JP2006032793A - Method for forming ferroelectric film and method for manufacturing semiconductor memory device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a ferroelectric film exhibiting sufficient polarization characteristics even in the case of a microvolume indispensable to obtain a high integration semiconductor memory device. <P>SOLUTION: In the method for forming a ferroelectric film comprising a step for depositing a ferroelectric material film on a supporting substrate, and a step for sintering the ferroelectric material film by performing a plurality of heat treatment steps one of which includes a temperature rising step A, a temperature holding step B, and a temperature lowering step C wherein the temperature rising step A includes a step for raising the temperature of the substrate at a rate lowering gradually as the temperature of the substrate rises. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for forming a ferroelectric film and a method for manufacturing a semiconductor memory device using the ferroelectric film as a capacitive insulating film.

  In recent years, with the advancement of digital technology, electronic devices have become more sophisticated as the tendency to process and store large volumes of data has been promoted, and semiconductor devices used have been rapidly miniaturized. .

  Accordingly, in order to realize high integration of the dynamic random access memory, a technique using a high dielectric as a capacitive insulating film instead of the conventional silicon oxide or nitride has been widely researched and developed.

  In addition, with the aim of commercializing a nonvolatile memory with low operating voltage and high-speed writing / reading that has never been seen before, research and development on a semiconductor memory device using a ferroelectric film having spontaneous polarization characteristics has been actively conducted. Memory is in practical use.

  Currently, in order to achieve higher integration of ferroelectric non-volatile memory, research and development on capacitive element miniaturization with a capacitive insulating film thin film made of a ferroelectric substance is particularly active. It has been broken.

  The most important issue for realizing these highly integrated ferroelectric nonvolatile memories is to develop a technique capable of integrating a minute capacitor element in a CMOS integrated circuit without deterioration of characteristics.

Examples of the ferroelectric material used as the capacitor insulating film include lead titanium zirconate (hereinafter referred to as PZT), strontium bismuth tantalate (hereinafter referred to as SBT), bismuth lanthanum titanate (hereinafter referred to as BLT), and bismuth titanate. Metal oxides having a perovskite structure or a layered perovskite structure are used. In particular, bismuth titanate and BLT are attracting attention as ferroelectrics that can be sintered at low temperature with good compatibility with CMOS integrated processes. For example, a conventional technique (Patent Document 1) for forming a ferroelectric film made of SBT will be described below with reference to FIG. In the steps S20 to S28 of FIG. 11, after the SBT precursor film is spin-coated on the substrate and the organic components in the precursor film are removed, in the steps S29 to S31, RTP (Rapid Thermal Process) or the like is performed. A step of rapidly heating and sintering the precursor film to form a ferroelectric film is performed. This sintering process includes a process called pre-sintering (S29) that is heated at a temperature of 500 to 600 ° C., and a process called main sintering (S31) that is heated at a temperature of 600 to 800 ° C. Ferroelectric crystal grains are grown in the ferroelectric film by the sintering process (Patent Document 1).
JP-A-9-260612

  However, when using BLT, bismuth titanate, or the like, which is a ferroelectric material in which Bi, which is a highly volatile element, exists at the A site of the perovskite structure as a capacitive insulating film, when performing the above-described sintering We found that the following problems occur.

  After a ferroelectric material film made of a ferroelectric material such as BLT or bismuth titanate is deposited on the substrate by MOD (Metal Organic Decomposition) method or MOCVD (Metal Organic Chemical Vapor Deposition) method, a lamp heating furnace is installed. When crystal grains grow in the ferroelectric material film by performing the rapid heating and heating sintering consisting of the above-mentioned temporary sintering and main sintering to the ferroelectric material film by the RTP method used It was found that a ferroelectric film having a sufficient polarizability could not be obtained. In particular, during the main sintering, when the temperature is raised at a constant temperature rise rate, if the temperature rise rate is low, the number of crystal nuclei in the crystal grains is excessively increased, and the crystal grains in the c-axis direction have a low polarizability. The orientation of is increased. On the other hand, when the temperature rising rate is low, the orientation of the crystal grains in the c-axis direction can be suppressed, but the crystal grains cannot be grown to a sufficient size, resulting in a low polarizability. End up.

  In general, a ferroelectric does not have an isotropic crystal structure, but has an asymmetric crystal structure composed of a polarization direction of a large spontaneous polarization value and a polarization direction of a small spontaneous polarization value or a nonpolar direction that does not generate polarization. FIG. 12 shows a schematic diagram of a unit crystal lattice of BLT. As shown in FIG. 12, the BLT has a structure in which bismuth oxide layers 81 and pseudo-perovskite layers 82 are alternately stacked in the c-axis direction. The bismuth oxide layer 81 is composed of oxygen 84 and Bi83, the pseudo-perovskite layer 82 is composed of oxygen 84, an A site element 85, and a B site element 86, La or Bi enters the A site, and the B site contains Ti enters. BLT has a direction with a large spontaneous polarization in the ab plane including the a-axis and b-axis directions, and a small spontaneous polarization in the c-axis direction. In order to retain data as a non-volatile memory, the ab surface having a large BLT polarization must be arranged substantially parallel to the direction of the electric field applied to the counter electrode. This is not limited to BLT, and is a problem common to ferroelectrics having a crystal structure having anisotropy in the crystal axis.

