JP4807901B2 - Thin film production method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a thin film by an ion plating method that performs pressure gradient arc discharge for producing a dielectric or semiconductor thin film. One example of the use of the thin film is a semiconductor.
[0002]
[Prior art]
FIG. 4 is a schematic diagram showing a configuration of a general 90-degree deflection pressure gradient arc discharge ion plating apparatus. In the figure, reference numeral 1 denotes a vacuum vessel (vacuum tank) in which a dielectric film or a semiconductor film is formed, and an arc discharge plasma 3 is generated in the vacuum vessel 1 by a plasma gun (UR gun) 2. The plasma gun (UR gun) 2 includes a cathode 4, an intermediate electrode 5, and an anode 6, and the cathode 4 is provided with a carrier gas (discharge gas) introduction tube 7. Reference numeral 8 denotes a magnetic field generation source for plasma control.
[0003]
A vapor deposition material evaporation source 9 is disposed below the vacuum vessel 1, and a permanent magnet 10 is disposed on the lower side thereof. A substrate (substrate) 11 on which vapor deposition (film formation) is performed is arranged above the vacuum vessel 1, and the substrate 11 is heated by a heater 12. In addition, a shutter 13 is provided below the base body 11, and a reaction gas is supplied from the introduction pipe 14 to the base body 11.
[0004]
FIG. 5 is a schematic diagram showing the configuration of a reflective pressure gradient arc discharge ion plating apparatus using a reflective plasma gun. This apparatus performs multiple simultaneous ion plating by arranging a plurality of evaporation sources 9, and the same components as those in FIG.
[0005]
In the pressure gradient arc discharge ion plating method, the hot cathode can be protected from physical and chemical damage by the carrier gas and the reactive gas by the pressure gradient, and the arc discharge plasma 3 having a large current can be stably generated. A high-density plasma is formed by the plasma gun (UR gun) 2 and the source atoms and molecules supplied from the evaporation source 9 are activated by the high-density plasma, thereby forming a dense and flat dielectric / semiconductor film at high speed. It is a thin film preparation method that can be deposited.
[0006]
In the apparatus shown in FIG. 4, the arc discharge plasma 3 can be deflected 90 degrees with a magnetic field from a permanent magnet 10 disposed just below the anode, whereby the evaporation source 9 can be heated and the atmosphere activated simultaneously. Further, in the apparatus called the reflection type shown in FIG. 5, it is possible to generate high density plasma without arranging the anode 6 in the vacuum chamber, and the combined use of the evaporation source 9 independent of the plasma gun 2 is possible. Thus, multi-factor simultaneous reaction deposition can be performed efficiently.
[0007]
The plasma gun 2 includes a disk-like cathode 4 that generates thermoelectrons, an intermediate electrode (grid) 5 that also serves as an orifice for forming a pressure gradient between the cathode 4 and a vacuum chamber, and a counter electrode thereof. It is comprised from the anode 6 which is. In the arrangement of the reflective UR gun, the anode 6 also acts as a ring-shaped grid. When the arc discharge occurs, the most central part of these grids is exposed to a high-temperature electron current, so that a grid orifice of a refractory metal (Mo, W, etc.) is loaded at the center of the water-cooled electrode flange. This prevents melting of the electrode.
[0008]
Further, since arc discharge plasma 3 having a plasma density 2 to 3 orders of magnitude higher than that of glow discharge is used, the generation efficiency of active species by excitation of carrier gas and reactive gas is high, and a thin film formed by conventional sputtering or MOCVD method. Thin film formation is possible at a temperature lower than the production temperature. Furthermore, a thin film that is dense and flat and has good adhesion can be deposited at high speed.
[0009]
Taking advantage of the above features, it has been applied to the fabrication of ferroelectric thin films / dielectric thin films having the so-called perovskite structure of ABO ₃ type and semiconductor thin films such as amorphous Si and polycrystalline Si thin films. . In particular, typical multi-element oxide ferroelectrics (PZT [Pb (Zr _x Ti _1-x ) O ₃ ] and PLZT [(Pb _1-x ) exhibiting excellent piezoelectricity, pyroelectricity, electro-optical properties, etc. _{la x) (Zr y Ti 1} -y) in the thin film formation of _{1-x / 4} O _3] and the like), despite the growth of at 100 ° C. lower temperature than the conventional method, without annealing treatment of the perovskite type crystal structure And good ferroelectric properties have been confirmed.
