Etching apparatus and etching method

According to one embodiment, an etching apparatus includes a stage in an etching chamber, the stage which holds one of a first substrate and a second substrate, a plasma generator in the etching chamber, the plasma generator which is opposite to the stage and irradiates an ion beam toward the stage, a grid which is provided between the plasma generator and the stage, a supporter supporting the stage, the supporter having a rotational axis in a direction in which the ion beam is irradiated, a controller which is configured to mount the first substrate on the stage and irradiate the ion beam with the beam angle larger than 0° to the first substrate, when an elapsed time from an end of an etching of a predetermined layer in the second substrate is equal to or larger than a predetermined time.

FIELD

Embodiments described herein relate generally to an etching apparatus and an etching method.

BACKGROUND

Various types of devices having magnetic layers have recently been developed. A magnetic memory STT (Spin Transfer Torque)-MRAM (magnetic random access memory) as one of those devices stores data in a magnetic layer.

In the devices, the magnetic layer is patterned by physical etching, such as ion beam etching (IBE). Thus, development of an etching apparatus for performing such physical etching is indispensable for the development of new devices having magnetic layers.

In physical etching, however, an etched magnetic and/or metal material may be re-deposited in an etching chamber. Such a re-deposited material in the etching chamber may serve as a source of dust or abnormal discharge, which shortens the maintenance cycle of the etching device. Namely, the re-deposit may cause reduction of the maintenance lifetime.

DETAILED DESCRIPTION

In general, according to one embodiment, an etching chamber; a stage in the etching chamber, the stage which holds one of a first substrate and a second substrate; a plasma generator in the etching chamber, the plasma generator which is opposite to the stage and irradiates an ion beam toward the stage; a grid which is provided between the plasma generator and the stage; a supporter supporting the stage, the supporter having a rotational axis in a direction in which the ion beam is irradiated; a first driver changing a beam angle between a direction which is perpendicular to an upper surface of the stage and the direction in which the ion beam is irradiated; a second driver which is rotated the stage on the rotational axis; and a controller which is configured to: mount the first substrate on the stage and irradiate the ion beam with the beam angle larger than 0° to the first substrate, when an elapsed time from an end of an etching of a predetermined layer in the second substrate is equal to or larger than a predetermined time.

FIG. 1shows an outline of an etching apparatus according to the embodiment.

An etching chamber1is a physical etching chamber for patterning an etching layer in a wafer2by, for example, IBE. The wafer2is a substrate on which a magnetic memory (such as an MRAM) is formed. Stage3ais located in the etching chamber1to place thereon the wafer2including an etching layer. Stage3ais supported by a support portion (a supporter)3b.

The orientation perpendicular to the upper surface of stage3a(or the upper surface of the wafer2) can be angled by θ with respect to the application direction of an ion beam. Namely, the angle θ between the orientation perpendicular to the upper surface of stage3aand the application direction of the ion beam can be varied. The angle θ corresponds to a beam angle and can be varied within a predetermined angle range.

In the embodiment, stage3awith a beam angle θ of 0° is indicated by the solid line, and stage3awith a beam angle θ of 45° is indicated by the broken lines.

Further, support portion3bhas rotation axis AS rotatable about point O. Rotatable axis AS is parallel to the application direction of the ion beam when the angle θ is 0°. Support portion3brotates along with stage3ainclined by, for example, the angle θ. Stage3aand support portion3bserve to rotate the wafer2during ion beam application. By this rotation, wafer in-plane uniformity (σ) in the etching rate of the wafer2can be enhanced.

A plasma generating portion (a plasma generator)4is provided in the etching chamber1. The plasma generating portion4is opposed to stage3aand is used to generate ions providing an ion beam. The plasma generating portion4is made separate from the stage2by means of a grid5.

