JP5770880B2 - Heat treatment method - Google Patents

Description

  The present invention is applied to thin precision electronic substrates (hereinafter simply referred to as “substrates”) such as semiconductor wafers into which impurities (ions) are implanted, glass substrates for liquid crystal display devices, glass substrates for photomasks, and substrates for optical disks. The present invention relates to a heat treatment method for heating a substrate by irradiating flash light.

  Conventionally, a lamp annealing apparatus using a halogen lamp has been generally used in an impurity activation process of a semiconductor wafer after impurity implantation. In such a lamp annealing apparatus, the semiconductor wafer is heated (annealed) to a temperature of about 1000 ° C. to 1100 ° C., for example, to activate the impurities of the semiconductor wafer. In such a heat treatment apparatus, the temperature of the substrate is raised at a rate of several hundred degrees per second by using the energy of light irradiated from the halogen lamp.

  On the other hand, in recent years, as semiconductor devices have been highly integrated, it is desired to reduce the junction depth as the gate length becomes shorter. However, even when the impurity activation of the semiconductor wafer is performed using the above-described lamp annealing apparatus that raises the temperature of the semiconductor wafer at a speed of about several hundred degrees per second, impurities such as boron and phosphorus implanted in the semiconductor wafer are heated. It was found that the phenomenon of deep diffusion occurs. When such a phenomenon occurs, there is a concern that the junction depth becomes deeper than required, which hinders good device formation.

  Therefore, the surface of the semiconductor wafer into which impurities have been implanted by irradiating the surface of the semiconductor wafer with flash light using a xenon flash lamp (hereinafter simply referred to as “flash lamp” means xenon flash lamp). Has been proposed (for example, Patent Documents 1 and 2) in which the temperature is raised only for a very short time (several milliseconds or less). The radiation spectral distribution of a xenon flash lamp ranges from the ultraviolet region to the near infrared region, has a shorter wavelength than the conventional halogen lamp, and almost coincides with the fundamental absorption band of a silicon semiconductor wafer. Therefore, when the semiconductor wafer is irradiated with flash light from the xenon flash lamp, the semiconductor wafer can be rapidly heated with little transmitted light. Further, it has been found that if the flash light is irradiated for a very short time of several milliseconds or less, only the vicinity of the surface of the semiconductor wafer can be selectively heated. For this reason, if the temperature is raised for a very short time by the xenon flash lamp, only the impurity activation can be performed without deeply diffusing the impurities.

JP 2004-55821 A JP 2004-88052 A

  By the way, the sheet resistance value Rs is used as a typical index indicating the characteristics of the semiconductor wafer into which impurities are implanted. The sheet resistance value on the surface of the semiconductor wafer decreases due to the activation of the impurities. Generally, the lower the sheet resistance value, the better the impurity activation process is performed. For this reason, further reduction of the sheet resistance value is desired. In order to further reduce the sheet resistance value, the temperature of the surface of the semiconductor wafer may be raised to a higher temperature.

  However, in order to raise the surface temperature of the semiconductor wafer to a higher temperature by flash light irradiation from the flash lamp, it is necessary to irradiate flash light with a larger irradiation energy in a very short time. In addition, the load on the drive circuit must be large. As a result, there also arises a problem that the life of the flash lamp is shortened.

  Further, the intensity distribution of the flash light in the plane of the semiconductor wafer is not completely uniform, and further, since the fine pattern is formed on the surface of the semiconductor wafer, the in-plane distribution of the light absorptance is not uniform. As a result, the in-plane temperature distribution of the semiconductor wafer at the time of flash light irradiation also varied. In addition, it is extremely difficult to eliminate variations in the in-plane temperature distribution by heat treatment by irradiation with flash light with an extremely short irradiation time.

  This invention is made | formed in view of the said subject, and it aims at providing the heat processing method which can heat-up a substrate surface to higher temperature and can reduce a sheet resistance value.

In order to solve the above-mentioned problem, the invention of claim 1 is a heat treatment method in which a substrate into which impurities are implanted is irradiated with flash light to heat the substrate, and carbon or a carbon compound is formed on the surface of the substrate into which impurities are implanted. Forming a thin film, accommodating a substrate on which the thin film is formed in a chamber, and introducing oxygen gas into the chamber after irradiating flash light after the substrate is accommodated in the chamber. Irradiating the substrate contained in the chamber with flash light from a flash lamp to heat the substrate in an oxygen atmosphere, oxidizing the thin film to vaporize, and unloading from the chamber time of removing the thin film remaining even after conducting the washing treatment to the substrate which is provided with, is irradiated with flash light The oxygen concentration in the chamber of characterized by higher than the oxygen concentration in the atmosphere.

  Further, the invention of claim 2 is the heat treatment method according to the invention of claim 1, wherein the cleaning treatment uses a mixed solution of sulfuric acid and hydrogen peroxide solution and a mixed solution of ammonia water and hydrogen peroxide solution. It is characterized by.

  According to a third aspect of the present invention, in the heat treatment method according to the first or second aspect of the present invention, the oxygen concentration in the chamber at the time of irradiation with flash light is 90% or more.

  According to the present invention, a thin film of carbon or a carbon compound is formed on the surface of a substrate into which impurities are implanted, and the substrate is irradiated with flash light from a flash lamp. The sheet resistance can be lowered by raising the temperature of the substrate surface to a higher temperature. Also, the substrate is heated by irradiating flash light in an oxygen atmosphere, and the thin film is consumed by being oxidized and vaporized. Therefore, it remains only by a normal cleaning process without performing a special ashing process after that. The thin film can be removed.

