JP2006032979A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device superior in the level difference covering characteristics of a ferroelectric film. <P>SOLUTION: This semiconductor device is provided with a electrode 9, formed on a substrate and having a concavity or a convex section on its surface, and the ferroelectric film 10 containing Sr, Bi and Ta, or Bi, La, and Ti, formed on the electrode 9. The level difference coverage of the ferroelectric film in the level difference, existing in the concavity or the convex section, is 80% or higher. The dispersion in the composition ratio of metallic elements constituting the ferroelectric film is ±15% or smaller. Plural kinds of source gases which constitutes a material gas and in which each contains an organometallic compound are introduced into a chamber, and by chemically reacting main components in the plural kinds of source gases with each other in reaction rate-controlling, the ferroelectric film is deposited on a surface of the electrode. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for forming a ferroelectric film that is an insulating metal oxide, and a semiconductor device including the ferroelectric film.

  In recent years, with the progress of digital technology, a tendency to process or store large amounts of data at high speed has been promoted, and higher integration and higher performance of semiconductor devices used in electronic devices are required. . Therefore, in order to realize high integration and low power consumption of a semiconductor device, a capacitive insulating film made of a high dielectric constant film is used as a capacitive element instead of a conventional capacitive insulating film made of silicon oxide or silicon nitride. The technology used is widely researched and developed. In addition, research and development on ferroelectric films having spontaneous polarization characteristics as capacitive insulating films have been conducted with the aim of putting nonvolatile RAMs that can operate at high speeds in writing and reading operations at low speeds unprecedented. It is actively performed.

  Among semiconductor memory devices using a high dielectric constant film or a ferroelectric film as a capacitor insulating film, a three-dimensional memory cell is used in an ultra-highly integrated semiconductor memory device instead of a conventional stacked memory cell. .

  When forming a three-dimensional memory cell, it is necessary to form a capacitor insulating film made of a ferroelectric film on a lower electrode having a step, so that a capacitor insulating film is formed using a CVD method having excellent step coverage. There is a strong demand for practical application of the method. In particular, as a method for forming a capacitive insulating film made of a ferroelectric film using a metal organic chemical vapor deposition method (hereinafter referred to as MOCVD method), a bismuth organometallic compound having a bismuth-oxygen bond is used as a raw material, and the MOCVD method is used. There is a method of forming bismuth oxide (for example, see Patent Document 1).

  Hereinafter, a conventional method of forming a ferroelectric film will be described with reference to FIG.

  As shown in FIG. 19, the tributoxy bismuth with which the stainless steel 1st raw material container 101 provided in the 1st thermostat 100 was filled is heated at 80-110 degreeC. After introducing argon gas having a flow rate of 50 to 100 mL / min (standard state) into the first raw material container 101, tributoxybismuth is sublimated under heating and reduced pressure. Thereafter, the sublimated tributoxy bismuth is introduced into the pipe 102 maintained at about 110 ° C. and transferred to the MOCVD chamber 103.

On the other hand, tantalum pentaethoxide [Ta (OC ₂ H ₅ ) ₅ ] filled in the second raw material container 105 provided in the second thermostat 104 is heated to 120 ° C., and the flow rate is 50 to 100 mL / Bubbling with min (standard state) argon gas. Thereafter, the vaporized tantalum pentaethoxide [Ta (OC ₂ H ₅ ) ₅ ] is introduced into the stainless steel pipe 106 heated to 130 ° C. and conveyed to the MOCVD reaction chamber 103. Further, strontium dipivaloylmethane tetraethylenepentamine (C ₃₈ H ₈₄ O ₄ N ₁₀ Sr) filled in a third raw material container (not shown). Is heated to 150 ° C. and bubbled with argon gas having a flow rate of 50 to 100 mL / min (standard state). Vaporized strontium DPM tetraethylenepentamine is introduced into a stainless steel pipe (not shown) heated to 160 ° C. and conveyed to the MOCVD reaction chamber 103.

The MOCVD reaction chamber 103 is provided with a substrate stage 108 having a substrate 107 made of platinum (Pt) on its upper surface. On the substrate 107 held at 400 to 800 ° C., preferably 450 to 700 ° C., oxygen Along with the gas and argon gas for dilution, the three source gases, tributoxy bismuth, tantalum pentaethoxide [Ta (OC ₂ H ₅ ) ₅ ] and strontium dipivaloylmethane tetraethylenepentamine (C ₃₈ H ₈₄ O ₄ N ₁₀ Sr) Are simultaneously introduced into the surface of the substrate 107, whereby a ferroelectric film made of an insulating oxide made of Bi, Sr, and Ta is formed on the surface of the substrate 107.

In order to obtain a ferroelectric film having a desired composition ratio (Bi: Sr: Ta = 2: 1: 2), the flow rate of argon gas introduced into the first to third raw material containers or the first to first The supply temperature of each source gas to the MOCVD reaction chamber 103 may be controlled by adjusting the heating temperature of the three raw material containers. Thereby, a ferroelectric film made of an insulating oxide represented by SrBi ₂ Ta ₂ O ₉ can be formed.
JP 09-142844 (5th page, 27th paragraph)

  As a result of various investigations on the above-described conventional example, a ferroelectric capacitor element having a capacitor insulating film made of a ferroelectric film can be obtained only by adjusting the flow rate of argon gas or the heating temperature of each source gas. It was found that it was difficult to control the composition ratio of the ferroelectric film to a desired composition ratio while realizing excellent step coverage of the ferroelectric film in the electrode.

That is, the flow rate of the argon gas or the heating temperature of each source gas is adjusted so that the composition ratio of the ferroelectric film made of the SBT film is, for example, Sr: Bi: Ta: O = 1: 2: 2: 9. At the same time, by adjusting the mixing ratio of each source gas introduced into the MOCVD chamber 103, a ferroelectric film represented by SrBi ₂ Ta ₂ O ₉ having a desired composition ratio could be realized.

  However, since each source gas is sufficiently supplied to the MOCVD reaction chamber 103 so that the composition ratio of the ferroelectric film is Sr: Bi: Ta: O = 1: 2: 2: 9, the MOCVD reaction chamber Since the chemical reaction in 103 proceeds at a gas supply rate-determined rate, there arises a problem that a ferroelectric film having excellent step coverage with respect to the electrode cannot be formed. In particular, in the case of a capacitive insulating film used in a three-dimensional ferroelectric capacitor element in which an ultrafine pattern necessary for high integration is formed, the step coverage of the ferroelectric film on the electrode is sufficient. Therefore, a problem has been found that desired polarization characteristics cannot be obtained.

  On the other hand, by adjusting the flow rate of the argon gas or the heating temperature of the source gas, the chemical reaction in the MOCVD reaction chamber 103 proceeds at the gas reaction rate to form a ferroelectric film made of an SBT (SrBiTa) film. In contrast, a ferroelectric film having excellent step coverage could be realized. Therefore, the argon gas flow rate or the heating temperature of each source gas is finely adjusted so that a ferroelectric film made of an SBT film having a desired composition ratio can be formed while a chemical reaction proceeds at a gas reaction rate-determining rate. Then, a ferroelectric film was formed. However, the composition ratio of the ferroelectric film made of the formed SBT film hardly changed, and desired polarization characteristics could not be obtained.

  In view of the above, an object of the present invention is to improve the step coverage of a ferroelectric film. Another object of the present invention is to improve the step coverage of the ferroelectric film and simultaneously control the composition ratio of the ferroelectric film to a desired composition ratio.

  In order to solve the above-mentioned problem, a first ferroelectric film forming method according to the present invention is formed on a substrate and has a concave or convex portion or is formed on a convex electrode surface. A method of forming a ferroelectric film made of an insulating metal oxide, comprising a source gas in a chamber, each of which introduces a plurality of types of source gases each containing an organometallic compound, and a plurality of types of sources A ferroelectric film is deposited on the surface of the electrode by chemically reacting the main components of the gas at a reaction rate.

  According to the first method for forming a ferroelectric film according to the present invention, the chemical reaction proceeds at a rate-determining rate of the source gas, so that the chemical reaction between the main components in the plurality of types of source gases proceeds near the surface of the electrode. Therefore, the step coverage of the ferroelectric film in the electrode is improved.

  In the first method for forming a ferroelectric film according to the present invention, the chemical reaction at the reaction rate is preferably performed under the condition that the substrate temperature during the chemical reaction is 470 ° C. or lower.

  In this way, by setting the substrate temperature to 470 ° C. or lower, the chemical reaction proceeds at the rate-determining rate of the source gas, so the chemical reaction between the main components in the plurality of types of source gases proceeds near the surface of the electrode. The step coverage of the ferroelectric film in the electrode is improved.

In the first method for forming a ferroelectric film according to the present invention, it is preferable that the reaction-controlled chemical reaction is performed under the condition that the chamber pressure during the chemical reaction is 6.99 × 10 ² Pa or less.

