JP2010010566A - Method of depositing metal oxide insulating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of depositing a metal oxide insulating film by which leakage current density can be reduced and device characteristics and reliability can be improved in the deposition of the insulating film for a nonvolatile semiconductor memory element. <P>SOLUTION: A noble gas having an atomic weight above Kr is introduced, and a metal oxide target containing a metal element which is heavier than the introduced noble gas is used to form, by sputtering, the metal oxide insulating film containing a metal element of La, Hf, etc., heavier than the introduced noble gas like LaHfO, LaAlO, and ZrAlO. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for forming a metal oxide insulating film on a substrate by introducing a sputtering gas into a vacuum vessel, applying a high voltage to cause ions of the sputtering gas to collide with a target and sputtering a target material. . Furthermore, the present invention relates to a nonvolatile semiconductor memory element manufactured using a method for forming a metal oxide insulating film, a manufacturing method thereof, a control program for a film forming apparatus, and a recording medium.

  Non-volatile semiconductor memory elements include FG (Floating Gate) type and MONOS (Metal Oxide Semiconductor Semiconductor) type as charge trapping means.

  The FG type uses a conductive film such as polysilicon buried in a gate insulating film as a charge storage layer. Since the FG type uses polysilicon or the like, the energy barrier with the gate insulating film is large, and there is little leakage of trapped charges to the semiconductor substrate surface or the gate electrode side.

  On the other hand, the MONOS type uses an insulating film such as a silicon nitride film stacked in a gate insulating film. The MONOS type has a small energy barrier because charges are accumulated in the stacked gate insulating films. Therefore, in general, the FG type has better memory retention characteristics at a higher temperature than the MONOS type.

  However, the FG type has a problem in thinning the silicon oxide film between the FG portion and the surface of the semiconductor substrate in terms of charge retention capability. That is, when an FN tunnel is injected into a silicon oxide film of 10 nm or less, a leakage current in a low electric field region called SILC (Stress Induced Leakage Current) is generated, and all charges accumulated in the FG are lost through this leakage path. Therefore, in the thinning of the tunnel oxide film in the FG type, 8 nm is the lower limit from the viewpoint of charge retention capability because SILC occurs. Therefore, in the FG type, it is difficult to achieve both reduction in operating voltage due to miniaturization and maintenance of holding capability.

  On the other hand, in the MONOS type, charge trapping sites responsible for charge accumulation exist spatially discretely in an insulating film including the site. Therefore, even if a leak path by SILC similar to that of the FG type occurs, only local charges around the leak path are lost, and the non-volatility of the entire element does not disappear. Therefore, the MONOS type can reduce the thickness of the silicon oxide film between the charge retention layer and the semiconductor substrate surface. As a result, the operating voltage of the device can be reduced by reducing the thickness as compared with the FG type.

  In recent years, from the viewpoint of miniaturization described above, MONOS type nonvolatile semiconductor memory elements have attracted attention for the purpose of further increasing the integration of semiconductor memory elements.

  The MONOS type generally has a structure in which a silicon oxide film as a first insulating film, a silicon nitride film as a second insulating film, and a silicon oxide film as a third insulating film are stacked from the surface side of the semiconductor substrate. The first silicon oxide film has a function of preventing stored charges from leaking to the semiconductor substrate. The second silicon nitride film functions as a charge storage layer. The third silicon oxide film functions as a blocking layer to prevent leakage of accumulated charges to the gate electrode side.

  With the miniaturization of the MONOS type semiconductor nonvolatile memory element, it is desired to apply an insulating film having a high dielectric constant as a blocking layer, and the application of a gate insulating film having a relative dielectric constant larger than that of a silicon oxide film is desired. It is being considered. This insulating film having a relative dielectric constant larger than that of the silicon oxide film is called a high dielectric constant film.

  Here, the equivalent oxide film thickness will be described. Regardless of the type of gate insulating film, assuming that the gate insulating film material is a silicon oxide film, the electrical film thickness of the insulating film obtained by calculating backward from the gate capacitance is the equivalent silicon oxide film thickness (EOT: Equivalent Oxide Thickness). That is, when the relative dielectric constant of the insulating film is εh, the relative dielectric constant of the silicon oxide film is εo, and the thickness of the insulating film is dh, the equivalent silicon oxide film thickness de is de = dh × (εo / εh ).

