Abstract:
A method of manufacturing a semiconductor device includes the steps of: (X) forming a first hydrophobic insulating layer above a semiconductor substrate; (Y) hydrophilizing a surface of the first hydrophobic insulating layer; and (Z) forming a low dielectric constant insulating layer having a specific dielectric constant lower than the specific dielectric constant of silicon oxide on the first hydrophobic insulating layer having a bydrophilized surface. A semiconductor device manufacturing method which can suppress peel-off of a low dielectric constant insulating layer from an underlying hydrophobic layer is provided.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on Japanese Patent Applications No. 2002-338294, filed on Nov. 21, 2002, and No. 2002-187802, filed on Jun. 27, 2002, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     A) Field of the Invention 
     The present invention relates to a semiconductor device manufacturing method, and more particularly to a method of manufacturing a semiconductor device having multilevel wiring layers. 
     B) Description of the Related Art 
     The integration degree and operation speed of large scale integrated circuits have been improved increasingly. As the integration degree is improved, semiconductor elements such as transistors constituting an, integrated circuit are becoming smaller and the operation speed of smaller semiconductor elements is also improved. 
     As the micro patterning and integration degree of semiconductor elements are improved, wiring in a large scale integrated circuit becomes fine and multileveled. A transmission speed of a signal in a wiring line is determined almost by a wiring resistance and a wiring parasitic capacitance. 
     Reduction in a wiring resistance can be realized by changing the main component of a wiring from aluminum (Al) to copper (Cu) having a lower resistivity. Making the resistance of wiring material lower than that of Cu is practically difficult. As Cu is used as the material of a wiring, it becomes necessary to prevent diffusion of Cu in the wiring into an interlayer insulating film. SiN, SiC or SiCO is mainly used as the material of a copper diffusion preventive layer. The copper diffusion preventive layer has generally a high water repellency. 
     If the distance between wiring lines becomes short because of high integration of semiconductor devices, the parasitic capacitance between wiring lines increases assuming that the wiring thickness is the same. If the parasitic capacitance is lowered by thinning the wiring thickness, the wiring resistance increases. In order to lower the wiring capacitance, it is most effective to use material having a low dielectric constant, so-called low k material. 
     In this specification, the value of dielectric constant will be referred to by the specific dielectric constant. 
     There are many reports on a method of forming an interlayer insulating film by using material having a dielectric constant lower than that of silicon oxide in order to realize a high speed operation of a semiconductor device. Since a wiring capacitance becomes serious particularly for lower level micro patterned wiring layers, it has been studied to form an interlayer insulating film by using a low dielectric constant material. 
     If a low dielectric constant insulating material layer is formed in a liquid phase on a copper diffusion preventive layer having a hydrophobic surface, adhesion is likely to be lowered. If a low dielectric constant insulating material layer is formed on a copper diffusion preventive layer, by a coating method in particular, adhesion is likely to be lowered. In the multilevel wiring structure, peel-off at the interface between a low dielectric constant insulating layer and a hydrophobic underlying layer may occur. As the number of wiring layers increases, peel-off of a low dielectric constant insulating layer becomes more conspicuous. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide a method of manufacturing a semiconductor device capable of suppressing peel-off of a low dielectric constant insulating layer from a hydrophobic underlying layer. 
     Another object of the invention is to provide a method of manufacturing a semiconductor device of a high performance, a high reliability and a high integration. 
     According to one aspect of the present invention, there is provided a method of manufacturing a semiconductor device comprising the steps of: (X) forming a first hydrophobic insulating layer above a semiconductor substrate; (Y) hydrophilizing a surface of said first hydrophobic insulating layer; and (Z) forming a low dielectric constant insulating layer having a specific dielectric constant lower than a specific dielectric constant of silicon oxide on said first hydrophobic insulating layer having a hydrophilized surface. 
     With this method, adhesion of a multilevel wiring structure can be improved and peel-off can be suppressed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A to  1 L are cross sectional views of a semiconductor substrate illustrating a method of manufacturing a semiconductor device according to an embodiment of the invention. 
     FIGS. 2A to  2 C are diagrams illustrating the effects of the embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the invention will be described with reference to the accompanying drawing. 
