CVD deposition of M-ON gate dielectrics

[0001] The invention is generally related to the field of forming high dielectric constant (high-k) films in semiconductor devices and more specifically to forming metal-oxynitride gate dielectrics by chemical vapor deposition or atomic layer deposition.

[0002] As semiconductor devices have scaled to smaller and smaller dimensions, the gate dielectric thickness has continued to shrink. Although further scaling of devices is still possible, scaling of the gate dielectric thickness has almost reached its practical limit with the conventional gate dielectric material, silicon dioxide, and silicon oxynitride. Further scaling of silicon dioxide gate dielectric thickness will involve a host of problems: extremely thin layers allow for large leakage currents due to direct tunneling through the oxide. Because such layers are formed literally from a few layers of atoms, exacting process control is required to repeatably produce such layers. Uniformity of coverage is also critical because device parameters may change dramatically based on the presence or absence of even a single monolayer of dielectric material. Finally, such thin layers form poor diffusion barriers to dopants from polycrystalline silicon electrodes.

[0003] Realizing the limitations of silicon dioxide, researchers have searched for alternative dielectric materials which can be formed in a thicker layer than silicon dioxide and yet still produce the same field effect performance. This performance is often expressed as equivalent oxide thickness: although the alternative material layer may be thicker, it has the equivalent effect of a much thinner layer of silicon dioxide (commonly called simply oxide). In some instances, silicon dioxide has been replaced with a SiON. However, even higher-k dielectrics will soon be needed. Some films currently being investigated include deposited oxides or nitrides such as ZrO2, ZrSiO, ZrSiON, HfO2, HfON, HfSiO, HfSiON, AlON, and AlZrO, HfAlO, YSiO, LaSiO, LaAlO, YalO etc.. Manufacturable processes for incorporating these materials into the CMOS flow are needed.

[0004] In the drawings:

[0005] FIG. 1 is a cross-sectional diagram of a HfSiO₂ gate dielectric with an interfacial oxide formed according to the prior art; and

[0006] FIGS. 2-6 are cross-sectional diagrams of a high-K gate dielectric formed according to an embodiment of the invention at various stages of fabrication.

[0007] One particularly desirable class of high-k films is the metal-silicon-oxides (MSiO₂), where the metal is Hf, Zr, La, Y, etc. Unfortunately, when a MSiO₂ such as HfSiO₂ 14 is deposited by CVD an interfacial oxide (silicon dioxide) 12 forms at the interface between the substrate 10 and the HfSiO₂, as shown in FIG. 1. The Si/O rich interface prevents scaling below 1.5 nm.

[0008] One possible solution is nitridation of the Si substrate surface. Nitridation of the surface is very effective in minimizing the oxidation of the Si substrate during the initial stages of deposition. However, nitridation of the Si substrate surface gives rise to a high interfacial trap density and low minority carrier mobility.

[0009] The current invention provides a method for forming a high-k dielectric without a SiO₂ interfacial layer. Embodiments of the invention deposit M-ON or M-N by CVD directly on the Si substrate surface. Post deposition anneals are then used to adjust the nitrogen concentration and to anneal out defects.

[0010] A first embodiment of the invention will now be described in conjunction with a method for forming a MOSFET transistor. Referring to FIG. 2, a semiconductor body 100 is processed through the formation of isolation structures 102 and any desired channel or threshold adjust implants. Semiconductor body 102 typically comprises a silicon substrate with or without additional epitaxial layers formed thereon as is known in the art.

[0011] The surface 104 of semiconductor body 100 is preferably a clean, oxide free surface. In addition, the surface 104 may be hydrogen terminated. Methods for providing such a surface are known in the art. U.S. Pat. No. 6,291,867, issued Sep. 18, 2001 assigned to Texas Instruments Incorporated and incorporated herein by reference describes several methods for providing such a surface.

