Process of CVD of Hf and Zr containing oxynitride films

[00002] The semiconductor fabrication industry requires materials and deposition technology adequate to deposit metals, metal mixtures and metal compound mixtures in thin layers, plugs, vias, and patterns on semiconductor and insulating or dielectric substrates to make appropriate electrical devices for integrated circuits, memory devices and flat panel display devices.

[00003] Various techniques are known for depositing metals, metal compounds and their mixtures on appropriate electronic materials substrates, including; physical methods sputtering, molecular beam epitaxy, evaporation and laser ablation, alloying, and chemical vapor deposition (plasma, photo or laser enhanced).

[00004] Chemical vapor deposition (CVD) has gained favor in recent years due to its properties of providing uniform and conformal deposition and its ability to deposit an array of materials under highly controllable conditions. Typically, chemical vapor deposition can provide high deposition rates of high purity materials in a controlled fashion.

[00005] Zirconium and hafnium oxynitride gate dielectrics and zirconium and hafnium silicon oxynitride gate dielectrics have been generated by multiple processes, e.g., sputter deposition, plasma deposition, and electron-beam. These gates afford higher dielectric constants than conventional thermal silicon oxide or silicon dielectric layers and they may be thicker.

[00006] Representative articles in the prior art illustrating the formation of zirconium and hafnium metal films, zirconium and hafnium oxynitride and zirconium and hafnium-silicon oxynitride dielectrics are as follows:

[00007] U.S. Pat. No. 6,503,561 discloses a thermal CVD process for the deposition of multiple metal layers on a substrate from a solventless mixture of two or more metal ligand complex precursors, e.g., zirconium, hafnium, aluminum, germanium, etc. where the ligand is selected from the alkyls, imides, amides, halides, nitrates, fluorine, by direct liquid injection to a flash vaporization zone and the solventless mixture is mixed with oxygen prior to deposition of the multiple metal compound layer.

[00008] U.S. Pat. No. 6,291,867 discloses the formation of hafnium and zirconium silicon-oxynitride gate dielectrics by plasma deposition. One process includes the plasma deposition of a zirconium silicide on a substrate, annealing in an atmosphere including oxygen and nitrogen, e.g., NO. In another method, the silicon silicide layer is annealed in a non-oxidizing atmosphere including NH₃ or nitrogen and then annealed in an oxidizing atmosphere. A CVD process is disclosed for forming the silicide layers.

[00009] The article, Thermally Stable CVD HfOxNy Advanced Gate Dielectrics With Poly-Si Gate Electrode, 2002 IEEE 0-7803-7463-X/02/$17.00 (C) discloses the formation of HfOxNy layers wherein a tetrakisdiethylamino hafnium precursor with N₂ carrier gas and ammonia is deposited by rapid thermal CVD followed by post deposition annealing at 800 to 900° C. In the process, the HfOxNy is grown at a temperature of from 700 to 800° C.

[00010] In a comparison example, HfO₂ was deposited at 500° C. using O₂ and the same precursor followed by post deposition annealing.

[00011] This invention relates to an improvement in a process for forming Zr and Hf oxynitride films (ZrOxNy and HfOxNy) and Zr and Hf silicon oxynitride films (Zr(Si)zOxNy and Hf(Si)zOxNy) suitable for use in electronic applications such as dielectric gates. The variable (x), the variable (y) and the variable z are positive numbers greater than 0. The improvement in the process comprises:

• • [00012] (a) forming a reaction mixture in a chemical vapor deposition chamber by introducing a Zr or Hf containing precursor, an oxygen source and a nitrogen source to said chemical vapor deposition chamber without mixing of the Zr or Hf containing precursor with the oxygen source and the nitrogen source prior to introduction to the chemical vapor deposition chamber; and,
  • [00013] (b) contacting a substrate with the reaction mixture at elevated temperature, e.g., a temperature between 300 and 700° C. in the chamber whereby a Zr and Hf oxynitride film is deposited.

[00014] Several advantages can be achieved by the process described, they include:

• • [00015] an ability to generate quality Zr/Hf oxynitride films and Zr/Hf—Si-oxynitride films;
  • [00016] an ability to incorporate significant nitrogen content into the oxynitride films;
  • [00017] an ability to use a chemical vapor deposition process to effect deposition,
  • [00018] an ability to use a low temperature process and maintain a low wafer (substrate) temperature when depositing Zr/Hf oxynitride films and Zr/Hf—Si-oxynitride films; and,
  • [00019] an ability to produce quality films in a single process step.

