JPH11323539A - Sputtering target material for forming bi-sr-ta-o ferroelectric thin film and formation using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a ferroelectric thin film having a wide area small in the dispersion in the content of Bi components by using a warm press formed body having a specified compsn. of metallic Bi powder having specified grain size and a powdery mixture of metallic Bi powder and Sr-Ta multiple oxide as a sputtering target material. SOLUTION: A powdery mixture obtd. by blending SrO and Ta2 O5 in a prescribed ratio is baked at about 1000 to 1400 deg.C in the air to obtain Sr-Ta multiple oxides of Srx Ta2 O5+x (x) is 0.8 to 1.2}. This multiple oxide powder is blended with a prescribed amt. of metallic Bi powder having 1 to 100 μm average grain size, this powdery mixture is subjected to warm press forming at about 200 to 250 deg.C under the pressure of about 100 to 200 kgf/cm<2> in a vacuum of about 10<-2> Torr to obtain a formed body having a structure in which multiple oxides are uniformly dispersed and distributed into a Bi base of Bi: 0.8 to 2.0 atomic ratio and having >=99.5 theoretical density. This warm press formed body is used as a target, and sputtering is executed to form a Bi-Sr-Ta- O series ferroelectric thin film having a prescribed compsn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a Bi-Sr-T
The present invention relates to a sputtering target material having a very small variation in the Bi component content between the formed thin films when the aO-based ferroelectric thin film is formed by a sputtering method, and a film forming method using the same. Things.

[0002]

2. Description of the Related Art Conventionally, generally, a composition formula: Biα Sr
β Taγ Oδ (However, when γ is 2.0 with respect to Ta in terms of atomic ratio, α: 1.8 to 2.4, β:
0.8 to 1.1, δ: 8.5 to 9.7) are formed by sputtering using a Bi-Sr-Ta-O-based ferroelectric thin film. . The atomic ratios of Bi, Sr, Ta and O in the above composition formula are determined empirically, and when these components satisfy the atomic ratios within the respective ranges, a film is formed. The thin film has predetermined ferroelectric properties, and therefore, if the atomic ratio of each component deviates from any of the above ranges, the thin film will not exhibit the desired ferroelectric properties. . For forming the ferroelectric thin film, bismuth oxide (hereinafter, referred to as Bi ₂ O ₃ ), strontium oxide (hereinafter, referred to as SrO), and tantalum oxide (hereinafter, referred to as Ta ₂ O ₅ ) are used. A sputtering target material containing a ferroelectric thin film at a ratio corresponding to the composition formula and having a single-phase structure composed of a complex oxide of Bi, Sr, and Ta is used. Further, the sputtering target material may be a powder of Bi ₂ O ₃ ,
Strontium carbonate (hereinafter, referred to as SrCO ₃ ) powder,
And Ta ₂ O ₅ powder, these raw material powders are blended in a proportion corresponding to the composition formula of the ferroelectric thin film, wet-mixed with a ball mill, and dried.
The composite oxide was produced by baking at 00 ° C. for 5 hours to produce a composite oxide. Then, the composite oxide was wet-crushed with a ball mill and adjusted to a particle size of ² ton / cm ² . It is also known that it is manufactured by cold isostatic pressing (CIP) molding under pressure and sintering the molded body in an oxygen atmosphere, for example, at a temperature of 1000 ° C. for 5 hours. Further, the ferroelectric thin film is produced by, for example, a high frequency sputtering device in an Ar atmosphere of 10 ^-2 Torr, a frequency of 13.56 MHz and an output of 3.3 W /
The target material was sputtered under a condition of cm ² to form an amorphous thin film having a thickness of, for example, 200 nm. Then, the temperature was raised to 800 ° C. in an oxygen atmosphere at a high speed, and then immediately allowed to cool. It is also known that they are formed by performing crystallization treatment under conditions.

[0003]

On the other hand, in recent years, for example, as semiconductor elements have become more highly integrated and the manufacturing equipment thereof has been increasing in size, the sputtering equipment has also increased in size, and naturally the sputtering equipment used in the equipment has become larger. -The size of the ferroelectric thin film having a large area is increased due to the increase in the size of the ferroelectric thin film. Bi of
Variations occur in the content, and as a result, the ferroelectric characteristics change from thin film to thin film, which is undesirable from the viewpoint of high integration.