Thus, by setting the chamber pressure to 6.99 × 10 ² Pa or less, the average free distance of the molecules increases, the diffusion coefficient of the source gas increases, and the chemical reaction proceeds at the reaction rate of the source gas. Therefore, the chemical reaction between the main components in the plurality of types of source gases proceeds near the surface of the electrode, so that the step coverage of the ferroelectric film in the electrode is improved.

  The second method for forming a ferroelectric film according to the present invention is formed on a substrate, and is formed of an insulating metal oxide on a surface of an electrode having a concave portion or a convex portion or formed in a convex shape. A method of forming a ferroelectric film, which comprises a source gas in a chamber, each of which introduces a plurality of types of source gases each containing an organometallic compound, It is preferable to deposit a ferroelectric film on the surface of the electrode by performing a chemical reaction under a growth condition in which the growth in the horizontal direction is dominant with respect to the surface.

  According to the second method for forming a ferroelectric film, since the chemical reaction proceeds in the horizontal growth dominant region, the rate at which the ferroelectric film grows in the horizontal direction rather than the vertical direction in the chamber increases. The step coverage of the ferroelectric film is improved.

  In the second method for forming a ferroelectric film according to the present invention, the chemical reaction is preferably performed so that the growth rate of the ferroelectric film during the chemical reaction is 7 nm or less per minute.

  In this way, by depositing the ferroelectric film on the surface of the electrode at a growth rate of 7 nm / min or less, the chemical reaction proceeds in the horizontal growth dominant region, so that the ferroelectric film in the chamber extends from the vertical direction. Since the rate of growth in the horizontal direction also increases, the step coverage of the ferroelectric film in the electrode is improved.

  The third method for forming a ferroelectric film according to the present invention is formed on a substrate, and is formed of an insulating metal oxide on a surface of an electrode having a concave portion or a convex portion or formed in a convex shape. A method of forming a ferroelectric film, which comprises a source gas in a chamber, each of which introduces a plurality of types of source gases containing an organometallic compound, and a chemical reaction between the main components of a plurality of types of source gases A step of forming an intermediate having local fluidity on the surface of the electrode, and a step of depositing a ferroelectric film on the surface of the electrode by chemically reacting the intermediate. And

  According to the third method for forming a ferroelectric film according to the present invention, the method includes the step of forming an intermediate having local fluidity in the course of a chemical reaction between main components in a plurality of types of source gases. The step coverage of the ferroelectric film is improved.

In the first to third ferroelectric film forming methods according to the present invention, the source gases are Sr [Ta (OC ₂ H ₅ ) ₅ (OC ₂ H ₄ OCH ₃ )] ₂ , Bi [OC (CH ₃ ) ₂ (CH ₂ OCH ₃ )] ₃ , Ta (OC ₂ H ₅ ) ₅ , Nb (OC ₂ H ₅ ) ₅ , La [OC (CH ₃ ) ₂ (CH ₂ OCH ₃ )] ₃ , La (OC ₂ It is preferable to include a plurality of types of source gases selected from source gases consisting of H ₅ ) ₄ , Ti (OC ₂ H ₅ ) ₄ and Ti [OC (CH ₃ ) ₂ (CH ₂ OCH ₃ )] _3. .

  In this case, since the organometallic solution is used as the plurality of types of source gases, the step coverage of the ferroelectric film in the electrode is further improved.

In the first to the third method of forming the ferroelectric film according to the present invention, the raw material gas, Ta (OC ₂ H ₅₎ consisting of ₅ first source gas and the _{Sr [Ta (OC 2 H 5} ) 5 ( OC ₂ H ₄ OCH ₃ )] ₂ is preferable as a mixed gas with the second source gas.

  In this case, when the mixing ratio of the first source gas to the second source gas is increased, only the composition ratio of the second source gas changes when exceeding the predetermined mixing ratio. The composition ratio of Sr (metal element constituting the A site) contained in the second source gas in the dielectric film can be controlled. This further enables control of the composition ratio of Bi and Ta in the ferroelectric film.

  In this case, the mixed gas may be a mixture of the first source gas and the second source gas at a desired mixing ratio before introduction into the chamber, or the first source gas and the second source gas. The gas may be mixed in a desired mixing ratio after introduction into the chamber.

  A fourth method for forming a ferroelectric film according to the present invention is a method for forming a ferroelectric film, which is an insulating metal oxide, on the surface of an electrode having a concave or convex portion or having a convex shape. A first step of determining a substrate temperature and a chamber pressure, which are growth conditions of the ferroelectric film, so that the step coverage of the ferroelectric film in the electrode is equal to or higher than a desired step coverage; By changing the mixing ratio of the first source gas composed of a plurality of types of source gases each containing an organometallic compound at the substrate temperature and chamber pressure determined in step 1, the ferroelectric material A second step of adjusting the composition ratio of the metal element constituting the A site in the film, and the introduction of the metal element constituting the A site into the chamber under a condition where the composition ratio of the metal element constituting the A site is constant. Including multiple The composition ratio of the ferroelectric film is determined by adjusting the composition ratio of the metal elements constituting the B site in the ferroelectric film by changing the mixing ratio of the second source gas composed of the various source gases. A ferroelectric film is deposited on the surface of the electrode based on the third step, the growth conditions determined in the first step, and the composition ratio determined in the second step and the third step. The process is provided.

  According to the fourth method for forming a ferroelectric film according to the present invention, a ferroelectric film having excellent step coverage with respect to an electrode can be formed, and the mixing ratio of source gases composed of a plurality of types of source gases can be increased. By determining by a simple method, a ferroelectric film having a desired composition ratio can be formed.

  In the fourth method for forming a ferroelectric film, the first source gas is a mixed gas of a source gas containing Bi and a source gas containing Sr, and the second source gas is a source gas containing Ti. It is preferably made of a mixed gas with a source gas containing Sr.

  In this case, when the mixing ratio of the source gas containing Ta in the first source gas to the source gas containing Sr is changed, the composition ratio of Bi in the ferroelectric film is almost constant. When the mixing ratio is exceeded, only the composition ratio of Sr (metal element constituting the A site) in the ferroelectric film changes, and the mixing ratio of the source gas containing Bi in the second source gas to the source gas containing Sr is changed. When changed, the composition ratio of Bi (metal element constituting the B site) in the ferroelectric film changes linearly, so that the composition ratio of the ferroelectric film can be controlled to a desired composition ratio.

  In the fourth method for forming a ferroelectric film, the first source gas is a mixed gas of a source gas containing Ti and a source gas containing La, and the second source gas is a source gas containing Bi. It is preferably made of a mixed gas with a source gas containing La.

  In this case, when the mixing ratio of the source gas containing Ti in the first source gas to the source gas containing La is changed, there is a composition ratio of Bi (metal element constituting the A site) in the ferroelectric film. When the mixture ratio is changed linearly after the linear change, and the source gas containing Bi in the second source gas is changed to the source gas containing La, the composition ratio of Bi in the ferroelectric film is changed. In spite of being almost constant, when a certain mixing ratio is exceeded, only the composition ratio of La (metal element constituting the B site) in the ferroelectric film changes, and the composition ratio of the ferroelectric film is set to a desired composition. The ratio can be controlled.

  The fifth method for forming a ferroelectric film according to the present invention is a method for forming a ferroelectric film that is an insulating metal oxide on the surface of an electrode that has a concave or convex portion or is formed in a convex shape. A first step of determining a substrate temperature and a chamber pressure, which are growth conditions of the ferroelectric film, so that the step coverage of the ferroelectric film in the electrode is equal to or higher than a desired step coverage; By changing the mixing ratio of the first source gas composed of a plurality of types of source gases each containing an organometallic compound at the substrate temperature and chamber pressure determined in step 1, the ferroelectric material A second step of adjusting the composition ratio of the metal element constituting the B site in the film, and introducing into the chamber under a condition in which the composition ratio of the metal element constituting the B site is constant; Including multiple The composition ratio of the ferroelectric film is determined by adjusting the composition ratio of the metal element constituting the A site in the ferroelectric film by changing the mixing ratio of the second source gas composed of the various source gases. A ferroelectric film is deposited on the surface of the electrode based on the third step, the growth conditions determined in the first step, and the composition ratio determined in the second step and the third step. The process is provided.

  According to the fifth method for forming a ferroelectric film according to the present invention, a ferroelectric film having excellent step coverage with respect to an electrode can be formed, and the mixing ratio of source gases composed of a plurality of types of source gases can be increased. By determining by a simple method, a ferroelectric film having a desired composition ratio can be formed.

  In the fifth method of forming a ferroelectric film according to the present invention, the first source gas is a mixed gas of a source gas containing Bi and a source gas containing Sr, and the second source gas is Ta. It is preferably made of a mixed gas of a source gas containing and a source gas containing Sr.

