JP2009518854A - Medium pressure plasma system for surface layer removal without substrate loss - Google Patents

Abstract

Systems and methods are provided for removing photoresist or other organic compounds from a semiconductor wafer. Non-fluorinated reaction gases (O ₂ , H ₂ , H ₂ O, N _2, etc.) are activated in the quartz tube by medium pressure surface wave emission. Since the plasma jet acts on the substrate, the vaporization reaction product (H ₂ O, CO or low molecular weight hydrocarbon) selectively removes the photoresist from the substrate surface. Also, this medium pressure provides an effective heat source in the reaction area on the wafer, and increases the etch rate and also provides a high gas temperature that provides the actual means of removing the ion implanted photoresist. Can do.

Description

(Cross-reference of related applications)
This invention claims the priority of US Provisional Application No. 60 / 633,673, filed June 12, 2004, based on 35 USC 119 (e).

  The present invention relates to semiconductor processing, and more particularly to semiconductor processing for selectively removing a surface layer from a workpiece such as a semiconductor wafer in the manufacture of integrated circuits, for example. It will be understood that the following description is directed to semiconductor manufacturing processes and that the present invention is not limited to semiconductor manufacturing as it can be applied to various manufacturing processes and apparatus.

From the front-end-of-line [FEOL] of the wafer process with ion implantation for isolation, P-type or N-type well doping, threshold voltage adjustment, and source-drain contact, Each layer of an integrated circuit (IC) is formed in the back-end-of-line (BEOL) of the wafer process for plasma etching, metal plating, or interlayer dielectric. These coatings must be effectively and completely removed after each level in the semiconductor device is formed.
Under such circumstances, resist removal has been variously described as a resist ashing, stripping, or etching step.

  While the discussion herein will be discussed in the context of etching, in the context of the present invention, the term “etching” generally includes ashing, stripping, or etching, or removal of a surface layer. It will be understood that reference is made to various other suitable processes. Currently, the use of downstream plasma generators has become the standard for resist removal in industry. In this approach, a normal non-reactive gas such as oxygen flows through a microwave or radio frequency discharge and is converted to a plasma that is formed as a mixture of excited molecules, radicals, ions, and electrons. Ion species charged in the plasma are recombined as they flow through the downstream distribution system. However, many radicals have a lifetime sufficient to reach the wafer. In the example of using oxygen as the flowing gas, singlet sigma metastable oxygen molecules exist on the wafer surface and ultimately interact (JTJeong et al., Science) Technology 7-282-285, 1998). High energy ion bombardment causes unnecessary damage to semiconductor device components or the wafer substrate itself. In the downstream ashing tool, the absence of charged particles can prevent electrical damage to the integrated circuit.

  In the following description, a novel plasma source is provided based on a surface waveguide discharge technique that has not been used in the semiconductor manufacturing process. Conventional implementations of plasma systems have used electromagnetic force sources to activate plasma gases such as the Surfaguide device developed by Moisson et al. (Moisson et al., IEEE Bulletin Plasma Chemistry PS-12) 203-214, 1984). However, the limited cooling effect of this device is limited to the resulting plasma power density. In the past, oil cooled plasma sources have been commonly used. However, operating the plasma with high energy involves becoming very hot. Under such conditions, the cooling oil is decomposed and a carbonized layer is deposited on the outer wall of the plasma discharge tube in the waveguide. Once in operation, the increasing microwave exposure causes an oil-based carbon layer to grow rapidly and eventually a catastrophic arc discharge occurs in the waveguide, destroying the plasma discharge tube.

  For this reason, oil cooled systems are unsuitable for high energy plasma discharges. Air-cooled, high-power plasma systems have been reported, but their operation is limited to atmospheric pressure, for example, under high pressure, the resulting plasma can be absorbed into organic surface layers such as photoresist. Does not contain the reactive species necessary for selective removal (Okamoto “High-power microwave plasma induced by helium at atmospheric pressure for determination of halogen in aqueous solution” Japan Journal 38, L338. 1999).

  In general, the wafer is heated to increase the reaction rate during downstream plasma ashing. The application time in conventional processing can be as little as 15 seconds at 270 ° C. as possible for oxygen-based plasma chemistry. Once the resist layer is exposed to ion implantation, the reactive mechanism using plasma becomes more complex, as required in the intermediate IC manufacturing stage. Since the ion implantation process produces a carbonized outer layer mixed with metal ions that exhibit extremely low intrinsic etch rates, the ion implanted resist is more difficult to remove than the unimplanted resist. . Vinogradova et al. (G. K. Vinogradova) J. Vac. Science and Technology B, 17, 1, January / February 1999; S. Fujimura et al. (S. Fujimura) Nucl. Nucl. Instrum. Methods B39, 1989 K.J. Orvek, Nucl. Nucl. Instrum. Methods B7 / 8, 1985, P501; T. Bausum, et al., “High dose dose-implanted resist for 300 mm production. "Removal" Semiconductor International 06/01/2003; JRWasson et al. "Ion Absorbing Stencil Mask Coating for Ion Beam Lithography" J. Vac. Science and Technology B, 15, 2214, 1997).