In the above formula, when a material having a dielectric constant εh larger than the relative dielectric constant εo of the silicon oxide film is used for the gate insulating film, the equivalent film thickness of the silicon oxide film is the film of the gate insulating film. It shows that it is equivalent to a silicon oxide film thinner than the thickness. The relative dielectric constant εo of the silicon oxide film is about 3.9. Therefore, for example, a film made of a high dielectric constant material with εh = 39 has a silicon oxide equivalent film thickness (electrical film thickness) of 1.5 nm even if its physical film thickness is 15 nm. Therefore, the tunnel current can be significantly reduced while keeping the capacitance value of the gate insulating film equal to that of the silicon oxide film having a thickness of 1.5 nm. Therefore, by applying a high dielectric constant film to the blocking layer, it is possible to reduce the operating voltage by reducing the thickness of the EOT without causing deterioration of the retention characteristics due to leakage. Examples of a method for forming a high dielectric constant film include a CVD (Chemical Vapor Deposition) method, an atomic layer adsorption deposition method, and a sputtering method. In the CVD method, since there is an incubation time in the formation process, controllability of film thickness, in-plane uniformity, and reproducibility are problems. On the other hand, in the sputtering method, the oxidation of the base and the formation of the interface layer due to plasma damage to the insulating film are problems. For the formation of a high dielectric constant film by this sputtering method, reactive sputtering using a mixed gas of a reactive gas such as Ar and O ₂ is used as a sputtering gas.

For example, Patent Document 1 proposes a technique for forming a tantalum oxide film having a thickness of 20 nm using a mixed gas of Ar and O ₂ .

  In Patent Document 2, an oxide target is used in a sputtering apparatus using radio frequency (RF) power, and only an Ar gas to which no oxygen-containing gas is added is introduced as a sputtering gas to form an insulating film. Techniques for performing membranes have been proposed.

  Patent Document 3 proposes a magnetron sputtering apparatus having a magnet on the back surface of a metal target, an RF coil on the target to increase the ionization rate, and a substrate facing the target. This magnetron sputtering apparatus alternately forms a metal film and converts the metal film into an insulating compound by oxidation to form an insulating film.

JP-A-62-128167 Japanese Patent Laid-Open No. 02-085355 Japanese Patent Laid-Open No. 11-200032

By the way, the following problems exist in the method for forming the insulating film described above. That is, in the method of Patent Document 1, since a mixed gas of Ar and O ₂ gas is used, there is a problem that the base of the insulating film (the lower layer of the insulating film or the substrate) is oxidized and EOT increases.

  Such a problem of base oxidation can be avoided, for example, by a method of introducing only Ar gas without adding an oxygen-containing gas to the sputtering gas as in Patent Document 2. However, since traps are formed by implanting the elements constituting the target into the base substrate, there is a problem that hysteresis occurs in the capacitance-voltage characteristics, resulting in variations in device characteristics and reliability.

  Further, the film forming method disclosed in Patent Document 3 also has a problem in that device characteristics are deteriorated because traps are formed by implanting elements constituting the target into the base substrate.

  As described above, in the conventional method for forming an insulating film, it is difficult to suppress deterioration of device characteristics due to low leakage current density and trap formation at the interface, which are required for insulating films of nonvolatile memory elements in recent years. .

  In view of the circumstances described above, an object of the present invention is to provide a method for forming a metal oxide insulating film that can reduce a leakage current density and improve hysteresis to improve device characteristics and reliability. And It is another object of the present invention to provide a nonvolatile semiconductor memory device manufactured using the metal oxide insulating film forming method according to the present invention, a manufacturing method thereof, a control program for the film forming apparatus, and a recording medium.

  The configuration of the present invention made to achieve the above object is as follows.

  That is, in a method of forming a metal oxide insulating film on a substrate by introducing a sputtering gas into the interior of a vacuum vessel, applying a high voltage to cause sputtering gas ions to collide with a target and sputtering a target material. A procedure for introducing a gas containing a rare gas having an atomic weight of at least Kr as the sputtering gas to generate plasma, and a target of a metal oxide containing a metal element having an atomic weight heavier than the rare gas in the plasma And forming a metal oxide insulating film containing at least one metal element having an atomic weight heavier than that of the rare gas, and forming a metal oxide insulating film.

  According to the present invention, a rare gas having an atomic weight of Kr or more is introduced as a sputtering gas, a plasma is generated by applying a high voltage, and a metal oxide target containing a metal element having an atomic weight heavier than the rare gas. Can be used, the resputtering rate can be lowered. Therefore, the leakage current density can be reduced without causing an increase in EOT due to the oxidation of the base as compared with the conventional sputtering film formation of the insulating film using Ar. Moreover, hysteresis can be improved and device characteristics and reliability can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments.

  FIG. 1 is a schematic view showing a film forming apparatus used for carrying out a method for forming a metal oxide insulating film according to the present invention.

  As shown in FIG. 1, a film forming apparatus 1 according to this embodiment includes a vacuum chamber (chamber) 2 that can be evacuated as a processing chamber, and physical vapor deposition (PVD: Physical Vapor Deposition or sputtering film formation) on a substrate 10. Device (also called). That is, the film forming apparatus 1 of the present embodiment introduces a sputtering gas (a gas used for sputtering film formation) into the vacuum vessel 2 and applies a high voltage to cause the cations of the sputtering gas to collide with the target. A target material is sputtered to form a metal oxide insulating film on the substrate 10.

