JPH07126845A - Formation of dielectric film - Google Patents

Abstract

PURPOSE:To form a dielectric film having good quality with decreased leak currents at a stable and high film forming speed without a change of a target with lapse of time by superposing DC electric power and high-frequency electric power and executing film formation sputtering. CONSTITUTION:The DC electric power and high-frequency electric power are superposed and are impressed on the target material in the method for forming the dielectric film on a substrate by a sputtering method using the ceramic material of <=10OMEGA.cm in the electric resistance measured at 1.5V applied voltage in a film thickness direction. As a result, the high-speed film formation is executed without the change of the target with lapse of time and without generating abnormal electric discharge by dielectric breakdown and dust and the generation of crazing in the target. Further, the formation of the dielectric film having the excellent leak current characteristic is possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a dielectric film, and more particularly to a method for forming a dielectric film for obtaining a dielectric film made of a ceramic material on a substrate by a sputtering method.

[0002]

2. Description of the Related Art Conventionally, the following five methods are known as film forming methods for obtaining a dielectric film made of a ceramic material. (1) A method of forming a ceramic material target having the same structure as the target film, that is, a metal oxide target having an infinite electric resistance by high frequency sputtering, (2) a metal material forming the target film (3) A target made of a metal material forming a target film, that is, an alloy target having an electric resistance of almost zero, is formed by using a high frequency sputtering method. DC sputtering method, (4) Metal whose electrical resistance is 10 Ω · cm or less due to the reason that the ceramic material target with the same structure as the target film causes oxygen deficiency during firing. Method of forming oxide target by high frequency sputtering method, (5) Ceramic material target with the same structure as target film causes oxygen deficiency during firing Electrical resistance is 1 due to reasons such as
A method of forming a film of a metal oxide target having a resistance of 0 Ω · cm or less by using a DC sputtering method. Incidentally, regarding the methods (4) and (5) among the above film forming methods, the present applicant has previously filed Japanese Patent Application No.
This is a film forming method proposed in No. 253383.

When a dielectric film is obtained by using these film forming methods, the oxygen composition of the film is generally smaller than the target composition. Therefore, in the cases of (1), (4) and (5), a relatively small amount of oxygen is used. In the case of (2) and (3), sputtering is generally performed while adding a large amount of oxygen gas to the sputtering gas.

In the case of (1), since the target is an insulator, only the high frequency sputtering method can be used, but (2)
In the cases of (3), (4), and (5), the target has an electric resistance capable of DC sputtering, so that the high frequency sputtering method or DC sputtering method can also be used.

[0005]

The conventional film forming methods (1), (2), (3), (4) and (5) have the following problems.
That is, in the case of the film forming method (1), the film forming rate is extremely slow because only the high frequency sputtering method can form the film.

In the case of the film forming method (2), the film forming speed is low when the film is formed by the high frequency sputtering method. Further, since the surface of the target is gradually oxidized by the oxygen gas added to the sputtering gas, the characteristics of the obtained dielectric film change with time.

In the case of the film forming method of (3), since the surface of the target is gradually oxidized by the oxygen gas added to the sputtering gas, the characteristics of the obtained dielectric film change with time. Further, since the insulating film is deposited on the non-sputtered portion on the target, that is, the so-called non-erosion portion, the insulating film is dielectrically broken down by the potential due to the application of DC power, and dust is generated to obtain the desired good dielectric film. Absent.

In the case of the film forming method of (4), since the target is already a metal oxide, the target does not change with time, but since it is a high frequency sputtering method, the film forming rate is slow.

In the case of the film forming method of (5), since the target is already a metal oxide, there is no change over time in the target and the film can be formed by the DC sputtering method. Is also early. However, since the film deposited on the non-erogen part is a perfect insulator film, dielectric breakdown occurs and dust is generated. In addition, the electric resistance of the target is almost 0 (for example, 10 ^−
5 Ω ・ cm), but at most 10 Ω ・ cm to several mΩ ・
Since it is in the range of cm, when a high DC power is applied to obtain a high film formation rate, a large amount of charge is accumulated on the boundary between the target surface and the part where the electric resistance is a little high and the target material is low. Dielectric breakdown causes dust and, in the worst case, the target cracks, making stable discharge impossible.

The present invention solves the above-mentioned problems, does not change the target with time, enables high-speed film formation without causing abnormal discharge due to dielectric breakdown, generation of dust, or cracking of the target. An object of the present invention is to provide a film forming method capable of obtaining a dielectric film having excellent current characteristics.

