JPH11158611A - Target for forming strontium titanate thin coating, its production and formation of strontium titanate thin coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a target for forming strontium titanate thin coating capable of increasing the relative permittivity of the formed SrTiO3 thin coating to about 50 to 100 even if the substrate temp. at the time of sputtering is <=200 deg.C, to provide a method therefor and to provide a method for forming strontium titanate thin coating high in relative permittivity by using this target for forming strontium titanate thin coating. SOLUTION: Relating to the target for forming strontium titanate thin coating the compositional formula is expressed by SrTiO3 ±δ in the case the excess and deficiency of oxygen from the stoichiometric compsn. of strontium titanate is defined as δ, where δ is <=0.020. This target for forming thin coating can be produced by baking a strontium titanate thin molded body at 1200 to 1350 deg.C for 3 to 14 hr in the air or in oxygen to obtain a baked body expressed by the compositional formula of SrTiO3±δin the case the excess and deficiency of oxygen from the stoichiometric compsn. of strontium titanate is defined as δ, where δ is <=0.020.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monolithic IC for microwaves obtained by forming a dielectric thin film on an IC or the like.
The present invention relates to a target for forming a dielectric thin film, used for manufacturing an (MMIC), a method for manufacturing the same, and a method for forming a dielectric thin film using the target.

[0002]

2. Description of the Related Art In recent years, miniaturization and high frequency of communication equipment have been rapidly progressing, and technology for directly forming a capacitor on an IC has been developed in terms of circuit design. SrTiO ₃ as a dielectric material has a relative permittivity in bulk of 200 or more, exhibits paraelectric properties near room temperature, and therefore has a small temperature change and a small decrease in permittivity in a high frequency region.

Since the operating frequency of a portable telephone is 1-2 GHz, it is necessary that the relative permittivity ε is 50 or more, preferably close to 100 in this frequency band. However, SrTi
In order to use O ₃ for an MMIC or the like, the thickness of the thin film must be 2
It needs to be about 00 nm. When SrTiO _{3 is formed} into such a thin film, the relative dielectric constant is as low as about 20. The relative dielectric constant of the thin film SrTiO ₃ is affected by the substrate temperature at the time of sputtering, and a certain relative dielectric constant cannot be obtained unless the substrate temperature is set to 200 ° C. or more, for example, 250 ° C. or more.

SrTiO ₃ in which a part of Sr is replaced by Ba can obtain a large relative dielectric constant, but in this case, the substrate temperature must be higher than in the case of SrTiO ₃ . By increasing the substrate temperature during sputtering in this way, a large relative dielectric constant can be obtained. However, when an IC is used as a substrate and a dielectric material is formed thereon, the IC substrate is heated to 250 ° C. or higher. Heating destroys the IC itself.

Therefore, Takashi Hirao et al., "Dielectric thin film material" (N
ational Technical Report Vol.40No.1 Feb. 1994 p.2
4) In the film formation conditions, a substrate temperature of about 200 ° C., RF
Power: 2.83 W / cm ² , gas flow rate: O ₂ / Ar ratio: 0.1
15. At a gas pressure of 4 mTorr, p-Si (1
00), a Pt / Ti multilayer film was deposited at room temperature by electron beam evaporation.
9.99% 6 inch diameter ceramic target Sr
The SrTiO ₃ thin film is formed using TiO ₃ .
When the thickness of the SrTiO ₃ thin film is small, the (200) plane of the X-ray diffraction pattern of SrTiO ₃ generated by the epitaxial relationship with the Pt substrate surface is strongly oriented, but the thickness of the SrTiO ₃ thin film increases. According to (1
10) It is reported that the orientation in the direction becomes stronger, and the relative dielectric constant increases accordingly. 200n thick
In the case of m, the relative dielectric constant was about 60, and the relative dielectric constant was about 110 when it exceeded 400 nm.

[0006]

As described above, SrTi
Even when an O ₃ thin film is formed at a substrate temperature of about 200 ° C., the
Although it has been reported that a SrTiO ₃ thin film having a relative dielectric constant of about 00 can be obtained, according to the experience of the present inventors, the relative dielectric constant of this thin film is affected by the oxygen content in the SrTiO ₃ thin film. It turned out to be. SrTi
The atmosphere in which the O ₃ thin film is formed is oxygen containing about 10 oxygen in Ar.
% Of the SrTiO ₃ thin film, the sputtering is performed without causing oxygen deficiency in the thin film. Affect.

Therefore, in the present invention, even when the substrate temperature during sputtering is 200 ° C. or less, the SrT
Increase the relative dielectric constant of the iO ₃ thin film, ie, 50-100
It is an object of the present invention to provide a target for forming a strontium titanate thin film which can be reduced to a degree and a method for manufacturing the same.

Another object of the present invention is to provide a method for forming a strontium titanate thin film using the above-described strontium titanate thin film target.

[0009]

According to the strontium titanate thin film deposition target of the present invention, when the excess or deficiency of oxygen from the stoichiometric composition of strontium titanate is represented by δ, the composition formula is SrTiO3 ± δ. And δ is 0.020 or less.

