JP2008235358A - Semiconductor device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device that uses a high-k film and has superior leak current characteristic even when high-temperature treatment is applied. <P>SOLUTION: The semiconductor device is provided with a semiconductor substrate; a pair of source-drain areas 6 that formed opposite to each other on the semiconductor substrate; a tunnel insulation film 2 formed on the semiconductor substrate between the source-drain areas; a floating electrode or a charge storage layer 3 formed on the tunnel insulation film; an interlayer insulation film 4 that is formed thereon and is provided with a cubic pyrochlore polycrystal insulation film containing La, Hf and O; and a control electrode 5 formed on the interlayer insulation film. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a semiconductor device in which leakage current of an interlayer insulating film or a gate insulating film is reduced, and a manufacturing method thereof.

  For example, a memory cell of a nonvolatile semiconductor memory device capable of electrical writing and erasing is replaced with a stack gate structure formed of a semiconductor substrate / tunnel insulating film / floating electrode / interlayer insulating film / control electrode, or a floating electrode. The stack gate structure using the charge storage layer. Along with the miniaturization of memory cells, in order to increase the electrical capacitance ratio between the floating electrode and the charge storage layer and the control electrode, the so-called high-k that has a higher dielectric constant than the silicon oxide film as an interlayer insulating film Application of a film has been studied (for example, see Patent Document 1).

In addition, in the gate insulating film of a field effect transistor, with the thinning of the gate insulating film for high performance, the conventional SiO ₂ film cannot suppress the leakage current due to the direct tunnel current, thereby reducing the power consumption. Since this causes an increase, it has been studied to apply a high-k film instead of the SiO ₂ film.

However, when a high-k film is used as an interlayer insulating film or a gate insulating film, a leakage current will occur after a high-temperature heat treatment process for impurity activation included in the manufacturing process of a nonvolatile semiconductor memory device or a field effect transistor. There is a problem that it cannot be sufficiently suppressed.
JP 2003-7861 A

  The present invention has been made in view of the above circumstances, and provides a semiconductor device having an insulating film with good leakage current characteristics even after a high-temperature heat treatment step, and a method for manufacturing the same.

  In order to solve the above problems, a first semiconductor device of the present invention includes a semiconductor substrate, a pair of source / drain regions formed opposite to each other on the semiconductor substrate, and the source / drain regions. A tunnel insulating film formed on the semiconductor substrate; a floating electrode or charge storage layer formed on the tunnel insulating film; and a cube formed on the floating electrode or charge storage layer and including La, Hf, and O An interlayer insulating film having a crystal pyrochlore type polycrystalline insulating film and a control electrode formed on the interlayer insulating film.

  The first method of manufacturing a semiconductor device of the present invention includes a step of forming a tunnel insulating film on a main surface of a semiconductor substrate, a step of forming a floating electrode or a charge storage layer on the tunnel insulating film, A step of forming an amorphous insulating film containing La, Hf, and O on a floating electrode or a charge storage layer; a step of forming a control electrode on the amorphous insulating film; and the substrate sandwiching the control electrode The method includes a step of introducing impurities into the main surface of the substrate and then performing an activation heat treatment, and a heat treatment step performed in an atmosphere containing hydrogen after the activation heat treatment.

  A second semiconductor device of the present invention is formed on the semiconductor substrate, a pair of source / drain regions formed opposite to each other on the semiconductor substrate, and the semiconductor substrate between the source / drain regions. And a gate insulating film having a cubic pyrochlore type polycrystalline insulating film containing La, Hf, and O, and a gate electrode formed on the gate insulating film.

  A second method of manufacturing a semiconductor device according to the present invention includes a step of forming an amorphous insulating film containing La, Hf, and O on a main surface of a semiconductor substrate, and a gate on the amorphous insulating film. A step of forming an electrode, a step of introducing impurities into the main surface of the substrate sandwiching the gate electrode, and then performing an activation heat treatment, and a step of performing a heat treatment in an atmosphere containing hydrogen after the activation heat treatment, It is characterized by comprising.

  ADVANTAGE OF THE INVENTION According to this invention, the semiconductor device which has a favorable leakage current characteristic even if it passes through a high temperature heat treatment process, and its manufacturing method can be provided.