  In order to prevent the release of fine particles, the wafer temperature must be kept below about 120 ° C., further reducing the processing capability. This release of fine particles occurs when the hard surface peels off under the pressure of gas, mainly NH3, and is released in response to heating above the hard bake temperature. This phenomenon is known as popping (D. Fleming et al. “Improved manufacturing methods achieved through optimized pre-injection UV / baking” Future Fab International 4,1,1977. , P177).

  Ion-implanted resist films, which are different from graphite or photoresist, are essentially inert and do not absorb atmospheric oxygen, nitrogen, or water vapor. The active energy for ion-implanted resist films that react with atomic oxygen is reported to be 2.4 eV, compared to 0.17 eV for non-ion-implanted resists (A. Josi et al. (A.Joshi) J.Vac. Science and Technology A, 8,3,5 / June 1990, pp2137).

  This additional activation energy explains why the ion implanted resist film cannot essentially be etched in a normal downstream plasma. In addition, RF-bias and fluorine chemistry has been used to increase the etch rate for ion implanted films (K.J. Orvek and C. Huffman Nucl.Nucl). Instrum. Methods B7 / 8, 1985, P501; JI McConmber et al. (JI. McOmber) Nucl. Nucl. Instrum. Methods B74 (1993) pp266-270; Kay Reinhardt et al. (K. Reinhardt) IBM Technology Symposium, France October 1999).

However, these more radical removal methods result in unprotected surface corrosion. Increasingly, such wafer surface losses become economically unacceptable as gate oxide and contact thickness, reducing the new generation of integrated circuits.
As a result, a new etching framework is important, which selectively removes substantially completely ion-implanted photoresist layers on silicon dioxide, silicon, or other thin dielectric films, and Can be made independent of fluorine chemistry as a whole. Also, commercially practiced while maintaining the substrate at a low temperature such that it can be applied over materials coated with inorganic or organic materials, including surface layers that are ion implanted or not ion implanted. There is a need for new technologies that provide possible removal rates.

  The present invention addresses the above needs by providing a new approach for removing surface layers from a semiconductor wafer. The present invention provides a method in which a reactive gas is activated by a medium pressure surface wave discharge. In addition, the method includes the formation of volatile reactants in the plasma gas that removes the photoresist from the surface of the wafer. The plasma gas forms a reactive plasma jet that impinges on the substrate, and the surface layer of the substrate is selectively, safely and efficiently etched. This method is performed in a commercially viable manner to remove the applied material from a large wafer by scanning in front of the plasma jet.

  In particular, the present invention is generally characterized as an apparatus for selectively removing a surface layer from a workpiece in a manufacturing process. The apparatus includes a processing chamber, a plasma applicator, and a cooling system. The processing chamber creates a subatomospheric (pressure below atmospheric pressure) that receives the workpiece to be processed so that the surface layer is removed. The plasma applicator generates a plasma and applies a pressurized source of reactive process gas, a plasma emission tube in fluid communication with the pressurized supply source, and an electromagnetic force acting on the plasma emission tube, An electromagnetic force supply source for generating plasma, and a nozzle opening disposed at one end of the plasma emission tube for radiating the plasma gas toward the workpiece into the processing chamber. Finally, a cooling system has a conduit disposed around the plasma discharge tube for circulating gaseous coolant and forming a cooling passage around the plasma discharge tube.

  Embodiments of the present invention are provided as an apparatus for performing material removal on a semiconductor wafer with a medium pressure (between about 10 Torr and about 500 Torr) plasma. In this device, a reactive process gas such as O2, H2, H2O, N2, etc. flows through a narrow discharge tube made of quartz, sapphire, or other electromagnetically unaffected material. And a surface wave is activated by the electromagnetic force supply source which can apply a microwave or RF power supply. In addition, a cooling system for a discharge tube using a gaseous coolant is provided that includes a cooling flange integrated on the discharge tube and is attached to the cooling passage.

The apparatus further includes a discharge tube nozzle from which gas from the discharge tube appears and collides with the substrate. As a result, volatile reaction products such as H 2 O, CO 2 or low molecular weight hydrocarbons are materials that selectively remove the surface layer of the wafer substrate. The apparatus further includes a positioning system for supporting the wafer chuck, which heats and positions the wafer and provides a fast scan of the wafer using a plasma source.
Using a surface wave discharge has the unique advantage of guiding this discharge, and an excitation power is applied to the wafer. Also, the method of providing a surface wave discharge can be performed over a wide pressure range without applying a significant amount of charge to the electromagnetic force system.

  The ideal operating pressure range of the present invention is a medium pressure type (about 10 torr or more and about 500 torr or less). Medium pressure plasma has the advantage of a high rate of electron-ion recombination and the thermal neutronization of the active particles removes the high energy charge species that appear in the low pressure plasma. Removing these high energy species eliminates the potential for potential damage to the substrate current and splitter erosion. Furthermore, the plasma gas temperature in the medium pressure type is very high compared to the low pressure type plasma. A higher plasma gas temperature provides an additional heat source in the reactive zone on the wafer, and is specifically required here. This concentrated thermal energy contributes to the rapid removal of organic material reactions.

