JP5620114B2 - Heat treatment method and heat treatment apparatus - 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 and a heat treatment apparatus 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). 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.

  In addition, the intensity distribution of the flash light in the plane of the semiconductor wafer is not completely uniform, and it is recognized that the intensity at the peripheral portion is stronger than the central portion of the semiconductor wafer due to the influence of reflection on the chamber wall surface. As a result, the in-plane temperature distribution of the semiconductor wafer at the time of flash light irradiation also has a variation in which the temperature at the peripheral portion tends to be higher than the central portion. 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.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a heat treatment method and a heat treatment apparatus capable of lowering the sheet resistance value by raising the temperature of the substrate surface more uniformly and at a higher temperature.

In order to solve the above-mentioned problem, the invention of claim 1 is a non-uniform film on the surface of a substrate into which impurities are implanted in a heat treatment method in which the substrate into which impurities are implanted is irradiated with flash light to heat the substrate. A thin film forming step of forming a thin film of a light-absorbing film having a thickness distribution; and a light irradiation step of irradiating flash light from a flash lamp onto the substrate on which the thin film is formed, the thin film forming step comprising: A thin film having a film thickness that gradually decreases gradually from the center to the periphery is formed on the surface.

According to a second aspect of the present invention, in the heat treatment method according to the first aspect of the present invention, the film thickness difference between the central portion and the peripheral portion of the thin film is 8 nm or more and 30 nm or less.

According to a third aspect of the present invention, in the heat treatment method according to the first or second aspect of the invention, the thin film forming step includes a thin film deposition step of depositing a thin film on the surface of the substrate, and a deposition on the surface of the substrate. And a thin film processing step for processing the thin film so that the thickness of the thin film decreases from the central portion toward the peripheral portion.

According to a fourth aspect of the present invention, in the heat treatment method according to the third aspect of the present invention, in the thin film deposition step, a thin film of carbon or a carbon compound is deposited on the surface of the substrate, and the thin film processing step is performed on the substrate. It has the process of supplying a large amount of oxygen gas to a peripheral part rather than a center part, heating.

According to a fifth aspect of the present invention, in the heat treatment method according to the first aspect of the invention, in the thin film forming step, a first thin film of carbon or a carbon compound is deposited on the surface of the substrate, and the center is formed on the first thin film. A second thin film of silicon nitride, polycrystalline silicon, or amorphous silicon whose film thickness decreases from the portion toward the peripheral portion is formed.

According to a sixth aspect of the present invention, a thin film of carbon or a carbon compound is formed on the surface of a heat treatment apparatus that heats a substrate into which impurities are implanted by irradiating the substrate with flash light after the impurities are implanted. A chamber for containing the substrate; a holding means for holding the substrate in the chamber; a preheating means for preheating the substrate held in the holding means; and a flash on the substrate held in the holding means A flash lamp for irradiating light; an oxygen gas supply means for supplying oxygen gas from the periphery of the substrate held by the holding means in the chamber; and the chamber from below the substrate held by the holding means An exhaust means for exhausting the atmosphere inside the substrate, and the substrate held by the holding means is heated by the preheating means to supply the oxygen gas. From the flash lamp, the thickness of the thin film formed on the surface of the substrate is reduced from the center to the peripheral edge by the exhaust means exhausting the atmosphere in the chamber while supplying oxygen gas from the means. And a control means for irradiating flash light.

The invention of claim 7 is the heat treatment apparatus according to the invention of claim 6 , wherein the film thickness difference between the central portion and the peripheral portion of the thin film at the time of flash light irradiation is 8 nm or more and 30 nm or less. .

According to the first to fifth aspects of the present invention, a thin film of a light absorption film having a non-uniform film thickness distribution 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. Therefore, the thin film absorbs flash light to increase the temperature, and the substrate surface can be heated to a higher temperature to decrease the sheet resistance value. In addition, variations in the intensity distribution of flash light can be eliminated by a thin film having a non-uniform film thickness distribution, and the substrate surface can be heated uniformly. Furthermore, since a thin film is formed on the surface of the substrate with the film thickness gradually and gradually decreasing from the center to the periphery, the variation in the intensity distribution of the flash light in which the light intensity at the periphery is stronger than the center. The temperature of the substrate surface can be uniformly increased by eliminating the temperature.