[0011]

The dielectric film forming method of the present invention is a sputtering method using a ceramic material target having an electric resistance of 10 Ω · cm or less measured in the plate thickness direction at an applied voltage of 1.5 V. A method of forming a dielectric film on a substrate is characterized in that direct-current power and high-frequency power are superimposed and applied to the target material to form a film by sputtering.

Further, the ceramic material target is S
rTiO ₃ _x, BaTiO ₃ _x, (BaSr) TiO ₃ _
x, LiNbO ₃ _x, LiTaO ₃ _x, PbTiO ₃ _x,
(PbLa) TiO ₃ _x, Pb (ZrTi) O ₃ _x, (P
bLa) (ZrTi) O ₃ _x ABO ₃ _x [A: B: O =
The ceramic material may be a metal oxide represented by a type of 1: 1: 3-x (x> 0)].

The ratio of the high frequency power to the total power of the direct current power and the high frequency power applied to the ceramic material target may be 10% to 90%.

[0014]

When direct current power and high frequency power are superimposed and applied to the ceramic material target by the sputtering method, the target is sputtered and a dielectric film of the ceramic material is formed on the substrate.

At that time, the ceramic material target has an electric resistance of 10 Ω in the thickness direction measured at an applied voltage of 1.5 V.
Since the target is less than cm, the target does not generate heat during sputtering, and since the high frequency power is superimposed on the DC power, the target is not destroyed by the charge accumulated in the target. However, the target is not cracked and a stable high film formation rate can be obtained.

[0016]

EXAMPLES First, in the present invention, when forming a dielectric film of a ceramic material, the target will not be cracked even when high power is applied, and the reason why a stable high film formation rate can be obtained will be explained. To do.

Generally, when depositing a ceramic dielectric film on a substrate by sputtering a ceramic material target, a high frequency sputtering method or a direct current sputtering method is used. Compared to the DC sputtering method, the high-frequency sputtering method has a drawback that the power applied to the target is lower in the rate at which the sputtering gas such as argon (Ar) is used for the energy for sputtering the target, so that the film forming speed is slow.

A target made of a ceramic material is generally an insulator, but if oxygen deficiency is caused during firing or an alloy target containing no oxygen is used, its electrical resistance is small, and therefore DC sputtering with a high deposition rate is achieved. Law becomes possible.

However, as described above, when an alloy target made entirely of metal is used, the target surface gradually oxidizes during sputtering, causing a change over time. Therefore, since the target has been oxidized in advance, it does not change with time, but since the electrical resistance is small to some extent, high-speed film formation by the DC sputtering method is possible, and thus low resistance (applied voltage 1.
The ceramic material target having an electric resistance of 10 Ω · cm or less measured at 5 V in the plate thickness direction is the best.

However, when DC sputtering is carried out using this low resistance target, if a high power is applied to increase the film formation rate, the DC potential applied to the target causes a charge (charge) on the target surface or inside. (Electric charge) is accumulated, and when the charge exceeds a certain amount, dielectric breakdown occurs in the target, micro-cracks and dust are generated, and in severe cases, the target is cracked. This has a low resistance such that the target can be subjected to the DC sputtering method, but it is not a perfect conductor like a metal, and there is insufficient oxygen deficiency inside the target during firing of the target. The parts are microscopically mixed, and the electric resistance measured in the plate thickness direction at an applied voltage of 1.5 V is as low as 10 Ω · cm or less as a whole, but the DC potential is continuously applied. And the oxygen deficiency is insufficient and the charge is accumulated in the part where the resistance is slightly higher than the surrounding part and the amount gradually increases,
Eventually it will cause dielectric breakdown.

In the method for forming a dielectric film of the present invention, when such a low resistance target is used, high frequency power is superimposed on DC power and applied, so that the accumulated charge is released and dielectric breakdown occurs. Therefore, it does not cause cracking of the target or generation of dust.

In the present invention, the ratio of the superimposed high frequency power to the total power (DC power + high frequency power) is 10%.
% To 90% means that it is difficult to completely release the charge accumulated in the target when the high frequency power ratio is less than 10%, and the high frequency power ratio exceeds 90%. This is because the film forming rate becomes slower in this case. Furthermore, since the high-frequency sputtering method has a higher ionization efficiency in plasma than the direct-current sputtering method, it has high reactivity, and even if the film formation rate is increased, the film deposited on the substrate is formed in a sufficiently oxidized state. Therefore, since an excellent film quality such as a small leak current can be obtained, there is also an advantage that a film having similarly excellent properties can be obtained even when high frequency power is superimposed on DC power.

Next, specific examples of the present invention will be described together with comparative examples.