It is a longitudinal cross-sectional view which shows the structure of the heat processing apparatus which concerns on this invention. It is sectional drawing which shows the gas path of the heat processing apparatus of FIG. It is sectional drawing which shows the structure of a holding | maintenance part. It is a top view which shows a hot plate. It is a longitudinal cross-sectional view which shows the structure of the heat processing apparatus of FIG. It is a block diagram which shows the structure of a control part. It is a flowchart which shows a part of processing flow with respect to a semiconductor wafer. It is a flowchart which shows the process sequence of the semiconductor wafer in the heat processing apparatus of FIG. It is sectional drawing of the semiconductor wafer formed by forming the carbon thin film on the surface of a silicon substrate. It is a schematic diagram which shows the state by which flash light was irradiated to the semiconductor wafer in which the carbon thin film was formed. It is a figure which shows the correlation of a charge voltage and a sheet resistance value. It is the figure which showed typically the variation of the film thickness fall of a carbon thin film.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  First, the overall configuration of the heat treatment apparatus according to the present invention will be outlined. FIG. 1 is a longitudinal sectional view showing a configuration of a heat treatment apparatus 1 according to the present invention. The heat treatment apparatus 1 is a lamp annealing apparatus that irradiates a substantially circular semiconductor wafer W as a substrate with flash light (flash light) and heats the semiconductor wafer W.

  The heat treatment apparatus 1 includes a substantially cylindrical chamber 6 that accommodates a semiconductor wafer W, and a lamp house 5 that houses a plurality of flash lamps FL. Further, the heat treatment apparatus 1 includes a control unit 3 that controls each operation mechanism provided in the chamber 6 and the lamp house 5 to execute the heat treatment of the semiconductor wafer W.

  The chamber 6 is provided below the lamp house 5 and includes a chamber side 63 having a substantially cylindrical inner wall and a chamber bottom 62 covering the lower part of the chamber side 63. A space surrounded by the chamber side 63 and the chamber bottom 62 is defined as a heat treatment space 65. An upper opening 60 is formed above the heat treatment space 65, and a chamber window 61 is attached to the upper opening 60 to be closed.

  The chamber window 61 constituting the ceiling portion of the chamber 6 is a disk-shaped member made of quartz, and functions as a quartz window that transmits the flash light emitted from the lamp house 5 to the heat treatment space 65. The chamber bottom 62 and the chamber side 63 constituting the main body of the chamber 6 are formed of, for example, a metal material having excellent strength and heat resistance such as stainless steel, and a ring on the upper side of the inner side surface of the chamber side 63. 631 is formed of an aluminum (Al) alloy or the like having durability superior to stainless steel against deterioration due to light irradiation.

  Further, in order to maintain the airtightness of the heat treatment space 65, the chamber window 61 and the chamber side portion 63 are sealed by an O-ring. That is, the O-ring is sandwiched between the lower surface peripheral portion of the chamber window 61 and the chamber side portion 63, the clamp ring 90 is brought into contact with the upper peripheral portion of the chamber window 61, and the clamp ring 90 is attached to the chamber side portion 63. The chamber window 61 is pressed against the O-ring by screwing.

  The chamber bottom 62 has a plurality (in this embodiment) for supporting the semiconductor wafer W from the lower surface (surface opposite to the side irradiated with light from the lamp house 5) through the holding portion 7. 3) support pins 70 are provided upright. The support pin 70 is made of, for example, quartz and is fixed from the outside of the chamber 6 and can be easily replaced.

The chamber side 63 has a transfer opening 66 for carrying in and out the semiconductor wafer W, and the transfer opening 66 can be opened and closed by a gate valve 185 that rotates about a shaft 662. A gas introduction path 81 for introducing a processing gas into the heat treatment space 65 is connected to a portion of the chamber side portion 63 opposite to the transfer opening 66. One end of the gas introduction path 81 is connected to a gas introduction buffer 83 formed inside the chamber side portion 63, and the other end is connected to a gas supply source 88. A gas valve 82 and a flow rate adjustment valve 85 are interposed in the middle of the gas introduction path 81. The gas supply source 88 is an inert gas such as nitrogen gas (N ₂ ), helium gas (He), or argon gas (Ar), or a reactive gas such as oxygen gas (O ₂ ) or ammonia gas (NH ₃ ). To the gas introduction path 81. The gas supply source 88 supplies these gases as a processing gas, alternatively or as a mixture. A discharge passage 86 for discharging the gas in the heat treatment space 65 is formed in the transfer opening 66 and is connected to an exhaust mechanism (not shown) via a gas valve 87.

  FIG. 2 is a cross-sectional view of the chamber 6 cut along a horizontal plane at the position of the gas introduction buffer 83. As shown in FIG. 2, the gas introduction buffer 83 is formed over about ３ of the inner periphery of the chamber side portion 63 on the opposite side of the transfer opening 66 shown in FIG. 1. By opening the gas valve 82, the processing gas is supplied from the gas supply source 88 to the gas introduction path 81, guided to the gas introduction buffer 83, and supplied into the heat treatment space 65 from the plurality of gas supply holes 84. The supply flow rate of the processing gas is determined by the flow rate adjustment valve 85. Further, the atmosphere in the heat treatment space 65 is exhausted from the exhaust path 86 by opening the gas valve 87. As a result, a gas flow of the processing gas is formed in the heat treatment space 65 as indicated by an arrow AR4 in FIG.

  Returning to FIG. 1, the heat treatment apparatus 1 is a substantially disk-like shape that pre-heats the semiconductor wafer W held before the flash light irradiation while the semiconductor wafer W is placed and held in a horizontal position inside the chamber 6. The holding part 7 and the holding part raising / lowering mechanism 4 for raising and lowering the holding part 7 with respect to the chamber bottom 62 which is the bottom surface of the chamber 6 are provided. 1 includes a substantially cylindrical shaft 41, a moving plate 42, guide members 43 (three arranged around the shaft 41 in the present embodiment), a fixed plate 44, a ball screw 45, It has a nut 46 and a motor 40. A substantially circular lower opening 64 having a smaller diameter than the holding portion 7 is formed in the chamber bottom 62 which is the lower portion of the chamber 6, and the stainless steel shaft 41 is inserted through the lower opening 64 to hold the holding portion. 7 (strictly speaking, the hot plate 71 of the holding unit 7) is connected to the lower surface of the holding unit 7 to support it.

  A nut 46 that is screwed into the ball screw 45 is fixed to the moving plate 42. The moving plate 42 is slidably guided by a guide member 43 that is fixed to the chamber bottom 62 and extends downward, and is movable in the vertical direction. Further, the moving plate 42 is connected to the holding unit 7 via the shaft 41.