In particular, according to the invention of claim 4 , since a thin film of carbon or a carbon compound is deposited on the surface of the substrate and a large amount of oxygen gas is supplied to the peripheral portion rather than the central portion while heating the substrate, It is possible to easily perform processing such that the thickness of the thin film deposited on the surface of the substrate becomes thinner from the central portion toward the peripheral portion.

In particular, according to the invention of claim 5 , a silicon nitride having a carbon or carbon compound first thin film deposited on the surface of the substrate and having a thickness decreasing from the central portion toward the peripheral portion on the first thin film, Since the second thin film of polycrystalline silicon or amorphous silicon is formed, the second thin film can suppress the scattering of carbon-based contaminants from the first thin film.

According to the inventions of claims 6 and 7 , the substrate on which the carbon or carbon compound thin film is formed after the impurities are implanted is heated by the preheating means, and the oxygen gas is supplied from the oxygen gas supply means. In order to irradiate flash light from the flash lamp after the film thickness is reduced from the central part to the peripheral part of the thin film formed on the surface of the substrate by the exhaust means exhausting the atmosphere in the chamber while supplying the thin film However, the temperature of the substrate can be increased by absorbing flash light, and the sheet resistance can be lowered by increasing the temperature of the substrate surface to a higher temperature. In addition, the thin film whose film thickness decreases from the center to the periphery, eliminates the variation in the intensity distribution of the flash light that increases the light intensity at the periphery rather than the center, and uniformly raises the temperature of the substrate surface. Can do.

It is a longitudinal cross-sectional view which shows the structure of the heat processing apparatus which concerns on this invention. It is a partial expanded sectional view which shows the gas supply mechanism to a chamber. It is the schematic plan view which cut | disconnected the chamber along the horizontal surface in the height position of the gas discharge outlet. 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 immediately after forming the carbon thin film on the surface of a silicon substrate. It is the schematic which shows the airflow formed in a chamber. It is sectional drawing of the semiconductor wafer after a carbon thin film is processed. It is sectional drawing of the semiconductor wafer which formed the thin film of the multiple layer on the surface of the silicon substrate.

  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. When the gate valve 185 closes the transfer opening 66, the heat treatment space 65 becomes a sealed space. When the gate valve 185 opens the transfer opening 66, the semiconductor wafer W can be carried into and out of the heat treatment space 65.

Further, a gas introduction path 81 for introducing a processing gas into the heat treatment space 65 is connected to the chamber side portion 63. The distal end of the gas introduction path 81 is connected to a gas introduction buffer 83 formed inside the chamber side portion 63, and the proximal 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), argon gas (Ar), or oxygen gas (O ₂ ), ammonia gas (NH ₃ ), ozone gas (O ₃ ). ) Or the like is fed to the gas introduction path 81. The gas supply source 88 supplies these gases as a processing gas, alternatively or as a mixture.

  FIG. 2 is a partial enlarged cross-sectional view showing a gas supply mechanism to the chamber 6. In the figure, the support pins 70 are omitted. As described above, the ring 631 made of aluminum alloy having excellent flash resistance is fitted into the upper part of the inner side surface of the chamber side portion 63 made of stainless steel. By fitting the ring 631 into the chamber side portion 63, a gas discharge port 89 is formed between the lower end of the ring 631 and the chamber side portion 63 as shown in FIG. FIG. 3 is a schematic plan view in which the chamber 6 is cut along the horizontal plane at the height position of the gas discharge port 89. The gas discharge port 89 formed between the ring 631 and the chamber side portion 63 is a slit formed in an annular shape along the horizontal direction. An annular slit-shaped gas discharge port 89 communicates with a gas introduction buffer 83 formed inside the chamber side portion 63. Three gas introduction paths 81 are connected to the gas introduction buffer 83 in communication. That is, the tip of the gas introduction path 81 is branched into three and connected to the gas introduction buffer 83. The leading ends of the three gas introduction paths 81 are connected to the gas introduction buffer 83 at equal intervals along the cylindrical circumferential direction of the chamber side portion 63 (that is, every 120 °).