  However, when a capacitor element is formed by a conventional method of manufacturing a capacitor insulating film, as described above, it is not easy to form a ferroelectric film that can be easily c-axis oriented and can secure a necessary charge amount for a nonvolatile memory. The above problem has been a major problem when miniaturizing a capacitor element in order to realize a highly integrated semiconductor memory device.

  In view of the above problems, the present invention provides a method for forming a ferroelectric film having sufficient polarization characteristics even in a minute volume indispensable for realizing a highly integrated semiconductor memory device, and uses the ferroelectric film as a capacitive insulating film. A method for manufacturing a semiconductor memory device is provided.

  The inventors pay attention to the temperature profile during the rapid temperature heating and sintering of the ferroelectric material, can promote the growth of ferroelectric crystal grains having an orientation component with a large polarization, and sufficient It has been found that crystal grains of a size can be grown.

  The first ferroelectric film forming method of the present invention includes a step of depositing a ferroelectric material film on a support substrate and performing a plurality of heat treatments on the ferroelectric material film, thereby In the method for forming a ferroelectric film including the step of sintering the dielectric material film, one of the heat treatments P includes a temperature raising step, a temperature holding step, and a temperature lowering step. And the temperature raising step includes a step of raising the temperature of the substrate at a rate of temperature rise that decreases as the temperature of the substrate increases.

  According to a second method for forming a ferroelectric film of the present invention, in the first method for forming a ferroelectric film, a heat treatment different from the one heat treatment P is performed before the one heat treatment P. The heat treatment different from the one heat treatment P includes a temperature raising step, a first temperature holding step, a first temperature holding step, and the first temperature holding step. Including a second temperature holding step of heating the substrate at a temperature higher than the temperature in step (b), and a temperature lowering step.

  The method of manufacturing a semiconductor memory device according to the present invention includes a step of forming a lower electrode on a support substrate, and a ferroelectric by the method for forming the first or second ferroelectric film of the present invention on the lower electrode. The method includes a step of forming a capacitive insulating film made of a body film, and a step of forming an upper electrode on the capacitive insulating film.

  According to the first and second ferroelectric film forming methods of the present invention, a ferroelectric film having sufficient polarization characteristics can be formed. That is, according to the first method for forming a ferroelectric film, the processing time in the temperature region where nucleation of ferroelectric crystal grains occurs is shortened, and in the temperature region where the crystal growth of ferroelectric crystal grains is performed. By lengthening the treatment time, it is possible to moderately suppress the nucleation of ferroelectric crystal grains, it is possible to promote the growth of ferroelectric crystal grains having an orientation component having a large polarization, and Crystal growth of a sufficiently large ferroelectric crystal grain can be performed. As a result, a ferroelectric film having sufficient polarization characteristics can be formed.

  Also, according to the second ferroelectric film forming method, in the first temperature holding step of the heating step before one heat treatment P, the highly volatile element such as Bi in the ferroelectric material film Since the ferroelectric material film can be pre-sintered at a temperature that prevents detachment, and nucleation of ferroelectric crystal grains can be performed in a state where c-axis orientation is suppressed in the second temperature holding step. In addition, the composition deviation of the ferroelectric film and the suppression of the c-axis orientation can be realized at the same time. Furthermore, in the main sintering in one heat treatment P, the growth of ferroelectric crystal grains having an orientation component with large polarization can be promoted, and the crystal growth of sufficiently large ferroelectric crystal grains can be promoted. It can be carried out. As a result, a ferroelectric film having sufficient polarization characteristics can be formed.

  According to the method for manufacturing a semiconductor memory device of the present invention, it is possible to realize a capacitor element using a ferroelectric film having sufficient polarization characteristics as a capacitor insulating film. Therefore, the capacitor element can be miniaturized and a highly integrated semiconductor memory device can be realized. Can be realized. That is, it has an orientation component with a large polarization and has a sufficiently large ferroelectric crystal grain, or in addition to this, suppression of c-axis orientation is realized, and composition deviation is prevented, Since a capacitor element using a ferroelectric film having sufficient polarization characteristics as a capacitor insulating film can be realized, the capacitor element can be miniaturized and a highly integrated semiconductor memory device can be realized.

  In the first method for forming a ferroelectric film of the present invention, the rate of temperature increase is 9 ° C./second or more when the temperature of the substrate is lower than 550 ° C., and 9 ° C./second when the temperature is 550 ° C. or higher. It is preferable that it is below second. In particular, when the temperature is less than 550 ° C., it is preferably 10 to 20 ° C./sec. In the first method for forming a ferroelectric film of the present invention, the maximum temperature in the temperature holding step is preferably 700 ° C. or lower. By adopting such a configuration, it is possible to promote the growth of ferroelectric crystal grains having an orientation component with a large polarization, and it is possible to perform crystal growth of sufficiently large ferroelectric crystal grains. . A more preferable maximum temperature in the temperature holding step is in the range of 600 ° C to 700 ° C.

