SPUTTERING DEVICE

Abstract: A sputtering device includes a vacuum chamber (VC), a target (16) disposed in the vacuum chamber (VC), a protection plate (15) formed to surround the target (16) with a space therebetween, having an opening formed in front of the target (16), a substrate holder (18) for holding a semiconductor wafer substrate (19) and substantially closing the opening of the target (16) in cooperation with the semiconductor wafer substrate (19), and an A.C. power source (20) for striking the target (16) with charged particles to emit target material when semiconductor wafer substrate (19) is set in front of the target (16), thereby depositing to target material thereon as a sputtering film. The sputtering device further includes a temperature sensor (SR), a heater unit (21, 22) and heater controller (HC) to heat at least the protection plate (15) to a specified tem­ perature and maintaining the specified temperature.

Description: This invention relates to a device for manufacturing semiconductor devices, and more particularly to a sputtering device for depositing insulation or metal material on a semiconductor wafer substrate. Conventionally, a high speed sputtering device for effecting sputtering process for each semiconductor wafer substrate is known (cf. JP-Journal: "Semicon News", 1986, Vol. 5, pages 34 and 35). Fig. 1 shows the internal structure of this type of high speed sputtering device. In the high speed sputtering device, the sputtering process is repeatedly effected in vacuum chamber VC which is kept in a low pressure condition. The pressure in vacuum chamber VC is reduced with cathode case CS inserted in cathode flange 11 and cathode flange 11 set in contact with chamber wall 13 via O-ring 12. Target 16 is previously mounted on backing plate 17 in vacuum chamber VC with an angle of approx. 85° which is close to right angles with respect to a horizontal plane. Further, semiconductor wafer substrate 19 is horizontally carried in pressure-reduced vaccum chamber VC, and is set onto substrate holder 18 disposed in a position corresponding to target 16. Substrate holder 18 is raised as shown by an arrow so as to set semiconductor wafer substrate 19 in parallel with target 16. The sputtering process is effected after semiconductor wafer substrate 19 is set in the above-described preset sputtering position. In the sputtering process, a sputtering film is formed by striking Ar⁺ ions to target 16 in the magnetron discharging atmosphere and attaching sputtering particles emitted from target 16 to semiconductor wafer substrate 19. In a case where a sputtering film of SiO₂ is formed, for example, the sputtering film normally grows at a rate of 150 nm/min. The sputtering particles are emitted from target 16 in various directions except those towards wafer substrate 19 in the sputtering process. Assume that sputtering particles are attached to chamber wall 13, for example, to form a sputtering film thereon. Then, part of the sputtering film may be peeled off from chamber wall and will drop as dust particles onto wafer substrate 19 which is carried in for the succeeding sputtering process, thus contaminating the surface of wafer substrate 19. For this reason, dome-shaped protection plate 15 is disposed to surround the peripheral region of target 16 in vacuum chamber VC. Protection plate 15 has opening 15A formed at the center thereof, and opening 15A is substantially closed by wafer substrate 19 and the periphery of substrate holder 18 when wafer substrate 19 is set in the preset sputtering position. In this case, sputtering particles emitted in directions different from those towards wafer substrate 19 will form sputtering films on protection plate 15 and the outer periphery of substrate holder 18. When part of the sputtering film is attached as dust particles to wafer substrate 19 in the sputtering process, the property of a sputtering film formed on wafer substrate 19 will be changed. For example, when the sputtering film is an insulation film, current leak, reduction is the withstanding voltage and the like may occur in the manufactured semiconductor device. In this case, in order to prevent part of the sputtering film peeled off from protection plate 15 and substrate holder 18 from dropping directly onto wafer substrate 19, wafer substrate 19 se set at an angle close to the right angles with respect to the horizontal plane. However, in this type of sputtering device, part of the sputtering film is peeled off from protection plate 15 and substrate holder 18 and then deposited on the bottom. In is impossible to sufficiently prevent the deposited sputtering parts from being whirled up and attached as dust particles to wafer substrate 19 in the succeeding sputtering process. Further, since the sputtering film grows at high speed on protection plate 15 and substrate holder 18 as well as on wafer substrate 19, it becomes necessary to frequently replace protection plate 15 and substrate holder 18 for cleaning. As a result, the operability of the sputtering device will be lowered. An object of this invention is to provide a sputtering device which can reduce dust particles attached to the semiconductor wafer substrate in the sputtering process. The object can be attained by a sputtering device comprising a vacuum chamber, a target disposed in the vacuum chamber, a protection member formed to surround the target with a space therebetween and having an opening formed in front of the target, a substrate holder for holding the semiconductor wafer substrate and substantially closing the opening of the protection member in cooperation with the semiconductor wafer