KR100233999B1 - Method for manufacturing pb(zr1-xtix)03(pzt)ferroelectric thin film - Google Patents

Abstract

In the present invention, _{Pb (Zr 1-X Ti X} ) O 3 ferroelectric thin film manufacturing method according to the sputtering method or a laser ebeul Corporate Law _{Pb (Zr 1-X Ti X} ) O 3 ferroelectric thin film manufacturing method using the ferroelectric Among the deposition conditions used in the manufacture of the thin film, the amount of Pb (or amount of PbO) of the target component is adjusted so that the composition of the deposited thin film contains an excess of PbO component in the range of 20-60%, or the deposition pressure is 5- By adjusting to 100mTorr, the Pb (Zr _1-X Ti _X ) O ₃ ferroelectric thin film is deposited at low temperature, 1) Pb (Zr ₁ having excellent crystallinity at a lower temperature than the conventional case without introducing a seed layer _-X Ti _X ) O ₃ ferroelectric thin film can be manufactured, and 2) difficulty in controlling thin film composition generated at high temperature deposition or deterioration in switching characteristics of ferroelectric memory devices manufactured using the thin film can be eliminated. , 3) fatigue properties of Pb (Zr _1-X Ti _X ) O ₃ ferroelectric thin films Highly reliable Pb (Zr _1-X Ti _X ) O ₃ ferroelectric thin films can be realized.

Description

Pb (Zr1-xTix) O3 (PZT) ferroelectric thin film manufacturing method

1 is a graph showing the results of X-ray diffraction (XRD) analysis of Pb (Zr _1-x Ti _x ) O ₃ ferroelectric thin film prepared by the present invention.

2a to 2f are graphs showing the change in PE (polarization-field) hysteresis curve according to the applied voltage change of the Pb (Zr _1-x Ti _x ) O ₃ ferroelectric thin film prepared by the present invention.

3 is a graph showing the fatigue characteristics of the Pb (Zr _1-x Ti _x ) O ₃ ferroelectric thin film prepared according to the present invention measured by applying a square pulse of 1MHz frequency.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a ferroelectric thin film, and in particular, to use in a nonvolatile ferroelectric random access memory (hereinafter referred to as NVFRAM) or a device using characteristics related to piezoelectric, pyroelectric, and nonlinear optical of a ferroelectric thin film. It relates to a Pb (Zr _1-x Ti _x ) O ₃ (hereinafter referred to as PZT) ferroelectric thin film manufacturing method.

PZT series ferroelectric thin film has high dielectric constant, excellent piezoelectricity and pyroelectricity, and excellent optical properties, making it suitable for DRAM (dynamic RAM) devices, microactuators, infrared detectors and other optical devices. In recent years, with the rapid development of semiconductor processing technology, it has been spotlighted as a main material of nonvolatile ferroelectric memory devices. In the present invention, as an application using the PZT ferroelectric thin film, the application to the non-volatile ferroelectric memory device currently commercialized will be described as a representative example.

In order for a ferroelectric thin film to be used as a capacitor of a nonvolatile ferroelectric memory device, the residual dielectric polarization (Pr) value must be high, while the leakage current value is low and the residual and spontaneous polarization values must not change over time. It should also have good fatigue characteristics and low dielectric loss.

Currently, PZT, various layered compounds (e.g., SrBi ₂ Ta ₂ O ₉ , BaBi ₂ Ta ₂ O ₉ , Bi ₄ Ti ₃ O _12, etc.), PLZT ((x / y / 1-y) and the like, and research on thinning to make a thin film having excellent characteristics is in progress.

The sputtering method is one of the most widely used methods for thinning various materials, but the method is not easy to control the composition of the thin film. In particular, the deposition of thin films containing highly volatile Pb or Bi is more difficult.

This difficulty in controlling the composition becomes larger as the temperature of the substrate is increased during thin film production, and therefore, it is advantageous to deposit at a low temperature as possible. In addition, oxygen vacancies or Pb cation vacancy present at the interface in contact with the electrode form a space charge layer, which may cause a deterioration in switching characteristics in which the voltage direction changes periodically.

The reason for the low temperature deposition as possible is essential to enable the generation using the existing semiconductor process as part of the large scale integrated circuit (LSIC) process, and the mutual diffusion between the substrate and the ferroelectric thin film The problem solving of the same interfacial reaction is one of the reasons.

As an example, Xinjiao et al. Deposited a PZT (composition ratio of 55/45: Zr and Ti) film at a temperature of 250 ° C by reactive sputtering, but as a result, non-perovskite phases other than PZT A decrease in the film quality was observed as present. Please refer to App. Phys. Lett., 63 2345 (1993).

