JP3428432B2 - Sputtering target material for forming a Bi-Sr-Ta-O-based ferroelectric thin film and a film forming method using the same - Google Patents

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 in which the content of Bi component between the formed thin films is extremely small when forming an a-O-based ferroelectric thin film by the sputtering method, and a film forming method using the same. It is a thing.

[0002]

2. Description of the Related Art Conventionally, in general, the composition formula: Biα Sr
β Taγ Oδ (However, in the atomic ratio, when Ta is used as a reference and γ is 2.0, α: 1.8 to 2.4, β:
A Bi-Sr-Ta-O-based ferroelectric thin film satisfying 0.8 to 1.1 and δ: 8.5 to 9.7) is formed by a sputtering method. . The atomic ratios of Bi, Sr, Ta and O in the above composition formulas are empirically determined, and when these components satisfy the atomic ratios within their respective ranges, a film is formed. The thin film has predetermined ferroelectric properties. Therefore, if the atomic ratio of each component deviates from any of the above ranges, the desired ferroelectric properties will not be exhibited. . Further, 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 for forming the ferroelectric thin film. A sputtering target material containing a ferroelectric thin film in a proportion 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 above-mentioned sputtering target material is used as a raw material powder for Bi ₂ O ₃ powder,
Strontium carbonate (hereinafter referred to as SrCO ₃ ) powder,
And Ta ₂ O ₅ powder, these raw material powders are mixed in a ratio corresponding to the composition formula of the ferroelectric thin film, wet-mixed by a ball mill and dried, and then, for example, in air, temperature: 10
A composite oxide was produced by baking at 00 ° C. for 5 hours, and 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 cold isostatic pressing (CIP) molding is performed under pressure, and the molded body is sintered, for example, in an oxygen atmosphere at a temperature of 1000 ° C. for 5 hours. Furthermore, the above ferroelectric thin film is used, for example, in a high frequency sputtering device in an Ar atmosphere of 10 ^-2 Torr, frequency: 13.56 MHz, output: 3.3 W /
The target material is sputtered under the condition of cm ² to form an amorphous thin film having a thickness of, for example, 200 nm, which is then rapidly heated to a temperature of 800 ° C. in an oxygen atmosphere and then immediately cooled. It is also known that it is formed by performing a crystallization treatment under the conditions.

[0003]

On the other hand, in recent years, for example, semiconductor devices have been highly integrated, and the manufacturing apparatus thereof has tended to be large in size. As a result, the sputtering apparatus has also been increased in size, and naturally the sputtering device used for this purpose has to be increased. -The size of the target material also becomes larger, and the ferroelectric thin film over a large area is formed. However, when the size of the conventional sputtering target material is increased, the formed ferroelectric thin film mutual Bi
Variations in the content occur, and as a result, the ferroelectric characteristics change from thin film to thin film, which is also unfavorable from the viewpoint of high integration.

[0004]

Therefore, the present inventors have
From the above viewpoints, as a result of research to develop a sputtering target material in which the Bi contents of the formed ferroelectric thin films do not vary, (a) the conventional sputtering target described above is obtained. In the material, the oxide species of Sr and Ta, which are these constituents, are extremely stable against sputtering and decompose regularly, but the oxide species of Bi are extremely unstable components, so Bi is generated by sputtering. Sputtering in a state in which regular decomposition and atmosphere emission accompanying this are not performed, and the bound oxygen of Bi is irregularly decomposed and released into the atmosphere, and / or to the target material surface in the state where the bound oxygen is deficient Since Bi is sputtered under unstable conditions such as sputtering, Bi is not stably released into the atmosphere. Under the condition that the Bi content in the film constantly changes, it is inevitable that the Bi content in the thin film varies. (B) However, the metal Bi (hereinafter , Bi)
Incorporation makes it possible to eliminate the instability that occurs when the complex oxide is used during sputtering, and Bi is stably released from the surface of the target material. In this case, Bi is used. Oxygen deficiency can be supplemented by allowing oxygen to exist in the sputtering atmosphere, whereby the Bi contents in the thin films are mutually constant, and the variation in Bi contents among the thin films is extremely small. ) As for the target material containing Bi, B having an average particle diameter of 1 to 100 μm is used as a raw material powder.
i powder and SrO, both of which are stable against spatter
Composite oxide powders and Ta ₂ O ₅ powder from Sr and Ta (S
r _X Ta _2.0 O _{5 + X} ), and using this, these raw material powders are in proportions corresponding to the proportions of Bi, Sr, and Ta in the above composition formula, that is, in terms of atomic ratio, with Ta as the reference, Ta When 2.0 is 2.0, Bi: 0.8 to 2.0 and Sr: 0.8 to 1.2 are blended in a satisfying ratio, and after mixing, this mixed powder is a low melting point metal Bi. Near the melting point of, ie 25
Warm press molding at a temperature of 0 to 300 ° C, 99.5%
The target material obtained as a result of the above theoretical density ratio has a structure in which the composite oxide of Sr and Ta (Sr _X Ta _2.0 O _{5 + X} ) is uniformly dispersed and distributed in the base material of Bi. (D) Using the target material described in (C) above, the 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. With an output power of 1.2 to 4.3 W / cm ^{2 and} a total sputtering gas pressure P of P: 5 in a volume ratio of the sputtering gas composition of O ₂ / Ar = 1/9 to 1/1. Sputtering is performed under the condition of 20 mTorr without heating the substrate temperature, and then the temperature is rapidly raised to 800 ° C. in an oxygen atmosphere, and then crystallization treatment of standing cooling is immediately performed to form a ferroelectric film. Desired good quality Bi-Sr The research results shown in (a) to (d) above were obtained, which is a film forming method for forming a -Ta-O ferroelectric thin film.