  Prior to the description of the embodiment, the knowledge obtained by the inventors through experiments will be described. An experiment was conducted in which a LaHfO insulating film as an insulating film was deposited on a silicon substrate by laser ablation. FIG. 2 shows the composition of a film obtained by depositing a LaHfO insulating film by about 5 nm at a temperature of 500 ° C. and 800 ° C. on a silicon substrate from which a natural oxide film has been removed by a diluted hydrofluoric acid solution treatment, respectively. The result evaluated by RBS (Rutherford Backscattering Spectroscopy) is shown. It can be seen that the composition ratio of the sample deposited at 800 ° C. is almost stoichiometric (La: Hf: O = 2: 2: 7), and La / (La + Hf) = 50%. On the other hand, the sample deposited at 500 ° C. was La richer than that, and La / (La + Hf) was 59%.

  FIG. 3 shows the leakage current-voltage characteristics after the La / (La + Hf) = 50%, 59% film was heat-treated at 1000 ° C. for 30 seconds in atmospheric pressure nitrogen. Here, the heat treatment step of 1000 ° C. for 30 seconds is a typical condition necessary for electrically activating the ions implanted into the source / drain regions.

As shown in FIG. 3, the characteristics are similar regardless of the film composition ratio, and the leakage current characteristics are extremely poor, showing a leakage current value of 10 A / cm ² at a small applied voltage of 2 V. Met.

  Next, the two types of films shown in FIG. 3 were subjected to heat treatment in a hydrogen atmosphere under the conditions of 10% hydrogen, 90% nitrogen, 450 ° C., and 30 minutes under atmospheric pressure. FIGS. 4 and 5 show the leakage current characteristics of the La / (La + Hf) = 50% and 59% films after the heat treatment in the hydrogen atmosphere together with the data before the heat treatment in the hydrogen atmosphere.

First, as shown in FIG. 4, in the film of La / (La + Hf) = 50%, no change was observed in the behavior of leakage current characteristics before and after the heat treatment in the hydrogen atmosphere, and there was no effect of the heat treatment in the hydrogen atmosphere. Conceivable. A behavior similar to the present result that the heat treatment process in the hydrogen atmosphere has no effect on the leakage current characteristics is also observed in the HfO ₂ film (for example, see 2002 Symposium On VLSI Technology Digest of Technical Papers p22-23). .

  On the other hand, in the film of La / (La + Hf) = 59% in FIG. 5, the behavior of the film of La / (La + Hf) = 50% (FIG. 4) is completely different, and the heat treatment process in a hydrogen atmosphere is performed. After this, it can be seen that the leakage current value can be dramatically reduced than before the same step.

  FIG. 6 shows capacity-voltage (CV) characteristics before and after the heat treatment step in the hydrogen atmosphere of the film shown in FIG. As shown in FIG. 6, the hysteresis that appears as the voltage sweep direction dependency of the capacitance is hardly observed after the heat treatment step in a hydrogen atmosphere, and it can be seen that there are very few electrical traps in the film. Since hysteresis of 100 mV or more is observed before the heat treatment process in the hydrogen atmosphere, the effect of the heat treatment in the hydrogen atmosphere on the film of La / (La + Hf) = 59% is not only the reduction of the leakage current but also the trap in the film It can be seen that this also contributes greatly to the reduction of The fact that the trap can be reduced indicates that the threshold shift can be suppressed, which is important in the operation of the nonvolatile memory device.

Next, FIG. 7 shows an In-Plane XRD (X-ray diffraction) pattern after a 1000 ° C. heat treatment step of a La / (La + Hf) = 59% film deposited at 500 ° C. and a subsequent heat treatment step in a hydrogen atmosphere. . The four straight lines shown in the figure indicate the positions and relative intensities of diffraction lines at each index based on powder X-ray diffraction data of La ₂ Hf ₂ O ₇ having a composition of stoichiometric ratio. (International Center for Diffraction Data PDF # 24-0552).

Before passing through the heat treatment step at 1000 ° C., that is, immediately after deposition at 500 ° C., no diffraction peak was observed in the XRD pattern, indicating that it was amorphous. As a result of the measurement, a pattern indicating a pyrochlore cubic system was observed as in the X-ray powder diffraction data of La ₂ Hf ₂ O ₇ having the composition of the stoichiometric ratio shown by the straight line in the figure. The positions of the respective diffraction lines were observed at higher angles than those of the powder X-ray diffraction data, as shown in FIG. As a result, the calculated lattice constant is a = 5.38 場合 in the case of the stoichiometric ratio, whereas the structure of the insulating film of the present embodiment has a smaller lattice constant, and a = 5.31 Å. It was. That is, as a structural feature of the insulating film of this embodiment, in addition to being richer in La than the stoichiometric ratio, a lattice constant is small.

