JP2679201B2 - Method for etching ruthenium oxide thin film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for etching a ruthenium oxide thin film used in various electronic devices.

2. Description of the Related Art In various electronic devices, ruthenium oxide resistors are widely used in hybrid ICs, thermal heads, chip resistors, resistor network components, sensors, etc. These ruthenium oxide-based resistors are generally powders of an inorganic material whose main component is RuO ₂ mixed with glass frit, resin, organic solvent,
It is a thick film resistor produced by printing and baking a paste.

Since these are formed by printing, it is naturally possible to form a pattern, but the pattern width is limited to about 100 μm, and it is impossible to form a fine pattern with high accuracy. In addition, these are dispersion-type thick films using an inorganic binder, and the variation in resistance characteristics is large compared to thin films,
Poor heat dissipation and power resistance.

Problems to be Solved by the Invention Since a thin film resistor is generally produced by using a vacuum device, it is necessary that the thin film resistor can be etched in order to form a pattern. Similar to the thick film, there is a method of obtaining a thin film by printing and firing, but the pattern accuracy and reproducibility can be obtained only to the same extent as the thick film. The etching is roughly classified into wet etching and dry etching. Wet etching is a method of etching with a chemical solution in a liquid bath. Further, dry etching is a method of etching with a neutral gas, gas phase ions, radicals and the like, and a method of making gas into plasma to perform etching is called plasma etching.

Thin-film resistors have better characteristics as resistors than thick-film, but RuO ₂ is insoluble in acid and there is no suitable etchant, so ruthenium oxide-based thin-film resistors cannot be patterned by wet etching. was there. Further, there has been no report of dry etching on a ruthenium oxide-based film, and a method for accurately forming a fine pattern of a ruthenium oxide-based thin film has not been known.

Therefore, ruthenium oxide-based thin film resistors have excellent characteristics such as good environmental stability and controllability of resistance value, but they are rarely used.

Therefore, an object of the present invention is to provide a method for patterning a ruthenium oxide thin film resistor, and to create a fine pattern of a ruthenium oxide thin film having excellent characteristics.

Means for Solving the Problem In order to solve the above problems, the present invention uses a RuO ₂ thin film or a ruthenium oxide based thin film having a composition ratio of an element other than O to Ru of 10 at% or less by using CF _4. Active ion etching is performed to form a pattern.

Operation By adopting the above etching method, a fine pattern of a RuO ₂ thin film or a ruthenium oxide based thin film can be created.

Examples Hereinafter, examples of the present invention will be described.

That is, the present invention provides a RuO ₂ thin film or a ruthenium oxide thin film in which the composition ratio of elements other than O to Ru is 10 at% or less,
It is characterized in that plasma etching is performed using a gas having at least F in the structure.

Although various devices are used for plasma etching, in the present invention, as shown in FIG. 1, a reaction chamber 11 has cathodes and anodes 12 and 14 which are parallel plate type electrodes, and is provided on the cathode 12. Reactive ion etching system (high frequency power frequency)
13.56MHz) is used. The reactive ion etching has the following features.

Since the ions are accelerated by the ion sheath on the cathode 12, etching due to a physical effect occurs.

There is little undercut because the ions have directionality.

Since a reactive gas is used, the selection ratio with respect to the mask and the substrate is large as compared with the sputter etching using an inert gas.

The etching mechanism of dry etching is basically divided into three types: physical reaction, chemical reaction, and physical / chemical composite reaction. In the case of reactive ion etching,
Etching proceeds due to the chemical compound reaction.

The invention is based on the discovery that reactive ion etching of RuO ₂ with CF ₄ is possible.

Reference numeral 15 is a sample stage, 16 is an insulator, 17 is a high frequency power source, 18 is a gas supply system, and 19 is an exhaust system.

