JP2013074247A - Laser annealing device, and laser annealing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve uniformity of an activation rate of impurities inside a semiconductor substrate surface.SOLUTION: A laser annealing device includes: a laser beam source for emitting a laser beam; a stage for holding a semiconductor substrate and moving it in a direction in parallel with a first direction; a propagation optical system for propagating the laser beam emitted from the laser beam source onto the semiconductor substrate held by the stage; and a controller for, while scanning n pieces of subregions defined in the view along the first direction on the semiconductor substrate held by the stage with the laser beam emitted from the laser beam source in the direction in parallel with the first direction on the semiconductor substrate when n is an integer equal to or larger than 3, making the laser beam be incident on a subregion to which the center of the semiconductor substrate belongs among the n pieces of subregions such that energy supplied per unit area becomes a first value, and making the laser beam be incident on a subregion at an end in the view along the direction in parallel with the first direction such that the energy supplied per unit area is a second value smaller than the first value.

Description

  The present invention relates to a laser annealing apparatus and a laser annealing method for activating, for example, an impurity added to a semiconductor substrate by irradiation with a laser beam.

  In recent years, in the manufacture of power devices, a method using a laser beam has attracted attention for activating impurities added to the back surface of a semiconductor substrate.

  For example, in the manufacture of an insulated gate bipolar transistor (IGBT), first, a device pattern having a structure such as an emitter and a gate is formed on the front surface of the silicon substrate, and a protective sheet is attached, The back surface is shaved to make the substrate thinner, and impurities are implanted into the back surface. An n-type impurity serving as a field stop layer, for example, phosphorus (P) or arsenic (As), and a p-type impurity serving as a collector layer, such as boron (B), are implanted into the back surface of the silicon substrate. Thereafter, the implanted impurities are activated by irradiating the back surface of the silicon substrate with a laser beam.

  The silicon substrate required in the manufacture of the IGBT is thin, and for example, a thickness of less than 100 μm is required. In laser annealing, the front surface is kept at a relatively low temperature and the back surface is heated to around the melting point of silicon in order to activate impurities implanted into the back surface while avoiding deterioration of device characteristics on the front surface due to thermal effects. There is a need to. For this reason, when performing activation annealing using a pulse laser beam, a laser beam having a short wavelength and pulse width is used, and when performing activation annealing using a continuous wave laser beam, the laser beam High speed scanning is adopted.

  Recently, activation of impurities added to a deeper position on the back surface of the substrate has been demanded, and adoption of a long wavelength laser having a long penetration depth into silicon or a laser having a long pulse width has been studied.

  When a crystalline silicon film formed on a glass substrate by laser annealing is used and a TFT arranged in a matrix is manufactured, the threshold voltage shows a U-shaped distribution in the substrate surface. Disclosure of the invention of a laser annealing method in which a glass substrate is flattened and placed on a stage at the time of laser annealing, so that the silicon film is uniformly irradiated with laser and the threshold voltage of the TFT is made uniform in the substrate surface. (For example, refer to Patent Document 1).

JP-A-9-63984

  As an index indicating the result of laser annealing of a semiconductor substrate (silicon wafer), the activation rate of impurities at a predetermined depth and the uniformity of the impurity activation rate within the wafer surface can be cited.

  In order to increase the uniformity of the impurity activation rate in the wafer surface, a method of making the intensity distribution of the laser beam uniform on the irradiated surface to obtain a top hat distribution is being implemented. However, even when laser irradiation is performed with the laser beam profile having a top hat distribution and the input energy in the wafer surface being constant regardless of position, there is a difference in device characteristics between the wafer center and the wafer periphery. It was found that the device characteristics were inferior to the peripheral part. It was also found that there is a difference of slightly less than 1% in terms of device characteristics between the central portion and the peripheral portion in terms of sheet resistance value.

  An object of the present invention is to provide a laser annealing apparatus and a laser annealing method capable of increasing the uniformity of the activation rate of impurities in the surface of a semiconductor substrate.

  According to one aspect of the present invention, a laser light source that emits a laser beam, a stage that holds a semiconductor substrate and moves in a direction parallel to a first direction, and a laser beam that emits the laser light source is applied to the stage. Propagation optical system that propagates on a held semiconductor substrate, and when n is an integer greater than or equal to 3, it is defined when viewed along the first direction on the semiconductor substrate held on the stage While scanning the laser beam emitted from the laser light source in the direction parallel to the first direction on the semiconductor substrate with respect to the n small regions, of the n small regions, When the laser beam is incident on the small region to which the center belongs so that the energy input per unit area becomes the first value and viewed along a direction parallel to the first direction, A small province The energy to be introduced per unit area such that the first value is less than the second value, the laser annealing apparatus is provided with a control device for incident laser beam.

