Substrate cleaning method, substrate cleaning device, and vacuum processing device

A substrate cleaning method for removing particles adhered to a substrate includes: acquiring particle information including diameters of the particles adhered to the substrate; controlling, based on the acquired particle information, a factor related to sizes of gas clusters having aggregates of atoms or molecules of a cleaning gas; ejecting the cleaning gas, at a higher pressure than a processing atmosphere where the substrate is provided, to the processing atmosphere and generating the gas clusters by adiabatic expansion; and removing the particles by irradiating the gas clusters in a perpendicular direction to a surface of the substrate. As a result, even if recesses for a circuit pattern are formed on the surface of the substrate, the particles in the recesses can be removed at a high removal rate.

FIELD OF THE INVENTION

The present invention relates to a technique for removing particles on a substrate by using a gas cluster.

BACKGROUND OF THE INVENTION

In a semiconductor manufacturing apparatus, a product yield is greatly affected by adhesion of particles to a substrate during a manufacturing process. To this end, the substrate is cleaned before or after the processing. However, it is required to develop a cleaning technique for simply and reliably removing particles while reducing damage to the substrate. As for a cleaning technique that is being currently studied and developed, there is suggested a technique for peeling off particles from a surface of a substrate by applying physical shearing force greater than adhesive force between the particles and the substrate. A technique using physical shearing force of a gas cluster is an example thereof.

The gas cluster is an aggregate of atoms or molecules obtained by ejecting a high-pressure gas in vacuum and cooling the gas to a condensation temperature by adiabatic expansion. During the cleaning of the substrate, particles are removed by irradiating to the substrate gas cluster with proper acceleration or no acceleration. The gas clusters are obliquely irradiated to the substrate. Therefore, in the case of removing the particles adhered to the pattern on the surface of the substrate, the pattern acts as a structure in view of the particles. Accordingly, it is difficult for the gas cluster disturbed by the structure to reach the particles, and this makes the removal of the particles in the recess difficult.

Further, the present inventors have discovered that the particle removal rate may vary even in the case of using the same gas cluster nozzle and the difference in the removal rate is related to diameters of the particles. When the particle removal rate is low, an acceleration voltage of gas clusters may be increased to increase kinetic energy. In that case, however, the surface of the substrate may be damaged.

In Japanese Patent Application Publication No. H4-155825, there is illustrated a drawing showing that clusters of a rare gas are perpendicularly incident on an object surface. However, a difference in a removal rate in accordance with diameters of particles is not described.

In addition, Japanese Patent Application Publication No. H11-330033 discloses a desired size of clusters for the case of removing micron particles or sub-micron particles. However, the object of the present invention and the solution thereto are not disclosed therein.

SUMMARY OF THE INVENTION

In view of the above, the present invention provides a technique capable of removing particles adhered to a surface of a substrate at a high removal rate.

In accordance with the present invention, there is provided a substrate cleaning method, for removing particles adhered to a substrate, including; acquiring particle information including diameters of the particles adhered to the substrate; controlling, based on the acquired particle information, a factor related to sizes of gas clusters having aggregates of atoms or molecules of a cleaning gas; ejecting the cleaning gas, at a higher pressure than a processing atmosphere where the substrate is provided, to the processing atmosphere and generating the gas clusters by adiabatic expansion; and removing the particles by irradiating the gas clusters in a perpendicular direction to a surface of the substrate.

In accordance with the present invention, there is provided a substrate cleaning device, for removing particles adhered to a substrate, including: a cleaning chamber where the substrate is provided and cleaned in a vacuum atmosphere; a nozzle unit configured to eject a cleaning gas, at a higher pressure than a processing atmosphere in the cleaning chamber, toward the substrate in the cleaning chamber and generating gas clusters having aggregates of atoms or molecules of the cleaning gas by adiabatic expansion; and a control unit configured to output a control signal for controlling a factor related to sizes of the gas clusters based on particle information including diameters of the particles adhered to the substrate, wherein the nozzle unit is set to irradiate the gas clusters in perpendicular direction to the surface of the substrate.

In accordance with the present invention, there is provided a vacuum processing apparatus, for performing vacuum processing on a substrate by using a vacuum processing module, including: the substrate cleaning device of the present invention; and a substrate transfer unit for transferring the substrate between the substrate cleaning device and the vacuum processing module.

Effect of the Invention

In the present invention, the particle information including the diameters of the particles adhered to the substrate is acquired, and the gas clusters are perpendicularly irradiated to the surface of the substrate by adjusting a factor related to the size of the gas clusters based on the acquired information. Therefore, the cleaning process can be performed by the gas clusters having the size corresponding to the diameters of the particles. As a result, even if a pattern recess is formed in the surface of the substrate, the particles in the recess can be removed at a high removal rate.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A vacuum processing apparatus including a substrate cleaning device in accordance with a first embodiment of the present invention will be described with reference to the drawings.FIG. 1is a top view showing an overall configuration of a vacuum processing apparatus1that is a multi-chamber system. In the vacuum processing apparatus1, a loading/unloading port12for mounting thereon a FOUP11that is an airtight transfer container accommodating therein25substrates, e.g., semiconductor wafers (hereinafter, referred to as “wafer”) is provided at, e.g., three locations, in a horizontal direction. An atmospheric transfer chamber13is provided along the arrangement of the loading/unloading ports12. A gate door GT that is opened/closed together with a cover of the FOUP11is provided at a front wall of the atmospheric transfer chamber13.