  By opening the gas valve 82, the processing gas is supplied from the gas supply source 88 to the gas introduction path 81 and guided to the gas introduction buffer 83 from three directions. The supply flow rate of the processing gas is determined by the flow rate adjustment valve 85. As shown in FIG. 3, the processing gas flowing into the gas introduction buffer 83 flows from the gas discharge port 89 into the heat treatment space 65 while flowing so as to expand in the gas introduction buffer 83 whose flow path resistance is smaller than that of the gas discharge port 89. And evenly discharged.

  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 to 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 to the shaft 41 by a hook-like member (not shown). 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.

  The bellows lower end plate 471 is formed with a gas exhaust port 472 for exhausting the gas in the heat treatment space 65. The gas exhaust port 472 is provided immediately below the lower opening 64, that is, near the bottom center of the chamber 6. The gas exhaust port 472 is connected to an exhaust pump 474 through a gas valve 473 and a flow rate adjustment valve 475. When the gas valve 473 is opened while the exhaust pump 474 is operated, the gas in the chamber 6 is discharged from the lower opening 64 to the outside of the chamber through the gas exhaust port 472. A discharge passage 86 for discharging the gas in the heat treatment space 65 is also formed in the transfer opening 66 and connected to an exhaust mechanism (not shown) via a gas valve 87. This exhaust mechanism may be the same as the exhaust pump 474 described above.

  When the atmosphere in the chamber 6 is exhausted from the gas exhaust port 472 while discharging the processing gas from the gas discharge port 89 to the heat treatment space 65 in the chamber 6, the processing gas discharged from the inside of the chamber side portion 63 is discharged from the chamber bottom portion 62. A gas flow toward the center of the heat treatment space 65 is formed.

  FIG. 4 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. 5 is a plan view showing the hot plate 71. As shown in FIG. 5, the hot plate 71 includes a disk-shaped zone 711 and an annular zone 712 that are concentrically arranged in the center of the region facing the semiconductor wafer W to be held, and the 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 disposed in each of the six zones 711 to 716 are connected to a plate power source 98 (see FIG. 7) 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. 7) 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. 7 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, 87, 473, flow rate adjustment valves 85, 475, gate valve 185 that opens and closes the transfer opening 66, plate power supply 98 that supplies power to the zones 711 to 716 of the hot plate 71, and an exhaust pump 474. 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 6). 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. 8 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. 10 ) using a photolithography technique, and impurities (ions) such as boron (B) and arsenic (As) are implanted into the source / drain regions (step S101). ). 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 into which impurities have been implanted (step S102). Various known methods can be employed to form the carbon thin film 12. For example, carbon may be deposited by plasma deposition to form the thin film 12. FIG. 10 is a cross-sectional view of the semiconductor wafer W immediately after the carbon thin film 12 is formed on the surface of the silicon substrate 11. In this embodiment, an amorphous carbon thin film 12 is deposited and formed by plasma deposition on the surface of a silicon substrate 11 into which impurities are implanted by an ion implantation method. The film thickness of the thin film 12 immediately after being deposited by plasma deposition is generally uniform in the plane of the silicon substrate 11. In this embodiment, the film thickness (film) of the amorphous carbon thin film 12 deposited on the surface of the silicon substrate 11 is used. The initial value of the thickness is 100 nm or more. As shown in FIG. 10, the carbon thin film 12 is formed so as to slightly wrap around the side end portion of the silicon substrate 11.

