RU2530534C1 - Ferroelectric capacitor manufacturing method - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: in order to manufacture a ferroelectric capacitor to the substrate (1) the lower electrode (2) is sprayed, and the film-forming solution based on lead titanate circonate is applied to its layer-by-layer with subsequent drying and pyrolysis to form several layers of solid solution (3-1)…(3-n). The formed several layers of solid solution (3-1)…(3-n) are subject to crystallization (4) in order to receive ferroelectric film (5). The upper electrode (6) is sprayed to the ferroelectric film (5). In order to receive solid solution layer (3-1) joining the lower electrode to the film-forming solution based on lead titanate circonate 0-7% lead excess is introduced beyond stochiometry and in order to form remaining solid solution layers (3-2)…3-n to the film-forming solution based on lead titanate circonate 8-30% lead excess is introduced beyond stochiometry.

EFFECT: improving electrical properties of ferroelectric film based on lead titanate circonate: improvement of residual polarization, dielectric non-linearity and reduction of leak current.

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Description

The invention relates to the field of manufacturing capacitors, and in particular to methods for manufacturing ferroelectric capacitors, and can be used in microelectronics technology in the manufacture of a wide class of elements controlled by an electric field, in particular for the production of non-volatile radiation-resistant ferroelectric storage devices.

A known method of producing thin ferroelectric films of lead zirconate titanate using the so-called seed layer PbTiO ₃ , which is applied to the lower electrode before forming a ferroelectric film [US Patent No. 5817170 MKI C30B 25/06 from 10/06/1998 (analogue)].

This method allows to obtain a fine-grained ferroelectric film, which positively affects its roughness, and also reduces the temperature of transformation of lead zirconate titanate into the ferroelectric phase of perovskite due to the reduced barrier of nucleation of crystallization centers PbTiO ₃ . It also simplifies the subsequent nucleation and epitaxial growth of lead zirconate-titanate grains due to uncritical mismatch of the crystal lattice parameters of these materials. When producing a ferroelectric film, an analogue uses a film-forming solution with a 10% excess of lead, which during the subsequent heat treatment compensates for the high volatility of lead oxide in comparison with the oxides of the other metals used. A disadvantage of the analogue is the small size of the bases of perovskite columnar grains, which increases the total area of grain boundaries where defects can form that contribute to an increase in the conductivity of the film. Also, particles of an impurity non-ferroelectric phase with a pyrochlore structure are formed at the grain boundaries of lead zirconate titanate, the presence of which negatively affects the residual polarization [Sigov AS, Vorotilov KA, Zhigalina OM Effect of Lead Content on Microstructure of Sol-Gel PZT Structure // Ferroelectrics. - V.433. - P.146-157].

The closest technical solution is a method of manufacturing a ferroelectric capacitor, including sputtering on the substrate of the lower electrode, layer-by-layer deposition on the lower electrode of a film-forming solution based on lead zirconate titanate, layered drying and pyrolysis to form several layers of a solid solution, crystallization of several layers of a solid solution to obtain a ferroelectric films and sputtering of the upper electrode [US Patent No. 6337032 MKI H01L 21/02 of 08/08/2002 (prototype)].

This method provides the manufacture of a ferroelectric capacitor with a sufficiently high dielectric constant, the values of which reach 550 rel. with a polarization of about 22 ÷ 30 μC / cm ² . It should be noted that for effective nucleation, the prototype uses a single film-forming solution based on lead zirconate-titanate with a relatively high lead content in excess of stoichiometry (16 ÷ 20% excess), which also contributes to increased nucleation on the surface of the lower electrode and an increase in the grain growth rate during crystallization. At the same time, the grain sizes are significantly reduced (more than 2–3 times compared with a 0–5% excess of lead) and, given the high grain growth rate, this leads to the fact that not all of the grains can grow to the full thickness ferroelectric film. This is the reason for the violation of the heredity of the crystalline orientation of the lower electrode in the ferroelectric film. In addition, with excessive lead content, the formation of PbO inclusions increases, whose crystals, although they have similar lattice parameters, contribute to strengthening the texture (100) [Sigov AS, Vorotilov KA, Zhigalina OM Effect of Lead Content on Microstructure of Sol-Gel PZT Structure // Ferroelectrics. - V.433. - P.146-157]. All this negatively affects both the conductivity of the ferroelectric film and the residual polarization.