  Thus, when the mixing ratio of the source gas containing Bi in the first source gas to the source gas containing Sr is changed, the composition ratio of Bi (metal constituting the B site) in the ferroelectric film changes linearly. When the mixing ratio of the source gas containing Ta in the second source gas to the source gas containing Sr is changed, a certain mixing ratio is obtained even though the composition ratio of Bi in the ferroelectric film is substantially constant. Since the composition ratio of Sr (metal element constituting the A site) in the ferroelectric film only changes, the composition ratio of the ferroelectric film can be controlled to a desired composition ratio.

  In the fifth method of forming a ferroelectric film according to the present invention, the first source gas is composed of a mixed gas of a source gas containing Ti and a source gas containing La, and the second source gas contains Bi. It is preferable to consist of a mixed gas of a source gas containing and a source gas containing La.

  In this case, when the mixing ratio of the source gas containing Ti in the first source gas to the source gas containing La is changed, the composition ratio of Bi in the ferroelectric film is almost constant. When the mixing ratio is exceeded, only the composition ratio of La (metal element constituting the B site) in the ferroelectric film changes, and the mixing ratio of the source gas containing Bi in the second source gas to the source gas containing La is changed. If changed, the composition ratio of Bi (metal element constituting the A site) in the ferroelectric film changes linearly until a certain mixing ratio and then changes nonlinearly. Therefore, the composition ratio of the ferroelectric film is changed to a desired composition. The ratio can be controlled.

  A semiconductor device according to the present invention is a semiconductor device including an electrode formed on a substrate and having a concave portion or a convex portion on a surface, and a ferroelectric film formed on the electrode. The step coverage of the ferroelectric film at the step existing in the portion is 80% or more, and the variation in the composition ratio of the metal elements constituting the ferroelectric film is ± 15% or less.

  According to the semiconductor device of the present invention, it is possible to realize a semiconductor device having excellent step coverage and a desired composition ratio.

  In the semiconductor device according to the present invention, the metal element constituting the ferroelectric film contains Sr, Bi, and Ta. When the Ta composition ratio is normalized by 2, the Sr composition ratio is 0.75. It is preferable that the value is in the range of 1.00 or less and the Bi composition ratio is 2.00 or more and 2.50 or less.

  Thus, a semiconductor device provided with a ferroelectric film that achieves a desired composition ratio can be obtained.

  In the semiconductor device according to the present invention, the metal element constituting the ferroelectric film contains Bi, La, and Ti. When the composition ratio of Ti is normalized by 3, the composition ratio of La is 0.5. It is preferable that the value is in the range of 1.0 or less and the Bi composition ratio is 3.0 or more and 3.5 or less.

  Thus, a semiconductor device provided with a ferroelectric film that achieves a desired composition ratio can be obtained.

  According to the semiconductor device of the present invention, it is possible to realize a semiconductor device having excellent step coverage and a desired composition ratio.

  First, an example of the structure of a ferroelectric capacitor having a ferroelectric film formed by the method of forming a ferroelectric film according to each embodiment of the present invention is shown in FIGS. 1 (a) to 1 (c). The description will be given with reference.

  As shown in FIG. 1A, an impurity diffusion layer 2 serving as a source region or a drain region is formed on a surface portion of a semiconductor substrate 1, and a gate electrode 3 is formed on the semiconductor substrate 1 via a gate insulating film. The field effect transistor 4 is formed by the impurity diffusion layer 2 and the gate electrode 3.

  A protective insulating film 5 is deposited on the semiconductor substrate 1 so as to cover the field effect transistor 4, and a contact plug 6 made of tungsten having a lower end connected to the impurity diffusion layer 2 is formed on the protective insulating film 5. Embedded.

  On the protective insulating film 5, an interlayer insulating film 8 having a concave opening 7 exposing the upper end of the contact plug 6 is formed. In the concave opening 7, in order from the bottom, the first electrode 9 whose lower surface is connected to the upper end of the contact plug 6, and the ferroelectric film 10 deposited by the ferroelectric film forming method according to each embodiment. A capacitor insulating film and the second electrode 11 are formed.

  As described above, in the ferroelectric capacitor shown in FIG. 1A, the case where the ferroelectric film 10 is formed on the surface of the first electrode 9 having the recess has been described. For example, FIG. As shown in FIG. 1B, the ferroelectric film 10 may be formed on the surface of the first electrode 9 having a convex portion, or as shown in FIG. The ferroelectric film 10 may be formed on the surface of the formed first electrode 9.

  Note that the step coverage used in each of the following embodiments refers to the thickness a at the top of the ferroelectric film 10 and the thickness b at the top of the ferroelectric film 10 as shown in FIG. Specifically, it is a value represented by step coverage = a / b × 100 (%).

(First embodiment)
In the first embodiment, the first and second ferroelectric film forming apparatuses used in the ferroelectric film forming methods according to second to seventh embodiments to be described later will be described with reference to FIGS. explain.

  First, the first ferroelectric film forming apparatus will be described with reference to FIG.

  As shown in FIG. 2, a susceptor 22 on which a semiconductor substrate 21 is mounted is installed in the chamber 20. Further, the chamber 20 is provided with a gas introduction unit 23 for introducing a source gas composed of a plurality of types of source gases adjusted to a desired mixing ratio together with a carrier gas such as oxygen gas via a mass flow controller (not shown). In addition, a gas discharge passage 24 that has a pressure control valve 25 and a pump 26 and discharges gas in the chamber 20 is provided.

  Next, a second ferroelectric film forming apparatus will be described with reference to FIG.

  As shown in FIG. 3, a susceptor 32 on which a semiconductor substrate 31 is mounted is installed in the chamber 30. Also, the chamber 30 has a first gas introduction part 33 for introducing a first source gas together with a carrier gas such as oxygen gas via a mass flow controller (not shown), and a second source together with a carrier gas such as oxygen gas. A second gas introduction unit 34 for introducing gas via a mass flow controller (not shown) or the like is provided. The carrier gas and the first and second source gases introduced into the chamber 30 are dispersed from the gas nozzle 35 and flow out. Further, the chamber 30 is provided with a gas discharge path 38 that has a pressure control valve 36 and a pump 37 and discharges the gas in the chamber 30.

  Further, in the first ferroelectric film forming apparatus, the ferroelectric film 10 is formed using a source gas composed of a plurality of types of source gases mixed at a desired mixing ratio before being introduced into the chamber 20. In the second ferroelectric film forming apparatus, the ferroelectric film is formed by using the source gas composed of the first and second source gases mixed at a desired mixing ratio after being introduced into the chamber 30. The ferroelectric film forming method according to the second to seventh embodiments is realized by using any one of the first and second ferroelectric film forming apparatuses. can do.

Further, the raw material gas composed of a plurality of types of source _{gas, Sr [Ta (OC 2 H} 5) 5 (OC 2 H 4 OCH 3)] 2, Bi [OC (CH 3) 2 (CH 2 OCH 3)] 3 , Ta (OC ₂ H ₅ ) ₅ , Nb (OC ₂ H ₅ ) ₅ , La [OC (CH ₃ ) ₂ (CH ₂ OCH ₃ )] ₃ , La (OC ₂ H ₅ ) ₄ , Ti (OC ₂ H ₅ ) It is preferable that a plurality of types of source gases selected from source gases consisting of ₄ and Ti [OC (CH ₃ ) ₂ (CH ₂ OCH ₃ )] ₃ are included. In this case, since the organometallic solution is used as a plurality of types of source gases, the step coverage of the ferroelectric film 10 in the first electrode 9 is further improved as will be described later.

The source gas composed of a plurality of types of source gas includes a source gas composed of Ta (OC ₂ H ₅ ) ₅ and a source gas composed of Sr [Ta (OC ₂ H ₅ ) ₅ (OC ₂ H ₄ OCH ₃ )] _2. As will be described later, the composition ratio of Sr, Bi and Ta in the ferroelectric film 10 can be easily controlled.

  The first and second ferroelectric film forming apparatuses are not limited to the apparatus having the structure shown in FIGS. Further, for example, it goes without saying that the number of gas introduction paths through which the carrier gas, source gas or source gas is introduced into the chambers 20 and 30 is not limited to the number shown in the figure.

(Second Embodiment)
Hereinafter, when the ferroelectric film 10 is deposited on the surface of the first electrode 9 by the MOCVD method, the step coverage of the ferroelectric film 10 in the first electrode 9 is improved while the ferroelectric film 10 A description will be given of the results of studies conducted as to whether there is a parameter that can control the composition ratio to a desired composition ratio.

  As a result of various studies, the step coverage of the ferroelectric film 10 in the first electrode 9 is formed under the condition that the temperature of the semiconductor substrate 1 (hereinafter referred to as the substrate temperature) is lowered. In this case, it was found that the step coverage of the ferroelectric film 10 in the first electrode 9 is improved.

  A method for forming a ferroelectric film according to the second embodiment of the present invention will be described below with reference to FIGS.

  A plurality of types of source gases constituting the source gas are introduced into the chambers 20 and 30 (see FIGS. 2 and 3), and the main types of the plurality of types of source gases are selected under some conditions where the substrate temperature is 470 ° C. or lower. The ferroelectric film 10 was formed on the surface of the first electrode 9 by chemically reacting the components.

