Silicide alloy film for semiconductor device electrode, and production method for silicide alloy film

Abstract

The present invention relates to a silicide alloy film that is formed on a substrate containing Si, the silicide alloy film including a metal M1 having a work function of 4.6 eV or more and 5.7 eV or less, a metal M2 having a work function of 2.5 eV or less and 4.0 eV or more, and Si, the silicide alloy film having a work function of 4.3 eV or more and 4.9 eV or less. Here, the metal M1 is preferably Pt, Pd, Mo, Ir, W or Ru, and the metal M2 is preferably Hf, La, Er, Ho, Er, Eu, Pr or Sm. The silicide alloy film according to the present invention is a thin-film which has excellent heat-resistance and favorable electrical property.

Claims

1. A silicide alloy film that is formed on a substrate containing Si: comprising, a metal M1 having a work function of 4.6 eV or more and 5.7 eV or less, a metal M2 having a work function of 4.0 eV or less, and Si having a work function of 4.3 eV or more and 4.9 eV or less; and in a relationship of the peak intensity (X) of a diffraction peak of a mixed crystal (M1.sub.xM2.sub.ySi) including the metal M1, the metal M2 and Si, the peak intensity (Y) of a diffraction peak of a silicide (M1.sub.aSi) of the metal M1 and the peak intensity (Z) of a diffraction peak of a silicide (M2.sub.bSi) of the metal M2, which are observed by X-ray diffraction analysis, the ratio ((Y+Z)/X) of the sum of Y and Z to X is 0.1 or less, wherein M1 is Pt and M2 is Hf.

2. The silicide alloy film according to claim 1, wherein the content of Si is 33 at % or more and 50 at % or less.

3. The silicide alloy film according to claim 1, wherein the total concentration of C and O as impurities is 5% by mass or less.

4. The silicide alloy film according to claim 1, wherein the root mean surface roughness (RMS) is 5 nm or less.

5. A method for producing the silicide alloy film according to claim 1, comprising forming on a Si substrate a thin-film including the metal M1 and the metal M2, and then heat-treating the Si substrate to silicify the metal M1 and the metal M2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a process for producing a device in a first embodiment.

(2) FIG. 2 shows a J-V characteristic of the device (PtHf silicide alloy film) produced in the first embodiment.

(3) FIG. 3 shows a J-V characteristic of a device (Pt silicide film) produced in Comparative Example 1.

(4) FIG. 4 shows results of analysis of the PtHf silicide alloy film of the first embodiment by XPS.

(5) FIG. 5 shows results of analysis of the PtHf silicide alloy film of the first embodiment by XRD.

(6) FIG. 6 shows results of measuring sheet resistance of a silicide electrode when a heat treatment temperature for silicidation is changed.

(7) FIG. 7 illustrates a process for forming a CBKR structure.

(8) FIG. 8 shows results of measuring contact resistance of a PtHf silicide alloy film by a CBKR method.

(9) FIG. 9 shows a J-V characteristic of a device (IrYb silicide alloy film) produced in a fourth embodiment.

(10) FIG. 10 shows a J-V characteristic of a device (Ir silicide film) produced in Comparative Example 2.

(11) FIG. 11 shows results of analysis of the IrYb silicide alloy film of the fourth embodiment by XRD.

(12) FIG. 12 shows a J-V characteristic of a device (PdYb silicide alloy film) produced in a fifth embodiment.

(13) FIG. 13 shows a J-V characteristic of a device (Pd silicide film) produced in Comparative Example 3.

(14) FIG. 14 shows results of analysis of the PdYb silicide alloy film of the fifth embodiment by XRD.

(15) FIG. 15 shows results of analysis of a PdEr silicide alloy film of the sixth embodiment by XRD.

DESCRIPTION OF EMBODIMENT

(16) Hereinafter, an embodiment of the present invention will be described.

First Embodiment

(17) In this embodiment, a PtHf silicide (Pt.sub.xHf.sub.ySi) alloy film having Pt as a metal M1 and Hf as a metal M2 was produced. Here, a PtHf silicide thin-film was formed on a Si substrate to produce a Schottky diode, and the electrical property of the device was evaluated.

