JPH08253881A - Dry etching method - Google Patents

Abstract

PURPOSE: To facilitate reactive ion etching for a magnetic material by using carbon monoxide gas, in which a nitrogen-containing compound gas is added, as a reactive gas to etch the surface of a metal or alloy. CONSTITUTION: At the time of etching the surface of the metal or alloy, carbon monoxide gas, in which the nitrogen-containing compound gas is added, is used as the reactive gas. A magnetic metal or magnetic alloy is etched by using the carbon monoxide gas, in which ammonia or an amine gas is further added. Any method using AC high voltage, high frequency wave or microwave can be used as a means for generating the plasma of the reactive gas only if it is a means for generating glow discharge plasma under a reduced pressure. Fine machining for the magnetic alloy is realized by the method. And even the production of a quantum effect ceramic element, which will be practical in future, is enabled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method. More specifically, the present invention is
Fabrication of thin film inductive magnetic heads, micro inductors, micro transformers, thin film magnetoresistive heads, micro magnetic elements and micro magnetic circuits such as thin film permanent magnets, spin scattering magnetoresistive effect elements, spin valve elements, ferromagnetic tunnel junction elements , Spin field effect device,
The present invention relates to a dry etching method useful for fine processing in the production of quantum effect magnetic elements such as spin field effect transistors and bipolar spin switches.

[0002]

2. Description of the Related Art Generally, a micro semiconductor element such as a VLSI or a magnetic element is manufactured by combining two processes of a lithography technique and an etching technique.
Lithography technology is a technology to create a fine pattern on a photosensitive film such as a resist film coated on the surface of a material to be processed (semiconductor film or magnetic film). Photolithography technology that uses ultraviolet rays to do this, electronic There are an electron beam lithography technique that uses an ion beam and an ion beam lithography technique that uses an ion beam.

The etching technique is a technique for forming an element by transferring a resist pattern produced by lithography to a target semiconductor thin film, magnetic thin film or the like. As the latter etching method, a wet etching technique is generally used in which only a workpiece is selectively dissolved in a resist using an acid or alkaline aqueous solution. However, the wet etching method has a problem that since the workpiece is isotropically dissolved, the shadow portion covered with the resist also wraps around and is corroded, which makes it impossible to form a minute structure. It was difficult. In particular, when processing a polycrystalline material which is a magnetic material, it is difficult to form a fine structure.

Therefore, in order to solve such a problem, a reactive ion etching method using plasma of a low pressure reaction gas has been developed. This reactive ion etching method is a method of chemically and physically stripping atoms on the surface of a workpiece by ions that are perpendicularly incident on the surface of the workpiece in plasma. It is possible. Therefore, since the erosion does not go around to the shadow portion covered with the resist, which is a problem of the wet etching method, fine processing is possible. Furthermore, the reactive ion etching method is superior to the wet etching method in that it requires less chemical adhesion between the resist mask and the workpiece and has less problems with pinholes in the resist mask.

Therefore, the reactive ion etching method has become one of the basic techniques of silicon technology since the mid-1970s and has made great progress in the microfabrication process of various semiconductor devices, particularly silicon VLSI. Dynamic Random Access Memory (DRA
Speaking of M), 16kbit DRAM of 5 μm rule
From the time. In addition, this technique has been applied to compound semiconductors such as gallium arsenide and gallium phosphide, and has recently reached the range of practical application.

However, in spite of the progress of such reactive ion etching technology in the semiconductor field, it has been difficult to apply the reactive ion etching having the above-mentioned characteristics in the field of magnetic materials. Therefore, magnetic bubble memory, Bloch line memory, thin film magnetic head, thin film magnetic sensor, magnetic head slider,
In the manufacturing process of Cu thin wires for conductors, coils, and the like, in addition to the wet etching method described above, for example, the argon ion etching method shown in FIG. 4 has been used.

According to this argon ion etching method, in a device in which a thermoelectron gun (3) and a movable work piece stage (4) are installed in a reaction vessel (2) equipped with a vacuum pump (1), a vacuum is used. Argon gas (5) introduced into the reaction vessel (2) evacuated by the pump (1)
Is excited by the thermionic gun (3) and becomes an argon ion source (6). Then, due to the potential difference applied to the extraction electrode (7), an argon ion beam (8) is formed, and the work piece (9) on the movable work piece stage (4) is formed.
It has a structure that is irradiated to.