  The motor 40 is installed on a fixed plate 44 attached to the lower end of the guide member 43, and is connected to the ball screw 45 via the timing belt 401. When the holding part 7 is raised and lowered by the holding part raising / lowering mechanism 4, the motor 40 as the driving part rotates the ball screw 45 under the control of the control part 3, and the moving plate 42 to which the nut 46 is fixed follows the guide member 43. Move vertically. As a result, the shaft 41 fixed to the moving plate 42 moves along the vertical direction, and the holding unit 7 connected to the shaft 41 moves between the delivery position of the semiconductor wafer W shown in FIG. 1 and the semiconductor wafer W shown in FIG. Move up and down smoothly between the processing positions.

  On the upper surface of the moving plate 42, a mechanical stopper 451 having a substantially semi-cylindrical shape (a shape obtained by cutting the cylinder in half along the longitudinal direction) is provided so as to extend along the ball screw 45. If the upper limit of the mechanical stopper 451 is struck against the end plate 452 provided at the end of the ball screw 45, the moving plate 42 is prevented from rising abnormally. Thereby, the holding part 7 does not rise above a predetermined position below the chamber window 61, and the collision between the holding part 7 and the chamber window 61 is prevented.

  The holding unit lifting mechanism 4 has a manual lifting unit 49 that manually lifts and lowers the holding unit 7 when performing maintenance inside the chamber 6. The manual elevating part 49 has a handle 491 and a rotating shaft 492. By rotating the rotating shaft 492 via the handle 491, the ball screw 45 connected to the rotating shaft 492 is rotated via the timing belt 495 to hold the holding part. 7 can be moved up and down.

  A telescopic bellows 47 that surrounds the shaft 41 and extends downward is provided below the chamber bottom 62, and its upper end is connected to the lower surface of the chamber bottom 62. On the other hand, the lower end of the bellows 47 is attached to the bellows lower end plate 471. The bellows lower end plate 471 is attached by being screwed to the shaft 41 by a flange-shaped member 411. The bellows 47 is contracted when the holding portion 7 is raised with respect to the chamber bottom 62 by the holding portion lifting mechanism 4, and the bellows 47 is expanded when the holding portion 7 is lowered. When the holding unit 7 moves up and down, the airtight state in the heat treatment space 65 is maintained by the expansion and contraction of the bellows 47.

  FIG. 3 is a cross-sectional view showing the configuration of the holding unit 7. The holding part 7 has a substantially disk shape with a larger diameter than the semiconductor wafer W. The holding unit 7 is installed on a hot plate (heating plate) 71 that preheats the semiconductor wafer W (so-called assist heating), and an upper surface of the hot plate 71 (a surface on the side where the holding unit 7 holds the semiconductor wafer W). The susceptor 72 is provided. As described above, the shaft 41 that moves up and down the holding unit 7 is connected to the lower surface of the holding unit 7. The susceptor 72 is made of quartz (or may be aluminum nitride (AIN) or the like), and a pin 75 for preventing displacement of the semiconductor wafer W is provided on the upper surface thereof. The susceptor 72 is installed on the hot plate 71 with its lower surface in surface contact with the upper surface of the hot plate 71. Thus, the susceptor 72 diffuses the thermal energy from the hot plate 71 and transmits it to the semiconductor wafer W placed on the upper surface of the susceptor 72, and can be removed from the hot plate 71 and cleaned during maintenance.

  The hot plate 71 includes an upper plate 73 and a lower plate 74 made of stainless steel. A resistance heating wire 76 such as a nichrome wire for heating the hot plate 71 is disposed between the upper plate 73 and the lower plate 74, and is filled with a conductive nickel (Ni) solder and sealed. The end portions of the upper plate 73 and the lower plate 74 are bonded by brazing.

  FIG. 4 is a plan view showing the hot plate 71. As shown in FIG. 4, the hot plate 71 includes a disc-shaped zone 711 and an annular zone 712 that are concentrically arranged in a central portion of a region facing the held semiconductor wafer W, and a zone 712. There are four zones 713 to 716 obtained by equally dividing a peripheral substantially annular region into four equal parts in the circumferential direction, and a slight gap is formed between the zones. The hot plate 71 is provided with three through holes 77 through which the support pins 70 are inserted, every 120 ° on the circumference of the gap between the zone 711 and the zone 712.

  In each of the six zones 711 to 716, heaters are individually formed so that mutually independent resistance heating wires 76 circulate, and each zone is individually formed by a heater built in each zone. Heated. The semiconductor wafer W held by the holding unit 7 is heated by heaters built in the six zones 711 to 716. Each of the zones 711 to 716 is provided with a sensor 710 that measures the temperature of each zone using a thermocouple. Each sensor 710 passes through the inside of a substantially cylindrical shaft 41 and is connected to the control unit 3.

  When the hot plate 71 is heated, the resistance heating wire disposed in each zone is set so that the temperature of each of the six zones 711 to 716 measured by the sensor 710 becomes a predetermined temperature. The amount of power supplied to 76 is controlled by the control unit 3. The temperature control of each zone by the control unit 3 is performed by PID (Proportional, Integral, Derivative) control. In the hot plate 71, the temperature of each of the zones 711 to 716 is continuously measured until the heat treatment of the semiconductor wafer W (when plural semiconductor wafers W are continuously processed, the heat treatment of all the semiconductor wafers W) is completed. Then, the power supply amount to the resistance heating wire 76 disposed in each zone is individually controlled, that is, the temperature of the heater built in each zone is individually controlled, and the temperature of each zone becomes the set temperature. Maintained. The set temperature of each zone can be changed by an offset value set individually from the reference temperature.

  The resistance heating wires 76 respectively disposed in the six zones 711 to 716 are connected to a plate power source 98 (see FIG. 6) via a power line passing through the inside of the shaft 41. In the middle of the path from the plate power source 98 to each zone, the power lines from the plate power source 98 are arranged so as to be electrically insulated from each other inside a stainless tube filled with an insulator such as magnesia (magnesium oxide). The The interior of the shaft 41 is open to the atmosphere.