[0010]
[Problems to be solved by the invention]
By the way, the plasma gun (UR gun) of the pressure gradient type arc discharge ion plating apparatus as described above has a pressure in the vicinity of the cathode maintained at several Torr by each intermediate grid also serving as an orifice, The cathode is protected from chemical damage caused by a reaction gas (for example, oxygen). However, each grid is directly exposed to a high-density plasma and slightly suffers sputter damage due to gas ions. And it has been a problem that the refractory metal constituting the grid orifice is scattered in the vacuum vessel by this sputtering and is taken into the thin film as an impurity. Usually, this mixing amount is as small as 0.1% or less, and it hardly affects the characteristics of various thin films, but may cause serious functional problems for some films. For example, the specific resistance of the non-doped semiconductor film is reduced, or the transmittance of the dielectric film is reduced.
[0011]
The most serious case is the case where a lead-based ferroelectric / dielectric thin film having a perovskite crystal structure is formed by a reflection type arc discharge ion plating method. In this reflective arrangement, the electron current in the plasma converges on a ring-shaped anode grid located on the most vacuum container side of the plasma gun. Although the anode flange is thermally protected by cooling water, a cylinder of refractory metal (Mo, W, etc.) is inserted as an inner to stabilize the plasma. These refractory metals are lead Together with this, it is known to form complex oxides.
[0012]
When the arc discharge current is Mo, 15 A or less, and when W is 30 A or less. When the plasma density is relatively low, the influence of the complex oxide is not seen, but as the discharge current increases, the inner surface The temperature also rises to form a complex oxide with lead. This composite oxide is mixed as an impurity in the thin film, and as shown in FIG. 6, the crystal quality of the thin film is lowered as a different phase from the perovskite phase. Further, when the amount of impurities mixed exceeds a certain amount, a serious problem arises that the perovskite phase itself can no longer be obtained as shown in FIG. 6 and 7 are diagrams showing X-ray diffraction results of the thin film at discharge currents 20A and 40A, respectively.
[0013]
In order to avoid the above problem of contamination with impurities, conventionally, measures have been taken to suppress the discharge current to 30 A or less or to remove the anode inner made of a refractory metal. However, the former also has a problem of limiting the amount of active oxygen species in proportion to the plasma density, and the latter has a problem of damage to the thin film due to an increase in plasma potential and electron temperature due to plasma destabilization. For this reason, the deposition rate of the lead-based ferroelectric / dielectric thin film is about 3 低 い / s, and the ion plating method has remained at a low level.
[0014]
The present invention has been made in view of the above-described problems, and can significantly suppress the mixing of impurities into the thin film, enable generation of high-density plasma, and the crystal quality of the thin film. The object of the present invention is to provide a method for producing a thin film by an ion plating method having a high film forming speed.
[0015]
[Means for Solving the Problems]
(1) A method for producing a thin film by an ion plating method of a perovskite type structure ferroelectric compound represented by the chemical formula ABO ₃ ,
The substrate is placed in a vacuum chamber equipped with a plurality of evaporation sources, a carrier gas introduction part, an oxygen gas introduction part, and a pressure gradient plasma gun loaded with a grid orifice made of sintered carbon on the intermediate electrode and anode. Process,
Thereafter, a high-density plasma generated by applying a DC bias voltage to the pressure gradient plasma gun and controlling it with a discharge current greater than 30 A to generate an arc discharge of the carrier gas is introduced into the vacuum chamber by a magnetic field generation source. A density plasma generation process;
In this state, generate active species of oxygen gas introduced from the oxygen gas introduction part,
A vapor deposition step of evaporating a metallic material from the evaporation source in the presence of the active species of the oxygen gas and depositing a ferroelectric compound having a perovskite structure represented by the chemical formula ABO ₃ on a substrate;
The evaporation source includes at least Pb;
In the vapor deposition step, when the sintered carbon of the grid orifice is scattered in the high density plasma generated in the high density plasma generation step, the vapor phase in which the sintered carbon reacts with the active species of the oxygen gas. A thin film production method for forming a compound.
(2) The thin film manufacturing method according to (1), wherein the evaporation source includes a plurality of compounds of any combination of elements of Pb, Zr, Ti, and La and oxides of these elements.
