JPH0784646B2 - Method for forming dielectric thin film - Google Patents

Description

The present invention relates to a method for forming a dielectric thin film and a heat treatment method after the film formation.

(Prior Art) BaTiO ₃ , SrTiO ₃ , PbTiO ₃ , PbTiO ₃ and some of them in La,
Zr-substituted oxide dielectric materials such as Pb (Zr, Ti) O ₃ , (Pb, La) (Zr, Ti) O ₃ or Bi ₄ Ti ₃ O ₁₂ are capacitors, piezoelectric elements, electro-optical elements, etc. Has been applied to various functional devices. In recent years, attempts have been made to reduce the thickness of these materials to meet the demands for device miniaturization and high integration, and devices using thin films such as pyroelectric infrared sensors, ultrasonic sensors, and optical switches have been prototyped. There is.

At present, a sputtering method is widely used as a method for forming these dielectric thin films. However, the sputtering method has drawbacks such as exposure of the substrate surface to plasma and a slow film formation rate, and as a method of compensating for this, research is currently being actively conducted to form a dielectric thin film by the CVD method, vacuum deposition method, or the like. It is becoming popular. Among them, the vacuum evaporation method has been attracting attention for a long time as a method capable of forming a thin film with high quality and a good interface, and the film formation on BaTiO ₃ is published in September 1963, Journal of Electrochemical Society. Magazine (Journal of The Electrochemical S
ociety) 969-973. In addition, the Applied Physics Letter magazine (Applied
Physics Letters) 527-529, it was also reported that the formation of thin films showing the ferroelectric properties of remanent polarization of 5 μc / cm ² and anti-electrolysis of 15 KV / cm by using oxygen plasma in the multi-source deposition method. There is. However, their characteristic values are about one fifth of the remanent polarization and about ten times the anti-electric field of the bulk crystal, and there is room for improvement as a ferroelectric film. In addition, there is almost no report on the deposition of dielectrics other than BaTiO ₃ by the vacuum deposition method.

(Problems to be Solved by the Invention) As described above, the reason why a film having the same characteristics as a bulk cannot be obtained in the vacuum deposition method is the non-uniform composition due to an unstable raw material and the incomplete crystal due to insufficient oxidation. It depends on the sex. That is, in order to oxidize the film, oxygen gas or active oxygen with strong oxidizing power must be introduced into the vacuum apparatus so that the oxygen partial pressure becomes 5.0 × 10 ⁻⁵ Torr or more.
With such a vacuum degree, the E-gun does not operate stably and S
Alkali metals such as r and Ba were oxidized, and it was not possible to stably supply the raw materials. On the contrary, when the film is formed under the condition that the E-gun operates stably and Sr, Ba, etc. are stable and the oxygen partial pressure is low (1.0 × 10 ⁻⁵ Torr or less), the film has a poor dielectric constant and has a good dielectric property. It depends on where the body membrane could not be obtained.

(Means for Solving the Problems) The present invention is represented by the general formula ABO ₃ on a substrate, where A is Sr, B
One or more elements selected from a, Pb, La, Li, and K, a dielectric composed of one or more elements selected from Ti, Zr, Nb, and Ta as B (except SrTiO ₃ ), or Bi ₄ Ti ₃ O ₁₂
In the method of depositing a film, the vacuum device is divided into a growth chamber in which the substrate is installed and a raw material chamber in which the vapor deposition source of the raw material metal is installed. 1.0 × 10 ^-5 or more and 5.0 × 10 ^-4 Torr or less, and the raw material chamber to 1.0 × 10 ^-5 Torr or less, and A or Bi is K-cel.
l and B are separately supplied to the growth chamber by using an E-gun, and the temperature rising rate of the K-cell that supplies A or Bi is 20 ° C / m.
and a substrate temperature of 300 ° C. or more and 800 ° C. or less, and a method of forming a dielectric thin film on the substrate represented by the general formula ABO ₃ , where A is Sr, Ba, Pb, La, A dielectric composed of one or more elements selected from Li and K, one or more elements selected from Ti, Zr, Nb and Ta as B, or Bi ₄ T
In the method of depositing i ₃ O ₁₂ , the vacuum device is divided into a growth chamber in which a substrate is installed and a raw material chamber in which a vapor deposition source of raw material metal is installed, and each is evacuated independently,
Oxygen partial pressure in the growth chamber is 1.0 × 10 ^-5 or more and 5.0 × 10 ^-4 Torr or less,
After forming the dielectric thin film by supplying the raw material chamber to 1.0 × 10 ⁻⁵ Torr or less and separately supplying A or Bi to the growth chamber by using K-cell and B using E-gun, It is characterized in that heat treatment is performed for 2 hours or more and 3 hours or less under a partial pressure of oxygen of 500 ° C to 800 ° C and 1.0x10 ^-4 Torr to 1.0x10 ^-3 Torr in a growth chamber of a vacuum apparatus. This is a method for forming a dielectric thin film.