  An exhaust device 9 such as an exhaust pump is connected through an exhaust port 8 of the vacuum vessel 2. Further, a gas introduction system 15 having a flow rate controller 15A and valves 15B, 15C, etc. is connected to the vacuum vessel 2 as means for introducing the sputtering gas, and the sputtering gas is introduced from the gas introduction system 15 at a predetermined flow rate. Is done. As the sputtering gas of the present embodiment, a gas containing a rare gas having an atomic weight of at least krypton (Kr) among the group 18 elements in the long periodic table is introduced. As the rare gas having an atomic weight of Kr or more, for example, Kr or xenon (Xe) is used alone, and argon (Ar) or the like is mixed and supplied into the vacuum vessel 2 as necessary.

  The vacuum vessel 2 includes a pressure measurement mechanism (not shown), a process pressure measurement mechanism (not shown), and a partial pressure measurement mechanism (not shown). The pressure measurement mechanism can measure the pressure in the chamber. The process pressure measuring mechanism can measure pressure during the process. The partial pressure measuring mechanism can measure the partial pressure of various gas components such as oxygen. An ion gauge or the like can be used as the pressure measuring mechanism. As the process pressure measuring mechanism, a mechanism corresponding to the process pressure such as a diaphragm gauge can be used. As the partial pressure measuring mechanism, a partial pressure measuring device using quadrupole mass spectrometry and other partial pressure measuring devices can be used as appropriate.

  In the film forming apparatus 1 of the present embodiment, a substrate holder 7 that holds a substrate 10 is disposed at the bottom of a vacuum vessel 2, and a target 4 supported by a cathode electrode 6 is disposed at the top.

  The substrate holder 7 is, for example, a disc-shaped holding table. The substrate holder 7 places the substrate 10 on the upper surface (front surface), and the substrate 10 is held with its processing surface facing upward. . The substrate holder 7 can be rotated in the in-plane direction of the substrate 10 by a rotation mechanism (not shown) such as a motor. The substrate holder 7 includes a heating mechanism (not shown) such as a heater.

  An example of the substrate 10 is a semiconductor wafer, and the substrate 10 is held by the substrate holder 7 in a state of only the substrate or mounted on a tray.

  For example, a high frequency power supply 12 is connected to the cathode electrode 6 via a matching unit 11 as a discharge power supply for supplying a high voltage. A magnet unit 13 for magnetron discharge is provided in the main body of the cathode electrode 6. The magnet unit 13 is connected to a rotation mechanism (not shown), is rotatable along the in-plane direction of the cathode electrode 6, and forms a magnetic flux parallel to the cathode surface.

  In the present embodiment, the target 4 is made of a metal oxide containing at least one metal element having an atomic weight heavier than that of the rare gas. The top of the vacuum vessel 2 is provided with a shutter mechanism 14 rotatably supported by a rotation mechanism (not shown), and the front surface of the target 4 is opened and closed by a rotation operation of the shutter mechanism 14.

  Note that a gate valve (not shown) for opening and closing a transfer path of the substrate 10 onto the substrate holder 7 is provided on the side wall of the vacuum vessel 2.

  Next, a method for forming a metal oxide insulating film according to the present invention will be described. FIG. 2 is a schematic view showing the concept of the method for forming an insulating film according to the present invention.

  With reference to FIGS. 1 and 2, first, a metal oxide target including at least one metal element having an atomic weight heavier than the rare gas is installed as a target 4 in the vacuum vessel 2. Then, the inside of the vacuum vessel 2 is exhausted to a predetermined degree of vacuum by the exhaust device 9 through the exhaust port 8.

  Next, a gate valve (not shown) on the side wall of the vacuum vessel 2 is opened, and the substrate 10 is transferred to the upper surface (front surface) of the substrate holder 7 using a transfer arm (not shown) such as a robot arm. After holding the substrate 10 on the substrate holder 7, the transfer arm is retracted and the gate valve is closed.

Next, sputtering gas is introduced into the vacuum vessel 2 from the gas introduction system 15. In this case, the sputtering gas, the oxygen-containing gas such as O ₂ is not mixed. As the sputtering gas, a gas having a high purity (usually about 99.999%) that is usually used in physical vapor deposition (PVD) is used. In the present embodiment, as the sputtering gas, a gas containing a rare gas having an atomic weight of at least Kr or more, for example, Kr among the Group 18 elements of the long periodic table, for example, Kr is introduced at a predetermined flow rate. At this time, the oxygen partial pressure of the vacuum vessel 2 is set to 1 × 10 ⁻⁶ Pa or less.

