JP2009081371A - Method of manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a semiconductor device which suppresses excessive diffusion of nitrogen atoms, and improves nitrogen concentrations of an insulating film, when the insulating film including nitrogen and silicon as constituent elements is formed. <P>SOLUTION: (a) A first insulating film including the nitrogen and the silicon is formed on a semiconductor substrate. (b) The first insulating film is exposed to a reducing atmosphere. (c) The first insulating film is exposed to a nitrogenous atmosphere after a process (b). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device having an insulating film suitable for a gate insulating film of a MOS field effect transistor and containing nitrogen and silicon as constituent elements.

  A gate insulating film of a MOS field effect transistor (hereinafter referred to as “MOSFET”) has a physical film thickness that can secure a predetermined capacitance and suppress gate leakage current. Desired. In order to increase the capacitance, it is preferable to make the gate insulating film thinner. However, reducing the thickness leads to an increase in leakage current. In order to maintain a certain level of capacitance without reducing the film thickness, a method using a high dielectric constant material such as hafnium oxide having a dielectric constant higher than that of silicon oxide for the gate insulating film, or nitrogen for the silicon oxide film For example, a method of increasing the dielectric constant by adding s.

  A method for incorporating nitrogen into the gate insulating film is described in Patent Document 1 below. In this method, a silicon oxide film is formed by oxidizing the surface of a silicon substrate, and nitrogen is introduced into the silicon oxide by nitriding the silicon oxide film.

  Patent Documents 2 and 3 below disclose gate insulating films having a structure in which a silicon oxide film and a silicon nitride film are stacked. In Patent Document 2, a silicon nitride film is formed by chemical vapor deposition (CVD), and in Patent Document 3, a silicon nitride film is formed by atomic layer deposition (ALD).

  In addition, a method for improving the nitrogen concentration by depositing a silicon nitride film and then further nitriding the silicon nitride film has been proposed.

Japanese Patent Laid-Open No. 2003-60198 JP 2003-318277 A JP 2004-6455 A

  In the method disclosed in Patent Document 1, when the gate insulating film is thinned, nitrogen atoms diffuse to the interface between the silicon substrate and the silicon oxide film when the silicon oxide film is nitrided. When nitrogen atoms diffuse to the interface between the silicon substrate and the silicon oxide film, the electrical characteristics of the MOSFET are degraded. If nitriding is performed under conditions where nitrogen atoms do not reach the interface between the silicon substrate and the silicon oxide film, the nitrogen concentration cannot be sufficiently increased, and it is difficult to increase the dielectric constant of the gate insulating film.

  In the methods disclosed in Patent Documents 2 and 3, for example, in order to reduce the thickness of the gate insulating film to about 2 μm, the thickness of the silicon nitride film must be about 1 μm. When depositing such an extremely thin silicon nitride film, it is difficult to sufficiently contain nitrogen atoms in the silicon nitride film. That is, it is difficult to sufficiently increase the dielectric constant of the gate insulating film.

  A method of increasing the nitrogen concentration by nitriding the deposited silicon nitride film has also been proposed, but if sufficient nitrogen is introduced by further nitriding the silicon nitride film, nitrogen atoms diffuse excessively, It reaches the interface between the silicon oxide film and the silicon substrate.

  An object of the present invention is to provide a method of manufacturing a semiconductor device capable of suppressing excessive diffusion of nitrogen atoms and increasing the nitrogen concentration of the insulating film when forming an insulating film containing nitrogen and silicon as constituent elements. Is to provide.

According to one aspect of the invention,
(A) forming a first insulating film containing nitrogen and silicon on a semiconductor substrate;
(B) exposing the first insulating film to a reducing atmosphere;
(C) After the step (b), there is provided a method for manufacturing a semiconductor device, comprising a step of exposing the first insulating film to a nitriding atmosphere.

  When the reduction treatment of at least the surface layer portion of the first insulating film is performed, the reduced portion is easily nitrided. Therefore, many nitrogen atoms can be introduced into the upper insulating film even under weak nitriding conditions.

  With reference to FIGS. 1A to 1D, a method of manufacturing a semiconductor device according to the first embodiment will be described.