The results of measuring the CF ₄ flow rate dependence of the etching rate under the following conditions are shown in FIG. Flow rate: 10-40 sccm, pressure: 0.0
8torr, high frequency power: 250W, electrode temperature: 20 ℃, electrode interval: 70m
m. The etching rate increases with an increase in the CF ₄ flow rate, indicating that the gas supply is rate-controlled. The pressure in the reaction chamber 11 is constant, and if it is merely sputter etching, the gas supply rate control should not be performed.
This is thought to be due to the formation of volatile products due to the chemical reaction, and indicates that reactive ion etching is occurring instead of etching simply due to the sputtering effect. Next, FIG. 3 shows the results of comparing the etching rates of RuO ₂ thin films of CF ₄ and Ar at a flow rate of 10 sccm. The conditions other than the flow rate are the same as in the case of FIG. The etching rate is higher when CF ₄ is used as shown in FIG.
The product species in the ^{_{plasma, F *, CF 3 *,}} F -, CF X + (x
= 1-3) is present (* indicates activation). Of these, CF _X ^* (x = 1- contributes to the sputtering effect.
3) only, and the sputtering rate of CF _X ^{+ (x = 1-3)} for Si is in the low ion energy range (1000 eV or less).
It is reported that the sputtering rate is lower than that of Ar ^{+ due} to the deposition of C or CF _x . Since the ion energy of the etching according to the present invention is several hundred eV, this means
Deposition of C, F, CF _X, etc. does not occur, and C,
It is considered to indicate that volatile products related to F, Ru, and O are formed. RuC _X F as a volatile product of Ru
_Y O _Z , RuC _X F _Y , RuF _X, etc. are conceivable, but in the case of SiO ₂ etc., the volatile products of Si containing C do not exist, and most of the C contained in CF _X is SiO ₂ It has been confirmed that it reacts with the O inside to form CO _X. Therefore, O of RuO ₂ and CF _X
It is highly probable that Ru undergoes a similar reaction, and the volatile product of Ru is likely to be RuF _X. Among the known fluorides, RuF ₅ has a melting point of 85.6 ° C, boiling point of 227 ° C, and RuF ₆ has a melting point of 5
It is a relatively low substance among the compounds of 0.4 ° C and Ru, and is a substance that easily vaporizes.

Similarly, even if CF ₄ was used, RuO ₂ was not etched by the barrel type plasma etching apparatus as shown in FIG. In the case of the barrel-type reaction chamber 42, the object 41 to be etched is placed in glow discharge and is substantially separated from the ground, and the surface potential of the object 41 to be etched is about 10 V with the potential of the glow around it. There is no difference. In the case of reactive ion etching, since the potential gradient of the ion sheath is several 100V, RuO ₂ mainly has a kinetic energy of several 100eV.
It is considered to be etched by F _X ⁺ (X = 1-3). This indicates that RuO ₂ can be etched by CF ₄ not only with a parallel plate type reactive ion etching apparatus but also with an ion beam type plasma etching apparatus.

In addition, since reactive ion etching also causes etching due to the sputtering effect, even if an additive is added to RuO ₂ , if it is in a small amount, it can be etched with only CF ₄ plasma. Binary oxide Ru-Zr-O, Ru-Al-O, Ru-
When Ca-O and Ru-Ba-O were etched under the same conditions as in Fig. 3, the composition ratio of elements other than O to Ru was found to be
If it was 10 at% or less, there was no significant difference from the etching rate of RuO ₂ . 43 is a sample stage, 44 is an electrode, 45 is a high frequency power source, 46 is a gas supply system, and 47 is an exhaust system.

 Hereinafter, specific examples will be described.

Example 1 A 500 Å RuO ₂ thin film was formed on a shelf silicate glass substrate (7059 manufactured by Corning Co., Ltd.) by RF sputtering with a RuO ₂ sintered body as a target, and a positive resist (OFPR manufactured by Tokyo Ohka Co., Ltd.) was formed thereon.
Pattern width of 20μ by applying photolithography process
A mask with m and a pitch of 5 μm was formed. CF ₄ flow rate 30 sccm, pressure 0.0 by the reactive ion etching device.
When etching was performed under the conditions of 8 torr, high frequency power of 250 W, and etching time of 5 min, the accuracy of the obtained pattern width was 18 ± 0.5 μm. Further, on the same substrate, the composition ratio of elements other than O to Ru is 10 at% or less, Ru-Zr-O, Ru
-Al-O, Ru-Ca-O, Ru-Ba-O thin film was formed by RF sputtering using a mixture target of 500 Å and patterned by the same method. The precision was 18.0 ± 0.5 μm, and reactive ion etching has a feature of less undercut as described above. Therefore, a fine pattern can be obtained with high precision as described above. Can be said to be extremely useful for miniaturizing ruthenium oxide thin film resistor patterns for hybrid ICs, thermal heads, sensors, etc.