  In the first method for forming a ferroelectric film of the present invention, it is preferable that the temperature lowering step includes a step of lowering the temperature of the substrate at a temperature lowering rate that decreases as the temperature of the substrate decreases. With this configuration, it is possible to perform crystal growth of sufficiently large ferroelectric crystal grains in the temperature lowering process. In particular, the cooling rate is preferably 5 ° C./second or more when the temperature of the substrate is 500 ° C. or more, and preferably 5 ° C./second or less when the temperature is less than 500 ° C. More preferably, the temperature is in the range of 7 to 15 ° C./second when the temperature of the substrate is 500 ° C. or higher, and in the range of 1 to 3 ° C./second when the temperature is lower than 500 ° C.

In the second method for forming a ferroelectric film of the present invention, it is preferable that the temperature lowering step in the heat treatment different from the one heat treatment P is performed following the second temperature holding step.
If it does in this way, the effect of suppression of c-axis orientation will become high.

  In the second method for forming a ferroelectric film of the present invention, the maximum temperature in the second temperature holding step is preferably lower than the maximum temperature in the temperature holding step in the one heat treatment P. By doing so, by making the maximum temperature in the second temperature holding step of the heating step before one heat treatment P lower than the maximum temperature in the temperature holding step in one heat treatment P that is the main sintering. The crystal grains can be made sufficiently large. In particular, the maximum temperature in the second temperature holding step is preferably 650 ° C. or lower. A more preferable maximum temperature in the second temperature holding step is in a range of 550 ° C to 650 ° C.

  In the second method for forming a ferroelectric film of the present invention, it is desirable that the rate of temperature increase to the maximum temperature in the second temperature holding step is 30 ° C./second on average. In this way, it is possible to effectively prevent the escape of highly volatile elements such as Bi in the ferroelectric material film when the temperature is raised to the maximum temperature in the second temperature holding step.

  In the second method for forming a ferroelectric film of the present invention, the time for maintaining the maximum temperature in the second temperature maintaining step is the time for maintaining the same temperature in the heat treatment different from the one heat treatment P. The shortest of these is desirable.

  In this way, it is possible to effectively prevent the escape of highly volatile elements such as Bi in the ferroelectric material film while maintaining the maximum temperature in the second temperature maintaining step, and The effect of suppressing c-axis orientation is enhanced. In particular, it is preferable that the time for maintaining the maximum temperature in the second temperature holding step is 2 seconds or less. Furthermore, the preferable holding time which hold | maintains to the highest temperature in a said 2nd temperature holding process is the range of 0.5 to 1 second.

In the second method for forming a ferroelectric film of the present invention, it is preferable that the temperature lowering step includes a step of lowering the temperature of the substrate at a temperature lowering rate that decreases as the temperature of the substrate decreases.
If it does in this way, the effect of suppression of c-axis orientation in the temperature-falling process in temporary sintering which is heat processing different from said one heat processing P will become high. Alternatively, the crystal grains can be made sufficiently large. In particular, the rate of temperature decrease is preferably 5 ° C./second or more when the substrate temperature is 500 ° C. or more, and 5 ° C./second or less when the temperature is less than 500 ° C. More preferably, the temperature is in the range of 7 to 15 ° C./second when the temperature of the substrate is 500 ° C. or higher, and in the range of 1 to 3 ° C./second when the temperature is lower than 500 ° C.

  In the second method for forming a ferroelectric film of the present invention, the temperature raising step in the heat treatment different from the one heat treatment P raises the temperature of the substrate at a temperature rise rate of 10 ° C./second or less. It is desirable to include the process to do.

  In this way, it is possible to effectively prevent escape of highly volatile elements such as Bi in the ferroelectric material film in the temperature raising step in the preliminary sintering, which is a heat treatment different from the one heat treatment P. And the effect of suppressing c-axis orientation is enhanced.

In the first or second method of forming a ferroelectric film of the present invention, the ferroelectric film may be Bi _{4-x + y} A _x Ti ₃ O ₁₂ (where A is La, Pr, Nd, Sm). , Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and V, and x and y are 0 ≦ x ≦ 2 and 0 <y ≦ (4-x It is desirable that the ferroelectric material is represented by the general formula: Thus, when forming a ferroelectric film using a ferroelectric material in which Bi is present at the A site of the perovskite structure, the c-axis orientation of the ferroelectric crystal grains during the main sintering is changed. It is possible to suppress the growth of sufficiently large ferroelectric crystal grains. Alternatively, in addition to this, it is possible to prevent the escape of Bi having high volatility during the preliminary sintering, and it is possible to prevent composition deviation. As a result, a ferroelectric film having sufficient polarization characteristics can be formed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  Here, the ferroelectric material film is a film containing an element constituting the ferroelectric material in the stage before passing through the sintering process. For example, the ferroelectric material film is deposited by the MOD method. It includes a film and a film deposited by MOCVD or sputtering and in the previous stage of the subsequent heat treatment process. In addition, the ferroelectric material film that has undergone the pre-sintering process may be referred to as a ferroelectric film.

(Embodiment 1)
Hereinafter, a method for forming a ferroelectric film according to an embodiment of the present invention and a method for manufacturing a semiconductor memory device using the ferroelectric film as a capacitive insulating film will be described with reference to FIGS.