  Next, the semiconductor wafer W on which the carbon thin film 12 is deposited is carried into the heat treatment apparatus 1, and the carbon thin film 12 is processed (step S103) and the light irradiation heat treatment (step S104) is performed on the semiconductor wafer W. The carbon thin film processing and light irradiation heat treatment 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 S105). 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. 9 is a flowchart showing a processing procedure for the semiconductor wafer W in the heat treatment apparatus 1. In the present embodiment, the heat treatment apparatus 1 performs both the processing of the carbon thin film 12 and the subsequent light irradiation heat treatment. The processing procedure of the semiconductor wafer W shown in FIG. 9 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. 6 to the delivery position shown in FIG. 1 (step S111). 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 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 valves 87 and 473 are opened, and the gas in the heat treatment space 65 is exhausted (step S112). The nitrogen gas supplied into the chamber 6 from the gas discharge port 89 flows downward toward the lower opening 64 located at the center of the chamber bottom 62 in the heat treatment space 65 and is exhausted out of the chamber through the gas exhaust port 472. . A part of the nitrogen gas supplied to the chamber 6 is also exhausted from the exhaust path 86.

  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 S113). 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 a processing position close to the chamber window 61 (step S114). 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. The semiconductor wafer W held at the processing position is located slightly above the gas discharge port 89.

  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 S115). .

  By this preheating, 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 this embodiment, 500 ° C.) at 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 S116). 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 flow rate adjustment valve 85.

  In addition, oxygen gas is supplied to the heat treatment space 65 and the atmosphere in the chamber 6 is continuously exhausted (step S117). That is, the gas valve 473 is opened and the gas in the heat treatment space 65 is exhausted from the gas exhaust port 472. The exhaust flow rate from the gas exhaust port 472 is adjusted by the control unit 3 controlling the flow rate adjustment valve 475. Part of the atmosphere in the chamber 6 is also exhausted from the exhaust path 86. Note that the exhaust flow rate from the gas exhaust port 472 is significantly larger than the exhaust flow rate exhausted from the exhaust path 86.

  FIG. 11 is a schematic view showing the airflow formed in the chamber 6. The gas discharge port 89 is a slit formed in an annular shape along the horizontal direction in the chamber side 63 (exactly between the chamber side 63 and the ring 631) slightly below the holding portion 7 at the processing position. It is. Therefore, the gas discharge port 89 is formed in a slit shape so as to surround the periphery of the semiconductor wafer W held by the holding unit 7 at the processing position, and a gas containing oxygen gas is uniformly supplied from the periphery of the semiconductor wafer W. Will be. On the other hand, the atmosphere in the chamber 6 is exhausted from the gas exhaust port 472 through the center of the chamber bottom 62, that is, the lower opening 64 located immediately below the center of the holding unit 7. Therefore, the atmosphere in the chamber 6 is exhausted from below the semiconductor wafer W held by the holding unit 7 at the processing position.

  As a result of the supply and exhaust as described above, an air flow containing oxygen gas as shown in FIG. 11 is formed inside the chamber 6. Most of the air flow including oxygen gas discharged from the slit-like gas discharge port 89 flows from the lower side of the holding part 7 at the processing position toward the lower opening 64, but a part thereof is above the holding part 7 (ie, the semiconductor wafer Also flows into the surface side of W). Inside the chamber 6, the periphery of the lower opening 64 has a negative pressure, so that the airflow that has flowed into the upper side of the holding unit 7 eventually passes through the side of the holding unit 7 and flows toward the lower opening 64. . As a result, the air stream containing oxygen gas is supplied to the peripheral edge of the semiconductor wafer W to some extent, but hardly reaches the vicinity of the center. That is, a larger amount of oxygen gas is supplied to the peripheral portion than the central portion of the semiconductor wafer W held by the holding portion 7 at the processing position.

When oxygen gas is supplied to the surface of the semiconductor wafer W heated up to the preheating temperature T1, carbon and oxygen in the thin film 12 react to generate carbon dioxide (CO ₂ ) or carbon monoxide (CO). Is done. 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 is etched by supplying oxygen gas to the preheated semiconductor wafer W. Since the generated carbon oxide is a gas, it is exhausted from the gas exhaust port 472 and the exhaust path 86 to the outside of the heat treatment apparatus 1 together with the atmosphere in the chamber 6.

  At this time, since a larger amount of oxygen gas is supplied to the peripheral portion than to the central portion of the semiconductor wafer W, the carbon consumption rate (that is, the etching rate of the thin film 12) is gradually increased in the peripheral portion. Become. As a result, processing is performed so that the film thickness of the amorphous carbon thin film 12 deposited on the surface of the silicon substrate 11 is gradually (analogically) gradually reduced from the central portion toward the peripheral portion. This is the carbon thin film processing in step S103 of FIG.