The grid5comprises first, second and third electrodes5a,5band5c, as shown inFIG. 2. For instance, by applying plus voltage V1and minus voltage V2and ground voltage V3to first, second and third electrodes5a,5band5c, respectively, ions generated by the plasma generating portion4are guided toward the wafer2via the grid5, whereby an ion beam is generated. The ion beam contains Ne, Ar, Kr, Xe, N2or O2, for example.

A shutter6is openable and closable, and is interposed between stage3aand the grid5. The shutter6is in the open state during etching, and is in the closed state at the other times so that no ion beams are applied to the wafer2.

A plasma power supply window10is an element for permitting an electromagnetic wave (energy) from an antenna11to be guided to the plasma generating portion4to thereby cause the same to generate plasma. The antenna11is in the shape of a ring and is extended around the etching chamber1.

A first drive portion (a first driver)7ais used to rotate stage3aabout the point O to change the orientation of stage3aand adjust the beam angle θ. Further, a second drive portion (a second driver)7bis used to rotate stage3aabout rotation axis AS (support portion3b).

Wafer supplying portion8asequentially supplies wafers2before etching (i.e., wafers waiting for processing) onto stage3ain the etching chamber1. Wafer storing portion8bsequentially stores wafers2after etching (i.e., already processed wafers) fed out of stage3aof the etching chamber1.

Dummy supplying/storing portion8csupplies a dummy (wafer) onto stage3ain the etching chamber1at the start of a warm-up operation, and recovers the dummy from stage3aof the etching chamber1at the end of the warm-up operation.

For instance, during the warm-up operation, the control portion9controls the beam angle θ using first drive portion7aand controls the rotation direction and rotational speed of stage3ausing second drive portion7b, so that a magnetic material or a metal material flying apart from the dummy during etching is prevented from being re-deposited on an important element, such as the grid5, in the etching chamber1.

The warm-up operation will now be described.

The warm-up operation means a tentative operation for stabilizing the state of the etching apparatus. Namely, by performing a warm-up operation (etching the dummy) under predetermined conditions, an ion beam current, for example, applied to wafer products during etching can be set to the same value, whereby variation in the etching rate among the wafer products can be suppressed.

For instance, if no warm-up operation is performed, a difference may occur in warpage due to, for example, thermal expansion of the grid5between the etching operation of a first wafer and the etching operation of each of second et seq. wafers, with the result that the etching rate of the magnetic layer may differ between the etching operation of the first wafer and the etching operation of each of the second et seq. wafers, and hence stability or uniformity of the etching rate of the magnetic layer cannot be secured.

For the above reason, a warm-up operation is performed under the predetermined conditions before starting the etching operation.

However, if during the warm-up operation, a magnetic material or a metal material flying apart from the dummy is re-deposited on an important element, such as the grid5, in the etching chamber1, the period in which the etching apparatus can be continuously operated without maintenance is reduced. This inevitably involves increase in COC (cost of consumable).

For instance, during the warm-up operation, if the ion beam angle is set to 0°, a much greater amount of re-deposit is deposited on the grid5than in the case where the ion beam angle is set to a value exceeding 0°. The re-deposit deposited on the grid5may cause abnormal discharge, for example, between first, second and third electrodes5a,5band5cshown inFIG. 2.

If such a state often occurs, a maintenance, for example, replacing the grid5having the re-deposit with a new or cleaned grid5becomes necessary. Namely, as described above, if re-deposition easily occurs on the grid5, the maintenance cycle is shortened, and accordingly COC is increased.

In view of the above, the embodiment proposes a technique of suppressing, during the warm-up operation, re-deposition of a magnetic and/or metal material, flying apart from a dummy by etching, on an important element, such as the grid5, in the etching chamber1, thereby elongating the maintenance cycle of the etching apparatus and reducing the COC.

More specifically, in the embodiment, during the warm-up operation, the ion beam angle θ is set to a value exceeding 0°. When the ion beam angle θ is 0°, a material flying apart from the wafer2by etching is directly guided onto an important element, such as the grid5. If the ion beam angle θ is set to a value exceeding 0°, i.e., if the ion beam is obliquely applied to stage3a, the amount of the material guided to an important element, such as the grid5, can be reduced.