     As shown in FIG. 1A, an element isolation trench or trenches are formed in the surface layer of a silicon substrate  10  and insulating material such as silicon oxide is filled in this trench to form a shallow trench isolation (STI)  11 . If necessary, before or after STI is formed, ions are implanted to form a desired well or wells in the surface layer of the silicon substrate  10 . A number of active regions are defined being surrounded by STI  11 . 
     On the surface of each active region of the silicon substrate  10 , an insulated gate electrode is formed which is made of a lamination of a gate insulating film  14 , a polysilicon gate electrode  15  and a silicide electrode  16 . Side wall spacers  17  are formed on both side walls of the insulated gate electrode. The insulated gate electrode structure is collectively represented by G. Before and after the side wall spacers  17  are formed, desired ions are implanted to form source/drain regions with extensions. A CMOS transistor structure can be formed by forming n- and p-channel transistors. 
     After semiconductor elements such as MOS transistors are formed, a phosphosilicate glass (PSG) layer  18  is deposited to a thickness of about 1.5 μm by chemical vapor deposition (CVD) at a substrate temperature of 600° C. for example. The deposited PSG layer  18  has an irregular surface which conforms with the surface of the underlying structure including the gate electrode and the like. The surface of the PSG layer  18  is planarized by chemical mechanical polishing (CMP). On the planarized surface, an SiC film  19  is formed as a passivation film. For example, the SiC film  19  is formed by plasma CVD to a thickness of about 50 nm by using the material ESL3 (registered trademark) available from Novellus Systems. The SiC layer  19  has also a copper diffusion preventing function of preventing Cu in a copper wiring formed on the SiC layer  19  from being diffused downward. 
     On the surface of the SiC layer  19 , a resist pattern PR 1  is formed. The resist pattern PR 1  has an opening to be used for forming a contact hole in an electrode deriving area of a semiconductor element. By using the resist pattern PR 1  as an etching mask, the SiC layer  19  and PSG layer  18  are etched to form a contact hole. 
     As shown in FIG. 1B, a barrier metal layer of TiN, Ta or the like is deposited covering the inner wall of the contact hole by sputtering, and thereafter a tungsten (W) layer is formed by CVD. Unnecessary metal layers deposited on the SiC film  19  are removed by CMP. In this manner, a conductive (contact) plug P is formed which is embedded in the contact hole and has a surface flush with the surface of the SiC film  19 . 
     As shown in FIG. 1C, surface treatment is performed by dispensing drops of alkaline ammonium fluoride (NH 4 F) 5% aqueous solution LQ 1  on the surface of the insulating film constituted of the PSG layer  18  and SiC layer  19  and embedded with the W conductive plug P, and maintaining the solution in contact with the surface of the insulating film for about 2 minutes at a room temperature. After the surface treatment, the surface of the semiconductor substrate is washed with pure water and dried with a spinner. With this surface treatment, the surface of the SiC layer  19  becomes hydrophilic. 
     As shown in FIG. 1D, on the surface of the SiC film  19 , a low dielectric constant layer LK 1 , which is a so-called low k material, is coated to a thickness of about 150 nm. For example, the low dielectric constant insulating layer LK 1  is coated by using the material SiLK-J150 (registered trademark) available from Dow Chemical Company. After the low dielectric constant film LK 1  is coated, it is baked to evaporate solvent and a curing process is performed, by heat treatment. On the surface of the low dielectric constant insulating film LK 1 , a cap layer  20  of silicon oxide (SiO) or the like is deposited to a thickness of about 100 nm by CVD for example. 
     On the surface of the cap layer  20 , a resist pattern PR 2  is formed. The resist pattern PR 2  has an opening corresponding to a wiring pattern of a first wiring layer. By using the resist pattern PR 2  as an etching mask, the cap layer  20  and low dielectric constant insulating film LK 1  are etched to form a wiring trench. The resist pattern PR 2  is thereafter removed. 
     As shown in FIG. 1E, on the inner surface of the wiring trench exposing the top of the conductive plug P and on the surface of the substrate, a barrier metal layer BM of TaN or the like is formed to a thickness of about 30 nm and a seed metal layer SM of Cu is formed to a thickness of about 30 nm, by sputtering. 
     As shown in FIG. 1F, on the surface of the seed metal layer SM, a copper wiring layer PM is formed by plating. Thereafter, CMP is performed to remove unnecessary metal layers on the surface of the cap layer  20 . 