  Next, the lamp house 5 is provided above the chamber 6. The lamp house 5 includes a light source including a plurality of (30 in the present embodiment) xenon flash lamps FL and a reflector 52 provided so as to cover the light source inside the housing 51. Composed. A lamp light emission window 53 is attached to the bottom of the casing 51 of the lamp house 5. The lamp light radiation window 53 constituting the floor of the lamp house 5 is a plate-like member made of quartz. By installing the lamp house 5 above the chamber 6, the lamp light emission window 53 faces the chamber window 61. The lamp house 5 heats the semiconductor wafer W by irradiating the semiconductor wafer W held by the holding unit 7 in the chamber 6 with flash light from the flash lamp FL via the lamp light emission window 53 and the chamber window 61. .

  Each of the plurality of flash lamps FL is a rod-shaped lamp having a long cylindrical shape, and the longitudinal direction of each of the flash lamps FL is along the main surface of the semiconductor wafer W held by the holding unit 7 (that is, along the horizontal direction). They are arranged in a plane so as to be parallel to each other. Therefore, the plane formed by the arrangement of the flash lamps FL is also a horizontal plane. The plane area of the plane formed by the arrangement of the plurality of flash lamps FL is at least larger than the semiconductor wafer W held by the holding unit 7.

  The xenon flash lamp FL has a rod-shaped glass tube (discharge tube) in which xenon gas is sealed and an anode and a cathode connected to a capacitor at both ends thereof, and an outer peripheral surface of the glass tube. And a triggered electrode. Since xenon gas is an electrical insulator, electricity does not flow into the glass tube under normal conditions even if electric charges are accumulated in the capacitor. However, when the insulation is broken by applying a high voltage to the trigger electrode, the electricity stored in the capacitor flows instantaneously in the glass tube, and light is emitted by excitation of atoms or molecules of xenon at that time. In such a xenon flash lamp FL, the electrostatic energy stored in the capacitor in advance is converted into an extremely short light pulse of 0.1 millisecond to 100 millisecond. It has the feature that it can irradiate strong light. The light emission time of the flash lamp FL can be adjusted by the coil constant of a lamp power source 99 (see FIG. 6) that supplies power to the flash lamp FL.

  In addition, the reflector 52 is provided above the plurality of flash lamps FL so as to cover all of them. The basic function of the reflector 52 is to reflect flash light emitted from the plurality of flash lamps FL toward the holding unit 7. The reflector 52 is formed of an aluminum alloy plate, and the surface (the surface facing the flash lamp FL) is roughened by blasting to exhibit a satin pattern. The roughening process is performed when the surface of the reflector 52 is a perfect mirror surface, and a regular pattern is generated in the intensity of the reflected light from the plurality of flash lamps FL, so that the surface temperature distribution of the semiconductor wafer W is obtained. This is because the uniformity of the is reduced.

  The control unit 3 controls the various operation mechanisms provided in the heat treatment apparatus 1. FIG. 6 is a block diagram illustrating a configuration of the control unit 3. The configuration of the control unit 3 as hardware is the same as that of a general computer. That is, the control unit 3 stores a CPU 31 that performs various arithmetic processes, a ROM 32 that is a read-only memory that stores basic programs, a RAM 33 that is a readable / writable memory that stores various information, control software, data, and the like. The magnetic disk 34 to be placed is connected to a bus line 39.

  Further, the bus line 39 includes a motor 40 of the holding unit lifting mechanism 4 that lifts and lowers the holding unit 7 in the chamber 6, a lamp power source 99 that supplies power to the flash lamp FL, and supply and discharge of processing gas into the chamber 6. Gas valves 82 and 87, the flow rate adjusting valve 85, a gate valve 185 for opening and closing the transfer opening 66, a plate power source 98 for supplying power to the zones 711 to 716 of the hot plate 71, and the like are electrically connected. The CPU 31 of the control unit 3 executes the control software stored in the magnetic disk 34 to control each of these operation mechanisms, and proceeds with the heat treatment of the semiconductor wafer W.

  Further, the display unit 35 and the input unit 36 are electrically connected to the bus line 39. The display unit 35 is configured by using, for example, a liquid crystal display and displays various information such as processing results and recipe contents. The input unit 36 is configured using, for example, a keyboard, a mouse, and the like, and receives input of commands, parameters, and the like. The operator of the apparatus can input commands and parameters from the input unit 36 while confirming the contents displayed on the display unit 35. The display unit 35 and the input unit 36 may be integrated to form a touch panel.

  In addition to the above configuration, the heat treatment apparatus 1 is used for various cooling purposes in order to prevent excessive temperature rise of the chamber 6 and the lamp house 5 due to the heat energy generated from the flash lamp FL and the hot plate 71 during the heat treatment of the semiconductor wafer W. It has the structure of For example, water-cooled tubes (not shown) are provided on the chamber side 63 and the chamber bottom 62 of the chamber 6. The lamp house 5 has an air cooling structure provided with a gas supply pipe 55 and an exhaust pipe 56 for exhausting heat by forming a gas flow therein (see FIGS. 1 and 5). Air is also supplied to the gap between the chamber window 61 and the lamp light emission window 53 to cool the lamp house 5 and the chamber window 61.

  Next, a processing procedure for the semiconductor wafer W will be described. FIG. 7 is a flowchart showing a part of the processing flow for the semiconductor wafer W. First, a pattern is formed on the surface of the silicon substrate 11 (see FIG. 9) using a photolithography technique, and impurities (ions) such as boron (B) and arsenic (As) are implanted into the source / drain regions (step S1). ). Impurity implantation is performed by an ion implantation method.

  Next, a carbon (C) thin film 12 is formed on the surface of the silicon substrate 11 implanted with impurities (step S2). Various known methods can be employed for forming the carbon thin film 12, and for example, it may be formed by plasma deposition. FIG. 9 is a cross-sectional view of a semiconductor wafer W formed by forming a carbon thin film 12 on the surface of a silicon substrate 11. In this embodiment, an amorphous carbon thin film 12 is formed by plasma deposition on the surface of a silicon substrate 11 into which impurities have been implanted by ion implantation. In this embodiment, the film thickness t (initial value of the film thickness) of the amorphous carbon thin film 12 formed on the surface of the silicon substrate 11 is 70 nm.