  According to another aspect of the present invention, (a) when n is an integer greater than or equal to 3, when viewed along the first direction on the semiconductor substrate, n small regions are defined, and the laser beam Are scanned in a direction parallel to the first direction on the semiconductor substrate, and among the n small regions, the small region to which the center of the semiconductor substrate belongs has energy input per unit area. When the laser beam is incident so as to have the first value and viewed along a direction parallel to the first direction, energy input per unit area is input to the small region at the end in the first region. A step of causing the laser beam to be incident so as to be a second value smaller than the value of (b), and (b) a step in which the incident position of the laser beam is not shifted in the second direction intersecting the first direction, c) Repeat step (a) after step (b) Laser annealing method and a degree is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the laser annealing apparatus and laser annealing method which can raise the uniformity of the activation rate of the impurity in a semiconductor substrate surface can be provided.

FIG. 1A is a schematic diagram showing a scanning mode of a laser beam on a silicon wafer, FIG. 1B is a schematic diagram showing a sheet resistance value distribution in the silicon wafer surface after laser beam irradiation, and FIG. 1C is a sheet It is a graph which shows the relationship between resistance value and the power density of the laser beam irradiated on a wafer. FIG. 2 is a schematic diagram showing a laser annealing apparatus according to the first embodiment. 3A to 3E are schematic plan views showing how the area is defined on the silicon wafer 60. FIG. 4A to 4C are schematic plan views showing how the areas 44 to 48 are defined. FIG. 5A is a schematic view showing a laser annealing apparatus according to the second embodiment, and FIG. 5B is a plan view of the chuck plate 73. FIG. 6 is a schematic view showing a scanning mode of the laser beam on the silicon wafers 60a to 60f. FIG. 7 is a schematic plan view showing another defining aspect of the areas 77 to 79.

  Even when laser irradiation is performed with the top-hat distribution of the laser beam profile and the input energy in the wafer surface being constant regardless of the position, there is a difference in device characteristics between the wafer center and the wafer periphery. The inventor of the present application relates to the fact that the device characteristics are inferior to the peripheral part and that the device characteristic is slightly less than 1% in terms of the sheet resistance value between the central part and the peripheral part. Two surveys were conducted.

  First, a laser beam was irradiated with an intensity higher than the laser intensity in normal laser annealing, and the occurrence distribution of device damage was examined (first investigation). When a laser beam with a certain intensity was scanned onto the semiconductor wafer, the peripheral device of the wafer suffered thermal damage as compared with the central device. From this, it was found that the temperature of the peripheral portion was higher than that of the central portion on the front surface of the silicon wafer during laser annealing.

  Next, the inventor of the present application investigated the distribution of the sheet resistance value after laser annealing in the wafer surface and the relationship between the sheet resistance value and the power density of the laser beam irradiated onto the wafer (second investigation). .

FIG. 1A is a schematic view showing a scanning mode of a laser beam on a silicon wafer. Boron (B) is ion-implanted with an energy of 45 keV and a dose of 1.0E + 15 / cm ^2. For example, a circular silicon wafer having a diameter of 6 inches is prepared as an annealing target, and an incident region is 2.5 mm in the X-axis direction. A laser pulse shaped to have a rectangular shape of 0.3 mm in the Y-axis direction and having a uniform power density in the incident region was irradiated onto the silicon wafer while scanning in the manner shown in this figure. Laser irradiation was started from the right end (X-axis positive direction end) of the silicon wafer, and the laser beam was irradiated onto the silicon wafer with the scan direction as the Y-axis direction and the step direction as the X-axis negative direction. That is, when the laser beam is scanned in the scanning direction and irradiated to the wafer end in the scanning direction (for example, the positive Y-axis direction), the incident position of the beam is shifted in the step direction, and then the laser beam is again scanned in the scanning direction ( For example, the other wafer end is scanned along the negative direction of the Y-axis, and when the scanning is completed, the incident position of the beam is shifted in the step direction. By repeating this, a laser beam is incident on the entire surface of the silicon wafer. Note that the overlapping rates of the laser beams in the X-axis direction and the Y-axis direction are both 80%, for example.

  FIG. 1B is a schematic diagram showing a sheet resistance value distribution in the silicon wafer surface after laser beam irradiation. The absolute value of the rate of change of the sheet resistance value is large in the Y-axis direction (direction parallel to the scanning direction) and small in the X-axis direction (direction parallel to the step direction). Further, the sheet resistance value decreases as the distance from the center of the silicon wafer increases in the Y-axis direction. For this reason, when the center of the silicon wafer is used as a reference, on the Y axis positive direction side, the peripheral area on the wafer including the radial end extending from the center of the silicon wafer in the Y axis positive direction is the lowest sheet resistance value. On the Y axis negative direction side, the peripheral area on the wafer including the end portion in the radial direction extending from the center of the silicon wafer in the Y axis negative direction shows the lowest sheet resistance value.