Two load-lock chambers14and15are airtightly connected to a side of the atmospheric transfer chamber13which is opposite to the loading/unloading ports12. Each of the load-lock chambers14and15includes a vacuum pump and a leakage valve (both not shown), so that an inner atmosphere thereof can be switched between an atmospheric atmosphere and a vacuum atmosphere. A notation G inFIG. 1denotes a gate valve (sluice valve). In the atmospheric transfer chamber13, a first substrate transfer unit16having a joint arm is provided to transfer a wafer W. When seen from a front side toward a rear side of the atmospheric transfer chamber13, a wafer inspection unit17that is a substrate inspection unit is provided at a right wall of the atmospheric transfer chamber13, and an alignment chamber18for adjusting eccentricity or an orientation of a wafer W is provided at a left wall of the atmospheric transfer chamber13. The first substrate transfer unit16transfers the wafer W with respect to the FOUP11, the load-lock chambers14and15, the wafer inspection unit17and the alignment chamber18. Accordingly, the first substrate transfer unit16is movable vertically and along the arrangement direction of the FOUP11(X direction inFIG. 1). Further, the first substrate transfer unit16is movable back and forth and rotatable about a vertical axis.

When seen from the atmospheric transfer chamber13, a vacuum transfer chamber2is airtightly connected to rear sides of the load-lock chambers14and15. The vacuum transfer chamber2is airtightly connected to a cleaning module3that is a substrate cleaning device and a plurality of, e.g., five in this example, vacuum processing modules21to25. In this example, the vacuum processing modules21to25are configured to perform sputtering or CVD (Chemical Vapor Deposition) for film formation including Cu wiring on a wafer W having recesses for forming a circuit pattern, e.g., via holes or grooves for filling Cu wiring.

The vacuum transfer chamber2includes a second substrate transfer unit26for transferring a wafer W in a vacuum atmosphere. The substrate transfer unit26transfers the wafer W between the load-lock chambers14and15, the cleaning module3, and the vacuum processing modules21to25. The second substrate transfer unit26has a multi-joint arm26acapable of moving back and forth and rotating about a vertical axis. The arm26acan be moved in a lengthwise direction (Y direction inFIG. 1) through a base26b.

Next, the wafer inspection unit17and the cleaning module3will be described. The wafer inspection unit17acquires particle information including diameters of particles adhered to the wafer W. The particle information shows, e.g., positions and sizes of the particles on the wafer W. As for the wafer inspection unit17, there may be used an apparatus capable of evaluating diameters of particles on a wafer surface, e.g., an optical type or electron beam type surface defect inspection device using regular reflection light or scattering light. It is also possible to use a scanning probe microscope such as a scanning electron microscope (SEM) or a scanning tunneling microscope (STM), an atomic force microscope (AFM) or the like.

Specifically, the wafer inspection unit17includes a Puma 9500 series dark-field pattern wafer inspection device manufactured by KLA Tencor Corporation, a 2830 series bright-field pattern wafer inspection device manufactured by KLA Tencor Corporation, a CG4000 series high resolution FEB measuring device manufactured by Hitachi High-Technologies Corporation, an RS6000 series defect review SEM device manufactured by Hitachi High-Technologies Corporation, and the like. The wafer that is a processing target of the present invention may have no pattern recess. In that case, as for the wafer inspection unit, there may be used, e.g., a SP3 dark-field non-pattern defect inspection device manufactured by KLA Tencor Corporation.

In the case of using such an inspection device, a loading/unloading port for transfer of a wafer W is provided, e.g., within an access range of the first substrate transfer unit16, and the wafer W may be transferred between an inspection region in the wafer inspection unit17and the first substrate transfer unit16through the loading/unloading port. The loading/unloading port of the inspection device may be omitted and the inspection device main body may be connected to the atmospheric transfer chamber13. The wafer inspection unit17detects a surface state of the wafer W, as shown inFIG. 2, for example. Accordingly, the particle information in which the positions and the sizes of the particles are associated each other is acquired. InFIG. 2, a reference numeral100denotes particles. The acquired particle information is transmitted to a control unit7to be described later.

Next, the cleaning module3will be described with reference toFIG. 3. The cleaning module3includes a cleaning chamber31that is a vacuum container where wafers W are accommodated and subjected to a deposit removal process. In the cleaning chamber31, a mounting table32for mounting thereon a wafer W is provided. At a central portion of a ceiling surface of the cleaning chamber31, an upwardly protruding portion39(e.g., of a cylindrical shape) is formed upward, and a nozzle unit4is provided as a gas cluster generation mechanism in the protruding portion39. InFIG. 3, a reference numeral34denotes a transfer port and a reference numeral35denotes a gate valve for opening/closing the transfer port34.

Although it is not illustrated, support pins (not shown) penetrating through holes formed in the mounting table32are provided, e.g., on a bottom surface of the cleaning chamber31at positions close to the transfer port35. An elevation mechanism (not shown) for vertically moving the support pins is provided below the mounting table32. The support pins and the elevation mechanism allow the wafer W to be transferred between the second substrate transfer unit26and the mounting table32. One end of a gas exhaust line36for vacuum-evacuating an atmosphere in the cleaning chamber31is connected to the bottom surface of the cleaning chamber31. The other end of the gas exhaust line36is connected to a vacuum pump38via a pressure control unit37such as a butterfly valve or the like.