(Example 2) A so-called glaze alumina substrate 53 in which a glass glaze layer 52 is formed on an alumina substrate 51 as shown in FIG.
The RuO ₂ thin film heating resistor 54 of 500 Å is formed on the above by the same method as in Example 1, and the conductor film 55 for wiring made of Au is sequentially laminated on this, and a positive resist (OFPR made by Tokyo Ohka) is formed on the entire surface. To form a positive resist film 56. Next, a positive resist mask 57 was formed by a photolithography process, and the wiring conductor film 55 was removed by etching to obtain a wiring pattern 58 as shown in FIG. 5B. Further, using this positive resist mask 57 as a mask, CF ₄ flow rate 30 sccm, pressure 0.08 torr, high frequency power 250 W, etching time is performed by the reactive ion etching apparatus under the conditions of 5 min,
Thereafter, the positive resist mask 57 was removed to obtain a thin film heating resistor pattern 59 as shown in FIG. 5c. The amount of undercut for the positive resist mask 57 was 0.5 μm or less, which was almost negligible. Next, unnecessary portions of the wiring pattern 58 were removed by a photolithography process to form a wear resistant protective film made of SiC. The structure is shown in FIG. 61 is an alumina substrate, 62 is a glass glaze layer, 63a and 63b are wiring conductor films, 64 is a thin film heating resistor, and 65 is a wear-resistant protective film. For the sake of convenience of description, it is shown that the abrasion resistant film 65 is not partially formed. The thin-film heat generating resistors 64 are arranged at a density of 8 lines / mm, and the variation in the resistance value is within ± 1%. When a thin film type thermal head having the same structure is formed by wet etching using TiC / SiO ₂ for the resistor film 64, the resistance value variation is within ± 10%, and the pattern according to the present invention is used by using a ruthenium oxide based thin film resistor. The thermal head created by the training method is far superior.

In addition, both were subjected to continuous pulse application with a pulse width of 1 msec and a pulse period of 10 msec, and the durability was compared. By comparing the electric power per unit area (W / mm ² ) (→ breaking power) of a thin film resistor that gives a resistance variation of 10 per set when 6 * 10 ⁴ pulses are applied, it was created by the patterning method of the present invention. thermal head 70 W / mm ^2, the conventional improved significantly with 40W / mm ^2. Moreover, when a Ru-Zr-O thin film in which the composition ratio of Zr to Ru was 10 at% instead of RuO ₂ was formed on a 500 Å glazed alumina substrate and a thermal head was created by the same method, the resistance variation was ± Within 1%, the breaking power was 68 W / mm ² , which was almost the same performance. It is considered that this is because the thermal head according to the present invention uses an oxide resistor and thus has excellent environmental stability such as oxidation resistance.

As described above, by forming the fine pattern of the ruthenium oxide thin film resistor which could not be prepared by the conventional method by the etching method according to the present invention, the thermal head having the characteristics superior to the conventional one can be prepared.

Although the thin film is formed by RF sputtering in this embodiment, it is needless to say that it is also effective for the thin film formed by reactive vapor deposition or thermal decomposition of organic metal.

EFFECTS OF THE INVENTION The present invention relates to a method of etching a ruthenium oxide-based thin film, which has not been heretofore known, whereby a fine pattern of a ruthenium oxide-based thin film can be obtained with high accuracy, and industrial effects are great. .

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a reactive ion etching device,
Figure 2 shows the relationship between etching time and etching amount as CF ₄ and A
Comparison of r, Fig. 3 shows CF ₄ flow rate dependence of etching rate, Fig. 4 is a schematic diagram of barrel type plasma etching device, and Fig. 5 is patterning of thin film heating resistor of thermal head. FIG. 6 is a schematic view showing the steps, and FIG. 6 is a perspective view showing the structure of the thin film thermal head. 51 …… Alumina substrate, 52 …… Glass glaze layer, 53 ……
Glazing alumina substrate, 54 ... Thin film heating resistor, 55 ...
… Wiring conductor film, 56 …… Positive resist film, 57 …… Positive resist mask, 58 …… Wiring pattern, 59 …… Thin film heating resistor pattern.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H05K 3/08 H01L 21/302 F B41J 3/20 111A 111H (56) Reference JP-A-57- 167602 (JP, A) JP 59-61160 (JP, A) JP 61-96704 (JP, A) JP 51-42317 (JP, B1)

Claims (2)

(57) [Claims] 1. A RuO ₂ thin film or a ruthenium oxide thin film in which the composition ratio of elements other than O to Ru is 10 at% or less
_{4. A} method for etching a ruthenium oxide-based thin film, characterized in that reactive ion etching is performed using ₄ . 2. A ruthenium oxide-based thin film composed of Ru and one or more elements selected from Zr, Al, Ca, and Ba.
2. The method for etching a ruthenium oxide-based thin film according to claim 1, wherein a composition ratio of elements other than Ru to 10 at% or less is etched.