JPH0772339B2 - Method for forming dielectric thin film - Google Patents

Description

The present invention relates to a method for forming a dielectric thin film.

(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. Of these vacuum evaporation method has attracted attention for a long time as a method that might capable of forming a good film at the interface with high-quality, issued deposited September 1963 relates to BaTiO ₃ Journal of Electro Chemical Seo Saia tee Magazine (Journal of The Electrochemical Socie
ty) 969-973. In addition, the Applied Physics Letter magazine (February 1989)
The size of remanent polarization is 5 μc / cm by using oxygen plasma in the multi-source deposition method as shown in pages 527-529.
^2. The formation of thin films with ferroelectric properties at an anti-electric field of 15 KV / cm has also been reported. 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, although it is desirable to introduce oxygen gas in order to oxidize the film, or active oxygen with strong oxidizing power 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 other hand, when the film is formed under conditions where the E-gun operates stably and Sr, Ba, etc. are stable and the oxygen partial pressure is low (conditions less than 1.0 × 10 ⁻⁵ Torr), the film is deficient in oxygen. This is because the dielectric film could not be obtained.

(Means for Solving the Problems) The present invention evacuates the film formation chamber and the source chamber during film formation independently, and keeps the oxygen partial pressure in the growth chamber at 3 ± 2 × 10 ⁻⁵ Torr while maintaining the source chamber. The E-gun can be operated stably, and the dielectric film can be formed by using a device capable of forming Sr with a vacuum degree of 3 ± 2 × 10 ⁻⁶ Torr, and the device after the film formation can be performed. In this method, heat treatment is carried out so as to accelerate the oxidation of the film and reduce the defects in the 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. Two K-cell3 containing Sr and an E-gun4 containing Ti are installed in the raw material chamber. FIG. 2 shows the relationship between the temperature of Sr and the film formation rate of SrTiO ₃ . The deposition rate increases exponentially with the temperature of Sr. When the temperature of Sr becomes 350 ° C. or higher, the evaporation amount of Sr becomes too large, and it becomes difficult to control the evaporation amount of Sr well. From this, for example, it is desirable to set the temperature of Sr to the temperature of 270 ° C. to 350 ° C. and the temperature of Sr to a temperature range in which the film forming rate is 20 Å / min or more and the controllability of Sr is good. When raising the temperature of Sr, 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 amount of Ti supplied was adjusted so that Sr / Ti of SrTiO ₃ was 1, and the amount was precisely controlled by a film thickness monitor using a crystal oscillator. 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 set to 800 ° C. or higher, 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 was used as an oxygen source and was supplied so as to be sprayed on the substrate.
FIG. 3 shows the relationship between relative permittivity and oxygen partial pressure. Oxygen partial pressure
If it is less than 1.0 × 10 ⁻⁵ Torr, the film cannot be sufficiently oxidized and the film is deteriorated, and the relative dielectric constant is rapidly decreased. In order to prevent the oxidation of Sr and operate the E-gun stably, it is necessary to set the degree of vacuum in the raw material chamber to 1.0 × 10 ^-5 Torr or less. It should be 5 × 10 ^-4 Torr or less. However, it is desirable that the oxygen partial pressure in the growth chamber is 3 ± 2 × 10 ⁻⁵ Torr and the oxygen partial pressure in the source chamber is 3 ± 2 × 10 ⁻⁶ Torr. The film formation rate is controlled by changing the temperature of Sr of two K-cells and the power of the E-gun that supplies Ti, and two K-cells are used and the temperature of Sr is set to 350 ° C. Up to 300
A deposition rate of SrTiO ₃ of Å / min could be obtained.

(Effects of the Invention) As described above, by using the present invention, it is possible to form a film of SrTiO ₃ even under conditions of high oxygen partial pressure while stably controlling the raw material part. The multi-source vacuum vapor deposition method of the present invention 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 the temperature of Sr and the film forming speed, and FIG. 3 is a partial pressure of oxygen in the growth chamber at the time of film forming. Relationship diagram of dielectric constant. 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.

Front Page Continuation (72) Inventor Toshiyuki Sakuma 5-7-1, Shiba, Minato-ku, Tokyo NEC Electric Co., Ltd. (72) Inventor Shintaro Yamamichi 5-7-1, Shiba, Minato-ku, Tokyo NEC Electricity Co., Ltd. In-house (56) References JP-A-2-107758 (JP, A)

Claims (1)

[Claims] 1. A method for forming a SrTiO ₃ film on a substrate, comprising:
The vacuum device is divided into a growth chamber where the substrate is installed and a raw material chamber where the source metal deposition source is installed. Each of them is evacuated independently and the oxygen partial pressure is 3 ± 2 × 10 ^{− in the} growth chamber. ^Five
Torr, the raw material chamber is set to 3 ± 2 × 10 ⁻⁶ Torr, Sr is K−
A method for forming a dielectric thin film, characterized in that cells and Ti are separately supplied to a growth chamber by using an E-gun.