The present invention has been made based on the above-mentioned research results. (A) Composition formula: BiαSrβTaγOδ (where Ta is the reference atomic ratio and γ is 2.0, α is :
1.8-2.4, β: 0.8-1.1, δ: 8.5
In the sputtering target material for forming a Bi-Sr-Ta-O-based ferroelectric thin film satisfying the condition (7), the sputtering target material is 1 to 1
Bi powder having an average particle size of 00 μm and a complex oxide composed of Sr and Ta: Sr _X Ta _2.0 O _{5 + X} (where X =
0.8 to 1.2), which is a warm pressed compact of a mixed powder. This warm pressed compact has an atomic ratio of Ta of 2.0, and Bi: 0. 8 to 2.0, Sr: 0.8 to 1.2, which is a compounding composition, and the complex oxide on the base material of Bi:
Bi-Sr-, which has a structure in which Sr _X Ta _2.0 O _{5 + X} is uniformly dispersed and has a theoretical density ratio of 99.5% or more.
Sputtering target material for film formation of Ta-O type ferroelectric thin film, (b) sputter target for film formation according to (a)
Bi-Sr-Ta sputtering using get material
-O-based ferroelectric thin film forming method, (c) Output of 1.2 to 4 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 ³ W / cm ² , the sputtering gas composition volume ratio is 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 zero. The sputtering film formation is performed in a heated state, and then the temperature is rapidly raised to 800 ° C. in an oxygen atmosphere, and then a crystallization treatment of standing cooling is immediately performed to form a ferroelectric film. The present invention is characterized by a method for forming a Sr-Ta-O-based ferroelectric thin film.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the sputtering target material of the present invention will be described. First, as raw material powders, Bi powder, SrO powder, and Ta ₂ O ₅ powder having a predetermined average particle diameter of the present invention are prepared.
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 crushing the obtained fired product, the crushed powder and the metal Bi powder were mixed in a ratio corresponding to the target composition of the ferroelectric thin film described above, and dry mixed by a ball mill for 1 hour, and then this mixture. 100 powder in a vacuum of 10 ^-2 Torr
20 at a given pressure within the range of up to 200 kgf / cm ^2.
By warm press forming under a condition of holding at a predetermined temperature within a range of 0 to 250 ° C. for 3 hours, the target of the present invention having a predetermined theoretical density ratio and a predetermined diameter × thickness.
Each get material can be manufactured.

In the sputtering target material of the present invention, the compounding atomic ratio of Bi, Sr, and Ta other than oxygen in the warm press-molded body constituting the sputter target material is determined by the above composition formula of the ferroelectric thin film to be formed. Therefore, the blending atomic ratio of Bi, Sr, and Ta in the warm press-formed product is based on Ta, and Ta is 2.
When it is set to 0, if it is out of the ranges of Bi: 0.8 to 2.0 and Sr: 0.8 to 1.2, respectively, Bi (1.8) defined in the above composition formula is obtained.
.About.2.4) and the atomic ratio of Sr (0.8 to 1.1) are out of the range, and it becomes impossible to provide the thin film with desired ferroelectric characteristics.

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, the Bi powder, which is a low melting point metal, is warmed. During the hot press molding, it is easily oxidized, and BiO is present so that the Bi content in the thin film varies as described above. On the other hand, when the average particle size exceeds 100 μm, it is particularly an insulator. This is based on the reason that abnormal discharge starts from SrO.

In warm press forming, the pressure is 1
A sputtering target material having a theoretical density ratio of 99.5% or more cannot be obtained in the range of 00 to 200 kgf / cm ² and a temperature of 200 ° C. or lower, and Bi at 300 ° C. or higher.
As a result of the melting only, segregation occurs and a uniform target material cannot be obtained, and it becomes difficult to reliably ensure the strength of the target material during sputtering and the uniformity of sputtering.