  The relationship between the substrate temperature and the step coverage of the ferroelectric film 10 with respect to the first electrode 9 will be described with reference to FIG.

  As shown in FIG. 4, when the ferroelectric film 10 is formed under the respective conditions where the substrate temperatures are 470 ° C., 400 ° C., and 360 ° C., the first It has been found that the step coverage of the ferroelectric film 10 with respect to the electrode 9 is 80% or more. Therefore, as one of the growth conditions for the ferroelectric film 10, if the substrate temperature is 470 ° C. or lower, the step coverage of the ferroelectric film 10 in the first electrode 9 is improved.

  On the other hand, although not disclosed in the drawings, if the ferroelectric film 10 is formed under a condition where the substrate temperature is 500 ° C. or higher, the chemical reaction proceeds at a rate limited by the supply of the source gas, thereby the first electrode 9. Since the step coverage of the ferroelectric film 10 is 20 to 30%, the ferroelectric film 10 having good step coverage with respect to the first electrode 9 cannot be formed.

  Here, a mechanism for improving the step coverage of the ferroelectric film 10 formed under the condition that the substrate temperature is 470 ° C. or less will be described.

  Since the chemical reaction proceeds at a rate-determining rate of the source gas by lowering the substrate temperature, the chemical reaction between the main components in the plurality of types of source gases proceeds near the surface of the first electrode 9 and the chemical reaction The time during which the intermediate fluid having a local fluidity formed in the process exists on the surface of the ferroelectric film 10 becomes longer. Thereby, the step coverage of the ferroelectric film 10 in the first electrode 9 is improved.

Further, the raw material gas composed of a plurality of types of source _{gas, Sr [Ta (OC 2 H} 5) 5 (OC 2 H 4 OCH 3)] 2, Bi [OC (CH 3) 2 (CH 2 OCH 3)] 3 , Ta (OC ₂ H ₅ ) ₅ , Nb (OC ₂ H ₅ ) ₅ , La [OC (CH ₃ ) ₂ (CH ₂ OCH ₃ )] ₃ , La (OC ₂ H ₅ ) ₄ , Ti (OC ₂ H ₅ ) It preferably contains a plurality of types of source gases selected from source gases consisting of ₄ and Ti [OC (CH ₃ ) ₂ (CH ₂ OCH ₃ )] ₃ . As described above, since the organometallic solution is used as the plurality of types of source gases, the step coverage of the ferroelectric film 10 in the first electrode 9 is further improved.

A source gas composed of a plurality of types of source gas is composed of a source gas composed of Ta (OC ₂ H ₅ ) ₅ and a source gas composed of Sr [Ta (OC ₂ H ₅ ) ₅ (OC ₂ H ₄ OCH ₃ )] _2. As will be described later, the composition ratio of Sr, Bi, and Ta in the ferroelectric film 10 can be easily controlled.

  As described above, according to the second embodiment, since the ferroelectric film 10 is formed under the condition that the substrate temperature is 470 ° C. or less, the chemical reaction proceeds at the rate-determining rate of the source gas. A chemical reaction between the main components of the source gas proceeds near the surface of the first electrode 9, and an intermediate having local fluidity formed in the course of the chemical reaction is formed on the surface of the ferroelectric film 10. Since the existing time becomes longer, the step coverage of the ferroelectric film 10 in the first electrode 9 is improved.

The ferroelectric film formed in the second embodiment is a ferroelectric film made of SBT (SrBi ₂ Ta ₂ O ₉ ) film, SrBiTaNb film or BiLaTi film and other Bi-based layered perovskite ferroelectrics. A ferroelectric film made of a body film or a PbZrTi film is conceivable.

(Third embodiment)
Hereinafter, when the ferroelectric film 10 is deposited on the first electrode 9 by the MOCVD method, the step coverage of the ferroelectric film 10 in the first electrode 9 is improved, and the ferroelectric film 10 As a parameter that can control the composition ratio to a desired composition ratio, a description will be given of the results of studies conducted on whether the composition ratio exists other than the above-described substrate temperature.

  As a result of further examination, the step coverage of the ferroelectric film 10 in the first electrode 9 is determined when the ferroelectric film 10 is formed under a condition where the pressure in the chamber (hereinafter referred to as chamber pressure) is reduced. Furthermore, it was further found that the step coverage of the ferroelectric film 10 in the first electrode 9 is improved.

  Hereinafter, a method of forming a ferroelectric film according to the third embodiment of the present invention will be described with reference to FIGS.

A plurality of types of source gases constituting the source gas are introduced into the chambers 20 and 30 (see FIG. 2 and FIG. 3), and a plurality of types are provided under several conditions where the chamber pressure is 6.99 × 10 ² Pa or less. The ferroelectric film 10 was formed on the surface of the first electrode 9 by chemically reacting the main components of the source gas.

  The relationship between the chamber pressure in this case and the step coverage of the ferroelectric film 10 with respect to the first electrode 9 will be described with reference to FIG.

As shown in FIG. 5, when the ferroelectric film 10 is formed under the respective conditions where the chamber pressure is 6.99 × 10 ² Pa, 5.32 × 10 ² Pa, and 1.33 × 10 ² Pa. In any case, it was found that the step coverage of the ferroelectric film 10 with respect to the first electrode 9 is 80% or more. Accordingly, as one of the growth conditions for the ferroelectric film 10, if the chamber pressure is 6.99 × 10 ² Pa or less, the step coverage of the ferroelectric film 10 in the first electrode 9 is improved.

On the other hand, although not disclosed in the drawings, if the ferroelectric film 10 is formed under a condition where the chamber pressure is 1.33 × 10 ³ Pa or more, the chemical reaction proceeds at the rate of supply of the source gas and the molecular Since the average free distance is shortened, the film formation proceeds in the upper part of the first electrode 9 rather than the lower part. For this reason, since the step coverage of the ferroelectric film 10 with respect to the first electrode 9 is 20 to 30%, the ferroelectric film 10 having good step coverage with respect to the first electrode 9 is formed. It is not possible.

Here, a mechanism for improving the step coverage of the ferroelectric film 10 formed under the condition where the chamber pressure is 6.99 × 10 ² Pa or less will be described.

  Lowering the chamber pressure increases the average free distance of molecules, increases the diffusion coefficient of multiple types of source gas introduced into the chamber, and the chemical reaction proceeds at the rate-determining rate of the source gas. The chemical reaction between the main components in the source gas proceeds near the surface of the first electrode 9. Thereby, the step coverage of the ferroelectric film 10 in the first electrode 9 is improved.

Further, the raw material gas composed of a plurality of types of source _{gas, Sr [Ta (OC 2 H} 5) 5 (OC 2 H 4 OCH 3)] 2, Bi [OC (CH 3) 2 (CH 2 OCH 3)] 3 , Ta (OC ₂ H ₅ ) ₅ , Nb (OC ₂ H ₅ ) ₅ , La [OC (CH ₃ ) ₂ (CH ₂ OCH ₃ )] ₃ , La (OC ₂ H ₅ ) ₄ , Ti (OC ₂ H ₅ ) It preferably contains a plurality of types of source gases selected from source gases consisting of ₄ and Ti [OC (CH ₃ ) ₂ (CH ₂ OCH ₃ )] ₃ . As described above, since the organometallic solution is used as the plurality of types of source gases, the step coverage of the ferroelectric film 10 in the first electrode 9 is further improved.

A source gas composed of a plurality of types of source gas is composed of a source gas composed of Ta (OC ₂ H ₅ ) ₅ and a source gas composed of Sr [Ta (OC ₂ H ₅ ) ₅ (OC ₂ H ₄ OCH ₃ )] _2. As will be described later, the composition ratio of Sr, Bi, and Ta in the ferroelectric film can be easily controlled.

As described above, according to the third embodiment, by forming the ferroelectric film 10 under the condition that the chamber pressure is 6.99 × 10 ² Pa or less, the average free distance of molecules is increased and the inside of the chamber is increased. As the diffusion coefficients of the plurality of types of source gases introduced into the gas increase and the chemical reaction proceeds at the rate-determining rate of the source gas, the chemical reaction between the main components in the plurality of types of source gases is caused to occur on the surface of the first electrode 9. Since it proceeds in the vicinity, the step coverage of the ferroelectric film 10 in the first electrode 9 is improved.

The ferroelectric film formed in the third embodiment is a ferroelectric film made of SBT (SrBi ₂ Ta ₂ O ₉ ) film, another Bi-based layered pebuloskite type ferroelectric such as a SrBiTaNb film or a BiLaTi film. A ferroelectric film made of a body film or a PbZrTi film is conceivable.

(Fourth embodiment)
Hereinafter, when the ferroelectric film 10 is deposited on the first electrode 9 by the MOCVD method, the step coverage of the ferroelectric film 10 in the first electrode 9 is improved, and the ferroelectric film 10 A description will be given of the results of further studies on whether there are parameters other than the aforementioned substrate temperature and chamber pressure as parameters that can control the composition ratio to a desired composition ratio.