  The process waits for a predetermined time in a state where the oxygen gas is supplied to the semiconductor wafer W held by the holding unit 7 at the processing position and preheated (step S118). The waiting time varies depending on the preheating temperature T1, and it is necessary to increase the waiting time as the preheating temperature T1 is lower. In the present embodiment, the preheating temperature T1 is 500 ° C. In this case, the standby time is 2 minutes to 3 minutes. As a result, processing is performed such that the film thickness of the carbon thin film 12 gradually decreases from the central part toward the peripheral part, and the film thickness difference between the central part and the peripheral part becomes a predetermined value or more.

FIG. 12 is a cross-sectional view of the semiconductor wafer W after the carbon thin film 12 has been processed. By supplying a larger amount of oxygen gas to the peripheral portion than the central portion to the surface of the pre-heated semiconductor wafer W, processing is performed so that the film thickness of the thin film 12 decreases from the central portion toward the peripheral portion. On the surface of the silicon substrate 11, a thin film 12 (convex lens-shaped thin film) is formed in which the film thickness gradually and gradually decreases from the center to the periphery. At the time when the predetermined standby time in step S118 has elapsed, the film thickness difference t _d between the film thickness t _{c at} the center of the carbon thin film 12 and the film thickness t _e at the peripheral edge is set to 8 nm to 30 nm. Yes. In the present embodiment, the thickness t _c of the center portion of the thin film 12 is about 80 nm, the film thickness t _e of the peripheral portion is about 70 nm.

  When the predetermined standby time in step S118 has elapsed, flash light is emitted from the flash lamp FL of the lamp house 5 toward the semiconductor wafer W under the control of the control unit 3 while the holding unit 7 is positioned at the processing position. (Step S119). 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. This process is the light irradiation heat treatment in step S104 of FIG.

  A carbon thin film 12 is formed on the surface of the semiconductor wafer W to be processed. As the film thickness of such a carbon thin film 12 increases, the surface reflectance of the semiconductor wafer W decreases, and is approximately 60% at a film thickness of 70 nm. 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. 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.

  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.

  In particular, in the present embodiment, the thin film 12 is formed in which the film thickness is gradually and gradually decreased from the central part to the peripheral part of the semiconductor wafer W. For this reason, the absorptivity of the flash light is higher in the central portion than in the peripheral portion of the semiconductor wafer W. On the other hand, as described above, the intensity distribution of the flash light in the surface of the semiconductor wafer W at the time of flash light irradiation is not completely uniform, and the central portion of the semiconductor wafer W is affected by the reflection at the chamber side portion 63 and the like. There exists a tendency for the light intensity in a peripheral part to become stronger. That is, the flash light absorptance is low at the periphery of the semiconductor wafer W where the light intensity during flash light irradiation is high, and conversely, the flash light absorptance is high at the center of the semiconductor wafer W where the light intensity is weak. As a result, the degree of temperature rise by the thin film 12 as the light absorption film is substantially uniform in the plane of the semiconductor wafer W, and the in-plane temperature distribution of the semiconductor wafer W during flash light irradiation can be made uniform. In this way, by forming the thin film 12 whose film thickness continuously and gradually decreases from the central part to the peripheral part of the semiconductor wafer W, the surface of the semiconductor wafer W is raised more uniformly at a higher temperature during flash light irradiation. It is possible to perform a favorable impurity activation process by heating, and the sheet resistance value can be reduced uniformly.

Here, the film thickness difference t _d between the film thickness t _{c at} the center of the thin film 12 and the film thickness t _e at the peripheral edge is set to 8 nm to 30 nm for the following reason. When the thickness difference t _d is less than 8 nm, the effect to increase the flash light absorptivity of the central portion than the peripheral portion as described above was hardly obtained, the periphery of the Strong semiconductor wafer W light intensity during the flash light irradiation Becomes hotter than the center. Conversely, it the thickness difference t _d is greater than 30 nm, too high a flash light absorptivity of the central portion than the peripheral portion, a temperature higher than it is the periphery of the central portion of the semiconductor wafer W during flash light irradiation . That is, if the film thickness difference t _d between the central portion and the peripheral portion of the thin film 12 is out of the range of 8 nm or more and 30 nm or less, it becomes difficult to make the in-plane temperature distribution of the semiconductor wafer W uniform during flash light irradiation. It is.