The mounting table32is horizontally movable by a driving unit33so that the wafer W on the mounting table32is relatively scanned by the nozzle unit4. The driving unit33includes an X-axis rail33aextending horizontally along an X-axis direction on the bottom surface of the cleaning chamber31which is located below the mounting table32, and a Y-axis rail33bextending horizontally along a Y-axis direction. The Y-axis rail33bis movable along the X-axis rail33a, and the mounting table32is supported above the Y-axis rail33b. Further, the mounting table32includes a temperature control mechanism (not shown) for controlling a temperature of the wafer W on the mounting table32.

The nozzle unit4ejects a cleaning gas at a higher pressure than a processing atmosphere of the cleaning chamber31toward the wafer W in the cleaning chamber31, and gas clusters as aggregates of atoms or molecules of the cleaning gas are generated by adiabatic expansion. As shown inFIG. 4, the nozzle unit4has a substantially cylindrical pressure chamber41having an opening at a lower end thereof. The lower end portion of the pressure chamber41is formed as an orifice42. The gas diffusion portion43that is widened downward is connected to the orifice62. The opening diameter of the orifice42is, e.g., about 0.1 mm.

As described above, the nozzle unit4irradiates the gas clusters to the surface of the wafer W in a perpendicular direction to the surface of the wafer W. Here, “irradiation in a perpendicular direction” indicates a state, as shown inFIG. 4, in which an angle θ between a central axis L in the lengthwise direction of the nozzle unit4and the mounting surface of the mounting table32(the surface of the wafer W) is within a range of 90°±15°. When the gas clusters from the nozzle unit4are ionized while moving and the moving path thereof is bent by a bending mechanism, “perpendicularly irradiates” means a state in which the angle between the designed path and the surface of the wafer W is within the above range. The angle θ between the central axis L and the surface of the wafer W corresponds to an irradiation angle of the gas cluster in test examples to be described later.

In the example shown inFIG. 3, the mounting table32is moved to change the irradiation position of the gas clusters onto the wafer W. However, in the present invention, the nozzle unit4may be moved without moving the mounting table32. In that case, a moving mechanism capable of moving the nozzle unit4in the X and the Y direction may be provided at a ceiling portion of the cleaning chamber31, and a flexible gas supply line may be connected to a gas inlet port of the nozzle unit4.

One end of a gas supply line6extending through the ceiling surface of the cleaning chamber31is connected to the upper end of the pressure chamber41. The gas supply line6is connected to a CO2gas supply line62and a He gas supply line63via a pressure control valve61constituting a pressure control unit. The CO2gas supply line62is connected to a CO2gas supply source62bvia an opening/closing valve V1 and a CO2gas flow rate control unit62a. The He gas supply line63is connected to a He gas supply source63bvia an opening/closing valve V2 and a He gas flow rate control unit63a.

The CO2gas is a cleaning gas and generates gas clusters. He gas is an extrusion gas and hardly generates clusters. If CO2gas is mixed with He gas, the speed of the clusters generated by CO2gas is increased. Further, a pressure detection unit64for detecting a pressure in the gas supply line6is provided at the gas supply line6. The control unit7to be later described controls an opening degree of the pressure control valve61based on the detection value of the pressure detection unit64, so that the gas pressure in the pressure chamber41is controlled. The pressure detection unit64may detect a pressure in the pressure chamber41.

The pressure control based on the detection value of the pressure detection unit64may be carried out by gas flow rate control of the CO2gas flow rate control unit62aand the He gas flow rate control unit63a. Further, a gas supply pressure may be increased by using, e.g., a boosting unit such as a gas booster, between the pressure control valve61and each of the opening/closing valves V1 and V2, and may be controlled by the pressure control valve61.

As shown inFIG. 5, the vacuum processing apparatus1includes the control unit7including, e.g., a computer, for controlling an overall operation of the apparatus. The control unit7includes a CPU71, a program72, and a storage unit73. The program72has steps for executing an operation of the apparatus which correspond to vacuum processing of the vacuum processing modules21to25in addition to a cleaning process to be described later. The program72is stored in a storage medium, e.g., a hard disk, a compact disk, a magneto-optical disk, a memory card, a flexible disk or the like, and installed in the control unit7.

The particle information74acquired from the wafer inspection unit17is stored in the storage unit73. The particle information74is information in which positions on the wafer W are associated with sizes of particles. The sizes of the particles are defined as diameter ranges of the particles, e.g., a range greater than or equal to 20 nm and smaller than 40 nm, a range greater than or equal to 40 nm and smaller than 60 nm and the like, which are set by the wafer inspection unit17. InFIG. 5, the sizes are expressed as P1, P2 . . . and treated as normalized values. Further, the positions on the wafer W indicate coordinates on the wafer which are managed by the wafer inspection unit17. InFIG. 5, the positions on the wafer W are expressed as K1, K2, K3 . . . . The coordinates on the wafer may be determined as positions on an XY coordinate system having an X-axis that is a line passing through the center of the wafer W and a center of a notch formed at the wafer W to indicate a crystal direction and a Y-axis that is a line perpendicular thereto.

Based on the particle information74, the control unit7has a function of creating a data table75showing associations between particle diameter ranges of the particles and positions of the particles in such diameter ranges. The diameter ranges of the particles are assigned on the basis of preset sizes (diameters) of the gas clusters. InFIG. 5, the diameter ranges of the particles in the data table75are expressed as PA, PB, . . . and treated as normalized values.