  As a result of further examination, the step coverage of the ferroelectric film 10 in the first electrode 9 is determined when the ferroelectric film 10 is formed under the condition that the growth rate of the ferroelectric film 10 is lowered. Further, it has been found that the step coverage of the ferroelectric film 10 in the first electrode 9 is improved.

  Hereinafter, a method of forming a ferroelectric film according to the fourth embodiment of the present invention will be described with reference to FIGS.

  A plurality of types of source gases constituting the source gas are introduced into the chambers 20 and 30 (see FIGS. 2 and 3), and a plurality of types of source gases are formed under several conditions with a growth rate of 7 nm / min or less. The ferroelectric film 10 was formed on the surface of the first electrode 9 by chemically reacting the main components.

  The relationship between the growth rate in this case and the step coverage of the ferroelectric film 10 with respect to the first electrode 9 will be described with reference to FIG.

  As shown in FIG. 6, when the ferroelectric film is formed under the respective conditions of the growth rates of 5 nm / min, 7 nm / min, and 10.5 nm / min or less, the growth rate is 7 nm / min or less. It was found that the step coverage of the ferroelectric film 10 with respect to one electrode 9 was 80% or more. Accordingly, as one of the growth conditions for the ferroelectric film 10, if the growth rate is 7 nm / min or less, the step coverage of the ferroelectric film 10 in the first electrode 9 is improved. In addition, in order to implement | achieve the growth rate of 7 nm / min or less, it can implement | achieve by adjusting a substrate temperature, a chamber pressure, the flow rate ratio of source gas, etc.

  On the other hand, when the growth rate increases beyond the vicinity of 7.5 nm / min, the step coverage of the ferroelectric film 10 with respect to the first electrode 9 rapidly decreases, so that a good step with respect to the first electrode 9 is obtained. The ferroelectric film 10 having a covering property cannot be formed.

  Here, a mechanism for improving the step coverage of the ferroelectric film 10 formed under a condition where the growth rate is 7 nm / min or less will be described.

  As the growth rate is lowered, the chemical reaction proceeds in the horizontal growth dominant region, so that the rate at which the ferroelectric film 10 grows in the horizontal direction rather than the vertical direction in the chamber increases. Thereby, the step coverage of the ferroelectric film 10 in the first electrode 9 is improved.

Further, the raw material gas composed of a plurality of types of source _{gas, Sr [Ta (OC 2 H} 5) 5 (OC 2 H 4 OCH 3)] 2, Bi [OC (CH 3) 2 (CH 2 OCH 3)] 3 , Ta (OC ₂ H ₅ ) ₅ , Nb (OC ₂ H ₅ ) ₅ , La [OC (CH ₃ ) ₂ (CH ₂ OCH ₃ )] ₃ , La (OC ₂ H ₅ ) ₄ , Ti (OC ₂ H ₅ ) It preferably contains a plurality of types of source gases selected from source gases consisting of ₄ and Ti [OC (CH ₃ ) ₂ (CH ₂ OCH ₃ )] ₃ . As described above, since the organometallic solution is used as the plurality of types of source gases, the step coverage of the ferroelectric film 10 in the first electrode 9 is further improved.

A source gas composed of a plurality of types of source gas is composed of a source gas composed of Ta (OC ₂ H ₅ ) ₅ and a source gas composed of Sr [Ta (OC ₂ H ₅ ) ₅ (OC ₂ H ₄ OCH ₃ )] _2. As will be described later, the composition ratio of Sr, Bi, and Ta in the ferroelectric film can be easily controlled.

  As described above, according to the fourth embodiment, since the ferroelectric film 19 is formed under the condition where the growth rate is 7 nm / min or less, the chemical reaction proceeds in the horizontal growth dominant region. The rate at which the ferroelectric film 10 grows in the horizontal direction rather than in the vertical direction increases. Thereby, the step coverage of the ferroelectric film 10 in the first electrode 9 is improved.

The ferroelectric film formed in the fourth embodiment is a ferroelectric film made of SBT (SrBi ₂ Ta ₂ O ₉ ) film, another Bi-based layered pebuloskite type ferroelectric such as SrBiTaNb film or BiLaTi film. A ferroelectric film made of a body film or a PbZrTi film is conceivable.

(Fifth embodiment)
A method for forming a ferroelectric film according to the fifth embodiment of the present invention will be described below with reference to FIG.

  As shown in FIG. 7, first, in step SA1, the substrate temperature and the chamber pressure are determined as growth conditions for the ferroelectric film 10. Next, in Step SA2, when the ferroelectric film 10 is formed on the surface of the first electrode 9 under the substrate temperature and chamber pressure determined in Step SA1, the ferroelectric film 10 for the first electrode 9 is formed. It is determined whether or not the step coverage of the desired step coverage is achieved. When the step coverage of the ferroelectric film 10 with respect to the first electrode 9 realizes a desired step coverage, the process proceeds to step SA3, while the step of the ferroelectric film 10 with respect to the first electrode 9 If the coverage does not realize the desired step coverage, the process returns to step SA1 and the above-described processing is repeated.

  Next, in step SA3, the mixing ratio of the first source gas to the second source gas in the first source gas which is a mixed gas of the first source gas containing Ta and the second source gas containing Sr. Adjust. Next, in step SA4, the first source gas is introduced into the chamber at the mixing ratio adjusted in step SA3, and the surface of the first electrode 9 is strongly applied under the substrate temperature and chamber pressure determined in step SA1. When the dielectric film 10 is formed, it is determined whether or not the composition ratio of Sr (metal element constituting the A site) in the ferroelectric film 10 is within the range of the desired composition ratio. If the Sr composition ratio in the ferroelectric film 10 is within the desired composition ratio range, the process proceeds to step SA5, while the Sr composition ratio in the ferroelectric film 10 is within the desired composition ratio range. If not, the process returns to step SA3 to repeat the above process.

  Here, as described in Steps SA3 and SA4, the experimental results of repeatedly adjusting the mixing ratio of the first source gas to the second source gas will be described with reference to FIG.

  FIG. 8 shows the relationship between the composition ratio of Sr and Bi in the ferroelectric film 10 when Ta is normalized by 2, and the mixing ratio of the first source gas to the second source gas. Yes.

As shown in FIG. 8, when the substrate temperature determined in step SA1 is 350 ° C. and the chamber pressure is 1.33 × 10 ² Pa, the first source gas is mixed with the second source gas. As a result of adjusting the ratio while increasing the ratio, it was found that the composition ratio of Sr in the ferroelectric film 10 sharply decreases from the vicinity of the mixing ratio of the first source gas to the second source gas of 2.5. . That is, when the mixing ratio of the first source gas to the second source gas is increased, the composition ratio of Sr in the ferroelectric film 10 is almost constant although the composition ratio of Bi in the ferroelectric film 10 is substantially constant. Only the ratio was found to change. Therefore, in step SA3, the first source gas is mixed with the second source gas so that the composition ratio of Sr in the ferroelectric film 10 is within the range of the composition ratio that provides the polarization characteristics shown in FIG. The ratio may be adjusted, whereby a desired composition ratio can be obtained as the composition ratio of Sr in the ferroelectric film 10 in step SA4.

  Next, in step SA5, the mixture is composed of a mixed gas of the third source gas containing Bi and the fourth source gas containing Sr under the condition that the composition ratio of Sr obtained in steps SA3 and SA4 is constant. The mixing ratio of the third source gas to the fourth source gas in the second source gas is adjusted. Next, in Step SA6, the second source gas is introduced into the chamber at the mixing ratio adjusted in Step SA5, and the ferroelectric material is applied to the surface of the first electrode 9 under the substrate temperature and chamber pressure determined in Step SA1. When the body film 10 is formed, it is determined whether or not the composition ratio of Bi (the metal element constituting the B site) and the composition ratio of Ta in the ferroelectric film 10 are within the range of the desired composition ratio. When the composition ratio of Bi and Ta in the ferroelectric film 10 is within the range of the desired composition ratio, the series of processes is terminated, while the composition ratio of Bi and Ta is within the range of the desired composition ratio. If not, the process returns to step SA5 to repeat the above process.

  Here, as described in Steps SA5 and SA6, the experimental results of repeatedly adjusting the mixing ratio of the third source gas to the fourth source gas will be described with reference to FIG.

  FIG. 9 shows the relationship between the composition ratio of Bi in the ferroelectric film 10 when Ta is normalized by 2 and the mixing ratio of the third source gas to the fourth source gas.

As shown in FIG. 9, when the substrate temperature determined in step SA1 is 350 ° C. and the chamber pressure is 1.33 × 10 ² Pa, the mixing ratio of the third source gas to the fourth source gas As a result of adjusting while increasing, it was found that the composition ratio of Bi in the ferroelectric film 10 increases linearly. Therefore, in step SA5, the mixing ratio may be adjusted so that the composition ratio of Bi in the ferroelectric film 10 is within the range of the composition ratio at which the polarization characteristics shown in FIG. 9 can be obtained. A desired composition ratio can be obtained as the composition ratio of Bi and the composition ratio of Ta in the ferroelectric film 10.