(3) The thin film production method according to (2), wherein the evaporation source includes elements of Pb, Ti, and Zr, and the evaporation amount of Pb is 10 to 30 times the evaporation amount of Ti and Zr.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0021]
FIG. 1 is a schematic diagram showing the configuration of the main part of a pressure gradient arc discharge ion plating apparatus according to the present invention. Here, the present invention (b) is compared with the conventional (b) pressure gradient arc discharge plasma gun. ) Shows a configuration of a pressure gradient arc discharge plasma gun. Also, the same reference numerals as those in FIG. 4 and FIG.
[0022]
The intermediate electrode 5 and the anode 6 of the conventional plasma gun (UR gun) 2 are loaded with the grid orifices 5a, 6a of refractory metal (Mo, W, etc.) as the inner as described above. Grid orifices 5b and 6b made of sintered carbon are loaded in the intermediate electrode 5 and the anode 6 of the plasma gun 2 as inners. In addition, since the structure in the other vacuum vessel 1 is the same as that of FIG.4 and FIG.5, description is abbreviate | omitted.
[0023]
In the ion plating apparatus of the present invention, the material of the grid orifices (inners) 5b and 6b to be loaded in the intermediate electrode 5 and the anode 6 of the UR plasma gun is changed from the conventional refractory metal (Mo, W, etc.) to sintered carbon. This makes it possible to increase the discharge current while suppressing impurities from being mixed into the thin film.
[0024]
That is, by using the sintered carbon grid orifices (inner) 5b and 6b, the mass is overwhelmingly smaller than that of the refractory metal even when sputtered by gas ions in the plasma. As a result, the amount of contamination into the vacuum vessel 1 is significantly reduced. As a result, it is possible to generate a higher-purity plasma than when conventional refractory metals are used for the grid orifices (inners) 5a, 6a, and to produce a high-purity and high-quality dielectric / semiconductor thin film. Can do.
[0025]
In addition, the problem of complex oxide formation between the anode inner and lead that occurs when the plasma gun 2 of the reflective type is used for the production of a lead-based dielectric thin film is suppressed by using sintered carbon as the inner material. can do. This is because even if the sintered carbon is heated in an oxygen atmosphere and reacts with oxygen, most of it is discharged out of the container as a gas phase compound such as CO ₂ . Therefore, even in the presence of lead vapor, high density plasma can be generated by large current discharge (up to 80 A) without mixing impurities. As a result, the amount of oxygen active species in the vacuum vessel 1 increases more than twice that of the conventional method, and a high-quality dielectric thin film can be formed at high speed.
[0026]
Further, since the sintered carbon has a low resistance value at high temperature, the efficiency of converging the electron current to the anode 6 is high, and the plasma potential and the electron temperature are lower than when a refractory metal is used for the inner anode, and the dielectric Further, it is possible to generate a low temperature plasma with little damage to the semiconductor thin film.
[0027]
In fact, when applied to oxide dielectrics, high-density and low-temperature plasma is generated by using sintered carbon grid orifices 5b and 6b, and high-energy charged particles that damage the film are suppressed, and thin film growth is achieved. As a result of increasing the effective oxygen active species, it has become possible to grow a thin film dielectric at a film formation rate more than twice that of the conventional method. As a result, a dense and developed columnar crystal structure film was obtained, and good dielectric properties were obtained.
[0028]
Next, an example in which a thin film is actually produced by the ion plating apparatus having the above configuration will be described.
[0029]
[Example 1]
A ferroelectric multi-element oxide thin film was manufactured using the reflective pressure gradient arc discharge ion plating apparatus shown in FIGS. First, as a thin film material were thin-film producing ternary composite oxide ferroelectric PZT _{[Pb (Zr x Ti 1-x} ) O 3 ].
[0030]
Each material of Pb, Zr, and Ti was used as the material of the evaporation source 9, and each was evaporated independently by electron beam heating. The substrate 11 was prepared by depositing the constituent materials in the order of SiO ₂ / Ti / Pt on a (100) plane Si wafer, and the film composition was adjusted to Pb (Zr _0.52 Ti _0.48 ) O ₃ .
