Method for cleaning target, and physical deposition apparatus

The present invention relates to a target cleaning method and a physical deposition apparatus, and in particular, in a physical deposition apparatus such as a sputtering film deposition apparatus, the surface of the target as a film forming material is always normally normal without wasting the target. It relates to a target cleaning method and a physical deposition device that are characteristic of the configuration for keeping.

In the thin film forming process in the manufacturing process of semiconductor devices, magnetic resistance elements, etc., film forming devices such as CVD devices, sputtering devices, and thin film deposition devices are used, but these film forming devices are as clean as possible. A film formation environment is desired.

However, even in a sputtering apparatus controlled in an ultra-high vacuum, adsorption of impure molecules to the target occurs, and the formation of an impurity layer and the formation of an oxide film on the target surface proceed with the passage of time.

If the sputtering film formation is performed with impurities such as moisture adhering to the target surface as described above, the film quality is adversely affected, such as an increase in the resistance of the deposited film formed on the wafer, which is the substrate to be grown. This situation will be explained with reference to FIGS. 7 and 8 as it becomes apparent.

See FIG. 7. FIG. 7 is an explanatory diagram of the dependence of the sheet resistance of the Al alloy film on the number of film formations when the Al alloy is formed on three wafers, and is a state in which impurities such as moisture are attached to the target surface. The sheet resistance of the first wafer to be sputtered in is the highest.

See FIG. 8 FIG. 8 is an explanatory diagram of the dependence of the reflectance of the Al alloy film on the number of film formations when the Al alloy is formed on three wafers, and the reflectance of the first wafer is the lowest. It has become.

In order to avoid the adverse effects of impurities in such initial sputtering, it becomes necessary to clean the surface of the target with Ar ions to keep the surface of the target clean.

Therefore, usually, when performing a sputtering film formation, in order to remove moisture and an oxide film adhering to the surface of the target, a film formation is performed on a dummy wafer prior to the film formation on the product forming wafer. As a result, the film is formed on the product forming wafer in a state where the target surface is clean.

Alternatively, in the case of a sputtering apparatus provided with a shutter mechanism, the wafer stage on which the product-forming wafer is mounted is covered with a shutter, and sputtering is performed on the shutter without using a dummy wafer (see, for example, Patent Document 1). As described above, it is a general film forming method to perform pre-sputtering immediately before forming a film on the product forming wafer.

There is also a method of forming a film on a dummy wafer during the standby time of the device in which the film is not formed to keep the surface of the target clean.<patcit num="1"><text>Japanese Patent Application Laid-Open No. 62-177170</text></patcit>

<p> The above-mentioned pre-sputtering is an indispensable work in sputtering film formation, and it is treated as a common sense, so it is not regarded as a problem relatively, but from the viewpoint of productivity, it is never considered. It's not a useful task.</p><p> That is, if there is no shutter mechanism, a dummy wafer is required, and a time for performing pre-sputtering on the dummy wafer is also required. During that time, the film forming apparatus naturally has a non-production time and the productivity is lowered.</p><p> Further, if there is a shutter mechanism, a dummy wafer is not required, but it still requires time to perform pre-sputtering on the shutter, and of course, during that time, the film forming apparatus becomes non-production time and is produced. The sex is reduced.</p><p> Further, when performing pre-sputtering, the target is consumed and the life of the target is shortened, and the cleaning cycle in the film forming apparatus is shortened due to the addition of film formation by pre-sputtering, and the replacement cycle of internal parts is also shortened. Become.</p><p> In the future, in view of productivity improvement, the running cost of film forming equipment such as sputtering equipment is expected to increase as the diameter of wafers increases, and in particular, wafers used for dummies are expected to increase. The price is by no means negligible.</p><p> Therefore, an object of the present invention is to clean the surface of the target without using a dummy wafer and without wasting the target.</p>

