JP2009238842A - Forming method of ferroelectric thin film and paraelectric thin film, and semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming a ferroelectric thin film and a paraelectric thin film on an insulating material substrate of a plastic substrate or glass substrate, and to provide a manufacturing method of a ferroelectric memory using the same. <P>SOLUTION: An amorphous PZT thin film 2 is deposited on an insulating material substrate 1 by a spin coating method. A continuous oscillation laser beam 4 which is shaped linear and has a wavelength of 532 nm is scan-radiated on a surface 3 of oxide 2 for crystallization, thereby excellent ferroelectric characteristics is provided. Since an optimum heat can be applied to a target oxide 2 concentrically for a short period, rising of temperature of the substrate 1 and other layer is suppressed. Since laser beam radiation is executed in a short period, even if the temperature of oxide film abruptly rises, dislocation in composition due to evaporation is minimum. In particular, the insulating material substrate 1 of plastic substrate or glass substrate is used to ensure less thermal loss to the substrate, resulting in effective crystallization. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for forming a ferroelectric thin film and a paraelectric thin film on an insulating material substrate such as a glass substrate or a plastic substrate, and a method for manufacturing a ferroelectric memory using the same.

  A ferroelectric memory is a non-volatile memory that uses a ferroelectric thin film having spontaneous polarization for cells arranged on a matrix and detects the polarization state of the cells. Since this memory uses high-speed polarization reversal and remanent polarization of a ferroelectric thin film, it has features such as high-speed writing and low power consumption. The direction of spontaneous polarization of a ferroelectric is reversed by applying an electric field. A positive or negative charge is induced on the surface by switching the applied voltage between positive and negative. Since the induced positive or negative charge is held in a nonvolatile manner, a nonvolatile memory is obtained. Conventionally, the ferroelectric memory has been mainly manufactured on a silicon substrate.

Ferroelectric materials include Pb (Zr, Ti) O3 (hereinafter referred to as PZT), a perovskite ferroelectric, and SrBi ₂ Ta ₂ O ₉ (hereinafter referred to as SBT), a Bi-layered ferroelectric. Oxides are well known. Ferroelectric thin film manufacturing methods include spin coating, chemical vapor deposition (CVD), sputtering, and metal organic chemical vapor deposition (MOCVD). There is also known a method of coating a film of a misted ferroelectric material on a substrate. In order to obtain a ferroelectric thin film such as a PZT film or an SBT film after film formation by these methods, it is usually necessary to perform heat treatment at a high temperature of 500 ° C. or higher to crystallize. Heat treatment at 700 ° C. to 700 ° C. and 700 ° C. to 800 ° C. are necessary for SBT films. Conventionally, a ferroelectric thin film is crystallized by heating the entire substrate with a quartz heating furnace or RTA (Rapid Thermal Anneal).

  Thin film transistors (TFTs) are widely used as pixel switches for active matrix operation in flat panel displays (FPDs) such as liquid crystal displays (LCDs) and organic EL displays. Due to demands for thinner and thinner displays and lower costs, a system-on-panel (SOP) is required, in which not only the pixel switch but also the control driver circuit, CPU, and memory are built on the same glass substrate. ing. As a memory to be manufactured in the SOP, a ferroelectric memory is optimal from the viewpoint of low power consumption. On the other hand, glass substrates are damaged or curved at temperatures of 500 ° C. or higher. Therefore, when these substrates are used, it is necessary to perform crystallization while maintaining a low temperature or room temperature below these temperatures. For this reason, in order to fabricate a ferroelectric memory on a glass substrate, it is necessary to form a ferroelectric thin film at a temperature of 500 ° C. or lower. However, a conventional quartz heating furnace or RTA heats the entire substrate. These manufacturing methods cannot be used.