The objective of the invention is to improve the electrical properties of a ferroelectric film based on lead zirconate-titanate by increasing the size of the bases of perovskite columnar grains, which allows to increase the residual polarization, increase the dielectric nonlinearity and reduce leakage currents without the use of seed layers, significantly different in composition, as well as complex technological methods and equipment.

This object is achieved in that in the known method of manufacturing a ferroelectric capacitor, including sputtering a lower electrode on a substrate, layer-by-layer deposition of a film-forming solution based on lead zirconate-titanate on the lower electrode, layer-by-layer drying and pyrolysis to form several layers of a solid solution, crystallization of several layers of a solid solution to obtain a ferroelectric film and the deposition of the upper electrode, it is new that in the film-forming solution based on circus lead nata-titanate to form a layer of a solid solution adjacent to the lower electrode, a 0-7% excess of lead is introduced in excess of stoichiometry, and 8 ÷ 30% is introduced into a film-forming solution based on lead zirconate-titanate to form the remaining layers of lead excess lead over stoichiometry.

In addition, after the formation of a layer of a solid solution adjacent to the lower electrode, it is additionally crystallized.

In addition, at least one of the alloying additives selected from the group consisting of metals, mainly rare-earth metals, and semimetals is additionally introduced into the film-forming solution based on lead zirconate titanate.

In addition, the lower electrode is made of conductive materials having a melting point not lower than 1500 ° C and a period of the crystal lattice with a deviation of not more than 12% relative to the period of the crystal lattice of a ferroelectric film.

In addition, before spraying the lower electrode on the substrate, at least one of the sublayers is additionally formed, providing the necessary insulating, adhesive and barrier properties.

In addition, the upper electrode is made of conductive materials having a melting point of at least 900 ° C.

In addition, drying is carried out at a temperature of 50 ÷ 250 ° C.

In addition, pyrolysis is performed at a temperature of 300 ÷ 450 ° C.

In addition, crystallization is performed at a temperature of 500 ÷ 1000 ° C.

The introduction of lead zirconate titanate into a film-forming solution to form a solid solution layer adjacent to the lower electrode, a 0-7% excess of lead in excess of stoichiometry, as a result of subsequent crystallization stimulates the formation of nucleation centers of perovskite grains of lead zirconate on the surface of the lower electrode, which, due to their low density, contribute to an increase in the size of the bases of columnar perovskite grains.

Introducing lead zirconate titanate into a film-forming solution to form the remaining layers of the solid solution, an 8-30% excess lead over stoichiometry allows, firstly, to fill the lead deficiency in the underlying solid solution layer, which is necessary for the effective growth of the ferroelectric perovskite phase from nucleation centers and their further germination over the entire thickness of the ferroelectric film, and secondly, to compensate for the evaporation of lead that occurs during subsequent heat treatment and buslovlennoe increased volatility of lead oxide as compared with other oxides of the metals used.

Additional crystallization of the formed solid solution layer adjacent to the lower electrode eliminates the possibility of lead diffusion from the subsequently formed overlying solid solution layer with an overestimated (8-30%) excess lead content, which leads to undesirable alignment of the lead content in the solid solution layers.

The additional introduction of at least one of the alloying additives selected from the group consisting of metals, mainly rare-earth metals and semimetals into the film-forming solution based on lead zirconate-titanate provides a decrease in conductivity as a result of alloying with p-type ferroelectric material by donor impurities.

The implementation of the lower electrode of conductive materials having a melting point not lower than 1500 ° C prevents their possible destruction or degradation as a result of crystallization and other possible technological operations during which thermal action occurs, and also prevents possible diffusion of materials as adhesive or barrier sublayers, and components of a ferroelectric film. The implementation of the lower electrode of materials having a crystal lattice period with a deviation of not more than 12% relative to the crystal lattice period of the ferroelectric film provides epitaxial growth of perovskite grains of lead zirconate titanate on the grain structure of the lower electrode, inheriting its crystal orientation.

The implementation of the lower electrode of conductive materials having a melting point not lower than 900 ° C prevents their possible destruction or degradation as a result of possible technological operations during which thermal action occurs, and also prevents possible diffusion of the components of the ferroelectric film.