     As shown in FIG. 1G, on the surface of the cap layer  20  embedded with a first wiring pattern W 1 , a copper diffusion preventive layer  21  is formed by plasma CVD similar to that described earlier. For example, the copper diffusion preventive layer  21  is made of an SiC layer having a thickness of 50 nm. After the copper diffusion preventive layer  21  is formed, surface treatment is performed by dispensing drops of alkaline ammonium fluoride 5% aqueous solution LQ 2  on the surface of the copper diffusion preventive layer  21 , and maintaining the solution in contact with the surface of the copper diffusion preventive layer for about 2 minutes at a room temperature. After the surface treatment, the surface of the semiconductor substrate is washed with pure water and dried with a spinner. With this surface treatment, the surface of the SiC layer  21  becomes hydrophilic. 
     As shown in FIG. 1H, on the surface of the SiC layer  21  subjected to the surface treatment, a low dielectric constant insulating layer LK 2  is coated to a thickness of about 400 nm. For example, the low dielectric constant insulating layer LK 2  is coated by using the material SiLK-J350 (registered trademark) available from Dow Chemical Company. After the liquid material is coated, a baking and curing process is performed to form the low dielectric constant insulating layer LK 2 . On the surface of the low dielectric constant insulating film LK 2 , a cap layer  23  of SiO or the like is deposited to a thickness of, e.g., about 100 nm and a hard mask layer  24  made of silicon nitride (SiN) is formed to a thickness of e.g., about 50 nm by CVD. 
     As shown in FIG. 11, a dual damascene wiring pattern  29  is embedded in the hard mask layer  24 , cap layer  23 , low dielectric constant insulating film LK 2  and copper diffusion preventive layer  21 . For example, an opening defining a wiring trench is formed in the hard mask  24  by using a resist pattern, and thereafter a via hole reaching the copper diffusion preventive layer  21  is formed by using a resist pattern. By using the hard mask layer  24  as an etching mask, a wiring trench is formed by etching the cap layer  23  and low dielectric constant insulating film LK 2 . Then, the copper diffusion preventive layer  21  exposed on the bottom of the via hole is etched to complete a dual damascene wiring trench. 
     Next, similar to the process described with reference to FIG. 1F, a barrier metal layer, a seed metal layer and a plated layer are laminated, and unnecessary portion of the metal layers on the hard mask layer  24  is removed by CMP to complete the second wiring pattern  29 . The hard mask layer  24  may be removed by CMP. 
     As shown in FIG. 1J, above the surface of the second interlayer insulating layer LK 2  embedded with the second wiring layer  29 , a copper diffusion preventive layer  31  of SiC having a thickness of, e.g., 50 nm is formed by plasma CVD. Surface treatment is performed by dispensing drops of alkaline ammonium fluoride 5% aqueous solution LQ 2  on the surface of the SiC layer  31 , and maintaining the solution in contact with the surface of the SiC layer  31  for about 2 minutes at a room temperature. The surface of the hydrophobic SiC layer  31  becomes hydrophilic. 
     As shown in FIG. 1K, on the SiC layer  31  subjected to the surface treatment, a low dielectric constant insulating layer LK 3  of the material SiLK-J350 (trademark) is coated to a thickness of about 450 nm by a process similar to that described earlier. On the surface of the low dielectric constant layer LK 3 , a cap layer  33  of SiO having a thickness of about 100 nm and a hard mask layer  34  of SiN having a thickness of about 50 nm are formed. A third wiring pattern is formed through the hard mask layer  34 , cap layer  33 , low dielectric constant insulating layer LK 3  and copper diffusion preventive layer  31  by a process similar to that described earlier. 
     Similar processes are repeated to form the wiring structure having, e.g., five wiring layers. 
     FIG. 1L shows an example of the structure of five wiring layers. The third wiring pattern  39  is embedded in the third interlayer insulating film. On the surface of this structure, a copper diffusion preventive layer  41 , a low dielectric constant insulating layer LK 4 , a cap layer  43  and a hard mask layer  44  are stacked, and a fourth wiring pattern  49  is embedded in this structure. On the surface of this structure including the fourth wiring pattern, a copper diffusion preventive layer  51 , a low dielectric constant insulating layer LK 5 , a cap layer  53  and a hard mask layer  54  are stacked, and a fifth wiring pattern  59  is embedded in this structure. Covering this structure including the fifth wiring pattern  59 , a cap layer  60  of SiC or the like is formed. An SiO 2  film as an interlayer insulating film and an aluminum pad are formed thereon. 