  In order to fabricate a ferroelectric memory or a ferroelectric thin film on an insulating material substrate such as a glass substrate or a plastic substrate, the substrate is damaged or bent at a temperature of 500 ° C or higher for a glass substrate and 200 ° C or higher for a plastic substrate. Therefore, when these substrates are used, it is necessary to perform crystallization while maintaining the temperature below these temperatures or at room temperature.

  Laser annealing is a low-temperature crystallization of ferroelectric thin films such as PZT and SBT films. However, on silicon substrates, the thermal conductivity of the silicon substrate is high, so heat loss is large. Is not heated and crystallization does not proceed. As conventional laser annealing, there is a pulse oscillation excimer laser annealing method of a ferroelectric thin film formed on a silicon substrate as described in Japanese Patent Publication No. 2002-314045. In such a pulse oscillation, even if the required amount of heat can be supplied to the target oxide film thin film on average, a very high energy beam is irradiated at the peak. Further, since the silicon substrate has a high thermal conductivity, even if the temperature of the oxide film thin film is once increased by laser irradiation, the heat of the oxide film thin film is transmitted to the silicon substrate and rapidly cooled after the laser pulse irradiation. For this reason, the crystal growth of a ferroelectric thin film intended to give predetermined energy continuously to the atoms in the oxide, facilitate the diffusion of active atoms, and promote crystallization is not possible on the silicon substrate. The pulsed excimer laser annealing method is not suitable for the ferroelectric thin film deposited on the substrate. On the other hand, the thermal conductivity is low on the glass substrate, which is about 1/100 of that of the silicon substrate, and is sufficiently heated by laser annealing. As a result, crystallization is promoted.

  However, when a ferroelectric thin film such as a PZT film or SBT film is formed on an insulating material substrate such as a glass substrate and crystallized using a laser beam, the insulating material substrate is damaged by the temperature rise of the ferroelectric thin film. . Conversely, the impurities in the insulating material substrate diffuse to the ferroelectric thin film during laser annealing, and the ferroelectric thin film characteristics deteriorate.

  When a thin film transistor is formed on an insulating material substrate such as a glass substrate, a ferroelectric thin film formed on the PZT film or SBT film formed on the thin film is crystallized using a laser beam. As the temperature rises, the thin film transistor is damaged.

  In the method for forming a ferroelectric thin film and a paraelectric thin film according to the present invention, an insulating substrate such as a glass substrate or a plastic substrate is used as a substrate, and an oxide thin film is deposited on the substrate directly or via another layer. Thereafter, the laser beam is irradiated to promote crystallization.

  Further, in the above method, the laser beam is irradiated and the oxide thin film is heated through the underlying laser light absorption layer of the oxide thin film that becomes a ferroelectric to promote crystallization.

  In the above method, another laser light absorption layer is formed on the oxide thin film, and then laser irradiation is performed to promote crystallization.

  In the above method, an oxide that becomes a ferroelectric or paraelectric by depositing an insulating thin film such as a silicon oxide film as a buffer layer on an insulating material substrate such as a glass substrate or a plastic substrate and crystallizing on the insulating thin film. By depositing a thin film, damage to the insulating material substrate during laser beam irradiation is prevented. At the same time, this insulating thin film buffer layer suppresses impurity diffusion into the ferroelectric thin film or paraelectric.

  In the above method, when a thin film transistor is formed on an insulating material substrate such as a glass substrate or a plastic substrate, an insulating thin film such as a silicon oxide film is deposited on the thin film transistor as a buffer layer, and further crystallized to produce a ferroelectric. By depositing an oxide thin film serving as a body, damage to the thin film transistor during laser beam irradiation is prevented.

  In the above method, another layer is formed on the oxide thin film, and then laser irradiation is performed to promote crystallization.

  In the above method, at least a part of the oxide thin film is an oxide having a perovskite phase crystal structure.

  In the above method, at least a part of the oxide thin film is an oxide having a pyrochlore phase crystal structure.