(18) FIG. 1 shows a process for producing a device in this embodiment. In this embodiment, the Si substrate (n-Si (100)) is chemically cleaned (FIG. 1(a)), and then wet-oxidized to form a SiO.sub.2 layer, and the layer is etched to perform patterning (FIG. 1(b)). A PtHf alloy thin-film is formed in the layer (FIG. 1(c)).

(19) For formation of the PtHf alloy thin-film, a sintered target including a PtHf alloy was used. The sintered target was obtained by sintering a fine powder of a PtHf alloy. The PtHf alloy powder was produced by arc-melting and alloying high-purity base metals of Pt and Hf to produce a button-shaped ingot, and mechanically crushing the ingot into a powder. The alloy composition ratio here is Pt:Hf=5:2 (at %). The alloy powder was sintered under the condition of 1000 kgf/cm.sup.2, 1500 C. and 1 hour in a HIP apparatus to obtain an alloy target (dimensions: a diameter of 76.2 mm and a thickness of 2.0 mm).

(20) In formation of the PtHf alloy thin-film, first a substrate surface was cleaned by performing preliminary sputtering (power: 100 W, time: 5 minutes). Thereafter, the PtHf alloy was sputtered. As conditions here, the temperature was room temperature, and the power was 40 W, and under the conditions, the alloy thin-film was deposited in a thickness of 20 nm. In this embodiment, Ar and Kr ions were used as gas ions in sputtering (the pressure of each of these gases was 0.7 Pa).

(21) After formation of the PtHf alloy thin-film, silicidation was performed by heat treatment. As conditions for silicidation, three conditions: 450 C., 500 C. and 600 C. were set for the treatment temperature. The treatment atmosphere was a nitrogen gas, and the treatment time was 5 minutes.

(22) After silicidation of PtHf, an unreacted metal was removed by etching, and an Al electrode was formed to obtain a device (FIG. 1(d)). The etching was performed by use of buffered hydrofluoric acid (BHF) and diluted aqua regia (HCl:HNO.sub.3:H.sub.2O=3:2:1, temperature: 40 C.).

Comparative Example 1

(23) As a comparative example to the first embodiment, a Pt thin-film was formed in place of a PtHf thin-film, and silicified to produce a device. Conditions for silicidation, and so on were essentially the same as in the first embodiment (only Ar sputtering was performed).

(24) For the device thus produced, electrical property was evaluated. An evaluation test was conducted by measuring a current density-voltage characteristic (J-V characteristic) by a semiconductor parameter analyzer.

(25) FIG. 2 shows the J-V characteristic of the device (PtHf silicide alloy film) produced in the first embodiment. The result in FIG. 2 shows that in the device produced in this embodiment, the current density linearly increased in application of a voltage in both a forward direction and a reverse direction (positive direction and negative direction). In this embodiment, the substrate is an n-Si substrate, and thus a behavior at a negative potential is important. The device of this embodiment can be said to have exhibited a favorable characteristic. On the other hand, FIG. 3 shows a J-V characteristic in Comparative Example 1. In Comparative Example 1, the current density did not increase in application of a negative potential.

(26) For the PtHf silicide alloy film according to this embodiment, a device with a favorable behavior was obtained at any of the treatment temperatures regarding the temperature for silicidation. Among devices subjected to an Ar sputtering treatment, a device treated at 450 C. had a high current density. Among devices subjected to a Kr sputtering treatment, a device treated at 450 C. had a high current density.

(27) A Schottky barrier height of each silicide alloy film was calculated from the measured J-V characteristic. These Schottky barrier heights are collectively shown in Table 1 below. Table 1 shows that the Schottky barrier height of the PtHf silicide in this embodiment was 0.47 to 0.51 eV, whereas the Schottky barrier height of the Pt silicide in the comparative example was 0.85 eV (Ar sputtering). The difference between the Schottky barrier heights of the silicides is associated with the work function of a metal to be silicified, and it can be said that the silicide in the comparative example had a high Schottky barrier height because of the high work function of Pt.