  The flash light emitted from the flash lamp FL is once absorbed by the carbon thin film 12 and heat is generated in the thin film 12, and the heat is conducted to the surface of the silicon 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.

Further, even when the flash light is irradiated from the flash lamp FL, oxygen gas is supplied from the gas discharge port 89 into the chamber 6 and the atmosphere in the chamber 6 is continuously exhausted from the gas exhaust port 472. For this reason, carbon and oxygen of the thin film 12 heated by flash light irradiation react 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 from the gas exhaust port 472 and the exhaust path 86 to the outside of the heat treatment apparatus 1 together with the atmosphere in the chamber 6.

  Nitrogen gas is again supplied from the gas supply source 88 to the heat treatment space 65 when a predetermined time (several seconds) has elapsed after the completion of the flash heating as described above, and the heat treatment space 65 is supplied from the gas exhaust port 472 and the exhaust passage 86. The gas containing oxygen gas is exhausted. Thereby, the atmosphere in the chamber 6 is replaced with nitrogen gas (step S120).

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 S121 ). 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 S 122 ).

  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, in the present embodiment, while preheating the semiconductor wafer W, a larger amount of oxygen gas is supplied to the peripheral portion than the central portion to the surface thereof, so that the film thickness of the carbon thin film 12 is changed from the central portion to the peripheral portion. Processing is performed to make it thinner. For this reason, a thin film 12 is formed on the surface of the semiconductor wafer W, the film thickness of which gradually and gradually decreases from the central part where the flash light intensity becomes weaker toward the peripheral part where the flash light intensity becomes strong. As a result, variations in the intensity distribution of the flash light are compensated, the in-plane temperature distribution of the semiconductor wafer W during flash light irradiation can be made uniform, and the surface of the semiconductor wafer W can be heated more uniformly and at a higher temperature. The sheet resistance value can be reduced. Further, by making the in-plane temperature distribution of the semiconductor wafer W at the time of flash light irradiation uniform, cracking of the semiconductor wafer W can be suppressed. Further, since the film thickness of the thin film 12 is continuously reduced, the light absorption rate does not change abruptly in the plane of the semiconductor wafer W, and the in-plane temperature distribution of the semiconductor wafer W can be made more uniform. .

  Further, since the semiconductor wafer W on which the carbon thin film 12 is formed is irradiated with flash light while oxygen gas is supplied into the chamber 6, the carbon in the heated thin film 12 is oxidized and vaporized to be consumed. Is done. As a result, the carbon thin film 12 peeling process proceeds 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 S105 in FIG. 8). . When flash light is irradiated while the inside of the chamber 6 is in an inert gas atmosphere such as nitrogen gas, the carbon of the thin film 12 is not consumed, so that the initial film thickness is generally maintained even after flash heating. In this case, the thin film 12 cannot be sufficiently removed by only ordinary SPM cleaning or APM cleaning, and it is necessary to perform an ashing process before the cleaning process in step S105. If the flash light irradiation is performed while supplying the oxygen gas into the chamber 6 as in the present embodiment, the thin film 12 can be peeled off at the same time when the flash is heated, and the ashing process is omitted and the normal cleaning is performed. The remaining film can be reliably removed only by the treatment. 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.

  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 embodiment, the thickness of the thin film 12 is reduced from the central portion toward the peripheral portion. However, the present invention is not limited to this, and the thin film compensates for variations in the intensity distribution of flash light. The film thickness distribution may be 12. For example, if there is an intensity distribution in which the light intensity at the center is stronger than the periphery of the semiconductor wafer W, the film thickness of the thin film 12 is directed from the periphery to the center, contrary to the above embodiment. To make it thinner (in the form of a concave lens). In other words, in order to compensate for variations in the intensity distribution of the flash light within the surface of the semiconductor wafer W during the irradiation of the flash light, more specifically, such a non-uniformity that the film thickness is reduced at a position where the intensity of the flash light is increased. A thin film having a film thickness distribution may be formed.

