DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] FIG. 1 illustrates a semiconductor device 10 on which a gate electrode will be fabricated, in accordance with one embodiment of the present invention. Gate electrodes are structures frequently found in common integrated circuit configurations, such as transistor arrays in memory circuits. The semiconductor device 10 includes a substrate 12 . While the illustrated substrate 12 comprises an intrinsically doped monocrystalline silicon wafer, it will be understood by one of skill in the art of semiconductor fabrication that the “substrate” in other arrangements can comprise other forms of semiconductor layers which include active or operable portions of semiconductor devices.

[0027] A gate oxide layer 14 is shown covering the substrate 12 . The gate oxide layer 14 is a dielectric that can be formed using any suitable process. For example, the gate oxide may be grown through a mask or formed through trench isolation. Other methods of forming the gate oxide layer 14 will become apparent to those of skill in the art in light of the present disclosure. Typically, the gate oxide layer 14 has a thickness of about 30 to 200 angstroms.

[0028] As illustrated in FIG. 2, a polysilicon layer 20 is formed over the gate oxide layer 14 . The polysilicon layer 20 can be formed using any suitable process. For example, the polysilicon layer 20 may be formed by conventional chemical vapor deposition (CVD) and can be in situ doped for conductivity. Other methods of forming the polysilicon layer 20 will become apparent to those of skill in the art in light of the present disclosure. The polysilicon layer 20 usually has a thickness of about 300 to 1,500 angstroms.

[0029] As illustrated in FIG. 3, a diffusion barrier layer 30 is then fabricated over the polysilicon layer 20 . The diffusion barrier layer 30 comprises TiN _x B _y . In forming the diffusion barrier layer 30 , any suitable process can be employed wherein the relative boron and nitrogen concentrations are controlled to fall within the desired ranges.

[0030] In one embodiment, for example, the diffusion barrier layer 30 is fabricated using a first process, which begins with the formation of a titanium nitride (TiN) layer over the polysilicon layer 20 followed by the incorporation of boron into the TiN layer. Any suitable process can be employed to form the TiN layer.

[0031] For example, the TiN layer may be formed by reactively sputtering a titanium target in a nitrogen-containing ambient. Suitable sputtering reactors are commercially available from Applied Materials of Santa Clara, Calif. or Tokyo Electron Ltd. of Japan. The sputtering plasma comprises a substantially inert gas, preferably argon, and nitrogen ions from a nitrogen source gas, preferably nitrogen (N2) or ammonia (NH ₃ ).

[0032] The concentration of the nitrogen-containing gas in the sputtering chamber determines the nitrogen concentration of the TiN layer. In one embodiment, the concentration of the nitrogen gas in the sputtering chamber is in the range of about 5% to 30%. To achieve a concentration in this range, nitrogen-containing gas can be introduced into the sputtering chamber at a rate of between about 1 and 15 standard cubic centimeters per minute (sccm) while the inert gas is introduced into the sputtering chamber at a rate of between about 30 and 50 sccm. The radio frequency (RF) energy of the preferred sputtering reactor is generally set between about 1 and 2 kilowatts (kW), preferably at 1.5 kW. In light of the present disclosure, however, one of skill in the art can readily determine the appropriate sputtering parameters through routine optimization to achieve the desired TiN composition in a given reactor configuration.

[0033] Alternatively, the TiN layer may be formed using a tetrakisdimethyl-aminotitanium (TDMAT) process. Such a process is described in U.S. Pat. No. 5,693,377 which is incorporated herein in its entirety by reference thereto. For example, a metal organic chemical vapor deposition process with a tetrakisdimethyl-amidotitanium (TDMAT) precursor and a carrier gas such as nitrogen (N2) can be used to create the TiN layer. The TDMAT process can be conducted in an Applied Materials TiN CVD chamber at between about 300° C. and 500° C., more preferably between 400° C. and 450° C. The chamber pressure is typically maintained between about 0.1 Torr and 2.0 Torr and preferably at about 0.5 Torr. TiN deposited by this method may also include small amounts of oxygen and carbon due organic content of the precursor.

[0034] In addition to the sputtering process and the TDMAT process described above, other methods of forming the TiN layer will become apparent to those of skill in the art in light of the present disclosure. After the TiN layer has been formed, boron is incorporated into the TiN layer by treating the device 10 with a boron-containing gas, such as diborane (B ₂ H ₆ ). The boron-containing gas may optionally include silane (SiH ₄ ) at a concentration in the range of about 1 to 50%. The device 10 is treated in a rapid thermal processing (RTP) chamber, such as a CVD chamber or the like. Suitable CVD reactors are commercially available from companies such as Applied Materials Inc. of Santa Clara, Calif. and PlasmaQuest of Dallas, Tex.

