Patent ID: 12198912

DETAILED DESCRIPTION

In all of the drawings for describing the embodiment, the same members are denoted by the same reference characters and repetitive descriptions thereof will be omitted in principle. Note that hatching may be applied even in a plan view in some cases in order to make the drawings easy to see.

<Configuration of Film Forming Apparatus>

FIG.1is a diagram showing a schematic configuration of a film forming apparatus. InFIG.1, a film forming apparatus1includes a chamber10which is a film forming chamber. In this chamber10, a workpiece holding unit11is provided and a film formation object SUB typified by a substrate is held by this workpiece holding unit11. This chamber10is provided with a gas introduction port10aand a gas exhaustion port10b.

Next, in the chamber10, a plasma generation unit13is provided at a position facing the film formation object SUB held by the workpiece holding unit11. The plasma generation unit13is configured to generate plasma, and a magnetic field generation unit14composed of, for example, a coil is arranged around the plasma generation unit13. Also, a waveguide15is connected to the plasma generation unit13, and microwaves propagating through the waveguide15are introduced into the plasma generation unit13. Further, a target TA having a cylindrical shape or the like is arranged at a position between the workpiece holding unit11and the plasma generation unit13and close to the plasma generation unit13, and the target TA is electrically connected to a power source16capable of supplying a high frequency power, a DC power, and a pulse power. Consequently, the target TA is configured such that the high frequency voltage from the power source16is applied. This target TA is fixed by a fixing unit17.

Further, the film forming apparatus1includes a ring-shaped shield member (first shield member)30and a ring-shaped shield member (second shield member)40. Assuming that the direction from the plasma generation unit13to the workpiece holding unit11is the Z direction, the shield member30is provided between the target TA and the plasma generation unit13in the Z direction. Also, the shield member40is provided between the target TA and the workpiece holding unit11.

<Film Forming Method>

Next, a film forming method using the film forming apparatus1will be described.FIG.2is a flowchart showing each step of a film forming method performed using the film forming apparatus shown inFIG.1.

First, inFIG.1, a gas typified by, for example, argon gas is introduced into the plasma generation unit13. Then, when a magnetic field is generated from the magnetic field generation unit14arranged around the plasma generation unit13, the electrons contained in the gas introduced into the plasma generation unit13receive a Lorentz force to make a circular motion. At this time, when microwaves (electromagnetic waves) having the same period (or frequency) as the period (or frequency) of the circular motion of the electrons are introduced from the waveguide15into the plasma generation unit13, the electrons making the circular motion and the microwaves are resonated, so that the energy of the microwaves is efficiently supplied to the electrons making the circular motion (electron cyclotron resonance phenomenon) (step S101inFIG.2). As a result, the kinetic energy of the electrons contained in the gas increases, and the gas separates into positive ions and electrons. In this manner, a plasma composed of positive ions and electrons is generated (step S102inFIG.2).

Next, inFIG.1, a high frequency voltage is supplied from the power source16to the target TA. In this case, the positive potential and the negative potential are alternately applied to the target TA to which the high frequency voltage is supplied. Here, of the positive ions and electrons constituting the plasma, the electrons having a light mass can follow the high frequency voltage applied to the target TA, while the positive ions having a heavy mass cannot follow the high frequency voltage. As a result, the positive potential that attracts the following electrons is canceled by the negative charge of the electrons, while the average value of the high frequency voltage shifts from 0 V to the negative potential because the negative potential remains. This means that it is possible to consider as if a negative potential is applied to the target TA, though a high frequency voltage is applied to the target TA. As a result, the positive ions are attracted to the target TA, which is considered to be applied with a negative potential on average, and collide with the target TA (step S103inFIG.2).

Subsequently, when the positive ions collide with the target TA, target particles constituting the target TA receive a part of the kinetic energy of the positive ions and are ejected from the target TA into the internal space of the chamber10(step S104inFIG.2). Thereafter, some of the target particles that have been ejected to the internal space of the chamber10adhere to the surface of the film formation object SUB held by the workpiece holding unit11(step S105inFIG.2). Then, by repeating such a phenomenon, a large number of target particles adhere to the surface of the film formation object SUB, so that a film is formed on the surface of the film formation object SUB (step S106inFIG.2).