  In the present embodiment, the case where the ferroelectric film according to the present embodiment is used as a capacitor insulating film of a ferroelectric capacitor (capacitor element) has been described, but the ferroelectric film according to the present embodiment is In addition to ferroelectric capacitors, semiconductor memories such as MFS (Metal-Ferroelectric-Semiconductor) type transistors, MFIS (Metal-Ferroelectric-Insulator-Semiconductor) type transistors, or MFMIS (Metal-Ferroelectric-Metal-Insulator-Semiconductor) type transistors It can also be used as a capacitive insulating film of the device.

(1) Manufacturing Method of Semiconductor Memory Device FIG. 1 is a cross-sectional view of main steps for explaining a manufacturing method of a semiconductor memory device according to the present embodiment. First, as shown in FIG. 1A, an element isolation region 12 is formed on a surface portion of a semiconductor substrate 11, and then a gate electrode 14 is formed on the semiconductor substrate 11 via a gate insulating film 13. Next, after ion-implanting low-concentration impurities using the gate electrode 14 as a mask, a gate protective insulating film 15 is formed on the upper surface and side surfaces of the gate electrode 14, and then using the gate electrode 14 and the gate protective insulating film 15 as a mask. Impurity diffusion layers 16 having an LDD structure to be a source region or a drain region of a field effect transistor 17 which is a memory cell transistor are formed by ion implantation of a high concentration impurity. Next, an insulating film 18 (thickness: about 600 nm) made of a silicon oxide film is deposited over the entire surface of the semiconductor substrate 11 so as to cover the field effect transistor 17, and the insulating film 18 is dry-etched by dry etching. A contact hole (diameter is about 0.24 μm) is formed. Next, a conductive film made of tungsten or a polysilicon film is deposited over the entire surface of the insulating film 18 by CVD, and then a portion of the conductive film existing on the insulating film 18 is etched back or CMP. As a result, the contact plug 19 connected to one of the impurity diffusion layers 16 to be the source region or drain region of the field effect transistor 17 is formed.

  Next, as shown in FIG. 1B, a laminated film composed of a titanium film, a titanium nitride film, an iridium, an iridium oxide film, and a platinum film sequentially deposited from below over the entire surface of the insulating film 18 by sputtering. (The total film thickness is about 200 nm), and then the laminated film is patterned by dry etching to form the lower electrode 20 connected to the contact plug 9 as shown in FIG.

  Next, as shown in FIG. 1C, the entire surface of the lower electrode 20 and the insulating film 18 is made of BLT having a bismuth layered perovskite structure by a MOD method, an MOCVD method, or a sputtering method. After forming a ferroelectric film having a thickness of 75 nm), the ferroelectric film is patterned to form a capacitive insulating film 21 that extends over the lower electrode 20 and extends outside the lower electrode 108. . A method for forming the ferroelectric film will be described in detail later.

  Next, as shown in FIG. 1D, a laminated film made of a platinum film and a titanium film or a laminated film made of a platinum film and a titanium nitride film is formed on the entire surface of the capacitor insulating film 21 sequentially from the bottom. After that, the upper electrode 22 is formed by patterning the laminated film by dry etching. As a result, a capacitive element 23 composed of the lower electrode 20, the capacitive insulating film 21 and the upper electrode 22 is formed.

  Thereafter, although not shown, wirings connected to the lower electrode 20 and the upper electrode 22 are formed to complete the semiconductor memory device.

(2) Method for Forming Ferroelectric Film Next, a method for forming a ferroelectric film according to the present embodiment, which becomes the capacitive insulating film 21, will be described with reference to FIG.

  FIG. 2 is a process diagram for explaining the method of forming a ferroelectric film according to the present embodiment.

  First, in step S11, a ferroelectric material composed of BLT having a bismuth layered perovskite structure over the entire surface of the lower electrode 20 and the insulating film 18 by a MOD method, an MOCVD method, or a sputtering method and having a thickness of 100 nm or less. Deposit material film.

  Next, in step S <b> 12, a first heat treatment that is so-called temporary sintering is performed on the substrate 11 by the RTP method. In the first heat treatment, a temperature profile A for holding the temperature at 550 ° C. for 1 minute or a first temperature holding step for holding the temperature at 550 ° C., followed by a second temperature for holding the temperature at 600 ° C. The temperature profile B including the holding process is performed. This temperature profile will be described in detail later.

  Next, in step S13, a laminated film or a platinum film and a titanium nitride film made of a platinum film and a titanium film sequentially deposited from the bottom over the entire surface of the ferroelectric material film (capacitive insulating film). After forming the laminated film, the upper electrode 22 is formed by patterning the laminated film by dry etching.

  Next, in step S14, the substrate 11 is subjected to a second heat treatment that is so-called main sintering by the RTP method. In the second heat treatment, the temperature is maintained at 700 ° C. for one minute following the temperature raising step of raising the temperature of the substrate 11 at a temperature lowering rate that decreases as the temperature of the substrate 11 rises.

  As described above, ferroelectric crystal grains can be grown in the ferroelectric material film, and a ferroelectric film to be the capacitor insulating film 21 can be formed.

  The formation of the upper electrode 22 in step S13 may be performed after the second heat treatment in step S14.