As will be described later, the normalized particle diameters are associated with the gas cluster sizes suitable for removal of the particles. Further, the gas cluster sizes are correlated to gas supply pressures as a factor for determining the gas cluster sizes. Therefore, the data table75of the storage unit73includes data on relationship between the gas cluster irradiation positions on the surface of the wafer W and the gas pressures. The program72reads out the data and outputs to the driving unit33of the cleaning module3a control signal for sequentially moving the wafer W to the gas cluster irradiation positions. Further, the program72outputs an instruction signal (control signal) for controlling an opening degree of the pressure control valve61to determine the gas pressure during the irradiation of the gas cluster.

Hereinafter, an operation of the above embodiment will be described. When the FOUP11is mounted on the loading/unloading port12, a wafer W is taken out from the FOUP11by the first substrate transfer unit16. As shown inFIG. 6, the wafer W has pattern recesses (grooves and via holes)81for filling Cu wiring. Next, the wafer W is transferred to the alignment chamber18via the atmospheric transfer chamber13in an atmospheric atmosphere and aligned therein. Then, the wafer W is transferred to the wafer inspection unit17by the first substrate transfer unit16, and the particle information is acquired in the wafer inspection unit17. The acquired particle information is transmitted to the control unit7, and the control unit7creates the aforementioned data table75.

The wafer W inspected by the wafer inspection unit17is loaded into the load-lock chamber14or15set to an atmospheric atmosphere by the first substrate transfer unit16. Then, the atmosphere in the load-lock chamber14or15is switched to a vacuum atmosphere. Next, the wafer W is transferred to the cleaning module3by the second substrate transfer unit26and subjected to a particle removal process. In this example, when the wafer W inspected by the wafer inspection unit17is transferred to the cleaning module3, the wafer W is transferred from the wafer inspection unit17to the first substrate transfer unit16. Thus, the first substrate transfer unit16corresponds to a substrate transfer unit for transmitting the wafer W inspected by the wafer inspection unit17to the cleaning module3.

In the cleaning module3, a process of removing particles from the surface of the wafer W by using gas clusters is carried out. The gas clusters are aggregates of atoms or molecules of a gas and generated by supplying a gas at a higher pressure than a processing atmosphere where the wafer W is disposed to the processing atmosphere and cooling the gas to a condensation temperature by adiabatic expansion. A processing pressure in the cleaning chamber31of the processing atmosphere is set to a vacuum atmosphere of, e.g., 0.1 Pa to 100 Pa, and a cleaning gas (CO2gas) is supplied to the nozzle unit4at a pressure of, e.g., 0.3 MPa to 5.0 MPa. When the cleaning gas is supplied to the processing atmosphere of the cleaning chamber31, the cleaning gas is cooled to a level lower than the condensation temperature by abrupt adiabatic expansion. As a consequence, as shown inFIG. 4, molecules201are bonded together by Van der Waals force, thereby forming gas clusters200as aggregates of the molecules201. In this example, the gas clusters200are neutral. For example, a single gas cluster including 5×103atoms (molecules) has a size of about 8 nm. Therefore, it is preferable to obtain a gas cluster of 5×103atoms (molecules) or above.

The gas clusters200generated from the nozzle unit4are irradiated toward the wafer W in a perpendicular direction to the surface of the wafer W. As shown inFIG. 6, the gas clusters200enter the recesses81for a circuit pattern of the wafer W and blow away the particles100in the recesses81. As a consequence, the particles100are removed.

FIGS. 7A to 7DandFIGS. 8A to 8Dschematically show the state in which the particle100on the wafer W is being removed by the gas cluster200.FIG. 7shows the case in which the gas cluster200collides with the particle100on the wafer W. In that case, as shown inFIG. 7A, the gas cluster200is irradiated to the surface of the wafer W in a perpendicular direction to the surface of the wafer W and is highly likely to collide with the particle100from an oblique upper side. If, as shown inFIG. 7B, the gas cluster200collides with the particle100in an offset state (the state in which the center of the gas cluster200and the center of the particle100are not aligned when seen from the top), as shown inFIG. 7C, a horizontal moving force is applied to the particle100by the shock from the collision. As a result, the particle100is peeled off from the surface of the wafer W and blown away in a lateral direction or in an obliquely upward direction.

As shown inFIG. 8A, the particle100can also be removed by irradiating the gas cluster200not directly to the particles100but to the vicinity of the particles100. When the gas cluster200collides with the wafer W, the molecules201of the gas cluster200are decomposed and diffused in a horizontal direction (seeFIG. 8B). At this time, a region of a high kinetic energy density is shifted in a horizontal direction, so that the particle100is peeled off from the wafer W and blown away (seeFIGS. 8C and 8D). In this manner, the particles100are sputtered from the recesses81to scatter in the cleaning chamber31of the vacuum atmosphere and to be discharged to the outside of the cleaning chamber31through the gas exhaust line36.

Hereinafter, the size of the gas cluster and the particle cleaning performance will be described. As clearly can be seen from the test examples to be described later, the size of the gas cluster200which is suitable for the cleaning varies depending on diameters of the particles100. If the gas clusters200are excessively larger than the particles100, a sufficient removal performance is not obtained and the pattern is excessively damaged. On the contrary, if the gas clusters200are excessively smaller than the particles100, physical peeling force sufficient for removal is not applied, so that sufficient removal performance is not obtained. Therefore, it is preferable to set the size of the gas cluster to be about 0.2 to 2 times greater than the diameter of the particle. As clearly can be seen from the following test examples, the size of the gas cluster depends on the supply pressure of CO2gas as a cleaning gas. Hence, as described above, the control unit7sets the supply pressure of CO2gas based on the particle information acquired from the wafer inspection unit17in order to obtain a desired size of the gas cluster200. The supply pressure of the CO2gas is controlled by, e.g., an opening degree of the pressure control valve61.