substrate, a discharging circuit for causing target material to be emitted from the target when the semiconductor wafer substrate is set in front of the target, thereby depositing the target material on the semiconductor wafer substrate as a sputtering film, and a heating section for heating at least the protection member to a specified temperature and maintaining the specified temperature. In the above sputtering device, even when the target material is deposited on the protection member and substrate holder to form sputtering films thereon, the sputtering films will hardly be peeled off as dust particles. In general, the temperature of the protection member will start to rise when the discharging circuit is started to operate and fall at the end of the operation. For example, when the temperature of the protection member is changed according to the operation condition of the discharging circuit, the sputtering film formed on the protection member may be peeled off by the stress due to the difference between the thermal expansion coefficients of the target material and the material constituting the protection member. However, in the above sputtering device, the temperature of the protection member is prevented from being set to be lower than the specified temperature. Thus, the range of temperature variation becomes small and peel-off the sputtering film will be prevented. If the specified temperature is set to be higher than the maximum temperature attained by the operation of the discharging circuit unit, the sputtering film will hardly be peeled off even when it continuously grows on the protection member. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a cross sectional view showing the internal structure of the conventional high speed sputtering device; Fig. 2 is a cross sectional view showing the internal structure of a high speed sputtering device according to a first embodiment of this invention; Fig. 3 is a graph showing the relation between the thickness of an SiO₂ film and the number of dust particles to illustrate the effect of the high speed sputtering device shown in Fig. 2; Fig. 4 is graph showing variation in temperature and variation in the number of dust particles before and after the sputtering process to illustrate the effect of the high speed sputtering device shown in Fig. 2; Fig. 5 is a cross sectional view showing the internal structure of a high speed sputtering device according to a second embodiment of this invention; and Fig. 6 is a cross sectional view showing the internal structure of a high speed sputtering device according to a third embodiment of this invention. There will now be described a high speed sputtering device for formation of an insulation film according to a first embodiment of this invention with reference to Figs. 2 to 4. Fig. 2 is a diagram showing the cross sectional structure of the sputtering device. Portions corresponding to those in the prior art device shown in Fig. 1 are denoted by the same reference numerals. The sputtering device includes cathode flange 11, O-ring 12, chamber wall 13, chamber side protection plates 14A and 14B, cathode case CS, backing plate 17, substrate holder 18, A.C. power source 20 and heater controller HC. Cathode flange 11, O-ring 12, chamber wall 13 and backing plate 17 are combined to constitute vacuum chamber VC in the same manner as in the conventional case. Chamber side protection plates 14A and 14B are respectively arranged on the upper and side portions of chamber wall 13. The sputtering device further includes three sputtering units each including target side protection plate 15, target 16, first and second heater units 21 and 22, and temperature sensors SR1 and SR2. In Fig. 2, only first sputtering unit SU which is one of the three sputtering units is shown and the other two sputtering units are not shown. Target 16 is formed of high purity quartz and mounted on backing plate 17 functioning as a target electrode. Backing plate 17 is mounted on the top of cathode case CS. Permanent magnet MG is embedded in cathode case CS. The pressure of vacuum chamber VC is reduced after cathode case CS is set in the slot of cathode flange 11 and cathode flange 11 is set in contact with chamber wall 13 via O-ring 12. At this time, target 16 is held at an angle of 85° with respect to the horizontal plane in vacuum chamber VC. Protection plate 15 is formed in a dome shape, and mounted on cathode flange 11 to surround target 16 and the peripheral portion thereof. Protection plate 15 has an opening OP which is slightly larger than the diameter (12.7 cm (5 inches)) of semiconductor wafer substrate 19. Opening OP is set to face target 16. Protection plate 15 and substrate holder 18 are formed of stainless steel, and target side surfaces of protection plate 15 and substrate holder 18 are entirely coated with quartz films 15A and 18A having substantially the same thermal expansion coefficient as the target material. Heater units 21 and 22 are fixed on chamber wall side surfaces of protection plate 15 and substrate holder 18. Temperature sensors SR1 and SR2 are used to measure the temperature of protection plate 15 and substrate holder 18 and generate output signals, respectively. Heater controller HC controls heater units 21 and 22 so as to heat protection plate 15 and substrate holder 18 to a preset temperature which is supplied from the outside and maintain the preset temperature based on the output signals from sensors SR1 and SR2. A.C. power source 20 is used to supply power to target 16 for each sputtering process to form a sputtering film on semiconductor wafer substrate 19. Semiconductor wafer substrate 