JPH03104101A - Conductive oxide thin film and etching thereof - Google Patents

Abstract

PURPOSE:To enable a fine pattern to be formed with high precision by etching process by a method wherein the title conductive oxide thin film is formed of one or multiple elements selected out of specific elements and Ru, Re, Rh as well as O. CONSTITUTION:The title conductive oxide thin film is composed of one or a multiple of elements selected out of Ti, Si, Mo, W, Pt as well as one or a multiple of elements selected out of Ru, Re, Rh and O. On the other hand, a fine pattern can be formed by plasma etching the conductive oxide thin film formed of the said elements using a gas especially having F in the composition thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a conductive oxide thin film used in various electronic devices such as chip resistors, hybrid ICs, and sensors, and a method for etching the same.

Conventional technology Precious metals (e.g. Ru, Rh, Re) are used in various electronic devices.
) Oxide-based resistors are widely used in hybrid ICs, thermal heads, chip resistors, sensors, etc. These noble metal oxide resistors are generally Ru02, Rh0
2. It is a thick film resistor made by mixing an inorganic powder mainly consisting of a conductive oxide such as Re05 with glass frit, resin, and an organic solvent and printing and baking the paste. .

Since these are produced 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 produce fine patterns with high precision. In addition, these are dispersed thick films using an inorganic binder, and their resistance characteristics vary widely compared to thin films.
Poor heat dissipation and power resistance.

Problems to be Solved by the Invention Since thin film resistors are generally manufactured using a vacuum device,
In order to form a pattern, it is necessary that the thin film resistor can be etched. As with thick films, there are methods of printing, baking, or printing to obtain thin films, but the precision and reproducibility of the putter is only comparable to that of thick films. Etching can be broadly divided into wet etching and dry etching. There are two methods: wet etching and etching using a chemical solution in a bath. Further, dry etching is a method of etching using neutral gas, gas phase ions, radical μ, etc. Among these, a method of etching by turning gas into plasma is called plasma etching.

Thin film resistors have better properties as resistors than thick films, but rhodium oxide and rhenium oxide are insoluble in acids and there is no suitable etchant, so rhodium oxide thin film resistors and rhenium oxide thin film resistors are used. had the disadvantage that it was not possible to create a pattern by wet etching.

Furthermore, there have been no reports of dry etching related to these, and no method has been known for creating fine patterns of rhodium oxide thin films and rhenium oxide thin films with high precision.

Therefore, rhodium oxide-based thin films and rhenium oxide-based thin films are not used in trenches, although they have excellent characteristics such as good environmental stability and ease of controlling resistance values.

Therefore, an object of the present invention is to provide a method for patterning these noble metal oxide thin films, and to create fine patterns of noble metal oxide thin films with excellent properties.

Means for Solving the Problems In order to solve the above problems, the present invention plasma-etches a rhodium oxide thin film or a rhenium oxide thin film using a gas having at least F in its structure to form a pattern. be.

Function: By using the above etching method, a fine pattern of rhodium oxide-based IT or rhenium oxide-based thin film can be created.

Example Examples of the present invention will be described below.

That is, the present invention is characterized in that rhodium oxide thin films and rhenium oxide thin films are plasma etched using a gas having at least F in its structure.

Various apparatuses are used for plasma etching, but in the present invention, as shown in FIG. A reactive ion etching apparatus (high frequency power frequency 13-66M) with a structure in which a material 13 is placed is used.

Reactive ion etching has the following characteristics.

■ Ions are accelerated by the ion sheath on the cathode, resulting in physical etching.

■ There is less undercutting because the ions have directionality.

(2) Since a reactive gas is used, the etching rate is faster and the selectivity is better than 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 combined reaction. In the case of reactive ion etching, etching progresses through a complex physical and chemical reaction.

The present invention is a rhodium oxide thin film (Rho2) using CF4.
The present invention is based on the discovery that active ion etching of rhenium oxide thin film (Re05) is possible.

Button 16 is the sample stage, 16 is the insulator, 1T is the high frequency power supply,
18 is a gas supply system, and 19 is an exhaust system.