  As the reaction rate of material removal increases, the processing speed (and commercial feasibility) increases. In contrast, the use of a low pressure type for plasma jet systems (less than about 10) is not preferred, and as the pressure decreases, the shape of the plasma jet expands, thereby allowing control of the spot size. Disappear. The high pressure type (greater than 500 Torr) is not advantageous and the reactive species required for surface removal recombine before reaching the wafer, resulting in selective removal. Reduce plasma efficiency. However, when the operation of the present invention is performed over a wide pressure range, wafer exchange in the atmosphere is possible while the plasma source is still in operation. Since plasma ignition typically requires low pressure (close to 1T), circulation of process pressure can be avoided if the output source can be maintained at about 760 Torr (atmospheric pressure) during wafer replacement. This should prevent the vacuum pump from dropping to a low pressure for plasma ignition. Then, in order to process each semiconductor wafer, re-pressurization is performed to obtain an intermediate pressure, thereby shortening a processing time that can be performed in an industrial setting.

  For the sake of better understanding, the features and technical advantages of the present invention have been described above in the detailed description of the present invention. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention.

For a more complete understanding of the present invention, advantages of the present invention will be referred to by the following description in conjunction with the accompanying drawings.
In the following description, numerous specific details are set forth, such as specific process values or parameters, in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without such specific details. In other instances, well-known components are shown in block diagram form in order to avoid obscuring the present invention. For the most part, details regarding the use of specific semiconductor products and equivalents are not necessary to obtain a thorough understanding of the present invention and are to the extent that they are within the skill of a person with ordinary skill in the relevant art. Has been.

Referring to the drawings, the illustrated components are not necessarily to scale, but identical or equivalent components are provided with the same reference signs in the several drawings.
FIG. 1 shows a schematic diagram of a plasma applicator 101, a processing chamber 102, and a high-speed wafer scanning stage 103. The plasma applicator 101 can be mounted on a chamber wall 104 of a semiconductor processing tool and includes a processing chamber 102 that forms a secondary atmospheric environment. In this chamber, the wafer or other workpiece is processed and the surface layer is removed. The electromagnetic force supply source supplies an output 105 to the plasma discharge tube 106 through a thin-walled coupling opening 110 provided in a portion where the height of the waveguide 111 is reduced. In one embodiment, a microwave output of 2.45 GHz is applied to a 6 mm diameter quartz plasma discharge tube. Since the surface wave travels in both directions along the boundary between the plasma discharge tube 106 and the plasma 108, the flow 112 of the process gas 114 suppresses charges upstream of the waveguide 111. This same flow 112 in contact with the downstream surface wave generates a plasma jet 108 that emerges from a nozzle opening 119 in a base flange 118 attached to the plasma discharge tube 106. In this situation, the plasma jet becomes a flow of pressurized plasma gas that emerges from the plasma applicator 101. In one example, the plasma jet is 2 mm away from the activated process gas for impinging on the semiconductor wafer. In another example, the wafer is about 20 mm away from the plasma jet.

  The high speed wafer scanning stage includes a chuck 130 having a wafer holder for clamping the wafer. The wafer holder can be actuated by vacuum, chamber pressure, or electrostatic force. The wafer holder can bring the wafer into contact with a thermally conductive or insulating material according to the desired degree of contact heat conduction to the wafer. In one example, the insulating material layer is directed between the wafer and the wafer holder to reduce contact heat conduction, thereby reducing the wafer temperature by reducing heat dissipation. Conversely, in one example, the conductive material layer is guided between the wafer and the wafer holder to increase contact thermal conductivity, thereby increasing the wafer temperature by increasing heat dissipation. Let Further, the chuck 130 can be connected to a power source via the coupling 133 to heat the wafer, and can be connected to a cooling supply source such as water via the coupling 133 to cool the wafer. You can also The chuck can also include a thermocouple sensor or other temperature sensor through the coupling 135 to monitor the chuck temperature.

  The chuck and wafer holder are mounted on a mechanical positioning system for scanning the wafer. In this regard, scanning the wafer corresponds to dynamically positioning the wafer while it is struck by the plasma jet to expose the area of the wafer to plasma processing. The plasma emission from the scanning operation can be made uniform over the entire area of the wafer, or can optionally include a processing portion of the wafer to vary the level of exposure to the plasma.

  In FIG. 1, the dual-axis orthogonal positioning system includes an x-axis linear drive 136 and a y-axis linear drive 134, and an exemplary embodiment is illustrated. In the present invention, other structures for mechanical positioning, such as a polar coordinate device having a rotation axis, mounted on a radial linear drive may be used. As an example, the mechanical positioning system includes two orthogonally driven stages driven by motors, which have an acceleration exceeding 2.5 times the gravitational acceleration and at a speed greater than 100 cm / s. Can be scanned. In one printing example, the present invention can perform a scan pattern based on computer control so that each point on the wafer passes within the plasma jet, which is an etched path. Having a diameter equal to about half of the maximum transverse width of the plasma jet. In a particular example, the present invention performs a scan pattern that provides a low scan speed on the edge of the wafer under computer control to increase the wafer temperature and compensate for the reduced etch rate due to edge effects.