In this manner, in the cleaning module3, the particles100are removed by locally irradiating the gas clusters200from the nozzle unit4in a state where the pressure control valve61is controlled in accordance with the sizes of the particles on the wafer W.

As described above with reference toFIG. 5, the particle information includes information on the adhesion positions of the particles on the wafer W (K1, K2 and the like shown inFIG. 5). The control unit7stores data on associations between particle sizes and particle positions. If the particle sizes are the same, the irradiation condition becomes the same. Therefore, the gas clusters are irradiated to the particle positions corresponding to the particle sizes under he same irradiation conditions. Specifically, if the particle size is PA, the gas clusters are irradiated to the positions K1, K2, K4, . . . under the irradiation conditions suitable for the removal of the particles having the particle size PA. Then, the gas cluster irradiation conditions are changed, and the gas cluster is irradiated to the positions K3, K5, . . . of the particle size PB under the irradiation conditions suitable for removal of the particles having the particle size PB. In this manner, the cleaning process is carried out.

The wafer W from which the particles100have been removed in the cleaning module3is transferred to the vacuum processing module for performing, e.g., sputtering via the vacuum transfer chamber2by the second substrate transfer unit26. Then, a barrier layer made of, e.g., titanium (Ti) or tungsten (W), is formed in the recesses81. Next, the wafer W is transferred to the vacuum processing module for performing CVD, and Cu is filled in the recesses81to form Cu wiring, for example. Thereafter, the wafer W is loaded into the load-lock chamber14or15set to the vacuum atmosphere by the second substrate transfer unit26. Then, the atmosphere in the load-lock chamber14or15is switched to the atmospheric atmosphere. Next, the wafer W is transferred to the atmospheric transfer chamber13and returned to the original FOUP11on the loading/unloading port12by the first substrate transfer unit16.

In accordance with the above embodiment, the particle information including the diameters of the particles100and the adhesion positions of the particles100is acquired by inspecting the surface of the wafer W. Since the gas clusters200having sizes that have been adjusted to correspond to the sizes of the particles100based on the particle information are irradiated to the surface of the wafer W, the performance of removing the particles100adhered to the wafer W can be improved. Further, the gas clusters200are irradiated to the wafer W in a perpendicular direction to the surface of the wafer W, so that the gas clusters200can be reliably irradiated into the recesses81without being disturbed by wall portions defining the recesses81. Accordingly, the gas clusters200reach the particles100in the recesses81, and the particles100can be removed at a high removal rate.

Since the particles can also be removed by irradiating the gas clusters200to the vicinity of the particles100, the irradiation amount (dose amount) of the gas clusters200can be decreased. This is because when the gas clusters200are irradiated to a certain point, a plurality of particles100near the irradiation point can be removed. Hence, the number of irradiated gas clusters200can be decreased.

This suppresses pressure increase of the processing atmosphere due to irradiation of the gas clusters, so that the pressure in the cleaning chamber31can be maintained at a low level. The speed of the gas clusters200is high under such a low pressure, so that the gas clusters200collide with the wafer W or the particles100at a high speed and the impact force at the time of the collision becomes large. Therefore, the breaking force at the time of decomposition of the gas cluster200into the molecules201becomes large, and the energy applied to the collided particles100and the particles100adjacent thereto is increased. By reducing the irradiation amount of the gas clusters200, the speed of the gas clusters200can be increased, which contributes the particle removal. From this, it is clear that the control of the irradiation amount of the gas clusters200is effective for the particle removal.

Meanwhile, the removal rate varies depending on the sizes of the particles100. In the case of performing the cleaning using a conventional two-fluid spray method, when the size of the particle100is smaller than 200 nm, the removal rate is decreased. In the two-fluid spray method, particles are removed by injecting a mixture of N2gas and waterdrops of several tens of μm to the wafer in a spray shape.

As clearly can be seen from the test examples to be described later, the particle removal by the irradiation of the gas clusters200is effective even for the particles100having a size of 12 nm to 49 nm. According to the test examples, the irradiation amount of the gas clusters is preferably in order of 1011to 1015/cm2. Here, the irradiation amount of the gas clusters indicates the number of gas clusters irradiated per unit area. The irradiation amount of the gas clusters is measured by the following measuring method.

First, the generated gas clusters are ionized and collide with a Faraday cup arranged against the moving direction of the gas cluster. At this time, the number of the gas clusters is calculated by measuring a current value of the Faraday cup.

Next, there will be described the case of removing particles adhered to the wafer W before and after the vacuum processing in the cleaning module3. In this example, the vacuum processing module performs etching or ashing. The wafer W accommodated in the FOUP11has on a surface thereof, e.g., a patterned photoresist mask. After the particle information is acquired by the wafer inspection unit17, the wafer W is aligned and transferred to the cleaning module3via the load-lock chamber14or15and the vacuum transfer chamber2. Then, the particles are removed as described above. Next, the wafer W is sequentially transferred to the vacuum processing module for performing etching and to the vacuum processing module for performing ashing. In this manner, as shown inFIG. 6, the pattern having the recesses81is formed. The reason of removing the particles on the wafer W before the etching is because the particles are considered as a part of the photoresist mask and cause etching defects.

If necessary, after the etching or the ashing, the particles may be removed again by the cleaning module3. In that case, the wafer W that has been etched or ashed is transferred to the first substrate transfer unit16via the vacuum transfer chamber2and the load-lock chamber14or15and then to the wafer inspection unit17, and the particle information is obtained. Then, the wafer W is transferred to the second substrate transfer unit26via the atmospheric transfer chamber13and the load-lock chamber14or15and then to the cleaning module3, and the particles adhered due to the etching are removed. The cleaned wafer W is transferred to the first substrate transfer unit16via the vacuum transfer chamber2and the load-lock chamber14or15and returned to the original FOUP11.