  Next, under the introduction of the sputtering gas, discharging power is applied to the cathode electrode 6 from the high-frequency power source 12 while rotating the magnet unit 13 by a rotating mechanism. When a high voltage is applied to the cathode electrode 6, magnetron discharge is performed between the cathode electrode 6 and the substrate holder 7 to generate plasma. Next, the front of the target 4 is opened by rotating the shutter mechanism 14. A target material is sputtered by a rare gas cation having an atomic weight equal to or greater than Kr in the plasma, and a metal oxide insulating film containing at least one metal element having an atomic weight heavier than the rare gas is formed on the processing surface of the substrate 10. Is done. As a result, the leakage current and hysteresis of the insulating film are improved as compared with the conventional case, and the equivalent silicon oxide film thickness (EOT) does not increase.

  After depositing a predetermined film thickness on the substrate 10, the power supply from the high-frequency power source 12 is stopped. Further, the introduction of the sputtering gas from the gas introduction system 15 is stopped, the front of the target 4 is closed by the turning operation of the shutter mechanism 14, and the inside of the vacuum vessel 2 is exhausted by the exhaust device 9.

  Next, after opening the gate valve, a transfer arm (not shown) is inserted, and the substrate 10 is unloaded from the vacuum chamber 2. Finally, the gate valve is closed to complete the entire process.

  In the present invention, a metal oxide insulating film containing at least one metal element having an atomic weight heavier than an introduced rare gas is formed on a substrate by PVD using a metal oxide target. At that time, a gas containing a rare gas having an atomic weight of at least Kr or more among the group 18 elements of the long periodic table is used as a sputtering gas, and the leakage current of the insulating film is formed by film formation in a non-oxidizing atmosphere. And based on the finding that the hysteresis is improved and the EOT does not increase.

  This is considered to be derived from the following principle. In general, when power is applied to a target to sputter target atoms with cations, sputtered particles such as atoms constituting the target and secondary electrons are emitted from the target with which the cations of the sputtering gas collide. In addition, cations that collide with the target are reflected or scattered without losing the charge. Furthermore, among the cations that collided with the target, there are noble gas atoms that lose their charge and reflect off and scatter out with considerable energy. This atom is called a “reflected atom” and attention is paid to this reflected atom. Since the reflected atoms have high energy, the film is re-sputtered by colliding with the deposited film on the substrate.

  This ratio, that is, the resputtering rate, is a function of ATOMIC MASS PARAMETER represented by the following formula when the atomic weight of the target constituent atom is Massstart and the atomic weight of the sputtering gas is Massgas (see DW Hoffman, J. et al. Vac.Sci.Technol.A8, 3707 (1990) “Intrinsic recycling-theory and experience”).

  ATOMIC MASS PARAMETER = (Massstartet-Massgas) / (Massstart + Massgas)

  When the target material is an atom heavier than Ar, such as La (atomic weight 138.906) and Hf (atomic weight 178.49), when sputtering is performed with Kr (atomic weight 83.798) compared to Ar (atomic weight 39.948). The resputtering rate on the substrate is lowered.

  For example, when the target material is lanthanum (La) and the sputtering gas is Ar, ATOMIC MASS PARAMETER = 0.553. W. According to FIG. 4 in Hoffman's document, the resputtering rate is about 11%. On the other hand, when the target material is La and the sputtering gas is Kr, ATOMIC MASS PARAMETER = 0.247, and the resputtering rate is about 6%. From the above, when the sputtering gas is Kr, the resputtering rate is about half that of Ar.

  Similarly, the resputtering rate is about 14% from ATOMIC MASS PARAMETER = 0.634 when the target material is hafnium (Hf) and the sputtering gas is Ar. Further, the resputtering rate is about 7% from ATOMIC MASS PARAMETER = 0.361 when the target material is Hf and the sputtering gas is Kr. Therefore, even in the case of Hf, if Kr is used, the resputtering rate can be made lower than that of Ar.

  Thus, it is clear that when the target material containing a metal element with an atomic weight heavier than the sputtering gas is used, the resputtering rate of the deposited film due to the reflected atoms increases as the target material atoms are heavier than the sputtering gas. It is. A low resputtering rate is considered to indicate that the density of the deposited film is high and a desired film can be formed. If the density of the film is low, there is a problem that when a voltage is applied, vacancies (vacant sites of atoms generated by resputtering) in the film are lined up to create a path through which a current flows, and the current easily flows.

  From this point of view, when the LaHfO film is formed using Kr gas as the sputtering gas, a higher density film can be formed and the leakage current density can be reduced as compared with the film formation using Ar gas as the sputtering gas. It is thought that the hysteresis characteristics could be improved.