  The present invention uses a cooling system that uses a gaseous coolant. A high speed gas flowing in the direction 113 facing the plasma gas 114 is used to cool the plasma discharge tube. Thereby, the operation of the plasma applicator 101 becomes possible with higher power loss. In one example, dry air or nitrogen cooling gas confined by the coaxial outer tube 116 cools the plasma emission tube 106.

  As shown in FIG. 1, the plasma emission tube 106 includes an integral base flange 118 to facilitate attachment to the applicator body. An important function of this base flange 118 is to separate the O-ring seal 140 from the immediate vicinity of the plasma emission tube 106 where the plasma emission tube 106 becomes extremely hot. The O-ring seal 140 has a relatively low melting point and is easily broken by transient temperature loads. The O-ring 140 that indirectly contacts the downstream side of the plasma discharge tube 106 will surely melt. The structure and design of the cooling system of the present invention has a sufficient temperature gradient across the base flange 118. As a result, the hot plasma that emerges from the central nozzle 119 of the base flange 118 does not cause alteration of the O-ring seal 140 on the edge of the base flange 118.

  In one example, an aluminum spacer 142 separates the plasma discharge tube flange 118 and the corresponding cooling flange 117 on the cooling outer tube 116. In the embodiment of the present invention shown in FIG. 1, the cooling system has a concentric, circular coaxial cross-sectional shape. Other cross-sectional shapes of the plasma emission tube surrounded by the cooling conduit can be, for example, rectangular, square, elliptical, or eccentric structures within the scope of the present invention. The liquid or gaseous coolant used in the various cooling systems provides the same cooling performance so that it can be implemented in the power system of the present invention and is included in the embodiments of the present invention.

  The present invention further includes a trap 120 incorporated under the flange of the inner tube to eliminate electromagnetic force leakage in the process chamber. In one example, a (1/4) λ transformer based on a microwave trap is used. The gaseous coolant flows radially inward toward the plasma discharge tube 106 via a passage provided on the lower surface of the trap 120 and between the plasma discharge tube 106 and the cooling outer tube 116. Enter the narrow space 105. As the cooling gas velocity enters this region, it substantially increases as the flow cross-sectional area decreases. As a result, the cooling of the plasma emission tube 106 is enhanced and becomes extremely high particularly in the hot zone in the waveguide 110. In one embodiment, a 1 mm gap width between the plasma discharge tube 106 and the cooling conduit results in a cooling gas velocity close to Mach 1. Thereby, a high microwave output level close to 2.5 kW is continuously maintained. In contrast to oil-based cooling systems, the air cooling of the present invention does not stay on the plasma emission tube, and can damage the plasma emission tube even after continuing the plasma jet at a high power level continuously. Absent.

  FIG. 2 is a photograph showing the operation of the plasma removal system in the embodiment of the present invention. The visible plasma jet is about 20 cm long and glows. The process gas used in the example illustrated in FIG. 2 is a mixture having a reactive oxygen to nitrogen ratio of about 9: 1 and a pressure of about 80 Torr is supplied at a flow rate of about 2 slpm [(liter) / min]. It was done. The electromagnetic radiation output is about 1 kW.

  The thermal power of the plasma jet provides the ability to locally heat the wafer, thereby increasing the etching reaction by increasing the reaction rate while simultaneously supplying reactive species that accelerate the organic surface layer etching reaction. . The total heat output P delivered to the substrate from the impinging plasma jet is the rise in temperature T with respect to time t, dT / dt of a thermally insulated aluminum block placed under the plasma jet according to the following equation: Determined by measuring rate.

P = CρV (dT / dt)
Here, heat capacity, C = 0.9J / K.g, density, ρ = 2.7g / cm ^3, the volume is V = 104.04cm ^3. These measurement results are shown in the data points of FIG. 3, which shows the change in temperature over time for a thermally isolated aluminum block. In this example, the block is heated by a reactive gas having an oxygen to nitrogen ratio of about 9: 1. This reactive gas is supplied at a pressure of 80 torr and a flow rate of 3 slpm under a microwave power of 1.8 kW applied to create a plasma jet impinging at a distance of 3 cm from the aluminum block. The aluminum block exhibited an initial temperature of 25 ° C. The graph of FIG. 3 shows the curve relationship between temperature and time, where dT / dt is the slope of the line. In this example, the overall heat output is P = 312W. This measurement is repeated at different microwave powers, gas compositions, and substrate distances to confirm that the thermal performance of the present invention has been improved.

  FIG. 4 shows measurement data points for plasma jet power versus loaded microwave power under another identical processing condition for the example shown in FIG. As shown in FIG. 4, the plasma jet output is linear with respect to the microwave output. In this example, when the target (semiconductor wafer) is measured from the nozzle opening 119 and is 0.9 cm and 2.9 cm away from the plasma source, respectively, the conversion efficiency is measured by the slope of the linear interpolation of the measurement data points. As such, it is about 19% and 21%.