The additional formation of a sublayer on the substrate, providing the necessary insulating properties, eliminates the electrical contact of the lower electrode with the substrate in case of its electrical conductivity. The additional formation of a sublayer on the substrate, providing the necessary adhesive properties, prevents peeling of the lower electrode due to strong adhesion. Additional formation before deposition of the lower electrode on the substrate of the sublayer, which provides the necessary barrier properties, eliminates the interaction of materials in contact due to inertness to them.

Performing drying at a temperature of 50 ÷ 250 ° C ensures the removal of organic solvents.

Performing pyrolysis at a temperature of 300 ÷ 450 ° C stimulates the thermal degradation of organic groups and compounds.

Performing crystallization at a temperature of 500-1000 ° C ensures the transformation of several amorphous layers of the solid solution into a single ferroelectric film, which is a sprouted columnar grain of lead zirconate titanate having a perovskite structure.

The following is a description of one of the many variants of the method of manufacturing a ferroelectric capacitor, each of which is subject to a single inventive concept, as shown in the claims.

The invention is illustrated by graphic materials, which show:

figure 1 is a cross section of a ferroelectric capacitor made according to claim 1 of the claims;

figure 2 is a cross section of a ferroelectric capacitor made according to claim 2;

figure 3 - dependence of the dielectric constant on the electric field for a sample made according to claim 1 of the claims;

figure 4 - dependence of polarization on the electric field for a sample made according to claim 1 of the claims;

figure 5 - dependence of the dielectric constant on the electric field for a sample made according to claim 2 of the claims;

figure 6 - dependence of polarization on the electric field for a sample made according to claim 2 of the claims.

A method of manufacturing a ferroelectric capacitor is as follows.

The manufacture of a ferroelectric capacitor is preceded by the preparation of a film-forming solution based on lead zirconate-titanate, carried out, for example, in accordance with the method described in RF Patent No. 2470866 of 12/27/2012. A film-forming solution based on lead zirconate-titanate may additionally contain at least , one of the alloying additives selected from the group consisting of metals, mainly rare-earth metals, and semimetals embedded in the structure of the ABO ₃ perovskite crystal lattice in polo reduction of A, mainly lanthanum, and / or in position B, mainly niobium, to compensate for free charge carriers (holes).

For the direct manufacture of a ferroelectric capacitor take a dielectric, semiconductor or conductive substrate 1, mainly a semiconductor silicon wafer. Then, if necessary, a dielectric sublayer, mainly SiO ₂ , is formed on the substrate 1, using, for example, the thermal oxidation method. After that, an adhesive layer is formed, mainly TiO ₂ or Ti. If necessary, form a barrier layer, mainly TiN. Then, the lower electrode 2 is sprayed onto the substrate 1 from refractory conductive materials such as platinum, palladium, iridium, rhodium, conductive oxides IrO ₂ , RuO ₂ , conductive perovskite-like oxides SrRuO ₃ , Sr ₂ RuO ₄ , LaNiO ₃ , LaCoO ₃ , LaNiCoO ₃ , LaSrCoO ₉ , BaSrRuO ₃ , hybrid bilayer materials Ir / IrO ₂ , Pt / Ru, Pt / SrRuO ₃ , Ru / BaSrRuO ₃ , etc., mainly from platinum, whose grains have a strict crystallographic orientation when formed on a semiconductor silicon wafer .

The next step is to apply a film-forming solution based on lead zirconate titanate with a 0-7% excess of lead over stoichiometry to the lower platinum electrode 2, mainly with a 5% excess of lead over stoichiometry. To apply the film-forming solution, one of the methods of chemical deposition from solutions is chosen: centrifugation, dipping, spraying (spraying) or staining, mainly the centrifugation method at a speed of rotation of 750-9000 rpm, mainly 3000 rpm. Then the resulting layer is dried using a hot plate (hot plate), infrared radiation or installation of rapid thermal annealing (RTA) at a temperature of 50 ÷ 250 ° C for 0.1 ÷ 15 min, mainly using a hot plate or infrared radiation for 5 min After drying, the layer is subjected to pyrolysis by means of a muffle furnace, a diffusion furnace, infrared radiation or a rapid thermal annealing (RTA) unit at a temperature of 300 ÷ 450 ° C for 0.5-30 minutes, mainly by means of a muffle furnace for 10 minutes. As a result of this operation, the so-called seed layer of solid solution 3-1 is formed. In one embodiment of the present invention, additionally crystallize 4 seed layer of solid solution 3-1 to obtain a thin ferroelectric film 5. After that, in the same way and under the same conditions (but without crystallization), the remaining layers of solid solution 3-2 ... 3 are formed on top -n (n is the number of layers) by layer-by-layer deposition, drying and pyrolysis of a film-forming solution based on lead zirconate-titanate with an 8-30% excess of lead, mainly with a 15-30% excess of lead over stoichiometry. The next step is crystallization 4 to obtain a ferroelectric film 5.