19 is set in a 24-sheets wafer carrier (not shown) and carried into pressure-reduced vacuum chamber VC. Then, semiconductor wafer substrate 19 is taken out of the wafer carrier, horizontally fed to substrate holder 18 disposed in front of target 16, and set on substrate holder 18. Substrate holder 18 is raised as shown by an arrow in Fig. 2 to set semiconductor wafer substrate 19 to a specified position in which it is set in parallel with target 16. The sputtering process is started after semiconductor wafer substrate 19 is set in the specified position. In the sputtering process, Ar gas is supplied into pressure-reduced vacuum chamber VC, and an A.C. power is supplied to target 16 via backing plate 17 functioning as the target electrode. At this time, Ar⁺ ions are struck against target 16 by the magnetron discharge, thereby causing target material to be emitted from target 16 as sputtering particles. The sputtering particles are attached to semiconductor wafer substrate 19 to form a sputtering film. At the same time, sputtering films are also formed on protection plate 15 and substrate holder 18. In the sputtering process, the temperature of protection plate 15 and substrate holder 18 is raised to 200°C at maximum. When the sputtering discharging operation or sputtering process is effected, heaters 21 and 22 are set in the OFF state but the temperature of protection plate 15 and substrate holder 18 is set at 200°C by heat generated in the sputtering process. After the end of the sputtering process, heaters 21 and 22 are set into the ON state to keep the temperature of protection plate 15 and substrate holder 18 at 200°C. Since, in this case, protection plate 15 and substrate holder 18 are kept at the constant temperature, increase in the number of particles due to peel-off of the sputtering film can be significantly suppressed even if the material of protection plate 15 and substrate holder 18 has a thermal expansion coefficient different from that of the material of the sputtering film deposited thereon. Fig. 3 shows the dependency of the number of particles of more than 0.3 µm attached to the wafer substrate of 12.7 cm (5 inch) diameter on the thickness of the sputtering film (the total thickness of the sputtering films deposited on the wafer substrates after protection plate 15 and substrate holder 18 are cleaned). In each sputtering process, one lot of 24 sheets of bare silicon wafers were subjected to the sputtering or film formation process, SiO₂ films were formed on 8 sheets of wafers in each sputtering unit so as to have a thickness of 100 nm (1000 Å) on the first and eighth ones of the wafers and a thickness of 1000 nm (10000 Å) on the second to seventh ones of the wafers, and the first and eighth ones of the wafers are subjected to the measurement. In this case, the numbers of particles measured in the three sputtering units were averaged to provide the measurement. The measurement was effected under the condition that the ultimate degree of vacuum was 2 × 10⁻⁵ Pa (1.5 × 10⁻⁷ Torr), the partial pressure of Ar in the sputtering process was 0,4 Pa (3.0 × 10⁻³ Torr), flow rate of Ar was 30 SCCM, and the sputtering formation speed was 150 nm/min (1500 Å/min). In the above embodiment, the preset temperature is set at 200°C. However, the ultimate or maximum attainable temperature of the protection plate will vary depending on the distance between target 16 and wafer substrate 19, the shape of chamber VC, target power and the like. For this reason, the optimum preset temperature of the protection plate may be different for each sputtering device. Therefore, the preset temperature may be determined depending on the stable temperature of protection plate 15 attained in the sputtering process of each sputtering device. Further, it is preferable that the preset temperature is not more than 20°C below the maximum attainable temperature of protection plate 15 attained during the sputtering process. In the above embodiment, the preset temperature is determined as shown in Fig. 4. Fig. 4 shows the relation between variation in the number of particles and variation in the temperature of protection plate 15 at the time of film formation (discharging operation) and after the end of film formation. As is clearly seen from Fig. 4, the number of particles rapidly increases as the temperature of the protection plate decreases after the discharging operation. Further, in this embodiment, the temperature of the sputtering film formation portion (protection plate 15 and substrate holder 18) is kept at 200°C, and the running test for formation of the SiO₂ sputtering film is effected. The dependency of the number of particles on the thickness of the sputtering film is attained as the result of the test. In Fig. 3, the dependency of the particle number on the film thickness is shown by solid lines X, and the dependency of the particle number on the film thickness attained as the result of the conventional running test effected without maintaining the preset temperature is shown by broken lines Y and one-dot-dash lines Z. The specified value of the number of particles (more than 0.3 µm is normally set less than 100. In the conventional method, the specified value will be exceeded when a film of 7 µm is formed. In contrast, according to this invention, the specified value will not be exceeded even when a film of approx. 