[0035] The concentration of the boron-containing gas in the CVD chamber determines the concentration of boron in the diffusion barrier layer 30 . In one embodiment, the concentration of boron in the diffusion barrier layer 30 ranges from about 0.01 to 10 atomic percent, preferably 0.1-3 atomic percent. To achieve a concentration in this range, the boron-containing gas can be introduced into the CVD chamber at a rate of between about 5 and 500 standard cubic centimeters per minute (sccm).

[0036] The pressure in the preferred CVD chamber is maintained between about 0.5 and 100 Torr. The temperature in the preferred CVD chamber is maintained between about 300° C. and 700° C., preferably at 450° C. Adjusting the flow rate, pressure, temperature, or other parameters of the reactants in the CVD chamber may cause, for example, the boron to become incorporated into the TiN layer more quickly, or the resulting TiN _x B _y layer to exhibit a greater concentration of boron. In light of the present disclosure, however, one of skill in the art can readily determine the appropriate CVD parameters through routine optimization to achieve the desired TiN _x B _y composition in a given reactor configuration.

[0037] In one embodiment, the diffusion barrier layer 30 is fabricated using the process described above. The TiN By of the diffusion barrier layer 30 has an x-factor in the range of about 0.2 to 0.499, and more preferably in the range of about 0.25 to 0.48. Furthermore, the TiN _x B _y of the diffusion barrier layer 30 has a y-factor in the range of about 0.01 to 10, and more preferably in the range of about 0.1 to 3. The diffusion barrier layer 30 typically has a thickness of about 50 to 500 angstroms.

[0038] In another embodiment, the diffusion barrier layer 30 is fabricated using a second process, in which a TiN _x B _y layer is formed directly over the polysilicon layer 20 . The TiN _x B _y layer is formed by incorporating boron into a TDMAT process. To form the TiN _x B _y layer using this method, TDMAT is decomposed in the presence of a boron-containing source gas, such as diborane (B ₂ H ₆ ), in a CVD chamber. The pressure in the preferred CVD chamber is maintained between about 0.5 and 100 Torr. The temperature in the preferred CVD chamber is maintained between about 300° C. and 600° C., preferably at 400° C. or 450° C. In light of the present disclosure, however, one of skill in the art can readily determine the appropriate TDMAT process parameters through routine optimization to achieve the desired TiN _x B _y composition in a given reactor configuration.

[0039] In one embodiment, the diffusion barrier layer 30 is fabricated over the polysilicon layer 20 using the TDMAT process including boron described above. The TiN _x B _y of the diffusion barrier layer 30 has an x-factor in the range of about 0.2 to 0.499, and more preferably in the range of about 0.25 to 0.48. Furthermore, the TiN _x B _y of the diffusion barrier layer 30 has a y-factor in the range of about 0.01 to 10, and more preferably in the range of about 0.1 to 3. The diffusion barrier layer 30 typically has a thickness of about 50 to 500 angstroms.

[0040] In another embodiment, the diffusion barrier layer 30 is fabricated using a third process, in which a TiN _x B _y layer is formed directly over the polysilicon layer 20 using a CVD process. To fabricate the diffusion barrier layer 30 using this method, the device 10 is placed in a suitable CVD chamber including a titanium-containing source gas, a nitrogen-containing source gas, and a boron-containing source gas. Each of these source gases may comprise a wide variety of suitable materials.

[0041] For example, the titanium-containing source gas may comprise titanium tetrachloride (TiCl ₄ ) or titanium tetraiodide (TiI ₄ ); the nitrogen containing source gas may comprise ammonia (NH3) or a plasma of nitrogen ions in a substantially inert gas, such as hydrogen or argon; and the boron-containing source gas may comprise diborane (B ₂ H ₆ ). Other suitable source gases will become apparent to those of skill in the art in light of the present disclosure.

[0042] The pressure in the preferred CVD chamber is maintained between about 0.5 and 100 Torr. The temperature in the preferred CVD chamber is maintained between about 500° C. and 700° C., preferably at 600° C. In light of the present disclosure, however, one of skill in the art can readily determine the appropriate CVD parameters through routine optimization to achieve the desired TiN _x B _y composition in a given reactor configuration.

[0043] In one embodiment, the diffusion barrier layer 30 is fabricated over the polysilicon layer 20 using the CVD process described above. The TiN _x B _y of the diffusion barrier layer 30 has an x-factor in the range of about 0.2 to 0.499, and more preferably in the range of about 0.25 to 0.48. Furthermore, the TiN _x B _y of the diffusion barrier layer 30 has a y-factor in the range of about 0.01 to 10, and more preferably in the range of about 0.1 to 3. The diffusion barrier layer 30 typically has a thickness of about 50 to 500 angstroms.