[0004]

Means for Solving the Problems Accordingly, the present inventors have
From the above viewpoints, a study was conducted to develop a sputtering target material having no variation in the Bi content between the formed ferroelectric thin films. As a result, (a) the conventional sputtering target described above was obtained. In the material, the oxide species of these constituents, Sr and Ta, are extremely stable to spatter and decompose regularly, but the oxide species of Bi are extremely unstable components. Sputtering is performed in a state in which Bi is decomposed irregularly and the atmosphere is released due to the regular decomposition and the accompanying release of the atmosphere is not performed, and / or the target material surface in a state where the bound oxygen is insufficient. Since Bi is sputtered under unstable conditions such as sputtering, stable release of Bi into the atmosphere is not performed. Under the condition that the Bi content in the film constantly changes, it is unavoidable that the Bi content in the thin film will vary, (b) However, metal Bi (hereinafter referred to as “B”) in the target material. , Bi)
Incorporation makes it possible to eliminate the instability that occurs when the composite oxide is used during sputtering, so that Bi can be stably released from the target material surface. In this case, Bi was used. Oxygen deficiency due to this can be supplemented by the presence of oxygen in the sputtering atmosphere, whereby the Bi content in the thin films becomes mutually constant, and the variation in Bi content between the thin films becomes extremely small; (c) The target material containing Bi has a mean particle size of 1 to 100 μm as a raw material powder.
i powder, and SrO, both of which are stable against sputtering
Powder and Ta ₂ O ₅ powder to form a composite oxide of Sr and Ta (S
r _X Ta _2.0 O _{5 + X} ) was synthesized and used, and these raw material powders were used in proportions corresponding to the proportions of Bi, Sr, and Ta in the above composition formula, that is, in terms of atomic ratio, based on Ta, Ta Is 2.0, Bi: 0.8 to 2.0, Sr: 0.8 to 1.2 are blended in a satisfying ratio and mixed, and then the mixed powder is mixed with a low melting point metal Bi. Temperature around the melting point of
Warm press molding at a temperature of 0 to 300 ° C, 99.5%
The target material having the above theoretical density ratio can be produced. The target material has a structure in which a composite oxide of Sr and Ta (Sr _x Ta _2.0 O _{5 + x} ) is uniformly dispersed and distributed on the base material of Bi. (D) using the target material described in (C) above, the alternating power having a period in which the potential of the sputtering target is positive with respect to the ground potential, from 50 kHz to 250 kHz; At an input power of 1.2 to 4.3 W / cm ² , the sputtering total gas pressure P is P: 5 to 5 when the volume ratio of the sputtering gas composition is in the range of O ₂ / Ar = 1/9 to 1/1. Sputter film formation is performed under the conditions of 20 mTorr and the substrate temperature is not heated, and then the temperature is increased to 800 ° C. in an oxygen atmosphere at a high speed, and then immediately cooled to form a ferroelectric film. Desired high quality Bi- The method for forming the r-Ta-O-based ferroelectric thin film formation, than it was obtained the results of a study that indicated above (a) ~ (d).

The present invention has been made on the basis of the above research results. (A) Composition formula: BiαSrβTaγOδ (However, when the atomic ratio is based on Ta and γ is 2.0, α :
1.8 to 2.4, β: 0.8 to 1.1, δ: 8.5
9.7), the sputtering target material for forming a Bi—Sr—Ta—O-based ferroelectric thin film satisfying the following condition:
A composite oxide composed of Bi powder having an average particle diameter of 00 μm and Sr and Ta: Sr _X Ta _2.0 O _{5 + X} (where X =
0.8 to 1.2). The warm press-formed body is made of a mixed powder consisting of 0.8 to 1.2). 8 to 2.0, Sr: 0.8 to 1.2, and a composite oxide:
Bi-Sr- having a structure in which Sr _X Ta _2.0 O _{5 + X} is uniformly dispersed and distributed and having a theoretical density ratio of 99.5% or more.
A sputtering target material for forming a Ta-O-based ferroelectric thin film, and a sputtering target for forming a film according to (b) or (a).
Bi-Sr-Ta sputtering using get material
A method of forming an -O-based ferroelectric thin film, (c) using alternating wave power of 50 kHz or more and 250 kHz or less having a period in which the potential of the sputtering target is positive with respect to the ground potential. At an input power of 0.3 W / cm ² , the sputtering gas composition P is in the range of O ₂ / Ar = 1/9 to 1/1, the total sputtering gas pressure P is P: 5 to 20 mTorr, and the substrate temperature is not changed. The Bi- film according to (2), wherein the ferroelectric film is formed by performing sputtering film formation in a heated state, and then rapidly raising the temperature in an oxygen atmosphere to a temperature of 800 ° C., and then immediately performing crystallization treatment of cooling. A method of forming an Sr—Ta—O-based ferroelectric thin film is characterized.

