gases, C 4 F 6 , CF 4 , CHF 3 , O 2  are about 1:10:3:3, has been used to etch through both the organic ARC layer  15  and the inorganic ARC layer  14 . The plasma etching environment has a pressure between about 5 and 50 mTorr and the plasma is generated by RF power between about 100 and 900 Watts, applied to an upper electrode and RF power between about 900 and 2000 Watts, applied to a lower electrode in a dual electrode plasma etch tool.  
         [0032]    FIGS.  2 A- 2 D illustrate in cross-sectional representation the method of a second embodiment of the present invention. Referring to FIG. 2A, semiconductor substrate  20  has a layer of first material  21  formed thereon. A second layer of dielectric material  22  is formed on the top surface of the layer of first material  21 . Semiconductor substrate  20  may be silicon, germanium or other such semiconductors. The layer of first material  21  is a dielectric, such as silicon nitride or SiON having a thickness between about 100 and 1000 Angstroms. The layer of first material  21  acts as an etch stop when etching holes in the second layer of dielectric material  22 , which comprises silicon oxide having a thickness between about 3000 and 10,000 Angstroms. Formed on the top surface of second layer of dielectric material  22  is a first inorganic ARC layer  24 , which comprises SiON and has a thickness between about 100 and 1000 Angstroms. Next, an organic ARC layer  25  is formed over the inorganic ARC layer  24 . The organic ARC layer  25  has a thickness between about 100 and 1000 Angstroms. Layer  26  is a patterned resist layer formed over the organic ARC layer  25 . Conventional exposure and development processes are used to form the desired pattern in the resist layer and to form holes in the resist layer at sites where contacts are to be made on the semiconductor substrate. Illustrated is one such hole  27 , which exposes the underlying organic ARC layer  25 .  
         [0033]    Now referring to FIG. 2B, the semiconductor substrate having thereon the structure illustrated in FIG. 2A is loaded into a plasma etch tool and exposed to a first anisotropic etching process in a plasma etching environment generated by RF or microwave power in a gaseous mixture of a fluorine containing gas, such as C 4 F 8 , C 5 F 8 , C 4 F 6 , CHF 3  or similar species, an inert gas, such as helium or argon, an optional weak oxidant, such as CO or O 2  or similar species, and a nitrogen source, such as N 2 , N 2 O or NH 3  or similar species, for a time sufficient to etch through the organic ARC layer  25  and the inorganic ARC layer  24 . A plasma generated in a gaseous mixture comprising C 4 F 6 , CF 4 , CHF 3 , O 2  and argon, where the volume ratios of gases, C 4 F 6 , CF 4 , CHF 3 , O 2  are about 1:10:3:4, has been used to etch through both the organic ARC layer  25  and the inorganic ARC layer  24 . The plasma etching environment has a pressure between about 5 and 50 mTorr and the plasma is generated by RF power between about 100 and 900 Watts, applied to an upper electrode and RF power between about 900 and 2000 Watts, applied to a lower electrode in a dual electrode plasma etch tool.  
         [0034]    The next step is to continue the first anisotropic etching process, as illustrated in FIG. 2C, to remove the second layer of dielectric material  22  at the site of hole  27 . The same plasma etch tool is used and the same gaseous components and etch process parameters as stated above are used for this continuation of the first anisotropic etching process.  
         [0035]    Now referring to FIG. 2D, a second anisotropic etching process is used to remove the layer of first material  21  at the site of hole  27 . This second anisotropic etching process is performed in a plasma etching environment in a gaseous mixture of CF x /H 2 /Ar, CH x F y /H 2 /Ar, CH x F y /N 2 /Ar, CH x F y /N 2 /H 2 /Ar, CH x F y /O 2 /Ar or CF x /O 2 /Ar for a time sufficient to etch through the layer of first material  21  at the site of hole  27 .  
         [0036]    As illustrated in FIGS. 2D and 2E, a plasma stripping process is next used to remove the remaining patterned mask layer  26  and the remaining second ARC layer  25  comprising an organic material to result in the structure as shown in FIG. 2E.  
         [0037]    Another method for forming a contact hole on a semiconductor substrate is illustrated in FIGS.  3 A- 3 D. Referring to FIG. 3A, a semiconductor substrate  30  is provided, having thereon a layer of first material  31 , comprising a dielectric, such as silicon nitride or SiON having a thickness between about 100 and 1000 Angstroms. Semiconductor substrate  30  may be silicon, germanium or other such semiconductors. The layer of first material  31  acts as an etch stop when etching holes in the second layer of dielectric material  32 , which comprises silicon oxide having a thickness between about 1000 and 20,000 Angstroms. Formed on the top surface of second layer of dielectric material  32  is a bottom ARC layer  33 , which comprises a non-silicon containing organic material and has a thickness between about 1000 and 5000 Angstroms. Formed on top of bottom ARC layer  33  is top ARC layer  34 , which comprises a silicon containing organic material having a thickness between about 500 to 3000 Angstroms. Layer  35  is a patterned resist layer formed over the top ARC layer  34 . Conventional exposure and development processes are used to form the desired pattern in the resist layer and to form holes in the resist layer at sites where contacts are to be made on the semiconductor substrate. Illustrated is one such hole  36 , which exposes the underlying top ARC layer  34 .  
         [0038]    Now referring to FIG. 3B, the semiconductor substrate having thereon the structure illustrated in FIG. 3A is loaded into a plasma etch tool and exposed to a first anisotropic etching process in a plasma etching environment generated by RF or microwave power in a gaseous mixture of a fluorine containing gas, such as C 4 F 8 , C 5 F 8 , C 4 F 6  CHF 3  or similar species, an inert gas, such as helium or argon, an optional weak oxidant, such as CO or O 2  or similar species, and a nitrogen source, such as N 2 , N 2 O or NH 3  or similar species for a time sufficient to etch through the top ARC layer  34  and the bottom ARC layer  33 . A plasma generated in a gaseous mixture comprising C 4 F 6 , CF 4 , CHF 3 , O 2  and argon, where the volume ratios of gases, C 4 F 6 , CF 4 , CHF 3 , O 2  are about 1:10:3:4, has been used to etch through top ARC layer  34  and bottom ARC layer  33 . The plasma etching environment has a pressure between about 5 and 50 mTorr and the plasma is generated by RF power between about 100 and 900 Watts, applied to an upper electrode and RF power between about 900 and 2000 Watts, applied to a lower electrode in a dual electrode plasma etch tool.  
         [0039]    The next step is to continue the first anisotropic etching process, as illustrated in FIG. 3C, to remove the layer of dielectric material  32  at the site of hole  36 . The same plasma etch tool is used and the same gaseous components and etch process parameters as stated above are used for this continuation of the first anisotropic etching process. At the same time patterned resist layer  35  is removed from the top surface of top ARC layer  34 .  
         [0040]    Now referring to FIG. 3D, a second anisotropic etching process is used to remove the layer of first material  31  at the site of hole  35 . This second anisotropic etching process is performed in a plasma etching environment in a gaseous mixture of CF x /H 2 /Ar, CH x F y /H 2 /Ar, CH x F y /N 2 /Ar, CH x F y /N 2 /H 2 /Ar, CH x F y /O 2 /Ar or CF x /O 2 /Ar for a time sufficient to etch through the layer of first material  31  at the site of hole  36 . At the same time the remaining ARC layers  33  and  34  are removed from the surface of the layer of dielectric material  32  resulting in the structure illustrated in FIG. 3D.  
         [0041]    A plasma stripping process may then be used to remove any remaining organic material from the surface of the structure illustrated in FIG. 3D.  
         [0042]    While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.