FIG. 2 shows the results of measuring the OF4 flow rate dependence of the etching rate under the following conditions. Flow rate = 10-4 0 Boo
m, pressure: 0,08 Torr, high frequency power = 2
s o W s Electrode temperature: 20'C, electrode spacing = 70
In both cases of the H0 rhodium oxide thin film and the rhenium oxide thin film, the etching rate increases as the F4 flow rate increases, indicating that the gas supply is rate-limiting. The pressure inside the reaction chamber 11 is constant, and if it is just sputter etching, it should not be the rate limiting factor for gas supply. This is thought to be due to the formation of volatile products due to chemical reactions, and indicates that active ion etching is occurring rather than etching simply due to the spatter effect. Next, FIG. 3 shows the results of comparing the etching rates of OF4 and ▲r for a rhodium oxide thin film and a rhenium oxide thin film at a flow rate of 10 BOOm. Conditions other than flow rate are the same as in FIG. 2. In either case, the etching rate is higher when CF4 is used as shown in FIG. The species generated in the plasma are F'', OF
3, F−, OFX” (X=1-3) exists (the umbrella is not activated). Of these, only OFx”OC=1-3) contributes to the sputtering effect, and OF ! ”
Regarding the sputtering rate for Si (X = 1-3), in the region of low ion energy (100067 or less), C
Alternatively, it has been reported that the sputtering rate is lower than that of ▲r+ due to the deposition of CFx. Since the energy of the ions in the etching according to the present invention is several hundreds of eV, this means that no deposition of C, F, OFx, etc. occurs, and volatile products related to C, F, R, O due to chemical reactions on the surface. This is thought to indicate that (R is Rllj
or Re). RCzFyOz, RCzFy, RFz, etc. can be considered as volatile products of H, but in the case of SiO2, etc., there is no volatile product of Si containing 1 C, and the C contained in CFx is Most are S
It has been confirmed that it reacts with O in iOz to form COx. Therefore, it is quite possible that 0 of ROx and OFx are undergoing a similar reaction, and it is highly likely that the volatile product of H is RFx.

There are known fluorides with relatively low boiling points and melting points as shown in Table 1.

(Margin below) As shown in FIGS. 2 and 3, the etching rate of rhenium oxide is considerably higher, but this is thought to reflect the difference in boiling point.

Similarly, even when CF4 was used, ROxki etching was not performed using a Balenore type plasma etching apparatus as shown in FIG. In the case of the barrel p type reaction chamber 42, the object to be etched 41 is buttoned during glow discharge and is substantially disconnected from the ground, and the surface potential of the object to be etched 41 is equal to the potential of the surrounding glow. There is only a difference of about 10v. In the case of reactive ion etching, the potential gradient of the ion sheath is several hundreds of volts, so it takes several tens of volts for a chemical reaction to occur.
CFz” (x=1
It is believed that an ion bombardment effect of -31 is required. This shows that it is possible to etch ROx with CF4 not only in a parallel plate type active ion etching apparatus but also in an ion beam type plasma etching apparatus.

However, in reactive ion etching, etching due to the Supanota effect also occurs, so even if an additive is added to ROx, if it is a small amount, etching can be achieved with AY4 plasma alone.

Specific examples will be described below.

(Example 1) Rh
SO by RF sputtering using O2 sintered body as a target.
A Rho2 thin film was formed and a positive resist (
OFPR-2) manufactured by Tokyo Ohka Co., Ltd. was applied and a mask with a pattern width of 20 Is and a pitch of 5 μm was formed by a photolithography process. The reactive ion etching apparatus was used at a CF4 flow rate of 30 scans and a pressure of O. ○B Tor
When etching was performed under the conditions of r, high frequency power of 250 W, and etching time of 5 hours, the accuracy of the obtained pattern width was 19±0.5 μm. Re on the same board as the housing.
When patterning an R605 thin film using RF Nupatta using a sintered target of No. 05 in a 100 OA type or a similar method, the accuracy of the pattern width obtained was 19. It was 0 + 0.5 μm. As mentioned above, reactive ion etching has the characteristic of having less undercuts, so it is possible to obtain fine-in patterns with high precision. It can be said that this method is extremely useful for miniaturizing noble metal oxide-based thin film patterns used in

(Example 2) Ruthenium oxide is a noble metal oxide that exhibits conductivity similar to rhodium oxide and rhenium oxide. Thenium oxide is also used as an electrode or resistor in hybrid ICs, thermal heads, sensors, etc. Wet etching of norethenium oxide is difficult, as is rhodium oxide and rhenium oxide. However, plasma etching using OF4 similar to the present invention is effective, and in this case, Ru, Rθ
, Ti, S which contains fluorides with low boiling points like Rh
It has been found that i, Mo, w, pt are suitable as additives for adjusting the resistance. Therefore, it can also be used as an additive for adjusting the resistance value to rhodium oxide and rhenium oxide.

Figure 5 shows the resistivity of Ru, Rh, Rθ and TCR (
The dependence of the temperature coefficient of resistance on Ti concentration is shown. TCR was calculated from the resistance value at room temperature (20'C) and 126°C. In either case, TCR was initially positive, but decreased in proportion to the Ti concentration and became negative. This is because the noble metal oxide serving as the base material has a metallic conduction mechanism and exhibits a positive TCR. In addition, the resistivity is Re-Ti-0 system (Ru-Ti
-0 series (Rh-Ti) The -0 series is the highest in order, but this is thought to reflect the difference in resistivity of the base noble metal oxides shown in Table 2. is the value of bap (from Shokabo, Electrically Conductive Oxide),
If the film is made thinner, it will be larger than this.