FIG. 3shows a first example associated with the ion beam direction and the discharge direction of the material flying apart from the wafer by etching.

This example shows conditions for enabling the material flying apart from the wafer2to be little deposited on the entire grid5.

Assuming that the distance between the upper surface of the wafer2and the grid5is L1, and that the distance between the center of the grid5and an end of the grid5is D1, the beam angle (incident angle or reflection angle) θ is set to X1° or more. For instance, the beam angle θ at the time of the warm-up operation is set to X1° or more. As a result, the material flying apart from the wafer2is mainly deposited on anti-deposition parts (shield member) provided on the inner wall of the etching chamber1, and is not easily deposited on the grid5.

Assume here that X1={tan−1(D1/L1)}/2, and that the ion beam angle (incident angle) X1 is equal to reflection angle X1 of the material flying apart from the wafer by etching with respect to the normal line NL perpendicular to the upper surface of the wafer2. Assume also that the grid5is, for example, circular, and D1 is the radius of the grid5.

FIG. 4shows a second example associated with the ion beam direction and the discharge direction of the material flying apart from the wafer by etching.

This example shows conditions for enabling the material flying apart from the wafer2to be little deposited on the plasma power supplying window10.

The plasma power supply window10is an element for permitting an electromagnetic wave (energy) from the antenna11to be guided to the plasma generating portion4to thereby cause the same to generate plasma. Accordingly, the plasma power supply window10is formed of a transparent material capable of easily transmitting therethrough the electromagnetic wave from the antenna11.

If the material flying apart from the wafer is re-deposited on the plasma power supplying window10, an electromagnetic wave from the antenna11cannot efficiently be transmitted to the plasma generating portion4, and therefore the re-deposition must be reduced.

In consideration of the above, the ion beam angle (incident angle or reflection angle) θ is set.

Assuming that the distance, parallel to rotation axis AS, between the upper surface of the wafer2and the plasma power supplying window10is L2, and that the distance between rotation axis SA and the plasma power supplying window10is D2, the ion beam angle θ is set equal to X2° or more.

For instance, the beam angle θ at the time of the warm-up operation is set to X2° or more. In this case, the material flying apart from the wafer and deposited on the plasma power supplying window10is less than in the case where the beam angle θ at the time of the warm-up operation is set to 0°. As a result, the maintenance lifetime can be increased.

Assume, however, that X2={tan−1(D2/L2)}/2, and that ion beam angle (incident angle) X2 is equal to reflection angle X2 of the re-deposit with respect to the normal line NL perpendicular to the upper surface of the wafer2.

FIG. 5shows a third example associated with the ion beam direction and the discharge direction of the material flying apart from the wafer by etching.

This example shows conditions for enabling the material flying apart from the wafer2to be little deposited on the effective area of the grid5.

The effective area of the grid5means an area through which the ion beam applied to the wafer2passes. For instance, if the wafer2and the grid5are both circular, and if they are coaxial with the rotation axis AS, the size D3 of the effective area of the grid5corresponds to the radius of the wafer2.

Assuming that the distance between the upper surface of the wafer2and the grid5is L3, and that the size of the effective area of the grid5is D3, the ion beam angle θ is set to X3° or more. For instance, the beam angle θ is set to X3° or more during the warm-up operation. This enables the material flying apart from the wafer2to be little deposited on the effective area of the entire grid5. Assume also that the grid5is, for example, circular, and D3 is the radius of the effective area of the grid5.

2. Operation of Etching Apparatus

The operation of the etching apparatus shown inFIGS. 1 to 5will be described.

FIG. 6shows an operation example of the etching apparatus.

This operation is controlled by the control portion9shown inFIG. 1.

Firstly, it is determined whether a warm-up operation should be performed before starting the etching operation (step ST11).