  Further, in order to evaluate the crystal orientation, the rocking curve of the diffraction peak at 29.12 ° in FIG. 7 was measured. The rocking curve is an incident angle (φ) dependence curve measured by rotating the sample while always making the relationship between the incident angle and the diffraction angle equal, and Bragg condition when oriented Since it has a peak at an angle satisfying the above, the orientation of the crystal can be evaluated. The result of the rocking curve measurement is shown in FIG. In this figure, since the X-ray incident angle dependence was not observed in the intensity of the diffraction peak, the structure of the insulating film of this embodiment is considered to be polycrystalline composed of non-oriented crystal grains. . Such a non-oriented crystal grain is preferable because a leak path is not easily formed and a breakdown voltage is easily improved.

  Next, it will be explained based on experimental results that the heat treatment in a hydrogen atmosphere is more effective in a polycrystalline structure than in an amorphous structure. Regarding a La—Hf—O-based heat treatment process in a hydrogen atmosphere containing La more than Hf in atomic ratio, an insulating film having an atomic ratio La / (La + Hf) = 66% has already been reported (Extended Abstracts of the 2006 International Conference on Solid State Devices and Materials, Yokohama, 2006, pp. 212-213, by Yamamoto).

  On the other hand, according to another document by the same presenter as described above, the larger La / Hf, the higher the crystallization temperature, and when La / (La + Hf) = 50%, it is amorphous at 900 ° C. (See the 53rd Joint Lecture on Applied Physics Lecture Proceedings p853 (Spring 2006)).

  Here, the document of the international conference does not disclose whether the structure is amorphous or crystalline, but it is disclosed that the heat treatment temperature condition before heat treatment in a hydrogen atmosphere is 600 ° C. Therefore, it is considered that the heat treatment in a hydrogen atmosphere in the above international conference document was performed on an amorphous structure. The inventors have found that the effect of heat treatment in a hydrogen atmosphere is greater on a polycrystalline structure than on an amorphous structure as follows.

  FIG. 9 shows the leakage current characteristics of a La / (La + Hf) = 59% film immediately after deposition at 500 ° C., that is, after the amorphous structure is subjected to heat treatment in a hydrogen atmosphere, and after deposition at 500 ° C. The leakage current characteristics after performing a heat treatment in a hydrogen atmosphere after performing a heat treatment step at 30 ° C. for 30 seconds, that is, changing to a non-oriented polycrystalline structure are shown.

  From FIG. 9, it can be seen that the heat treatment effect in the hydrogen atmosphere is greater after the heat treatment step at 1000 ° C. for 30 seconds, and the leakage current can be reduced. This result shows that the heat treatment step in the hydrogen atmosphere works more effectively in the polycrystalline structure.

  Although the results on the silicon substrate were used to explain the above effect, the fact that the substrate is a silicon substrate does not limit the effect of the invention, and the difference in film quality shown above indicates that the substrate is, for example, polycrystalline silicon. Even a film or a SiN film is expressed.

  In the above description, the insulating film deposition using laser ablation has been described. However, this technique does not limit the effect of the invention, and this condition forms a high dielectric constant insulating film as in the above technique. If it is a method, you may use methods, such as sputtering method, MBE method, CVD method, and ALD method.

  In addition, the present invention is not limited to the insulating film used for the nonvolatile memory, but the same effect can be obtained even when applied to a high-k gate insulating film used for a complementary metal oxide semiconductor transistor (CMISFET). You may apply to. Hereinafter, specific embodiments applied to these devices will be described.

(First embodiment)
FIG. 1 is a schematic cross-sectional view of the nonvolatile semiconductor memory device according to the first embodiment. A tunnel insulating film 2 is provided on the main surface of the p-type silicon substrate 1. The tunnel insulating film 2 is composed of, for example, a SiO ₂ film. A floating electrode 3 is provided on the tunnel insulating film 2. The floating gate electrode 3 is made of, for example, a polycrystalline silicon film. An insulating film 4 containing La, Hf, and O according to the present invention is formed on the floating electrode 3. On the insulating film 4, a control electrode 5 made of, for example, a polycrystalline silicon film is provided.