  Moreover, in the said embodiment, while preheating the semiconductor wafer W, by supplying a large amount of oxygen gas to the peripheral part rather than the central part to the surface, the film thickness of the carbon thin film 12 is changed from the central part to the peripheral part. However, the method of processing the carbon thin film 12 is not limited to this. For example, a plurality of flash lamps having different diameters are concentrically arranged in the lamp house 5, and oxygen gas is supplied to the surface of the semiconductor wafer W, and weak flash light irradiation is performed only on the peripheral portion to give a film thickness difference. You may do it. In this case, after the weak flash light irradiation for processing the carbon thin film 12 is performed, the flash light irradiation for impurity activation similar to step S119 of FIG. 9 is performed. Alternatively, since the hot plate 71 of the holding unit 7 for preheating the semiconductor wafer W is divided into a plurality of zones arranged concentrically (see FIG. 5), oxygen gas is supplied to the surface of the semiconductor wafer W. However, it may be possible to make a difference in film thickness by performing preheating such that the peripheral portion is hotter than the central portion. Specifically, in the preliminary heating, the control unit 3 controls the plate power source 98 so that the zone 712 is hotter than the zone 711 and the zones 713 to 716 are hotter than the zone 712.

  Further, the carbon thin film processing may be separately performed before the semiconductor wafer W (the wafer in the state of FIG. 10) on which the carbon thin film 12 is deposited is carried into the heat treatment apparatus 1. For example, the semiconductor wafer W on which the carbon thin film 12 is deposited may be carried into an apparatus for performing bevel etching, and only the peripheral portion of the semiconductor wafer W may be etched using hydrofluoric acid or the like. Further, a thin film 12 whose film thickness gradually decreases from the central part to the peripheral part of the semiconductor wafer W may be deposited on the surface of the silicon substrate 11 at the stage of performing plasma vapor deposition.

  In the above embodiment, the amorphous carbon thin film 12 is formed on the surface of the silicon substrate 11 into which the impurities are implanted. However, the thin film 12 is made of carbon (for example, graphite) having a crystal structure 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.

The material of the thin film 12 formed on the surface of the silicon substrate 11 is not limited to carbon, and any material having physical properties that absorbs flash light may be used. For example, the thin film 12 may be formed of silicon nitride (SiN), or may be formed of a metal-based reflection film / absorption film. Examples of metal-based reflective films include polycrystalline silicon + germanium (Ge), polycrystalline silicon + arsenic (As), MgF ₂ , CaF ₂ , SiGe, Ge, GaAs, InSb, Cr, Mo, Nb, Zr, Y, A compound of Ti, La and O, N, or C, AlN can be used. As the metal-based absorption film, SiO ₂ , SiON, or Si ₃ N _{4 in} which H or O is contained in crystallized C can be used. Even if the thin film 12 is formed of these materials, if the thin film 12 whose film thickness is gradually reduced from the central portion of the semiconductor wafer W toward the peripheral portion is formed, the central portion of the semiconductor wafer W is more than the peripheral portion. The flash light absorption rate is higher. As a result, as in the above embodiment, the in-plane temperature distribution of the semiconductor wafer W at the time of flash light irradiation can be made uniform. However, when the thin film 12 is formed of silicon nitride or a metal-based reflective film, the thin film 12 cannot be processed by heating and oxygen gas supply, and thus hydrofluoric acid was used before being carried into the heat treatment apparatus 1. It is necessary to carry out a process for differentiating the film thickness by bevel etching or the like.