  As described above, when a target material containing a metal element having an atomic weight heavier than the sputtering gas is used, the resputtering rate can be lowered by using Kr as the sputtering gas. Therefore, when a metal oxide insulating film containing at least one metal element having an atomic weight heavier than the sputtering gas is formed by PVD using a metal oxide target, even if Xe is used as the sputtering gas, Ar and In comparison, the electrical characteristics of the deposited film can be dramatically improved.

If the atomic weight of the sputtering gas atom and the target material atom are close to each other, or if the atomic weight of the target material atom is lighter than the sputtering gas atom, there is a difference in the weight of the target material atom. The effect on the resputtering rate is reduced. That is, the use of a heavy rare gas such as Kr or Xe as the sputtering gas is more effective than the formation of SiO ₂ or Al ₂ O ₃ which is an oxide of an element lighter than Kr, for example, an element lighter than Ar. It is considered that the method is particularly effective for forming an insulating film containing a heavy element such as Hf or Hf. On the other hand, a metal oxide target containing other elements heavier than heavier rare gases such as Kr and Xe, for example, if the rare gas is Kr, Hf, La, Zr, Dy, Y, Ta, Ce, This is effective when Pr or the like is included in the target material. Further, if the rare gas is Xe, it is effective when Hf, La, Dy, Ta, Ce, Pr, etc. are included in the target material.

  Further, not only when only Kr is used as the sputtering gas, but also when a mixed gas of Kr and Ar is used, the above-described effect of improving the electrical characteristics can be obtained according to the partial pressure of Kr. It is presumed that the resputtering rate due to the reflected atoms decreases by the amount of Kr mixed. The same applies to Xe.

  The conceptual diagram of FIG. 2 illustrates the case where the target 4 is parallel to the substrate 10, but when the target 4 is disposed obliquely above the substrate 10 as shown in FIG. 1, the target diameter may be small. It is more preferable because the cost can be reduced.

Next, the reason why it is important to form a film in a non-oxidizing atmosphere will be described. Here, the non-oxidizing atmosphere means that the sputtering gas does not contain an oxygen-containing gas such as O ₂ . More specifically, the oxygen partial pressure in the film forming atmosphere of the vacuum vessel 2 is 1 × 10 ⁻⁶ Pa or less. In the conventional reactive sputtering method comprising an oxygen containing gas such as O ₂ in the sputtering gas, EOT increases. However, in the method of the present invention, the sputtered particles of the oxide material sputtered from the target are not necessarily atomic but have a considerable number of clusters. As a result of film formation in a non-oxidizing atmosphere, active atomic oxygen and molecular oxygen that affect the increase in EOT are extremely reduced in the atmosphere, and an increase in EOT is caused by adding an oxygen-containing gas such as O _{2 to the} sputtering gas. Compared to the case where it is added, it is considered that there is almost no problem.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these Examples.

[Example 1]
Example 1 describes a case in which hafnium lanthanum oxide which is a high dielectric constant film is formed using Kr as a sputtering gas in the film forming method according to the present invention.

  In Example 1, the film forming apparatus 1 shown in FIG. 1 is used, and this film forming apparatus 1 further includes a control device 16 shown in FIG. FIG. 3 is a block diagram illustrating the film forming apparatus and the control apparatus according to the first embodiment.

  With reference to FIG. 1 again, the film forming apparatus 1 will be schematically described. The film forming apparatus 1 includes a vacuum container 2 that can be evacuated, an exhaust system apparatus 9 that exhausts the inside of the vacuum container 2 through an exhaust port 8, a gas introduction system 15 that introduces a predetermined gas into the vacuum container 2, It has. In this vacuum vessel 2, a cathode electrode 6 including a target 4 provided with a surface to be sputtered exposed, a substrate holder 7 for holding a substrate 10 at a predetermined position where sputtered particles emitted from the target 4 reach, It has.

  The gas introduction system 15 is configured so that Ar gas can be introduced for Kr, Xe, and comparative experiments. A magnetic unit 13 for realizing magnetron sputtering is disposed in the main body of the cathode electrode 6. The cathode electrode 6 including the target 4 is installed obliquely above the substrate 10. The cathode electrode 6 is connected to a high frequency power source 12 for applying sputtering discharge power to the target 4 and a matching unit 11. The shutter mechanism 14 opens and closes between the target 4 and the substrate 10 by the rotation operation. At the time of film formation, the shutter mechanism 14 is opened.

  Referring to FIG. 3, the control device 16 is formed by a computer, and the computer includes a CPU (Central Processing Unit) 17, a storage device 18 storing a control program, and an input device 19 for inputting setting information and the like. Has been. The computer 16 is electrically connected to and can communicate with a control element of the film forming apparatus 1, and transmits an operation command necessary for film formation to the film forming apparatus 1.