In the method for producing a strontium titanate thin film target according to the present invention, the strontium titanate compact is fired in air or oxygen at a temperature of 1200 to 1350 ° C. for 3 to 14 hours to obtain strontium titanate. When the excess or deficiency of oxygen from the stoichiometric composition is represented by δ, a sintered body represented by the composition formula SrTiO3 ± δ and δ of 0.020 or less is obtained.

In the method of forming a strontium titanate thin film according to the present invention, when the excess or deficiency of oxygen from the stoichiometric composition of strontium titanate is represented by δ, the composition formula Sr
Using a strontium titanate thin film deposition target represented by TiO3 ± δ and having a δ of 0.020 or less, sputtering was performed at a substrate temperature of 200 ° C or less in an atmosphere containing oxygen, and the X-ray diffraction pattern (110 The present invention is characterized in that a strontium titanate thin film having a peak intensity of (1) plane which is 1/10 or more of a peak intensity of (200) plane is obtained.

When the excess or deficiency of oxygen from the stoichiometric composition of strontium titanate is represented by δ, the composition formula SrTi
O3 ± δ, where δ is 0.020 or less, may cause other inclusions if the oxygen content is more than 0.020. Also, if the amount of oxygen becomes less than 0.020,
Defects occur due to lack of oxygen, and the specific resistance also decreases. When the substrate temperature is 200 ° C. or less when sputtering is performed using a target having an insufficient amount of oxygen, the value of the relative dielectric constant ε is less than 30. Substrate temperature 250
The value of the relative dielectric constant ε does not become 50 even at ℃. On the other hand, if δ is 0.020 or less, the relative dielectric constant ε becomes 50 or more even when sputtering is performed at a substrate temperature of 200 ° C. or less, and ε of 90 to 100 is obtained from 200 ° C. to 250 ° C.

The firing temperature was from 1200 ° C. to 1350 ° C., and the firing time was from 3 hours to 14 hours. If the firing temperature is too high, strontium titanate grains grow, and the oxygen in the strontium titanate is released, resulting in SrTiO ₃ oxygen deficiency. If the firing time is lengthened, grain growth occurs even at about 1400 ° C., resulting in insufficient oxygen. Firing temperature 12
If the temperature is lower than 00 ° C., the sintering does not proceed sufficiently and the density becomes too low.

The fact that the substrate temperature at the time of sputtering is set to 200 ° C. or less is apparent from the above description. However, in the case of MMIC, etc., if the IC substrate is heated to a temperature exceeding 200 ° C., the IC will be broken. It is desirable that the temperature be as close to room temperature as possible.

SrTiO deposited by sputtering_Three
(110) plane / (200) plane of X-ray diffraction pattern of thin film
Is 1/10 or more. This is SrT
iO _ThreeThe X-ray diffraction pattern of the thin film has a (111) plane.
It occurs most strongly, followed by the peak of the (200) plane. Only
However, in order to increase the relative dielectric constant, the peak of the (110) plane must be increased.
Work must occur. When the relative permittivity is 20 or less
In this case, no peak on the (110) plane is observed. Relative permittivity
When it takes a value of 40 to 50, (11
A peak on the 0) plane is observed. (110) face / (2)
The peak ratio of the (00) plane becomes about 1/10 (110)
When the peak of the surface is recognized, the relative dielectric constant ε also becomes 4
It becomes 0-50.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The production of a strontium titanate thin film target according to the present invention and a comparative example will be described. Using commercially available strontium titanate hydrothermally synthesized powder having a purity of 3N (particle size: 0.3 μm) as a starting material, 1% of polyvinyl alcohol was added and mixed and granulated using a Raikai machine. The particles passed through a 32 mesh sieve were subjected to molding. The temporary molding is performed using a 180 mm diameter mold.
5 tons / cm ² of pressure is applied and this temporary molded product is
The main molding was performed by applying a pressure of 3 ton / cm ² using IP. This molded product is placed in an oxygen stream (flow rate 10 liters /
(Min) Firing at 1200 ° C. for 5 hours and then at 1300 ° C. for 5 hours to obtain a strontium titanate thin film deposition target of the present invention.

At the same time, the molded article obtained in the same manner was placed in an oxygen stream (flow rate 10 l / min) at 1200 ° C. for 5 hours.
Subsequently, baking was performed at 1500 ° C. for 5 hours to obtain a strontium titanate thin film deposition target of Comparative Example.

[0018]

[Table 1]

The strontium titanate titanate thin film forming target of the comparative example fired at 1500 ° C. has a high sintering density, but the excess / deficiency δ of oxygen is as large as -0.0245, deviating from the stoichiometric composition. Due to this shortage, it seems that the crystal structure also contains a different phase, the specific resistance is small,
Defects generated on the crystal made it easier for electricity to flow. However, in the target of the present invention which was finally baked at 1300 ° C., there was no excess or deficiency of oxygen, and the crystal structure and the X-ray diffraction showed uniform microcrystals and high specific resistance. That is, there was no defect.