  Next, the light irradiation heat treatment by the heat treatment apparatus 1 is performed on the semiconductor wafer W on which the carbon thin film 12 is formed (step S3). The light irradiation heat treatment of the semiconductor wafer W in the heat treatment apparatus 1 will be further described later.

  The semiconductor wafer W that has been subjected to the light irradiation heat treatment in the heat treatment apparatus 1 is subjected to a cleaning process (step S4). The cleaning treatment here is so-called SPM cleaning (cleaning using a mixed solution of sulfuric acid and hydrogen peroxide solution) and APM cleaning (cleaning using a mixed solution of ammonia water and hydrogen peroxide solution). By this cleaning process, the carbon thin film 12 is completely removed from the surface of the silicon substrate 11. In this specification, the “semiconductor wafer W” includes both the silicon substrate 11 on which no thin film is formed on the surface and the silicon substrate 11 on which the thin film 12 is formed on the surface.

  FIG. 8 is a flowchart showing a processing procedure for the semiconductor wafer W in the heat treatment apparatus 1. The processing procedure of the semiconductor wafer W shown in FIG. 8 is executed by the control unit 3 controlling each operation mechanism of the heat treatment apparatus 1.

  First, the holding unit 7 is lowered from the processing position shown in FIG. 5 to the delivery position shown in FIG. 1 (step S20). The “processing position” is the position of the holding unit 7 when the semiconductor wafer W is irradiated with light from the flash lamp FL, and is the position in the chamber 6 of the holding unit 7 shown in FIG. Further, the “delivery position” is the position of the holding unit 7 when the semiconductor wafer W is carried in and out of the chamber 6, and is the position of the holding unit 7 shown in FIG. The reference position of the holding unit 7 in the heat treatment apparatus 1 is the processing position. Before the processing, the holding unit 7 is located at the processing position, and this is lowered to the delivery position at the start of processing.

  The holding unit 7 is moved up and down with respect to the support pin 70 fixedly installed in the chamber 6. As shown in FIG. 1, when the holding unit 7 is lowered to the delivery position, the holding unit 7 comes close to the chamber bottom 62 and moves to the support pin 70. The tip of the through hole protrudes above the holding portion 7 through the holding portion 7.

  Next, after the holding unit 7 is lowered to the delivery position, the gas valve 82 is opened, and an inert gas (in this embodiment, nitrogen gas) is supplied from the gas supply source 88 into the heat treatment space 65 of the chamber 6. At the same time, the gas valve 87 is opened and the gas in the heat treatment space 65 is exhausted (step S21). The nitrogen gas supplied to the chamber 6 flows from the gas introduction buffer 83 in the direction of the arrow AR4 shown in FIG. 2 in the heat treatment space 65, and is exhausted by utility exhaust through the exhaust path 86 and the gas valve 87. A part of the nitrogen gas supplied to the chamber 6 is also discharged from an outlet (not shown) provided inside the bellows 47.

  Subsequently, the gate valve 185 is opened to open the transfer opening 66, and the semiconductor wafer W having the carbon thin film 12 formed on the surface is transferred into the chamber 6 through the transfer opening 66 by the transfer robot outside the apparatus. Then, it is placed on the plurality of support pins 70 (step S22). When the semiconductor wafer W is loaded into the chamber 6, the transfer opening 66 is closed by the gate valve 185. Then, the holding unit elevating mechanism 4 raises the holding unit 7 from the delivery position to the processing position close to the chamber window 61 (step S23). In the process in which the holding unit 7 is lifted from the delivery position, the semiconductor wafer W is transferred from the support pins 70 to the susceptor 72 of the holding unit 7 and is placed and held on the upper surface of the susceptor 72. When the holding unit 7 is raised to the processing position, the semiconductor wafer W held by the susceptor 72 is also held at the processing position.

  Each of the six zones 711 to 716 of the hot plate 71 is heated to a predetermined temperature by a heater (resistive heating wire 76) individually incorporated in each zone (between the upper plate 73 and the lower plate 74). ing. When the holding unit 7 rises to the processing position and the semiconductor wafer W comes into contact with the holding unit 7, the semiconductor wafer W is preheated by the heater built in the hot plate 71, and the temperature gradually rises (step S24). .

  Preheating for about 60 seconds is performed at this processing position, and the temperature of the semiconductor wafer W rises to a preset preheating temperature T1. The preheating temperature T1 is set to about 200 ° C. to 600 ° C., preferably about 350 ° C. to 550 ° C., in which impurities added to the semiconductor wafer W are not likely to diffuse due to heat. Further, the distance between the holding unit 7 and the chamber window 61 can be arbitrarily adjusted by controlling the rotation amount of the motor 40 of the holding unit lifting mechanism 4.

  In parallel with the preheating of the semiconductor wafer W at the processing position, oxygen gas is introduced into the heat treatment space 65 of the chamber 6 (step S25). That is, oxygen gas is supplied from the gas supply source 88 to the heat treatment space 65 via the gas introduction path 81. At this time, only oxygen gas may be supplied, or oxygen gas may be supplied as a mixed gas mixed with nitrogen gas. The flow rate of the oxygen gas supplied from the gas supply source 88 to the heat treatment space 65 is adjusted by the control unit 3 controlling the gas valve 82 and the flow rate adjusting valve 85. In the present embodiment, the oxygen concentration in the heat treatment space 65 in the chamber 6 is set to 90% or more by supplying the oxygen gas in step S25.

  After the preheating time of about 60 seconds elapses and the oxygen concentration in the chamber 6 reaches 90% or more, the control unit 3 controls the flash lamp FL of the lamp house 5 while the holding unit 7 remains in the processing position. Flash light is irradiated toward the semiconductor wafer W (step S26). At this time, a part of the flash light emitted from the flash lamp FL goes directly to the holding part 7 in the chamber 6, and the other part is once reflected by the reflector 52 and then goes into the chamber 6. Flash heating of the semiconductor wafer W is performed by irradiation of the flash light. Since the flash heating is performed by flash irradiation from the flash lamp FL, the surface temperature of the semiconductor wafer W can be increased in a short time.