  Thus, from the experimental results shown in FIGS. 8 and 9, when the mixing ratio of the first source gas to the second source gas is increased, the composition ratio of Sr in the ferroelectric film 10 is linearly increased. It has been found that only the composition ratio of Sr can be changed at a certain mixing ratio or more without changing. The parameters that determine the mixing ratio of the first source gas to the second source gas and the mixing ratio of the third source gas to the fourth source gas are the substrate temperatures in the second to fourth embodiments described above. This parameter is different from the parameters for lowering the temperature, lowering the chamber pressure, and lowering the growth rate. Therefore, the existence of a parameter that can independently control the mixing ratio of the source gases composed of a plurality of types of source gas without affecting the step coverage of the ferroelectric film 10 in the first electrode 9 is observed. As described above, the composition ratio of, for example, Sr, Bi, Ta constituting the ferroelectric film 10 can be controlled to a desired composition ratio as described above.

  Further, by combining the formation conditions of the MOCVD method obtained in the second to fourth embodiments with low temperature, low pressure, low growth rate, etc., step coverage is high and good polarization characteristics are obtained. A ferroelectric BLT film can be formed.

Further, the first source gas described with reference to FIGS. 8 and 9 is preferably made of Ta (OC ₂ H ₅ ) ₅ , and the second source gas is Sr [Ta (OC ₂ H ₅ ) _5. (OC ₂ H ₄ OCH ₃ )] ₂ is preferable.

  Here, as an example, in the case where the ferroelectric film 10 is formed using the first ferroelectric film forming apparatus shown in FIG. 2, the growth of the ferroelectric film 10 obtained by the series of steps described above is performed. As the conditions and the source gas introduced into the chamber 20, the results shown in the following [Table 1] could be obtained.

  Hereinafter, a method for forming the ferroelectric film 10 using the first ferroelectric film forming apparatus under the conditions shown in [Table 1] will be specifically described with reference to FIGS. 2, 10, and 11. explain.

  First, as shown in FIG. 2, the semiconductor substrate 21 is mounted on the susceptor 22 in the chamber 20. The semiconductor substrate 21 is heated by a heater inside the susceptor 22 so that the substrate temperature becomes 350 ° C.

Next, an Sr / Ta mixed gas in which a source gas containing Sr and a source gas containing Ta are mixed at a ratio of 1: 3 is introduced into the chamber 20 at a flow rate of 0.275 mL / min (standard state). A source gas containing Bi is introduced into the chamber 20 at a flow rate of 0.24 mL / min (standard state). Although not shown, the source gas is vaporized using a vaporizer, and the vaporization temperature is 200 ° C. Further, oxygen gas as an oxidant is introduced into the chamber 20 at a flow rate of 1.0 L / min (standard state). Furthermore, the chamber pressure is set to 1.33 × 10 ² Pa. Under such conditions, the ferroelectric film 10 is deposited on the semiconductor substrate 21 by the chemical reaction between the main components of the Sr / Ta mixed gas, the source gas containing Bi, and the oxygen gas. Note that the ferroelectric film 10 is annealed for heat treatment. This annealing is performed, for example, by using an RTA (rapid heat treatment) method under an annealing temperature of 600 [° C.] for 1 minute in an oxygen atmosphere.

  Next, the formation of the ferroelectric film 10 is completed by removing the semiconductor substrate 21 on which the ferroelectric film 10 is formed from the susceptor 22.

  The step coverage and polarization characteristics of the ferroelectric film 10 thus formed will be described with reference to FIGS.

  As shown in FIG. 10, when the step coverage of the ferroelectric film 10 with respect to the first electrode 9 is determined from the SEM image of the ferroelectric film 10 when the aspect ratio is 2.0, the step coverage is obtained. 85% is achieved, and the ferroelectric film 10 having excellent step coverage with respect to the first electrode 9 is realized.

Further, as shown in FIG. 11, according to the evaluation result of the polarization characteristic of the ferroelectric film 10, the polarization characteristic of the ferroelectric film 10 has achieved 15 μC / cm ^2, which is excellent as the ferroelectric film 10. Realized polarization characteristics.

  Further, as a result of analyzing the composition ratio of the ferroelectric film 10 thus formed, the composition ratio of Sr is 15.2%, the composition ratio of Bi is 44.4%, and the composition ratio of Ta is 40.4. Thus, the composition ratio of the ferroelectric film 10 is approximately Sr: Bi: Ta = 1: 2: 2, and a ferroelectric film having a desired composition ratio is realized.

  As described above, according to the fifth embodiment, the ferroelectric film 10 having excellent step coverage with respect to the first electrode 9 can be formed, and the mixing ratio of the source gases composed of a plurality of types of source gases Is determined by a simple method, a ferroelectric film having a desired composition ratio can be formed.

In the fifth embodiment, the case of the ferroelectric film 10 made of an SBT (SrBi ₂ Ta ₂ O ₉ ) film has been described. It may be a ferroelectric film made of a ferroelectric film or a PbZrTi film.

  In the fifth embodiment, the method for forming a ferroelectric film using the first ferroelectric film forming apparatus has been described under the conditions shown in Table 1. However, the second ferroelectric substance has been described. A film forming apparatus may be used.

(Sixth embodiment)
A ferroelectric film forming method according to the sixth embodiment of the present invention will be described below with reference to FIG.

  As shown in FIG. 12, first, in step SB1, the substrate temperature and the chamber pressure are determined as growth conditions for the ferroelectric film 10. Next, in Step SB2, when the ferroelectric film 10 is formed on the surface of the first electrode 9 under the substrate temperature and the chamber pressure determined in Step SB1, the ferroelectric film 10 for the first electrode 9 is formed. It is determined whether or not the step coverage of the desired step coverage is achieved. When the step coverage of the ferroelectric film 10 with respect to the first electrode 9 realizes a desired step coverage, the process proceeds to step SB3, while the step of the ferroelectric film 10 with respect to the first electrode 9 If the coverage does not realize the desired step coverage, the process returns to step SB1 and the above-described processing is repeated.

  Next, in step SB3, the mixing ratio of the third source gas to the fourth source gas in the first source gas that is a mixed gas of the third source gas containing Bi and the fourth source gas containing Sr Adjust. Next, in step SB4, the first source gas is introduced into the chamber at the mixing ratio adjusted in step SB3, and the surface of the first electrode 9 is strongly applied under the substrate temperature and chamber pressure determined in step SB1. In the case where the dielectric film 10 is formed, it is determined whether or not the composition ratio of Bi (metal element constituting the B site) and the composition ratio of Ta in the ferroelectric film 10 are within the range of the desired composition ratio. . When the composition ratio of Bi and the composition ratio of Ta in the ferroelectric film 10 are within the range of the desired composition ratio, the process proceeds to step SB5, while the composition ratio of Bi and the composition of Ta in the ferroelectric film 10 If the ratio is not within the range of the desired composition ratio, the process returns to step SB3 and the above processing is repeated.

  Here, the adjustment of the mixing ratio of the third source gas to the fourth source gas described in Steps SB3 and SB4 is adjusted in the same manner as described with reference to FIG. 9 in the fifth embodiment. realizable.

  Next, in step SB5, it is composed of a mixed gas of the first source gas containing Ta and the second source gas containing Sr under the condition that the composition ratio of Bi obtained in steps SB3 and SB4 is constant. The mixing ratio of the first source gas to the second source gas in the second source gas is adjusted. Next, in step SB6, the second source gas is introduced into the chamber at the mixing ratio adjusted in step SB5, and the ferroelectric material is applied to the surface of the first electrode 9 under the substrate temperature and chamber pressure determined in step SB1. When the body film 10 is formed, it is determined whether or not the composition ratio of Sr (metal element constituting the A site) in the ferroelectric film 10 is within a desired composition ratio range. When the Sr composition ratio in the ferroelectric film 10 is within the desired range, the series of processes is terminated, while the Sr composition ratio in the ferroelectric film 10 is not within the desired composition ratio range. In that case, the process returns to step SB5 and the above-described processing is repeated.

Here, regarding the adjustment of the mixing ratio of the first source gas to the second source gas described in steps SB5 and SB6, the description using FIG. 8 in the fifth embodiment is similarly adjusted. realizable. Further, by combining the formation conditions of the MOCVD method obtained in the second to fourth embodiments with low temperature, low pressure, low growth rate, etc., step coverage is high and good polarization characteristics are obtained. A ferroelectric BLT film can be formed. The first source gas is preferably made of Ta (OC ₂ H ₅ ) ₅ , and the second source gas is Sr [Ta (OC ₂ H ₅ ) ₅ (OC ₂ H ₄ OCH ₃ )] _2. Preferably it consists of.