Using these targets, a substrate formed by forming a Pt / Ti multilayer film on a 3-inch diameter Si wafer as a substrate and changing the substrate temperature from room temperature to 250 ° C. at every 50 ° C. At 200nm
A thin strontium titanate thin film was formed. Atmosphere sputtering, the O ₂ 5% in Ar, 10%, 2
It was changed to 0%.

FIG. 1 and FIG. 1 show the relationship between the substrate temperature and the relative dielectric constant ε of the strontium titanate thin film formed at the time of sputtering, using the oxygen amount in the atmosphere at the time of sputtering as a parameter. 3. Here, FIG. 1 uses the target of the present invention, and FIG. 3 uses the target of the comparative example.

FIG. 3 shows a strontium titanate thin film formed using the target of the comparative example lacking oxygen.
As is clear from the above, even when the amount of oxygen in the atmosphere during sputtering is increased from 5% to 20%, the relative permittivity of the obtained thin film is low, and the substrate temperature is around 20 when the substrate temperature is 200 ° C. or lower. At 250 ° C., a relative dielectric constant of about 40 was finally obtained. In such a target, the MMI
In order to form a thin film used for C and the like, it is necessary to raise the substrate temperature to 250 ° C. or higher, and a sufficient relative dielectric constant could not be obtained.

In contrast, in the strontium titanate thin film formed by using the target of the present invention, as shown in FIG. 1, even when the oxygen amount in the atmosphere at the time of sputtering is 10%, the substrate temperature is low. A relative dielectric constant of about 50 to about 70 was obtained at 200 ° C. or less, and a higher relative dielectric constant was obtained when the oxygen content in the atmosphere was 20%.

FIGS. 2 and 4 show X-ray diffraction patterns of the strontium titanate thin film formed above. Here, FIG. 2 uses the target of the present invention, and FIG. 4 uses the target of the comparative example. These X-ray diffraction patterns were measured for thin films formed with the oxygen content in the atmosphere during sputtering set to 10%.

In the thin film formed by using the target of the present invention shown in FIG. 2, the substrate temperature is from room temperature to 250 ° C.
The peak of the (110) plane occurs in any of
Even at room temperature, the peak ratio of the (110) plane / (200) plane is 0.33. However, the thin film formed using the target of the comparative example shown in FIG.
When the substrate temperature is room temperature and when the substrate temperature is 150 ° C., (11
0) No peak on the plane was observed. Substrate temperature 250
The peak ratio of the (110) plane / (200) plane was only 0.33 when the temperature reached ° C.

[0026]

As is clear from the above description, when the excess or deficiency of oxygen from the stoichiometric composition of strontium titanate is represented by δ, it is represented by the composition formula SrTiO3 ± δ,
When a strontium titanate thin film is formed by sputtering using a strontium titanate thin film deposition target having a δ of 0.020 or less, even if the thin film has a thickness of 200 nm, the substrate temperature is not more than 50 ° C. A relative dielectric constant ε of around −100 is obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the substrate temperature and the relative dielectric constant ε of a strontium titanate thin film formed by using the target of the present invention at the time of sputtering and the amount of oxygen in the atmosphere at the time of sputtering as a parameter. is there.

FIG. 2 is a view showing an X-ray diffraction pattern of a strontium titanate thin film formed using the target of the present invention.

FIG. 3 is a graph showing the relationship between the substrate temperature and the relative permittivity ε of a strontium titanate thin film formed using the target of the comparative example during sputtering, using the oxygen amount in the atmosphere during sputtering as a parameter. is there.

FIG. 4 is a view showing an X-ray diffraction pattern of a strontium titanate thin film formed using a target of a comparative example.

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI H01L 21/31 H01G 4/06 102

Claims (3)

[Claims] When the excess or deficiency of oxygen from the stoichiometric composition of strontium titanate is represented by δ, the composition formula SrT
iO3 ± δ (in SrTiO3 ± δ, “3 ±
“δ” is a subscript of O. ) And δ is 0.02
A strontium titanate thin film target for forming a strontium titanate thin film having a thickness of 0 or less. 2. The strontium titanate compact is fired in air or oxygen at a temperature of 1200 to 1350 ° C. for 3 to 14 hours to determine the excess or deficiency of oxygen from the stoichiometric composition of strontium titanate by δ. When shown, the composition formula SrTiO3 ±
A method for producing a target for forming a strontium titanate thin film, characterized by obtaining a fired body represented by δ and having δ of 0.020 or less. 3. When the excess or deficiency of oxygen from the stoichiometric composition of strontium titanate is represented by δ, the composition formula SrT
Using a strontium titanate thin film deposition target represented by iO3 ± δ and δ of 0.020 or less, sputtering was performed at a substrate temperature of 200 ° C. or less in an atmosphere containing oxygen, and the X-ray diffraction pattern (110 A method for forming a strontium titanate thin film, characterized in that a strontium titanate thin film having a peak intensity of 1/10 or more of the peak intensity of the (200) plane is obtained.