(Example) Next, the Example of this invention is described with reference to drawings. FIG. 1 shows the structure of the film forming apparatus of this embodiment. The apparatus is divided into a film forming chamber 1 and a raw material chamber 2, which can be independently evacuated. The substrate 6 is installed in the growth chamber and has a structure that can be heated up to 800 ° C. by the carbon heater 7. In the raw material chamber, Sr, Ba,
2 K-cell3 containing Pb, La, Li, K, Bi, etc.
E-gun4 containing Ti, Zr, Nb, Ta, etc. is installed. Further, the film formation rate exponentially increases with the temperature of the K-cell. If the temperature of the K-cell exceeds a predetermined temperature, the amount of evaporation of S, Ba, Pb, etc. becomes too large, and it becomes difficult to control the amount of evaporation well. Therefore, it is necessary to set a temperature range with good controllability according to Sr, Ba, Pb, etc. Further, when raising the temperature of the K-cell, it is very important to set the heating rate to 20 ° C./min or less in order to prevent bumping of the raw materials and eliminate the temperature difference between the raw materials. The supply amount of A element is adjusted so that A / B of ABO ₃ is 1 (Bi ₄ Ti ₃ O ₁₂ is Bi / Ti = 4/3), and the amount is the film thickness using a crystal oscillator. It was controlled precisely by a monitor. The formed thin film begins to exhibit properties as a crystalline dielectric at a substrate temperature of 300 ° C. or higher, and the higher the substrate temperature, the higher the crystallinity and the better film can be obtained. However, if the substrate temperature is 80
If the temperature is higher than 0 ° C, cracks will occur in the film due to the stress relationship with the substrate. Therefore, in order to obtain a crack-free dielectric thin film, it is desirable to form the film at a substrate temperature of 300 ° C. or higher and 800 ° C. or lower. O ₂ gas 5 is used as the oxygen source,
It was supplied so as to be sprayed on the substrate. FIG. 2 shows the relationship between the relative permittivity and the oxygen partial pressure. When the oxygen partial pressure is less than 1.0 × 10 ⁻⁵ Torr, the film cannot be sufficiently oxidized and the film deteriorates, resulting in a rapid decrease in the relative dielectric constant. Also Sr, Ba,
In order to prevent the oxidation of Pb etc. and operate the E-gun stably, it is desirable to set the vacuum degree of the raw material chamber to 1.0 × 10 ^-5 Torr or less. For that purpose, the oxygen partial pressure in the growth chamber is 5 ×. 10 ^-4
It is desirable to set it to Torr or less. From the above, the oxygen partial pressure in the growth chamber must be 1.0 × 10 ⁻⁵ Torr or more and 5 × 10 ⁴ Torr or less. The film formation rate is two K-cell temperatures, E
-Control by changing the power of the gun.
For example, by using two K-cells and setting the temperature of Sr to 350 ° C., a film forming rate of SrTiO ₃ of 300 Å / min at maximum can be obtained.

Depending on the film formation conditions, the film formation rate is too fast, so the oxygen in the film is insufficient, or the film formation proceeds before the atoms adsorbed on the substrate surface have diffused sufficiently, and many pores are formed in the film. It may not be possible to obtain a good film. Therefore, the film was heat-treated in the apparatus. After the film formation, the heat treatment requires the substrate temperature to be higher than the film formation temperature in order to easily diffuse the atoms in the film. The effect is not observed unless the heat treatment temperature is 200 ° C. higher than the substrate temperature at the time of film formation. If the temperature is higher than 800 ° C, the film will crack. Therefore, the heat treatment temperature was set to 500 ° C or higher and 800 ° C or lower. Further, in order to promote the oxidation of the film, it is necessary to raise the oxygen partial pressure in the growth chamber from the time of film formation. However, the oxygen partial pressure is 1.0 × 10
^If it is higher than ^-3 Torr, the relative dielectric constant will decrease,
The heat treatment has the opposite effect. From this, the oxygen partial pressure for effective heat treatment is 1.0 × 10 ^-4 Torr or more 1.0 × 10
^-3 Torr or less is desirable. FIG. 3 shows the relationship between the heat treatment time at each heat treatment temperature and the relative dielectric constant of the film. Regarding the relative permittivity, the effect of heat treatment is not sufficiently expressed when the heat treatment time is within 2 hours. Therefore, it is necessary to perform heat treatment for at least 2 hours. However, if the heat treatment is performed for more than 3 hours, the interface between the substrate and the film is deteriorated and the dielectric constant is lowered.
From this, it is necessary to set the heat treatment time to 2 hours or more and 3 hours or less.