Table 2 (Unit: Ω・CIM) Resistors used in electronic circuits such as chip resistors have a small temperature change in resistance value (TCR is 0), as well as resistance accuracy.
) is required.

As shown in FIG. 6, the Re-Ti-0 system shows a TCR of less than 0.0. 46 ~0. 98
mΩ・α, 0.54 for Ru-Ti-0 system
~1,02mΩ・z, Rh-Ti-0 series 10.8~2
It becomes 4.4 mΩ-3. And for intermediate values, R
e -Rh-Ti 10 series or Ru-Rh-Ti-0
By adjusting the combination of Ru, Rh, and Re as a system, the resistivity is +50pp in the range of 0.46 to 24.4 mΩ-3.
A resistor within m/°c can be obtained. In particular, Ru
-Rh-Ti-10 series is Ru02, Rh02, Ti02
Since it has a type IV crystal structure, it is easy to control. 1.Resistivity becomes constant when the film thickness is 300 or more, so if the film is made with a film thickness of 300 to 6000, the TOR will be within the sheet resistance range of 9.2Q/0 to 8.1kΩ/O. Resistors within ±60 ppm/(: can be manufactured.

Specifically, Ru 60Ti aoOx (group p
at%) and TCR are 0. 84 mΩ・Resistivity and TCR of -30ppm/゜Cs Rh6oTi4oOx (at%) are 15.2 mΩ-cm
, +3oppm/”C, so RuxR
By making a film with the set h 6o x Ti 4o0y (set or at%) and changing X from O to 601, the resistivity was ±5 in the range of 0.84 to 15.2 mΩ.
It is possible to make a resistor of 0 ppm/'C or less. For example, RuO2h on a 3 inch diameter Ti02 target
and Rh02 pellets (diameter 10mm, thickness 2mm) were placed so that the area ratio was 4:4:2, and a film was coated with a film thickness of 1000mm by RF sputtering, resulting in a resistivity of 4.5mΩ・α ( Sheet resistance value 450Ω/mouth), TCR
A thin film resistor of +11 ppm/'C was obtained.

A positive resist (TOKYO OHKA OFPR) is applied on this thin film resistor.
-2) was applied to the entire surface, and a mask with a pattern width of 20 μm and a pitch of 5 μm was formed by a 7-otolithography process. CF4 flow rate by reactive ion etching equipment:
Etching was performed at 30 scans, pressure: 0.08 Torr, high frequency power: 260 W, and etching time: 10 -, and the accuracy of the pattern width was 19±0.5 μm.

We then fabricated a 9R'-Si-0 thin film (
(R' represents any one of Re, Rh, Ru), the TCR is proportional to the Si concentration.
changes from positive to negative, resistivity and TCR can be adjusted in a similar manner.

The etching method of the present invention is also effective for this resistive film! not.

As described above, TCR can be adjusted by utilizing the difference in resistivity of noble metal oxides that have a metallic conduction mechanism. In addition, fine patterns can be created with high accuracy by active ion etching of the thin film resistor according to the present invention.

In this example, the thin film was formed by RF sputtering, but it is also effective for thin films formed by reactive vapor deposition or thermal decomposition of organic metals!
not.

Effects of the Invention According to the present invention, fine patterns can be obtained with high accuracy by etching even rhodium oxide thin films or rhenium oxide thin films, which were hitherto unknown.

[Brief explanation of drawings]

Figure 1: Schematic diagram of beam active ion etching equipment.
Figure 2 is a diagram showing the OF4 flow rate dependence of etching rate, Figures 3a and b are diagrams comparing the relationship between etching time and etching amount for CF4 and ▲r, and Figure 3a and b are diagrams comparing the relationship between etching time and etching amount for CF4 and ▲r. Figure 4 is a schematic diagram of a Balenore type plasma etching device, Figure 5 a N
0 is a diagram showing the resistivity buttons of Ru, Rh, and Re and the dependence of TCR (temperature coefficient of resistance) on Ti concentration. 11... Reaction chamber, 13... Object to be etched.

Claims (4)

[Claims] (1) A conductive oxide consisting of one or more elements selected from Ti, Si, Mo, W, and Pt, one or more elements selected from Ru, Re, and Rh, and O. Thin film. (2) A method for etching a conductive oxide thin film, comprising plasma etching the rhodium oxide thin film using a gas having at least F in its structure. (3) A method for etching a conductive oxide thin film, comprising plasma etching the rhenium oxide thin film using a gas having at least F in its structure. (4) At least an oxide thin film consisting of one or more elements selected from Ti, Si, Mo, W, and pt, one or more elements selected from Ru, Re, and Rh, and O. A method for etching a conductive oxide thin film, characterized by plasma etching using a gas having F in its structure.