  FIG. 5 shows the measured data points of the jet power versus the distance from the plasma source under another identical processing condition for the example shown in FIG. As shown in FIG. 5, as the distance from the plasma source increases from about 1 cm to about 5 cm, the plasma jet power decreases. This is because the plasma jet is cooled by mixing with the atmospheric temperature gas in the processing chamber 102.

  FIG. 6 shows measurement data points for plasma jet output versus O2 concentration when the target from the plasma source is 2.9 under the same processing conditions for the example shown in FIG. FIG. 6 shows that the plasma jet output is relatively constant for O2 concentrations from about 20% to about 90% m. This result indicates that the plasma jet power is essentially independent of the oxygen gas / nitrogen gas mixture.

  FIG. 7 shows measured data points for contact thermal conductivity for the space between the wafer and the chuck. Under dynamic conditions while being scanned by the plasma jet, the ability to control the wafer temperature determines whether the ashing process can be successful. Controlling the wafer temperature is suppressed by the thermal contact conductivity (k) between the wafer and the chuck. The value for k was measured for various gaps between the wafer and the chuck by determining the steady state temperature of the aluminum block attached to the chuck having a constant temperature. The space between the block and the chuck is maintained using thin mica spacers. This k is given by the following equation.

k = A (T-To) / P
Here, A is the contact area between the block and the chuck, To is the chuck temperature, and P is the output. The measured value for thermal conductivity was found to be k = 55 mW / cm ² K when the chuck and block were in close contact and were in good agreement with the other measured values. As shown in FIG. 8, the thermal conductivity decreases as the gap between the wafer and the chuck increases. A time constant τ for heat conduction between the chuck and the wafer is given by the following equation.

τ = C / k
Here, C is the heat capacity of the wafer per unit area. This time constant is about 2 seconds when the 300 mm silicon wafer is in intimate contact with the chuck and increases by about 10 seconds for a 0.01 inch gap. Variations in contact thermal conductivity and associated time constants require precise gap control, necessitating the need for electrostatic or vacuum clamping of the wafer on the chuck. Thus, another advantage of the present invention is that it can operate at moderate pressure ranges over conventional low pressure systems, and a wafer vacuum clamp on the chuck can be used instead of requiring an electrostatic clamp.

  To completely remove the resist, the wafer is scanned with a serpentine raster pattern 1014 as shown in FIG. In FIG. 8, the line scan 1014 along the x-axis 1010 moves back and forth in both directions with respect to the semiconductor wafer 1016 during a short displacement, that is, with a track interval along the y-axis 1012. The track spacing of such a pattern is smaller than the diameter of the plasma jet and provides a uniform etching profile across the wafer. In one embodiment of the invention, the track spacing was set to 0.7 cm. With a track spacing of 0.7 cm, the variation in etch depth between tracks is less than 2% of the resist thickness of the process at the center and midpoint between tracks.

A heat treatment that includes removing the photoresist using scanning of the plasma jet 1521 in an embodiment of the present invention is shown in FIG. The plasma jet 1521 is scanned on the semiconductor wafer substrate 1530 and coated on the surface layer of the organic resist 1531. As the wafer is scanned in the x-axis direction 1511 at high speed, a plasma jet 1521 emerges from the high energy plasma source in the direction 1523 of the wafer 1530 under medium pressure to create a heated track 1522. The track is cooled from the side via heat conduction and is cooled perpendicularly via contact heat conduction to the wafer holder, i.e. chuck. The associated heat flux F _{transverse direction} 1524 and F _{longitudinal direction} 1526 correspond to lateral heat flow and vertical heat conduction, respectively.

  The chuck is heated to increase the resist etch rate on the wafer. Also, the chuck can dissipate transient heat given by the plasma jet. The heat of the plasma jet is rapidly diffused through the wafer, and the diffusion length corresponds to the dwell time of the plasma jet and is greater than the wafer thickness for the fastest scanning speed. In one example of the present invention, while increasing the width of the heated zone by about 50%, the lateral diffusion length is only 0. 0 during a track scan time of about 0.2-0.4 seconds. 5 cm. As a result, in a first approximation, fast scan can be understood as a thermodynamic equilibrium of the line heater, which moves across the wafer in the y direction 1510 perpendicular to the fast scan direction. In one example, the vertical heat flow is slowly processed with a time constant of 2-10 seconds relative to the silicon substrate and may be ignored within the time required to scan a single track. . However, the vertical heat flow becomes an important temperature factor after several tracks are scanned.

  The balance between jet power, operating speed, and vertical heat flow determines the efficiency of a particular ashing process. In order to maximize throughput, embodiments of the present invention are operated with a high level of electromagnetic force that activates the plasma jet and translates to a higher etch rate. In addition, the output is increased to maximize the generation of reactive gas in the plasma and to provide heat for activating the ashing reaction between the resist and the etching gas.