However, the wet etching method has a limit in miniaturization as described above, and the argon ion etching method is a method of physically scraping a workpiece by using the sputtering action of argon ions. Since it has no effect, it has no selectivity, and since the etching rate is about several nm / min, it takes a long time to process a depth of several μm, resulting in low efficiency.

The reason why it is difficult to apply the reactive ion etching method in the case of a magnetic material is as follows. That is, in reactive ion etching, ions, radicals, which are chemically active species of the reaction gas generated in plasma,
Neutral species are adsorbed on the surface of the material to be processed and chemically react with the surface of the material to be processed to form a reaction layer having low binding energy. Therefore, the surface of the work piece is exposed to the vertical impact of positive ions in the plasma. For this reason, the surface reaction layer with loose binding energy is likely to be physically peeled off (due to the sputtering action). As described above, the reactive ion etching is a process in which a chemical action and a physical action occur at the same time, so that the selectivity by the substance is obtained and the workpiece is cut perpendicularly to its surface. You can get the direction.

The binding energy of the surface reaction layer depends on the material
It has almost the same physical meaning as vapor pressure, and is shaped by plasma.
Whether the surface reaction layer substance formed is easily evaporated in vacuum
And whether reactive ion etching works
To be judged. However, transition metal elements (for example, Fe,
Ni) a magnetic material whose main component is (for example, permalloy)
Is CF used in reactive ion etching_Four, CC
l_FourThe same plasma as semiconductor materials can be
Rogen compounds (eg FeCl₂, FeCl ₃, Ni
Cl₂) Are formed, but these transition metal halogenations
Compound is SiCl _Four, GaCl₃Halogen of semiconductor elements such as
Binding energy is much higher than that of
Therefore, it is hard to evaporate and is less susceptible to spattering,
The problem is that the reaction stops there.

Then, as a solution to this problem,
Temperature-programmed ion etching method by K. Kinoshita et al.
oshita, K. Yamada and H. Matutera. IEEE Trans. Mag
n., 27 (1981), 4888.) has been proposed, and in addition to a general plus chemical reaction system using CCl ₄ plasma, the workpiece is irradiated with infrared rays from a halogen lamp to It is characterized by heating to 270 to 370 ° C. It is a method of thermally evaporating the transition metal halide by this heating.

However, in this method, the heating temperature is
Beyond the heat resistance limit of polymer compound resist masks
Therefore, the glass (S
iO ₂) And alumina (Al₂O₃), Etc. with good heat resistance
It is necessary to use the material as a mask material.
There is a point. In addition, this method is based on Sendust alloy (Fe-S
i-Al alloy), but other magnetic materials,
Pure Fe, Permalloy (Fe-Ni alloy), and Cu
The disadvantage is that a high etching speed cannot be obtained
was there.

On the other hand, efforts have been made to establish a new reaction system for the reactive ion etching method for magnetic materials. Methods using plasma of carbon monoxide (CO) gas have been studied by, for example, MJ Vasile and J. Mogab. (MJ Vasile and J. Mogab, J. Vac. Sci.
Technol. A4 (1986), 1841.). In this method, the transition metal carbonyl compound (Fe (CO) ₅ , Ni (CO) ₄ , C on the surface of the transition metal of the workpiece is generated by the active radicals of CO.
O ₂ (CO) ₅ etc. is generated, and the principle is to strip it off by an evaporation action or a sputtering action in a vacuum and etch it. The transition metal carbonyl compound is the only compound having a small binding energy among the transition metal compounds. However, this method has an extremely low etching rate, and this series of studies was not successful.

The present invention has been made in view of the above circumstances, and solves the problems of the prior art and enables reactive ion etching for a magnetic material containing a transition metal element as a main component. The aim is to provide a new way of doing things.

[0015]

In order to solve the above problems, the present invention is characterized in that a surface of a metal or alloy is etched by using carbon monoxide gas added with a nitrogen-containing compound gas as a reaction gas. An etching method is provided. The present invention also provides, as an aspect of the above method, a dry etching method characterized by using ammonia or an amine gas as a reaction gas, and further performing surface etching of a magnetic metal or a magnetic alloy. .

[0016]

In other words, the present invention has conducted intensive studies on the cause of the fact that the expected chemical reaction does not proceed in the plasma in the method using the carbon monoxide gas plasma, and based on the findings obtained as a result, It has been completed. That is, the CO molecule is decomposed into a CO ₂ molecule composed of a zero-valent carbon simple substance and a tetravalent carbon ion in the plasma by the heterogeneous reaction of the following formula, and the introduced CO molecule produces a transition metal carbonyl. There is a problem of not contributing.