As another example, Gifford et al. Deposited PZT thin films on Pt / Ti / MgO substrates or RuO ₂ / SiO ₂ / Si substrates at a temperature as low as 500 ° C. using ion beam sputtering. For related information, see Mater. Res. Soc. Symp. Proc. 243, 191 (1992).

Unlike the low temperature deposition study of the thin film without the seed layer between the substrate and the ferroelectric thin film, Kwok et al. Deposited a 450 Å PbTiO ₃ film as a seed layer by the sol-gel method. A PZT thin film was deposited thereon to lower the transition temperature onto the perovskite phase by about 100 ° C., and Kanno et al. (Pb, La) TiO ₃ (hereinafter referred to as PLT) by using a multi ion beam sputtering method ) Layer was deposited as a seed layer, and then a PZT thin film was deposited thereon at a temperature of about 415 ° C. For related information, see J. Mater. Res., 8, 339 (1992), and Jpn. J. Appl. Phys., 32, 4057 (1994), respectively.

However, using a sputtering method that is still readily available as a production equipment, a report on the successful deposition of PZT ferroelectric thin films with properties applicable to applications such as nonvolatile ferroelectric memory devices at low temperatures of around 500 ° C without seed layers There is no.

Accordingly, the present invention is made to solve the above problems caused when the ferroelectric thin film is deposited at a high temperature, Pb easy to occur during the production of PZT ferroelectric thin film using the sputtering method or laser ablation method. Sufficiently add Pb or PbO to the target so that more of the excess PbO component (e.g., 20-60% excess PbO component) is contained in the deposited thin film, which is enough to offset the lack of ions. By manufacturing a ferroelectric thin film using a method of controlling the deposition pressure of the sputtering gas or by sputtering gas, it is possible to produce a PZT ferroelectric thin film having excellent crystallinity at a lower temperature than the conventional case without introducing a seed layer. Its purpose is to provide a PZT ferroelectric thin film manufacturing method.

The first manufacturing method of the PZT ferroelectric thin film according to the present invention for achieving the above object, in the method for producing a Pb (Zr _1-x Ti _x ) O ₃ ferroelectric thin film using the sputtering method, used in the production of the ferroelectric thin film Among the deposition conditions, the Pb amount of the target component is controlled to contain an excess PbO component in the range of 20-60% of the deposited thin film, so that the PZT ferroelectric thin film is formed at a low temperature.

A second method for producing a PZT ferroelectric thin film according to the present invention for achieving the above object, in the Pb (Zr _1-x Ti _x ) O ₃ ferroelectric thin film manufacturing method using the sputtering method or laser ablation method, Among the deposition conditions used in the production of ferroelectric thin films, the PbO amount of the target component is controlled to contain an excess Pbo component in the range of 20-60%, thereby forming a PZT ferroelectric thin film at low temperature. It is done.

A third method for producing a PZT ferroelectric thin film according to the present invention for achieving the above object, in the method for producing a Pb (Zr _1-x Ti _x ) O ₃ ferroelectric thin film using the sputtering method, used in the production of the ferroelectric thin film By controlling the deposition pressure to 5-100 mTorr, the composition of the thin film to be deposited without changing the target composition (i.e. without adding excess Pb component) contains 20% to 60% of the excess PbO component, The PZT ferroelectric thin film is formed at a low temperature.

As a result of the above process, it is possible to lower the deposition temperature of the thin film required for manufacturing the PZT ferroelectric thin film by about 100 ° C.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

The present invention provides a filmable temperature of a PZT ferroelectric thin film deposited by using a radio frequency (RF) or direct current (DC) sputtering method, an ion beam sputtering method, a laser ablation method, etc. without introducing a seed layer. The deposition method is lowered to a temperature as low as 500-550 ℃, in order to realize this method presented in the present invention is largely divided into two.

One method is to lower the deposition temperature of the PZT ferroelectric thin film by adjusting the composition of the target used in manufacturing the PZT ferroelectric thin film, and the other is to control the deposition pressure of the PZT ferroelectric thin film. It is a lower way.

First, look at the method of ①.

In general, when depositing a PZT ferroelectric thin film by sputtering or laser ablation, a shortage of Pb ions is likely to occur due to strong volatility before, after or after the deposition of the thin film.

Therefore, in the method of (1) above, the amount of PbO is targeted so that the deposited thin film contains more PbO components (e.g., excess Pb component of about 20-60%) more than can compensate for the shortage of Pb ions. By sufficiently adding to the Pb component, the Pb component which is easily volatilized in the composition of the thin film to be deposited is sufficiently contained as an excess component, and the excessively added Pb component does not affect the crystallinity of the thin film to be deposited (excess component This means that the PZO ferroelectric thin film containing PbO components and other independent PbO phases are not formed by the excessively added PbO.) It is possible to deposit PZT ferroelectric thin films having excellent crystallinity even at low temperatures.