  In the case of an ion-implanted resist, the initial chuck temperature is set below the hard baking temperature of the resist. In one example, the initial chuck temperature is set about 10 degrees below the resist hard bake temperature of about 125 ° C. The resist is stable at this temperature and no popping occurs. Contact heat transfer between the wafer and the chuck is maximized, for example, helium backside cooling minimizes the wafer temperature for a given input density. Finally, the scanning speed can be increased to reduce the effective power density in the wafer and allow the wafer to be scanned without popping where the wafer is scanned. The required speed is much greater than 1 m / s. As the scanning procedure progresses, the wafer temperature gradually increases, and the scanning plasma jet creates small holes in the hard surface of the implanted photoresist, creating a surface through which the gas released from the base resist is transmitted. To do. Once transparency is achieved, the temperature can be increased by reducing the scanning speed or by reducing the contact heat transfer between the wafer holder and the chuck. This reduces the amount of heat dissipated through the wafer holder. As a result of the pre-scan process for passing through the photoresist surface, the resist can be rapidly removed from the wafer surface during the second scanning operation.

  Etching unimplanted resist involves fewer thermal limitations. That is, the initial chuck temperature is increased by about 200 to 350 ° C. in one example, and the contact thermal conductivity and scanning speed can be set lower, leading to higher wafer temperature and higher etching rate. For resists that are not implanted, contact thermal conduction can be significantly reduced. In one example, the wafer is lifted from the chuck by a few tenths of an inch.

As a result of the above, ashing of photoresist ion-implanted at a high dose occurs as a two-step process in which the resist surface is rendered permeable by pre-treatment at a low temperature, followed by a resist at a high temperature. A removal process is performed. This pretreatment is performed at a chuck temperature lower than the resist bake temperature, for example, 120 ° C. This relatively low temperature is required to prevent the release of particulates when the resist surface is destroyed by a gas generated by the thermal decomposition of the resist. In this case, the carbonized surface is not removed / ruptured. This process is also known as popping. When the pre-process scan of the present invention makes the photoresist surface permeable to gas, the wafer temperature is safely increased to increase the resist removal rate. The measurements establish parameter conditions and resist removal in a scanned plasma jet ashing of implanted (P, 40 Kev, 5 × 10 15 / cm ² ) I-line photoresist from a silicon wafer.

  10-17 are photographs of a sample semiconductor wafer, which shows the surface layer of the photoresist processed according to an embodiment of the present invention. FIG. 10 shows a network of gas filled blisters formed by the heat of a plasma jet of 1 KW and 15 cm / s. FIG. 11 shows a crushed blister when the substrate is cut, and the pressure of this filled gas splits the hard surface from the underlying unimplanted resist base into a thin layer. In this example, the blister height is 3-4 times the original resist thickness. This presto effect is related to the popping operation, although it is not obvious, so that a plate with a large surface is blown off the surface. However, blister formation is acceptable in this case, so that no fine particle fragments are generated. Once the blister is formed, the heat transfer from the surface to the substrate is dramatically reduced, and this temperature rises several hundred degrees Celsius or more above the temperature of the substrate. The high temperature localized by delamination accelerates surface etching, as shown in FIG. When these openings appear on the surface 1901, the base resist is exposed to a plasma jet and lateral etching 1902, as shown in FIG. 13, occurs below the surface. FIG. 14 shows the subsequent etching step, where most of the surface 1211 is removed and the blister 2010 is integrated.

  Using embodiments of the present invention, the plasma jet is operated with the maximum possible electromagnetic force applied to maximize the material removal throughput. In order to prevent popping in the pre-processing stage, it is necessary to scan the plasma jet fast enough to prevent transient temperature increases. In one illustration, multiple pre-processing scans need to achieve sufficient transparency to prevent popping during the resist removal step. In one embodiment of the present invention, the resist can be completely removed by a single scan at a rate on the order of 50-100 cm / s without changes in the temperature of the substrate. Other settings for process parameters can be used to achieve similar results in different but related embodiments of the invention.

  In addition to blister formation, other processes lead to surface transparency in the ion implanted photoresist. FIG. 15 shows, for example, a reticulated resist surface that develops during the initial stages of parameter processing. This surface is permeable as shown in FIG. 16 in the final stage of the pretreatment step.

In an exemplary embodiment for practicing the invention, multiple pre-processing scans (microwave power = 2.15 KW, substrate temperature = 100 ° C., scan rate = 105 cm / s, O 2: N 2 = 9: 1, flow rate. = 3 slpm, pressure 80T), implanted I-line photoresist (1.2 micron I-line base resist, 120 ° C. hard bake, and phosphorus implanted at 40 keV energy, 5 × Optimal treatment was applied for a high injection density of 10 ¹⁵ / cm ² . This pretreatment was then followed by a resist removal scan at 2.5 KW, 40 cm / s (while other conditions were maintained as in the pretreatment). All surface and base resists were: It is removed from the wafer and, as is apparent from FIG. 17, there is no residue as seen with a scanning electronic microscope.