  Here, as an example, in the case where the ferroelectric film 10 is formed using the second ferroelectric film forming apparatus shown in FIG. 3, the growth of the ferroelectric film 10 obtained by the series of steps described above is performed. As the conditions and the source gas introduced into the chamber 30, the following results shown in [Table 2] could be obtained.

  Hereinafter, a method of forming a ferroelectric film using the second ferroelectric film forming apparatus under the conditions shown in [Table 2] will be specifically described with reference to FIG. 3, FIG. 13, and FIG. explain.

  First, as shown in FIG. 3, the semiconductor substrate 31 is mounted on the susceptor 32 in the chamber 30. The semiconductor substrate 31 is heated by a heater inside the susceptor 32 so that the substrate temperature becomes 350 ° C.

Next, a source gas containing Sr is introduced into the chamber 30 at a flow rate of 0.07 mL / min (standard state), a source gas containing Ta is introduced at a flow rate of 0.03 mL / min (standard state), and a flow rate of 0 Source gas containing Bi is introduced into the chamber 30 at 0.08 mL / min (standard state). Although not shown, the source gas is vaporized using a vaporizer, and the vaporization temperature is 250 ° C. In addition, oxygen gas as an oxidant is introduced into the chamber 30 at a flow rate of 1.23 L / min (standard state). Furthermore, the chamber pressure is set to 1.33 × 10 ² Pa. Under such conditions, the main components of the source gas containing Sr, the source gas containing Ta, the source gas containing Bi, and the oxygen gas chemically react with each other, whereby the ferroelectric film 10 is formed on the semiconductor substrate 31. Is deposited. Note that the ferroelectric film 10 is annealed for heat treatment. This annealing is performed, for example, by using an RTA (rapid heat treatment) method under an annealing temperature of 600 [° C.] for 1 minute in an oxygen atmosphere.

  Next, the formation of the ferroelectric film 10 is completed by removing the semiconductor substrate 31 on which the ferroelectric film 10 is formed from the susceptor 32.

  The step coverage and polarization characteristics of the ferroelectric film 10 thus formed will be described with reference to FIGS.

  As shown in FIG. 13, when the step coverage of the ferroelectric film 10 with respect to the first electrode 9 is obtained from the SEM image of the ferroelectric film 10 when the aspect ratio is 2.0, the step coverage is obtained. 90% is achieved, and the ferroelectric film 10 having an excellent step coverage with respect to the first electrode 9 is realized.

Further, as shown in FIG. 14, according to the evaluation result of the polarization characteristics of the ferroelectric film 10, the polarization characteristics of the ferroelectric film 10 achieve ²⁰ μC / cm ² , and the ferroelectric film having excellent polarization characteristics. The body membrane 10 is realized.

  Further, as a result of analyzing the composition ratio of the ferroelectric film 10 thus formed, the composition ratio of Sr was 16.3%, the composition ratio of Bi was 42.9%, and the composition ratio of Ta was 40.8. Therefore, the composition of the ferroelectric film 10 is almost Sr: Bi: Ta = 1: 2: 2, and the ferroelectric film 10 having a desired composition ratio is realized.

  Thus, even when the second ferroelectric film forming apparatus different from the first ferroelectric film forming apparatus used in the fifth embodiment is used, as described above, the first electrode The ferroelectric film 10 having excellent step coverage with respect to 9 and having a desired composition ratio can be formed.

  As described above, according to the sixth embodiment, the ferroelectric film 10 having excellent step coverage with respect to the first electrode 9 can be formed, and the mixing ratio of the source gases composed of a plurality of types of source gases Is determined by a simple method, a ferroelectric film having a desired composition ratio can be formed.

In the sixth embodiment, the case of a ferroelectric film made of an SBT (SrBi ₂ Ta ₂ O ₉ ) film has been described. However, for example, other Bi-based layered perovskite-type strong films such as a SrBiTaNb film or a BiLaTi film are used. A ferroelectric film made of a dielectric film or a PbZrTi film may be used.

  In the sixth embodiment, the method for forming the ferroelectric film 10 using the second ferroelectric film forming apparatus has been described under the conditions shown in Table 2 above. A body film forming apparatus may be used.

(Seventh embodiment)
A ferroelectric film forming method according to the seventh embodiment of the present invention will be described below with reference to FIG.

  As shown in FIG. 15, first, in step SC1, the substrate temperature and the chamber pressure are determined as the growth conditions of the ferroelectric film 10. Next, in Step SC2, when the ferroelectric film 10 is formed on the surface of the first electrode 9 under the substrate temperature and chamber pressure determined in Step SC1, the ferroelectric film 10 for the first electrode 9 is formed. It is determined whether or not the step coverage of the desired step coverage is achieved. When the step coverage of the ferroelectric film 10 with respect to the first electrode 9 realizes a desired step coverage, the process proceeds to step SC3, while the step of the ferroelectric film 10 with respect to the first electrode 9 If the coverage does not realize the desired step coverage, the process returns to step SC1 and the above-described processing is repeated.

  Next, in step SC3, the mixing ratio of the first source gas to the second source gas in the first source gas composed of the mixed gas of the first source gas containing Bi and the second source gas containing La Adjust. Next, in step SC4, the first source gas is introduced into the chamber at the mixing ratio adjusted in step SC3, and the ferroelectric is applied to the surface of the first electrode 9 under the substrate temperature and chamber pressure determined in step SC1. When the body film 10 is formed, it is determined whether or not the composition ratio of Bi (metal element constituting the A site) and the composition ratio of Ti in the ferroelectric film 10 are within the range of the desired composition ratio. If the composition ratio of Bi and Ti in the ferroelectric film 10 is within the range of the desired composition ratio, the process proceeds to step SC5, while the composition ratio of Bi and Ti is not within the range of the desired composition ratio. In step SC3, the above-described processing is repeated.

  Here, as described in steps SC3 and SC4, the experimental results of repeatedly adjusting the mixing ratio of the first source gas to the second source gas will be described with reference to FIG.

  FIG. 16 shows the relationship between the composition ratio of Bi in the ferroelectric film 10 when Ti is normalized by 3 and the mixing ratio of the first source gas to the second source gas.

As shown in FIG. 16, when the substrate temperature determined in step SC1 is 450 ° C. and the chamber pressure is 2.66 × 10 ² Pa, the mixing ratio of the first source gas to the second source gas. As a result of adjustment while increasing the ratio, the Bi composition ratio in the ferroelectric film 10 increases linearly up to about 3.5, and increases non-linearly when the Bi composition ratio exceeds about 3.5. It was found. Accordingly, in step SC3, the mixing ratio may be adjusted so that the composition ratio of Bi in the ferroelectric film 10 is within the range of the composition ratio at which the polarization characteristic shown in FIG. 16 is obtained. A desired composition ratio can be obtained as the composition ratio of Bi and the composition ratio of Ti in the ferroelectric film 10.

  Next, in step SC5, a mixed gas of the third source gas containing Ti and the fourth source gas containing La under the condition that the composition ratio of Bi obtained in steps SC3 and SC4 is constant. The mixing ratio of the third source gas to the fourth source gas in the second source gas is adjusted. Next, in Step SC6, the second source gas is introduced into the chamber at the mixing ratio adjusted in Step SC5, and the surface of the first electrode 9 is strongly applied under the substrate temperature and chamber pressure determined in Step SC1. When the dielectric film 10 is formed, it is determined whether or not the composition ratio of La (metal element constituting the B site) in the ferroelectric film 10 is within a desired composition ratio range. When the La composition ratio in the ferroelectric film 10 is within the range of the desired composition ratio, the series of processes is terminated, while the La composition ratio in the ferroelectric film 10 is within the desired composition ratio range. If not, the process returns to step SC5 to repeat the above process.

  Here, as described in steps SC5 and SC6, the experimental results of repeatedly adjusting the mixing ratio of the third source gas to the fourth source gas will be described with reference to FIG.

  FIG. 17 shows the relationship between the composition ratio of La and the composition ratio of Bi in the ferroelectric film 10 when Ti is normalized by 3, and the mixing ratio of the third source gas to the fourth source gas. Yes.

As shown in FIG. 17, when the substrate temperature determined in step SC1 is 450 ° C. and the chamber pressure is 2.66 × 10 ² Pa, the third source gas is mixed with the fourth source gas. As a result of adjusting the ratio while increasing the ratio, it was found that the composition ratio of La in the ferroelectric film 10 sharply decreased from the vicinity of the mixing ratio of the third source gas to the fourth source gas of 1.2. . That is, when the mixing ratio of the third source gas to the fourth source gas is increased, the composition ratio of La in the ferroelectric film 10 is set despite the fact that the composition ratio of Bi in the ferroelectric film 10 is substantially constant. Only the ratio was found to change. Accordingly, in step SC5, the third source gas is mixed with the fourth source gas so that the La composition ratio in the ferroelectric film 10 is within the range of the composition ratio that provides the polarization characteristics shown in FIG. The ratio may be adjusted, and in step SC6, a desired composition ratio can be obtained as the composition ratio of La in the ferroelectric film 10.