  That is, the flash light irradiated from the flash lamp FL of the lamp house 5 is converted into a light pulse having a very short electrostatic energy stored in advance, and the irradiation time is about 0.1 milliseconds to 100 milliseconds. It is a very short and strong flash. Then, the surface temperature of the semiconductor wafer W that is flash-heated by flash irradiation from the flash lamp FL (more precisely, the surface temperature of the carbon thin film 12) instantaneously rises to the processing temperature T2, and is injected into the semiconductor wafer W. After the impurities are activated, the surface temperature drops rapidly. As described above, in the heat treatment apparatus 1, the surface temperature of the semiconductor wafer W can be raised and lowered in a very short time, so that the impurities are activated while suppressing diffusion of the impurities injected into the semiconductor wafer W due to heat. Can do. Since the time required for the activation of impurities is extremely short compared to the time required for the thermal diffusion, the activation is possible even in a short time in which diffusion of about 0.1 millisecond to 100 millisecond does not occur. Complete.

  FIG. 10 is a schematic diagram showing a state in which flash light is irradiated onto the semiconductor wafer W on which the carbon thin film 12 is formed. As the film thickness of the carbon thin film 12 formed on the surface increases, the surface reflectance of the semiconductor wafer W decreases, and is about 60% at the film thickness of 70 nm of this embodiment. The decrease in the surface reflectance means that the flash light absorption rate of the semiconductor wafer W is increased, more specifically, the flash light absorption rate of the carbon thin film 12 is increased. Note that the emission spectral distribution of the flash light from the xenon flash lamp FL is from the ultraviolet region to the near infrared region, and hardly transmits the silicon substrate 11.

  The decrease in the surface reflectance of the semiconductor wafer W accompanying the increase in the film thickness of the carbon thin film 12 is due to the increase in the flash light absorption rate of the thin film 12 itself as the film thickness increases. That is, when the carbon thin film 12 becomes thicker than a certain level, a part of the irradiated flash light is absorbed by the thin film 12 as indicated by an arrow AR10 in FIG. The absorptance increases as the thickness of the thin film 12 increases. Heat is generated on the surface of the carbon thin film 12 that has absorbed the flash light, and the heat is conducted to the surface of the silicon substrate 11 as indicated by an arrow AR11.

  Thus, the carbon thin film 12 having a certain thickness or more functions as a light absorption film, and increases the flash light absorption rate of the semiconductor wafer W. As a result of the increase of the flash light absorption rate of the semiconductor wafer W, the thin film 12 forms the surface arrival temperature of the semiconductor wafer W at the time of flash light irradiation (strictly speaking, the surface arrival temperature of the silicon substrate 11 into which impurities are implanted). As a result, the impurity is activated more satisfactorily than when not being performed.

  FIG. 11 is a diagram illustrating a correlation between the charge voltage and the sheet resistance value. The charge voltage shown on the horizontal axis is a voltage applied to a capacitor of a lamp power source 99 (see FIG. 6) that supplies power to the flash lamp FL, and is an index indicating the magnitude of the energy of flash light emitted from the flash lamp FL. It is. The sheet resistance value Rs shown on the vertical axis is an index indicating the degree of impurity activation. The lower the sheet resistance value, the higher the surface of the semiconductor wafer W is heated and the better the impurity activation process is performed. It is shown that. In FIG. 11, a solid line indicates a correlation with respect to the semiconductor wafer W of the present embodiment in which the carbon thin film 12 is formed, and a dotted line indicates a semiconductor wafer in which the carbon thin film 12 is not formed. Is the correlation.

  As shown in the figure, when the charge voltage is the same, the sheet resistance value is lower when the carbon thin film 12 is formed, that is, the surface of the semiconductor wafer W is heated to a higher temperature. The difference in sheet resistance value is particularly noticeable when the charge voltage is low. If the semiconductor wafer W is formed with the carbon thin film 12 as in this embodiment, the sheet resistance value is sufficiently low even at a low charge voltage. Can be obtained. That is, if the carbon thin film 12 is formed on the surface of the semiconductor wafer W, even if the energy of flash light from the flash lamp FL is relatively small, the surface temperature is raised to a higher temperature and the sheet resistance value is lowered. Can do it.

  Further, as shown in FIG. 10, the flash light irradiated from the flash lamp FL is once absorbed by the uniformly formed carbon thin film 12, and heat is generated in the thin film 12, and the heat is generated by silicon as indicated by an arrow AR11. It will conduct to the surface of the substrate 11. For this reason, even if there is a variation in the absorptance due to pattern formation on the surface of the silicon substrate 11, the variation in the absorptance is alleviated as compared with the case where the thin film 12 is not formed, and impurities are implanted. The surface of the silicon substrate 11 is heated uniformly.

In the present embodiment, the oxygen concentration in the chamber 6 at the time of irradiating flash light from the flash lamp FL is 90% or more. For this reason, carbon and oxygen of the thin film 12 heated by flash light irradiation react with each other to generate carbon dioxide (CO ₂ ) or carbon monoxide (CO). As a result, the carbon of the thin film 12 is vaporized and consumed, and the film thickness of the thin film 12 decreases. That is, the carbon thin film 12 functions as a light absorbing film during flash light irradiation, and at the same time, the carbon thin film 12 is peeled by introducing oxygen into the chamber 6. Since the generated carbon oxide is a gas, it is exhausted to the outside of the heat treatment apparatus 1 through the exhaust path 86 and the gas valve 87 together with the atmospheric gas in the chamber 6.

  The rate at which carbon is consumed during the flash light irradiation and the film thickness of the thin film 12 decreases is not uniform in the plane of the semiconductor wafer W. That is, the intensity of the flash light irradiated from the flash lamp FL to the heat treatment space 65 through the lamp light emission window 53 and the chamber window 61 is not necessarily uniform, and the intensity distribution varies in the plane of the semiconductor wafer W. . For this reason, variation in the in-plane temperature distribution of the thin film 12 results in nonuniform film thickness reduction rate.