As shown in FIG. 1A, a lower insulating film 2 made of silicon oxide is formed on the surface of a substrate 1 made of silicon. The lower insulating film 2 is formed, for example, by performing a heat treatment on the substrate 1 in an oxidizing gas atmosphere. The heat treatment conditions are, for example, as follows.
・ Pressure: 13.3 Pa to 1.01 × 10 ⁵ Pa
-Substrate temperature: 500 ° C to 1000 ° C
・ Heat treatment time: 1s to 600s
As the oxidizing gas, nitrogen monoxide, dinitrogen monoxide, nitrogen dioxide, water vapor, ozone, a mixed gas of hydrogen and oxygen, oxygen, or a mixed gas containing two or more of these gases can be used. Alternatively, a mixed gas obtained by adding an inert gas such as nitrogen gas or argon gas to these oxidizing gases may be used. The thickness of the lower insulating film 2 is, for example, in the range of 0.3 nm to 2.0 nm.

  It is also possible to form the lower insulating film 2 by exposing the surface of the substrate 1 to plasma containing oxygen. Oxidation conditions using plasma, for example, input power for generating plasma, pressure, and the like vary depending on the plasma processing apparatus.

  As shown in FIG. 1B, an upper insulating film 3 made of silicon nitride is formed on the lower insulating film 2 by CVD. As a silicon raw material, for example, silane, disilane, dichlorosilane, hexachlorodisilane, bistertiary butylaminosilane or the like can be used, and as a nitrogen raw material, for example, ammonia or the like can be used. The substrate temperature during film formation is preferably 450 ° C. to 600 ° C. If the substrate temperature is too high, nitrogen atoms diffuse in the lower insulating film 2 during film formation and reach the interface between the lower insulating film 2 and the substrate 1. On the other hand, when the substrate temperature is too low, the deposition rate is lowered, which is not preferable in terms of productivity. The film formation time is set so that the thickness of the upper insulating film 3 is in the range of 0.3 nm to 2.0 nm.

As shown in FIG. 1C, at least the surface layer portion of the upper insulating film 3 is reduced by exposing the upper insulating film 3 to the reducing gas 4 and heating the substrate 1. At this time, the bond between the silicon atom and the nitrogen atom in the upper insulating film 3 is cut, and a part of the nitrogen atoms is detached from the upper insulating film 3. A hydrogen atom is bonded to the broken bond of Si and N. As the reducing gas, hydrogen gas, silane-based gas, or a mixed gas containing these gases can be used. As an example, hydrogen gas is used as the reducing gas, and the reduction treatment can be performed under conditions of a pressure of 13.3 Pa to 1.01 × 10 ⁵ Pa, a substrate temperature of 700 ° C. to 1100 ° C., and a heat treatment time of 1 s to 600 s.

  Further, reduction treatment may be performed using plasma of the reducing gas. At this time, it is preferable to set the plasma processing conditions so that a part of nitrogen atoms in the upper insulating film 3 is not desorbed and the film thickness of the upper insulating film 3 is not significantly reduced.

  As shown in FIG. 1D, the reduced upper insulating film 3 is exposed to nitriding plasma 5, thereby introducing nitrogen atoms into the upper insulating film 5 and nitriding the upper insulating film 5. As the nitriding plasma 5, nitrogen plasma, ammonia plasma, nitrogen monoxide plasma, or the like can be used. Plasma nitriding conditions, such as input power for generating plasma, pressure, and the like, vary depending on the plasma processing apparatus. However, it is preferable that the nitrogen atoms introduced into the upper insulating film 5 are diffused in the lower insulating film 2 and do not reach the interface between the lower insulating film 2 and the substrate 1.

  After performing plasma nitridation, heat treatment is performed under conditions of a temperature of 800 ° C. to 1100 ° C., and nitrogen atoms introduced into the upper insulating film 3 are bonded to silicon atoms. Thereby, the nitrogen concentration of the upper insulating film 3 can be made higher than the nitrogen concentration immediately after the film formation.