  FIG. 18 illustrates, in flowchart form, a method 2401 for implementing the present invention. The method begins at step 2402, which leads the wafer to a processing chamber equipped with a plasma applicator device, as illustrated in FIG. If the plasma is pre-ignited at low temperature, step 2402 is performed while the plasma is operating at ambient pressure.

  In step 2404, the clamp interface between the wafer and the wafer holder is adjusted for the desired heat transfer, either high or low heat transfer. In step 2406, the semiconductor wafer is clamped to the chuck using atmospheric, or vacuum, or electrical means. As described above, in step 2408, operation of the cooling system to start the plasma emission tube is initiated. Next, activation of the reactive process gas begins at step 2410. After plasma activation, in step 2412 the wafer surface is treated with a plasma jet. Method 2401 is one exemplary embodiment of the present invention, and various combinations of the illustrated processing steps may be used, omitting certain steps or using a different configuration than the predetermined order, according to processing and equipment requirements. The same can be done. For example, in one embodiment of method 2401, pretreatment of ion implanted resist is performed to allow gas to permeate the resist surface. In another embodiment of method 2401, unimplanted or pre-implanted resist is processed to selectively ash and remove only the photoresist layer.

FIG. 19 shows one exemplary method 2501 for performing method step 2410 shown in FIG. First, as described above, electromagnetic force is activated in step 2502. This electromagnetic radiation is transmitted in step 2504 to the plasma emission tube via the waveguide. In step 2506, electromagnetic force is included in a trap to protect the wafer from uncontrolled radiation.
Although the invention and its advantages have been described in detail, various changes, alternatives, and modifications can be made without departing from the spirit and scope of the invention as defined by the appended claims.

FIG. 1 shows a cross-sectional view of a plasma removal system according to an embodiment of the present invention. FIG. 2 is a photograph showing the operation of the plasma removal system according to the embodiment of the present invention. FIG. 3 is a diagram illustrating empirical data collected in an embodiment of the present invention. FIG. 4 is a diagram illustrating empirical data collected in an embodiment of the present invention. FIG. 5 is a diagram illustrating empirical data collected in an embodiment of the present invention. FIG. 6 is a diagram illustrating empirical data collected in an embodiment of the present invention. FIG. 7 is a diagram illustrating empirical data collected in an embodiment of the present invention. FIG. 3 is a diagram schematically showing a scanning pattern in the embodiment of the present invention. FIG. 9 is a diagram schematically showing a heat flow in the embodiment of the present invention. FIG. 10 is a photograph of a sample processed using an embodiment of the present invention. FIG. 11 is a photograph of a sample processed using an embodiment of the present invention. FIG. 12 is a photograph of a sample processed using an embodiment of the present invention. FIG. 13 is a photograph of a sample processed using an embodiment of the present invention. FIG. 14 is a photograph of a sample processed using an embodiment of the present invention. FIG. 15 is a photograph of a sample processed using an embodiment of the present invention. FIG. 16 is a photograph of a sample processed using an embodiment of the present invention. FIG. 17 is a photograph of a sample processed using an embodiment of the present invention. FIG. 18 is a diagram illustrating method steps in a flowchart format according to an embodiment of the present invention. FIG. 19 is a diagram illustrating method steps in a flowchart format according to an embodiment of the present invention.

Claims (33)

