Etching apparatus and etching method

According to one embodiment, an etching apparatus includes an etching chamber, a stage in the etching chamber, a plasma generator in the etching chamber, the plasma generator being opposite to the stage and irradiating an ion beam toward 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, and a second driver which rotates the stage on the rotational axis.

FIELD

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

BACKGROUND

Recently, various types of devices comprising a magnetic layer have been developed. One of the devices is a magnetic memory. For example, a spin-transfer-torque (STT) magnetic random access memory (MRAM) stores data in a magnetic layer.

These devices have a common problem. When a magnetic layer is patterned, redeposition of a magnetic material is collaterally caused. The redeposition degrades the characteristics of the devices.

DETAILED DESCRIPTION

In general, according to one embodiment, an etching apparatus comprises: an etching chamber; a stage in the etching chamber; a plasma generator in the etching chamber, the plasma generator being opposite to the stage and irradiating an ion beam toward 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 rotates the stage on the rotational axis; and a controller which is configured to: execute a first irradiation which irradiates the ion beam with the beam angle of a first value; and execute a second irradiation which irradiates the ion beam with the beam angle of a second value different from the first value after the first irradiation.

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

An etching chamber1is, for example, a physical etching chamber for patterning an etching layer in a wafer2by IBE. The wafer2is, for example, a substrate in which a magnetic memory (for example, an MRAM) is formed. A stage3ais provided in the etching chamber1and holds the wafer2including the etching layer. The stage3ais supported by a support portion (a supporter)3b.

A direction perpendicular to the upper surface of the stage3a(or the upper surface of the wafer2) can be inclined at only θ with respect to a direction in which an ion beam is irradiated. In other words, the angle θ between the direction perpendicular to the upper surface of the stage3aand the direction in which an ion beam is irradiated can be changed. The angle θ is equivalent to a beam angle, and can be changed within a predetermined angle range.

This example shows the stage3a(solid line) when the beam angle θ is 0°, and the stage3a(broken line) when the beam angle θ is 45°.

The support portion3bcomprises a rotational axis AS based on an O point. When the angle θ is 0°, the rotational axis AS is parallel to the direction in which the ion beam is irradiated. The support portion3brotates with, for example, the stage3ainclined at the angle θ. While the ion beam is irradiated, the stage3aand the support portion3bserve to rotate the wafer2. By this rotation, the wafer in-plane uniformity (σ) of the etching rate of the wafer2can be improved.

A plasma generating portion (a plasma generator)4is provided in the etching chamber1. The plasma generating portion4faces a stage3, and produces an ion which is the base of an ion beam. The plasma generating portion4is separated from the stage2by a grid5.

The ion of the plasma generating portion4is drawn to the wafer2side via the grid5, thereby producing an ion beam. The ion beam includes, for example, one of Ne, Ar, Kr, Xe, N2and O2.

A plasma power supply window8is, for example, an element for producing plasma by delivering an electromagnetic wave (energy) from antenna9to the plasma generating portion4. Antenna9has a ring shape, and surrounds the etching chamber1.

A first drive portion (a first driver)6ais a drive portion for adjusting the beam angle θ by rotating the stage3abased on the O point and changing the orientation of the stage3a. A second drive portion (a second driver)6bis a drive portion for rotating the stage3abased on the rotational axis AS.

A control portion (a controller)7controls the beam angle θ by the first drive portion6aand controls the rotational direction and the rotational speed of the stage3by the second drive portion6b.

For example, the control portion7conducts a first irradiation to irradiate an ion beam having a beam angle θ which is a first value to the etching layer in the wafer2. After the first irradiation, the control portion7conducts a second irradiation to irradiate an ion beam having a beam angle θ which a second value different from the first value to the etching layer in the wafer2. The control portion7repeats the first and second irradiations n times (n is a natural number).

In the first and second irradiations, the rotational direction and the rotational speed of the stage3are preferably constant. However, in the first and second irradiations, the rotational direction and the rotational speed of the stage3may be changed.

FIG. 2shows an example of the operation of the etching apparatus ofFIG. 1.

This operation is controlled by the control portion7ofFIG. 7.

First, the number of etching times n is set (n is a natural number greater than or equal to 2), and beam angles θlow and θhigh are set (steps ST1to ST2).

The beam angle θlow corresponds to the first value of the beam angle θ explained inFIG. 1, and refers to a low angle. The beam angle θhigh corresponds to the second value of the beam angle θ explained inFIG. 1, and refers to a high angle which is higher than the low angle θlow.

