Ion beam etching method of magnetic film and ion beam etching apparatus

To restrict generation of particles or deterioration in process reproducibility caused by a large amount or carbon polymers generated in a plasma generation portion in an ion beam etching apparatus when a magnetic film on a substrate is etched with reactive ion beam etching in manufacturing a magnetic device. In an ion beam etching apparatus, first carbon-containing gas is introduced by a first gas introduction part into a plasma generation portion, and second carbon-containing gas is additionally introduced by a second gas introduction part into a substrate processing space to perform reactive ion beam etching, thereby etching a magnetic material at preferable selection ratio and etching rate while restricting carbon polymers from being formed in the plasma generation portion.

TECHNICAL FIELD

The present invention relates to an ion beam etching method used for etching a magnetic film formed on a substrate and an ion beam etching apparatus used for the method in manufacturing a magnetic device.

BACKGROUND ART

MRAM (Magnetic Random Access Memory) is a non-volatile memory utilizing a magnetoresistive effect such as TMR (Tunneling Magneto Resistive), has as high an integration density as DRAM (Dynamic Random Access Memory) and as much a high-speed performance as SRAM (Static Random Access Memory), and is paid global attention as a revolutionary next-generation memory capable of rewriting data unlimitedly.

An etching technique is typically employed for processing a magnetoresistive effect element contained in MRAM. There is proposed a reactive ion beam etching method using carbon-containing gas such as hydrocarbon in order to efficiently etch a magnetic material such as Co or Fe as an etching material hard to etch in etching a magnetic film of the magnetoresistive effect element (Patent Literature 1).

PRIOR ART REFERENCE

Patent Literature

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

In the ion beam etching method, however, when carbon-containing gas is used as process gas as described in Patent Literature 1, a large amount of carbon polymers is generated in a plasma generation portion. The large amount of carbon polymers causes a problem such as generation of particles or deterioration in process reproducibility.

The present invention has been made in terms of the problem, and it is an object thereof to provide an ion beam etching method capable of reducing generation of carbon polymers in the plasma generation portion and selectively etching a magnetic film, and an ion beam etching apparatus used for the method.

Means for Solving the Problem

A gist of the present invention is to introduce carbon-containing gas into not only a plasma generation portion but also a substrate processing space in ion beam etching of a magnetic film by use of carbon-containing gas.

That is, in order to solve the above problem, an ion beam etching method of a magnetic film according to the present invention includes steps of:

introducing first carbon-containing gas from a first gas introduction part to generate plasma in an ion beam etching apparatus;

extracting ions from the plasma to form an ion beam; and

etching a magnetic film formed on a substrate by the ion beam,

wherein second carbon-containing gas is introduced into a processing space in which the substrate is placed from a second gas introduction part different from the first gas introduction part during the etching.

In order to solve the above problem, an ion beam etching apparatus according to the present invention includes:

a plasma generation portion;

a first gas introduction part for introducing gas into the plasma generation portion:

a grid for extracting ions from the plasma generation portion; and

a processing space in which a substrate is placed,

wherein a second gas introduction part for introducing gas into the processing space is provided, and

the grid is made of titanium or titanium carbide or its surface is coated with Ti or titanium carbide.

In order to solve the above problem, an ion beam etching apparatus according to the present invention includes:

a plasma generation portion;

a first gas introduction part for introducing first carbon-containing gas into the plasma generation portion;

a grid for extracting ions from the plasma generation portion; and

a processing space in which a substrate is placed,

wherein a second gas introduction part for introducing second carbon-containing gas into the processing space is provided.

EFFECTS OF THE INVENTION

According to the present invention, it is possible to selectively etch a magnetic film while restricting generation of particles or deterioration in process reproducibility in ion beam etching of a magnetic film of magnetic devices by reducing generation of carbon polymers in an ion beam etching apparatus.

MODE FOR CARRYING OUT THE INVENTION

First Embodiment

Embodiments according to the present invention will be described below with reference to the drawings, but the present invention is not limited to the embodiments, and can be changed as needed without departing from its spirit. The same reference numerals are denoted to members having same function in the drawings described later, and a repeated description thereof may be omitted.