An apparatus for selectively removing a surface layer from a workpiece during a manufacturing process,
A processing chamber for forming an atmosphere in the sub-atmosphere environment and receiving the workpiece in the environment;
A plasma applicator for generating plasma;
A cooling system having a conduit disposed around the plasma discharge tube for circulating a gaseous coolant and forming a cooling passage around the plasma discharge tube;
The plasma applicator is
A pressurized source of reactive processing gas,
A plasma discharge tube in fluid communication with the pressurized source;
An electromagnetic force supply source for causing an electromagnetic force to act on the plasma emission tube to generate plasma in the emission tube; and
An apparatus having a nozzle opening disposed at one end of the plasma emission tube for emitting the plasma gas toward the workpiece into the processing chamber.   The apparatus of claim 1, further comprising a waveguide for transmitting electromagnetic force to the plasma emission tube.   The apparatus of claim 2, further comprising a microwave trap for containing electromagnetic force in the plasma applicator. The reactive process _{gas, O 2, H 2, H} 2 O, apparatus according to claim 1, characterized in that it consists of N ₂ or a combination thereof. The apparatus according to claim 1, wherein the reactive processing gas is made of O ₂ , H ₂ , H ₂ O, N ₂ , or a combination thereof, and the reactive processing gas does not contain fluorine.   The apparatus of claim 1, wherein the plasma emission tube is made from quartz or other electromagnetically unaffected ceramic material. The cooling system of claim 1, wherein the electromagnetic power source has a thermodynamic capability of operating at a power loss of at least 2.5 kW or a power density of at least 1.5 kW / cm ³ . apparatus.   The apparatus of claim 1, wherein the electromagnetic force source operates at a frequency in the range of about 100 Hz to 2.45 GHz.   And a mechanical positioning system including a chuck for receiving and holding the workpiece to cause the nozzle to scan the workpiece such that a surface layer of the workpiece is exposed to the plasma. The apparatus of claim 1, comprising:   The mechanical positioning system includes a plurality of mechatronic translation stages for scanning the surface of the workpiece, and the chuck is accelerated by more than 2.5 times gravitational acceleration and is a straight line of about 100 cm / s or more. The apparatus of claim 9, wherein the apparatus is operable to be positioned at a speed.   The apparatus of claim 1, wherein the distance between the nozzle and the workpiece is greater than or equal to about 2 mm and less than about 20 mm.   The apparatus of claim 9, wherein the mechatronic translation stage is arranged for positioning according to Cartesian or polar coordinates.   The chuck further includes a layer of thermal insulation on its surface, the thermal insulation layer being thermally insulative or conductive to modify the contact thermal conductivity between the chuck and the workpiece. 10. The device according to claim 9, wherein the device has the property of gender. Further comprising means for carrying in and out of the workpiece on the chuck while maintaining the operation of the plasma applicator while maintaining the pressure in the processing chamber at a pressure higher than atmospheric pressure;
The apparatus of claim 9, wherein there is no need to extinguish and generate plasma for each workpiece to be processed in the processing chamber.   10. The apparatus of claim 9, further comprising means for clamping a workpiece onto the chuck by a force supplied by processing atmospheric pressure or vacuum, or electrostatic force. A method for selectively removing a surface layer from a wafer in a semiconductor manufacturing process,
Introducing a wafer into a processing chamber that creates air in a sub-atmospheric processing environment;
Exposing the reactive gas flowing in the discharge tube to surface wave radiation provided by an electromagnetic force source to generate an activated reactive gas flowing through the discharge tube; and
Radiating the activated reactive gas into the processing chamber and onto the surface of the wafer such that the surface layer of the wafer is selectively removed without substantial loss of substrate material. A method characterized by being.   The method of claim 1, further comprising cooling the plasma discharge tube by forming a cooling passage around the plasma discharge tube and circulating a gaseous coolant through the cooling passage. 16. The method according to 16. The reactive process _{gas, O 2, H 2, H} 2 O, N 2 or method of claim 16, wherein the formed of a combination thereof.   The method of claim 16, wherein the surface layer comprises unimplanted photoresist or other organic or inorganic material.   The method of claim 16, wherein the surface layer comprises an ion implanted photoresist material or other organic or inorganic material.   The method further comprises scanning the wafer by moving the wafer relative to the reactive gas emitted at the first velocity, whereby the implanted outer photoresist layer is infiltrated with the gas. The method of claim 16.   The method further includes scanning the wafer by moving the wafer relative to the reactive gas emitted at the second velocity, whereby the photoresist and / or its outer layer is removed from the wafer. The method of claim 21.   The method of claim 16, further comprising exposing the reactive gas to a surface wave emitted at a first power level, whereby the implanted outer photoresist layer is infiltrated with the gas.   24. The method of claim 23, further comprising exposing the reactive gas to the surface wave emitted at the second power level, whereby the implanted photoresist and / or its outer layer is removed from the wafer. the method of.   The method further includes scanning the wafer by moving the wafer relative to the reactive gas emitted at the first temperature, whereby the implanted outer photoresist layer is infiltrated with the gas. The method of claim 16.   The method further includes scanning the wafer by moving the wafer relative to the reactive gas emitted at the second temperature, whereby the photoresist and / or its outer layer is removed from the wafer. 26. The method of claim 25. Emitting the activated reactive gas comprises:
In order to generate surface waves in the plasma emission tube, an electromagnetic force source is excited,
Transmitting electromagnetic force to the plasma emission tube through a waveguide engaged with the plasma emission tube;
The method of claim 16, comprising each step comprising electromagnetic radiation using a trap in the plasma applicator.   The method of claim 16, wherein the electromagnetic force source operates at a frequency in the range of about 100 kHz to 2.45 GHz. Placing the wafer on the chuck;
Scanning the chuck for reactive gas emitted through a mechanical positioning system attached to the chuck, thereby
The method of claim 16, wherein the chuck on which the wafer is placed is positioned such that the surface layer of the wafer is exposed to the emitted reactive gas.   The mechanical positioning system is operable such that the chuck is accelerated at about 2.5 times gravitational acceleration and positioned at a linear velocity of about 100 cm / s or more. 29. The method according to 29.   Further comprising changing the temperature of the wafer through a layer of heat resistant insulating or conductive material disposed between the wafer and a wafer holder mounted on the chuck, whereby the wafer 30. The method of claim 29, wherein the contact thermal conductivity between the holder and the wafer is modified.   When the pressure in the processing chamber is atmospheric pressure, the method further includes a step of loading / unloading the wafer onto / from the chuck, whereby an activated reactive gas is supplied to each wafer processed in the processing chamber. 30. The method of claim 29, wherein there is no need to radiate.   32. The method of claim 31, further comprising clamping the semiconductor wafer onto the chuck by a force supplied by atmospheric pressure or vacuum for processing, or electromagnetic force.

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