Next, the first irradiation of ion beam is conducted. By IBE at a beam angle (low angle) θlow (=θlow_1), the etching layer (for example, a magnetic layer or a metal layer) is etched (step ST3).

In the first irradiation, redeposition of the etching layer is caused together with the etching of the etching layer.

Subsequently, the second irradiation of ion beam is conducted. By IBE at a beam angle (high angle) θhigh (=θhigh_1), the etching layer is etched while the redeposition is reduced (step ST4).

The first and second irradiations are repeated n times (step ST5).

Through the above steps, the patterning of the etching layer in the wafer2shown inFIG. 1is completed.

FIG. 3AandFIG. 3Bshow examples in which a beam angle is changed.

In the examples, to simplify the explanation, θlow and θhigh are set to be constant with respect to each etching time n.

For example, as shown inFIG. 3A, the switching between the first irradiation (step ST3inFIG. 2) and the second irradiation (step ST4inFIG. 2) may be conducted based on a discrete change between the low angle θlow and the high angle θhigh with respect to the etching time. This switching is called a discontinuous switching.

As shown inFIG. 3B, the switching between the first irradiation (step ST3inFIG. 2) and the second irradiation (step ST4inFIG. 2) may be conducted based on a continuous change between the low angle θlow and the high angle θhigh with respect to the etching time. This switching is called a continuous switching.

(1) First Embodiment

FIG. 4toFIG. 6show an etching method according to a first embodiment.

First, as shown inFIG. 4, an etching layer2bhaving a thickness A is formed on a foundation layer2a. On the etching layer2b, a mask layer (for example, a hard mask layer)2cis formed. Each of the foundation layer2aand the mask layer2cmay be a conductive layer or may be an insulating layer. The etching layer2bincludes a conductive layer such as a magnetic layer or a metal layer.

Subsequently, a first time etching is performed.

The first time etching comprises a first irradiation (first low angle IBE) and a second irradiation (first high angle IBE) which is performed after the first irradiation.

The first low angle IBE is conducted mainly for the purpose of patterning the etching layer2b. In the first low angle IBE, the etching layer2bis etched by using an ion beam having a beam angle which is low angle θlow_1. θlow_1is selected from the range of, for example, 0° to 30°. In this example, the ion beam is shown on the assumption that θlow_1=0°.

Since the main purpose of the first low angle IBE is the patterning of the etching layer2b, the beam angle which is low angle θlow_1is adopted.

However, the ion beam having low angle θlow_1produces redeposition2d1of the etching layer2bscattered by the etching on a side wall of the mask layer2c, a side wall of the patterned etching layer2b, etc.

In consideration of the above problem, the first high angle IBE is conducted after the first low angle IBE.

The first high angle IBE is performed mainly for the purpose of patterning the etching layer2bwhile redeposition2d1is removed. In the first high angle IBE, redeposition2d1is eliminated by using an ion beam having a beam angle which is high angle θhigh_1. θhigh_1is selected from the range of, for example, 30° to 89°, or more preferably, 30° to 60°.

In the first high angle IBE, the following matters should be noted when the etching layer2bis a magnetic layer or a metal layer in a magnetic memory (for example, an MRAM).

For example, as shown inFIG. 4, when the width of the space between the mask layers2C is L, and the height of the mask layer2cis d, and the etching amount of the etching layer2bby the first low angle IBE (the distance between the upper surface of the exposed etching layer2band the bottom surface of the mask layer2c) is D1, an acceptable angle α1is given by tan−1(L/(D1+d)). The beam angle (high angle) θhigh_1in the first high angle IBE has to be less than or equal to the acceptable angle α1for the following reason.

When θhigh_1>α1, adjacent mask layers2cserve as walls, thereby leaving a shadow which the ion beam does not reach in the lower edge of the etching layer2b. In this manner, the redeposition in the shadow cannot be removed.

Next, as shown inFIG. 5, a second time etching is performed.

The second time etching comprises, in a manner similar to the first time etching, a first irradiation (second low angle IBE) and a second irradiation (second high angle IBE) which is conducted after the first irradiation.

The second low angle IBE is conducted mainly for the purpose of patterning the etching layer2b. In the second low angle IBE, the etching layer2bis etched by using an ion beam having a beam angle which is low angle θlow_2. θlow_2is selected from the range of, for example, 0° to 30°. In this example, the ion beam is shown on the assumption that θlow_2=0°.

After the second low angle IBE, the second high angle IBE is performed.

The second high angle IBE is performed mainly for the purpose of patterning the etching layer2bwhile redeposition2d2is removed. In the second high angle IBE, redeposition2d2is eliminated by using an ion beam having a beam angle which is high angle θhigh_2. θhigh_2is selected from the range of, for example, 30° to 89°, or more preferably, 30° to 60°.