The wafer inspection unit17may be connected to the vacuum transfer chamber2at a location different from the cleaning module3. As for the wafer inspection unit17, a vacuum gauge device such as SEM (scanning electron microscope) or the like may be used. In this case, the substrate transfer unit for transferring the wafer inspected by the wafer inspection unit to the cleaning module3is also used as the substrate transfer unit for transferring the substrate between the washing module3and the vacuum processing module. The wafer inspection unit17may be used as a standalone device without being built in the vacuum processing apparatus. In that case, the acquired measurement information is transmitted to the control unit4.

In the present invention, the particle information may be acquired by inspecting particles on a front wafer W in a lot and all the wafers W in the lot may be subjected to the particle removing treatment in the cleaning module3by using the same gas cluster irradiation condition set based on the acquired particle information. Otherwise, the particle information may be acquired by inspecting particles on all the wafers W in a lot and each of the wafers in the lot may be subjected to the particle removing treatment by using gas cluster irradiation conditions set based on the corresponding particle information.

In the above embodiment, the gas clusters are locally irradiated to the particle adhesion region on the surface of the wafer W, but, the present invention is not limited thereto. If the amount of the particles is large, the particle adhesion region may be normalized as, e.g., divided rectangular regions S of a predetermined size, on the basis of the particle sizes (normalized values by the range of the particle sizes). As shown inFIG. 9, for example, when the surface of the wafer W is divided in a checkerboard pattern and particles are included in a divided area S, there may be employed a method for selecting a gas cluster size in accordance with a particle size in the divided area S and irradiating gas clusters to the divided area S.

The gas clusters may be irradiated to the entire surface of the wafer W. In this case, the diameters of the particles on the wafer W are detected and the gas cluster size is controlled to correspond to the particle diameters. Depending on diameters of the particles, the gas clusters are controlled to have a plurality of sizes, and the entire surface is irradiated with the gas clusters of each size, for example.

Hereinafter, a second embodiment of the present invention will be described with reference toFIG. 10. In this embodiment, a temperature of CO2gas is controlled as a factor of controlling a gas cluster size. In this example, a temperature control chamber91is provided, e.g., so as to surround the nozzle unit4and the periphery of the gas supply line6near the nozzle unit4. In the temperature control chamber91, a temperature control medium supply line92runs along the sidewall of the pressure chamber41and opens near the bottom of the pressure chamber41. A chiller93is connected to the temperature control medium supply line92, and a temperature control medium controlled to a predetermined temperature by the chiller93is supplied to the temperature control chamber91through the temperature control medium supply line92. A supply line94for circularly supplying the temperature control medium in the temperature control chamber91to the chiller93is provided in the temperature control chamber91. InFIG. 10, reference numerals95and96denote a temperature detection unit and a flow rate control valve, respectively. In the present embodiment, the temperature control chamber91, the temperature control medium supply line92and the chiller93forms a temperature control unit for controlling a temperature of CO2gas.

As can be clearly seen from the test examples to be described later, the size of the gas cluster200is correlated with the temperature of the cleaning gas (CO2gas) supplied to the pressure chamber41. As the gas temperature is decreased, the size of the gas cluster200is increased. Therefore, in this example, the size of the gas cluster200is determined in accordance with the diameter of the particle100on the surface of the wafer W and, then, the chiller93is controlled to correspond to the determined size. In other words, the temperature of the temperature control medium in the temperature control medium circulation path, e.g., the supply line94, is detected by the temperature detection unit95. The temperature of the temperature control medium is controlled by the chiller93based on the detection value, and the temperature control medium of the controlled temperature is circulated around the nozzle unit4and the gas supply unit6. In this manner, in the second embodiment, the gas cluster size is controlled by adjusting the temperature of CO2gas. The temperature of CO2gas may be adjusted by controlling the supply amount of the temperature control medium by controlling the opening degree of the flow rate control valve96.

In the present embodiment as well as the first embodiment, the gas clusters200having sizes controlled in accordance with the diameters of the particles100are irradiated to the particles100, so that the performance of removing the particles100adhered to the wafer W can be improved. The gas clusters200are perpendicularly irradiated to the wafer W, so that the particles100in the recesses81can be removed at a high removal rate. In the present invention, the acceleration of the gas clusters200may be controlled by the mixing ratio of CO2gas and He gas. He gas hardly generates clusters and increases the speed of the clusters generated by the CO2gas when He gas is mixed with CO2gas. Therefore, when the amount of He gas mixed with the CO2gas is increased, the acceleration of the gas clusters200is increased. Accordingly, proper mixing ratios of He gas may be obtained in advance on the basis of gas cluster sizes and the mixing ratio of He gas may be controlled to the predetermined level during the cleaning of particles. For example, the control unit7may have data on correlation between a mixing ratio of CO2gas and He gas and a gas cluster size, the flow rate of CO2gas being fixed, and controls the mixing ratio (e.g., the flow rate of He gas) in accordance with the gas cluster size.

Further, the size of the gas cluster may be controlled by controlling both of the pressure of the cleaning gas and the temperature of the cleaning gas.