This excess PbO component not only compensates for the shortage of Pb itself generated during film formation, but also facilitates the transition to the perovskite phase during the application of an optimal film with ferroelectricity, which is typically above 600 ° C. It serves to lower the deposition temperature requiring about 100 ℃.

That is, in the method of ①, a target is manufactured and used as a deposition source so that the deposition thin film contains an excess of 20-60% of PbO component, and the deposition temperature of the substrate is maintained at 500-550 ° C. PZT ferroelectric thin film is deposited by the ablation method.

Here, as an example, a case of depositing a PZT ferroelectric thin film at a temperature of 500-550 ° C. using a sputtering method will be described through the examples shown in Table 1 below.

(Where 52/48 of PZT (52/48) represents the composition ratio of Zr and Ti)

Table 1 shows a typical deposition condition when a thin film is deposited by a conventional sputtering method at a substrate temperature of 520 ° C. using a ceramic target in which an excess of 50% PbO component is added to deposit a PZT thin film using the method of ①. Is shown.

In this case, low temperature deposition is possible even if various conditions necessary for depositing a thin film are changed in addition to the conditions shown in Table 1 as an example. For example, instead of a target containing excess PbO component, or using a target containing excess Pb component so that the PbO component of the deposited film falls within the 20-60% range (eg 50%), or This is the case of changing the gas flow rate ratio of oxygen. However, when the ferroelectric thin film is deposited at a low temperature by controlling the amount of Pb contained in the target, the thin film deposition process should be performed using sputtering instead of laser ablation.

Even when the composition of the target is changed by including an excess of Pb component so that the PbO content of the deposited thin film is changed in the range of 20-60%, the excessively added Pb component does not affect the crystallinity of the thin film to be deposited. (Meaning that Pb added with excess component does not form PZT ferroelectric thin film containing PbO component and other independent PbO phase), and only Pb component which is easy to volatilize in the composition of the deposited film is sufficient as excess component. As a result, PZT ferroelectric thin films having excellent crystallinity can be deposited at low temperatures. As described above, when depositing a PZT ferroelectric thin film using a target containing excess Pb, the temperature of the substrate during deposition must be maintained at 500-550 ° C.

In addition to the ratio of 9: 1 mentioned in Table 1, the gas flow rate change range may not include any oxygen gas, or may be added in the range of 10-100% to improve the quality of the film. Therefore, in this case, the amount of oxygen gas may be added by adjusting the amount according to the amount of argon gas added.

This gas flow rate change was determined by sputtering at a substrate temperature of 500-550 ° C. (eg 520 ° C.) using a target containing excess Pb so that a deposited thin film containing 20-60% of excess PbO was formed. PZT ferroelectric thin films were deposited by sputtering at a substrate temperature of 400-600 ° C. using a target containing excess PbO to deposit ferroelectric thin films and to form a deposition thin film containing 20-60% of excess PbO. In this case, all of them apply equally.

The PZT ferroelectric thin film deposited by sputtering at low temperature may be heat-treated within a temperature range of 500-700 ° C. after depositing the thin film to improve the film quality. The heat treatment method includes an electric furnace charging and heating method for directing crystallinity, a direct heating method through a hot zone of a tube furnace, and a rapid thermal heating method. Etc., and the heat treatment is performed in an air atmosphere or an oxygen atmosphere.

The sputtering method performed for the study of the present invention deposited as large a thin film as possible and deposited using off-axis sputtering method in order to reduce the influence of oxygen anions in the plasma. Irrelevant

Table 2 shows the results of analyzing the composition of the PZT thin film deposited under the conditions as shown in Table 1 by using an electron probe micro analysis (EPMA) method.

FIG. 1 shows the results of X-ray diffraction (hereinafter referred to as XRD) analysis of a PZT ferroelectric thin film (hereinafter referred to as As-grown thin film) having a thickness of 4000Å at a deposition temperature of 520 ° C. A graph showing the results of XRD analysis after annealing the thin film at a temperature range between 500-700 ° C. is shown.

In the graph, since only the As-grown thin film is observed except for the PZT perovskite phase, it can be seen that low-temperature deposition is possible using the deposition conditions shown in Table 1.

2A to 2F show graphs showing changes in hysteresis curves of P-E (polarization-electric field) showing typical ferroelectric properties of these PZT ferroelectric thin films. In the graph, the point where the hysteresis curve meets the electric field axis indicates the coercive electric field value (Ec value), and the point where the hysteresis curve meets the polarization axis indicates the residual polarization value (Pr value). The closed curve on the innermost side of the hysteresis curve indicates a case where a voltage of 3 V is applied, and the closed closed curves on the outer side indicate a case where voltages of 5 V, 7 V, 10 V, and 12 V are sequentially applied.