In the second high angle IBE, in a manner similar to the first high angle IBE, when the width of the space between the mask layers2C is L, and the height of the mask layer2cis d, and the etching amount of the etching layer2bby the second low angle IBE (the distance between the upper surface of the exposed etching layer2band the bottom surface of the mask layer2c) is D2, an acceptable angle α2is given by tan−1(L/(D1+D2+d)). As being clear from this equation, when L is constant, α2<α1. The beam angle (high angle) θhigh_2in the second high angle IBE has to be less than or equal to the acceptable angle α2.

The nthtime etching comprises, in a manner similar to the first time etching, a first irradiation (nthlow angle IBE) and a second irradiation (nthhigh angle IBE) which is conducted after the first irradiation.

The nthlow angle IBE is conducted mainly for the purpose of patterning the etching layer2b. In the nthlow angle IBE, the etching layer2bis etched by using an ion beam having a beam angle which is low angle θlow_n. θlow_n is selected from the range of, for example, 0° to 30°. In this example, the ion beam is shown on the assumption that θlow_n=0°.

The patterning of the etching layer2bis completed by the nthtime etching.

After the nthlow angle IBE, the nthhigh angle IBE is performed.

The nthhigh angle IBE is performed mainly for the purpose of patterning the etching layer2bwhile redeposition2dn is removed. In the nthhigh angle IBE, redeposition2dn is eliminated by using an ion beam having a beam angle which is high angle θhigh_n. θhigh_n is selected from the range of, for example, 30° to 89°, or more preferably, 30° to 60°.

In the nthhigh angle IBE, in a manner similar to the first high angle IBE, when the width of the space between the mask layers2C is L, and the height of the mask layer2cis d, and the etching amount of the etching layer2bby the nthlow angle IBE (the distance between the upper surface of the exposed etching layer2band the bottom surface of the mask layer2c) is Dn, an acceptable angle αn is given by tan−1(L/(D_sum+d)), where D_sum is the distance between the upper surface of the exposed etching layer2band the bottom surface of the mask layer2c, or in other words, the sum (D1+D2+ . . . +Dn) of the etching amount of the etching layer2b. The beam angle (high angle) θhigh_n in the nthhigh angle IBE has to be less than or equal to the acceptable angle αn.

The patterning of the etching layer2bis completed by the nthtime etching. Therefore, D_sum is greater than or equal to the thickness A of the etching layer2b.

The amount of the redeposition which is produced by the combination of the low angle IBE and the high angle IBE in each etching time n in this embodiment is very small compared with the amount of the redeposition which is produced when all of the etching layers are patterned by one-time etching.

Therefore, in each etching time n, the redeposition produced by the low angle IBE can be easily removed by the high angle IBE.

In particular, the larger the ion beam angle is, the more easily the redeposition can be removed. However, the acceptable angle αn in the nthtime etching shown inFIG. 6is less than the acceptable angle α1in the first time etching. For this reason, for example, the removal of redeposition2dn in the nthtime etching is more difficult than the removal of redeposition2d1in the first time etching.

Even in such a case, the whole redeposition2dn can be easily removed by the nthhigh angle IBE since the amount of the redeposition produced by the nthlow angle IBE is small in the nthtime etching in the present embodiment as explained above.

In the first embodiment, it is possible to omit the first irradiation (first low angle IBE) in the first time etching and the second irradiation (nthhigh angle IBE) in the nthtime etching. Even in this case, the amount of redeposition can be reduced by shortening the time of the second irradiation in the nthtime etching.

FIG. 7shows a comparative example of the etching method.

In this example, the whole etching layer2bis patterned by one-time etching. In this case, the amount of redeposition2dproduced by the low angle IBE is very large. The acceptable angle α is the same as the acceptable angle αn shown inFIG. 6. Thus, the beam angle (high angle) θhigh is the same as the beam angle (high angle) θhigh_n shown inFIG. 6.

In this manner, in the low angle IBE, the etching layer2bhas a trapezoidal shape in which the bottom portion is broadened, and the amount of redeposition2dis large. In the high angle IBE, it is difficult to eliminate redeposition2din the bottom portion of the etching layer2b.

(2) Second Embodiment

FIG. 8toFIG. 10show an etching method according to a second embodiment.

Compared to the first embodiment, the second embodiment features the following point: as the etching time n is increased, the thickness of a mask layer2cis gradually reduced.