  FIG. 12 is a diagram schematically showing the variation in the film thickness reduction of the carbon thin film 12. The flash light irradiated from the flash lamp FL to the heat treatment space 65 through the lamp light emission window 53 and the chamber window 61 has a weak flash light as indicated by an arrow AR12 and a strong intensity as indicated by an arrow AR13. Suppose that the flash light is included. In this case, the region irradiated with the flash light stronger than the region irradiated with the weak flash light on the surface of the carbon thin film 12 is heated to a higher temperature. As a result, the reaction with the oxygen in the surrounding atmosphere is activated in the region irradiated with the stronger flash light than the region irradiated with the weak flash light, the film thickness reduction rate is increased, and the film of the carbon thin film 12 is increased. The thickness becomes non-uniform as shown in FIG.

  The flash light absorptance of the carbon thin film 12 depends on the film thickness, and the greater the film thickness, the greater the absorptance. Therefore, as a result of the non-uniform thickness of the thin film 12 as described above, the remaining film thickness is larger in the region irradiated with the weak flash light than in the region irradiated with the strong flash light, and the flash light. Absorption rate increases. In the region where the intensity of the flash light to be irradiated is stronger, the film thickness of the thin film 12 becomes thinner and the flash light absorption rate becomes smaller. As a result, the surface temperature of the region decreases. Is uniform. That is, the non-uniformity of the film thickness of the thin film 12 caused by the difference in the intensity of the flash light acts so as to eliminate the variation in the in-plane temperature distribution. If the in-plane temperature distribution of the thin film 12 as a whole becomes uniform, the surface of the silicon substrate 11 into which the impurities are implanted is also heated uniformly.

  When a predetermined time (several seconds) has elapsed after the end of the flash heating, nitrogen gas is again supplied from the gas supply source 88 to the heat treatment space 65, and gas containing oxygen gas in the heat treatment space 65 is exhausted from the discharge path 86. . Thereby, the atmosphere in the chamber 6 is replaced with nitrogen gas (step S27).

  Thereafter, the holding unit 7 is lowered again to the delivery position shown in FIG. 1 by the holding unit lifting mechanism 4, and the semiconductor wafer W is transferred from the holding unit 7 to the support pins 70 (step S28). Subsequently, the transfer opening 66 closed by the gate valve 185 is opened, and the semiconductor wafer W placed on the support pins 70 is unloaded by a transfer robot outside the apparatus, and the semiconductor wafer W is flushed in the heat treatment apparatus 1. The heating process (annealing process) is completed (step S29).

  As described above, in the present embodiment, by forming the carbon thin film 12 on the surface of the semiconductor wafer W, the flash light is absorbed by the carbon thin film 12. The carbon thin film 12 is heated by absorbing the flash light, and the surface resistance of the silicon substrate 11 into which impurities are implanted is raised to a higher temperature than the case where the thin film 12 is not formed. Can be reduced.

  In particular, if the carbon thin film 12 is formed on the surface of the semiconductor wafer W, a sufficiently low sheet resistance value can be obtained even at a low charge voltage as shown in FIG. Therefore, a low sheet resistance value can be realized without increasing the loads of the flash lamp FL and the lamp power source 99.

  Further, since the oxygen concentration in the chamber 6 is set to 90% or more and the semiconductor wafer W on which the carbon thin film 12 is formed is irradiated with flash light, the heated thin film 12 is oxidized and vaporized. Is consumed. As a result, the carbon thin film 12 is peeled off during flash heating, and the remaining carbon film can be removed only by ordinary SPM cleaning and APM cleaning in the subsequent cleaning process (step S4). When the flash light is irradiated without introducing oxygen gas into the chamber 6, the carbon of the thin film 12 is not consumed, so that the initial film thickness is generally maintained as it is even after the flash heating. In this case, the thin film 12 cannot be sufficiently removed only by ordinary SPM cleaning or APM cleaning, and it is necessary to perform a separate ashing process before the cleaning process in step S4. As in this embodiment, if oxygen gas is introduced into the chamber 6 and the oxygen concentration at the time of flash light irradiation is 90% or more, the thin film 12 can be simultaneously peeled off by flash light irradiation. The remaining film can be surely removed by omitting the ashing process and performing only a normal cleaning process. Note that the carbon thin film 12 does not completely vaporize when irradiated with flash light, and the remaining film also functions as an antioxidant film on the surface of the silicon substrate 11.

  Furthermore, in the present embodiment, when the flash light from the flash lamp FL varies, the film thickness reduction rate of the thin film 12 also varies and the film thickness becomes non-uniform. Acts to eliminate the variation in the in-plane temperature distribution of the semiconductor wafer W. That is, as the intensity of the irradiated flash light is higher, the film thickness of the carbon thin film 12 becomes thinner and the flash light absorptance becomes lower. As a result, the surface temperature of the area decreases, and the surface of the semiconductor wafer W is reduced. As a whole, the in-plane temperature distribution becomes uniform.

  By the way, when the semiconductor wafer W on which the carbon thin film 12 is formed is subjected to flash heat treatment, carbon-based contamination may adhere to the inside of the chamber 6. When such contamination occurs, without containing the semiconductor wafer W in the chamber 6, oxygen gas is introduced into the chamber 6 to increase the oxygen concentration to 90% or more, and flash light is emitted from the flash lamp FL. To do. That is, the empty flash process is performed with the oxygen concentration in the chamber 6 set to 90% or more. Similar to the flash heating process of the semiconductor wafer W, the controller 3 controls each operation mechanism (the gas valves 82 and 87, the flow rate adjustment valve 85, the lamp power supply 99, etc.) of the heat treatment apparatus 1 as well. Executed. By irradiating the flash light from the flash lamp FL with the oxygen concentration in the chamber 6 being 90% or more without accommodating the semiconductor wafer W in the chamber 6, the carbon-based contaminants are oxidized and removed. That is, the cleaning process in the chamber 6 is performed by performing the empty flash process with the oxygen concentration in the chamber 6 being 90% or more.