In the graph, it is observed that as the heat treatment temperature increases from the As-grown thin film, the residual polarization Pr increases and the coercive electric field value Ec decreases. In the case of As-grown thin film, the residual polarization value was 17-30μC / ㎠ according to the applied voltage change of 5-12V, and the constant electric field value was 24-64㎸ / cm. It was observed that the peak value was further increased to obtain a maximum value of 45 μC / cm 2. The constant electric field value shown here represents a value converted to 항 / cm, which is a constant electric field value unit, because the unit of the electric field axis is presented in V in the graph.

FIG. 3 is a graph showing the fatigue characteristics of the PZT ferroelectric thin film deposited at low temperature measured by applying a square pulse (Vpp = 10V) at a frequency of 1 MHz.

In the case of the conventional general PZT ferroelectric thin film, the degradation of residual polarization generally occurs in 10 ⁷ -10 ⁸ cycles, whereas the low-temperature deposited PZT ferroelectric thin film of the present invention can be seen in the graph, 10 ⁹ Only about 10-20% up to -10 ¹⁰ cycles shows deterioration of residual polarization, resulting in better fatigue characteristics. The reason for such high fatigue resistance is considered to be due to the excess Pb or PbO component added as a surplus component, which indicates that the excess Pb or PbO component not only lowers the deposition temperature but also improves the fatigue properties. .

Next, look at the method of ②.

Although the above method does not add excess Pb or PbO components as described in the method of ①, thin film deposition conditions used in the production of PZT ferroelectric thin films using conventional RF or DC sputtering, ion beam sputtering, laser ablation, etc. This method is applied as it is, but only the deposition pressure is adjusted to 5mTorr-100mtorr, so that the PZT ferroelectric thin film can be deposited at a low temperature (for example, 500-550 ℃).

At this time, the range of gas flow rate change may not include any oxygen gas as mentioned in the method of ①, and argon gas may be added within the range of 10-100% in order to improve film quality properties. What is necessary is just to add the quantity of the oxygen gas added by adjusting the quantity according to the addition amount of argon gas.

As described above, the PZT ferroelectric thin film deposited by controlling only the deposition pressure may also be heat-treated within a temperature range of 500-700 ° C. after depositing the thin film to improve the film quality as described above. In this case, the heat treatment method used may include an electric furnace charging and heating method for directing crystallinity, a direct heating method through a hot zone of a tube furnace, and a high-speed heat treatment heating method ( rapid thermal heating), and the heat treatment is performed in an air atmosphere or an oxygen atmosphere.

As a result, even when the PZT ferroelectric thin film is deposited at low temperature on the substrate using the method of ②, excellent fatigue characteristics can be obtained as in the case of depositing the PZT ferroelectric thin film using the method of ①.

As described above, according to the present invention, 1) a PZT ferroelectric thin film having excellent crystallinity can be manufactured at a lower temperature than a conventional case without introducing a seed layer, and 2) controlling the composition of a thin film generated during high temperature deposition. Difficulties such as difficulty in reducing the switching characteristics of ferroelectric memory devices manufactured using the thin film, and 3) improve fatigue characteristics of the PZT ferroelectric thin film.

Claims (5)

In the method of manufacturing Pb (Zr _1-X Ti _X ) O ₃ ferroelectric thin film by sputtering or laser ablation, the Pb of the target component is contained so that the deposited ferroelectric thin film contains an excess of PbO component in the range of 20% -60%. Or Pb (Zr _1-X Ti _X ) O ₃ Ferroelectric thin film manufacturing method characterized in that the deposition at a temperature of 500 ℃ ~ 550 ℃ by adjusting the amount of PbO. The method of claim 1, wherein the _{Pb (Zr 1-X Ti X} ) O 3 ferroelectric depositing a thin film, as further characterized by comprising a step of heat treatment _{Pb (Zr 1-X Ti X} ) O 3 ferroelectric thin films Manufacturing method. The Pb (Zr _1-X Ti _X ) O ₃ ferroelectric thin film manufacturing method according to claim 2, wherein the heat treatment is performed in an air atmosphere or an oxygen atmosphere. The method of claim 2, wherein the heat treatment step is Pb (Zr _1-X Ti), characterized in that any one selected from electric furnace charging heating method, direct heating method through the hot zone of the furnace for the furnace, high-speed heat treatment heating method. _X ) O ₃ ferroelectric thin film manufacturing method. In _{Pb (Zr 1-X Ti X} ) O 3 ferroelectric thin film manufacturing method using a sputtering method, Pb (Zr _1, characterized in that said depositing said ferroelectric thin film at a pressure 5mT ~ 100mT, at a temperature of 450 ℃ ~ 600 ℃ _-X Ti _X ) O ₃ Ferroelectric thin film manufacturing method.