FIG. 1is a schematic diagram of one embodiment of an ion beam etching apparatus according to the present invention. An ion beam etching apparatus100is composed of a processing space101and a plasma generation portion102. The processing space101is provided with an exhaust pump103. The plasma generation portion102is provided with a discharge vessel104, a first gas introduction part105, a RF antenna106, a matching unit107, and an electromagnetic coil108, and a grid109is provided on a boundary with the processing space101. The plasma generation portion102is formed by the grid109, inner walls of the ion beam etching apparatus100, and the discharge vessel104.

The grid109is composed of a plurality of electrodes. According to the present invention, the grid109consists of three electrodes, for example. First electrode115, second electrode116and third electrode117are present in this order from the discharge vessel104side. A positive voltage is applied to the first electrode and a negative voltage is applied to the second elect rode so that ions are accelerated due to a difference of their potentials. The third electrode117is also called earth electrode, and is grounded. A difference in potentials between the second electrode116and the third electrode117is controlled, thereby controlling a diameter of an ion beam within a predetermined numerical range by use of an electrostatic lens effect. The ion beam is neutralized by a neutralizer113.

The grid109is preferably made of a material having a resistance to process gas used for the present invention, namely, carbon-containing gas. Molybdenum, titanium or titanium carbide having such a property may be employed. Thus, the grid109itself is made of any of molybdenum, titanium or titanium carbide or the surface of the grid109is coated with molybdenum, titanium or titanium carbide so that at least the surface of the grid109is preferably made of any of molybdenum, titanium or titanium carbide.

The processing space101has a substrate holder110therein, and a substrate111is placed on an electrostatic chuck (ESC) electrode112. Gas is introduced from the first gas introduction part105and a high frequency is applied to the RF antenna106, thereby generating gas plasma inside the plasma generation portion102. The first gas introduction part105is connected with a pipe (not illustrated), a valve, a flow controller and the like from a tank storing process gas therein (not illustrated), and gas at a predetermined flow rate is introduced into the plasma generation portion102through them. A DC voltage is applied to the grid109, and ions inside the plasma generation portion102are extracted as a beam to be irradiated on the substrate111, so that the substrate111is processed. The extracted ion beam is electrically neutralized by the neutralizer113to be irradiated on the substrate111. The processing space101is provided with a second gas introduction part114, through which process gas can be introduced. The substrate holder110can be arbitrarily tilted toward an ion beam. The substrate111can rotate in the in-plane direction.

A magnetic film of magnetic devices is etched with the ion beam etching method according to the present invention by use of the apparatus illustrated inFIG. 1.FIGS. 2A and 2Bschematically illustrate steps of etching a magnetic film of a magnetoresistive effect element with the ion beam etching method.

As illustrated inFIGS. 2A and 2B, a lamination structure with the magnetoresistive effect element according to the present embodiment is such that an underlying layer23as a lower electrode is formed on a substrate24made of silicon or glass, for example. A multilayer film22having a magnetoresistive effect element is formed on the underlying layer23. A cap layer21as an upper electrode is formed on the multilayer film22.FIGS. 2A and 2Billustrate the states of the cap layer21subjected to a patterning process by use of photoresist or the like. A layer above the cap layer21is selected as needed by an etching method or an object to be etched.

The underlying layer23is processed to a lower electrode in a later step, and thus a conductive material is used therefor. Ta, Ti, Ru or the like may be used as the underlying layer23.

A multilayer film according to the present embodiment has a basic structure in the magnetoresistive effect element. The basic structure comprises a pair of ferromagnetic layer and non-magnetic intermediate layer, and causes a magnetoresistive effect.

The magnetoresistive effect element having the multilayer film22is such that an anti-ferromagnetic layer224(PtMn), a magnetization fixed layer223(CoFoB), a barrier layer222(MgO), and a free layer221(CoFeB) are sequentially stacked from below.

The cap layer21is used as a hard mask for etching the multilayer film22. The cap layer21according to the present embodiment is used as an upper electrode after the multilayer film22is processed, but the upper electrode layer may be provided separately from the hard mask. A monolayer film or a laminated film of Ta, Ti, or a conductive compound thereof such as TaN, TiN, TaC or TiC may be used as the cap layer21.

In particular, Ta and its compounds are preferable in terms of selection ratio to the multilayer film22during ion beam etching.

The multilayer film22is etched by use of the ion beam etching method according to the present invention in processing from the state inFIG. 2Ato the state inFIG. 2B. Operations of the ion beam etching apparatus at this time will be described with reference toFIG. 1.