[00021] This invention relates to an improvement in processes for depositing Zr/Hf oxynitride films and Zr/Hf Si-oxynitride films on a substrate such as a silicon wafer for use in semiconductor devices. In the process for depositing Zr/Hf oxynitride films, a reaction mixture is formed in the chemical vapor deposition chamber comprised of a zirconium or hafnium precursor, a nitrogen source and an oxygen source and, in preparing Zr/Hf Si-oxynitride films, a silicon precursor is added to the reaction mixture.

[00022] A wide variety of zirconium and hafnium precursors containing at least one ligand can be used in implementing the process. These include zirconium and hafnium chlorides, zirconium and hafnium amides. Other ligands for zirconium and hafnium precursors include the C_1-4 Alkyls and alkoxides; siloxides, halides, hydrides, imides, azides, nitrates, cyclopentadienyls, and carbonyls. Preferably, the precursor is liquid at ambient conditions.

[00023] Specific halide examples include zirconium and hafnium tetrachloride, and specific amides include those selected from the group consisting of dimethyl amido Zr(N(CH₃)₂)₄, or Hf(N(CH₃)₂)₄, diethyl amido Zr(N(CH₂CH₃)₂)₄ or Hf(N(CH₂CH₃)₂)₄, ethylmethyl amido Zr[N(CH₂CH₃)(CH₃)]₄, or Hf[N(CH₂CH₃)(CH₃)]₄, or, butyl amido, dipropyl amido, methylpropyl amido, ethylpropyl amido. Specific alkoxides are selected from the group methoxy, ethoxy, propoxy, and butoxy Zr(OC₄H₉)₄ or Hf(OC₄H₉)₄.

[00024] A wide variety of Si precursors can be used when Zr—Si and Hf—Si oxynitride films are desired. Preferably, the ligand of the Si precursor is the same as or similar to that employed for the zirconium and hafnium precursor to produce Zr/Hf Si oxynitride films. One type of silicon amide is of the form (H)_xSi(NR¹R²)_4-x where R¹ and R² are C_1-8 alkyls and x is the integer 0, 1, 2 or 3. A specific form of silicon amide is selected from the group consisting of Si[N(CH₂CH₃)₂]₄, Si[N(CH₂CH₃)(CH₃)]₄, Si[N(CH₃)₂]₄, HSi[N(CH₂CH₃)₂]₃, HSi[N(CH₂CH₃)(CH₃)₂]₃, HSi[N(CH₃)₂]₃ or H₂Si[NH(C₄H₉)]₂. The level of silicon precursor employed in forming the Zr—Si and Hf—Si oxynitride films is at the discretion of the film designer, i.e., z is positive when Zr—Si and Hf—Si oxynitride films are produced.

[00025] In the CVD process described herein, the preferred ligand form is the amide. It affords the ability to effect deposition of zirconium and hafnium oxynitride films and zirconium or hafnium silicon oxynitride films on a substrate such as a silicon wafer at low substrate temperatures, e.g., 400 to 500° C., typically at or below 10 Torr.

[00026] Conventional oxygen and nitrogen sources may be used in the formation of the Zr/Hf oxynitride films and Zr/Hf—Si-oxynitride films. Oxygen sources include oxygen, water, NO₂, NO, N₂O, ozone and air while nitrogen sources include the amide, ammonia, NO, air, N₂O, NO₂, N₂H₂ and so forth. For ease of operation and control, oxygen and ammonia are preferred as the oxygen and nitrogen sources respectively. The nitrogen/oxygen source, NO, typically requires higher processing temperatures.

[00027] A key to the successful deposition of quality Zr/Hf oxynitride films and Zr/Hf—Si-oxynitride films on a substrate such as a silicon wafer by chemical vapor deposition is the delivery of the precursor separately to the chemical vapor deposition reaction chamber from the oxygen source and nitrogen source, i.e., without prior mixing. The use of separate delivery lines enables one to eliminate mixing of the precursors with the protic nitrogen sources and with the the oxygen sources prior to entering the reaction chamber. It has been found that prior mixing of the precursor with either of the oxygen or nitrogen sources, although common in CVD processes, leads to reaction prior to reaching the chamber. When this happens, the deposition is ineffective and difficult to control.