40 µm is formed. Assume that one lot of 24 wafers are simultaneously processed in a sputtering device with the three targets and films are formed on 8 sheets of wafers by each target. In this condition, if a film of 1 µm is formed on each wafer, a film of 8 µm will be deposited for each target in each sputtering process. Therefore, each time films are formed for one lot of wafers according to the conventional method, it is necessary to clean the portion on which the sputtering film is deposited. However, in this invention, the cleaning operation is required only once each time five lots are processed. When the protection plate is replaced, it is necessary to set the pressure of the vacuum chamber to the atmospheric pressure and it takes a long time to reduce the pressure of the vacuum chamber after the replacement. Generally, it takes total of 5 hours at minimum to set a ready condition again if the replacement is effected. In this invention, the loss time is significantly reduced, thus improving the through put of the sputtering device. Fig. 6 shows another embodiment of this invention. Unlike the dome-shaped protection plate in the former embodiment, protection plate 15″ in this embodiment is formed in the form of partition wall and heater 21 is mounted on protection plate 15″. In this case, target power dispersing opening 31 and groove 32 are provided in the lower portion of vacuum chamber VC. Opening 31 is connected to a vacuum pump (not shown). With this construction, the same effect as in the former embodiment can be attained. In Fig. 6, 33 denotes a target earth shield. This invention is not limited to the above described embodiments, and can be variously modified. For example, in the above embodiment, high purity quartz (SiO₂) is used as the source target material. However, this invention is effective when metals such as alloy of Mo series and alloy of W series whose internal stress is large to cause easy peel-off are used as the target material. In this case, A.C. power source 20 is replaced by a D.C. power source. Further, in the above embodiment, heater units 21 and 22 are mounted on protection plate 15 and substrate holder 18. However, the same effect can be attained even when only heater unit 21 is mounted on protection plate 15 as shown in Fig. 5. As described above, according to this invention, a sputtering device can be provided in which the number of particles produced in the chamber in the sputtering process can be reduced while the advantage of a high speed sputtering device with the wafer substrate and target facing each other can be maintained.

Claims: A sputtering device comprising: a vacuum chamber (VC); a target (16) disposed in the vacuum chamber (VC); a protection member (15, 15″) formed to surround said target (16) with a space therebetween and having an opening (OP) formed in front of said target (16); a substrate holder (18) for holding the semiconductor wafer substrate (19) and substantially closing the opening (OP) of said protection member (15, 15″) in cooperation with the semiconductor wafer substrate (19); and electrical discharge means (20, MG) for causing target material to be emitted from said target (16) when the semiconductor wafer substrate (19) is set in front of said target (16), thereby depositing the target material on said semiconductor wafer substrate (19) as a sputtered film, characterized by further comprising heating means (21, 22, SR1, SR2, HC) for heating at least said protection member (15, 15″) to a specified temperature and maintaining the specified temperature. A sputtering device according to claim 1, characterized in that said specified temperature is not more than 20°C below the maximum attainable temperature of said protection member (15, 15″) attained with the heating means (21, 22, SR1, SR2, HC) in the OFF state during a sputtering process in which said sputtering film is formed. A sputtering device according to claim 2, characterized in that said specified temperature is not lower than said maximum attainable temperature. A sputtering device according to claim 3, characterized in that said heating means includes a heater unit (21) for heating said protection member (15, 15″), a temperature sensor (SR1) for measuring the temperature of said protection member (15, 15″), and heat control means (HC) for controlling the heating operation of said heater unit (21) in accordance with an output signal generated from said temperature sensor (SR1) to maintain said specified temperature. A sputtering device according to claim 3, characterized in that said heating means includes first and second heater units (21, 22) for heating said protection member (15, 15″) and substrate holder (18), respectively; first and second temperature sensors (SR1, SR2) for measuring the temperature of said protection member (15, 15″) and the temperature of said substrate holder (18), respectively; and heat control means (HC) for controlling the heating operations of said first and second heater units (21, 22) in accordance with output signals generated from the respective first and second temperature sensors (SR1, SR2) to maintain said specified temperature. A sputtering device according to claim 1, characterized in that said heating means includes a heater unit (21) for heating said protection member (15, 15″). A sputtering device according to claim 4, characterized in that said heating means further includes a heater unit (22) for heating said substrate holder (18). A sputtering device according to claim 1, characterized in that said target (16) is formed of insulation material. A sputtering device according to claim 1, characterized in that said target (16) is formed of metal or metal alloy material.

Inventors: ABE, MASAHIRO C/O PATENT DIVISION, KATSURA, TOSHIHIKO C/O PATENT DIVISION
Applicants: KABUSHIKI KAISHA TOSHIBA
Application year: 1988
Main classification: C23C14
IPC codes: H01J37, C23C14, H01L21