  As the computer 16, for example, a widely used personal computer (PC) having a predetermined performance can be used.

  The CPU 17 performs control of each control element and various arithmetic processes according to the control program.

  Examples of the storage device 18 include a mask ROM and a hard disk (HDD). The ROM stores various programs and parameters for controlling the basic operation of the film forming apparatus. The RAM temporarily stores programs and data as a work area. The HDD stores various programs, parameters, and data. As the recording medium, various computer-readable recording media such as compact discs such as CD-ROM and CD-R, magneto-optical disc (MO), floppy (registered trademark) disc (FD), and flash memory are used.

  The input device 19 can use any other input means such as a keyboard, a mouse, a touch panel, and voice input.

  The storage device 18 stores an algorithm for executing the metal oxide insulating film forming method according to the present invention as a control program. In other words, the control program is mounted as a mask ROM or used by being installed from a recording medium in the HDD. The control program includes a procedure for introducing a gas containing a rare gas having an atomic weight of Kr or more into the vacuum vessel 2 and applying a high voltage to generate plasma, and a metal element having an atomic weight heavier than the rare gas. Performing a procedure of exposing the metal oxide target to the plasma.

  The input device 19 inputs a command to the CPU 17 such as execution of a control program. The CPU 17 reads the control program from the storage device 18 and executes it. The film forming apparatus 1 is controlled based on a program execution command, and a plasma is generated in the presence of a gas containing a rare gas having an atomic weight of Kr or more, and a metal element having an atomic weight heavier than the rare gas is included in the plasma. And a step of exposing the metal oxide target comprising.

Next, a method for forming an insulating film using the film forming apparatus 1 and the control apparatus 16 will be described. The cathode electrode 6 in the vacuum vessel 2 has La ₂ O ₃ and HfO ₂ containing metal elements (La, Hf) having a heavier atomic weight than the introduced rare gas as the target 4 in a 1: 2 (molar ratio). the La ₂ Hf ₂ O ₇ formed on the installation.

First, the gate valve (not shown) of the vacuum vessel 2 is opened, the substrate 10 is loaded into the vacuum vessel 2 using a transfer arm (not shown), and placed on the substrate holder 7. After holding the substrate 10 on the substrate holder 7, the transfer arm is retracted and the gate valve is closed. Further, the exhaust system device 9 exhausts the pressure in the vacuum vessel 2 until it becomes 5 × 10 ⁻⁶ Pa or less. At this time, when the oxygen partial pressure value of the vacuum vessel 2 was measured by the partial pressure measuring mechanism, it was 1 × 10 ⁻⁹ Pa.

  Next, a gas containing a rare gas having an atomic weight of at least Kr or more is introduced as a sputtering gas. When a high frequency voltage is applied from the high frequency power source 12 to the target 4 while introducing the sputtering gas from the gas introduction system 15, sputter discharge occurs in the space where the target 4 faces, and the target 4 is sputtered by the self-bias voltage. As a result, hafnium lanthanum oxide (hereinafter referred to as “LaHfO film”) is formed on the surface of the substrate 10. In this specification, the LaHfO film used as the name of the film is not related to the composition ratio of elements in the film. (Also for other films) films are deposited.

  During this film formation, the substrate holder 7 is rotated by a rotation mechanism (not shown), and the substrate 10 is rotated with respect to the stationary target 4. Thereby, the LaHfO film formed on the substrate 10 becomes a uniform film. By using the deposition apparatus 1 that rotates the substrate 10 while sputtering particles are deposited from the target 4 that is installed obliquely with respect to the substrate 10, an extremely uniform and high-quality film can be obtained. it can.

Next, film forming conditions will be described. The La ₂ Hf ₂ O ₇ target was supplied with 300 W of high-frequency power (frequency of 13.56 MHz). An insulating film of LaHfO having a thickness of 20 nm was formed on a silicon substrate having a specific resistance of 8 to 12 Ω · cm at a pressure of 0.1 Pa by introducing Ksc gas having a purity of 99.999% as a sputtering gas. Note that sccm is an abbreviation for standard cc per minute, and is a unit of gas flow rate supplied per minute in terms of cm ^{3 at} 0 ° C. and 1 atm, which is the standard state. The oxygen partial pressure value during film formation by the partial pressure measuring mechanism was 1 × 10 ⁻⁷ to 1 × 10 ⁻⁸ Pa.

  In addition, for comparison with this example, Ar gas of 140 sccm having a purity of 99.9999% was introduced to a pressure of 0.1 Pa, and similarly, a 20 nm LaHfO film was formed on a silicon substrate having a specific resistance of 8 to 12 Ω · cm. An insulating film was formed.

  Thereafter, an Al pad having a diameter of 1 mm was deposited as the upper electrode by vapor deposition using a mask for measuring the electrical characteristics of the formed LaHfO film. In was used as the lower electrode.