[0031]
Then, 5-15 sccm Ar gas was introduced as a carrier gas into a pressure gradient arc discharge plasma gun (UR gun) 2 and a DC bias voltage was applied to generate arc discharge. The discharge voltage was controlled at 70V and the discharge current was 40A. High-density plasma (plasma density> 10 ¹² cm ⁻³ ) generated by this arc discharge was introduced into the vacuum chamber 1 by a magnetic field of about 50 to 300 gauss generated by the magnetic field generation source 8 for plasma control. In this state, 100 sccm of O ₂ gas was introduced as a reaction gas from the introduction tube 14 to generate high-density oxygen plasma and oxygen active species in the vacuum vessel 1.
[0032]
A thin film was formed on the substrate 11 heated to about 500 ° C. by the heater 12 in the presence of the oxygen active species. At this time, in the crystal oscillator type film thickness monitor, the Pb evaporation amount is in the range of 20 times the total evaporation amount of Zr and Ti, and the evaporation amounts of Zr and Ti are substantially equal. Furthermore, a thin film ferroelectric having a perovskite crystal structure was formed by controlling the power of the evaporation source 9. FIG. 2 shows the X-ray diffraction results of the thin film obtained. It can be seen that no peak due to the impurity phase is observed even at a discharge current of 40 A. The internal pressure of the vacuum vessel 1 at the time of forming the thin film was 1 to 5 mTorr, the plasma potential was measured by a Langmuir probe to be about 7 V, and the electron temperature was about 1.5 eV. Thereby, the low temperature of the plasma by the effect of the anode inner made of sintered carbon was confirmed.
[0033]
As a result, a high deposition rate of 5 Å / s was obtained for the formation of the thin film ferroelectric. This value corresponds to twice the discharge current of 40A when the anode inner is not used. When the ferroelectric characteristics of the capacitor cell having the Pt upper electrode formed on the obtained PZT film were measured, a very well saturated PE (polarization-electric field) hysteresis curve as shown in FIG. Was observed. That is, it was found that a high-quality ferroelectric ternary oxide thin film was formed at high speed at a low temperature by the method of Example 1.
[0034]
[Example 2]
Next, a thin film of a binary composite oxide ferroelectric PT [PbTiO ₃ ] was prepared under the same apparatus and conditions as in Example 1.
[0035]
As a result of increasing the amount of active oxygen species by raising the discharge current to 70 A, the as-depo. Thus, a perovskite single-phase PT film was obtained. The obtained PT film had a relative dielectric constant ε = 480 and a loss tan δ = 0.01, and had good dielectric properties. Further, when the ferroelectric characteristics were measured for the capacitor cell of the same film, a PE hysteresis curve similar to that in FIG. 3 was observed, the residual polarization Pr = 22.4 μC / cm ² , the coercive electric field Ec = A ferroelectric characteristic of 95 kV / cm was obtained. Thus, it was found that PT can be formed at a very high speed by the method of Example 2.
[0036]
The embodiments of the present invention have been described above. In the present invention, among the elements of P (Pb), Z (Zr), T (Ti), and L (La), the chemical formula ABO of PT, PZT, or PLZT _This is effective for the production of a thin film of a perovskite type ferroelectric compound represented by ₃ and a plurality of these elements or their oxides may be used as the evaporation source 9. Also, the evaporation amount of Pb can be 10 to 30 times that of (Ti + Zr).
[0037]
It is also effective to use a rare gas such as He or Ar as the carrier gas and O ₂ gas as the reaction gas. The evaporation source 9 can be individually heated by an EB (electron beam) heating source or a resistance heating source.
[0038]
The present invention also includes a piezoelectric transformer or a piezoelectric inverter, a micromirror or a lens-driven optical switch, a waveguide optical switch, an optical component such as an optical shutter, an optical modulator, a dielectric for a semiconductor memory (FRAM), and an ink jet printer. The present invention can be applied to head driving members, various sensors (vibration gyroscope, acceleration sensor, infrared (thermal) sensor, specific light sensor, ultrasonic sensor, etc.), optical scanner, photographic paper writing micro light source unit, and the like.
[0039]
【The invention's effect】
As described above, according to the present invention, contamination of impurities into the thin film can be remarkably suppressed, high-density plasma can be generated, the crystal quality of the thin film is high, and the film formation rate is also high. The effect of being fast is obtained.