For example, when the target TA is made of aluminum, the target particles are aluminum atoms, and the film formed on the film formation object SUB is an aluminum film. However, when the above-mentioned film forming operation is performed while introducing oxygen gas or nitrogen gas through the gas introduction port10aprovided in the chamber10of the film forming apparatus1shown inFIG.1, an aluminum oxide film or an aluminum nitride film can be formed on the surface of the film formation object SUB.

Similarly, when the target TA is made of, for example, silicon, the target particles are silicon atoms, and the film formed on the film formation object SUB is a silicon film. However, when the above-mentioned film forming operation is performed while introducing oxygen gas or nitrogen gas through the gas introduction port10aprovided in the chamber10of the film forming apparatus1shown inFIG.1, a silicon oxide film or a silicon nitride film can be formed on the surface of the film formation object SUB.

<Advantages of Film Forming Apparatus>

In the film forming apparatus1described above, the film formation object SUB is irradiated with a plasma flow generated by utilizing the electron cyclotron resonance (ECR) phenomenon and the divergent magnetic field, and a high frequency voltage is simultaneously applied between the target TA and the ground, whereby ions in the plasma are caused to collide with the target TA to form a film on the film formation object SUB. If this film forming method is called an ECR sputtering method, this ECR sputtering method has the following advantages.

For example, in the magnetron sputtering method, the order of 10−3Torr (10−3×133.32 Pa) or more is necessary to obtain the stable plasma. On the other hand, in the ECR sputtering method, the stable ECR plasma can be obtained at a pressure on the order of 10−4Torr (10−4×133.32 Pa). Further, in the ECR sputtering method, since the sputtering is performed by applying the particles (positive ions) in the plasma to the target TA by a high frequency voltage, a film can be formed on the film formation object SUB at a low pressure.

In the ECR sputtering method, the film formation object SUB is irradiated with the ECR plasma flow and the sputtered particles. Since the ions of the ECR plasma flow have an energy of 10 eV to several tens of eV and the pressure is low, the ion current density of the ions reaching the film formation object SUB can be increased. Therefore, the ions of the ECR plasma flow give energy to the raw material particles that are sputtered and fly onto the film formation object SUB, and promote the bonding reaction between the raw material particles and oxygen, so that the quality of the film deposited on the film formation object SUB by the ECR sputtering method is improved. In the ECR sputtering method mentioned above, it is particularly advantageous that a high-quality film can be formed on the film formation object at a low substrate temperature (temperature of the film formation object SUB).

From the above, the film forming apparatus1is superior in that it can form a high-quality film. In particular, it can be said that the film forming apparatus1is excellent in that a high-quality film can be formed on the surface of the film formation object without exposing the film formation object SUB to a high temperature. Namely, it can be said that the film forming apparatus1is excellent in that a high-quality film can be formed on the surface of the film formation object SUB while reducing the damage given to the film formation object SUB.

<Target>

FIG.3is a perspective view showing an external configuration of the target used in the film forming apparatus inFIG.1. As shown inFIG.3, the target TA has a cylindrical shape. The target TA includes a cylindrical backing tube (supporting member)20made of, for example, a copper material, and a cylindrical target member21made of, for example, aluminum is adhered to an inner wall of the backing tube20by a bonding material (adhesive material) (not shown).

In the case of the film forming method using the cylindrical target TA configured in this way, it is possible to reduce the damage given to the film formation object SUB shown inFIG.1as compared with the case of using a generally used disk-shaped target. When forming a film by using the cylindrical target TA, the probability that the ions (for example, argon ions) that have recoiled after colliding with the target member21collide with the film formation object SUB is reduced in comparison with the case of forming a film by using a disk-shaped target. Therefore, in the film forming apparatus having the configuration in which the cylindrical target TA is used to form a film on the surface of the film formation object SUB, the probability that the recoiled argon ions collide with the film formation object SUB is reduced, so that it is possible to reduce the damage to the film formation object SUB due to the collision of the recoiled argon ions with the film formation object SUB.

<Shield Member>

FIG.4is a perspective view showing an external configuration of shield members used in the film forming apparatus inFIG.1.FIG.5is a cross-sectional view showing a positional relationship between the shield members and the target in the film forming apparatus. As shown inFIG.4, each of the shield member30and the shield member40has a ring shape.