  In the above method, the laser beam is irradiated with laser output control and scan control to promote crystallization of the ferroelectric thin film or the paraelectric thin film.

  If a laser beam is applied to an oxide film that becomes a ferroelectric film formed on an insulating material substrate such as a glass substrate or a plastic substrate according to the present invention, the thermal conductivity of the insulating material substrate is low. The temperature can be maintained, and therefore, crystallization of perovskite is promoted, and an excellent ferroelectric thin film having a c-axis orientation particularly necessary for ferroelectricity can be produced.

  According to the present invention, an insulating thin film such as a silicon oxide film is deposited on an insulating material substrate such as a glass substrate or a plastic substrate, and an oxide thin film that becomes a ferroelectric substance is crystallized on the insulating thin film directly or on the substrate. By depositing through another layer, damage to the insulating material substrate at the time of laser beam irradiation can be prevented, and at the same time, diffusion of impurities into the ferroelectric thin film can be suppressed by this insulating thin film. Even when a thin film transistor is formed on an insulating material substrate such as a glass substrate or a plastic substrate, the present invention can prevent damage to the thin film transistor. By using the present invention, a ferroelectric memory using a TFT can be fabricated on an insulating material substrate such as a glass substrate or a plastic substrate.

  Examples will be shown below, but these are examples of the present invention, and the present invention is not limited to these, and can be applied to the formation of other ferroelectric films.

  A schematic diagram of Example (1) of the present invention is shown in FIG. A PZT thin film 2 having a thickness of 250 nm is deposited on the glass substrate 1 by spin coating. According to the X-diffraction method, this oxide is not crystallized and is amorphous (amorphous state). Thereafter, a continuous wave laser beam 4 having a wavelength of 532 nm shaped into a line is scanned and irradiated on the oxide surface 3 to be crystallized. 1 in FIG. 1 indicates the scanning direction. The laser power is 1.0-4.0 W. By moving the Si substrate on which the oxide film deposited on the X-Y stage is moved, the laser is irradiated to the oxide laser. The method for forming a ferroelectric thin film of the present invention has an advantage that excellent ferroelectric properties can be obtained by accelerating crystallization of the ferroelectric thin film on the glass substrate by laser beam irradiation. Since optimum heat can be applied to the target oxide in a concentrated manner in a short time, the temperature rise of the substrate and other layers can be suppressed. In addition, even if the temperature of the oxide film is rapidly increased by laser beam irradiation, the treatment can be performed in a short time, and compositional deviation due to evaporation or the like can be minimized. In particular, since an insulating material substrate such as a glass substrate or a plastic substrate is used, the heat loss to the substrate is small and crystallization can be performed effectively.

  A schematic diagram of Example (2) of the present invention is shown in FIG. On the glass substrate 1, a Ti thin film 50 nm is formed 6 by sputtering, a Pt thin film 200 nm is formed 7, and then a PZT thin film 2 having a thickness of 250 nm is deposited by spin coating. The Ti thin film 6 is formed in order to improve the adhesion between the Pt thin film 7 and the glass substrate 1. The Pt thin film 7 is formed as a base electrode of the PZT thin film 2, but is also used as a laser light absorption layer at the time of laser irradiation. Thereafter, a continuous wave laser beam 4 having a wavelength of 532 nm shaped into a line is scanned and irradiated on the oxide surface 3 to be crystallized. 2 in FIG. 2 indicates the scanning direction. The laser power is 1.0-4.0 W. By moving the Si substrate on which the oxide film deposited on the X-Y stage is moved, the laser is irradiated to the oxide laser.

