Method of fabricating semiconductor devices utilizing in situ passivation of dielectric thin films

[0002] 1. The Field of the Invention

[0003] The present invention relates to methods for manufacturing semiconductor devices. More particularly, the present invention relates to methods for fabricating a semiconductor device, such as a capacitor, which utilize in situ passivation of dielectric thin films during fabrication.

[0004] 2. The Relevant Technology

[0005] As integrated circuit technology has progressed, it has become possible to store ever-increasing amounts of digital data in a smaller space at less expense and still access the data randomly, quickly and reliably. Central to this increased ability to store and retrieve data has been the dynamic random access memory (DRAM), fabricated as an integrated circuit. The memory cells of DRAMs are comprised of two main components, a transistor and a capacitor. The capacitor of each memory cell functions to store an electrical charge representing a digital value (e.g., a charged capacitor representing a 1 and a discharged capacitor representing a 0) with the transistor acting as a switch to connect the capacitor to the “outside world” via decoding and other circuitry. In order to function properly, the capacitor must possess a minimum amount of capacitance. If a capacitor exhibits too little capacitance, it will cause errors in data storage.

[0006] The capacitive value of a capacitor is dependent upon the dielectric constant of the material placed between the plates of the capacitor, the distance between the plates, and the effective area of the plates. In the case of integrated circuits, the material used as a dielectric between the plates is generally limited to only a few materials.

[0007] The interaction of dielectric materials and capacitor electrode materials plays a critical role in determining electrical properties such as leakage current of capacitors in integrated circuits and advanced packages. The electrode material can interact with the dielectric material during deposition and further processing. For example, the electrode material can adsorb some of the oxygen from the dielectric film, making the dielectric film oxygen deficient. The oxygen deficient dielectric film demonstrates current leakage , and is unacceptable for use in a DRAM or other semiconductor applications.

[0008] Various approaches have been developed in an attempt to reduce leakage current problems in capacitors. For example, U.S. Pat. No. 5,641,702 to Imai et al. discloses a method of forming an integrated circuit capacitor with an insulating film having a high permittivity, which includes annealing the insulating film in a reactive oxygen atmosphere to reduce leakage current in the capacitor. In U.S. Pat. No. 5,189,503 to Suguro et al., a capacitor having a two-part dielectric insulating layer is disclosed, including a first metal oxide film with pieces of a dissimilar metal element added to the oxide, such as tantalum oxide with a zirconium additive, and a second metal oxide film such as tungsten oxide. The disclosure in the Suguro patent indicates that excessive oxygen may be added to a tantalum oxide layer to reduce oxygen deficiency and the associated leakage current. In U.S. Pat. No. 5,153,685 to Murata et al., an integrated circuit capacitor having a two-part dielectric layer including silicon nitride and silicon dioxide is disclosed. The silicon nitride is formed on the lower electrode, and the silicon dioxide is formed from the silicon nitride by a high pressure oxidation process.

[0009] While the above approaches have made some progress in reducing leakage current problems in capacitors, there is still a need for improved capacitor fabrication methods that further reduce or prevent the adsorption of oxygen from dielectric films by capacitor electrodes.

[0010] The present invention is directed to methods of fabrication for semiconductor devices such as capacitors and novel capacitor structures formed thereby which can be used in memory cells of a DRAM device. The present methods provide a protective barrier in the form of one or more passivation layers in a capacitor structure, which reduce the interaction of an electrode and dielectric film in the capacitor at their interface. This reduces the diffusion of oxygen from the dielectric film to the electrode, thereby reducing current leakage and the like.

[0011] In one aspect of the present invention, various methods are provided for fabricating capacitor structures. In one method of the present invention, a first conductive layer or electrode is formed on a semiconductor substrate, and a dielectric layer is formed on the first conductive layer. The dielectric layer is exposed to or annealed in a reactive environment in order to form a passivation layer on the dielectric layer. The reactive environment that is used in forming the passivation layer is a gas or mixture of gases, which can optionally be altered using any type of plasma or energy. The dielectric layer can be optionally annealed in an oxidizing environment prior to forming the passivation layer thereover. A second conductive layer is then formed on the passivation layer to complete construction of the capacitor structure.

[0012] In an alternative method of the invention, the above steps are performed, except that the passivation layer and dielectric layer are annealed in an oxidative environment to saturate the passivation layer and the dielectric layer with oxygen prior to forming the second conductive layer. In a further alternative method, the steps of annealing in the reactive environment and annealing in the oxidative environment are repeated in a cyclic process prior to forming the second conductive layer.