[0006]

Next, an embodiment of the sputtering target material of the present invention will be described. First, Bi powder, SrO powder, and Ta ₂ O ₅ powder having a predetermined average particle size of the present invention are prepared as raw material powders.
The rO + Ta ₂ O ₅ powder were mixed after weighing predetermined amounts, the mixed powder in air 1000 ° C. to 1400 ° C., held for 3-5 hours. After the obtained fired product is pulverized, the pulverized powder and the metal Bi powder are blended in a ratio corresponding to the target composition of the ferroelectric thin film described above, and dry-mixed in a ball mill for 1 hour. Powder was placed in a vacuum of 10 ^-2 Torr, 100
At a predetermined pressure within the range of ~ 200 kgf / cm ² ,
The hot press forming under the condition of holding at a predetermined temperature within a range of 0 to 250 ° C. for 3 hours allows the present invention to have a predetermined theoretical density ratio and a predetermined diameter × thickness.
Get materials can be manufactured respectively.

In the sputtering target material of the present invention, the compound atomic ratio of Bi, Sr, and Ta other than oxygen in the warm press-formed body constituting the sputtering target material is determined by the above composition formula of the ferroelectric thin film to be formed. Therefore, the compounding atomic ratio of Bi, Sr, and Ta in the warm press-formed body is based on Ta, and Ta is set at 2.
In the case of 0, Bi: 0.8 to 2.0 and Sr: 0.8 to 1.2, respectively, and Bi (1.8) defined in the above composition formula.
-2.4) and Sr (0.8-1.1) are out of the range of atomic ratios, and the thin film cannot have desired ferroelectric properties.

Further, in the sputtering target material of the present invention, the average particle size of the mixed powder is set to 1 to 100 μm. When the average particle size is less than 1 μm, Bi powder, which is a low melting point metal, becomes particularly hot. It becomes easy to oxidize at the time of hot press molding, BiO is present, and the Bi content in the thin film is varied as described above. On the other hand, if the average particle size exceeds 100 μm, it is particularly an insulator. This is based on the reason that an abnormal discharge starts from SrO.

In warm press forming, a pressure of 1
When the temperature is in the range of 00 to 200 kgf / cm ² and the temperature is 200 ° C. or less, a sputtering target material having a theoretical density ratio of 99.5% or more cannot be obtained.
As a result of only melting, segregation occurs and a uniform target material cannot be obtained, and it is difficult to reliably ensure the strength of the target material and uniformity of sputtering during sputtering.

The sputtering method of the present invention is preferably a high frequency sputtering method, and uses an alternating wave power of 50 kHz to 250 kHz having a period in which the potential of the sputtering target is positive with respect to the ground potential. At an input power of 0.3 W / cm ² , the sputtering gas composition P is in the range of O ₂ / Ar = 1/9 to 1/1, the total sputtering gas pressure P is P: 5 to 20 mTorr, and the substrate temperature is not changed. It is preferable to form a ferroelectric film by performing sputtering film formation in a heated state, and then rapidly raising the temperature in an oxygen atmosphere to a temperature of 800 ° C., and then immediately performing crystallization treatment of cooling.

[0011]

EXAMPLES Next, the sputtering target material of the present invention will be specifically described with reference to examples. First, Bi having the average particle size shown in Table 1 was used as the raw material powder.
A powder, Sr _X Ta _2.0 O _{5 + X} mixed powder was prepared, and these raw material powders were mixed at a ratio corresponding to the target composition of the ferroelectric thin film, as shown in Table 1, and then dried by a ball mill for 1 hour. After mixing, the mixed powder was subjected to warm press molding in a vacuum of 10 ^-2 Torr at a pressure shown in Table 2 and at a temperature shown in Table 2 for 3 hours. Having the theoretical density ratios indicated, and both having a diameter:
The present invention having a dimension of 300 mm × thickness: 10 mm.
Get materials 1 to 9 were produced, respectively. Incidentally, the present invention data - was the target material 1 to 9 tissues were observed by a metal microscope, both in the matrix of Bi, indicates the Sr _X Ta _2.0 O _{5 + X} composite oxide are uniformly dispersed distribution tissue Met.