Note that the upper insulating film 3 may be nitrided by performing a heat treatment in a nitriding gas atmosphere instead of nitriding using plasma. As the nitriding gas, ammonia gas, nitrogen monoxide gas, dinitrogen monoxide gas, or the like can be used. As an example, the pressure may be 13.3 Pa to 1.01 × 10 ⁵ Pa, the substrate temperature may be 500 ° C. to 1000 ° C., and the heat treatment time may be 1 s to 600 s. In this case, the heat treatment after nitriding is preferably performed at a temperature higher than the substrate temperature during nitriding.

  Two layers of the lower insulating film 2 made of silicon oxide and the upper insulating film 3 made of silicon nitride are applied to a gate insulating film of a MOSFET, for example. The lower insulating film 2 may be made of silicon oxynitride containing a small amount of nitrogen that does not cause a decrease in the performance of the MOSFET.

  The upper insulating film 3 may be made of an insulating material containing nitrogen and silicon as constituent elements, and the lower insulating film 2 may be made of an insulating material containing oxygen and silicon as constituent elements. In this case, even if the lower insulating film 2 does not contain nitrogen or contains nitrogen, the nitrogen atom concentration is preferably lower than the nitrogen atom concentration of the upper insulating film 3.

  In FIG. 1D, the boundary between the lower insulating film 2 and the upper insulating film 3 is clearly shown, but in reality, the boundary between them will not be clear. For example, as the distance from the surface of the substrate 1 increases, the nitrogen concentration increases and the oxygen concentration decreases. A position where the nitrogen concentration rapidly increases or a position where the oxygen concentration rapidly decreases can be considered as a boundary between the lower insulating film 2 and the upper insulating film 3.

  Next, the effect of the semiconductor device manufacturing method according to the first embodiment will be described. When the thickness of the upper insulating film 3 made of silicon nitride shown in FIG. 1B is about 1 nm, it is difficult to increase the nitrogen concentration to about 60 atomic%, which is a stoichiometric composition. The nitrogen concentration is only about 20 atomic%. In order to further nitride the upper insulating film 3 made of silicon nitride in which silicon atoms and silicon atoms and nitrogen atoms are strongly bonded, these bonds must be broken during nitriding. For this reason, in order to increase the nitrogen concentration of the upper insulating film 3, it is necessary to perform nitriding by applying large thermal energy to the upper insulating film 3 (under strong nitriding conditions). When nitriding is performed under such strong nitriding conditions, not only the nitrogen concentration in the surface layer portion of the upper insulating film 3 is increased, but also nitrogen atoms diffuse to the interface between the lower insulating film 2 and the substrate 1.

  In the first embodiment, in the step shown in FIG. 1C, the upper insulating film 3 is reduced to cut bonds between silicon atoms and bonds between silicon atoms and nitrogen atoms. For this reason, it is not necessary to provide the upper insulating film 3 with large heat energy for cutting these bonds during nitriding. Thus, since nitriding is performed in a state where nitrogen is easily introduced, a large amount of nitrogen atoms can be introduced into the upper insulating film 3 even under relatively weak nitriding conditions.

  Since it is not necessary to give large heat energy during nitriding, diffusion of nitrogen atoms introduced into the upper insulating film 3 is suppressed. Therefore, a large amount of nitrogen atoms can be introduced into the upper insulating film 3 under nitriding conditions in which nitrogen atoms do not reach the interface between the lower insulating film 2 and the substrate 1. Even if nitrogen atoms reach the interface between the lower insulating film 2 and the substrate 1, the amount of nitrogen atoms reaching the interface can be reduced as compared with the case where nitriding is performed under strong nitriding conditions. Thereby, the remarkable increase in the nitrogen concentration at the interface can be prevented.

  Actually, a plurality of samples including the lower insulating film 2 and the upper insulating film 3 were prepared by the method according to the first embodiment, and the nitrogen concentration was measured. Note that a sample was also produced by a method of performing nitriding without performing the reduction treatment of the upper insulating film 2 (a method according to a comparative example).