[0013] In another method of the invention, a first conductive layer is formed on a semiconductor substrate, and the first conductive layer is exposed to a reactive environment in order to form a passivation layer on the first conductive layer. A dielectric layer is then formed on the passivation layer, and a second conductive layer is formed on the dielectric layer to complete construction of the capacitor structure. Alternatively, a second passivation layer can be formed on the dielectric layer prior to forming the second conductive layer.

[0014] In a further method of the invention, a first conductive layer is formed on a semiconductor substrate, and a thin first dielectric layer is formed on the first conductive layer. The first dielectric layer is then exposed to a reactive environment in order to form a passivation layer on the first dielectric layer. A second dielectric layer is then formed on the passivation layer, and a second conductive layer is formed on the second dielectric layer to complete construction of the capacitor structure. Alternatively, a second passivation layer can be formed on the second dielectric layer prior to forming the second conductive layer.

[0015] In another aspect of the invention, various capacitor structure embodiments fabricated according to the above described methods are provided.

[0016] Other aspects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.

[0017] In order to more fully understand the manner in which the above-recited and other advantages and objects of the invention are obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0018] FIGS. 1A-1C are partial cross-sectional schematic views showing successive steps in one method for manufacturing a semiconductor device according to the present invention;

[0019] FIGS. 2A-2D are partial cross-sectional schematic views showing successive steps in another method for manufacturing a semiconductor device according to the present invention;

[0020] FIGS. 3A-3C are partial cross-sectional schematic views showing successive steps in a further method for manufacturing a semiconductor device according to the present invention;

[0021] FIGS. 4A-4D are partial cross-sectional schematic views showing successive steps in another method for manufacturing a semiconductor device according to the present invention;

[0022] FIGS. 5A and 5B are partial cross-sectional schematic views of alternative capacitor structure embodiments formed utilizing the method of FIGS. 4A-4D; and

[0023] FIG. 6 is a process flow diagram showing successive steps in an alternative method for manufacturing a capacitor according to the present invention.

[0024] The present invention is directed to methods for fabricating a semiconductor device such as capacitors used in memory cells of a DRAM device. As discussed in greater detail below, a capacitor formed according to the present invention generally includes a first conductive layer in the form of a lower capacitor plate or electrode, a dielectric layer over the first conductive layer, and a second conductive layer in the form of an upper capacitor plate or electrode over the dielectric layer. One or more passivation layers are formed at the interface between the dielectric layer and an electrode in order to reduce the interaction of the electrode and the dielectric layer. This reduces the diffusion of oxygen from the dielectric layer to the electrode, resulting in improved leakage current properties in the capacitor.

[0025] As used herein, the term “semiconductor substrate” is defined to mean any construction comprising semiconductive material, including but not limited to bulk semiconductive material such as a semiconductive wafer, either alone or in assemblies comprising other materials thereon, and semiconductive material layers, either alone or in assemblies comprising other materials. The term “substrate” refers to any supporting structure including but not limited to the semiconductor substrates described above. The term semiconductor substrate is contemplated to include such structures as silicon-on-insulator and silicon-on-sapphire.

[0026] Referring to the drawings, wherein like structures are provided with like reference designations, the drawings are schematic representations showing successive steps in various alternative methods according to the present invention for manufacturing a capacitor used in integrated circuit structures. The drawings only show the structures necessary to understand the present invention, and thus additional structures known in the art have not been included to maintain the clarity of the drawings.

[0027] FIGS. 1A-1C show successive steps in a method for manufacturing a capacitor structure 10 for a semiconductor device, such as a DRAM device, according to the present invention. As depicted in FIG. 1A, the capacitor structure 10 has been partially fabricated according to techniques known in the art, and includes a semiconductor substrate 12 such as a silicon substrate, and a first conductive layer in the form of a lower electrode 14 made of a conductive material which is formed over substrate 12. The lower electrode 14 is formed by conventional techniques such as chemical vapor deposition (CVD), and can have a thickness in the range from about 100 angstroms to about 3,000 angstroms. The lower electrode 14 can be formed of various conductive materials such as polysilicon, titanium nitride, tungsten, molybdenum, tungsten silicide, tantalum, tungsten nitride, Pt, Ru, RuO_x, Ir, IrO_x, Pt combinations thereof, and the like. The lower electrode 14 functions as a lower capacitor plate such as for a memory cell of a DRAM device, and is conductively connected to active areas (not shown) in the device.