<p> FIG. 1 is a principle configuration diagram of the present invention, and here, with reference to FIG. 1, means for solving the problems in the present invention will be described. It is an electrode. See FIG. 1. In order to solve the above problems, the present invention presents a method for cleaning target 2 of a physical vapor deposition (PVD) apparatus, in which the constituent substances of target 2 are sublimated on the surface of target 2 during the time when film formation is not performed. It is characterized in that the surface of the target 2 is cleaned by irradiating the inactive ion 4 with an energy of 6 times or less the energy.</p><p> As described above, inactive ions having an energy of 6 times or less, preferably 5 times or less, and more preferably 4 times or less the sublimation energy of the constituent substances of the target 2 on the surface of the target 2 during the time when the film is not formed. By irradiating 4, it is possible to clean the surface of the target 2 without wasting the target 2, and it is possible to shorten the manufacturing time and reduce the cost by not requiring a dummy wafer. become.</p><p> That is, the sputter rate has a correlation with the ion energy, and in a relatively low region where the ion energy is 100 eV or less, the spatter rate is proportional to the square of the ion energy, and when the ion energy is lowered, the ion energy at which sputtering does not occur. It is known that there is a value.</p><p> The ion energy value at which this sputtering does not occur is called the threshold energy, and below this ion energy, the sputtering rate becomes 0. This threshold energy varies depending on the sputtering conditions and the material of the target 2, but is generally four times the sublimation energy of the material of the target 2.</p><p> Therefore, by irradiating the surface of the target 2 with the inert ion 4 with an ion power equal to or lower than this threshold energy, impurities can be removed or impure molecules can be prevented from adhering without causing sputtering of the target base material. Is possible.</p><p> That is, since the target base material is not sputtered, it does not affect the usable time of the target 2 and the internal jig, and there is no problem of generating particles, so that the particles do not affect the film formation in the sputtering process. , A film having stable characteristics can always be formed.</p><p> However, the ion energy to be irradiated does not have to be strictly below the threshold energy, and if it is 1.5 times or less of the threshold energy, that is, if the sublimation energy is 6 times or less, sputtering hardly occurs, so target 2 The consumption of energy can be significantly reduced as compared with the conventional case.</p><p> Further, it is desirable that the physical deposition apparatus is provided with a shield 5 that prevents substances ejected from the target 2 from scattering to a place other than the substrate to be filmed, and the polarity of rejecting the inert ions 4 to the shield 5 during the cleaning process. It is desirable to apply the DC voltage of.</p><p> By providing the shield 5 and applying a DC voltage to the shield 5 in this way, it becomes easy to maintain a stable discharge under a low voltage, and the action of a trigger for generating the discharge can be expected.</p><p> In addition, it is desirable that the cleaning process be performed at all times during the standby time of the physical deposition equipment, and in that case, the cleaning process should be performed with ion energy of 4 times or less of the sublimation energy so that the consumption of the target 2 is minimized. desirable.</p><p> Alternatively, the cleaning step may be performed only when necessary, and in this case, the cleaning time is shortened. Therefore, in order to improve the cleaning efficiency, it is desirable to perform the cleaning step with ion energy of 6 times or less of the sublimation energy.</p><p> Further, as a physical deposition device, the power supply system for supplying electric power to the target 2 is composed of a first power supply 6 for sputtering for film formation and a second power supply 7 for cleaning. Is desirable, so that the switching between the sputtering process and the cleaning process can be smoothly performed.</p><p> The most typical physical deposition device in the present invention is a sputtering device, but it is also applied to a laser ablation device or the like. In that case, a discharge electrode for cleaning is provided. Just do it.</p><p> Further, although Ar gas is typical as the inert gas to be irradiated, other rare gas such as Kr or Xe may be used. Further, as the target base material, a metal is typical, but it is also applied to a non-metal target such as an oxide.</p>

<p> In the present invention, the surface of the target can be kept clean at all times without using a dummy wafer, without consuming the target, and without reducing the production time, thereby forming a film. It is possible to maintain good properties with good reproducibility, which in turn contributes greatly to cost reduction and high quality of products.</p>

According to the present invention, the surface of the target is irradiated with Ar ions with an ion power that does not cause sputtering during the standby time during which the film is not formed to remove impurities or prevent the adhesion of impure molecules.

In this case, a shield is provided to prevent the substance ejected from the target from scattering to a place other than the substrate, and a DC voltage is applied to the shield to realize a stable discharge state even at a low voltage.