As shown inFIG.4andFIG.5, each of the shield member30, the shield member40, and the target member21is stacked in the Z direction around an axis (virtual line) VL1as a central axis extending in the Z direction. More specifically, the shield member30, the target member21, and the shield member40are stacked in this order from the side of the plasma generation unit13(seeFIG.1) so as to be separated from each other.

The shield members30and40are protective members for suppressing the collision of the plasma with the backing tube20that holds the target member21. By arranging the shield members30and40at positions overlapping the target member21in the Z direction, it is possible to reduce the occurrence frequency of the collision of the plasma with the backing tube20arranged outside the target member21. As a result, it is possible to suppress the sputtering by the plasma to the backing tube20.

Also, the shield members30and40are arranged so as to face each other with the target member21interposed therebetween in the Z direction. In this way, it is possible to suppress the high frequency voltage supplied to the target TA from diffusing around the target member21. In other words, the shield members30and40function as diffusion preventing members for preventing the diffusion of the high frequency voltage supplied to the target TA.

From the viewpoint of effectively exerting the function as the protective member and the function as the diffusion preventing member, each of the shield members30and40is preferably made of a metal material. For example, stainless steel can be presented as the metal material forming the shield members30and40. In order to prevent the short-circuit between the shield members30and40made of metal and the target member21, each of the shield members30and40is arranged so as to be separated from target member21. In other words, each of the shield members30and40is electrically isolated from the target member21. However, if the separation distances between the target member21and each of the shield members30and40become extremely large, the probability that the plasma enters through the gaps between the target member21and each of the shield members30and40increases, and it is thus preferable that the separation distances are small. According to the studies by the inventor of this application, each of a separation distance G1between the target member21and the shield member30and a separation distance G2between the target member21and the shield member40is preferably 5 mm or less, and particularly preferably 3 mm or less. However, each of the separation distances G1and G2needs to be larger than 0 mm.

The plasma generated by the plasma generation unit13(seeFIG.1) passes through an opening30H of the ring-shaped shield member30and collides with the target member21. Therefore, it has been considered that an inner diameter D1of the opening30H of the shield member30is preferably the same as an inner diameter D2of the cylindrical target member21in order for the plasma ions to efficiently collide with the target member21.

According to the studies by the inventor of this application, it has been found that another problem occurs when the inner diameter D1of the opening30H of the shield member30is the same as the inner diameter D2of the cylindrical target member21. Hereinafter, a film forming apparatus100shown inFIG.6will be described as a studied example with respect toFIG.5.FIG.6is a cross-sectional view showing a positional relationship between shield members and a target in a film forming apparatus that is a studied example with respect toFIG.5.FIG.7is an enlarged cross-sectional view showing a state where a target member is sputtered in a part of the target and the shield members shown inFIG.6. Note that the inner diameter D2of the target member21described in this specification means the inner diameter D2of the target member21in a brand-new state before the plasma irradiation process unless otherwise specified particularly. Since the thickness of the target member21gradually decreases as the ions of the plasma collide with the target member21, the value of the inner diameter D2also changes. Therefore, in this specification, the value of the inner diameter D2of the brand-new target member21is used as an index in principle.

The film forming apparatus100shown inFIG.6differs from the film forming apparatus100shown inFIG.5in that the inner diameter D2of the target member21and the inner diameter D1of the shield member30are the same. The others are the same as those of the film forming apparatus1shown inFIG.5. Each of the target member21and the shield member30is arranged around the axis VL1as a central axis. Therefore, an inner wall surface21aof the target member21and an inner wall surface30aof the shield member30are arranged to be flush with each other in the Z direction (in other words, arranged in the same plane). In such a configuration, by setting the value of the separation distance G1to 5 mm or less, it is possible to suppress the collision of plasma ions with the backing tube20. In addition, since the entire target member21overlaps the shield member30in the Z direction, it is possible to suppress the high frequency voltage supplied to the target TA from diffusing around the target member21.