At first, first carbon-containing gas is introduced from the first gas introduction part105into the discharge vessel104. As the first carbon-containing gas, carbon monoxide, carbon dioxide, hydrocarbon or alcohol may be used. Gas having less carbons such as methane, ethane, ethylene or acetylene is suitable as hydrocarbon, and lower alcohol such as methanol or ethanol is suitable as alcohol. In particular, alkane such as methane or ethane, or alcohol is more suitable since carbon polymers are less generated. Mixed gas thereof may be used. The first carbon-containing gas may be added with an inert gas such as argon, krypton, xenon or nitrogen, hydrogen, carbon, oxygen, or the like other than the first carbon-containing gas.

The first carbon-containing gas is introduced into the discharge vessel104to generate plasma. A voltage is applied to the grid and ions are extracted from the plasma thereby to form an ion beam.

At this time, the amount of the first carbon-containing gas to be introduced is selected in consideration of an exchange frequency of the discharge vessel104due to carbon polymers formed inside the discharge vessel104.

On the other hand, second carbon-containing gas is introduced also from the second gas introduction part114provided in the processing space101. The second gas introduction part114is connected with a pipe (not illustrated), a valve, a flow controller, and the like from a tank storing process gas therein (not illustrated), and gas at a predetermined flow rate is introduced into the processing space101through them. Carbon monoxide, carbon dioxide, hydrocarbon, or alcohol may be used as the second carbon-containing gas. Gas having less carbons such as methane, ethane, ethylene or acetylene is suitable as hydrocarbon, and lower alcohol such as methanol or ethanol is suitable as alcohol. Mixed gas thereof may be used.

The second carbon-containing gas may be added with an inert gas such as argon, krypton or nitrogen, carbon, oxygen, or the like other than the second carbon-containing gas. The first carbon-containing gas may be the same as the second carbon-containing gas. In this case, an atmosphere inside the ion beam etching apparatus can be made uniform, thereby increasing stability of the process. The same gas supply source (tank) may be used.

The second carbon-containing gas may be introduced after the first gas is introduced and discharged in the plasma generation portion102to form an ion beam, or the second carbon-containing gas may be previously introduced into the processing space.

According to the present invention, carbon-containing gas is introduced also into the processing space101thereby to promote a reaction between a substrate to be processed and the carbon-containing gas even when the amount of carbon-containing gas to be introduced into the plasma generation portion is reduced. The second carbon-containing gas does not pass through the plasma generation portion102when it is supplied to the substrate111. Consequently, it is possible to process a magnetic film at preferable selection ratio and etching rate while restricting carbon polymers generated in the plasma generation portion. At this time, an electron gun or electron source separate from the neutralizer113for neutralizing ion beams is used to introduce electrons or energy into the second carbon-containing gas, thereby enhancing a reactivity.

Alternatively, the substrate111is heated by a heater, thereby enhancing a reactivity between the second carbon-containing gas and the reactive ion beam.

Second Embodiment

A second embodiment will be described with reference toFIG. 3.

The present embodiment is different from the first embodiment in the shape of the second gas introduction part114in the ion beam etching apparatus100. As illustrated inFIG. 3, the second gas introduction part114according to the present embodiment has a circular injection part, and is configured to inject gas uniformly from the surroundings of a substrate. The substrate surface can be more uniformly processed with such a form.

Third Embodiment

A third embodiment will be described with reference toFIG. 4toFIG. 6. As illustrated inFIG. 4, an ion gun119is provided inside the processing space101according to the present embodiment. The ion gun119is connected with the second gas introduction part114, and gas at a predetermined flow rate can be introduced into the ion gun119.

FIG. 5is a diagram illustrating an exemplary ion gun119according to the present invention.

InFIG. 5, 301denotes an anode,302denotes a cathode and303denotes an insulator for insulating the anode301from the cathode302. The cathode302is cylindrical, is opened at one end to be opposed to the anode301, and is closed at the other end. The cathode302has a hollow part307for forming plasma therein. A cross-section shape of the hollow part of the cathode302is typically circular, but may be regular octagonal or regular hexagonal as far as a space capable of forming plasma therein is present. The anode301and the cathode302are connected to a power supply306for applying a predetermined voltage respectively304denotes a gas introduction path for introducing discharging gas into a neutralizer, and gas is introduced by the second gas introduction pare114into the ion gun119.

The second gas introduction part114may be configured such that gas is directly introduced into the processing space101and diffused to be supplied to a discharging part of the ion gun119, but the substrate111can be processed without lowering a degree of vacuum in the processing space101when gas is directly introduced into the ion gun119.