  FIG. 2 shows the measurement results of the nitrogen atom concentration of each sample. The horizontal axis represents the substrate temperature when the upper insulating film 3 is subjected to the reduction treatment in the unit “° C.”, and the vertical axis represents the nitrogen atom concentration in the unit “atomic%”. In any sample, the thickness of the lower insulating film 2 was 1 nm, and the thickness of the upper insulating film 3 was 1.5 nm. The upper insulating film 3 was formed by thermal CVD under the condition of a substrate temperature of 500 ° C., using bister butylaminosilane and ammonia as raw materials.

  The reduction treatment of the upper insulating film 3 was performed using hydrogen gas as the reducing gas and a heat treatment time of 10 s.

The nitriding treatment of the upper insulating film 3 after the reduction treatment was performed using a parallel plate type plasma processing apparatus. N ₂ was used as the nitriding gas, the input RF power was 180 W, the pressure was 6.7 Pa (50 mTorr), and the nitriding time was 30 s. The substrate 1 has a diameter of 8 inches.

  The nitrogen atom concentration on the vertical axis in FIG. 2 is a value measured by X-ray photoelectron spectroscopy, and is a value obtained by averaging the concentration of nitrogen contained in the lower insulating film 2 and the upper insulating film 3 in the thickness direction. Become. A sample with a temperature of 0 ° C. on the horizontal axis is obtained by performing a nitriding process without performing a reducing process after forming the upper insulating film 3.

  It can be seen that the nitrogen concentration of the sample subjected to the reduction treatment at a temperature of 800 ° C. to 900 ° C. is higher than the nitrogen concentration of the sample not subjected to the reduction treatment. From this evaluation result, it is understood that the nitrogen concentration after nitriding can be increased by performing the reduction treatment. The nitrogen concentration shown in FIG. 2 is an average value in the thickness direction of the lower insulating film 2 and the upper insulating film 3, but the nitrogen atom concentration is actually high in the surface layer portion of the upper insulating film 3, It has a distribution that becomes lower at the interface between the lower insulating film 2 and the substrate 1. When averaged in the thickness direction, the increase amount of the nitrogen atom concentration seems to be slight, but the increase amount of the nitrogen atom concentration becomes remarkable when attention is paid to a region where the nitrogen concentration is relatively high.

  Due to the reduction treatment, a part of the nitrogen atoms in the upper insulating film 3 is desorbed, so that the nitrogen atom concentration is once lowered. However, the upper insulating film 3 is easily nitrided by this reduction treatment. Thus, although the nitrogen atom concentration once decreases, the nitrogen atom concentration of the upper insulating film 3 made of silicon nitride finally obtained can be further increased.

  When the temperature of the reduction treatment is 1000 ° C., the nitrogen atom concentration is reduced as compared with the case where the reduction treatment is not performed. This is because many nitrogen atoms and the like are desorbed during the reduction process, and the upper insulating film 3 becomes thin. If the reduction treatment time is shorter than 10 s, it is possible to introduce many nitrogen atoms even if the reduction treatment temperature is 1000 ° C.

  The reduction treatment of the upper insulating film 3 is preferably performed under the condition that the upper insulating film 3 is hardly thinned, for example, under the condition that the thickness reduction is 3% or less of the original film thickness.

  Suitable temperature conditions during the reduction process depend on gas, pressure, processing time, and the like during the reduction process. For example, if the pressure during the reduction treatment is increased, the treatment temperature may be lowered. Also, if the treatment time is lengthened, the treatment temperature may be lowered. However, it is preferable that the nitrogen atoms in the upper insulating film 3 are diffused in the lower insulating film 2 and do not reach the interface between the lower insulating film 2 and the substrate 1 during the reduction process.

  Next, with reference to FIGS. 3A to 3D, a method for fabricating a semiconductor device according to the second embodiment will be described.

  As shown in FIG. 3A, a lower insulating film 2 made of silicon oxide is formed on the surface of a substrate 1 made of silicon. The lower insulating film 2 is formed by the same method as the lower insulating film 2 of the first embodiment shown in FIG. 1A.