[0040]
That is, in the conventional method, a high melting point metal (Mo, W, etc.) which is an intermediate electrode of the plasma gun or an inner (grid orifice) material of the anode is sputtered by collision of gas ions in the plasma and mixed into the thin film as impurities. However, by using sintered carbon having a small specific gravity as the inner material, scattering of the same member due to sputtering can be retained in the plasma gun, and mixing into the thin film can be remarkably suppressed. The contamination level of carbon itself is also extremely small, 0.1% or less, and high purity plasma can be supplied.
[0041]
In addition, the problem of complex oxide formation between the anode inner and lead, which occurs when a plasma gun with a reflection type is used for the production of a lead-based dielectric thin film, is also suppressed by using sintered carbon as the inner material. It is possible to generate high-density plasma by large current discharge (up to 80 A) without mixing impurities even in the presence of lead vapor. By increasing the discharge current, a high-density plasma can be generated. As a result, it is possible to increase the amount of oxygen active species effective for the growth of the thin film dielectric. Therefore, a dielectric thin film having a high crystal quality can be easily obtained.
[0042]
Also, the carbon anode inner has a low resistance at high temperature, improves the convergence efficiency of the electron current in the plasma to the anode, and promotes so-called low temperature plasma formation in which the plasma potential and the electron temperature are reduced. As a result, damage and re-evaporation of the film due to charged particles are suppressed, and the film formation rate is increased by about twice.
[0043]
Further, even when exposed to high-density oxygen plasma, the surface is not insulated and can be stably used for a long time as an anode inner.
[0044]
In addition, the excellent film forming performance of the pressure gradient arc discharge ion plating method, which is a conventional method, is maintained as it is.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration of a main part of an ion plating apparatus according to the present invention. FIG. 2 is a diagram showing an X-ray diffraction result of a thin film obtained in Example 1 of the present invention. FIG. 4 is a schematic diagram showing a configuration of a pressure gradient arc discharge ion plating apparatus. FIG. 5 is a pressure gradient using a reflection type plasma gun. Schematic diagram showing the configuration of the type arc discharge ion plating apparatus [Fig. 6] Fig. 7 shows the X-ray diffraction result of the thin film mixed with impurities. [Fig. Explanation of symbols]
1 Vacuum container (vacuum chamber)
2 Plasma Gun 3 Arc Discharge Plasma 4 Cathode 5 Intermediate Electrode 5b Grid Orifice 6 Anode 6b Grid Orifice 7 Introducing Tube 8 Magnetic Field Source 9 Evaporating Source 10 Permanent Magnet 11 Base 12 Heater 13 Shutter 14 Introducing Tube

Claims (3)

A method for producing a thin film by ion plating of a perovskite type ferroelectric compound represented by the chemical formula ABO ₃ ,
The substrate is placed in a vacuum chamber equipped with a plurality of evaporation sources, a carrier gas introduction part, an oxygen gas introduction part, and a pressure gradient plasma gun loaded with a grid orifice made of sintered carbon on the intermediate electrode and anode. Process,
Thereafter, a high-density plasma generated by applying a DC bias voltage to the pressure gradient plasma gun and controlling it with a discharge current greater than 30 A to generate an arc discharge of the carrier gas is introduced into the vacuum chamber by a magnetic field generation source. A density plasma generation process;
In this state, generate active species of oxygen gas introduced from the oxygen gas introduction part,
A vapor deposition step of evaporating a metallic material from the evaporation source in the presence of the active species of the oxygen gas and depositing a ferroelectric compound having a perovskite structure represented by the chemical formula ABO ₃ on a substrate;
The evaporation source includes at least Pb;
In the vapor deposition step, when the sintered carbon of the grid orifice is scattered in the high density plasma generated in the high density plasma generation step, the vapor phase in which the sintered carbon reacts with the active species of the oxygen gas. A thin film manufacturing method characterized by forming a compound.   2. The thin film manufacturing method according to claim 1, wherein the evaporation source is composed of a plurality of compounds of any combination of elements of Pb, Zr, Ti, and La and oxides of these elements.   3. The thin film production method according to claim 2, wherein the evaporation source has elements of Pb, Ti, and Zr, and the evaporation amount of Pb is 10 to 30 times the evaporation amount of Ti and Zr combined. .

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