However, according to the studies by the inventor of this application, it has been found that the film forming apparatus100has the following problems caused by a deposit50(seeFIG.7) deposited on the shield member30. For example, when the target member21is made of a conductive material such as metal, the deposit50has conductive properties. When the deposit50grows and the distance between the target member21or the backing tube20and the deposit50becomes closer, the bias voltage generated during the discharge of the target member21and the power supplied from the power source cause an abnormal discharge between the shield member30and the deposit50, with the result that the film formation becomes unstable in some cases. Even if the deposit50is made of an insulating material or made of a semi-conductive material, the deposit50becomes the cause of the abnormal discharge when charge is accumulated in the grown deposit50. Moreover, if the deposit50grows further and the target member21or the backing tube20and the deposit50come into contact with each other, the target TA and the shield member30may be short-circuited. In order to prevent the occurrence of unstable film formation and the short-circuit of the shield member30, it is necessary to stop the film forming process and replace the shield member30when the deposit50has grown to some extent. As a result, the efficiency of the film forming process is lowered. Note that the deposits50and51shown inFIG.7are substances formed by a part of the target particles adhering to the shield members30and40, respectively. Therefore, the deposits50and51grow when the film forming process is performed.

Therefore, the inventor of this application studied a method of reducing the growth rate of the deposit50and a method of preventing the occurrence of unstable film formation and the short-circuit even if the deposit grew, as a method of improving the efficiency of the film forming process.FIG.8is an enlarged cross-sectional view showing a state where the target member is sputtered in a part of the target and the shield members shown inFIG.5.

In the case of the film forming apparatus1shown inFIG.5, the inner diameter D1of the opening30H of the shield member30is smaller than the inner diameter D2of the cylindrical target member21(inner diameter D2of the target member21in a brand-new state before performing the film forming process as described above). With this configuration, it is possible to suppress the increase of plasma density near the target TA on the side of the shield member30.

More specifically, the cylindrical target TA is arranged between the plasma generation unit13and the film formation object SUB as described with reference toFIG.1. In this case, the plasma density near the target TA on the side of the plasma generation unit13is higher than the plasma density near the target TA on the side of the film formation object SUB. In other words, the plasma density near the target TA on the side of the film formation object SUB is lower than the plasma density near the target TA on the side of the plasma generation unit13. When there is the difference in the distribution of the plasma density in the vicinity of the target TA in this way, the frequency of the sputtering phenomenon by argon ions increases in the part having relatively high plasma density.

In the case of the film forming apparatus shown inFIG.7, since the plasma density distribution in the Z direction near the target member21is higher on the side of the shield member30than on the side of the shield member40, the frequency of the sputtering phenomenon is higher near the target member21on the side of the shield member30than near the target member21on the side of the shield member40. As a result, when comparing the degree of consumption of the target member21, the consumption of the target member21becomes larger in the target TA on the side of the shield member30than in the target TA on the side of the shield member40.

Since the deposits50and51are made of target particles ejected by the sputtering of the target member21, the deposit50formed on the shield member30having a relatively higher frequency of the sputtering phenomenon has a growth rate higher than that of the deposit51formed on the shield member40.

In the case of the film forming apparatus1shown inFIG.8, as can be seen by the comparison withFIG.7, the inner diameter of the ring-shaped shield member30is small, and thus the inner wall surface30aof the shield member30protrudes inward than the inner wall surface21aof the target member21. In other words, the target member21is covered with an eaves portion (visor portion)31inside the shield member30in the Z direction. Since plasma ions reach the target member21via the inner opening of the shield member30, the increase of plasma density near the target member21can be suppressed in the vicinity of the shield member30when the shield member30has the eaves portion31.

As a result, as shown inFIG.8, it is possible to prevent the part of the target member21on the side of the shield member30from being consumed faster than the other parts. Consequently, since it is possible to decrease the growth rate of the deposit50, the replacement frequency of the shield member30can be reduced.

Also, the deposit50is mainly formed near the boundary between the shield member30and the opening30H (seeFIG.5). Accordingly, by increasing a protruding length L31of the eaves portion31in the X direction orthogonal to the Z direction as shown inFIG.8, the separation distance between the target member21and the deposit50is less likely to be reduced even if the deposit50grows. Therefore, it is possible to prevent the occurrence of unstable film formation by application to the target member21or the short-circuit between the target member21and the shield member30. In other words, it is possible to use the shield member30without replacing it until the target member21is consumed while suppressing the occurrence of unstable film formation and the short-circuit of the shield member30. In still other words, the sputtering can be stabilized even when the deposit50is formed.