[00028] One advantage achieved by the practice herein is that it is possible to consistently achieve high levels of nitrogen in the oxynitride film. On an atomic basis, nitrogen levels, i.e., the value (y) in the formula ZrOxNy or HfOxNy is from a low of 1% to generally 5% and above. Typically, y can range from 10 to 30%. The value x in the films range from 40 to 50, although other values can be generated by control of the oxygen level in the reaction mixture.

[00029] The following examples are intended to illustrate various embodiments of the invention.

[00030] A liquid precursor mixture comprised of a 1:2 weight ratio of Hf[N(CH₂CH₃)₂)₄ and Si[N(CH₃)₂]₄ respectively was transported via liquid delivery to a heated vaporizer and delivered to a CVD reaction chamber using a 200 sccm flow of He sweep gas through an injector ring located above the substrate which can be raised or lowered. An oxidant mix comprised of up to 15 sccm O₂, up to 15 sccm of NH₃ and up to 300 sccm He dilute gas was delivered separately to the chamber, and the entry point of the oxidant mixture was separated from the precursor injector ring by a diffusion plate which could be raised or lowered. The precursor and oxidants were reacted at a heated substrate (300-700° C.) to produce films containing Hf, Si, O, and N as determined by RBS. The chamber pressure was held at 1 Torr using a pressure control valve. Using flows of 5 to 10 sccm O₂ and 1.85 sccm NH₃ and 0.1 mL/min precursor, the film compositions as represented in the graph of the drawing were realized at the indicated estimated wafer temperatures, i.e., 410, 430 and 450° C.

[00031] The results in the graph in the drawing show films having nitrogen levels of greater than 10 atomic % up to about 28 atomic % nitrogen. The graph also shows that it is possible to maintain a low wafer temperature, e.g., from 410 to 450° C. in the CVD chamber.

[00032] A liquid precursor mixture comprised of a 5:7 weight ratio of Hf[N(CH₂CH₃)₂]₄ and Si[N(CH₃)₂]₄ respectively was transported via liquid delivery to a heated vaporizer and delivered to a CVD reaction chamber using a 200 sccm flow of He sweep gas through an injector ring located above the substrate which can be raised or lowered. An oxidant mix comprised of up to 30 sccm O₂, up to 5 sccm of NH₃ and up to 200 sccm He dilute gas was delivered separately to the chamber, and the entry point of the oxidant mixture was separated from the precursor injector ring by a diffusion plate which could be raised or lowered. The precursor and oxidants were reacted at a heated substrate (300-7000° C.) to produce films containing Hf, Si, O, and N as determined by RBS. The chamber pressure was held at 1 to 1.5 Torr using a pressure control valve. Using flows of 15 to 30 sccm O₂, 1.85 to 5 sccm NH₃ and 0.1 to 0.2 mL/min precursor at substrate temperatures estimated to be between 400 and 500° C. reasonable deposition rates and film quality were obtained.

[00033] The procedure of Example 1 is followed except that Hf[N(CH₂CH₃)₂]₄ was transported via liquid delivery to a heated vaporizer and delivered to a CVD reaction chamber using a 200 sccm flow of He sweep gas through an injector ring located above the substrate which can be raised or lowered. Deposition occurs and a hafnium oxynitride film is produced.

[00034] The procedure of Example 1 is followed except in accordance with the procedure of a typical CVD process wherein the precursor stream and oxidant stream containing ammonia is delivered together through a showerhead.

[00035] When this configuration is tried typically there is either no deposition or there is either no or insignificant nitrogen incorporation in the film. Although not intending to be bound one can speculate that this result is due to a difficulty in reacting the nitrogen source.

[00036] The procedure of Example 3 is repeated except that a specialized showerhead is used in which there is separation of the ammonia and the precursor, i.e., the precursor and ammonia containing streams are delivered through alternating holes in the showerhead. Film deposition occurs as in Examples 1-3.

[00037] The procedure of Example 1 is followed except the hafnium precursor is hafnium chloride. Although these precursors are acceptable, their use is not without problems. These precursors are solids under conventional conditions and therefore present difficulties in delivery to the chemical vapor deposition chamber. In addition, use of these precursors with ammonia can result in the formation of ammonium chloride particles in the chamber which are detrimental to integrated circuit production.