  Here, the second heat treatment includes a temperature raising step of raising the temperature of the substrate at a temperature lowering rate that decreases with an increase in the temperature of the substrate, whereby a temperature at which nucleation of ferroelectric crystal grains occurs. By shortening the processing time in the region and increasing the processing time in the temperature region where the crystal growth of the ferroelectric crystal grains is performed, it is possible to moderately suppress the nucleation of the ferroelectric crystal grains, Crystal growth of a sufficiently large ferroelectric crystal grain can be performed.

  In the first heat treatment, the first temperature holding step, the first temperature holding step, and after heating the substrate at a temperature higher than the temperature in the first temperature holding step. By including the temperature holding step of 2, the ferroelectric material film can be pre-sintered at a temperature that prevents escape of highly volatile Bi in the ferroelectric material film in the first temperature holding step, Since the nucleation of the ferroelectric crystal grains can be performed in a state where the c-axis orientation is suppressed in the second temperature holding step, it is possible to simultaneously realize the compositional deviation of the ferroelectric film and the suppression of the c-axis orientation. it can.

  As a result, a ferroelectric film having sufficient polarization characteristics can be formed. Further, by using such a ferroelectric film as a capacitive insulating film of a capacitive element, the capacitive element can be miniaturized and a highly integrated semiconductor memory device can be realized.

Example 1
3A and 3B are temperature profiles of the second heat treatment, the horizontal axis is time, and the vertical axis is the substrate temperature. FIG. 3C is a temperature profile of the first heat treatment.

  FIG. 3A is a temperature profile of the second heat treatment in the method for forming a ferroelectric film according to Example 1 of the present embodiment, and FIG. 3B is a temperature profile of the second heat treatment for comparison. It is.

  The temperature profile shown in FIG. 3A includes a temperature raising step A, a temperature holding step B, and a temperature lowering step C. In the temperature raising step A, the rate of temperature rise is 1 to 13 ° C./second, 9 ° C./second or more when the substrate temperature is less than 550 ° C., and 9 ° C./second or less when the substrate temperature is 550 ° C. or more. The holding temperature and holding time in the temperature holding process B are 700 ° C. and 1 minute, and in the temperature lowering process C, the temperature lowering rate is 5 ° C./second or more when the substrate temperature is 500 ° C. or more, and less than 500 ° C. In some cases, it is set to 5 ° C./second or less.

  On the other hand, the temperature profile shown in FIG. 3B includes a temperature raising step A ′, a temperature holding step B ′, and a temperature lowering step C ′. In the temperature raising step A ′, the temperature raising rate is 30 ° C./second, and the holding temperature and holding time in the temperature holding step B ′ are 700 ° C. and 1 minute.

  Note that the temperature profile of the first heat treatment shown in FIG. 3C includes a temperature raising step a ′, a temperature holding step b ′, and a temperature lowering step c ′. In the temperature raising step a ′, the temperature raising rate is 5 ° C./second, and the holding temperature and holding time in the temperature holding step b ′ are 550 ° C. and 1 minute.

  Hereinafter, the effect of the method for forming a ferroelectric film according to Example 1 of the embodiment of the present invention will be described with reference to FIGS.

4A and 4B show the results of measuring hysteresis loops showing the polarization characteristics of the ferroelectric film formed by the temperature profiles of FIGS. 3A and 3B, respectively. The horizontal axis is the applied voltage (V), and the vertical axis is the polarizability (μmC / cm ² ). In addition, the measurement is performed with three kinds of maximum applied voltages (1.8 V, 3 V, and 5 V), and plotted in an overlapping manner.

  5A and 5B show the results of measuring the X-ray diffraction profile of the ferroelectric film formed by the temperature profiles of FIGS. 3A and 3B, respectively.

  6A and 6B are surface SEM photographs of the ferroelectric film formed by the temperature profiles of FIGS. 3A and 3B, respectively.

In FIG. 4B which is a comparative example, the polarizability 2Pr indicating the polarization characteristics of the ferroelectric film is 8.2 μmC / cm ² when the maximum applied voltage is 1.8 V, which is the present invention. In FIG. 4A, it can be seen that a large polarizability of 15.5 μm C / cm ² can be realized. Here, 2Pr is given by 2Pr = + Pr − (− Pr) in FIGS. 4A and 4B, where the positive intersection of the hysteresis curve indicating the polarization characteristics and the vertical axis is + Pr and the negative intersection is −Pr. .

  Moreover, in FIG. 5B which is a comparative example, the X-ray diffraction peak intensity from the (117) plane which is an orientation component having a large polarization is relatively small, whereas in FIG. It can be seen that the X-ray diffraction peak intensity from the (117) plane is much larger than that of the comparative example.

  Further, when comparing the surface SEM photographs of FIGS. 6A and B, the size of the ferroelectric crystal grains is small in FIG. 6B which is a comparative example, whereas in FIG. 6A which is the present invention, the ferroelectric crystal grains are small. It can be seen that is larger than the comparative example.

  From the above results, according to the method for forming a ferroelectric film according to Example 1 of the embodiment of the present invention, it is possible to promote the growth of ferroelectric crystal grains having an orientation component with large polarization, and It can be seen that a sufficiently large ferroelectric crystal grain can be grown, and as a result, a ferroelectric film having sufficient polarization characteristics can be formed.