  While the embodiments of the present invention have been described above, the present invention can be modified in various ways other than those described above without departing from the spirit of the present invention. For example, in the above-described embodiment, the amorphous carbon thin film 12 is formed on the surface of the silicon substrate 11 into which impurities are implanted. However, the thin film 12 is made of carbon having a crystal structure (for example, graphite) instead of amorphous carbon. May be formed. Even if the thin film 12 is formed of carbon having a crystal structure, the same effect as the above embodiment can be obtained. However, if the thin film 12 is formed of amorphous carbon, the thin film 12 is more easily oxidized during flash heating, and the peeling treatment of the thin film 12 proceeds more easily.

  Moreover, you may make it form the thin film 12 with a carbon compound. Examples of the carbon compound suitable for forming the thin film 12 as the light absorption film include organic compounds, and carbon and hydrogen, or a compound containing oxygen in addition to them is preferable. That is, any form may be used as long as the thin film 12 of carbon or carbon compound is formed on the surface of the silicon substrate 11 into which impurities are implanted.

  In the above embodiment, the film thickness t of the amorphous carbon thin film 12 formed on the surface of the silicon substrate 11 is 70 nm. However, the present invention is not limited to this. At least the film thickness t is 20 nm or more. If the carbon compound thin film 12 is formed, an effect as a light absorption film can be obtained. However, since the flash light absorptance of the thin film 12 increases as the film thickness of the thin film 12 increases, the film thickness of the thin film 12 is required to absorb the flash light and raise the temperature of the silicon substrate 11 more effectively. It is preferable that t is 70 nm or more. On the other hand, even if the film thickness t of the thin film 12 exceeds 280 nm, there is no significant change in the temperature rise effect as the light absorption film. Rather, the thickness of the remaining film after flash heating is increased and the subsequent cleaning process is performed. There is a risk that it will not be able to be removed sufficiently. Therefore, the preferred film thickness t of the carbon or carbon compound thin film 12 formed on the surface of the silicon substrate 11 is 70 nm or more and 280 nm or less.

  In the above embodiment, the oxygen concentration in the chamber 6 at the time of flash light irradiation is set to 90% or more. However, the present invention is not limited to this, and there is a slight amount around the semiconductor wafer W at the time of flash light irradiation. However, if oxygen gas is present, the effect of oxidizing and peeling off the carbon of the thin film 12 can be obtained. However, in order to obtain a sufficient peeling effect of the thin film 12 and to eliminate the non-uniformity of the in-plane temperature distribution due to the variation in the intensity distribution of the flash light, the inside of the chamber 6 at the time of flash light irradiation is obtained. The oxygen concentration is preferably as high as possible, and the oxygen concentration is particularly preferably 90% or more. If the oxygen concentration in the chamber 6 is 90% or more, it is possible to prevent carbon-based contamination from adhering to the inside of the chamber 6 when irradiated with flash light.

  On the other hand, from the viewpoint of obtaining a lower sheet resistance value, it is preferable that the oxygen concentration in the chamber 6 is lower when the flash light is irradiated. However, in order to obtain an effective peeling effect of the thin film 12, an anti-contamination effect on the inside of the chamber 6, and an effect of eliminating unevenness of the in-plane temperature distribution, the inside of the chamber 6 at the time of irradiation with flash light It is desirable that the oxygen concentration is higher than the oxygen concentration in the atmosphere, that is, the oxygen concentration is 21% or more. Therefore, the oxygen concentration in the chamber 6 at the time of irradiation with flash light is 21% or more and 100% in consideration of the balance of required sheet resistance value, uniformity of in-plane temperature distribution, peeling effect of the thin film 12, and the like. Any value between% and below can be used. In order to obtain only a low sheet resistance value, a semiconductor in which a carbon thin film 12 is formed on the surface without introducing oxygen gas into the chamber 6 (for example, the interior of the chamber 6 is a nitrogen atmosphere). The wafer W may be irradiated with flash light.

  Further, the timing of introducing the oxygen gas into the chamber 6 is not limited to the example of FIG. 8, and may be introduced before the preheating. That is, the timing for introducing oxygen gas into the chamber 6 is arbitrary as long as the oxygen concentration in the chamber 6 at the time of flash light irradiation is a predetermined value.

  In the above embodiment, the lamp house 5 is provided with 30 flash lamps FL. However, the present invention is not limited to this, and the number of flash lamps FL can be any number. The flash lamp FL is not limited to a xenon flash lamp, and may be a krypton flash lamp.

  In the above embodiment, the semiconductor wafer W is preheated by heat transfer from the holding unit 7 including the hot plate 71. However, a halogen lamp is provided at the bottom of the chamber 6, and light irradiation from the halogen lamp is performed. Thus, the semiconductor wafer W may be preheated.

  The technique according to the present invention can also be applied to a glass substrate on which a silicon film is formed.

DESCRIPTION OF SYMBOLS 1 Heat processing apparatus 3 Control part 4 Holding part raising / lowering mechanism 5 Lamp house 6 Chamber 7 Holding part 11 Silicon substrate 12 Thin film 60 Upper opening 61 Chamber window 65 Heat treatment space 71 Hot plate 72 Susceptor 81 Gas introduction path 82, 87 Gas valve 85 Flow control valve 88 Gas supply source 99 Lamp power supply FL Flash lamp W Semiconductor wafer

Claims (3)

A heat treatment method for heating a substrate by irradiating flash light onto the substrate into which impurities are implanted,
Forming a thin film of carbon or a carbon compound on the surface of the substrate into which impurities are implanted;
Accommodating a substrate on which a thin film is formed in a chamber;
Introducing oxygen gas into the chamber after irradiating flash light after accommodating the substrate in the chamber;
Irradiating the substrate contained in the chamber with flash light from a flash lamp to heat the substrate in an oxygen atmosphere and oxidize and vaporize the thin film; and
Removing the thin film remaining by performing a cleaning process on the substrate unloaded from the chamber;
Equipped with a,
A heat treatment method , wherein an oxygen concentration in the chamber at the time of irradiation with flash light is made higher than an oxygen concentration in the atmosphere . The heat treatment method according to claim 1,
In the cleaning process, a mixed solution of sulfuric acid and hydrogen peroxide solution and a mixed solution of ammonia water and hydrogen peroxide solution are used. In the heat processing method of Claim 1 or Claim 2,
A heat treatment method, wherein the oxygen concentration in the chamber at the time of irradiation with flash light is 90% or more.

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