For example, the etching selection ratio of the etching layer and the mask layer in the second embodiment has to be less than the ratio in the first embodiment. This case has the advantage that the acceptable angles α2, . . . , αn of ion beams in and after the second time etching are larger than the angles in the first embodiment.

First, as shown inFIG. 8, an etching layer2bhaving a thickness A is formed on a foundation layer2a. On the etching layer2b, the mask layer (for example, a hard mask layer)2cis formed.

Subsequently, a first time etching is performed.

The first time etching comprises a first irradiation (first low angle IBE) and a second irradiation (first high angle IBE) which is performed after the first irradiation.

The first low angle IBE is conducted mainly for the purpose of patterning the etching layer2b. In the first low angle IBE, the etching layer2bis etched by using an ion beam having a beam angle which is low angle θlow_1.

In a manner similar to the first embodiment, the first low angle IBE produces redeposition2d1on a side wall of the mask layer2c, a side wall of the patterned etching layer2b, etc.

In consideration of the above problem, the first high angle IBE is conducted after the first low angle IBE.

The first high angle IBE is performed mainly for the purpose of patterning the etching layer2bwhile redeposition2d1is removed. In the first high angle IBE, redeposition2d1is eliminated by using an ion beam having a beam angle which is high angle θhigh_1.

In the first high angle IBE, when the etching layer2bis a magnetic layer or a metal layer in a magnetic memory (for example, an MRAM), an acceptable angle α1is given by tan−1(L/(D1+d1)), where L is the width of the space between the mask layers2C, and d1is the height of the mask layer2c, and D1is the etching amount of the etching layer2bby the first low angle IBE (the distance between the upper surface of the exposed etching layer2band the bottom surface of the mask layer2c).

The beam angle (high angle) θhigh_1in the first high angle IBE has to be less than or equal to the acceptable angle α1.

Next, as shown inFIG. 9, a second time etching is performed.

The second time etching comprises, in a manner similar to the first time etching, a first irradiation (second low angle IBE) and a second irradiation (second high angle IBE) which is conducted after the first irradiation.

The second low angle IBE is conducted mainly for the purpose of patterning the etching layer2b. In the second low angle IBE, the etching layer2bis etched by using an ion beam having a beam angle which is low angle θhigh_2.

After the second low angle IBE, the second high angle IBE is performed.

The second high angle IBE is conducted mainly for the purpose of patterning the etching layer2bwhile redeposition2d2is removed. In the second high angle IBE, redeposition2d2is eliminated by using an ion beam having a beam angle which is high angle θhigh_2.

In the second high angle IBE, in a manner similar to the first high angle IBE, when the etching layer2bis a magnetic layer or a metal layer in a magnetic memory (for example, an MRAM), an acceptable angle α2is given by tan−1(L/(D1+D2+d2)), where L is the width of the space between the mask layers2C, and d2is the height of the mask layer2c. In addition, d2<d1.

The beam angle (high angle) θhigh_2in the first high angle IBE has to be less than or equal to the acceptable angle α2.

The nthtime etching comprises, in a manner similar to the first time etching, a first irradiation (nthlow angle IBE) and a second irradiation (nthhigh angle IBE) which is conducted after the first irradiation.

The nthlow angle IBE is conducted mainly for the purpose of patterning the etching layer2b. In the nthlow angle IBE, the etching layer2bis etched by using an ion beam having a beam angle which is low angle θlow_n.

The patterning of the etching layer2bis completed by the nthtime etching.

After the nthlow angle IBE, the nthhigh angle IBE is performed.

The nthhigh angle IBE is performed mainly for the purpose of patterning the etching layer2bwhile redeposition2dn is removed. In the nthhigh angle IBE, redeposition2dn is eliminated by using an ion beam having a beam angle which is high angle θhigh_n.

In the nthhigh angle IBE, in a manner similar to the first high angle IBE, when the etching layer2bis a magnetic layer or a metal layer in a magnetic memory (for example, an MRAM), an acceptable angle αn is given by tan−1(L/(D_sum+dn)), where L is the width of the space between the mask layers2C, and dn is the height of the mask layer2c, and D_sum is the distance between the upper surface of the exposed etching layer2band the bottom surface of the mask layer2c, or in other words, the sum (D1+D2+ . . . +Dn) of the etching amount of the etching layer2bby the first to nthlow angle IBE. In addition, dn< . . . <d2<d1. The beam angle (high angle) θhigh_n in the first high angle IBE has to be less than or equal to the acceptable angle αn.

The patterning of the etching layer2bis completed by the nthtime etching. Therefore, D_sum is greater than or equal to the thickness A of the etching layer2b.