  Further, a plurality of thin films may be formed on the surface of the silicon substrate 11. FIG. 13 is a cross-sectional view of a semiconductor wafer W in which two layers of thin films are formed on the surface of the silicon substrate 11. Similar to the above-described embodiment, a carbon or carbon compound thin film 12a (first thin film) is deposited by plasma deposition on the surface of the silicon substrate 11 into which impurities have been implanted by ion implantation, and the center is further formed thereon. A thin film 12b (second thin film) of polycrystalline silicon (polysilicon) whose thickness decreases from the portion toward the peripheral portion is formed. The film thickness processing of polycrystalline silicon can be performed by bevel etching using hydrofluoric acid. Even in this case, the absorption rate of the flash light is higher in the central portion than in the peripheral portion of the semiconductor wafer W, and the in-plane temperature distribution of the semiconductor wafer W at the time of flash light irradiation can be made uniform. Furthermore, the scattering of carbon-based contaminants from the lower thin film 12a during flash light irradiation can be suppressed by the upper thin film 12b, and such contaminants are prevented from adhering to the structure in the chamber 6. Can be prevented. In FIG. 13, the same effect can be obtained even if the thin film 12b is formed of amorphous silicon or silicon nitride.

  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. While preheating the semiconductor wafer W by irradiating light from a halogen lamp, a large amount of oxygen gas is supplied to the surface of the semiconductor wafer W from the center to the periphery, so that the film thickness of the carbon thin film 12 changes from the center to the periphery. Even if the processing is performed so as to become thinner, the same effect as in the above embodiment can be obtained.

  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, 12a, 12b Thin film 60 Upper opening 61 Chamber window 65 Heat treatment space 71 Hot plate 72 Susceptor 81 Gas introduction path 82,87, 473 Gas valve 85,475 Flow control valve 88 Gas supply source 89 Gas discharge port 99 Lamp power supply 472 Gas exhaust port 474 Exhaust pump FL Flash lamp W Semiconductor wafer

Claims (7)

A heat treatment method for heating a substrate by irradiating flash light onto the substrate into which impurities are implanted,
A thin film forming step of forming a thin film of a light absorption film having a non-uniform film thickness distribution on the surface of the substrate into which impurities are implanted;
A light irradiation step of irradiating flash light from a flash lamp onto the substrate on which the thin film is formed;
With
The thin film forming step forms a thin film having a film thickness that gradually and gradually decreases from the center to the periphery on the surface of the substrate. The heat treatment method according to claim 1,
The film thickness difference between the central portion and the peripheral portion of the thin film is 8 nm or more and 30 nm or less. In the heat processing method of Claim 1 or Claim 2,
The thin film forming step includes
A thin film deposition step of depositing a thin film on the surface of the substrate;
A thin film processing step of processing so that the film thickness of the thin film deposited on the surface of the substrate becomes thinner from the central part toward the peripheral part;
The heat processing method characterized by having. In the heat processing method of Claim 3,
The thin film deposition step deposits a carbon or carbon compound thin film on the surface of the substrate,
The thin film processing step includes a step of supplying a larger amount of oxygen gas to a peripheral portion than a central portion while heating the substrate. The heat treatment method according to claim 1,
The thin film forming step includes depositing a first thin film of carbon or a carbon compound on the surface of the substrate, and forming silicon nitride, polycrystalline silicon, A heat treatment method comprising forming a second thin film of amorphous silicon. A heat treatment apparatus for heating a substrate by irradiating flash light onto the substrate into which impurities are implanted,
A chamber for accommodating a substrate on which a thin film of carbon or a carbon compound is formed after impurities are implanted;
Holding means for holding the substrate in the chamber;
Preheating means for preheating the substrate held by the holding means;
A flash lamp for irradiating the substrate held by the holding means with flash light;
Oxygen gas supply means for supplying oxygen gas from the periphery of the substrate held by the holding means in the chamber;
Exhaust means for exhausting the atmosphere in the chamber from below the substrate held by the holding means;
The substrate held by the holding means is heated by the preliminary heating means, and the exhaust means exhausts the atmosphere in the chamber while supplying oxygen gas from the oxygen gas supply means, and is formed on the surface of the substrate. Control means for irradiating flash light from the flash lamp after reducing the film thickness from the center to the periphery of the thin film;
A heat treatment apparatus comprising: The heat treatment apparatus according to claim 6, wherein
A heat treatment apparatus characterized in that a film thickness difference between a central portion and a peripheral portion of the thin film during flash light irradiation is 8 nm or more and 30 nm or less.

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