     A capacitance of the second wiring pattern in the multilevel wiring structure constructed as above, was measured. A sample of the wiring pattern used was a comb-shaped wiring pattern having a pitch of 0.24 μm and a total length of 30 cm. The measured capacitance was about 180 fF/mm. After heat treatment for 30 minutes at 400° C. was repeated five times, film peel-off was not found at all. 
     A similar heat cycle test was performed for a semiconductor device having a multilevel wiring structure formed without the surface treatment of an SiC layer. Peel-off occurred at the interface between a SiC copper diffusion preventive layer and a SiLK low dielectric constant insulating layer thereon. These results elucidate the effects of the surface treatment of a copper diffusion preventive layer. 
     How a water contact angle of an SiC layer changes with the surface treatment was measured. The water contact angle of an SiC layer before the surface treatment was 48 degrees, whereas the water contact angle of an SiC layer after the surface treatment by ammonium fluoride 5% aqueous solution for 2 minutes at a room temperature was 33 degrees. 
     In the embodiment, ammonium fluoride 5% aqueous solution was used as hydrophilic process liquid. The hydrophilic process liquid is not limited only to this. Instead of ammonium fluoride, ammonium primary phosphate 30% aqueous solution was used as the hydrophilic process liquid. This surface process is performed for 2 minutes at a room temperature similar to the above-described embodiment. After heat treatment for 30 minutes at 400° C. was repeated five times, film peel-off was not found at all. 
     A change in a water contact angle of an SiC layer was measured. The water contact angle of an SiC layer before the surface treatment was 48 degrees as described above. The water contact angle of an SiC layer after the surface treatment by ammonium primary phosphate 30% aqueous solution for 2 minutes at a room temperature was 36 degrees. It is apparent that the SiC becomes hydrophilic by the surface treatment. 
     These results may be ascribed to the followings. 
     As shown in FIG. 2A, it can be considered that the surface of the SiC layer  21  ( 31 ,  41 ,  51 ) is terminated by SiH. The surface of the SiC layer is therefore hydrophobic. Adhesion lowers because wettability of a low dielectric constant insulating layer to be formed on the surface of the SiC layer  21  is degraded. 
     As shown in FIG. 2B, as the surface of the SiC layer  21  is processed by alkaline solution which contains water, the SiH group is changed to an SiOH group. The surface of the SiC layer with H being replaced with OH becomes hydrophilic. 
     As shown in FIG. 2C, as an organic low dielectric constant insulating layer is formed on the SiC layer  21  subjected to the surface treatment, hydrogen bond or dehydration and condensation occur between the OH group and C of aryl ether R—O—C—C═C, O of siloxane bond Si—O—Si, O of phenyl ether R—O—R′, hydrogen of R—H, and the like. The low dielectric constant insulating layer LK and SiC layer  21  are therefore formed with good adhesion. 
     Alkaline aqueous solution may be aqueous solution of the mixture of pure water and ammonium phosphate, ammonium fluoride, ammonium sulfate, 1,4-naphthhydroquinone-2-ammonium sulfonate, ammonium nitrate, ammonium acetate, ammonium calcium nitrate, ammonium iron citrate or the like. Changing the SiH group on the surface to the SiOH group is not limited only to using ammonium aqueous solution, but using alkaline solution having the OH group may be effective. If the surface of the SiC layer is washed thereafter to completely remove the hydrophilic process liquid, various kinds of alkaline solution may be used. Alkaline solution which contains alkaline metal such as Na may also be used. 
     Liquid material for forming the low dielectric constant insulating layer may contain adhesion accelerator. The adhesion accelerator may be Si compound having an unsaturated bond such as (RO) 3 SiCH═CH 2 , (RO) 3 SiCCH, SiCH 2 CH═CH 2 , and Si—CH 2 CCH. By using these materials, adhesion can be improved. After the adhesion accelerator is coated on the underlying layer, a low dielectric constant insulating layer may be formed. 