In a manner similar to the first embodiment, the amount of the redeposition which is produced by the combination of the low angle IBE and the high angle IBE in each etching time n in the present embodiment is very small compared to the amount of the redeposition which is produced when all of the etching layers are patterned by one-time etching.

Therefore, in each etching time n, the redeposition produced by the low angle IBE can be easily removed by the high angle IBE.

In each etching time n, the mask layer2cis etched little by little. Therefore, it is possible to enlarge the acceptable angles α2, . . . , αn of ion beams in and after the second time etching.

In this manner, in each etching time n, the whole redeposition can be easily removed by the high angle IBE.

In the second embodiment, in a manner to similar to the first embodiment, it is possible to omit the first irradiation (first low angle IBE) in the first time etching and the second irradiation (nthhigh angle IBE) in the nthtime etching.

FIG. 11shows a comparative example of the etching method.

In this example, all of the etching layers2bare patterned by one-time etching. In this case, in the low angle IBE, the etching layer2bhas a trapezoidal shape in which the bottom portion is broadened, and the amount of redeposition2dis large. In the high angle IBE, it is difficult to eliminate redeposition2din the bottom portion of the etching layer2b.

This embodiment is related to the relationship between the etching amount in the low angle IBE (first irradiation) and the beam angle (high angle) in the high angle IBE (second irradiation) in each etching time n in the first and second embodiments.

First Example

Beam Angle (Low Angle): No Limitation

This is a basic example. The conditions in each etching time n are set to be identical such that the final pattern to be obtained can be easily predicted.

The beam angle (low angle) is not particularly limited. However, the beam angle is preferably set as θlow_1=θlow_2= . . . =θlow_n.

Second Example

Beam Angle (Low Angle): No Limitation

This example is particularly advantageous to a case where the etching selection ratio of the etching layer and the mask layer is small (the second embodiment). In this case, in each etching time n, the sum (d+D_sum) of the height d (one of d1, d2, . . . , dn) of the mask layer and the sum (D_sum) of the etching amount of the etching layer does not largely change for the following reason: as the number of etching times is advanced, d is gradually reduced, but D_sum is gradually increased.

In consideration of the above factor, in early stages of etching times n, the etching amount in the low angle IBE is set to be large for the purpose of advancing the patterning as fast as possible. In late stages of etching times n, the beam angle (high angle) in the high angle IBE is set to be large for the purpose of surely removing the redeposition.

The beam angle (low angle) is not particularly limited. However, the beam angle is preferably set as θlow_1=θlow_2= . . . =θlow_n.

Third Example

Beam Angle (Low Angle): No Limitation

This example is particularly advantageous to a case where the etching selection ratio of the etching layer and the mask layer is large (the first embodiment). In this case, in late stages of etching times n, the sum (d+D_sum) of the height d of the mask layer (substantially constant) and the sum (D_sum) of the etching amount of the etching layer is large. For this reason, in late stages of etching times n, the beam angle (high angle) in the high angle has to be small.

Therefore, in early stages of etching times n, the etching amount in the low angle IBE is set to be large, and the beam angle (high angle) in the high angle IBE is set to be large, for the purpose of advancing the patterning as fast as possible and surely removing the redeposition. In late stages of etching times n, the etching amount in the low angle IBE is set to be small for the purpose of reducing the production of redeposition.

The beam angle (low angle) is not particularly limited. However, the beam angle is preferably set as θlow_1=θlow_2= . . . =θlow_n.

In the third embodiment, it is possible to omit the first irradiation (first low angle IBE) θlow_1in the first time etching, and the second irradiation (nthhigh angle IBE) θhigh_nin the nthtime etching.

3. Magnetic Memory

This specification explains an example of a magnetic memory which can be manufactured by the above-described etching apparatus or etching method.

FIG. 12toFIG. 14show a memory cell of an MRAM as an application example.FIG. 12is a plan view of the memory cell of the MRAM.FIG. 13is a cross-sectional view taken along line XIII-XIII ofFIG. 12.FIG. 14is a cross-sectional view taken along line XIV-XIV ofFIG. 12.

In this example, the memory cell of the magnetic memory comprises a select transistor (for example, an FET) ST and a magnetoresistive element MTJ.

The select transistor ST is provided in an active area AA in a semiconductor substrate21. The active area AA is surrounded by an element separation insulating layer22in the semiconductor substrate21. In this example, the element separation insulating layer22has a shallow trench isolation (STI) structure.

The select transistor ST comprises source/drain diffusion layers23aand23bin the semiconductor substrate21, a gate insulating layer24and a gate electrode (word line)25. The gate insulating layer24and the gate electrode (word line)25are formed between source/drain diffusion layers23aand23bin the semiconductor substrate21. In this example, the select transistor ST has a buried gate structure in which the gate electrode25is buried in the semiconductor substrate21.