Hereinafter, a third embodiment of the present invention will be described with reference toFIG. 11. In the third embodiment, gas clusters are ionized and accelerated by an acceleration voltage. Between the nozzle unit4and the mounting unit32, a differential gas exhaust unit51, an ionization unit52, an acceleration unit including an acceleration electrode53, and a magnet54are provided in that order from the nozzle unit4side. The differential gas exhaust unit51has a skimmer51aand a separation plate51bhaving at a center thereof an opening through which a cluster beam passes. A region between the skimmer51aand the separation plate51bis exhausted by a dedicated vacuum pump (not shown) and set to a high vacuum state.

The ionization unit52has a filament, an anode52aand a drawing electrode52b. By applying an ionizing voltage between the filament and the anode52a, the clusters passing through the anode52aare ionized by collision with electrons. A negative potential is applied from the DC power supply52cto the drawing electrode52b, so that cluster ions are drawn. The acceleration electrode53is connected to a voltage variable DC power supply55. The acceleration electrode53has an acceleration voltage by the application of a positive high voltage with respect to the potential of the wafer W, and accordingly the cluster ions are accelerated toward the wafer W. Therefore, the mounting table32serves as, e.g., a ground potential. The magnet54removes monomer ions included in the cluster ions.

In the third embodiment as well as the device shown inFIG. 3(non-ionization type), the factor related to the cluster size is controlled in accordance with the particle information. However, when higher kinetic energy is required, the kinetic energy can be increased by accelerating the gas clusters by the ionization unit provided below the nozzle unit4. Therefore, the DC voltage (acceleration voltage) is controlled by the control unit7, and the optimal cluster energy can be obtained. Further, a desired acceleration voltage may be obtained in advance on the basis of cluster sizes, for example, and the acceleration voltage may be controlled to the predetermined level during the cleaning of the particles.

Further, a plurality of nozzle units may be provided for each particle size. Such a case may be applied to the device shown inFIG. 3(non-ionization type) or the device shown inFIG. 11(ionization type). In such a configuration, for example, the particle size is set to two levels (Pα and Pβ). The gas clusters are irradiated from one of the nozzle units to particles having the particle size Pα under the irradiation condition suitable for the removal of the particles having the particle size Pα. Further, gas clusters are irradiated from the other nozzle unit to particles having the particle size Pβ under the irradiation condition suitable for the removal of the particles having the particle size Pβ. Accordingly, the particles are removed. Alternatively, particles of different diameters may be removed by each of the nozzle units.

Hereinafter, a fourth embodiment of the present invention will be described. In this embodiment, the wafer inspection unit is connected to the vacuum transfer chamber2. In this case, for example, the wafer inspection unit17may be combined with the cleaning module3as shown inFIG. 12. In the example shown inFIG. 12, the cleaning chamber31is also used as the inspection chamber. An accommodating member82accommodating therein the wafer inspection device is provided on the top wall30of the cleaning chamber31and near the protruding portion39. InFIG. 12, a reference numeral30adenotes an inspection opening formed in the top wall30, and a space below the opening30aserves as an inspection region. In this example, the mounting table32is positioned at the inspection region below the accommodating member82, and the particles are inspected through the opening30a. Then, the mounting table32is positioned below the protruding portion39, and the particles are removed.

TEST EXAMPLES

Next, test examples performed to examine the effects of the present invention will be described.

Test Example 1: Relationship Between Kinetic Energy and Particle Removal Rate

In the cleaning module3shown inFIG. 11, when performing the particle removal process by using gas clusters of CO2gas, the particle removal rate was evaluated while varying kinetic energy. At this time, a processing condition was set as follows, and the kinetic energy was varied by controlling a voltage (acceleration voltage) applied to the acceleration electrode53. Next, the number of particles was detected by monitoring a wafer surface by using the SEM before and after cleaning to obtain the removal rate.

Cleaning target substrate: single crystal silicon wafer

Supply pressure of CO2gas into pressure chamber: 2.0 MPa

Irradiation amount of gas cluster: 3×1014/cm2

Particle: SiO2having a particle diameter of 23 nm

The results are shown inFIG. 13. As will be described later, the kinetic energy of the gas clusters is not fixed. InFIG. 13, the horizontal axis represents the kinetic energy with a peak intensity and the vertical axis represents a particle removal rate. The kinetic energy referred in the following test examples indicates kinetic energy with a peak intensity. It is clear fromFIG. 13that the kinetic energy and the particle removal rate are positively correlated and the removal rate is increased as the kinetic energy is increased. At this time, it has been confirmed that when the cluster had a kinetic energy of 50 keV, the removal rate was 92%. From this, it is clear that by setting the kinetic energy to 50 keV/cluster, a sufficient force to peel off SiO2particles having a particle diameter of 23 nm can be obtained. Here, the gas clusters having a kinetic energy of 50 keV/cluster were irradiated to the wafer W having a pattern formed thereon and the pattern was monitored by the SEM. As a monitoring result, it was found that there was no damage.

When the kinetic energy was 25 keV/cluster, the removal rate of particles (SiO2particles) having a diameter of 23 nm was about 11%. Therefore, it is expected that the removal rate of 90% or above can be acquired by setting the irradiation amount to be ten times greater than 3×1014/cm2. From the above, the present inventors have found that it is preferable to set the irradiation amount of the gas cluster per 1 cm2in order of 1015or less.

Test Example 2: Removal of Particles in Pattern

In the cleaning module3shown inFIG. 11, the particles in a pattern were removed by the gas clusters of CO2gas and a particle removal rate was evaluated. At this time, a processing condition was set as follows, and removal efficiency was evaluated by monitoring a wafer surface by the SEM before and after cleaning.