(28) TABLE-US-00001 TABLE 1 Schottky barrier height A Kr 450 C. 0.48 eV 0.47 eV 500 C. 0.48 eV 0.48 eV 600 C. 0.51 eV 0.51 eV

(29) Here, composition analysis was performed by use of XPS for the PtHf silicide alloy film (heat treatment temperature: 450 C.). The measurement results are shown in FIG. 4. For the analysis result, a composition ratio was calculated from a peak area attributed to each element, and the result showed that the composition ratio was Pt:Hf:Si=30:20:50 (atom ratio). The content of impurities was confirmed to be 2.05 wt % for oxygen and 0.14 wt % or less (below detection limit) for carbon. The difference between the ratio of Pt and Hf in the silicide film and the composition ratio (Pt:Hf=5:2) in the PtHf alloy as a target is ascribable to composition deviation of formed silicides due to a difference between the vapor pressures of Pt and Hf and a difference between the diffusion speeds of Pt and Hf to the Si substrate.

(30) The results of X-ray diffraction analysis (XRD) of the PtHf silicide alloy film (heat treatment temperature: 450 C.) of this embodiment are shown in FIG. 5. The silicide alloy film clearly presents a peak of a mixed crystal (Pt.sub.xHf.sub.ySi), but presents little peaks of individual silicides (PtSi and HfSi) of the metals of Pt and Hf. The peak intensity ratio ((Y+Z)/X) of the silicides was about 0.05.

(31) Further, for the PtHf silicide alloy film (heat treatment temperature: 450 C.), a root mean square (RMS) roughness was measured (scan width: 3 m) by an AFM (atomic force microscope), the result showed that the surface of a film deposited by Ar sputtering had a RMS of 2.16 nm. The surface of a film deposited by Kr sputtering was 0.45 nm. Both the films showed a favorable surface form. The Pt silicide film of the comparative example had a RMS of 6.40 nm.

Second Embodiment

(32) For conditions for silicidation of the PtHf alloy thin-film, a test for evaluating heat resistance in application of a high-temperature treatment was conducted. A chemically cleaned n-Si (111) substrate was provided, and a PtHf alloy thin-film was formed under the same conditions as in the first embodiment (preliminary sputtering done, thickness: 20 nm). The alloy thin-film was heat-treated at respective temperatures of 400 C., 500 C. and 600 C., and etched with a diluted aqua regia to prepare samples. For these samples, sheet resistance was measured by a four-probe measurement method.

(33) The measurement results are shown in FIG. 6. The PtHf alloy thin-film has high sheet resistance just after being deposited, but the sheet resistance is decreased by silicidation. The sheet resistance of the silicide remains low even when the silicide is treated at a high temperature of 600 C. Thus, it was confirmed that PtHf had favorable thermal stability, and the resistance of PtHf did not increase even at a high temperature.

Third Embodiment

(34) Here, for the PtHf silicide alloy film, contact resistance (interface contact resistance) in a four-terminal Kelvin test structure was evaluated by a cross-bridge Kelvin resistance method (hereinafter, referred to as a CBKR method) for reproduction and evaluation of a state closer to that in semiconductor device packaging. FIG. 7 schematically illustrates a process for forming a CBKR structure.

(35) FIG. 8 shows results of measuring contact resistance with a contact area for the PtHf silicide alloy film by a CBKR method. From the evaluation results, it is understood that the PtHf silicide alloy film of 2 m square attains a low contact resistance of 810.sup.8 cm. It was confirmed that the PtHf silicide alloy film was expected to be applied to an actual device.

Fourth Embodiment

(36) In this embodiment, an IrYb silicide (Ir.sub.xYb.sub.ySi) alloy film having Ir (work function: 5.27 eV) as a metal M1 and Yb (work function: 2.6 eV) as a metal M2 was produced. Specifically, as with the first embodiment, a Schottky diode including an electrode composed of an IrYb silicide thin-film on a Si substrate was produced, and the electrical property of the device was evaluated.