An interlayer insulating layer (for example, a silicon oxide layer)26covers the select transistor ST. Contact plugs BEC and SC are provided in the interlayer insulating layer26. Contact plug BEC is connected to source/drain diffusion layer23a. Contact plug SC is connected to source/drain diffusion layer23b. Contact plugs BEC and SC include, for example, one of W, Ta, Ru and Ti.

The magnetoresistive element MTJ is provided on contact plug BEC. Contact plug TEC is provided on the magnetoresistive element MTJ.

Bit line BL1is connected to the magnetoresistive element MTJ via contact plug TEC. Bit line BL2is connected to source/drain diffusion layer23bvia contact plug SC. Bit line BL2also functions as, for example, a source line SL to which a ground potential is applied at the time of reading.

InFIG. 15, elements identical to those ofFIG. 12toFIG. 14are designated by the same reference numbers.

The magnetoresistive element MTJ comprises shift cancelling layer SCL (11), a first metal layer12on shift cancelling layer SCL (11), a second metal layer13on the first metal layer12, a first magnetic layer14aon the second metal layer13, a nonmagnetic insulating layer (tunnel barrier layer)14bon the first magnetic layer14a, a second magnetic layer14con the nonmagnetic insulating layer14b, a nonmagnetic conductive layer15on the second magnetic layer14c, shift cancelling layer SCL (16) on the nonmagnetic conductive layer15, and a third metal layer17on shift cancelling layer SCL (16).

The third metal layer17functions as, for example, a mask layer (hard mask layer) when the magnetoresistive element MTJ is processed. The third metal layer17includes, for example, W, Ta, Ru, Ti, TaN, Ti or N. The third metal layer17preferably has a material which is low in electric resistance and is excellent in diffusion resistance, etching resistance and milling resistance, such as a lamination of Ta/Ru.

One of the first and second magnetic layers14aand14cis a reference layer having an invariable magnetization, and the other one is a storage layer having a variable magnetization.

Invariable magnetization means that the magnetization direction before and after writing is the same. Variable magnetization means that the magnetization direction before writing may change to the opposite direction after writing.

Writing refers to spin transfer writing which applies spin torque to the magnetization of the storage layer by supplying a spin injection current (spin-polarized electrons) to the magnetoresistive element MTJ.

When the first magnetic layer14ais a storage layer, and the second magnetic layer14cis a reference layer, the magnetoresistive element MTJ is called a top-pin type.FIG. 17AandFIG. 17Bshow magnetization states of the top-pin type magnetoresistive element MTJ. When the first magnetic layer14ais a reference layer, and the second magnetic layer14cis a storage layer, the magnetoresistive element MTJ is called a bottom-pin type.FIG. 18AandFIG. 18Bshow magnetization states of the bottom-pin type magnetoresistive element MTJ.

Each of the first and second magnetic layers14aand14cpreferably has a perpendicular magnetization, or in other words, a remnant magnetization in a perpendicular direction in which the first and second magnetic layers14aand14care stacked.FIG. 17AandFIG. 18Ashow magnetization states of the perpendicular-magnetization type magnetoresistive element MTJ. Each of the first and second magnetic layers14aand14cmay have an in-plane magnetization, or in other words, a remnant magnetization in an in-plane direction perpendicular to the direction in which the first and second magnetic layers14aand14care stacked.FIG. 17BandFIG. 18Bshow magnetization states of the in-plane-magnetization type magnetoresistive element MTJ.

The resistance of the magnetoresistive element MTJ changes depending on the relative magnetization directions of the storage layer and the reference layer by the magnetoresistive effect. For example, when the magnetization directions of the storage layer and the reference layer are the same (this state is referred to as a parallel state), the resistance of the magnetoresistive element MTJ is low. When the magnetization directions of the storage layer and the reference layer are opposite (this state is referred to as an anti-parallel state), the resistance of the magnetoresistive element MTJ is high.

The first and second magnetic layers14aand14ccomprises, for example, CoFe, MgFeO, or a lamination of them. When the magnetoresistive element has a perpendicular magnetization, the first and second magnetic layers14aand14cpreferably comprise, for example, TbCoFe having a perpendicular magnetic anisotropy, an artificial lattice in which Co and Pt are stacked, or L1o-ordered FePt. In this case, CoFeB may be provided as an interface layer between the first magnetic layer14aand the nonmagnetic insulating layer14bor between the nonmagnetic insulating layer14band the second magnetic layer14c.