[0012] A M-ON gate dielectric 106 is deposited by CVD on the surface of semiconductor body 102, as shown in FIG. 3. M-ON gate dielectric 106 may, for example, comprise HfON, ZrON, LaON, YON, GdON, EuON, or PrON. Including nitrogen in the CVD deposition prevents or at least minimizes the formation of an interfacial oxide. The deposition process may be a thermal CVD process at a temperature in the range of 200-900 C. and a pressure in the range of 0.1 Torr to 760 Torr with any of the following precursor gases:

[0013] Where MHf, Zr, La, Y, etc,

[0014] M(i-OPr)₂(thd)₂ is bis(isopropoxy)bis(tetramethylheptanedionato) metal, and

[0015] RG is a reactant gas or combination of reactant gases comprising NH₃, N₂O, NO or other nitriding gases in any relative ratio (e.g., 50% NH₃, 50% N₂O, and 0% NO).

[0016] Alternatively, the M-ON can be formed by using plasma enhanced CVD techniques to break down the metalorganic species and decrease the carbon content. There are many embodiments that one can generate using the plasma enhanced techniques.

[0017] Referring to FIG. 3, M-ON gate dielectric 106 may be subjected to an oxidizing anneal. The purpose of the anneal is to adjust the nitrogen concentration and to anneal out defects. An oxidizing anneal increases the oxygen content and decreases the nitrogen content. In the preferred embodiment, a two-step anneal, such as that described in co-pending U.S. patent application Ser. No. ______ (TI-33776) filed ______, assigned to Texas Instruments Incorporated and incorporated herein by reference. The two-step anneal comprises a first high temperature anneal (e.g., 700-1100 C.) in a non-oxidizing ambient (e.g., N₂) followed by a lower temperature anneal (e.g., <a maximum of 1100 C.) in an oxidizing ambient (e.g., O₂, N₂O, NO, ozone, UV O₂, H₂O₂).

[0018] A M-ON formed by the above CVD process has several advantages. First, the interfacial oxide thickness is reduced versus a MSiO₂ deposition. In the example of FIG. 1, 9 of interfacial oxide formed at the interface when a 36 HfSiO₂ was formed. Incorporating nitrogen in the CVD process according to the invention decreases this interfacial oxide. Second, the addition of nitrogen further increases the dielectric constant. Finally, dopant penetration is decreased because of the presence of nitrogen and thermal stability is increased.

[0019] After the anneal, a gate electrode material 110 is deposited over the high-k gate dielectric 106, as shown in FIG. 4. Processing then continues by patterning and etching to form the gate electrode, forming the source/drain junction regions, forming interconnects and packaging the device.

[0020] A second embodiment of the invention will now be described in conjunction with a method for forming a MOSFET transistor. As in the first embodiment, a semiconductor body 100 is processed through the formation of isolation structures 102 and any desired channel or threshold adjust implants. Semiconductor body 102 typically comprises a silicon substrate with or without additional epitaxial layers formed thereon as is known in the art.

[0021] The surface 104 of semiconductor body 100 is preferably a clean, oxide free surface. In addition, the surface 104 may be hydrogen terminated. Methods for providing such a surface are known in the art. U.S. Pat. No. 6,291,867, issued Sep. 18, 2001 assigned to Texas Instruments Incorporated and incorporated herein by reference describes several methods for providing such a surface.

[0022] A M-N gate dielectric 108 is deposited by CVD on the surface of semiconductor body 102, as shown in FIG. 5. MN gate dielectric 108 may, for example, comprise HfN, ZrN, LaN, YN, GdN, EuN, or PrN. Including nitrogen in the CVD deposition prevents or at least minimizes the formation of an interfacial oxide. The MN film 108 can be deposited using a number of precursors such as amido precursors Tetrakis(dimethylamido)hafniumor other metal, and Tetrakis(diethylamido)hafniumor other metal, beta diketontates, tertiary butoxide metal precursors, etc.

[0023] Alternatively, the M-N can be formed by using plasma enhanced CVD techniques to break down the metalorganic species and decrease the carbon content. There are many embodiments that one can generate using the plasma enhanced techniques.

[0024] Referring to FIG. 6, M-N gate dielectric 108 is subjected to an oxidizing anneal to form M-ON 106. The purpose of the anneal is to adjust the nitrogen concentration, to anneal out defects, and incorporate oxygen. As described above, a two-step anneal sequence may be used.

[0025] After the anneal, a gate electrode material 110 is deposited over the high-k gate dielectric 106, as shown in FIG. 4. Processing then continues by patterning and etching to form the gate electrode, forming the source/drain junction regions, forming interconnects and packaging the device.

[0026] While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.