JP2006019366A - Method for forming insulating film in semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a reliable gate insulating film by introducing high-concentration nitrogen only near the surface of a silicon oxide film without segregating nitrogen near the interface of a silicon substrate in the nitriding treatment of the silicon oxide film using a plasma nitriding method. <P>SOLUTION: A method for forming an insulating film comprises a process for irradiating a substrate surface having a silicon oxide thin film on a semiconductor substrate with vacuum ultraviolet rays in a vacuum container retained in high vacuum; and a process for performing either nitriding or oxynitriding treatment in the vacuum container retained in a high vacuum state without exposing the substrate to the atmosphere after the irradiation of vacuum ultraviolet rays. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a semiconductor device having a highly reliable insulating film formed on a semiconductor substrate.

  With the progress of high integration of LSIs, thinning of gate insulating films of MOS (Metal Oxide Semiconductor) transistors, capacitor insulating films of memories, and the like is progressing.

  However, for example, a silicon oxide film that has been conventionally used as a gate insulating film in a MOS transistor has a physical film thickness that cannot be ignored when the film thickness drops below 2 nm, and the increase in leakage current due to direct tunneling current decreases. It has become difficult to reduce. Another adverse effect of thinning the film is that the boron implanted into the P + polysilicon gate electrode penetrates through the thin insulating film and diffuses into the silicon substrate by the heat treatment performed in the subsequent process, thereby changing the threshold voltage. There is also a problem that causes a decrease in reliability.

  As a means for overcoming such a problem, since the dielectric constant is higher than that of the silicon oxide film, an electric capacitance value can be obtained even if the physical film thickness is ensured to be thicker than that of the silicon oxide film. A silicon oxynitride film having excellent characteristics such as reducing the thickness of Thickness (EOT) and suppressing diffusion of boron to the substrate has attracted attention, and various film formation methods have been proposed.

  As a means for forming a silicon oxynitride film, for example, there is a thermal nitriding method in which nitrogen is introduced into the film by heating the silicon oxide film at a high temperature in a nitrogen-containing atmosphere.

  Hereinafter, an oxynitride film formed by using the thermal nitriding method will be described in detail with reference to FIG.

  Here, 101 is a silicon substrate, 102 is a silicon oxide film, 105 is a high concentration nitrided oxide film layer, 501 is a nitriding reaction gas, 502 is an oxidation reaction gas, and 503 is a low concentration nitriding oxide film layer.

First, a silicon substrate 101 having a silicon oxide film 102 formed on the surface thereof by a film forming method such as a dry thermal oxidation method or a pyrogenic method is introduced into a reaction furnace heated to a high temperature of 800 to 1200 ° C. Next, a nitriding reaction gas 501 containing nitrogen such as N ₂ , NO, N ₂ O, and NH ₃ is flowed under a predetermined pressure. Nitrogen atoms are taken into the silicon oxide film 102 by the high temperature heating in the nitrogen atmosphere as described above, and the nitriding reaction proceeds. When the distribution of nitrogen atoms in the film obtained at this time is viewed macroscopically, the surface of the silicon oxide film 102 and the oxynitride film 105 containing nitrogen at a high concentration at the interface between the silicon oxide film and the silicon substrate 101, and A three-layer structure having an oxynitride film 503 containing a low concentration of nitrogen is formed so as to be sandwiched between these regions. Further, the substrate thus formed is further subjected to re-oxidation treatment by heating at a high temperature in an atmosphere of an oxidation reaction gas 502 such as O ₂ or O ₃ , whereby an interface between the silicon substrate 101 and the silicon oxide film 102 is obtained. It is also possible to form an oxynitride film having a two-layer structure of an oxynitride film layer 105 containing a high concentration of nitrogen and an oxynitride film layer 503 having a low nitrogen concentration on the surface of the silicon oxide film 102.

  It is possible to introduce several to several tens of atomic percent of nitrogen atoms into the silicon oxide film by the method as described above, and it has excellent characteristics such as improvement of the dielectric constant of the insulating film and suppression of impurity diffusion such as boron. An insulating film having the same can be obtained.