(Example 2)
7A and 7B are temperature profiles of the second heat treatment, the horizontal axis is time, and the vertical axis is the substrate temperature. FIG. 7C is a temperature profile of the first heat treatment.

  FIG. 7A is a temperature profile of the second heat treatment in the method for forming a ferroelectric film according to Example 1 of the present embodiment, and FIG. 7B is a temperature profile of the second heat treatment for comparison. It is.

  The temperature profile shown in FIG. 7A is the same as the temperature profile shown in FIG. 3A.

  On the other hand, the temperature profile shown in FIG. 7B is the same as the temperature profile shown in FIG. 3B.

  Note that the temperature profile of the first heat treatment in the method for forming a ferroelectric film according to Example 2 of the present embodiment shown in FIG. 7C is as follows: a temperature raising step a, a first temperature holding step b, It consists of a second temperature holding step d and a temperature lowering step e, and a temperature raising step c is provided between the first temperature holding step and the second temperature holding step. In the temperature raising step a, the temperature raising rate is 5 ° C./second, the holding temperature and holding time in the first temperature holding step b are 550 ° C. and 1 minute, and holding in the second temperature holding step d The temperature and holding time are 600 ° C. and 1 second, and in the temperature lowering step e, the rate of temperature decrease is 5 ° C./second or more when the substrate temperature is 500 ° C. or more, and 5 ° C./second or less when the temperature is less than 500 ° C. In the temperature raising step c, the temperature raising rate is set at an average of 30 ° C./second.

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

8A and 8B show the results of measuring hysteresis loops showing the polarization characteristics of the ferroelectric film formed by the temperature profiles of FIGS. 7A and 7B, respectively. The horizontal axis is the applied voltage (V), and the vertical axis is the polarizability (μmC / cm ² ). In addition, the measurement is performed with three kinds of maximum applied voltages (1.8 V, 3 V, and 5 V), and plotted in an overlapping manner.

  8A and 8B show the results of measuring the X-ray diffraction profile of the ferroelectric film formed by the temperature profiles of FIGS. 7A and 7B, respectively.

In FIG. 8B, which is a comparative example, the polarizability 2Pr indicating the polarization characteristics of the ferroelectric film is 14.6 μmC / cm ² when the maximum applied voltage is 1.8 V, which is the present invention. In FIG. 4A, it can be seen that a very large polarizability of 20.5 μm C / cm ² can be realized.

  In FIG. 9B, which is a comparative example, the X-ray diffraction peak intensity from the (117) plane, which is an orientation component having a large polarization, is relatively small, whereas in FIG. It can be seen that the X-ray diffraction peak intensity from the (117) plane is much larger than that of the comparative example. Further, compared with FIG. 5A of Example 1 of the present embodiment, the X-ray diffraction peak intensity from the (004) plane, (006) plane, and (008) plane, which are c-axis alignment components, is suppressed. I understand.

  Further, comparing the surface SEM photographs of FIGS. 10A and 10B, the size of the ferroelectric crystal grains is small in FIG. 10B which is a comparative example, whereas in FIG. 10A which is the present invention, the ferroelectric crystal grains are small. It can be seen that is larger than the comparative example.

  From the above results, according to the method for forming a ferroelectric film according to Example 2 of the embodiment of the present invention, it is possible to promote the growth of ferroelectric crystal grains having an orientation component having a large polarization, and Crystal growth of a sufficiently large ferroelectric crystal grain can be performed. And by making the first temperature profile as shown in FIG. 7C, the ferroelectric material film can be pre-sintered at a temperature that prevents escape of highly volatile Bi in the ferroelectric film, In addition, it can be seen that ferroelectric crystal grains can be nucleated in a state in which c-axis orientation is suppressed, and as a result, a ferroelectric film having sufficient polarization characteristics can be formed.

  In the temperature profiles of FIGS. 3A and 7A in Example 1 and Example 2, in the temperature rising step A, the temperature rising rate is 1 to 13 ° C./second, and the substrate temperature is less than 550 ° C. When the temperature is 550 ° C. or more and 9 ° C./second or less, the processing time in the temperature region where the nucleation of the ferroelectric crystal grains occurs is shortened, and the crystal growth of the ferroelectric crystal grains is performed. By increasing the processing time in the temperature range, it is possible to moderately suppress the nucleation of ferroelectric crystal grains, it is possible to promote the growth of crystal grains having an orientation component having a large polarization, and Crystal growth of sufficiently large ferroelectric crystal grains can be performed. Note that the rate of temperature increase in the temperature increasing step A is not limited to this, and a certain degree of effect can be obtained by setting the rate of temperature increase to a minimum as the substrate temperature increases.

  Further, by setting the holding temperature in the temperature holding step B to 700 ° C. or less, the c-axis orientation of the ferroelectric crystal grains can be suppressed.

  Further, in the temperature lowering step C, the temperature lowering rate is 5 ° C./second or more when the substrate temperature is 500 ° C. or more, and 5 ° C./second or less when the substrate temperature is less than 500 ° C .. Crystal growth of ferroelectric crystal grains having a size can be performed. The temperature decreasing rate in the temperature decreasing step C is not limited to this, and a certain degree of effect can be obtained by setting the temperature decreasing rate to decrease with a decrease in the substrate temperature.