[0028] A dielectric insulating film in the form of a dielectric layer 16 is formed over lower electrode 14, as shown in FIG. 1A, by conventional techniques. For example, dielectric layer 16 can be formed by a CVD process in a tube furnace. The dielectric layer 16 can have a thickness in the range from about 10 angstroms to about 1000 angstroms. Dielectric layer 16 can be made of various insulating materials, such as silicon nitride, silicon dioxide, tantalum oxide, strontium titanate, and barium strontium titanate.

[0029] The partially formed capacitor structure as shown in FIG. 1A is then exposed to a suitable reactive environment in situ in order to form or grow a passivation layer 18aon the upper surface of dielectric layer 16 as shown in FIG. 1B. For example, passivation layer 18acan be formed by annealing dielectric layer 16 in an oxygen-free or reducing reactive atmosphere while the partially formed capacitor structure is still in a deposition chamber for depositing dielectric layer 16. Optionally, dielectric layer 16 can be annealed in an oxidizing atmosphere if desired prior to forming passivation layer 18a.

[0030] The passivation layer 18ais preferably formed by annealing dielectric layer 16 in the reactive atmosphere at a temperature in the range from about 100° C. to about 1100° C. The reactive atmosphere for producing passivation layer 18acan be composed of various gaseous materials, such as nitrogen, hydrogen, ammonia, hydrazine (N₂H₄), monomethyl hydrazine (MMH), forming gas (gas mixture of H₂+N₂), carbon tetrafluoride (CF₄), CHF₃, hydrochloric acid (HCl), boron trichloride (BCl₃), mixtures thereof, and the like. The nature of the reactive gaseous environment can be altered or enhanced if desired by using any type of plasma source (e.g., electron cyclotron residence (ECR), inductive coupled plasma (ICP), radio frequency (RF), remote, etc.), rapid thermal nitridization (RTN), or other energy sources.

[0031] The exposure of dielectric layer 16 to the reactive environment converts the top few monolayers of dielectric layer 16 into passivation layer 18a, which limits or stops oxygen, carbon, and other species from transporting between dielectric layer 16 and an upper electrode material, which is discussed in further detail below. The thickness of the passivation layer can be optimized to provide an effective diffusion barrier without sacrificing charge storage capacity of the capacitor. Accordingly, the passivation layer can have a thickness in the range from about 10 angstroms to about 100 angstroms. Stated otherwise, the passivation layer can have thickness in the range from a fraction of a monolayer to about one (1) monolayer. The formed passivation layer can include compounds having the formula M(O)_yX_z, M(O)_yX_zW_n, M_xX_y, or any other compound where M can be any specie or all species in the oxide dielectric layer other than oxygen or nitrogen, such as silicon, tantalum, strontium titanate, barium strontium titanate, boron, boron phosphate, phosphorus, etc.; X and W can be nitrogen, fluorine, carbon, chlorine, iodine, and CO₃; and n, x, y and z can be integers from 1 to 6. Various combinations of chemical compounds having the above formulas can also be present in the passivation layer.

[0032] The passivation layer forms a protective barrier at the interface between the dielectric layer and the electrode. For example, if tantalum oxide is used to form the dielectric layer, and ammonia gas is present in the reactive environment, a very thin film of tantalum nitride or tantalum oxynitride is grown by reaction of the ammonia gas with the surface of the dielectric layer exposed to the ammonia gas. This thin film acts as a diffusion barrier between the upper electrode and the dielectric layer. Other compounds such as tantalum fluoride and tantalum carbide can be formed in the passivation layer when other types of gaseous materials are present in the reactive environment.

[0033] As shown in FIG. 1C, a second conductive layer in the form of an upper electrode 19 made of a conductive material is then formed over passivation layer 18aand dielectric layer 16. The upper electrode 19 is formed by conventional techniques such as CVD, and can have a thickness in the range from about 200 angstroms to about 4,000 angstroms. The upper electrode 19 can be formed of various conductive materials, such as the materials used to form lower electrode 14. The upper electrode 19 functions as an upper capacitor plate such as for a memory cell of a DRAM device. The formation of upper electrode 19 completes construction of the capacitor elements for capacitor structure 10.