[0024] Example 1 barium titanate (BaTiO ₃₎ powder and was mixed with strontium titanate (SrTiO ₃₎ powder, barium strontium titanate that caused oxygen deficiency by hot pressing in a vacuum (Ba _{0. 5} Sr _{0. 5)} T
A ceramic material target made of iO ₃ _x was prepared. Applied voltage of this ceramic material target 1.5V
The electric resistance measured in the plate thickness direction was 10 Ω · cm.

[0025] was placed the ceramic material target in a sputtering apparatus, the pressure in the sputtering apparatus 1 × 10 ^- was evacuated to ⁴ Pa, the oxygen (O ₂₎ argon containing 20% gas (Ar) gas partial A ceramic dielectric film made of (BaSr) TiO ₃ having a film thickness of 800 Å was formed on a substrate made of a Si wafer heated to 600 ° C. under a pressure of 1 Pa.

The sputtering film formation was performed by using a magnetron sputtering method in which DC power of 500 W and high frequency power of 500 W were superposed (ratio of high frequency power was 50%). The high-frequency power superimposed on the DC power has an oscillation frequency of 13.56 MH.
The one of z was used.

During the sputtering, the number of abnormal discharges was measured by measuring and visually observing the applied DC voltage and the high frequency reflected wave. The film formation rate during film formation was 60 Å / min, and the number of abnormal discharges was 0 times.

After the film formation, the target surface was observed, but there was no change. Also, a film was formed on the substrate (BaSr)
A result of measuring the leakage current when 3V is applied the dielectric film made of TiO _3, 2 × 10 ^- was ⁹ A / cm ^2.

Comparative Example 1 (BaSr) T was formed on a substrate in the same manner as in Example 1 except that the power applied to the ceramic material target was high-frequency power of 1000 W (ratio of high-frequency power was 100%).
A ceramic dielectric film of iO ₃ _x was formed.

The film formation rate during film formation was 15 Å / min, and the number of abnormal discharges was zero.

After the film formation, the target surface was observed and there was no change. Also, the leakage current of the deposited dielectric film on a substrate 1 × 10 ^- was ⁹ A / cm ^2.

COMPARATIVE EXAMPLE 2 The power applied to the ceramic material target was DC power 1
(BaSr) TiO _{3 —} on the substrate in the same manner as in Example 1 except that the power was set to 000 W (the ratio of high frequency power was 0%).
A ceramic dielectric film made of x was formed.

The film formation rate during film formation was 75Å / min, but the number of abnormal discharges during film formation was 20 times.

When the surface of the target was observed after the film formation, about 10 cracks and chips were found. In addition, the leak current of the dielectric film formed on the substrate was often short-circuited because the target fine powder that had fallen on the substrate was attached and adhered, but the value at the place where there is no fine powder is 3 × 10 ^{-
It was 7} A / cm ² .

Example 2 The total power applied to the ceramic material target is 1000
W, and the ratio of superposed high frequency power to total power is 0
A ceramic dielectric film made of (BaSr) TiO ₃ was formed on the substrate in the same manner as in Example 1 except that various changes were made from 100% to 100%.

The relationship between the ratio of the high frequency power at the time of film formation by sputtering and the film forming speed and the number of abnormal discharges was investigated, and the results are shown in FIG.

From the results of this example, when the ratio of the high frequency power is 10% or more, the number of abnormal discharges drastically decreases and stable film formation can be performed. When the ratio of high frequency power is 90% or less, only the high frequency power (the ratio of high frequency power is 100
%), The film formation rate gradually increases, which indicates that high-speed film formation is possible.

Example 3 As a ceramics material target, SrTiO ₃ _x, BaTiO ₃ _x, LiNbO in which oxygen composition in the ceramics material composition is less than stoichiometric composition and so-called oxygen deficiency occurred.
_{3 _x, LaTaO 3 _x, PbTiO} 3 _x, (Pb 0. 8 La 0.
_{2) TiO 3 _x, Pb (} Zr 0. 5 Ti 0. 5) O 3 _x, (P
_{b 0. 8 La 0. 2} ) (Zr 0. 5 Ti 0. 5) O 3 with each ceramic material target _x, 0% the proportion of high-frequency power to the total applied power 1000W to be applied to the target, 50
% And 100%, various dielectric films were formed on the substrate by the same method as in Example 1 above.

The type of ceramic material target, the electric resistance of the target when an applied voltage of 1.5 V was applied in the plate thickness direction, the film formation rate, the number of abnormal discharges, and the leakage current when 3 V was applied were examined respectively, and the results are shown in table form. Shown in 1.