As shown in FIG. 3B, the lower insulating film 2 is exposed to nitriding plasma 10 to nitride the surface layer portion. Thereby, the upper insulating film 3 made of silicon oxynitride is formed. The plasma nitriding conditions are set so that the upper insulating film 3 has a thickness of 0.1 nm to 1.5 nm. Under the upper insulating film 3, the lower insulating film 2 that is not nitrided remains. Instead of plasma nitriding with the nitriding plasma 10, thermal nitriding may be performed in a nitriding gas atmosphere. The pressure during thermal nitriding is 13.3 Pa to 1.01 × 10 ⁵ Pa, the substrate temperature is 500 ° C. to 1000 ° C., and the nitriding time is 1 s to 600 s. Also in this case, the conditions are set so that the upper insulating film 3 has a thickness of 0.1 nm to 1.5 nm.

  As shown in FIG. 3C, the upper insulating film 3 made of silicon oxynitride is exposed to a reducing gas 4 to perform a reduction process. As shown in FIG. 3D, the reduced upper insulating film 3 is exposed to nitriding plasma 5 to perform nitriding treatment. The reduction process shown in FIG. 3C and the nitridation process shown in FIG. 3D are the same as the reduction process of the first example shown in FIG. 1C and the nitridation process of the first example shown in FIG. 1D, respectively. Can be done by the method.

  Also in the second embodiment, since the reduction process is performed as shown in FIG. 3C, the nitrogen concentration of the upper insulating film 3 can be increased and the lower insulating film 2 and the substrate can be increased as in the first embodiment. The increase in the nitrogen concentration at the interface with 1 can be suppressed.

  With reference to FIGS. 4A to 4F, description will be made on a MOSFET manufacturing method to which the first and second embodiments are applied.

  As shown in FIG. 4A, an element isolation insulating film 21 is formed on the surface layer portion of a substrate 20 made of silicon using a shallow trench isolation (STI) method or the like. An active region 22 surrounded by the element isolation insulating film 21 is defined. If necessary, channel implantation for adjusting the threshold voltage is performed in the surface layer portion of the active region 22.

  As shown in FIG. 4B, the lower insulating film 25 made of silicon oxide is formed by thermally oxidizing the surface layer portion of the active region 22. The lower insulating film 25 is formed by the same method as the lower insulating film 2 of the first and second embodiments shown in FIGS. 1A and 3A.

  As shown in FIG. 4C, an upper insulating film 30 made of silicon nitride is formed on the lower insulating film 25 and the element isolation insulating film 21. The upper insulating film 30 is formed by performing the film forming process, the reducing process, and the nitriding process shown in FIGS. 1B to 1D of the first embodiment. As shown in FIGS. 3B to 3D of the second embodiment, the first nitriding treatment, the reducing treatment, and the second nitriding treatment may be performed.

  As shown in FIG. 4D, a polycrystalline silicon film 35 is formed on the upper insulating film 30 by CVD or the like.

  As shown in FIG. 4E, the polycrystalline silicon film 35, the upper insulating film 30, and the lower insulating film 25 are patterned. As a result, a two-layered gate insulating film 40 composed of the upper insulating film 30 and the lower insulating film 25 and a gate electrode 41 composed of the polycrystalline silicon film 35 are formed.

  As shown in FIG. 4F, the extension regions of the source 42 and the drain 43, the sidewall spacers 44, the deep regions of the source 42 and the drain 43, and the metal silicide film 50 are sequentially formed. The metal silicide film 50 is formed on the upper surfaces of the source 42, the drain 43, and the gate electrode 41. For the metal silicide film 50, cobalt silicide or nickel silicide is used.

  The upper insulating film 30 constituting the gate insulating film 40 is formed by the method according to the first or second embodiment. For this reason, it is possible to increase the nitrogen concentration of the upper insulating film 30 while suppressing an increase in the nitrogen atom concentration at the interface between the substrate 20 and the gate insulating film 40.

  Since the nitrogen concentration of the upper insulating film 30 is increased, the effective dielectric constant of the gate insulating film 40 can be increased. Moreover, since the increase in the nitrogen concentration at the interface between the gate insulating film 40 and the substrate 20 is suppressed, the decrease in carrier mobility is suppressed.

  In the example shown in FIGS. 4A to 4F, a silicon substrate is used as the substrate 20, but an SOI (silicon on insulator) substrate or the like may be used.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

  Regarding the embodiment including the first and second examples, the following additional notes are disclosed.