Further, the ion guns119are symmetrically arranged about the center axis of the substrate111in the processing space101so that the substrate111can be more uniformly etched.

Gas is introduced into the ion gun119and a negative voltage is applied to the cathode302so that plasma is formed in the hollow part307. Further, a positive voltage is applied to the anode301so that negative ions are extracted from the opening of the anode301.

Mixed gas of inert gas and carbon-containing gas is preferable as gas to be introduced into the ion gun119in order to restrict a film from being deposited in the ion gun119.

There will be assumed a case in which mixed gas of Ar and methane is introduced into the ion gun119by way of example. In this case, plasma is formed near the cathode302and various negative ions such as CH3−and CH22−are generated from the plasma. Then, the negative ions are accelerated due to a potential difference between the cathode302and the anode301, and are extracted from the opening of the anode301.

As gas to be introduced into the ion gun119, carbon monoxide, carbon dioxide, hydrocarbon, or alcohol may be used as in other embodiments.

Titanium is used as the anode301and the cathode302in consideration of heat resistance or anti-spattering property, for example. The material may be changed in consideration of a reactivity with gas to be introduced into the ion gun119.

The ion gun119may employ other form, not limited to the above structure. For example, the anode301and the cathode302may be inversely configured to extract positive ions. Plasma may be formed by use of any other than hollow type electrode.

The substrate holder110can be tilted at an arbitrary angle toward the grid109. The amount of ions to be irradiated on the substrate111from the ion gun119changes due to a position of the ion gun119and a tilt angle of the substrate111. The amount of irradiated ions also changes at each point in the substrate111.

In this viewpoint, as illustrated inFIG. 6, a placement table121is provided on the substrate holder110and the ion gun119is provided on the placement table121to integrate the substrate holder110and the ion gun119so that even when a tilt angle of the substrate111changes, a change of the amount of irradiated ions from the ion gun119can be reduced.

Even if the substrate holder110and the ion gun119are not integrated, the ion gun119is provided around the rotation axis when a tilt angle of the substrate holder110is changed, so that also when a tilt angle of the substrate111changes, a change of the amount of irradiated ions from the ion gun119can be reduced.

Alternatively, when the ion gun119is placed on the substrate holder110to be tilted integral with the substrate111, the amount of irradiated ions can be constant irrespective of the tilt angle of the substrate111. At this time, a spacer may be provided as needed between the substrate holder110and the ion gun119in order to optimize an angle at which ions are irradiated onto the substrate111.

Fourth Embodiment

As illustrated inFIG. 7, a third gas introduction part120may be provided in addition to the second gas introduction part114and the ion gun119to introduce third carbon-containing gas. With the structure, even when the amount of second carbon-containing gas to be introduced into the ion gun119from the second gas introduction part114is reduced, a reduction in reactivity can be restricted. The amount of carbon-containing gas to be introduced into the ion gun119can be reduced, and thus the substrate111can be processed while the amount of carbon polymers to be formed in the ion gun119is reduced.

Carbon monoxide, carbon dioxide, hydrocarbon, or alcohol is used as the third carbon-containing gas. Gas having less carbons such as methane, ethane, ethylene or acetylene is suitable as hydrocarbon, and lower alcohol such as methanol or ethanol is suitable as alcohol. In particular, alkane such as methane or ethane, or alcohol is more suitable since carbon polymers are less generated. Mixed gas thereof may be employed. The third carbon-containing gas may be added with an inert gas such as argon, krypton, xenon or nitrogen, hydrogen, carbon, oxygen, or the like other than the third carbon-containing gas.

As described above, according to the present invention, the second carbon-containing gas is introduced also into the processing space101in addition to the first carbon-containing gas to be introduced into the discharge vessel104. Thus, also when the amount of carbon-containing gas to be introduced into the discharge vessel104is reduced, the multilayer film22can be selectively etched with respect to the cap layer21, and generation of carbon polymers in the discharge vessel104can be reduced.

Etching a magnetic film of a magnetoresistive effect element has been described according to the above embodiments, but the present invention is effective also in etching a magnetic film of other magnetic device. A specific example is to etch a magnetic film for forming a write part of a magnetic head or to etch a magnetic film for manufacturing a magnetic recording medium such as DTM (Discrete Track Media) and BPM (Bit Patterned Media).

EXPLANATION OF REFERENCE NUMERALS