(37) The process for producing the device is essentially the same as in the first embodiment (FIG. 1). The Si substrate (n-Si (100)) was chemically cleaned, and a SiO.sub.2 layer was then formed, and etched to perform patterning. A Yb thin-film was deposited in the layer, an Ir thin-film was then deposited, and a heat treatment was performed to form an IrYb silicide alloy film.

(38) For formation of the Yb thin-film and the Ir thin-film, targets including metals of Ir and Yb, respectively, were used. For production of the thin-film, a cast ingot of Yb was cold-rolled, annealed and mechanically processed to be finally finished, so that a Yb molten target (dimensions: a diameter of 76.1 mm and a thickness of 2 mm) was provided. Further, an Ir cast ingot obtained by plasma melting was hot-forged, hot-rolled, laser-cut, and finally finished by trimming and polishing to provide an Ir molten target.

(39) In formation of the Yb thin-film and the Ir thin-film, first a substrate surface was cleaned by performing preliminary sputtering (power: 100 W, time: 5 minutes). The Yb thin-film and the Ir thin-film were deposited at a Kr gas pressure of 0.65 Pa by RF magnetron sputtering. As conditions for deposition of the Yb thin-film, the temperature was room temperature, and the power was 180 W, and under the conditions, Yb was deposited in a thickness of 6 nm. As conditions for deposition of the Ir thin-film subsequent to deposition of Yb, the temperature was room temperature, and the power was 80 W, and under the conditions, the Ir thin-film was deposited in a thickness of 14 nm.

(40) In this embodiment, after formation of the Yb thin-film and the Ir thin-film, a cap layer including a HfN thin-film was formed on the thin-film, and a heat treatment was then performed to form a silicide alloy film. For formation of the cap layer, a Hf target was used, and the cap layer (thickness: 10 nm) was deposited by reactive sputtering with Kr/N.sub.2 as a deposition atmosphere (RF magnetron sputtering, room temperature, power: 200 W). As conditions for silicidation, the treatment temperature was 500 C., the treatment atmosphere was a nitrogen gas atmosphere, and the treatment time was 1 minute. After the silicidation, the cap layer and an unreacted metal were removed by etching, and an Al electrode was formed to obtain a device.

Comparative Example 2

(41) As a comparative example to the fourth embodiment, only an Ir thin-film was formed, and silicified to produce a device. Conditions for deposition of the Ir thin-film, conditions for silicidation, and so on were the same as in the fourth embodiment.

(42) FIG. 9 shows a J-V characteristic of a device (IrYb silicide alloy film) produced in a fourth embodiment. The current density linearly increased in application of a voltage in both a forward direction and a reverse direction (positive direction and negative direction). On the other hand, FIG. 10 shows a J-V characteristic of the device in Comparative Example 2. The current density did not increase in application of a negative potential.

(43) The measured J-V characteristic showed that the silicide alloy film (IrYb silicide alloy film) of the fourth embodiment had a Schottky barrier height of 0.47 eV. On the other hand, the silicide alloy film (Ir silicide alloy film) of Comparative Example 2 had a Schottky barrier height of 0.89 eV. It was confirmed that the Ir silicide film of Comparative Example 2 had a high Schottky barrier height because of the high work function of Ir, and the Schottky barrier height decreased in the fourth embodiment where Ir was alloyed with Yb.

(44) The sheet resistance of the silicide film of each of the fourth embodiment and Comparative Example 2 was measured by a four-probe measurement method, and the result showed that the sheet resistance in the fourth embodiment was 63.0 /sq, and the sheet resistance in Comparative Example 2 was 63.6 /sq. Therefore, it was confirmed that the sheet resistance in the fourth embodiment was slightly lower than that in Comparative Example 2.

(45) Next, FIG. 11 shows results of XRD of the IrYb silicide alloy film of the fourth embodiment. The silicide alloy film presents a peak of an alloy of Yb and Ir in addition to a peak of Ir.sub.xYb.sub.ySi (y=z and x=1z) as a mixed crystal. Further, a peak of a silicide (Yb.sub.5Si.sub.3) of Yb slightly appears. In this embodiment, the peak intensity ratio ((Y+Z)/X) of the silicides was about 0.05.