[0034] In a variation of the method of manufacture shown in FIGS. 1A-1C, the above described steps are followed except that the passivation layer is further annealed in an oxidizing environment, to saturate the passivation layer and dielectric layer with oxygen, prior to formation of the upper electrode. Thus, the partially formed capacitor structure shown in FIG. 1B, including passivation layer 18aover dielectric layer 16, is annealed in an oxidizing atmosphere prior to formation of upper electrode 19 to complete the capacitor structure.

[0035] FIGS. 2A-2D show successive steps in manufacturing a capacitor structure 20 for a semiconductor device according to another method of the invention. As depicted in FIG. 2A, the capacitor structure 20 has been partially fabricated according to techniques known in the art, and includes a semiconductor substrate 12 such as a silicon substrate, and a first conductive layer in the form of a lower electrode 14 which is formed over substrate 12.

[0036] The partially formed capacitor structure as shown in FIG. 2A is then exposed to a suitable reactive environment in situ in order to form a passivation layer 18bon lower electrode 14 as shown in FIG. 2B. The passivation layer 18bis formed in the same manner and from the same gaseous materials as discussed above for passivation layer 18aof FIG. 1B. Optionally, lower electrode 14 can be annealed prior to forming passivation layer 18b. The exposure of lower electrode 14 to the reactive environment converts the top few monolayers of lower electrode 14 into passivation layer 18b, which can have a thickness in the range from about 4 angstroms to about 30 angstroms. Stated otherwise, the passivation layer can have thickness in the range from a fraction of a monolayer to about one (1) monolayer. The passivating layer 18bcan include the same chemical compounds as discussed above for passivation layer 18a.

[0037] An insulating dielectric layer 16 is then formed over passivation layer 18band lower electrode 14, as shown in FIG. 2C, by conventional techniques. The passivation layer 18bprovides a protective barrier for lower electrode 14 during formation of dielectric layer 16 to prevent oxidation of lower electrode 14. Optionally, passivation layer 18bcan be annealed in an oxidizing environment to saturate passivation layer 18bwith oxygen prior to formation of dielectric layer 16. The passivation layer 18blimits or stops oxygen, carbon, and other species from transporting between dielectric layer 16 and lower electrode 14.

[0038] A second conductive layer in the form of an upper electrode 19 is then formed over dielectric layer 16 by conventional techniques, as depicted in FIG. 2D. The formation of upper electrode 19 completes construction of the capacitor elements for capacitor structure 20.

[0039] FIGS. 3A-3C show successive steps in manufacturing a capacitor structure 30 for a semiconductor device according to a further method of the invention, which incorporates steps from both the methods shown in FIGS. 1A-1C and FIGS. 2A-2D. Accordingly, as depicted in FIG. 3A, the capacitor structure 30 has been partially fabricated as discussed above and shown in FIG. 2C, and includes a semiconductor substrate 12, a lower electrode 14 formed over substrate 12, a passivation layer 18bon lower electrode 14, and a dielectric layer 16 formed over passivation layer 18band lower electrode 14.

[0040] As shown in FIG. 3B, a passivation layer 18ais then formed over dielectric layer 16 in the same manner as discussed above in relation to FIG. 1B. An upper electrode 19 is then formed over passivation layer 18a, as shown in FIG. 3C, to complete construction of the capacitor elements for capacitor structure 30. Optionally, passivation layer 18acan be annealed in an oxidizing environment prior to forming upper electrode 19 thereover. The passivation layer 18bin capacitor structure 30 provides a barrier to the transport of oxygen, carbon, and other species from dielectric layer 16 to lower electrode 14, while passivation layer 18aprovides a similar species transport barrier between dielectric layer 16 and upper electrode 19.

[0041] FIGS. 4A-4D show successive steps in manufacturing a capacitor structure for a semiconductor device according to another method of the invention. As depicted in FIG. 4A, a capacitor structure has been partially fabricated according to techniques known in the art, and includes a semiconductor substrate 12, and a lower electrode 14 which is formed over substrate 12. As shown in FIG. 4B, a thin first dielectric layer 16ais formed over lower electrode 14 by conventional techniques. The first dielectric layer 16acan have a thickness in the range from about 10 angstroms to about 1000 angstroms.