  Thus, from the experimental results shown in FIGS. 16 and 17, when the mixing ratio of the first source gas to the second source gas is increased, the composition ratio of La in the ferroelectric film 10 is linearly increased. It has been found that only the composition ratio of La can be changed at a certain mixing ratio or more without changing. The parameters that determine the mixing ratio of the first source gas to the second source gas and the mixing ratio of the third source gas to the fourth source gas are the substrate temperatures in the second to fourth embodiments described above. This parameter is different from the parameters for lowering the temperature, lowering the chamber pressure, and lowering the growth rate. Therefore, the existence of a parameter that can independently control the mixing ratio of the source gases composed of a plurality of types of source gas without affecting the step coverage of the ferroelectric film 10 in the first electrode 9 is observed. As described above, the composition ratio of, for example, Bi, La, and Ti constituting the ferroelectric film 10 can be controlled to a desired composition ratio as described above.

  Further, by combining the formation conditions of the MOCVD method obtained in the second to fourth embodiments with low temperature, low pressure, low growth rate, etc., step coverage is high and good polarization characteristics are obtained. A ferroelectric BLT film can be formed.

  In the present embodiment, as shown in FIG. 15, the case where the desired composition ratio of La is obtained by steps SC5 and SC6 after obtaining the desired composition ratio of Bi and Ti by steps SC3 and SC4 has been described. However, a desired composition ratio of Bi and Ti may be obtained after obtaining a desired composition ratio of La. That is, step SC3 and SC4 may be performed after step SC2 and step SC5 and SC6.

  From the above, for example, in the case of forming the ferroelectric film 10 using the first or second ferroelectric film forming apparatus shown in FIG. 2 or FIG. 3, the ferroelectric obtained in the above-described series of steps. As the growth conditions of the body film 10 and the source gas introduced into the chamber 20 or 30, the results shown in the following [Table 3] can be obtained.

  Hereinafter, a method for forming the ferroelectric film 10 using the first ferroelectric film forming apparatus as an example under the conditions shown in [Table 3] will be specifically described with reference to FIGS. .

  First, as shown in FIG. 2, the semiconductor substrate 21 is mounted on the susceptor 22 in the chamber 20. The semiconductor substrate 21 is heated by a heater inside the susceptor 22 so that the substrate temperature becomes 450 ° C. or lower.

Next, a plurality of types of source gases are introduced into the chamber 20. For example, La (OC ₂ H ₅ ) ₄ is 0.03 mL / min (standard state) as a source gas containing La, and Ti (OC ₂ H ₅ ) ₄ is 0.05 mL / min (standard state) as a source gas containing Ti. ), A mixed gas in which Bi [OC (CH ₃ ) ₂ (CH ₂ OCH ₃ )] ₃ is mixed as a source gas containing Bi at a rate of 0.08 mL / min (standard state) is introduced. Although not shown, the source gas is vaporized using a vaporizer, and the vaporization temperature is 300 ° C. Further, oxygen gas as an oxidant is introduced into the chamber 20 at a flow rate of 1.5 L / min (standard state). Furthermore, the chamber pressure is set to 2.66 × 10 ² Pa. Under such conditions, the ferroelectric film 10 is deposited on the semiconductor substrate 21 by a chemical reaction of a plurality of types of source gases. Note that the ferroelectric film 10 is annealed for heat treatment. This annealing is performed, for example, by using an RTA (rapid heat treatment) method under an annealing temperature of 600 [° C.] for 1 minute in an oxygen atmosphere.

  Next, the formation of the ferroelectric film 10 is completed by removing the semiconductor substrate 21 on which the ferroelectric film 10 is formed from the susceptor 22.

  The polarization characteristics of the ferroelectric film 10 thus formed will be described with reference to FIG.

As shown in FIG. 18, according to the evaluation result of the polarization characteristics of the ferroelectric film 10, the polarization characteristics of the ferroelectric film 10 achieved 18 μC / cm ² when 1.8 V was applied. Even if it is 10, excellent polarization characteristics are realized.

  As described above, according to the seventh embodiment, the ferroelectric film 10 having excellent step coverage with respect to the first electrode 9 can be formed, and the mixing ratio of the source gases composed of a plurality of types of source gases Is determined by a simple method, a ferroelectric film having a desired composition ratio can be formed.

  In the seventh embodiment, the method for forming a ferroelectric film using the first ferroelectric film forming apparatus has been described under the conditions shown in Table 3 above. A film forming apparatus may be used.

  As described above, the present invention is useful for a method of manufacturing a ferroelectric film that can improve the step coverage and control the composition ratio. The present invention is useful for a semiconductor device having a ferroelectric film.

(A)-(c) is sectional drawing of the ferroelectric capacitive element which has the ferroelectric film formed by the formation method of the ferroelectric film which concerns on each embodiment of this invention. It is sectional drawing of the 1st ferroelectric formation apparatus which concerns on the 1st Embodiment of this invention. It is sectional drawing of the 2nd ferroelectric formation apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the relationship between a substrate temperature and a level | step difference coverage in the formation method of the ferroelectric film which concerns on the 2nd Embodiment of this invention. It is a figure which shows the relationship between chamber pressure and level | step difference coverage in the formation method of the ferroelectric film which concerns on the 3rd Embodiment of this invention. It is a figure which shows the relationship between a growth rate and a level | step difference coverage in the formation method of the ferroelectric film which concerns on the 4th Embodiment of this invention. It is a flowchart which shows the formation method of the ferroelectric film which concerns on the 5th Embodiment of this invention. It is a figure which shows the relationship between the mixture ratio of Ta source gas with respect to Sr source gas in the 5th Embodiment of this invention, and Sr composition ratio and Bi composition ratio in a ferroelectric film. It is a figure which shows the relationship between the mixture ratio with respect to Sr source gas of Bi source gas in the 5th Embodiment of this invention, and Bi composition ratio in a ferroelectric film. It is a SEM image figure which shows the cross section of the ferroelectric film formed by the formation method of the ferroelectric film which concerns on the 5th Embodiment of this invention. It is a figure which shows the polarization characteristic of the ferroelectric film formed by the formation method of the ferroelectric film which concerns on the 5th Embodiment of this invention. It is a flowchart which shows the formation method of the ferroelectric film which concerns on the 6th Embodiment of this invention. It is a SEM image figure which shows the cross section of the ferroelectric film formed by the formation method of the ferroelectric film which concerns on the 6th Embodiment of this invention. It is a figure which shows the polarization characteristic of the ferroelectric film formed by the formation method of the ferroelectric film which concerns on the 6th Embodiment of this invention. It is a flowchart which shows the formation method of the ferroelectric film which concerns on the 7th Embodiment of this invention. It is a figure which shows the relationship between the mixture ratio with respect to La source gas of Bi source gas in the 7th Embodiment of this invention, and Bi composition ratio in a ferroelectric film. It is a figure which shows the relationship between the mixture ratio with respect to La source gas of Ti source gas in the 7th Embodiment of this invention, and La composition ratio and Bi composition ratio in a ferroelectric film. It is a figure which shows the polarization characteristic of the ferroelectric film formed by the formation method of the ferroelectric film which concerns on the 7th Embodiment of this invention. It is the schematic of the ferroelectric film formation apparatus used for the formation method of the conventional ferroelectric film.

Explanation of symbols

1, 21, 31 Semiconductor substrate 2 Impurity diffusion layer 3 Gate electrode 4 Field effect transistor 5 Protective insulating film 6 Contact plug 7 Recessed opening 8 Interlayer insulating film 9 First electrode 10 Ferroelectric film 11 Second electrode 20, 30 Chamber 22, 32 Susceptor 23, 33, 34 Gas introduction path 24, 36 Pressure control valve 25, 37 Pump 26, 38 Gas discharge path 35 Gas nozzle

Claims (3)

An electrode formed on a substrate and having a concave or convex portion on the surface;
A semiconductor device comprising a ferroelectric film formed on the electrode,
The step coverage of the ferroelectric film at the step existing in the concave portion or the convex portion is 80% or more,
Variation in composition ratio of metal elements constituting the ferroelectric film is ± 15% or less. The metal element constituting the ferroelectric film contains Sr, Bi and Ta,
When the Ta composition ratio is normalized by 2, the Sr composition ratio is 0.75 or more and a value within a range of 1.00 or less, and the Bi composition ratio is 2.00 or more. 2. The semiconductor device according to claim 1, wherein the value is within a range of 2.50 or less. The metal element constituting the ferroelectric film contains Bi, La and Ti,
When the composition ratio of Ti is normalized by 3, the composition ratio of La is 0.5 or more and a value within a range of 1.0 or less, and the composition ratio of Bi is 3.0 or more. The semiconductor device according to claim 1, wherein the semiconductor device has a value within a range of 3.5 or less.