     In this embodiment, although the SiC layer is used as the copper diffusion preventive layer, an SiN layer or an SiOC layer may also be used as the copper diffusion preventive layer, with expected improvement of adhesion. A change in the water contact angle on an SiOC layer subjected to the surface treatment was measured. The water contact angle of the SiOC layer before the surface treatment was 98 degrees. The water contact angle after the surface treatment by ammonium fluoride 5% aqueous solution for 2 minutes at a room temperature was 65 degrees. The water contact angle after the surface treatment by ammonium primary phosphate 30% aqueous solution for 2 minutes at a room temperature was 80 degrees. It is apparent that the copper diffusion preventive layer becomes hydrophilic by the surface treatment. 
     Hydrophilization improves wettability with L-butyrolactone or the like contained in varnish in low dielectric constant insulating material. Adhesion with the low dielectric constant insulating layer can therefore be improved. 
     Hydrophilization may be performed by using acidic aqueous solution having an OH group. Acetic acid, oxalic acid, citric acid, oxalo acid, succinic acid, fumaric acid, tartaric acid, formic acid, lactic acid, hydrogen peroxide, ozonized water and nitric acid may be used for acidic aqueous solution. Hydrophilization is performed by directly oxidizing the SiH group in the SiC layer and changing it to SiOH. The water contact angle on the SiC layer subjected to the surface treatment by acetic acid 3% aqueous solution for 2 minutes at a room temperature was 33 degrees. 
     When chemical solution is used, this may be heated if necessary. Heating can change the SiH group to the OH group in a short time. The temperature is set to 30 to 95° C. or more preferably to 35 to 50° C. If ammonium fluoride aqueous solution is used, both a process for 5 minutes at a room temperature and a process for 2 minutes at 40° C. are equivalent in terms of improvement of adhesion. 
     Prevention of a film peel-off and improvement of adhesion may be ascribed to changing the hydrophobic surface with the SiH group to the hydrophilic surface. In order to form a hydrophilic surface, an oxide film may be formed on the hydrophobic surface. Instead of the above-described surface treatment using solution, the hydrophobic surface may be exposed in oxygen-containing plasm to form an oxide film on the hydrophobic surface, with expected similar effects. In this case, LQ shown in FIG. 2B is plasma of oxygen-containing oxidizing gas. 
     Although an organic insulating layer of SiLK (registered trademark) is used as the low dielectric constant insulating layer, an organic insulating layer of FLARE (registered trademark) may also be used with expected similar effects. Porous silica of hydrogensilsesquioxane, methylsilsesquioxane or the like may also be used. An insulating layer made of porous silica coating material having an inorganic methyl group or the like is also hydrophobic. Also in this case, adhesion is expected to be improved by the surface treatment. 
     Silicon oxycarbide (SiOC) formed by CVD has a specific dielectric constant of, e.g., about 3 lower than that of about 4.1 of silicon oxide. An interlayer insulating film may be formed by CVD using TORAL (c.f. JP-A-2002-315900, which is incorporated here in by reference) or the like. TORAL is formed under the conditions that a flow rate of tetramethylcyclotetrasiloxane (TOMCOTS) as source gas is set to one fifth, an oxygen flow rate is set to one fifth or lower, and the power is set to one second and so on, by changing the manufacture conditions of CORAL (registered trademark) of Novellus Systems, Black Diamond (registered trademark) of Applied Materials (AMAT), Inc. and CORAL (registered trademark) of Novellus Systems. 
     In a multilevel wiring structure having, e.g., ten or more layers, SiLK, FLARE or the like is used as the material of the fourth and lower level interlayer insulating films, and silicon oxycarbide is used as the material of the fifth to eighth intermediate level interlayer insulating films. Good characteristics of the multilevel wiring structure can be obtained. 
     Silicon oxycarbide deposited by CVD is likely to become hydrophobic so that adhesion to the (copper diffusion preventive) underlying layer such as an SiC layer is degraded. By hydrophilizing the underlying layer surface and forming a silicon oxycarbide layer thereon, the hydroxyl group on the surface of an SiC or SiN layer reacts with the SiH group or the like of the low dielectric constant insulating layer. 
     The present invention has been described in connection with the preferred embodiments. The invention is not limited only to the above embodiments. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.