(46) The Ir.sub.xYb.sub.ySi mixed crystal observed in the XRD was a mixed crystal (Ir.sub.1-zYb.sub.zSi) formed with Yb replacing some Ir sites of a silicide (IrSi) of Ir. Here, when assuming that the mixed crystal has the same structure as that of an IrSi orthorhombic crystal, the composition ratio of the alloy film was supposed to be Ir:Yb:Si=43.8:6.2:50 (atom ratio).

Fifth Embodiment

(47) In this embodiment, a device including a PdYb silicide (Pd.sub.xYb.sub.ySi) alloy film having Pd (work function: 4.9 eV) as a metal M1 and Yb (work function: 2.6 eV) as a metal M2 was produced. A Si substrate provided in the same manner as in the fourth embodiment, a Yb thin-film was deposited, a Pd thin-film was then deposited, and a heat treatment was performed to form a PdYb silicide alloy film.

(48) For formation of the Yb thin-film and the Pd thin-film, targets including metals of Pd and Yb, respectively, were used. As the Yb target, a Yb target identical to that in the fourth embodiment was used. Further, a Pd cast ingot obtained by air melting was hot-forged, hot-rolled, laser-cut, and finally finished by trimming and polishing to provide a Pd molten target. The Yb thin-film and the Pd thin-film were deposited at a Kr gas pressure of 0.65 Pa by RF magnetron sputtering. Conditions for deposition of the Yb thin-film include room temperature and power of 180 W, and under the conditions, Yb was deposited in a thickness of 6 nm. Conditions for deposition of the Pd thin-film subsequent to deposition of Yb include room temperature and power of 80 W, and under the conditions, the Pd thin-film was deposited in a thickness of 14 nm.

(49) As with the fourth embodiment, silicidation was performed by heat treatment after formation of the Yb thin-film and the Pd thin-film, and formation of a cap layer. As conditions for silicidation, the treatment temperature was 500 C., the atmosphere was a nitrogen gas atmosphere, and the treatment time was 1 minute. After the silicidation, the cap layer and an unreacted metal were removed by etching, and an Al electrode was formed to obtain a device.

Comparative Example 3

(50) As a comparative example to the fifth embodiment, only a Pd thin-film was formed, and silicified to produce a device. Conditions for deposition of the Pd thin-film, conditions for silicidation, and so on were the same as in the fifth embodiment.

(51) FIG. 12 shows a J-V characteristic of the device (PdYb silicide alloy film) produced in a fifth embodiment. FIG. 13 shows a J-V characteristic of the device of Comparative Example 3. In the device of this embodiment, the current density linearly increased in application of a voltage in both a forward direction and a reverse direction (positive direction and negative direction). On the other hand, in the device of Comparative Example 3, the current density did not increase in application of a negative potential.

(52) The measured J-V characteristic showed that the silicide alloy film (PdYb silicide alloy film) of the fifth embodiment had a Schottky barrier height of 0.4 eV. On the other hand, the silicide alloy film (Pd silicide alloy film) of Comparative Example 3 had a Schottky barrier height of 0.73 eV. It was confirmed that the Pd silicide film of Comparative Example 3 had a high Schottky barrier height because of the high work function of Pd, and the Schottky barrier height decreased in the fifth embodiment where Pd was alloyed with Yb.

(53) The sheet resistance of the silicide film of each of the fifth embodiment and Comparative Example 3 was measured by a four-probe measurement method, and the result showed that the sheet resistance in the fifth embodiment was 20.9 /sq, and the sheet resistance in Comparative Example 3 was 27 /sq. Therefore, it was confirmed that the sheet resistance in the fifth embodiment was lower than that in Comparative Example 3.