  However, according to the above method, nitrogen atoms act to alleviate the interstitial stress generated in the transition layer existing in the vicinity of the interface between the silicon substrate 101 and the silicon oxide film 102. Nitrogen segregation occurs. Nitrogen atoms segregated in the vicinity of the silicon substrate 101 interface have advantages such as suppressing impurity diffusion from the substrate to the insulator and improving hot electron resistance compared to a pure silicon oxide film. It has been pointed out that it has a demerit that it causes a decrease in the thickness and an increase in the interface state density.

  In addition, as described above, the nitriding method using thermal energy for reaction heats not only the silicon oxide film but also the substrate to a high temperature, so that impurities doped in the substrate to form a channel region also thermally diffuse. The distribution is changed. For this reason, there is a problem that formation of a shallow junction of the transistor is hindered.

  In recent years, plasma nitriding methods (or radical nitriding methods) using nitrogen radicals or nitrogen ions generated in a plasma state by high-frequency excitation of a nitrogen-containing gas have been proposed as means for solving such problems.

  Hereinafter, a method for nitriding a silicon oxide film by plasma nitriding will be described with reference to FIG.

  Here, reference numeral 701 is a vacuum vessel, 702 is a substrate support base, 703 is a plasma generation chamber, 704 is a substrate processing chamber, 705 is a reactive gas introduction means, 706 is an exhaust means, 707 is a high frequency power supply means, and 708 is a temperature control means. is there.

  First, after the inside of the vacuum vessel 701 of the plasma processing apparatus is sufficiently evacuated by the exhaust means 706, a nitriding gas at a predetermined flow rate is introduced into the plasma generation chamber 703 through the reaction gas introduction means 705 and provided in the exhaust means. The desired pressure is maintained by a conductance valve (not shown). Subsequently, discharge is performed via the high frequency power supply means 707 to generate plasma in the plasma generation chamber 703. When the reaction gas is brought into a plasma state by high frequency excitation, highly reactive neutral active species (radicals), ions, and the like are generated in the plasma. The various particles move by diffusion from the plasma generation chamber 703 to the object processing chamber 704 having the substrate 101 installed on the support table 702, reach the surface of the substrate 101, and undergo a nitriding reaction. At this time, since the support table 702 is kept at a relatively low temperature of about room temperature to about 500 ° C. by the temperature adjusting means 708 and nitriding is performed, the nitrogen introduced into the film is rapidly diffused as in the thermal nitriding method. Therefore, the nitriding reaction can be performed only in the vicinity of the surface of the silicon oxide film. Furthermore, there is no possibility of causing redistribution of impurities in the silicon substrate by performing the treatment at a low temperature.

By the plasma nitriding method as described above, an oxynitride film having a structure in which almost no nitrogen atoms exist at the silicon substrate interface can be formed as shown in the schematic diagram of FIG.
JP-A-6-140392 Jpn. J. et al. App. Phys. Vol. 33 pp. 2175-2178

  However, even in the radical nitriding method, when nitriding the surface of the silicon oxide film at a high concentration, before the nitrogen concentration in the vicinity of the oxide film surface rises and the nitrogen atoms are saturated, the diffusion of nitrogen into the film as shown in FIG. This causes an increase in the number of nitrogen atoms on the interface side between the silicon substrate and the silicon oxide film with the nitriding time, which may cause the deterioration of the transistor characteristics as described above.

  The present invention introduces a high concentration of nitrogen only in the vicinity of the silicon oxide film surface without causing segregation of nitrogen in the vicinity of the silicon substrate interface in the nitridation processing of the silicon oxide film using the plasma nitriding method, thereby providing a reliable gate insulation. The object is to form a film.

  In order to achieve the above object, an insulating film forming method according to the present invention includes a step of irradiating a vacuum ultraviolet light in a vacuum container in which a substrate surface having a silicon oxide thin film on a semiconductor substrate is held in a high vacuum, And a step of performing either nitriding or oxynitriding in a vacuum container kept in a high vacuum state without exposing the substrate to the atmosphere after light irradiation.

The energy of the vacuum ultraviolet light is light having a wavelength having energy at least equal to or higher than the band gap energy of the silicon oxide film, more preferably light having a wavelength having an absorption coefficient of 1 × 10 7 cm ⁻¹ or more with respect to the silicon oxide film. And

  The nitriding and oxynitriding treatment means is a plasma treatment.