FIG. 4 is an explanatory diagram showing current-voltage characteristics of the LaHfO film obtained by the above film forming method. As shown in FIG. 4, it can be seen that the leakage current density is lower when the sputter deposition is performed using Kr gas than when the sputtering deposition is performed using Ar gas. In particular, at 5 [−MV / cm], the leakage current density when sputtering with Ar gas is 7.4 × 10 ⁻⁹ [A / cm ² ], compared with 7.4 × 10 ⁻⁹ [A / cm ² ]. When the film was formed, it was 1.4 × 10 ⁻⁹ [A / cm ² ], which was as low as about 1/5.

  Next, FIG. 5 is an explanatory diagram showing capacitance-voltage characteristics of the LaHfO film of FIG. As shown in FIG. 5, it can be seen that the width of the hysteresis is narrower when the sputter film is formed with Kr gas than when the sputter film is formed with Ar gas. That is, in FIG. 5, the hysteresis width in the case of the conventional Ar is 0.4V, whereas Kr is 0.28V, and as a result, the hysteresis is improved to about 70% of Ar in Kr. .

Further, unlike the conventional sputtering film formation of an insulating film using a mixed gas of Ar and O ₂ , there is no problem that the EOT is increased by oxidizing the base.

[Example 2]
In the second embodiment, a case where Xe is used as a sputtering gas and hafnium lanthanum oxide which is a high dielectric constant film is formed in the method for forming an insulating film according to the present invention will be described.

In this example, the same apparatus as in Example 1 was used, and the film was formed under the same procedure and the same conditions except for the sputtering gas. That is, 300 W of high-frequency power (frequency: 13.56 MHz) was input to the La ₂ Hf ₂ O ₇ target. An Xe gas having a purity of 99.9999% was introduced as a sputtering gas to a pressure of 0.1 Pa, and a 20 nm LaHfO insulating film was formed on a silicon substrate having a specific resistance of 8 to 12 Ω · cm.

When current-voltage characteristics and capacitance-voltage characteristics were measured in the same manner as in Example 1, a leakage current density lower than that of Kr and good hysteresis characteristics, that is, a narrow hysteresis width were obtained. Further, unlike the conventional sputtering film formation of an insulating film using a mixed gas of Ar and O ₂ , there is no problem that the base is oxidized and EOT is increased.

Example 3
With reference to FIG. 6, the manufacturing method of the semiconductor memory element of Example 3 is demonstrated. FIG. 6 is a cross-sectional view showing a manufacturing process of the semiconductor memory device of Example 3.

  The semiconductor memory device of this embodiment includes a substrate having at least a surface composed of a semiconductor layer, a gate electrode formed on the substrate, and a stacked gate insulating layer sequentially stacked between the substrate and the gate electrode. And a membrane. The metal oxide insulating film constituting at least one layer of the stacked gate insulating film is stacked by using the metal oxide insulating film forming method according to the present invention.

  Specifically, first, as shown in FIG. 6A, the element isolation layer 24 was formed on the surface of the silicon substrate 23 by using STI (Shallow Trench Isolation) technology.

  Next, a silicon oxide film 25 having a thickness of 30 to 100 mm is formed as a first insulating film on the element-isolated silicon substrate 23 by a thermal oxide film method.

  On the silicon oxide film 25, a silicon nitride film 26 having a thickness of 30 to 100 mm is formed as a second insulating film by LPCVD (Low Pressure Chemical Vapor Deposition).

  On this silicon nitride film 26, an aluminum oxide film 27 is formed as a third insulating film with a thickness of 5 to 50 mm. For the aluminum oxide film 27, an MOCVD method, an ALD (Atomic Layer Deposition) method, or a PVD (Physical Vapor Deposition) method may be used.

  On this aluminum oxide film 27, a LaHfO film 28 is formed as a fourth insulating film with a thickness of 10 to 200 mm. The formation of LaHfO is the same as the formation conditions of Example 1 and Example 2.

  On this LaHfO film 28, an aluminum oxide film 29 is formed as a fifth insulating film with a thickness of 5 to 50 mm. As a film formation method, an MOCVD method, an ALD method, or a PVD method is used.

  Next, a poly-Si film 30 having a thickness of 150 nm was formed on the aluminum oxide film 29 as a gate electrode.

  Thereafter, as shown in FIG. 6 (b), the gate electrode is processed by using lithography technology and RIE (Reactive Ion Etching) technology, and then ion implantation is performed, and the gate electrode is formed by using the extension diffusion region 31 as a mask. Consistently formed.

  Further, as shown in FIG. 6C, a gate side wall 32 is formed by sequentially depositing a silicon nitride film and a silicon oxide film and then performing etch back. In this state, ion implantation was performed again, and source / drain diffusion layers 33 were formed through activation annealing.