Note that the protruding length L31of the eaves portion31in the X direction orthogonal to the Z direction is defined as follows. That is, a surface of the backing tube20facing the target member21is defined as a target holding surface20a. At this time, a position where an extended surface of the target holding surface20aand the shield member30intersect is defined as a reference position, and the distance from the reference position to the inner wall surface30aof the shield member30is defined as the length L31. According to this definition, the length L31is at least larger than the thickness of the target member21in a brand-new state.

By the way, according to the studies by the inventor of this application, it has been found that the growth rate of the deposit50can be reduced and the decrease of the occurrence frequency of the sputtering can be suppressed by adjusting the inner diameter D2of the shield member30shown inFIG.5. As to the preferable range of the inner diameter D1of the shield member30based on the inner diameter D2of the target member21shown inFIG.5, it is possible to suppress the decrease of the occurrence frequency of the sputtering if the inner diameter D1is 90% or more of the inner diameter D2. On the other hand, from the viewpoint of suppressing the growth of the deposit50by the effect of the eaves portion31, the inner diameter D1is preferably 99% or less of the inner diameter D2. Further, from the viewpoint of preventing the contact between the grown deposit50and the target member21, the inner diameter D1is preferably 96% or less of the inner diameter D2.

In the example shown inFIG.8, each of the separation distances G1and G2is, for example, 3 mm. The thickness of the target member21in a brand-new state (distance from an outer wall surface facing the backing tube20to the inner wall surface21a) is, for example, 3 mm. The inner diameter D2(seeFIG.5) of the target member21is, for example, 120 mm. The inner diameter D1(seeFIG.5) of the shield member30is 114 mm. In this case, the inner diameter D1is 96% of the inner diameter D2. The protruding length L31of the eaves portion31in the X direction is 3.0 mm. The thickness (length in the Z direction) of the shield member30is, for example, 2 mm.

Also, the deposit51formed on the shield member40shown inFIG.5is smaller than the deposit50. Therefore, the inner wall surface21aof the target member21and an inner wall surface40aof the shield member40are arranged to be flush with each other in the Z direction (in other words, arranged in the same plane). Therefore, when the inner diameter D1of the shield member30and the inner diameter D3of the shield member40are compared, they can be expressed as follows. That is, the inner diameter D1of the shield member30is smaller than the inner diameter D3of the shield member40.

Although not shown, there is an embodiment in which the inner diameter D3of the shield member40is smaller than the inner diameter D2of the target member21as a modification with respect toFIG.5. In the case of this modification, it is possible to suppress the occurrence of unstable high frequency voltage due to the influence of the deposit51. However, since the deposit51is less likely to grow compared with the deposit50as described above, the probability that the deposit51grows to the extent that the high frequency voltage becomes unstable is low even with the configuration shown inFIG.5. On the other hand, from the viewpoint of efficiently carrying the target particles ejected from the target member21to the film formation object SUB (seeFIG.1), it is preferable that the opening40H is large. The inner diameter D1of the shield member30smaller than the inner diameter D3of the shield member40as shown inFIG.8is preferable in that the target particles can efficiently reach the film formation object SUB.

<Modification>

Next, a modification with respect to the film forming apparatus shown inFIG.5andFIG.8will be described.FIG.9is an enlarged cross-sectional view showing a modification with respect to the film forming apparatus shown inFIG.8. A film forming apparatus101shown inFIG.9is the same as the film forming apparatus1shown inFIG.1except for the differences described below. In the following, the differences from the film forming apparatus1will be described, and redundant description will be omitted in principle. Also, a shield member30A of the film forming apparatus101has a ring shape like the shield member30shown inFIG.4. The ring-shaped shield member30A has the structure similar to that of the enlarged cross-section shown inFIG.9over the entire circumference. Further, unlikeFIG.8, the target member21in a brand-new state before being consumed is illustrated inFIG.9in order to clarify the positional relationship between the target member21in a brand-new state and a portion34.