  According to the present invention, only the vicinity of the surface can be nitrided in a high concentration in a short time while avoiding the segregation of nitrogen to the silicon substrate interface in the gate silicon oxide film of the semiconductor device, whereby a highly reliable semiconductor An apparatus can be provided.

  The operation based on the above solution will be described below with reference to FIGS. FIG. 1 shows a nitriding treatment procedure of a silicon oxide film and a nitrogen concentration distribution in the film according to the present invention. FIG. 2 shows silicon atoms when a vacuum ultraviolet light according to the present invention is irradiated on the silicon oxide film. It shows the bond change between oxygen atoms.

  Here, 103 is vacuum ultraviolet light, 104 is plasma particles, 201 is a strong bond between silicon atoms and oxygen atoms, 202 is precipitated silicon, 203 is a weak bond between silicon atoms and oxygen atoms, and 204 is a dangling bond. is there.

  The silicon oxide film 102 formed on the silicon substrate 101 is irradiated with vacuum ultraviolet light 103 having energy equal to or higher than the band gap energy of the silicon oxide film.

  The wavelength of light having energy corresponding to the band gap energy of the silicon oxide film corresponds to about 138 nm when the band gap energy is 9 eV. Light in such a wavelength region is called vacuum ultraviolet (VUV), and can be irradiated with an excimer lamp or the like. Further, since the VUV light is absorbed in the atmosphere, it is necessary to irradiate the silicon substrate 101 with the VUV light in a high vacuum.

  When the silicon oxide film 102 is irradiated with the vacuum ultraviolet light having the energy as described above, electrons forming a strong bond between a silicon atom and an oxygen atom jump over the forbidden gap and behave as free electrons. The strong bond 201 between the silicon atom and the oxygen atom in the silicon oxide film is cut. As a result, a damaged layer having various defects such as silicon deposition 202, weak bonds 203 between silicon atoms and oxygen atoms due to lattice distortion, or dangling bonds 204 is formed in the silicon oxide film.

The depth of such a damage layer depends on the wavelength of the vacuum ultraviolet light to be irradiated. For example, in the case of VUV light having a wavelength band of 60 nm to 120 nm, the absorption coefficient for the silicon oxide film is as extremely high as 1 × 10 7 cm ⁻¹ or more. There is a report that a damage layer is formed near the outermost surface of less than 1 nm from the outermost surface of the silicon oxide film. (Jpn. J. App. Phys. Vol. 33 pp. 2175-2178)
The damaged layer in the silicon oxide film is highly reactive. When the silicon substrate 101 is exposed to the atmosphere in such a state, oxygen and moisture in the atmosphere immediately react with the silicon oxide film 102 and are close to a natural oxide film. A low-quality oxide film is re-formed. Therefore, by continuously exposing the nitrogen plasma particles 104 to the surface of the silicon oxide film 102 while keeping the silicon substrate 101 in a high vacuum environment, the reaction probability is higher than the plasma nitridation for the oxide film not irradiated with VUV light. Thus, a nitriding reaction can be caused in the silicon oxide film 102, and a large amount of nitrogen atoms can be introduced into the silicon oxide film surface in a short time. Therefore, in order to introduce a high concentration of nitrogen atoms into the film, it is possible to suppress an increase in the nitrogen concentration near the substrate interface due to the diffusion of nitrogen atoms, which is observed when radical nitriding is performed for a long time. In addition, a highly reliable semiconductor element can be formed.

  Incidentally, a method for nitriding an oxide film using VUV light is described in, for example, Japanese Patent Laid-Open No. 6-140392. In this nitriding treatment, VUV light is used to generate photoexcited plasma, and the substrate is simultaneously irradiated to nitride the silicon oxide film with active nitrogen radicals. However, in the above method, since the generation of plasma and the VUV irradiation to the substrate are the same, it is impossible to control each process condition independently. Furthermore, when VUV irradiation is performed during plasma nitriding, nitrogen atoms introduced into the film receive energy from VUV and diffuse into the film in the same way as thermal nitridation, accelerating the increase in nitrogen concentration at the silicon substrate interface. There is a problem.