  As a result of evaluating the electrical characteristics of the fabricated nonvolatile semiconductor memory element, it was confirmed that there was no characteristic variation or reliability deterioration due to the influence of traps in the blocking layer and the reduction of leakage current.

  As described above, it has been found that good characteristics can be obtained even when the method for forming an insulating film according to the present invention is applied to a method for manufacturing a nonvolatile semiconductor memory element.

  In this embodiment, a poly-Si film is used as the gate electrode. However, the same effect can be obtained by using TiN, TaN, W, WN, Pt, Ir, Pt, Ta, Ti as the gate electrode. did it.

  Furthermore, in this embodiment, the first insulating film, the second insulating film, the third insulating film, the fourth insulating film, and the fifth insulating film are annealed by activation annealing after ion implantation. However, annealing may be performed after each insulating film is formed.

  In this embodiment, as the blocking layer of the nonvolatile semiconductor memory element, a stacked insulating film of the third insulating film, the fourth insulating film, and the fifth insulating film is used. The same effect could be obtained with a laminated insulating film of the film and the fourth insulating film.

  The metal oxide insulating film deposition method of the present invention can be widely applied to the manufacture of nonvolatile semiconductor memory elements.

It is a schematic diagram which shows the film-forming apparatus used for implementation of the film-forming method of the insulating film concerning this invention. It is the schematic which shows the concept of the film-forming method of the insulating film concerning this invention. 1 is a block diagram illustrating a film forming apparatus and a control apparatus of Example 1. FIG. 6 is an explanatory diagram showing current-voltage characteristics of a LaHfO film in Example 1. FIG. 6 is an explanatory diagram showing capacitance-voltage characteristics of a LaHfO film in Example 1. FIG. 7 is a cross-sectional view showing a manufacturing process of the semiconductor memory element of Example 3. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Film-forming apparatus 2 Vacuum container 4 Target 6 Cathode electrode 10 Board | substrate 12 High frequency power supply 13 Magnet unit 15 Gas supply system 16 Control apparatus 18 Memory | storage device 23 Silicon substrate 24 Element isolation area 25 1st insulating film 26 2nd insulating film 27 Third insulating film 28 Fourth insulating film 29 Fifth insulating film 30 Gate electrode

Claims (10)

In a method of forming a metal oxide insulating film on a substrate by introducing a sputtering gas into the inside of a vacuum vessel, sputtering a target material by applying a high voltage to cause ions of the sputtering gas to collide with the target,
Introducing a gas containing a rare gas having an atomic weight of at least Kr as the sputtering gas to generate plasma;
A step of exposing a metal oxide target including a metal element having an atomic weight heavier than the rare gas to the plasma and forming a metal oxide insulating film including at least one metal element having an atomic weight heavier than the rare gas; ,
A method for forming a metal oxide insulating film, comprising: 2. The method of forming a metal oxide insulating film according to claim 1, wherein the sputtering gas has an oxygen partial pressure of an oxygen-containing gas of 1 × 10 ⁻⁶ Pa or less.   The method of forming a metal oxide insulating film according to claim 1, wherein the sputtering gas is Kr.   The method of forming a metal oxide insulating film according to claim 1, wherein the sputtering gas is Xe.   The metal oxide insulating film forming method according to claim 1, wherein the sputtering gas is a mixed gas containing Kr or Xe.   6. The method for forming a metal oxide insulating film according to claim 1, wherein the target includes at least one of Hf and La. A method for manufacturing a nonvolatile semiconductor memory element having a metal oxide insulating film,
A method for manufacturing a nonvolatile semiconductor memory element, wherein the metal oxide insulating film is stacked by the film forming method according to claim 1. A substrate having at least a surface composed of a semiconductor layer;
A gate electrode formed on the substrate;
A stacked gate insulating film sequentially stacked between the substrate and the gate electrode;
Have
7. A nonvolatile semiconductor memory element, wherein a metal oxide insulating film constituting at least one layer of the stacked gate insulating film is formed by the film forming method according to claim 1. A deposition apparatus that introduces a sputtering gas into a vacuum vessel, applies a high voltage to cause ions of the sputtering gas to collide with the target, sputters the target material, and forms a metal oxide insulating film on the substrate. A controlling program,
Introducing a gas containing a rare gas having an atomic weight of at least Kr as the sputtering gas to generate plasma;
A step of exposing a metal oxide target including a metal element having an atomic weight heavier than the rare gas to the plasma and forming a metal oxide insulating film including at least one metal element having an atomic weight heavier than the rare gas; ,
A control program for causing a film forming apparatus to execute the above.   A computer-readable recording medium having the control program according to claim 9 recorded thereon.

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