(54) Next, FIG. 14 shows results of XRD of the PdYb silicide alloy film of the fifth embodiment. The silicide alloy film presented a peak of Pd.sub.xYb.sub.ySi (y=z and x=2z) as a mixed crystal. A peak of a silicide (Pd.sub.2Si) of Pd slightly appears. In this embodiment, the peak intensity ratio ((Y+Z)/X) of the silicides was about 0.05.

(55) The Pd.sub.xYb.sub.ySi mixed crystal observed in the XRD was a mixed crystal (Pd.sub.2-zYb.sub.zSi) formed with Yb replacing some Pd sites of a silicide (Pd.sub.2Si) of Pd. Here, when assuming that the mixed crystal has the same structure as that of a Pd.sub.2Si hexagonal crystal, the composition ratio of the alloy film was supposed to be Pd:Yb:Si=57.8:8.9:33.3 (atom ratio).

Sixth Embodiment

(56) In this embodiment, a PdEr silicide (Pd.sub.xEr.sub.ySi) alloy film having Pd (work function: 4.9 eV) as a metal M1 and Er (work function: 3.2 eV) as a metal M2 was produced. Here, a sintered target including a PdEr alloy was used to deposit a PdEr alloy thin-film, a heat treatment for silicidation was then performed, and whether silicidation was possible or not was checked.

(57) The sintered target including a PdEr alloy was obtained by sintering a fine powder of a PdEr alloy. The PdEr alloy powder was produced by arc-melting and alloying high-purity base metals of Pd and Er to produce a button-shaped ingot, and mechanically crushing the ingot into a powder. The alloy composition ratio here is Pd:Er=3:2 (at %). The alloy powder was sintered under the condition of 255 kgf/cm.sup.2, 1140 C. and 1 hour in a HIP apparatus to obtain an alloy target (dimensions: a diameter of 76.0 mm and a thickness of 3.0 mm).

(58) In formation of the PdEr alloy thin-film, first a surface of an n-Si (100) substrate was cleaned by performing preliminary sputtering (power: 200 W, time: 30 minutes). Thereafter, the PdEr alloy film was sputtered. Conditions include room temperature, power of 80 W, pressure of 0.65 Pa, and a Kr gas as a sputtering gas. Under the above conditions, the PdEr alloy thin-film was deposited in a thickness of 20 nm.

(59) After formation of the PdEr alloy thin-film, the HfN cap layer was formed, and a heat treatment was performed to silicify the PdEr alloy thin-film. For formation of the cap layer, a Hf target was used, and the cap layer (thickness: 20 nm) was deposited by reactive sputtering with Kr/N.sub.2 as a deposition atmosphere (RF magnetron sputtering, room temperature, power: 200 W). The silicidation was performed at a treatment temperature of 550 C. in a nitrogen gas as a treatment atmosphere for a treatment time of 30 minutes. After the silicidation treatment, the cap layer and an unreacted metal were removed by etching.

(60) FIG. 15 shows results of XRD of the PdEr silicide alloy film produced in the above-mentioned process. The silicide alloy film presented an intense peak of Pd.sub.xEr.sub.ySi (y=z and x=2z) as a mixed crystal. The peaks of the Pd silicide and the Er silicide were extremely weak. In this embodiment, the peak intensity ratio ((Y+Z)/X) of the silicides was less than 0.01. The Pd.sub.xEr.sub.ySi mixed crystal observed in the XRD was a mixed crystal (Pd.sub.2-zEr.sub.zSi) formed with Er replacing some Pd sites of a silicide (Pd.sub.2Si) of Pd. Here, when assuming that the mixed crystal has the same structure as that of a Pd.sub.2Si hexagonal crystal, the composition ratio of the alloy film was supposed to be Pd:Er:Si=40:26.7:33.3 (atom ratio).

INDUSTRIAL APPLICABILITY

(61) The silicide alloy film according to the present invention includes a silicide of a metal M1 and a metal M2 having mutually different work functions, and has favorable thermal stability. Moreover, the silicide alloy film has a work function in the vicinity of midgap with respect to a Si substrate. The silicide alloy film according to the present invention is useful as a constituent material of a silicide electrode in various kinds of semiconductor devices such as a MOSFET.