Crystallization 4 is carried out in a muffle furnace, a diffusion furnace or a rapid thermal annealing (RTA) unit at a temperature of 500 ÷ 1000 ° C for 0.5 ÷ 90 minutes, mainly in a muffle furnace at a temperature of 600 ° C for 15 minutes.

All stages of heat treatment (drying, pyrolysis and crystallization 4) are carried out in air or vacuum in the presence of at least one gas selected from the group comprising nitrogen, oxygen and inert gases, mainly in air.

The manufacture of a ferroelectric capacitor ends with the deposition of the upper electrode 6 from conductive materials such as platinum, palladium, iridium, rhodium, gold, silver, conductive oxides IrO ₂ , RuO ₂ , conductive perovskite-like oxides SrRuO ₃ , Sr ₂ RuO ₄ , LaNiO ₃ , LaCoO ₃ , LaNiCoO ₃ , LaSrCoO ₉ , BaSrRuO ₃ , hybrid bilayer materials Ir / IrO ₂ , Pt / Ru, Pt / SrRuO ₃ , Ru / BaSrRuO ₃ , etc., mainly from platinum.

Thus, the invention is based on the following two competing processes.

1. With an insufficient concentration of lead and a relatively thick ferroelectric film 5, obtained from several layers of a solid solution 3-1 ... 3-n, the grains grow in breadth, but cannot grow up to the full thickness of the ferroelectric film.

2. With an increase in the excess of lead, it is possible to form columnar epitaxial grains of perovskite, but the grain sizes, more precisely their bases, decrease, which means that not every grain can grow through the entire thickness of the ferroelectric film 5.

Thus, the layer of solid solution 3-1 with a relatively low excess of lead plays the role of a seed layer for subsequent epitaxial growth of more perfect perovskite grains of lead zirconate-titanate, because Due to the low density of nucleation centers during the germination of grains along the plane of the ferroelectric film 5, there is no active competition between the grain growth. Grain growth proceeds in three directions from the centers of nucleation until the perovskites begin to come into contact with each other, after which there is growth only upward, forming a columnar structure.

An increase in the lead content in the layers of the solid solution 3-2 ... 3-n located above the seed layer 3-1 promotes the epitaxial continuous growth of large columnar grains of lead zirconate titanate over the entire thickness of the ferroelectric film 5.

More perfect epitaxial growth is realized through the use of film-forming solutions that are as close as possible in composition, differing only in lead content, which, in fact, affects only nucleation and subsequent growth of perovskite grains, but not causing a mismatch in the crystal lattice parameters.

With additional crystallization of the layer of solid solution 3-1 adjacent to the lower electrode 2, a thin epitaxial ferroelectric film 5 consisting of large perovskite grains of lead zirconate is directly grown on the lower electrode 2. Additional crystallization eliminates the possibility of lead diffusion from the subsequently formed overlying layer of solid solution 3-2 with a large (8-30%) excess lead content, preventing violation of the conditions for a reduced (0-7%) excess lead content in the solid solution layer 3 -1 adjacent to the lower electrode 2.

Thus, large columnar perovskite grains obtained in the volume of the ferroelectric film 5 improve the homogeneity of the polycrystalline film of lead zirconate titanate and, accordingly, its electrical properties.

The proposed technical solution is illustrated by the following two examples.

Example 1

As the substrate 1, a semiconductor silicon wafer is used. An insulating silicon dioxide sublayer (300 ÷ 500 nm) is formed on it by the method of thermal oxidation, on which an adhesive sublayer of titanium dioxide (10 ÷ 15 im) is formed. The lower electrode 2 of platinum (100 ÷ 200 im) with a strict crystallographic orientation (111) is sprayed from above.