The film forming apparatus101shown inFIG.9differs from the film forming apparatus1shown inFIG.8in the following points. That is, the shield member30A of the film forming apparatus101has a portion (first portion)33overlapping the backing tube20of the target TA in the Z direction and a portion (second portion)34not overlapping the target TA in the Z direction. Note that the portion34is a portion that does not overlap the target TA even if the target member21is in a brand-new state before being consumed. A thickness T2of the portion34is smaller than a thickness T1of portion33. Also, when the surface of the target member21facing the shield member30A is defined as a reference surface21b, the shortest distance from the portion34to the reference surface21bis larger than the shortest distance from the portion33to the reference surface21b. In other words, in the portion34that does not overlap the target TA, the surface facing the target TA is shaved and thinned.

When thinning the portion34by shaving the surface facing the target TA, the space between the portion34and the target member21can be increased. Since the deposit50is formed on the portion34, the distance between the deposit50and the target member21can be increased as the thickness of the portion34is reduced.

In the case of this modification, it is possible to secure the separation distance between the deposit50and the target member21in the Z direction. Therefore, even if the length L31is shortened compared with the case of the film forming apparatus1described with reference toFIG.8, it is possible to suppress the occurrence of unstable high frequency voltage or the short-circuit between the shield member30A and the target member21.

The thickness T2of the portion34needs to be thick enough to prevent the deformation of the portion34, but it is preferably as thin as possible. For example, in the example shown inFIG.9, the thickness T1is 2 mm and the thickness T2is 1 mm.

In the case of the film forming apparatus101, the portion34has a uniform thickness. Namely, the shield member30A has a stepped portion35between the portion33and the portion34. The thickness of the portion outside the stepped portion35(on the outer peripheral side of the shield member30A) is equal to the thickness of the portion33, and the thickness of the portion inside the stepped portion35(on the side of the opening of the shield member30A) is equal to the thickness of portion34. In this way, when the thickness T2of the portion34is uniform, the separation distance between the target member21and the deposit50can be ensured regardless of the position of the deposit50formed on the portion34.

Further, as shown inFIG.9, the stepped portion35overlaps the target member21in the Z direction. As a modification with respect toFIG.9, the position of the stepped portion35may be a position overlapping the backing tube20or a position overlapping the fixing unit17. However, considering the function of preventing the collision of ions with the backing tube20among the functions of the shield member30A, it is preferable that the separation distance between the backing tube20and the shield member30A is short. When the stepped portion35is arranged at a position overlapping the target member21, the separation distance between the backing tube20and the shield member30A can be reduced, and the separation distance between the portion34and the target member21can be increased.

FIG.10is an enlarged cross-sectional view showing another modification with respect toFIG.9. Note that a film forming apparatus102shown inFIG.10is the same as the film forming apparatus101described with reference toFIG.9except for the differences described below. In the following, the differences from the film forming apparatus101will be described, and redundant description will be omitted in principle. Also, a shield member30B of the film forming apparatus102has a ring shape like the shield member30shown inFIG.4. The ring-shaped shield member30B has the structure similar to that of the enlarged cross-section shown inFIG.10over the entire circumference. Further, unlikeFIG.8, the target member21in a brand-new state before being consumed is illustrated inFIG.10in order to clarify the positional relationship between the target member21in a brand-new state and a portion34.

The film forming apparatus102shown inFIG.10differs from the film forming apparatus101shown inFIG.9in that the surface of the portion34facing the target TA is an inclined surface inclined with respect to the X direction orthogonal to the Z direction. In the case of the shield member30B of the film forming apparatus102, the stepped portion35shown inFIG.9does not exist. Further, in the case of the shield member30B, the thickness T2of the portion34becomes smaller as approaching an inner tip of the shield member30B. However, as shown inFIG.10, a starting point36of the inclined surface is located at a position overlapping the target member21. Moreover, the inclination angle of the inclined surface with respect to the X direction is uniform. Therefore, even at the position where the thickness T2of the portion34is the largest, the thickness T2is smaller than the thickness T1of the portion33.

In the case of the shield member30B, the strength of the portion34can be improved compared with the shield member30A shown inFIG.9, and thus the thickness of the tip portion (the portion close to the opening30H shown inFIG.5) can be made smaller than that of the shield member30A. The shield member30B shown inFIG.10is more advantageous than the shield member30A shown inFIG.9when the deposit50is formed particularly thickly at the tip portion of the shield member30B.

In the foregoing, the invention made by the inventor of this application has been specifically described based on the embodiments, but it is needless to say that the present invention is not limited to the embodiments described above and can be variously modified within the range not departing from the gist thereof.