A schematic diagram of Example (3) of the present invention is shown in FIG. A 400 nm silicon oxide film is deposited 8 on the glass substrate 1 by APCVD, a 50 nm Ti film is deposited 6 by sputtering, a 200 nm Pt film 7 is deposited, and then 250 nm is deposited by spin coating. A PZT thin film 2 having a thickness is deposited. The silicon oxide film 8 is deposited as a buffer layer. This buffer layer prevents damage to the glass substrate during laser beam irradiation, and suppresses impurity diffusion from the glass substrate to the ferroelectric thin film. According to the X-diffraction method, this oxide is not crystallized and is amorphous (amorphous state). Thereafter, a continuous wave laser beam 4 having a wavelength of 532 nm shaped into a line is scanned and irradiated on the oxide surface 3 to be crystallized. 3 in FIG. 3 indicates the scanning direction. The laser power is 1.0-4.0 W. By moving the Si substrate on which the oxide film deposited on the XY stage is moved, laser irradiation is performed on the oxide laser component. An optical micrograph of the surface of the obtained ferroelectric thin film is shown in FIG. As shown in this figure, the state of the ferroelectric thin film depends on the speed of laser scanning. FIG. 5 shows the laser output and scan speed dependence of the crystallization state of the ferroelectric thin film. FIG. 6 shows the measurement results by X-ray diffraction (XRD). In the microcrystalline region (scanning speed 9, 11 cm / s), a pyrochlore phase Py (222), which is a paraelectric phase, is observed, and no peak of the perovskite phase showing ferroelectric properties is observed. The phase Py (222) was not expressed and the peak of the perovskite phase was observed. In particular, it became clear that c-axis Per (001), which exhibits ferroelectric properties, becomes particularly prominent at an island grain crystallization region scan speed of 5.0 cm / s. The polarization characteristics under this island-shaped grain crystal condition are shown in FIG. The measurement was performed under the condition of island-shaped grain crystals at a laser output of 1.0 W. Although the remanent polarization was very low at a scan speed of 3.0 cm / s, the remanent polarization increased as the scan speed was slowed down, and a high remanent polarization characteristic of 13 μC / cm ² was exhibited at a scan speed of 0.9 cm / s.

  FIG. 8 shows a schematic cross-sectional view of a ferroelectric memory cell of Example (4) according to the present invention. As shown in FIG. 8A, a ferroelectric capacitor 14 is provided in connection with the drain electrode of the thin film transistor 11 formed on the glass substrate 9. One electrode is connected to the wiring 13. In the case of the 1T1C type ferroelectric memory, the wiring 13 is a bit line and the wiring 15 is a plate line. As a silicon oxide film buffer layer, a buffer layer 10 on a glass substrate and a buffer layer 12 on a thin film transistor are formed. In the method for manufacturing a ferroelectric memory according to the present invention, the laser capacitor is selectively irradiated to the formation portion of the ferroelectric capacitor, so that the influence of heat on the substrate and other layers is small. Therefore, if necessary, the temperature of the oxide film can be raised to a higher temperature than when processing in a heat treatment furnace as in the prior art. This makes it possible to form a ferroelectric thin film memory cell under ideal conditions. FIG. 8B is a memory circuit model. A voltage is applied to the word line and the bit line, and a differential voltage from the plate voltage is applied to the ferroelectric capacitor 17 through the thin film transistor 16, and the memory operation is performed according to the polarity. By implementing the present invention, a ferroelectric thin film memory cell can be manufactured on an insulating material substrate such as a glass substrate or a plastic substrate.

  By implementing the present invention, a ferroelectric capacitor can be formed on an insulating material substrate such as a glass substrate or a plastic substrate, and thus a ferroelectric memory combined with a thin film transistor can be manufactured on the insulating material substrate. Practical value in industrial production is high, and it can be expected to contribute widely to the electronics industry.