Here, the target cleaning method of the first embodiment of the present invention will be described with reference to FIGS. 2 to 6, but first, the sputtering apparatus used for the first embodiment of the present invention will be described with reference to FIG. .. See FIG. 2 FIG. 2 is a schematic configuration diagram of the sputtering apparatus according to the first embodiment of the present invention. For example, a chamber 11 made of an Al alloy, a target 12 also serving as one discharge electrode, and the other discharge facing the target 12. A substrate stage 13 for mounting a wafer 14 that also serves as an electrode and a substrate to be processed, a cryopump 15 that exhausts the inside of the chamber 11 to a high vacuum, an MFC (mass flow controller) 16 that supplies Ar gas in the chamber 11. A shield 17 that prevents the sputtered target base material from scattering to locations other than the wafer 14, a DC power supply 19 for applying a voltage that prevents the collision of Ar ions 18 to the shield 17, a power supply 20 for film formation, and It is composed of a cleaning power supply 21.

In this case, the film forming power supply 20 can be used under the condition of 10 kW or more, and the cleaning power supply 21 can be used under the condition of 100 W or less. Further, the substrate stage 13 is used by being grounded.

Next, a sputtering step including a cleaning step of the target of Example 1 of the present invention will be described with reference to FIGS. 3 to 6, but here, a film formation of an Al alloy film using a target made of an Al alloy will be described. It will be described as a process. See FIG. 3. First, with the wafer 14 placed on the substrate stage 13, Ar gas is flowed from the MFC 16 into the chamber 11 by, for example, 50 sccm, and the pressure in the chamber 11 is stabilized to, for example, 2 m Torr, and then the power supply for film formation. A DC power of 15 kW at 500 V is applied to a target 12 made of an Al alloy using 20, and a sputtering film is formed on the wafer 14. At this time, there is no bias with respect to the shield 17.

See FIG. 4. Next, after the wafer 14 having been film-formed is taken out of the chamber 11, the inside of the chamber 11 is 1 × 10 using the cryopump 15.^-8Exhaust to a base pressure below Torr. In this case, the higher the vacuum, the more the adhesion of impure molecules to the target surface is promoted. Therefore, the residual gas at the time of film formation is exhausted as much as possible, including degassing from the wafer 14.

See FIG. 5. Next, Ar gas is flowed from the MFC 16 into the chamber 11, for example, 500 sccm, the pressure in the chamber 11 is stabilized to, for example, 10 mTorr, and then the cleaning power supply 21 is used to reach the target 12 at -100 V and 50 W DC. Along with applying power, a voltage of + 30V is applied to the shield 17 to irradiate the surface of the target 12 with Ar ions 18 for cleaning.

In this case, since the ion energy of Ar ion 18 is equal to or less than the threshold energy, ion cleaning is started with the sputtering rate being 0, and the discharge is always maintained during the waiting time until the next film forming step. Continue cleaning. The threshold energy varies depending on the material of the target 11, but is four times the sublimation energy of the target base material, and is usually in the range of 20 to 100 eV.

Further, during cleaning, a positive DC voltage having a polarity that rejects Ar ions 18 having a positive charge is applied to the shield 17, so that the discharge can be stably maintained even at a low voltage, and for cleaning. It can also be expected to have a triggering action when generating an electric charge.

See FIG. 6. Next, after turning off the cleaning power supply 21, with the next wafer 14 placed on the substrate stage 13, Ar gas, for example, 50 sccm was flowed from the MFC 16 into the chamber 11 again, and the inside of the chamber 11 was formed. After stabilizing the pressure to, for example, 2 mTorr, a DC power of 15 kW at 500 V is applied to the target 12 using the film forming power source 20, and sputtering film formation is performed on the wafer 14.

As described above, in the present invention, during the waiting time from the start of ion cleaning immediately after the completion of film formation to the next film formation, as in "film formation-&gt; ion cleaning-&gt; film formation". Since it continues, impurities, particularly water molecules, can be prevented from adhering to form an alumina-based oxide on the surface of the target 11. By the way, if an alumina-based oxide is formed, it becomes difficult to remove it by ion cleaning having a sputtering rate of 0.

Further, since this ion cleaning is performed under the condition of a sputtering rate of 0, the target 12 is not consumed during the ion cleaning, and therefore the target base material is not sputtered during the ion cleaning, so that the film is formed. The replacement cycle of internal parts of the device can be lengthened.