  In the temperature profile of FIG. 7C in Example 2, in the temperature raising step a, the rate of temperature rise is 5 ° C./second, but by setting it to 10 ° C./second or less, the ferroelectric material in the temperature raising step a The escape of Bi in the film can be effectively prevented, and the effect of suppressing c-axis orientation is enhanced.

  Further, the holding temperature in the second temperature holding step d is set to 600 ° C., but the maximum temperature in the second temperature holding step d is set to a temperature lower than the holding temperature in the second heat treatment. Thus, the crystal grains can be made sufficiently large. When the holding temperature in the second heat treatment is 700 ° C., the temperature may be 650 ° C. or lower. Further, by reducing the holding time in the second temperature holding step d by 2 seconds, the volatilization of Bi or the like in the ferroelectric material film during the holding at the maximum temperature in the second temperature holding step d. Of high-performance elements can be effectively prevented, and the effect of suppressing c-axis orientation is enhanced. The holding time in the second temperature holding step d is not limited to this, and a certain degree of effect can be obtained by making it shorter than the holding time in the first temperature holding step b.

  In the temperature lowering step e, the temperature decreasing rate is 5 ° C./second or more when the substrate temperature is 500 ° C. or higher, and 5 ° C./second or lower when the substrate temperature is less than 500 ° C. The effect of suppressing the axial orientation is enhanced. Alternatively, the crystal grains can be made sufficiently large. The temperature decreasing rate in the temperature decreasing step e is not limited to this, and a certain degree of effect can be obtained by setting the temperature decreasing rate to decrease with a decrease in the substrate temperature.

  Further, in the temperature raising step c, the rate of temperature rise is set to an average of 30 ° C./second, so that Bi in the ferroelectric material film is eliminated during the temperature rise to the maximum temperature in the second temperature holding step d. It can be effectively prevented.

  Further, by providing the temperature lowering step e subsequent to the second temperature holding step d, the effect of suppressing the c-axis orientation is enhanced.

In this embodiment, BLT is used as the ferroelectric material constituting the capacitive insulating film 21, but Bi _{4-x + y} A _x Ti ₃ O ₁₂ (A is La, Pr, Nd, Sm). , Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and V are elements selected from the group consisting of x and y in the general formula: 0 ≦ x ≦ 2 and 0 <y ≦ A ferroelectric material represented by the general formula (4−x) × 0.1) may be used. Also in this case, it is possible to suppress the loss of Bi at the A site. The ferroelectric material constituting the capacitive insulating film 21 is not limited to the ferroelectric material containing Bi, and the same effect can be obtained as long as it is a ferroelectric material having a highly volatile element as a constituent element. It is done. Furthermore, in the case of a ferroelectric material having a crystal structure having anisotropy in the crystal axis, the growth of crystal grains having an orientation component having a large polarization is suppressed while suppressing the orientation to a crystal axis having a small spontaneous polarization. The effect which can be made is acquired.

  In the present embodiment, the capacitor element 23 has a planar shape, but may be a capacitor element having a three-dimensional structure having a concave shape or a convex shape in a cross section perpendicular to the substrate.

  The method for forming a ferroelectric film and the method for manufacturing a semiconductor memory device according to the present invention are useful for a memory using a ferroelectric capacitor.

It is process sectional drawing which shows the manufacturing method of the semiconductor memory device which concerns on one Embodiment of this invention. It is a process flow which shows the formation method of the ferroelectric film which concerns on one Embodiment of this invention. A is a temperature profile of the second heat treatment in the method for forming a ferroelectric film according to Example 1 of one embodiment of the present invention, B is a temperature profile of the second heat treatment for comparison, C is a temperature profile of the first heat treatment. A is a hysteresis loop measured for a ferroelectric film (Invention 1) formed by the method of forming a ferroelectric film according to Example 1 of one embodiment of the present invention, and B is a strong loop formed for comparison. It is the hysteresis loop measured about the dielectric material film (comparative example 1). A is an X-ray diffraction profile measured for a ferroelectric film (Invention 1) formed by the method of forming a ferroelectric film according to Example 1 of one embodiment of the present invention, and B is formed for comparison. 3 is an X-ray diffraction profile measured for the ferroelectric film (Comparative Example 1). A is a surface SEM photograph of a ferroelectric film (Invention 1) formed by the method of forming a ferroelectric film according to Example 1 of one embodiment of the present invention, and B is a strong film formed for comparison. It is a surface SEM photograph about a dielectric film (comparative example 1). A is a temperature profile of the second heat treatment in the method of forming a ferroelectric film according to Example 2 of one embodiment of the present invention, B is a temperature profile of the second heat treatment for comparison, C is a temperature profile of the first heat treatment in the method for forming a ferroelectric film according to Example 2 of one embodiment of the present invention. A is a hysteresis loop (invention 2) measured for a ferroelectric film formed by the method for forming a ferroelectric film according to Example 2 of one embodiment of the present invention, and B is a strong loop formed for comparison. It is a hysteresis loop (comparative example 2) measured about the dielectric film. A is an X-ray diffraction profile (invention 2) measured for a ferroelectric film formed by the ferroelectric film forming method according to Example 2 of one embodiment of the present invention, and B is formed for comparison. 3 is an X-ray diffraction profile (Comparative Example 2) measured for the ferroelectric film. A is a surface SEM photograph (invention 2) of a ferroelectric film formed by the method of forming a ferroelectric film according to Example 2 of one embodiment of the present invention, and B is a strong film formed for comparison. It is a surface SEM photograph (comparative example 2) about a dielectric material film. It is a process flow which shows the formation method of the ferroelectric film based on a prior art. It is a crystal lattice structure diagram of BLT.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Semiconductor substrate 12 Element isolation region 13 Gate insulating film 14 Gate electrode 15 Gate protective insulating film 16 Impurity diffusion layer 17 Field effect transistor 18 which is a memory cell transistor Insulating film 19 Contact plug 20 Lower electrode 21 Capacitor insulating film 22 Upper electrode 23 Capacitance element 81 Bismuth oxide layer 82 Pseudo perovskite layer 83 Bi
84 Oxygen 85 A-site element 86 B-site element