[0012]

[Table 1]

[0013]

[Table 2]

For the purpose of comparison, Bi ₂ O ₃ powder, SrCO ₃ powder and Ta ₂ O ₅ powder having average particle diameters shown in Table 3 were prepared as raw material powders, and these raw material powders were prepared. Similarly, as shown in Table 3, the ferroelectric thin films were blended in proportions corresponding to the target composition, wet-mixed with a ball mill, dried, and then dried in air at a temperature of 1000 ° C.
The mixture was calcined under the condition of holding time to produce a composite oxide, and then the composite oxide was wet-crushed with a ball mill and adjusted for particle size, and then cold-statically pressed at ² ton / cm ^2. It is formed by hydraulic press (CIP) and sintering the formed body in an oxygen atmosphere at a temperature of 1000 ° C. for 5 hours to obtain a theoretical density ratio also shown in Table 3,
In addition, conventional target materials 1 to 9 each having a size of diameter: 300 mm × thickness: 10 mm were manufactured.
When the structures of the above-mentioned conventional target materials 1 to 9 were similarly observed with a metallurgical microscope, all showed a single-phase structure composed of a complex oxide of Bi, Sr and Ta.

[0015]

[Table 3]

Using the various target materials obtained as a result, the target materials 1 to 9 of the present invention were subjected to Ar / O ₂ = 4/1 and a total pressure of 12 mTorr by using an ordinary high-frequency sputtering apparatus. Under the conditions of a 100 kHz rectangular wave power of 2.0 W / cm ² having a period in which the target has a positive potential, and in the above-mentioned conventional target materials 1 to 9, 10 ⁻² To
An Ar atmosphere of rr was used, and a thin film having a thickness of 200 nm was formed on the surface of 10 Si wafers (diameter: 150 mm) for each kind of target material. Immediately after the temperature was raised to 800 ° C. in the atmosphere at a high speed, the crystallizing treatment was immediately performed to form a ferroelectric thin film.

Next, in order to evaluate the mutual variation in the Bi content of the ferroelectric thin film, the center of each of the Si wafers on which the ferroelectric thin film was formed was 20 mm × 20 mm.
A test piece having a size of 1 mm was cut out, and Bi in a range of a diameter of 15 mm at the central portion of the test piece was measured with a fluorescent X-ray apparatus.
The atomic ratio of / (Sr + Ta) was measured. From the measurement results of 10 test pieces per one type of target material, the minimum value and the maximum value were picked up, and are shown in Tables 1 and 3 together with their average values.

[0018]

From the results shown in Tables 1 and 3, the Bi content in the ferroelectric thin film formed using the target materials 1 to 9 of the present invention is extremely stable.
While there is almost no variation between the thin films, it is clear that the Bi content of the ferroelectric thin films conventionally formed using the target materials 1 to 9 has a large variation between the thin films. As described above, the sputtering target material of the present invention can form a ferroelectric thin film having a constant Bi content only by changing the film formation atmosphere to an oxidizing atmosphere using a normal sputtering apparatus. This contributes to stabilization of the ferroelectric characteristics of the thin film, and can sufficiently satisfy, for example, high integration of semiconductor elements and enlargement of a manufacturing apparatus thereof.

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI H01L 21/285 H01L 21/285 S

Claims (3)

[Claims] 1. Composition formula: BiαSrβ Taγ Oδ
(However, when the atomic ratio is based on Ta and γ is 2.0, α: 1.8 to 2.4, β: 0.8 to 1.1,
Bi: Sr-T satisfying?: 8.5 to 9.7)
In a sputtering target for forming an aO-based ferroelectric thin film, the sputtering target material is composed of a metal Bi powder having an average particle diameter of 1 to 100 μm and a composite oxide composed of Sr and Ta: Sr _X Ta _2.0 O
_{5 + X} (where X = 0.8 to 1.2) and a warm press-formed body composed of a mixed powder, and this warm press-formed body has an atomic ratio of 2. When it is set to 0, Bi: 0.8 to 2.0, Sr: 0.8 to 1.2.
A Bi—Sr—Ta—O-based ferroelectric thin film having a structure in which Sr _X Ta _2.0 O _{5 + X} is uniformly dispersed and distributed, and having a theoretical density ratio of 99.5% or more. Sputtering target material for film. 2. A method for forming a Bi—Sr—Ta—O-based ferroelectric thin film using a sputtering target material for film formation according to claim 1. 3. An alternating-wave power of 50 kHz or more and 250 kHz or less having a period in which the potential of the sputtering target is positive with respect to the ground potential. Sputtering is performed at an input power of 1.2 to 4.3 W / cm ^2. A sputtering film formation is carried out under the condition that the volume ratio of the gas composition is O ₂ / Ar = 1/9 to 1/1 and the total sputtering gas pressure P is P: 5 to 20 mTorr, and the substrate temperature is not heated. 3. The Bi-Sr- according to claim 2, wherein the ferroelectric film is formed by immediately performing a crystallization treatment of cooling after the temperature is rapidly increased to 800 ° C in an oxygen atmosphere.
A method for forming a Ta-O-based ferroelectric thin film.