For instance, it is determined whether an elapsed time Te after a preceding etching operation is equal to or more than a predetermined period Twarm-up required for the warm-up operation. If Te Twarm-up, it is determined that the etching apparatus is in a cold state, and hence a warm-up operation is performed. In contrast, if Te<Twarm-up, it is determined that the etching apparatus is in a steady state, and hence an etching operation is performed without performing the warm-up operation.

However, if it is determined for each wafer (i.e., whenever an etching operation is performed) whether the warm-up operation should be performed, the control of, for example, the control portion9becomes complex.

In view of this, it is assumed, for example, that a plurality of wafers (e.g., 25 wafers) belonging to one lot will be continuously processed, and for the etching operations of the wafers belonging to the one lot, the determination as to whether the warm-up operation should be performed may be carried out only one time, i.e., only before the etching of the leading wafer.

Further, the maintenance work (such as exchange of the grid and anti-deposition parts (shield member)) of the etching apparatus generally requires one hour or more. Therefore, the warm-up operation may be always performed after the maintenance work of the etching apparatus.

After starting the warm-up operation, the start of the etching operation is postponed until the warm-up operation finishes (steps ST12and ST13).

The warm-up operation is executed in accordance with, for example, the flowchart ofFIG. 7.

Firstly, a dummy (wafer) is placed on the stage in the etching chamber (step ST21).

Subsequently, an ion beam of a beam angle (incident angle) θetch is applied to the dummy, thereby performing warm-up etching for a predetermined period (step ST22). The beam angle θwarm-up in this etching operation is determined in consideration of the relationship between the direction of the ion beam and the discharge direction of material during etching, shown in, for example,FIGS. 3 to 5.

After the warm-up operation, the dummy is removed from the etching chamber (steps ST23and ST24).

When Te<Twarm-up or the warm-up operation has finished, an etching operation is started.

Firstly, a wafer (product wafer) is placed onto the stage in the etching chamber (step ST14).

Subsequently, an ion beam of a beam angle (incident angle) θwarm-up is applied to the wafer to etch the etching layer (e.g., a magnetoresistive effect element) (step ST15).

After the etching operation, the wafer is removed from the etching chamber (steps ST16and ST17).

3. Magnetic Memory

A description will be given of an example of a magnetic memory that can be produced by the above-described etching apparatus and method.

FIGS. 8 to 10show an MRAM memory cell to which the etching apparatus and method are applied.FIG. 8is a plan view showing memory cells of an MRAM.FIG. 9is a cross-sectional view taken along line IX-IX ofFIG. 8.FIG. 10is a cross-sectional view taken along line X-X ofFIG. 8.

In this example, the memory cells of the magnetic memory each comprise a selective transistor (e.g., a FET) ST and a magnetoresistive effect element MTJ.

The selective transistor ST is located in the active area AA of a semiconductor substrate21. The active area AA is surrounded by an element isolating layer22in the semiconductor substrate21. In the embodiment, the element isolating layer22has a Shallow Trench Isolation (STI) structure.

The selective transistor ST comprises source/drain diffusion layers23aand23bin the semiconductor substrate21, and a gate insulating layer24and a gate electrode (word line)25formed in the semiconductor substrate21between source/drain diffusion layers23aand23b. The selective transistor ST of the embodiment has a so-called embedded gate structure in which the gate electrode25is embedded in the semiconductor substrate21.

An interlayer insulation layer (e.g., an oxide silicon layer)26covers the selective transistor ST. Contact plugs BEC and SC are provided in the interlayer insulation layer26. Each contact plug BEC is connected to corresponding source/drain diffusion layer23a, and each contact plug SC is connected to corresponding source/drain diffusion layer23b. The contact plugs BEC and SC contain, for example, W, Ta, Ru or Ti.

Magnetoresistive effect elements MTJ are provided on the respective contact plugs BEC, contact plugs TEC are provided on the respective magnetoresistive effect elements MTJ.