  Here, instead of the floating gate electrode 3 including the polycrystalline silicon film, a so-called SONOS type semiconductor memory device may be configured by using, for example, a SiN film as the charge storage layer 3. Further, on the surface of the silicon substrate, source / drain regions 6 formed by ion implantation of phosphorus (P) are provided on the main surface of the substrate corresponding to the control electrodes.

Next, a method for manufacturing the semiconductor device of this embodiment will be briefly described with reference to the flowchart of FIG. First, the SiO ₂ film 2 is formed as a tunnel insulating film on the surface of the silicon substrate 1 by, for example, thermal oxidation (S1). Next, a polycrystalline silicon film 3 to be a floating electrode is formed by a CVD process (S2), and then a LaHfO film 4 and a polycrystalline silicon film 5 to be a control electrode are formed by sputtering, for example (S3). , S4). At this time, the LaHfO film 4 is deposited in an amorphous state at 500 ° C., for example, and the atomic ratio La / (La + Hf) of the LaHfO film 4 is larger than 50%.

  Next, the tunnel insulating film 2, the floating electrode film 3, the LaHfO film 4, and the control electrode film 5 are processed by a PEP (Photo Engraving Process) process and an RIE (Reactive Ion Etching) process (S5). Next, P is ion-implanted by a known method using the processed structure below the control electrode 5 as a mask (S6), and then a heat treatment for activation is performed at 1000 ° C. for 30 seconds (S7). ), The source / drain region 6 is formed. During this heat treatment, the LaHfO insulating film is polycrystallized. Next, heat treatment is performed in a hydrogen atmosphere under the conditions of 450 ° C., 30 minutes, and H 2 / N 2 ratio of 10%. As a result, a nonvolatile semiconductor memory cell having excellent leakage current characteristics can be obtained (S8).

  Thus, according to the first embodiment, a nonvolatile semiconductor memory device having good leakage current characteristics can be realized even after a high-temperature heat treatment step of about 1000 ° C.

(Second Embodiment)
FIG. 11 is a schematic cross-sectional view of a field effect transistor according to the second embodiment. For example, a gate insulating film 13 containing La, Hf, and O is provided on the main surface of the p-type silicon substrate 11. On the gate insulating film 13, a gate electrode 14 made of, for example, polycrystalline silicon is provided. Further, a source / drain region 16 formed by ion implantation of P, for example, is provided on the surface of the silicon substrate 11 so as to face the gate electrode 15 therebetween. Further, a gate sidewall insulating film 15 of a silicon nitride layer is formed on the sidewalls of the gate electrode 14 and the gate insulating film 13.

  With reference to the flowchart of FIG. 12, the manufacturing method of the semiconductor device according to the second embodiment will be briefly described. First, a LaHfO film 13 and a polycrystalline silicon film 14 to be a gate electrode are formed on the surface of the silicon substrate 11 by, for example, sputtering (S11, 312). At this time, the LaHfO film 13 is deposited in an amorphous state at 500 ° C., for example, and the atomic ratio La / (La + Hf) of the LaHfO film 13 is larger than 50%.

  Next, the gate insulating film 13 and the gate electrode film 14 are processed by the PEP process and the RIE process. Next, for example, P is ion-implanted by a known method using the processed structure below the gate electrode 14 as a mask (S14).

  Thereafter, a SiN layer is deposited on the entire surface by a known method, and a gate sidewall insulating film 15 is formed by RIE (S15). Thereafter, further P ions are implanted using the gate electrode 14 and the gate sidewall insulating film 15 as a mask. Thereafter, a heat treatment at 1000 ° C. for activation is performed to form the source / drain regions 16 including the shallow extension source / drain portions, and at the same time, the LaHfO film 13 is polycrystallized. Next, heat treatment is performed in a hydrogen atmosphere under the conditions of 450 ° C., 30 minutes, and a H2 / N2 ratio of 10%. As a result, the field effect transistor shown in FIG. 11 is obtained.

  According to the second embodiment, a field effect transistor having good leakage current characteristics can be realized even after a high-temperature heat treatment step of about 1000 ° C.

  In the first embodiment, the interlayer insulating film is formed from a single layer of LaHfO film, and in the second embodiment, the gate insulating film is formed from a single layer of LaHfO film. However, it goes without saying that the LaHfO film may be applied as an interlayer insulating film or a gate insulating film by forming a laminated structure with another insulating film such as a silicon oxide film or a silicon oxynitride film.