In this example, the device structure is a double shift cancelling structure in which shift cancelling layers SCL (11,16) are present in the upper and lower portions of the magnetoresistive element MTJ. However, one of shift cancelling layers SCL (11,16) may be omitted.

When shift cancelling layer SCL (11) is omitted, the structure is a top-shift cancelling structure in which shift cancelling layer SCL (16) is present in the upper portion of the magnetoresistive element MTJ. When shift cancelling layer SCL (16) is omitted, the structure is a bottom-shift cancelling structure in which shift cancelling layer SCL (11) is present in the lower portion of the magnetoresistive element MTJ.

Each of shift cancelling layers SCL (11,16) preferably comprises, for example, a structure of [Co/Pt]n, in which Co and Pt layers are stacked n times.

Shift cancelling layers SCL (11,16) have a magnetization direction opposite to the magnetization direction of the reference layer. This structure enables shift cancelling layers SCL (11,16) to cancel the shift of the magnetization inversion property (hysteresis curve) of the storage layer by the stray magnetic field from the reference layer.

Redeposition18is formed on a side wall of the magnetoresistive element MTJ. Redeposition18is insulated to prevent the electrical short failure of the first and second magnetic layers14aand14c. A spacer layer19covers redeposition18. The spacer layer19comprises an insulating layer formed of, for example, an oxide or a nitride.

A protective layer PL covers the whole magnetoresistive element MTJ. The protective layer PL preferably comprises a layer configured to block oxygen; for example, preferably has a nitride such as SiN, AlN or HfN.

The above-described magnetoresistive element MTJ is patterned by, for example, a semi-side wall process. This process is advantageous to the realization of both of the prevention of the electrical short failure and the improvement of the MR ratio of the magnetoresistive element MTJ.

In this case, for example, while the third metal layer17is used as a mask, IBE is applied to the extent that the first metal layer12is partway etched. Subsequently, the spacer layer19is added. The spacer layer19and the third metal layer17are used as masks in order to apply IBE to the extent that shift cancelling layer SCL (11) is etched.

However, particularly in the latter etching, for example, as shown inFIG. 16, redeposition20from shift cancelling layer SCL (11) is produced since the thickness of shift cancelling layer SCL (11) is large. This redeposition has a harmful influence on the characteristics of the magnetoresistive element MTJ. It is necessary to prevent the production of redeposition20.

Use of the etching apparatus and the etching method in the embodiments explained above enable shift cancelling layer SCL (11) to be patterned without producing redeposition20shown inFIG. 16in the etching of shift cancelling layer SCL (11).

The mechanism is explained in detail below.

4. Method of Manufacturing Magnetic Memory

This specification explains a method for manufacturing the magnetic memory comprising the magnetoresistive element shown inFIG. 12toFIG. 15.

First, a lamination structure is formed by, for example, a chemical vapor deposition (CVD) process as shown inFIG. 19. In the lamination structure, shift cancelling layer SLC (11), the first metal layer12, the second metal layer13, the first magnetic layer14a, the nonmagnetic insulating layer14b, the second magnetic layer14c, the nonmagnetic conductive layer15and shift cancelling layer SCL (16) are stacked on contact plug BEC in the interlayer insulating layer26. Subsequently, the third metal layer17is formed as a mask layer on shift cancelling layer SCL (16) by, for example, the CVD process and a photo engraving process (PEP).

Next, a first etching process is performed as shown inFIG. 20.

The first etching process is executed by, for example, ion beam etching (IBE). The first etching process is performed for the purpose of etching the magnetoresistive element MTJ, the second metal layer13and the first metal layer12while the third metal layer17is used as a mask.

In this case, the shape of the magnetoresistive element MTJ can be close to the ideal shape since the magnetoresistive element MTJ is patterned by one-time etching. In a direction parallel to the upper surface of the first metal layer12, the width of the first and second magnetic layers14aand14ccan be made substantially the same in a portion X which contacts the nonmagnetic insulating layer14b. In this manner, the variation in the MR ratio of the magnetoresistive element MTJ can be reduced.

The first etching process is stopped in the middle of the first metal layer12for the following reasons.

In the first etching process, for example, the magnetoresistive element MTJ is patterned while redeposition18′ attached to a side wall of the magnetoresistive element MTJ in the etching is removed by controlling the beam angle and energy of ion beam.

In the first etching process, it is difficult to completely eliminate redeposition18′ of the metal layer which is lastly etched.