Bit lines BL1are connected to the respective magnetoresistive effect elements MTJ via the respective contact plugs TEC. Bit lines BL2are connected to respective source/drain diffusion layers23bvia the respective contact plugs SC. Bit lines BL2also function as source lines SL, to which a ground potential is applied, during, for example, reading.

FIG. 11shows an example of the magnetoresistive effect element MTJ shown inFIGS. 8 to 10.

InFIG. 11, elements similar to those shown inFIGS. 8 to 10are denoted by corresponding reference numbers.

Each magnetoresistive effect element MTJ comprises a first ferromagnetic layer31on the corresponding contact plug BEC, a nonmagnetic insulating layer (tunnel barrier layer)32on the first ferromagnetic layer31, a second ferromagnetic layer33on the nonmagnetic insulating layer32, and a hard mask layer13on the second ferromagnetic layer33.

The hard mask layer13functions as a mask layer used to process, for example, the magnetoresistive effect element MTJ. The hard mask layer13contains, for example, W, Ta, Ru, Ti, TaN, TiN, etc. It is desirable that the hard mask layer13comprise stacked layers of materials, such as Ta and Ru, that have a low electrical resistance and high diffusion, etching and milling resistances.

One of the first and second ferromagnetic layers31and33is a reference layer having invariable magnetization, and the other is a storage layer having variable magnetization.

“Invariable magnetization” means that the direction of magnetization does not change before and after writing, while “variable magnetization” means that the direction of magnetization is inverted before and after writing.

Further, “writing” means spin transfer writing in which spin torque is applied to the magnetization of the storage layer by applying a spin injection current (spin polarized electrons) to the magnetoresistive effect element MTJ.

If the first ferromagnetic layer31is a storage layer, and the second ferromagnetic layer33is a reference layer, the magnetoresistive effect element MTJ is called a top-pin type. In contrast, if the first ferromagnetic layer31is a reference layer, and the second ferromagnetic layer33is a storage layer, the magnetoresistive effect element MTJ is called a bottom-pin type.

It is desirable that each of the first and second ferromagnetic layers31and33have perpendicular magnetization, i.e., residual magnetization parallel to an axis along which the first and second ferromagnetic layers31and33are stacked. However, each of the first and second ferromagnetic layers31and33may have in-plane magnetization, i.e., residual magnetization perpendicular to the axis along which the first and second ferromagnetic layers31and33are stacked.

The resistance of the magnetoresistive effect element MTJ varies, as a result of the magnetoresistive effect, depending upon the relative magnetization direction of the storage and reference layers. For instance, the resistance of the magnetoresistive effect element MTJ is low in a parallel state wherein the storage and reference layers have the same magnetization direction, while the resistance is high in an anti-parallel state wherein the storage and reference layers have opposite magnetization directions.

The first and second ferromagnetic layers31and33each comprise, for example, CoFeB, MgFeO, or a stacked structure of these materials. In the case of a magnetoresistive effect element having perpendicular magnetization, it is desirable that the first and second ferromagnetic layers31and33each comprise, for example, TbCoFe having perpendicular magnetic anisotropy, an artificial grating formed by stacking Co and Pt layers, or FePt regulated by L1o. In this case, an interface layer of CoFeB may be interposed between the first ferromagnetic layer31and the nonmagnetic insulating layer32or between the nonmagnetic insulating layer32and the second ferromagnetic layer33.

The first and second ferromagnetic layers31and33may each comprise a shift cancel layer. The shift cancel layer has magnetization of a direction opposite to the magnetization direction of the reference layer. In this case, the shift cancel layer cancels shift of the magnetization inversion characteristic (hysteresis curve) of the storage layer due to the stray magnetic field of the reference layer. It is desirable that the shift cancel layer comprise, for example, a structure [Co/Pt]n in which n layers each comprising Co and Pt films are stacked on each other.

As described above, the embodiment can increase the maintenance cycle of the etching apparatus and reduce the COC.