  On the other hand, in the present invention, irradiation with VUV light is performed separately from nitriding treatment. This is because the damaged layer generated by VUV irradiated in the silicon oxide film remains in the film even after irradiation, and it is not necessary to simultaneously perform the formation of the damaged layer and the nitriding treatment. For this reason, the difference is that the nitriding treatment can be performed without causing the above-described diffusion phenomenon of nitrogen by the VUV light.

(Embodiment)
Hereinafter, an embodiment of the present invention will be described with reference to FIG. Here, 301 is a vacuum ultraviolet light irradiation chamber, 302 is a plasma nitridation chamber, 303 is a substrate loading chamber, 304 is a substrate transfer chamber, and 305 is a substrate transfer means.

  The vacuum ultraviolet light irradiation chamber 301, the plasma nitriding chamber 302, and the substrate transfer chamber 304 are each evacuated by an evacuation means (not shown) and kept at a high vacuum. First, the substrate 101 is pulled into a high vacuum in the load chamber 303 by an exhaust unit (not shown), introduced into the substrate transfer chamber 304 by the transfer unit 305, and then transferred to the vacuum ultraviolet light irradiation chamber 301. In the vacuum ultraviolet light processing chamber 301, vacuum ultraviolet light irradiation means (not shown) irradiates the surface of the substrate 101 with vacuum ultraviolet light under a predetermined condition, and then is carried out by the transport means 305 and then transported to the plasma nitriding chamber 302. After the substrate 101 is subjected to plasma nitriding treatment under a predetermined condition in the plasma nitriding chamber, the substrate 101 is unloaded into the substrate load chamber 303 by the transfer means 305 through the substrate transfer chamber 304 and then vented with an inert gas. Then it is released to the atmosphere.

  When the substrate 101 is irradiated with vacuum ultraviolet light, defects such as silicon deposition and dangling bonds occur near the surface of the silicon oxide film. For this reason, if the surface of the substrate 101 is exposed to the atmosphere before nitriding, it will recombine with moisture, oxygen, etc. in the atmosphere and form a low-quality film similar to the natural oxide film. As described above, the substrate 101 is subjected to vacuum ultraviolet light irradiation in the vacuum ultraviolet light irradiation chamber 301 and then subjected to nitridation processing in the plasma nitriding chamber 302 through a transfer chamber held in an ultrahigh vacuum. This prevents the formation of an oxide film.

  In the example shown in the embodiment of the present invention, a processing method in which a processing chamber for performing vacuum ultraviolet light irradiation and plasma nitriding is separated is shown. However, after the vacuum ultraviolet light irradiation, plasma is continuously maintained while the processing chamber is kept at a high vacuum. Of course, if nitriding can be performed, these treatments can be performed in the same chamber.

  The silicon oxide film on the silicon substrate used in the present invention can be applied to a film formed by any oxide film forming method such as a dry thermal oxidation method, a pyrogenic method, a chemical oxidation method, a CVD method, or a plasma oxidation method.

The reaction gas for nitriding or oxynitriding used in the present invention is a nitrogen-containing gas such as N ₂ , NO, N ₂ O, NH ₃ , N ₂ H ₄ , NF ₃ , a mixed gas thereof, or a mixture thereof, or He, Ne. Any gas mixture diluted with Ar, Kr, Xe, etc. can be applied.

  The plasma nitridation plasma generation source used in the present invention is applicable to any plasma source of inductive coupling type, capacitive coupling type, surface wave type, magnetron type, electron cyclotron resonance type and the like.