If the film is rapidly cooled after the heat treatment, the film may be cracked due to the difference in stress between the substrate and the film. Therefore, it is necessary to gradually cool the film. If the slow cooling rate is higher than 20 ° C / min, cracks may occur on the film surface. Therefore, it is desirable to set the cooling rate to 20 ° C / min or less.

In addition to the formation of the SrTiO ₃ film of this embodiment, in the ABO ₃ type dielectric source, A is Ba, Pb, La, Li, K, B is Ti, Zr, Nb, Ta, or Bi ₄ Ti ₃ O. similar results are obtained for _12.

(Effects of the Invention) As described above, by using the present invention, the ABO ₃ type dielectric film or the Bi ₄ Ti ₃ O ₁₂ film can be formed under the condition that the oxygen partial pressure is high while the raw material part is stably controlled. can do.
Further, even if a film is formed with defects due to an excessively high film forming rate, or even if the film is deficient in oxygen, a thin film having good film quality can be obtained by performing heat treatment. The multi-source vacuum vapor deposition method is a method capable of easily controlling the composition, obtaining a high quality film having a good interface with the substrate. From this, the present invention makes it possible to obtain a dielectric thin film of higher quality than ever before, which is of great industrial significance.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a film forming apparatus for a dielectric film by a vacuum vapor deposition method, FIG. 2 is a relationship diagram between Sr temperature and film forming rate, and FIG. 3 is a relative dielectric constant at each heat treatment temperature and heat treatment time. Relationship diagram. In the figure, 1 is a growth chamber, 2 is a raw material chamber, 3 is a K-cell, 4 is an E-
gun, 5 is an O ₂ gas path, 6 is a substrate, and 7 is a heater.

Claims (2)

[Claims] 1. A substrate represented by the general formula ABO ₃ , where A is S
One or more elements selected from r, Ba, Pb, La, Li, K, a dielectric composed of one or more elements selected from Ti, Zr, Nb, Ta as B (excluding SrTiO ₃ ), or Bi _In the method of depositing ₄ Ti ₃ O ₁₂ , the vacuum device is divided into a growth chamber where the substrate is installed and a source chamber where the source of evaporation of the source metal is installed. Partial pressure in growth chamber is 1.0 × 10 ^-5 or more and 5.0 × 10 ^-4 Torr or less, raw material chamber is 1.
0 × 10 ^-5 Torr or less, A or Bi K-cell,
B is separately supplied to the growth chamber by using the E-gun, and the temperature rising rate of the K-cell supplying A or Bi is 20 ° C / m 2.
A method for forming a dielectric thin film, wherein the substrate temperature is 300 ° C. or higher and 800 ° C. or lower. 2. A substrate represented by the general formula ABO ₃ , where A is S
Deposition of one or more elements selected from r, Ba, Pb, La, Li, K, a dielectric composed of one or more elements selected from Ti, Zr, Nb, Ta as B, or Bi ₄ Ti ₃ O ₁₂ In the method, the vacuum device is divided into a growth chamber in which the substrate is installed and a raw material chamber in which an evaporation source for the raw material metal is installed.Each of them is independently evacuated and the oxygen partial pressure is 1.0 × in the growth chamber. 10 ^-5 or more 5.0
By supplying the raw material chamber to a growth chamber of not more than × 10 ^-4 Torr or less and 1.0 × 10 ^-5 Torr or less, and using A-Bi as a K-cell and B as an E-gun, A or Bi is separately supplied to the growth chamber. Supply K
-Set the temperature of the cell to 20 ℃ / min or less and the substrate temperature to 300
After forming the dielectric thin film by setting the temperature to ℃ or more and 800 ℃ or less, raise the substrate temperature to 500 ℃ or more and 800 ℃ in the growth chamber of the above vacuum equipment.
A method for forming a dielectric thin film, which comprises performing a heat treatment for 2 hours or more and 3 hours or less under an oxygen partial pressure of 1.0 × 10 ⁻⁴ Torr or more and 1.0 × 10 ⁻³ Torr or less.