Furthermore, since cleaning is always performed using the waiting time, the film forming process can be started immediately after the wafer is inserted, and it is not necessary to perform pre-sputtering prior to the film forming process as in the conventional case, so that productivity is achieved. Can be improved.

Although the examples of the present invention have been described above, the present invention is not limited to the conditions and configurations described in the examples, and various changes can be made. For example, the applied voltage and pressure described in the examples. The numerical values such as are not limited to the described numerical values.

Further, in the description of the above-mentioned examples, the process of forming an Al alloy is described, but the process is not limited to the process of forming an Al alloy, and the process of forming a film of other metals such as TiN and Ti. It is also applied to the film formation process of magnetic films such as NiFe and PdPtMn, and further to the film formation process of oxides such as oxide superconductors or other insulators. ..

Further, in the above description of the embodiment, the ion cleaning is always performed during the standby time, but depending on the operation of the sputtering apparatus, the ion cleaning is performed at a fixed cycle, that is, "film formation standby". It may be performed in a cycle of ion cleaning standby film formation.

Further, in the above description of the embodiment, the ion cleaning is performed under the condition of the sputtering rate of 0, but the sputtering rate does not necessarily have to be 0. For example, if it is 1.5 times or less of the threshold energy, the target There is no problem because the consumption is small, and especially in the case of the above-mentioned cycle of "deposition standby ion cleaning standby film formation", the cleaning time is short, so it is within the range of 1.5 times or less of the threshold energy. The cleaning effect is enhanced when the ion energy is higher.

Further, although Ar gas is used in the above description of the embodiment, it is not limited to Ar gas, and a rare gas such as Xe gas or Kr gas may be used.

Further, in the above description of the examples, the gas for film formation and the gas for ion cleaning are the same gas type, but different gas types may be used.

Further, in the above description of the embodiment, the power supply for film formation and the power supply for cleaning are used as separate power supplies, but a single variable voltage power supply may be used.

Further, in the above description of the embodiment, although the DC voltage is applied to the shield in the ion cleaning step, it is not always necessary to apply the voltage to the shield, and further, a type of sputtering not provided with the shield. It also applies to devices.

Further, in the above description of the embodiment, the sputtering is performed using DC power, but it goes without saying that the sputtering may be performed using AC power.

Further, in the description of the above-described embodiment, the film forming apparatus is described as a sputtering apparatus, but the present invention is not limited to the sputtering apparatus, and other physical film forming is performed using a target such as a laser ablation apparatus. It is also applied to a depositing device, and when the device does not have a discharge electrode, a discharge electrode structure for cleaning may be provided so that the target becomes one electrode.

Further, in the description of the above-described embodiment, it is described as a single-target film forming apparatus, but it goes without saying that it is also applied to a film forming apparatus using a multi-target.

As an example of utilization of the present invention, the ion cleaning step of the target of the sputtering apparatus is typical, but it is also applied to other physical deposition apparatus that performs film formation using the target.

<figref num="1">It is explanatory drawing of the principle structure of this invention.</figref><figref num="2">It is a schematic block diagram of the sputtering apparatus of Example 1 of this invention.</figref><figref num="3">It is explanatory drawing of the sputtering process to the middle of Example 1 of this invention.</figref><figref num="4">It is explanatory drawing of the sputtering process to the middle after FIG. 3 of Example 1 of this invention.</figref><figref num="5">It is explanatory drawing of the sputtering process to the middle after FIG. 4 of Example 1 of this invention.</figref><figref num="6">It is explanatory drawing of the sputtering process after FIG. 5 of Example 1 of this invention.</figref><figref num="7">It is explanatory drawing of the film resistance dependence of the sheet resistance of the formed Al alloy film.</figref><figref num="8">It is explanatory drawing of the dependence of the reflectance of the formed Al alloy film on the number of film formations.</figref>

Code description

1 Film formation chamber 2 Target 3 Opposite electrode 4 Inactive ion 5 Shield 6 First power supply 7 Second power supply 11 Chamber 12 Target 13 Substrate stage 14 Wafer 15 Cryopump 16 MFC17 Shield 18 Ar ion 19 DC power supply 20 For film formation Power supply 21 Cleaning power supply