Using the plasma nitriding apparatus as shown in FIG. 3, the plasma nitriding treatment of the semiconductor element gate oxide film was performed.
As the substrate 101, 8-inch P-type single crystal silicon (plane orientation 100, resistivity 10 Ωcm) having a 2.5 nm thick thermal oxide film formed on its surface by a rapid thermal processing method was used. First, the silicon substrate 101 was placed in the load chamber 303, and the load chamber was depressurized to 1 × 10 ⁻² by an exhaust pump (not shown). Next, the substrate 101 was transferred by the transfer arm 305 through the substrate transfer chamber 304 to the vacuum ultraviolet light irradiation chamber 301 maintained at 1 × 10 ⁻³ by an exhaust pump. After irradiating the surface of the substrate 101 with Xe excimer light having a wavelength of 120 nm in the vacuum ultraviolet light processing chamber 301, it was carried out by the transfer arm 305 and then transferred to the plasma nitriding chamber 302 maintained at 1 × 10 ⁻³ Pa. At this time, the silicon substrate 101 was heated and held at 300 ° C. by a heater (not shown).

  N 2 gas was introduced into the plasma nitriding chamber at a flow rate of 200 sccm, the opening of a conductance valve (not shown) provided in the exhaust system was adjusted, and the pressure in the plasma nitriding chamber 302 was maintained at 133 Pa. Thereafter, plasma was generated by 2.45 GHz and 1 kW microwaves, and the silicon oxide film 102 was nitrided for 60 seconds.

  A capacitor having a MOS structure was created using the silicon oxynitride film produced by the above process, and the insulating film was evaluated.

  As a result, the measurement result of the equivalent silicon oxide film thickness (EOT) by CV characteristics was 2.2 nm, and it was confirmed that the thinning effect was obtained by introducing nitrogen into the oxide film.

  In addition, when the nitrogen concentration distribution in the film was measured using RBS (Rutherford Back Scattering Spectroscopy), it was confirmed that nitrogen atoms had a concentration peak near the surface of the silicon oxide film and no nitrogen atoms appeared at the silicon substrate interface. did.

It is a schematic diagram explaining the nitriding method of this invention. It is a schematic diagram explaining the effect when the vacuum ultraviolet light of this invention is irradiated to a silicon oxide film. It is a schematic diagram explaining embodiment of this invention. It is a schematic diagram explaining the time dependence of the depth distribution of the nitrogen concentration by the conventional plasma nitriding method. It is a schematic diagram explaining the conventional thermal nitriding method. It is a schematic diagram explaining the conventional plasma nitriding method. It is a schematic diagram explaining a plasma nitriding apparatus. It is a measurement result of nitrogen concentration distribution by RBS of the oxynitride film created by the example of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Silicon substrate 102 Silicon oxide film 103 Vacuum ultraviolet light 104 Plasma particle 105 High concentration nitrided oxide film layer 201 Strong bond between silicon atom and oxygen atom 202 Precipitated silicon 203 Weak bond between silicon atom and oxygen atom 204 Dangling bond 301 Vacuum Ultraviolet Light Irradiation Chamber 302 Plasma Nitriding Chamber 303 Substrate Loading Chamber 304 Substrate Transfer Chamber 305 Substrate Transfer Means 501 Nitriding Reaction Gas 502 Oxidation Reaction Gas 503 Low Concentration Nitride Oxide Film Layer 701 Vacuum Container 702 Substrate Support Stand 703 Plasma Generation Chamber 704 Base Processing chamber 705 Reaction gas introduction means 706 Exhaust means 707 High frequency power supply means 708 Temperature adjustment means

Claims (4)

  A process of irradiating the substrate surface having a silicon oxide thin film on a semiconductor substrate with vacuum ultraviolet light in a vacuum vessel maintained in a high vacuum, and maintaining the substrate in a high vacuum state without exposing the substrate to the atmosphere after the vacuum ultraviolet light irradiation. And a step of performing either nitridation or oxynitridation treatment in the vacuum vessel. 2. The light according to claim 1, wherein the vacuum ultraviolet light is light having a wavelength that has at least energy equal to or higher than a band gap energy of the silicon oxide film and an absorption coefficient of 1 × 10 7 cm ⁻¹ or more for the silicon oxide film. A method for forming an insulating film of a semiconductor device.   3. The method of forming an insulating film in a semiconductor device according to claim 1, wherein the nitriding and oxynitriding treatment means is a plasma treatment.   4. The method of forming an insulating film of a semiconductor device according to claim 1, wherein the insulating film of the semiconductor device is used as an interlayer film between a substrate of a MOS transistor and a gate electrode or a capacitor element of a capacitor. .

Images