[0017]

Embedded image

Therefore, the inventor of the present invention has made this heterogeneous reaction
Molecules to prevent or delay
I considered adding it to Zuma. More specifically, NH
₃Gas, organic amine gas, H₂S gas, SO₂Gas, S
Steam, SF_FourGas, H₂S gas, H₂Gas, HCl gas
Su, CCl_FourSteam, CH_FourGas, CHCl₃Gas, CH
₂Cl₂Gas, CHCl₃Gas, CF_FourGas, CHF₃
Gas, CH₂F₂Gas, CHF₃Gas etc.
Introduced into the Zuma reaction vessel along with CO gas
Then, use a mass spectrometer to measure the type of molecular species produced.
Was. As a result, especially NH₃And amine gases are above
It was found that it has the effect of suppressing the heterogeneous reaction (1).
Was. In addition, next, it is introduced into the reactive ion etching device
NH₃While changing the mixing ratio of CO gas and other gases,
In doing so, reactive ion etching of permalloy thin film is performed,
The etching rate was measured. For comparison, Si (10
0) Single crystal, aluminoborosilicate glass (Corning 70
59 glass) is also etched under the same conditions
Was.

FIG. 1 summarizes the results. That is, the etching rate for permalloy with CO gas alone is 1.3 nm / min, whereas it increases as the concentration of NH ₃ gas increases to 49 mol% NH 3.
The composition of _3- CO shows the maximum, and the etching speed is about 11
nm / min. Furthermore, as the NH ₃ concentration is increased, the etching rate decreases, and NH ₃ alone is about 4 n
It was m / min. This indicates that coexistence of NH ₃ gas and CO gas in plasma is essentially important from the viewpoint of action and effect. Further, FIG. 2 shows that the reaction gas of the reaction gas having a composition of 49 mol% NH ₃ —CO, which has the most remarkable effect, is supplied to the reactive ion etching reaction vessel while changing the exhaust speed of the vacuum exhaust pump. The results of measuring the etching rate by changing the pressure in the reaction vessel are shown. This figure 2
Shows that the etching rate greatly depends on the pressure of the reaction vessel, and shows a maximum at a pressure of 2.4 × 10 ⁻⁸ Torr.
It was found to be about 35 nm / min. This etching rate is about 8 times faster than the argon ion etching method, which has conventionally been used to etch magnetic materials.
Further, as shown in FIG. 3, the ratio of the etching rate of permalloy to Si and the ratio of the etching rate of permalloy to aluminoborosilicate glass are 4 and 9, respectively. That is, it is understood that the reactive ion etching method of the present invention selectively acts on a magnetic material and has excellent effectiveness on a magnetic material containing a transition metal as a component.

The method of the present invention using a gas such as CO gas and NH ₃ gas, and nitrogen-containing amines is not limited to the above-mentioned permalloy, but a magnetic material containing a transition metal as a component, such as Fe or Ni. , Co, Co-Cr alloys,
The same effect can be obtained for sendust alloys (Fe-Si-Al), Cu, Mo, and alloys and compounds of these various elements. The means for generating plasma of these reaction gases may be any method using direct current high voltage, high frequency, or microwave as long as it is means for generating glow discharge plasma under reduced pressure, and the electrode structure has a capacitance. Any parallel plate electrode, magnetron electrode, inductively coupled electrode, cyclotron resonance plasma, helicon wave plasma, super magnetron electrode, etc. may be used.

Regarding the etching operation, the composition of the target magnetic material is taken into consideration, for example, in consideration of the optimum conditions in the case of permalloy, that is, 49 mol% NH ₃ —CO, 2.4 × 10 ⁻⁸ Torr vacuum degree and the like. , Film thickness, required etching accuracy, etc. Similarly, the temperature condition can be appropriately set.

Hereinafter, the present invention will be described in more detail with reference to examples.

[0023]

EXAMPLES Example 1 Reactive ion etching according to the present invention was performed using 80 permalloy (80% Ni-Fe) as a workpiece. First, the object to be processed was one in which a thin film of about 600 nm of 80 permalloy was formed on a Si single crystal having a (100) plane by a sputtering method, and a part of the surface was covered with a SiO ₂ mask.