The sputtering method of the present invention is preferably a high frequency sputtering method, and outputs 1.2 to 4 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 ³ W / cm ² , the sputtering gas composition volume ratio is 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 zero. Desirably, a method of forming a ferroelectric film by performing sputtering film formation in a heated state, then rapidly raising the temperature to 800 ° C. in an oxygen atmosphere, and then immediately performing crystallization treatment by allowing it to cool.

[0011]

EXAMPLES Next, the sputtering target material of the present invention will be specifically described by way of examples. First, as the raw material powder, Bi having the average particle size shown in Table 1 was used.
Powder, Sr _X Ta _2.0 O _{5 + X} mixed powder are prepared, and these raw material powders are blended in a ratio corresponding to the target composition of the ferroelectric thin film as shown in Table 1 and dried by a ball mill for 1 hour. After mixing, the mixed powder was warm press-molded 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. They have the theoretical density ratios shown and both have diameters:
300 mm × thickness: the present invention type having a size of 10 mm
Get materials 1 to 9 were manufactured. When the structures of the target materials 1 to 9 of the present invention were observed with a metallurgical microscope, they all showed a structure in which the Sr _X Ta _2.0 O _{5 + X} composite oxide was uniformly dispersed and distributed in the base material of Bi. Met.

[0012]

[Table 1]

[0013]

[Table 2]

For comparison purposes, Bi ₂ O ₃ powder, SrCO ₃ powder, and Ta ₂ O ₅ powder having the 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, after blending in a ratio corresponding to the target composition of the ferroelectric thin film, wet mixing with a ball mill, and drying, in the air, at a temperature of 1000 ° C., 5
It is fired under the condition of holding time to form a composite oxide, and then the composite oxide is wet crushed with a ball mill and subjected to a particle size adjustment in a cold static condition at a pressure of ² ton / cm ^2. By hydraulic pressing (CIP) molding, and sintering the molded body in an oxygen atmosphere at a temperature of 1000 ° C. for 5 hours, the theoretical density ratios shown in Table 3 are also obtained.
In addition, conventional target materials 1 to 9 each having a diameter of 300 mm and a thickness of 10 mm were manufactured.
When the structures of the above-mentioned conventional target materials 1 to 9 were also observed with a metallurgical microscope, they 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 Ar / O ₂ = 4/1 and the total pressure was 12 mTorr in an ordinary high frequency sputtering apparatus. , A rectangular wave power of 100 kHz having a period in which the target has a positive potential, and 2.0 W / cm ² of the conventional target materials, and 10 ⁻² To in the conventional target materials 1 to 9.
An Ar atmosphere of rr was used, and a thin film having a thickness of 200 nm was formed on each surface of 10 Si wafers (diameter: 150 mm) per target material. After rapidly raising the temperature to 800 ° C. in the atmosphere, crystallization treatment of standing cooling was immediately performed to form a ferroelectric thin film.

Then, for the purpose of evaluating the mutual variation of the Bi content of the ferroelectric thin film, 20 mm × 20 from each center of the Si wafer on which the ferroelectric thin film is formed.
A test piece having a size of mm is cut out, and the center portion of the test piece with a fluorescent X-ray device has a Bi diameter of 15 mm
The atomic ratio of / (Sr + Ta) was measured. The minimum value and the maximum value were picked up from the measurement results of 10 test pieces per one kind of the target material, and shown in Table 1 and Table 3 together with the average values.

[0018]

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

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI H01L 21/285 H01L 21/285 S (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 14/00-14 / 58 C30B 29/22 H01L 21/203 H01L 21/285

Claims (2)

(57) [Claims] 1. Compositional formula: BiαSrβ Taγ Oδ
(However, in terms of atomic ratio, when Ta is used as a reference and γ is 2.0, α: 1.8 to 2.4, β: 0.8 to 1.1,
Bi-Sr-T satisfying δ: 8.5 to 9.7)
In a sputtering target for forming an a-O-based ferroelectric thin film, the sputtering target material is a metal Bi powder having an average particle size of 1 to 100 μm, and a complex 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 compact with a mixed powder. The warm press compact had an atomic ratio of Ta of 2.0. In this case, the compounding composition satisfies Bi: 0.8 to 2.0 and Sr: 0.8 to 1.2, and the complex oxide is added to the base material of Bi:
Formation of 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. Sputtering is carried out at an input power of 1.2 to 4.3 W / cm ² using alternating wave power of 50 kHz or more and 250 kHz or less having a positive potential with respect to the ground potential of the sputtering target. Under the condition that the volume ratio of the gas composition is O ₂ / Ar = 1/9 to 1/1 and the total gas pressure P of the sputtering is P: 5 to 20 mTorr, the film formation is performed by sputtering without heating the substrate temperature. in an oxygen atmosphere, temperature: 800 ° C. high speed temperature in Yutakago immediately sputtering for film deposition according to claim 1, characterized in that to form the ferroelectric film is subjected to crystallization treatment cool
Method for forming Bi-Sr-Ta-O-based ferroelectric thin film using a targeting material