A film-forming solution of lead zirconate titanate with a 5% excess lead is applied to the lower electrode 2 by centrifugation at a rotation speed of 3000 rpm. Then, the resulting layer was dried using infrared radiation at a temperature of 180 ° C for 5 minutes. After drying, the layer is subjected to pyrolysis at a temperature of 400 ° C for 10 min to form a seed layer of solid solution 3-1. After that, in the same way and under the same conditions, the remaining five layers of a solid solution 3-2 ... 3-5 are formed from above by layer-by-layer application, drying and pyrolysis of a film-forming solution of lead zirconate-titanate with a 30% excess of lead. The final ferroelectric film 5 is obtained by crystallization 4 at a temperature of 600 ° C for 15 minutes

All stages of heat treatment (drying, pyrolysis and crystallization 4) are carried out in air. Pyrolysis and crystallization 4 are carried out in a muffle furnace.

The thickness of the obtained ferroelectric film 5 is 226 them.

For the experimental study of samples of ferroelectric films, mercury was used as the upper electrode 6.

The capacitance-voltage characteristics were measured on a measuring complex of Materials Development Corporation, equipped with an Agilent 4284A high-precision LCR meter and an MDC 802-150 mercury probe with a contact area of 0.53 mm ² and a point-to-ring connection with a scan voltage of ± 6 V.

Hysteresis loops were measured using the specialized AixACCT TF Analyzer 2000 complex at a scan voltage of ± 8 ... 10 V and a signal frequency of 100 Hz.

The obtained sample has a rather high dielectric nonlinearity (ε _max ≈ 764, ε _min ≈ 257) and residual polarization values P _r ≈ 24.2 μC / cm ² .

Example 2

This example fully repeats Example 1, but after the formation of the seed layer of solid solution 3-1, it is crystallized 4 at a temperature of 600 ° C for 15 minutes

The thickness of the obtained ferroelectric film 5 is 300 nm.

The sample is characterized by high dielectric nonlinearity (ε _max ≈ 949, ε _min ≈ 326), sufficiently large values of the residual polarization P _r ≈ 33.8 μC / cm ² and a better loop squareness compared to Example 1.

The technical and economic effect consists in increasing the reliability and energy efficiency of devices that use ferroelectric capacitors manufactured in accordance with this method.

Claims (9)

1. A method of manufacturing a ferroelectric capacitor, including sputtering a lower electrode on a substrate, layer-by-layer deposition of a film-forming solution based on lead zirconate-titanate on the lower electrode, layer-by-layer drying and pyrolysis to form several layers of a solid solution, crystallization of several layers of a solid solution to obtain a ferroelectric film and sputtering the upper electrode, characterized in that in a film-forming solution based on lead zirconate-titanate to form a layer of solid astvora adjacent to the lower electrode, is administered 0 ÷ 7% excess over stoichiometry of lead, and a coating solution based on lead zirconate titanate to form the other layers of the solid solution administered 8 ÷ 30% excess over stoichiometry of lead. 2. The method according to claim 1, characterized in that after the formation of a layer of a solid solution adjacent to the lower electrode, it is additionally crystallized. 3. The method according to claim 1, characterized in that at least one of the alloying additives selected from the group consisting of metals, mainly rare-earth metals, and semimetals is additionally introduced into the film-forming solution based on lead zirconate-titanate. 4. The method according to claim 1, characterized in that the lower electrode is made of conductive materials having a melting point of at least 1500 ° C and a period of the crystal lattice with a deviation of not more than 12% relative to the period of the crystal lattice of the ferroelectric film. 5. The method according to claim 1, characterized in that before spraying the lower electrode on the substrate, at least one of the sublayers is additionally formed, providing the necessary insulating, adhesive and barrier properties. 6. The method according to claim 1, characterized in that the upper electrode is made of conductive materials having a melting point of at least 900 ° C. 7. The method according to claim 1, characterized in that the drying is performed at a temperature of 50 ÷ 250 ° C. 8. The method according to claim 1, characterized in that the pyrolysis is performed at a temperature of 300 ÷ 450 ° C. 9. The method according to claim 1, characterized in that the crystallization is performed at a temperature of 500 ÷ 1000 ° C.

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