Claims (17)

A ferroelectric comprising a step of depositing a ferroelectric material film on a support substrate and a step of sintering the ferroelectric material film by performing a plurality of heat treatments on the ferroelectric material film In the film formation method,
One heat treatment P of the plurality of heat treatments includes a temperature raising step, a temperature holding step, and a temperature lowering step,
The method of forming a ferroelectric film, wherein the temperature raising step includes a step of raising the temperature of the substrate at a rate of temperature rise that decreases with an increase in the temperature of the substrate.   2. The formation of a ferroelectric film according to claim 1, wherein the rate of temperature rise is 9 ° C./second or more when the temperature of the substrate is less than 550 ° C. and 9 ° C./second or more when the temperature is 550 ° C. or more. Method.   The method for forming a ferroelectric film according to claim 1, wherein a maximum temperature in the temperature holding step is 700 ° C. or lower.   The method of forming a ferroelectric film according to claim 1, wherein the temperature lowering step includes a step of lowering the temperature of the substrate at a temperature lowering rate that decreases with a decrease in the temperature of the substrate.   5. The method of forming a ferroelectric film according to claim 4, wherein the temperature lowering rate is 5 ° C./second or more when the temperature of the substrate is 500 ° C. or more and 5 ° C./second or less when the temperature is less than 500 ° C. 6. . Before the one heat treatment P, including a step of performing a heat treatment different from the one heating step,
The heat treatment different from the one heat treatment P is higher than the temperature in the temperature raising step, the first temperature holding step, and the first temperature holding step, and in the first temperature holding step. The method for forming a ferroelectric film according to claim 1, further comprising a second temperature holding step of heating the substrate at a temperature and a temperature lowering step.   The method of forming a ferroelectric film according to claim 6, wherein the temperature lowering step in the heat treatment different from the one heat treatment P is performed subsequent to the second temperature holding step.   The method for forming a ferroelectric film according to claim 6, wherein the maximum temperature in the second temperature holding step is lower than the maximum temperature in the temperature holding step in the one heat treatment P.   The method for forming a ferroelectric film according to claim 8, wherein a maximum temperature in the second temperature holding step is 650 ° C. or less.   The method for forming a ferroelectric film according to claim 6, wherein the rate of temperature increase to the maximum temperature in the second temperature holding step is 30 ° C./second on average.   7. The ferroelectric film according to claim 6, wherein the time for maintaining the maximum temperature in the second temperature maintaining step is the shortest of the time for maintaining the same temperature in the heat treatment different from the one heat treatment P. 8. Forming method.   The method for forming a ferroelectric film according to claim 11, wherein the time for maintaining the maximum temperature in the second temperature holding step is 2 seconds or less.   The ferroelectric material according to claim 6, wherein the temperature lowering step in the heat treatment different from the one heat treatment P includes a step of lowering the temperature of the substrate at a temperature lowering rate that decreases with a decrease in the temperature of the substrate. Method for forming a film.   The temperature lowering rate in a heat treatment different from the one heat treatment P is 5 ° C./second or more when the temperature of the substrate is 500 ° C. or more, and 5 ° C./second or less when the temperature is less than 500 ° C. Item 14. A method for forming a ferroelectric film according to Item 13.   The ferroelectric film according to claim 6, wherein the temperature raising step in the heat treatment different from the one heat treatment P includes a step of raising the temperature of the substrate at a temperature raising rate of 10 ° C./second or less. Forming method. The ferroelectric film is Bi _{4-x + y} A _x Ti ₃ O ₁₂ (where A is La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu And V, wherein x and y satisfy the following formula: 0 ≦ x ≦ 2 and 0 <y ≦ (4-x) × 0.1) The method of forming a ferroelectric film according to claim 1, wherein the ferroelectric film is a material. Forming a lower electrode on the support substrate;
Forming a capacitive insulating film made of a ferroelectric film on the lower electrode by the ferroelectric film forming method according to any one of claims 1 to 16,
And a step of forming an upper electrode on the capacitor insulating film.