(Appendix 1)
(A) forming a first insulating film containing nitrogen and silicon on a semiconductor substrate;
(B) exposing the first insulating film to a reducing atmosphere;
(C) After the step (b), the method further comprises a step of exposing the first insulating film to a nitriding atmosphere.

(Appendix 2)
Item 2. The supplementary note 1, wherein in the step (b), part of nitrogen atoms in the first insulating film is desorbed by exposing the first insulating film to the reducing atmosphere. A method for manufacturing a semiconductor device.

(Appendix 3)
The step (a) further includes a second insulating layer containing oxygen and silicon on the semiconductor substrate and not containing nitrogen or having a nitrogen concentration lower than a nitrogen atom concentration of the first insulating film. 3. The method of manufacturing a semiconductor device according to appendix 1 or 2, further comprising forming a film, wherein the first insulating film is formed on the second insulating film.

(Appendix 4)
4. The method of manufacturing a semiconductor device according to appendix 3, wherein in the step (a), the first insulating film is deposited by chemical vapor deposition.

(Appendix 5)
In the step (c), the first insulating film is exposed to the nitriding atmosphere while heating the semiconductor substrate at a first temperature, and after the step (c), further from the first temperature. The method for manufacturing a semiconductor device according to any one of appendices 1 to 4, further comprising a step of heating the semiconductor substrate at a higher temperature.

(Appendix 6)
After the step (c),
Forming a gate electrode on the first insulating film;
The method for manufacturing a semiconductor device according to any one of appendices 1 to 5, further comprising: implanting impurity ions into the semiconductor substrate on both sides of the gate electrode.

(Appendix 7)
4. The method of manufacturing a semiconductor device according to appendix 3, wherein, in the step (a), the first insulating film is formed by nitriding a surface layer portion of the second insulating film.

It is board | substrate sectional drawing in the middle of manufacture of the manufacturing method of the semiconductor device by a 1st Example. It is a graph which shows the nitrogen atom density | concentration of the sample produced with the method by a 1st Example and a comparative example. It is board | substrate sectional drawing of the middle stage of manufacture of the manufacturing method of the semiconductor device by a 2nd Example. It is sectional drawing of MOSFET in the middle of manufacture of the manufacturing method of MOSFET to which the method by the 1st or 2nd Example is applied. It is sectional drawing of MOSFET in the middle stage of manufacture of the manufacturing method of MOSFET which applied the method by the 1st or 2nd Example, and sectional drawing of completed MOSFET.

Explanation of symbols

1 Substrate 2 Lower insulating film (second insulating film)
3 Upper insulating film (first insulating film)
4 Reducing gas 5, 10 Nitride plasma 20 Substrate 21 Element isolation insulating film 22 Active region 25 Lower insulating film 30 Upper insulating film 35 Polycrystalline silicon film 40 Gate insulating film 41 Gate electrode 42 Source 43 Drain 44 Side wall spacer 50 Metal silicide film

Claims (5)

(A) forming a first insulating film containing nitrogen and silicon on a semiconductor substrate;
(B) exposing the first insulating film to a reducing atmosphere;
(C) After the step (b), the method further comprises a step of exposing the first insulating film to a nitriding atmosphere.   The step (a) further includes a second insulating layer containing oxygen and silicon on the semiconductor substrate and not containing nitrogen or having a nitrogen concentration lower than a nitrogen atom concentration of the first insulating film. The method of manufacturing a semiconductor device according to claim 1, further comprising a step of forming a film, wherein the first insulating film is formed on the second insulating film.   The method of manufacturing a semiconductor device according to claim 2, wherein in the step (a), the first insulating film is deposited by chemical vapor deposition.   In the step (c), the first insulating film is exposed to the nitriding atmosphere while heating the semiconductor substrate at a first temperature, and after the step (c), further from the first temperature. The method of manufacturing a semiconductor device according to claim 1, further comprising a step of heating the semiconductor substrate at a higher temperature. After the step (c),
Forming a gate electrode on the first insulating film;
5. The method of manufacturing a semiconductor device according to claim 1, further comprising a step of implanting impurity ions into the semiconductor substrate on both sides of the gate electrode.

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