[0040]

[Table 1]

As is clear from the results of each of the examples and the comparative examples of the present invention, the ratio of the high frequency power to be superimposed in the examples 1 and 2 is in the range of 10% to 90%, and in the example 3. When the ratio of the superimposed high frequency power is 50%, the high frequency power is superimposed on the applied DC potential, so that the charge (charge) that causes cracks on the surface of the target or on the inside of the target is broken. Since it was released, it was confirmed that there was no abnormal discharge and stable film formation was possible.

Since the high frequency power is superposed,
Since the ionization rate in plasma was improved and the ceramic dielectric film to be deposited was sufficiently oxidized, Example 3
As shown in (4), the leakage current was smaller than that in the case of only DC power without superimposing high frequency power.

On the other hand, the ratio of the high frequency power of Comparative Example 1 (the ratio of the high frequency power is 100%) and that of the third embodiment are 100%.
In this case, the film formation rate is extremely slow and not practical.

Comparative example 2 (the ratio of high frequency power is 0
%) And the ratio of the high frequency power of Example 3 is 0%,
Since the target is cracked and abnormal discharge occurs, stable discharge cannot be performed and it cannot be put to practical use.

Therefore, it was confirmed that the range of the ratio of the high frequency electric power to the total electric power which is capable of high speed film formation and stable film formation without abnormal discharge is 10% to 90% by the embodiment of the present invention. . That is, the ratio of high frequency power in the total power is 1
If it is less than 0%, the DC power is large, and the charge accumulated on the target surface or inside cannot be completely released by the DC potential applied to the target. Further, when the ratio of the high frequency power in the total power exceeds 90%, the film forming rate is almost the same as when only the high frequency power is applied, and as a result, only a low film forming rate is obtained.

In the above embodiment, the high frequency power to be superimposed on the direct current power has an oscillation frequency of 13.56 MHz, but an alternating current having a frequency capable of releasing the charge accumulated in the target may be used.

In the above embodiment, the ceramic material target is ABO ₃ _x [A: B: O = 1: 1: 3-x.
(X> 0)] type ceramic material was used.
A composition may be used in which the oxygen content in the composition causes oxygen vacancies smaller than the stoichiometric composition, and the electrical resistance in the plate thickness direction becomes 10 Ω · cm or less when a voltage of 1.5 V is measured.

[0048]

According to the present invention, a dielectric film made of a ceramic material is formed on a substrate by a sputtering method using a target whose electric resistance is 10 Ω · cm or less when measured in the plate thickness direction at an applied voltage of 1.5 V. When forming a film, by superimposing DC power and high frequency power as the power applied to the target to form a film by sputtering, there is no change over time in the target,
It is possible to obtain a stable and high film formation rate and to form a high-quality dielectric film with a small leak current without causing abnormal discharge or dust generation due to dielectric breakdown or cracking of the target. is there.

[Brief description of drawings]

FIG. 1 is a characteristic line showing the relationship between the ratio of high frequency power in the total power applied to a target and the number of abnormal discharges, and the relationship between the ratio of high frequency power in the total power and the film formation rate according to one embodiment of the present invention. Fig.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01L 21/31 21/314 A 7352-4M (72) Inventor Hisami Nakamura Sanmu-cho, Sanmu-gun, Chiba Prefecture Yokota 523 Japan Vacuum Technology Co., Ltd. Chiba Institute for Supermaterials (72) Inventor Zhong Hong ▲ Ko ▼ Yokota 523 Yamatake Town, Yamatake District, Chiba Japan Vacuum Technology Co. Ltd. Chiba Institute for Supermaterials

Claims (3)

[Claims] 1. A method of forming a dielectric film on a substrate by a sputtering method using a ceramic material target having an electric resistance of 10 Ω · cm or less measured in the plate thickness direction at an applied voltage of 1.5 V, the target material comprising: A method for forming a dielectric film, characterized in that direct-current power and high-frequency power are superimposed on each other and applied to form a film by sputtering. 2. The ceramic material target is SrT.
iO ₃ _x, BaTiO ₃ _x, (BaSr) TiO ₃ _x, L
iNbO ₃ _x, LiTaO ₃ _x, PbTiO ₃ _x, (Pb
La) TiO ₃ _x, Pb (ZrTi) O ₃ _x, (PbL
a) ABO ₃ _x of [ZrTi) O ₃ _x [A: B: O = 1:
The method for forming a dielectric film according to claim 1, wherein the ceramic material is a ceramic material made of a metal oxide represented by 1: 3-x (x> 0) type. 3. The ratio of the high frequency power to the total power of the direct current power and the high frequency power applied to the ceramic material target is 1.
It is 0% -90%, The film-forming method of the dielectric film of Claim 1 or 2 characterized by the above-mentioned.