[0044] As illustrated in FIG. 4, a conductive layer 40 is formed over the diffusion barrier layer 30 . The conductive layer 40 may comprise any of a number of highly conductive materials containing metals, and particularly materials that can be deposited by CVD. In one embodiment, for example, the conductive layer 40 comprises tungsten (W). In another embodiment, the conductive layer 40 comprises tungsten silicide (WSi _x ). Other suitable materials for the conductive layer 40 will become apparent to those of skill in the art in light of the present disclosure.

[0045] In the illustrated embodiment, the conductive layer 40 comprises tungsten silicide (WSi _x ), which is formed by CVD with tungsten hexafluoride (WF ₆ ) and silicon tetrahydride (SiH ₄ ) as set forth in the following formula:

WF ₆ +SiH ₄ →WSi _x +F ₂ +H ₂

[0046] Alternatively, other silicon source gases (such as disilane, trisilane, di-chlorosilane, etc.) can be used in place of silane, and similarly other metal sources (such as titanium tetrachloride, etc.) can be used in the deposition process. The conductive layer 40 typically has a thickness of about 200 to 4,000 angstroms.

[0047] Fluorine atoms are typically incorporated into the conductive layer 40 during the CVD process described above. Similarly, many CVD processes result in hydrogen residue within the deposited conductive layer 40 . Post-deposition high-temperature steps tend to cause diffusion of such contaminants through the underlying polysilicon layer 20 in conventional gate electrodes. Fluorine, for example, easily diffuses down through the grain boundaries of the polysilicon layer 20 .

[0048] After the formation of the conductive layer 40 , the device 10 undergoes an anneal step. This anneal is performed to convert the deposited silicide to a lower resistance phase through grain growth and re-orientation during the anneal. The anneal typically takes place at between about 600° C. and 900° C. for about 25 minutes. During this anneal, contaminants such as fluorine typically tend to diffuse from the conductive layer 40 to the gate oxide layer 14 .

[0049] The diffusion barrier layer 30 comprising TiN _x B _y tends to inhibit contaminant diffusion from the conductive layer 40 to the gate oxide layer 14 , such that at least a portion of the contaminants are not allowed to reach and degrade the gate oxide layer 14 . To reduce contaminant diffusion, the diffusion barrier layer 30 is formed between the conductive layer 40 and the gate oxide layer 14 . In the illustrated embodiment, for example, the diffusion barrier layer 30 is formed between the polysilicon layer 20 and the conductive layer 40 .

[0050] In other embodiments, the diffusion barrier layer 30 may be formed between the gate oxide layer 14 and the polysilicon layer 20 . Furthermore, other configurations will become apparent to those of skill in the art in light of the present disclosure.

[0051] As illustrated in FIG. 5 , after the gate oxide layer 14 , polysilicon layer 20 , diffusion barrier layer 30 , and conductive layer 40 have been formed, the layers are patterned using conventional photolithography and etching techniques to form a gate electrode 50 . The layers are masked with photoresist, and etched through to expose the gate oxide layer 14 over transistor source and drain regions. These regions are formed by later doping the substrate 12 to either side of the gate electrode 50 .

[0052] The TiN _x B _y of the diffusion barrier layer 30 demonstrates certain advantages over conventional diffusion barrier materials. One advantage is that TiN _x B _y is relatively hard. For example, TiN _0.4 B exhibits a nano-hardness of more than 50 Gpa, which is comparable to the hardness of tungsten carbide (WC).

[0053] Another advantage of TiN _x B _y is that it is thermally stable at high temperatures. For example, some embodiments of TiN _x B _y exhibit thermal stability up to approximately 1,500° C. The thermal stability of TiN _x B _y allows it to be used in devices that are manufactured at high temperatures or are subject to high temperatures.

[0054] Yet another advantage of TiN _x B _y is that it adheres well to metal layers and semiconductor substrates. The good adhesion properties of TiN _x B _y allow it to be applied without using expensive adhesives, thereby reducing the complexity and expense of applying the diffusion barrier layer 30 .

[0055] These advantages, either individually or in combination, impede the diffusion of more fluorine atoms than conventional diffusion barrier materials. Although the foregoing invention has been described in terms of certain preferred embodiments, other embodiments will become apparent to those of ordinary skill in the art in view of the disclosure herein. Accordingly, the present invention is not intended to be limited by the recitation of preferred embodiments, but is intended to be defined solely by reference to the appended claims.