It is a schematic diagram of continuous wave laser beam irradiation implementing the present invention. The beam is scanned over the PZT thin film deposited on the glass substrate. It is a schematic diagram of continuous wave laser beam irradiation implementing the present invention. A Pt thin film is formed as a lower electrode of the PZT thin film, and this Pt thin film is also used as a laser light absorption layer during laser irradiation. It is a schematic diagram of continuous wave laser beam irradiation implementing the present invention. A silicon oxide film is deposited on the glass substrate as a buffer layer, and this buffer layer prevents damage to the glass substrate during laser beam irradiation, and this buffer layer suppresses impurity diffusion from the glass substrate to the ferroelectric thin film. . 2 is an optical micrograph of a ferroelectric film according to an embodiment of the present invention. Crystallization can be performed by continuous wave laser beam irradiation, and three patterns of crystallization can be performed: lateral crystal growth, island grain growth, and microcrystallization, depending on the laser irradiation conditions. The laser crystallization conditions according to the practice of the present invention are shown. 3 is an X diffraction pattern of a ferroelectric film according to an embodiment of the present invention. By the continuous wave laser beam irradiation, the intensity of the perovskite phase (indicated by “Per” in the figure) showing the ferroelectric characteristics is increased. 3 shows polarization characteristics of a ferroelectric film according to an embodiment of the present invention. The cross-sectional schematic diagram and circuit model of the ferroelectric memory cell by this invention are shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 PZT thin film 3 Surface 4 Laser beam 5 Scanning direction 6 Ti thin film 7 Pt thin film 8 Silicon oxide film 9 Glass substrate 10 Buffer layer 11 on glass substrate Thin film transistor 12 Buffer layer 13 on thin film transistor Wiring (bit line)
14 Ferroelectric capacitor 15 Wiring (plate line)
16 Circuit symbol of thin film transistor 17 Circuit symbol of ferroelectric capacitor

Claims (9)

  An insulating material substrate such as a glass substrate or a plastic substrate is used as a substrate, and an oxide thin film that becomes a ferroelectric or paraelectric material is deposited on the substrate directly or through another layer by crystallization, and then a laser is formed. A method for forming a ferroelectric thin film and a paraelectric thin film, which comprises irradiating a beam to promote crystallization.   A laser light absorption layer is formed directly or through another layer on an insulating material substrate such as a glass substrate or a plastic substrate, and an oxide thin film that becomes a ferroelectric or paraelectric material is formed thereon, and then a laser beam is irradiated. The method for forming a ferroelectric thin film and a paraelectric thin film according to claim 1, wherein the oxide thin film is heated through the laser light absorption layer to promote crystallization.   2. The ferroelectric thin film and the paraelectric thin film according to claim 1, wherein another laser light absorbing layer is further formed on the oxide thin film, and thereafter laser irradiation is performed to promote crystallization. Forming method.   An insulating thin film such as a silicon oxide film is deposited as a buffer layer on an insulating material substrate such as a glass substrate or a plastic substrate, and an oxide thin film serving as a ferroelectric or paraelectric is deposited thereon. 2. The method for forming a ferroelectric thin film and a paraelectric thin film according to 1.   A thin film transistor is formed on an insulating material substrate such as a glass substrate or a plastic substrate, an insulating thin film such as a silicon oxide film is deposited thereon as a buffer layer, and an oxide thin film serving as a ferroelectric or paraelectric is further formed on the substrate. 2. The method for forming a ferroelectric thin film and a paraelectric thin film according to claim 1, wherein the thin film is deposited directly or via another layer.   6. The method for forming a ferroelectric thin film and a paraelectric thin film according to claim 1, wherein at least a part of the oxide thin film is an oxide having a perovskite phase crystal structure.   4. The method of forming a ferroelectric thin film and a paraelectric thin film according to claim 1, wherein at least a part of the oxide thin film is an oxide having a pyrochlore phase crystal structure.   5. The ferroelectric thin film according to claim 1, wherein the laser thin film is irradiated with a laser output control and a scan control to promote crystallization of the ferroelectric thin film or the paraelectric thin film. Method for forming a paraelectric thin film.   A semiconductor device manufactured using the method for forming a ferroelectric thin film and a paraelectric thin film according to any one of claims 1 to 8.