  As mentioned above, although this invention was demonstrated through embodiment, this invention is not limited to this, A various deformation | transformation can be implemented in the range which does not deviate from the summary of this invention.

1 is a schematic cross-sectional view of a nonvolatile semiconductor memory device according to a first embodiment. The chart which shows the relationship between the film-forming temperature and composition ratio of the insulating film which consists of La, Hf, and O. The figure which shows that the insulating film which consists of La, Hf, and O is inferior in leak current characteristic regardless of LaHfO composition ratio after 1000 degreeC heat processing. FIG. 4 is a diagram showing a comparison with the present invention, and showing that there is no effect of heat treatment in a hydrogen atmosphere on leakage current characteristics in the case of a film having a La / (La + Hf) ratio = 50%. FIG. 5 is a diagram for explaining the effect of the present invention, and showing that the leakage current characteristics are dramatically improved by heat treatment in a hydrogen atmosphere in the case of a film of La / (La + Hf) = 59%. FIG. 5 is a diagram for explaining the effect of the present invention, and showing that the capacity-voltage characteristic after heat treatment in a hydrogen atmosphere is good when the film is La / (La + Hf) = 59%. In the case of a film of La / (La + Hf) = 59%, the crystal structure of LaHfO is cubic as in the stoichiometric ratio, but the lattice constant is smaller than that in the stoichiometric ratio. in-plane XRD spectrum. The figure which shows the rocking curve measurement result in a 29.12 degree diffraction peak. The figure which shows that the effect of the heat treatment process in the hydrogen atmosphere is greater when the film is La / (La + Hf) = 59% than when it is amorphous. 5 is a flowchart illustrating a method for manufacturing the memory according to the first embodiment. FIG. 5 is a schematic cross-sectional view of a field effect transistor according to a second embodiment. 9 is a flowchart showing a method for manufacturing a transistor according to the second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,11 ... Silicon substrate 2 ... Tunnel insulating film 3 ... Floating electrode (charge storage layer)
4 ... Interlayer insulating film 5 ... Control electrode 6, 16 ... Source / drain region 13 ... Gate insulating film 14 ... Gate electrode 15 ... Gate sidewall insulating film

Claims (8)

A semiconductor substrate;
A pair of source / drain regions formed opposite to each other on the semiconductor substrate;
A tunnel insulating film formed on the semiconductor substrate between the source / drain regions;
A floating electrode or a charge storage layer formed on the tunnel insulating film;
An interlayer insulating film formed on the floating electrode or the charge storage layer and having a cubic pyrochlore type polycrystalline insulating film containing La, Hf, and O;
A control electrode formed on the interlayer insulating film;
A semiconductor device comprising:   2. The semiconductor device according to claim 1, wherein an atomic ratio of La in the polycrystalline insulating film is larger than an atomic ratio of Hf.   2. The semiconductor device according to claim 1, wherein a lattice constant of the polycrystalline insulating film is less than 5.38 cm.   The semiconductor device according to claim 1, wherein the polycrystalline insulating film is non-oriented. Forming a tunnel insulating film on the main surface of the semiconductor substrate;
Forming a floating electrode or a charge storage layer on the tunnel insulating film;
Forming an amorphous insulating film containing La, Hf, and O on the floating electrode;
Forming a control electrode on the amorphous insulating film;
Introducing impurities into the main surface of the semiconductor substrate sandwiching the control electrode, and then performing an activation heat treatment;
A heat treatment step performed in an atmosphere containing hydrogen after the activation heat treatment;
A method for manufacturing a semiconductor device, comprising: A semiconductor substrate;
A pair of source / drain regions formed opposite to each other on the semiconductor substrate;
A gate insulating film formed on the semiconductor substrate between the source / drain regions and having a cubic pyrochlore type polycrystalline insulating film containing La, Hf, and O;
A gate electrode formed on the gate insulating film;
A semiconductor device comprising: Forming an amorphous insulating film containing La, Hf, and O on the main surface of the semiconductor substrate;
Forming a gate electrode on the amorphous insulating film;
Introducing impurities into the main surface of the substrate sandwiching the gate electrode and then performing an activation heat treatment;
After the activation heat treatment, heat treatment in an atmosphere containing hydrogen;
A method for manufacturing a semiconductor device, comprising:   7. The method of manufacturing a semiconductor device according to claim 4, wherein the activation heat treatment changes the amorphous insulating film into a cubic piecroa-type polycrystalline.

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