As shown in FIG. 3, in the reaction part of the reactive ion etching apparatus, there is an electrode (12) having a capacitive coupling type parallel plate electrode and having an area of 100 cm ² holding a workpiece (11). High frequency of 13.56MHz (13)
Can be applied via a blocking capacitor (14). A grounded counter electrode (15) having a large area was provided on the electrode (11) at a distance of 35 mm.
The electrode (12) holding the work piece was cooled with water (1
6) Then, the temperature of the workpiece (1) was kept at room temperature. on the other hand,
49 mol% NH ₃ —CO mixed gas (17) was added at 9 cc /
While introducing at a minute flow rate, exhaust with a large displacement turbo molecular pump (18), throttle valve (19) at the exhaust port
The degree of vacuum in the reaction vessel to 2.4 × 10 ⁻⁸ To
Hold at rr.

Next, a high frequency of 50 W was applied to generate plasma between the electrodes, and etching treatment was performed for 10 minutes.
The power density was 0.5 W / cm ² . After the reaction is completed, Si
The O ₂ mask was removed, and the step between the portion covered with the mask and the portion not covered with the mask was measured with a Fabry-Perot interferometer, and the shape of the step was observed with a scanning electron microscope.

As a result, it was found that the step difference caused by etching was 347 nm, and the etching rate per unit time was 35 nm / min. Further, the shape of the step was vertically sharp and sharp, no undercut or bulging of burrs was observed, and the finished shape after etching was good. Example 2 Reactive ion etching according to the present invention was performed using a Co-Cr alloy (Co-9.98% Cr) as a workpiece.

The work piece was formed on a Si single crystal wafer having a (100) plane by a vacuum evaporation method to a thickness of about 300 n.
m is a Co-Cr alloy thin film. The pressure in the reaction vessel is approximately the same as in Example 1, is 2.5 × 10 ⁻⁸ Torr, and the reaction time is 5.0 minutes. Other conditions are the same as in Example 1. As described above, the step difference at the boundary between the mask-covered portion and the mask-uncovered portion on the Co—Cr alloy thin film, that is, the boundary between the unetched portion and the etched portion, The steepness of was observed.

As a result, the height of the step was 122 nm, and the etching rate for the Co--Cr alloy was 24.4 n.
It was found to be m / min. Further, the shape of the step was vertical and there was little flash, which was good.

[0029]

As described in detail above, according to the present invention, it is possible to perform reactive ion etching on a magnetic material containing a transition metal element as a main component, which has been difficult in the past, and to realize fine processing of a magnetic alloy. Further, it becomes possible to manufacture a quantum effect magnetic element that will be realized in the future. further,
Since the etching speed is high, the time required for the microfabrication process of the magnetic material can be shortened and the production efficiency can be improved. Furthermore, since there is a property that only the transition metal is selectively etched, the conditions for limiting the mask material are reduced, and the flexibility of the configuration of the microfabrication process is improved.

[Brief description of drawings]

[1] In the reactive ion etching method according to the invention, the reaction gas introduced into the plasma reaction vessel, NH ₃
When the flow rate of the mixed gas of CO and CO is 9 cc / min and the pressure in the reaction tank is constant at 3.6 × 10 ⁻³ Torr, N
FIG. 6 is a relational diagram showing the relation between the etching rate of permalloy and the molar concentration of H ₃ .

In Figure 2 a reactive ion etching method according to the invention, the reaction gas introduced into the plasma reaction vessel, NH ₃
The flow rate of the mixed gas of CO and CO is 9 cc / min, and NH ₃
FIG. 4 is a relationship diagram showing the relationship of the etching rate of permalloy with respect to the pressure in the reaction tank when the molar concentration of is constant at 49 mol%.

FIG. 3 is a schematic diagram showing the configuration of a reactive ion etching apparatus according to an embodiment of the present invention.

FIG. 4 is a schematic diagram showing a configuration of a conventional argon ion etching apparatus.

[Explanation of symbols]

11 the workpiece 12 frequency electrode 13 RF transmitter 14 blocking capacitor 15 counter electrode (ground electrode) 16 cooling water 17 NH ₃ -CO mixed gas 18 turbo-molecular pump 19 throttle valve

Claims (3)

[Claims] 1. A dry etching method, which comprises etching a surface of a metal or an alloy using a carbon monoxide gas added with a nitrogen-containing compound gas as a reaction gas. 2. The dry etching method according to claim 1, wherein the surface etching is performed by using carbon monoxide gas added with ammonia or amines gas as a reaction gas. 3. The dry etching method according to claim 1, wherein the magnetic metal or magnetic alloy is etched.