[0042] This partially formed capacitor structure is then exposed to a suitable reactive environment in order to form a passivation layer 18bon first dielectric layer 16a, as illustrated in FIG. 4C. Optionally, first dielectric layer 16acan be converted to passivating layer 18bcompletely, which may be conductive. A second dielectric layer 16bis then formed over passivation layer 18bon first dielectric layer 16a, as shown in FIG. 4D, by conventional techniques. The second dielectric layer 16bcan have a thickness in the range from about 10 angstroms to about 1000 angstroms. Optionally, passivation layer 18bcan be annealed in an oxidizing environment to saturate passivation layer 18band first dielectric layer 16awith oxygen prior to formation of second dielectric layer 16b.

[0043] FIGS. 5A and 5B show alternative capacitor structures which can be constructed utilizing the method steps of FIGS. 4A-4D. Accordingly, the partially constructed capacitor of FIG. 4D is subjected to further processing to form a capacitor structure 40 as shown in FIG. 5A, or a capacitor structure 50 as shown in FIG. 5B.

[0044] In order to form capacitor structure 40 of FIG. 5A, an upper electrode 19 is formed over second dielectric layer 16bby conventional techniques. The formation of upper electrode 19 completes construction of the capacitor elements for capacitor structure 40.

[0045] In order to form capacitor structure 50 of FIG. 5B, the partially formed capacitor structure of FIG. 4D is exposed to a suitable reactive environment in order to form a passivation layer 18aon second dielectric layer 16b. An upper electrode 19 is then formed over passivation layer 18aand second dielectric layer 16bby conventional techniques. Optionally, passivation layer 18acan be annealed in an oxidizing environment to saturate passivation layer 18aand second dielectric layer 16bwith oxygen prior to formation of upper electrode 19. The formation of upper electrode 19 completes construction of the capacitor elements for capacitor structure 50.

[0046] FIG. 6 is a process flow diagram showing successive steps in an alternative method for manufacturing a capacitor according to the present invention. A substrate with a lower electrode and a dielectric layer, such as shown in FIG. 1A, is treated in a suitable reactive environment to form a passivation layer over the dielectric layer, such as shown in FIG. 1B, which in turn is annealed in an oxidizing environment to form an oxygen-saturated saturated passivation layer. The process steps of treating in a reactive environment and annealing in an oxidizing environment can then be cyclically repeated a desired number of times in order to make a saturated passivation layer which does not show any transient diffusion processes. Once the treatment and annealing cycle has been completed, an upper electrode is deposited over the passivation layer to complete formation of the capacitor structure, such as shown in FIG. 1C.

[0047] The cycling treatment and annealing process represented in FIG. 6 provides increased integrity, strength and thickness to the passivation layer. The cycle of treatment and annealing can be repeated as many times as needed to achieve the desired properties for the passivation layer. For example, the cycle can be repeated 2 or 3 times or more if desired.

[0048] It should be understood that the cycling treatment and annealing process represented in FIG. 6 can be used anytime a passivation layer is formed according to the methods of the present invention. Accordingly, the cycling process of FIG. 6 can be used as part of any of the methods discussed herein, such as when the passivation layer is formed on the lower electrode as shown in FIG. 2B, or when passivation layers are formed over the lower electrode and the dielectric layer, as shown in FIG. 3B.

[0049] The methods of the present invention provide many advantages and benefits. The passivation layer formed according to the present invention at the interface between the dielectric layer and an electrode reduces or minimizes the chemical interaction of the electrode and the dielectric layer. This reduces the diffusion of oxygen from the dielectric layer to the electrode, resulting in improved leakage current properties for capacitors fabricated according to the present invention. Without passivation, the electrical properties of a capacitor can significantly deteriorate. Thus, the present invention particularly allows for the successful integration of oxide dielectric films and electrodes on chips such as DRAM chips.

[0050] The passivation layer also provides protection to capacitor layers in a wafer during transfer of the wafer to different chambers for deposition of the electrode and dielectric materials during fabrication. For example, a dielectric layer that has not been passified can pick up moisture and hydrogen when exposed to an ambient environment, which can be detrimental and can degrade the dielectric layer. By forming the passivating layer, a protective barrier is formed which prevents unwanted interaction with the ambient environment during wafer transfer.

[0051] The present invention provides flexibility in formation of the passivation layer where it is needed. Thus, passivation can be easily achieved at an interface of a capacitor where leakage problems are occurring, such as where high stress is applied at an interface during processing. Standard failure analysis testing can be done to determine the interface or interfaces where passivation should be applied in the capacitor.

[0052] The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.