For example, if the first etching process is applied until the interlayer insulating layer26is exposed, the metal layer which is lastly etched might be contact plug BEC. Contact plug BEC contains a metal which is difficult to be oxidized (for example, W, Ta, Ru or Ti). If such a metal is reattached to a side wall of the magnetoresistive element MTJ, thereby producing redeposition18′, it is difficult to completely insulate redeposition18′ by oxidation. As a result, an electrical short failure is caused in the first and second magnetic layers14aand14c.

In consideration of the above problem, in this example, the metal layer which is lastly etched in the first etching process is the first metal layer12containing a metal which is easily oxidized (for example, Al, Be, Mg, Ca, Sr, Ba, Sc, Y, La, Zr or Hf). Specifically, as stated above, the first etching process is stopped in the middle of the first metal layer12.

In this case, even if the metal which is easily oxidized in the first metal layer12is reattached to a side wall of the magnetoresistive element MTJ, thereby producing redeposition18′, it is possible to completely insulate redeposition18′ by oxidation. Therefore, it is possible to prevent the electrical short failure of the first and second magnetic layers14aand14c.

Subsequently, redeposition18′ is converted into an oxide by oxidation (for example, thermal oxidation). As a result, as shown inFIG. 21, redeposition18containing the oxide of the metal which is easily oxidized is formed in a side wall of the magnetoresistive element MTJ.

Next, as shown inFIG. 22, the spacer layer19covering redeposition18is formed by CVD and RIE. The spacer layer19comprises, for example, a silicon oxide or a silicon nitride.

The spacer layer19has a width which is at least greater than the width of redeposition18(for example, 1 nm) in a direction parallel to the upper surface of the first metal layer12in order to function as a mask layer. For example, the spacer layer19preferably has a width which is greater than 1 nm and less than 10 nm in the direction parallel to the upper surface of the first metal layer12.

Redeposition18is shown as a layer in the drawings. However, in practice, redeposition18is attached to a side wall of the magnetoresistive element MTJ based on a unit of several atoms. Thus, the width of redeposition18refers to the thickest portion of redeposition18.

Next, as shown inFIG. 23toFIG. 25, a second etching process is performed.

In a manner similar to the first etching process, the second etching process is performed by, for example, IBE. The second etching process is executed for the purpose of etching shift cancelling layer SCL (11) while the third metal layer17and the spacer layer19are used as masks.

The second etching process is conducted until the interlayer insulating layer26which is the foundation of shift cancelling layer SCL (11) is exposed. This is because the magnetic memory comprises an array of a plurality of magnetoresistive elements MTJ. It is possible to electrically separate the plurality of magnetoresistive elements MTJ in the magnetic memory from each other by etching shift cancelling layer SCL (11) to the last.

In the second etching process, shift cancelling layer SCL (11) which is relatively thick has to be etched. If this etching is done by one-time etching, a large amount of redeposition20is produced. It is difficult to remove or insulate redeposition20.

When the etching method in the present embodiment is applied to the second etching process, shift cancelling layer SCL (11) can be patterned while redeposition20is surely removed. Further, when the etching method in the present embodiment is applied, it is possible to certainly eliminate the redeposition of contact plug (a metal which is difficult to be oxidized) BEC which is lastly etched in the second etching process.

For example, as shown inFIG. 23, a low angle IBE process which irradiates an ion beam having a beam angle θlow is performed in order to apply a patterning process to the extent that shift cancelling layer SCL (11) is partway etched. At this time, redeposition20of an element contained in shift cancelling layer SCL (11) is produced. Redeposition20shown inFIG. 23is removed by performing a high angle IBE process which irradiates an ion beam having a beam angle θhigh after the low angle IBE process as shown inFIG. 24. The low angle IBE and high angle IBE processes are repeated n times (n is a natural number).

As a result, as shown inFIG. 25, the second etching process which patterns shift cancelling layer SCL (11) is finished.

Subsequently, as shown inFIG. 25, the protective layer PL which covers the magnetoresistive element MTJ is formed by CVD.

As shown inFIG. 26, redeposition18can be completely eliminated or can be very small depending on the conditions of the first etching process. As shown inFIG. 27, shift cancelling layer SCL may be provided on only the lower side of the magnetoresistive element MTJ.

The magnetic memory comprising the magnetoresistive element MTJ inFIG. 12toFIG. 15is manufactured by the above method.

According to an embodiment, a magnetic layer or a metal layer is patterned by repeating the etching of the magnetic layer or the metal layer and the removal of the redeposition caused by the etching. Therefore, with respect to the final pattern of the magnetic layer or the metal layer, the redeposition can be vanishingly removed. Thus, it is possible to improve the characteristics of an element including a magnetic layer or a metal layer, such as a magnetoresistive element.