Supply pressure of CO2gas into pressure chamber: 2.0 MPa

Irradiation angle of gas cluster: 90°

Irradiation amount of gas cluster: 3×1014/cm2

FIGS. 14A and 14Bshow traced images of a part of a pattern captured by the SEM.FIG. 14Ashows a state of a portion before the gas clusters are irradiated thereto, andFIG. 14Bshows a state of the portion after the gas clusters have been irradiated thereto. In the gas cluster non-irradiation portion, there were the particles100on the bottom portion or the side surfaces of the recesses81of the pattern. On the contrary, in the gas cluster irradiation portion, there were no particles100. Accordingly, it was recognized that the particles100in the recesses81of the pattern were removed at a high removal rate by setting the supply pressure of CO2gas to 2.0 MPa, setting the kinetic energy of the gas clusters to 40 keV/cluster and irradiating the gas clusters perpendicularly to the wafer W.

Test Example 3: Relationship Between Gas Cluster Size and Pressure

In the cleaning module3shown inFIG. 11, the gas clusters of CO2gas were generated at various supply pressures of the CO2gas supplied to the pressure chamber41, and the gas cluster sizes were evaluated. At this time, the supply pressure of the CO2gas was set to 1 MPa, 2 MPa and 4 MPa, and the cluster size distribution, i.e., the relationship between the number of constituent molecules of the clusters and intensity, was obtained by using a time-of-flight method and a theoretical formula. The intensity indicates the number of clusters having the number of constituent molecules.

The time-of-flight method is a mass selection method using a feature that ions accelerated by the same energy have different flight velocities depending on mass. On the assumption that a mass of ion is m, an acceleration voltage is Va, charge of ion is q and a flight distance is L, flight time t of ion is calculated by the following equation. Since L and Va are known values, m/q can be obtained by measuring t. Specifically, the gas clusters are ionized and a current is detected by an MCP detector provided at a cluster irradiation region.
t=Lx{m/(2qVa)}1/2

The result thereof is shown inFIG. 15. InFIG. 15, the horizontal axis represents the number of CO2molecules forming a single gas cluster, and the vertical axis represents the intensity. As the supply pressure of CO2gas is increased, the intensity distribution and the peak value are shifted toward a direction in which the number of molecules forming a single gas cluster is increased. When the number of molecules forming a single gas cluster is increased, the cluster size is increased. Therefore, the gas cluster size can be controlled by the gas pressure.

Test Example 4: Removal Performance Depending on Particle Diameter

In the cleaning module3shown inFIG. 11, the particle removal process was performed for the various particle diameters by using gas clusters of CO2gas, and the particle removal rate was evaluated. At this time, there were used four substrates (bare wafers) to which particles having diameters of 12 nm, 23 nm, 49 nm, and 109 nm were adhered, and the particle removal rate was evaluated while setting the size of the gas cluster to 26 nm. Processing conditions were set as follows, and the evaluation was carried out while setting a different kinetic energy for each substrate. The particle removal rate was obtained by monitoring the wafer surfaces by using the SEM before and after cleaning.

Cleaning target substrate: single crystal silicon wafer

Supply pressure of CO2gas into pressure chamber: 2.0 MPa

Irradiation angle of gas cluster: 90°

Irradiation amount of gas cluster: 3×1012/cm2

The results are shown inFIG. 16. InFIG. 16, the horizontal axis represents the kinetic energy, and the vertical axis represents the particle removal rate. Data of the particles having diameters of 12 nm, 23 nm, 49 nm and 109 nm are plotted as Δ, □, ●, and ∘, respectively. From this, in the case of the particles having diameters of 12 nm, 23 nm and 49 nm, it was found that the particle removal rate was improved as the kinetic energy was increased and, the particle removal rate of about 70% or above can be acquired by setting the kinetic energy to 50 keV/cluster or above. On the other hand, in the case of the particles having a diameter of about 109 nm, the particles cannot be completely removed even by applying high kinetic energy of 90 keV/cluster. Therefore, if gas clusters having relatively excessively smaller sizes than the particle sizes are used, the particles cannot be removed. This proves that it is effective to use gas clusters having a size corresponding to the particle diameter. Further, it is preferable to set the gas cluster size (diameter) to be 0.2 to 2 times the particle size (diameter).

According to this test example, when the irradiation amount of the gas cluster is 3×1012/cm2, the particles having sizes of 12 nm, 23 nm, and 49 nm can be removed. The following can be understood based on a mechanism that the irradiation of gas clusters to the vicinity of particles can result in removal of the particles and a fact that a plurality of particles near the irradiation point can be removed. Specifically, when the irradiation amount of gas clusters per 1 cm2is in order of 1011or above, the particles of the above sizes can be removed. Meanwhile, the increase in the irradiation amount of the gas clusters leads to the increase in the number of gas clusters irradiated to the particles, so that the particles can be effectively removed. Accordingly, in accordance with the result of the test example 1, the particles smaller than or equal to 49 nm or less can be effectively removed by setting the irradiation amount of gas clusters per 1 cm2to in order of 1011to 1015.

Test Example 5: Relationship Between Gas Cluster Size and Temperature

FIG. 17shows relationship between a temperature of the nozzle unit4and kinetic energy of the gas clusters at different pressures in the case of generating gas clusters of CO2gas. When the temperature of the nozzle unit4is decreased, the kinetic energy of the gas clusters is increased and, hence, the gas cluster size is increased. Accordingly, the gas cluster size can be controlled by adjusting the gas temperature.