FIG. 1C is a graph showing the relationship between the sheet resistance value and the power density of the laser beam irradiated onto the wafer. The horizontal axis of the graph represents the power density of the laser beam irradiated on the wafer in the unit “kW / cm ² ”, and the vertical axis of the graph represents the sheet resistance value in the unit “kΩ / □”. In an experiment for obtaining the result shown in this graph, a silicon wafer into which boron (B) was ion-implanted with an energy of 40 keV and a dose of 1.0E + 13 / cm ² was an annealing target.

  From the results shown in this figure, it can be seen that the sheet resistance value decreases as the power density of the laser beam increases. That is, there is a correlation between the temperature of the silicon wafer and the sheet resistance value, and the higher the temperature of the silicon wafer, the lower the sheet resistance value.

  From the results shown in FIG. 1B and FIG. 1C, the absolute value of the change rate of the wafer temperature is large in the Y-axis direction and small in the X-axis direction, and the wafer temperature increases with increasing distance from the center of the silicon wafer in the Y-axis direction. For this reason, when the center of the silicon wafer is used as a reference, the peripheral region on the wafer including the end portion in the radial direction extending from the center of the silicon wafer in the Y-axis positive direction is the most on the Y-axis positive direction side. It can be seen that on the Y axis negative direction side, the peripheral region on the wafer including the end portion in the radial direction extending from the center of the silicon wafer in the Y axis negative direction shows the highest temperature. This is a more detailed investigation result obtained as a whole when compared with the first investigation result obtained from the thermal damage received by the device and compared with the first investigation result that the peripheral part of the wafer is higher in temperature than the central part. Further, according to this investigation result, it is possible to explain the fact that there is a difference in device characteristics between the wafer central portion and the wafer peripheral portion, for example, the device characteristics inferior to the peripheral portion in the central portion.

  From the relationship that the sheet resistance value decreases as the temperature of the silicon wafer increases, it can also be seen that a temporary evaluation of the distribution of device characteristics is possible with the distribution of the sheet resistance value.

  The inventor of the present application has a top-hat distribution of the laser beam profile, and even when laser irradiation is performed with the input energy in the wafer surface being constant regardless of the position, for example, the incident region of one shot laser pulse is applied to the silicon wafer. It was thought that this was due to the fact that the temperature distribution and the impurity activation rate distribution were nonuniform in the wafer surface, and the device characteristics corresponding to the distribution were uneven.

  FIG. 2 is a schematic diagram showing a laser annealing apparatus according to the first embodiment. The laser annealing apparatus according to the first embodiment includes a laser light source 50, an attenuator 51, a beam shaping optical system 52, a folding mirror 53, a focus lens 54, a stage 55, and a control device 56.

The laser light source 50 includes, for example, an Nd: YAG laser oscillator and a nonlinear optical crystal, and emits a pulse laser beam that is a second harmonic (wavelength 532 nm) of the Nd: YAG laser at a repetition frequency of 3 kHz. Not only the Nd: YAG laser but also a second harmonic (light in the green wavelength region) of a solid-state laser such as an Nd: YLF laser or an Nd: YVO ₄ laser may be used. For example, a semiconductor laser with a wavelength of 800 nm to 1000 nm, for example, 808 nm can be used.

  The stage 55 is, for example, an XY stage, and can hold a semiconductor substrate (silicon wafer 60) that is an object to be annealed and move it in a horizontal plane (X-axis direction and Y-axis direction).

  The silicon wafer 60 is a semiconductor substrate that appears, for example, in one step of IGBT manufacturing. A device pattern is formed on the front surface, and impurities such as boron (B) are added from the back surface. The silicon wafer 60 has a circular shape with a diameter of 6 to 8 inches, for example, and a thickness of about 100 μm. The added impurity is activated by irradiating the back surface of the silicon wafer 60 with a laser beam using the laser annealing apparatus according to the first embodiment.

  The attenuator 51, the beam shaping optical system 52, the folding mirror 53, and the focus lens 54 constitute a propagation optical system. The propagation optical system propagates the laser beam emitted from the laser light source 50 onto the silicon wafer 60 held on the stage 55. The attenuator 51 attenuates the energy of the incident laser beam with a variable attenuation factor and emits it. The beam shaping optical system 52, for example, a homogenizer shapes the laser beam incident area on the laser irradiation surface (the back surface of the silicon wafer 60) into a rectangular shape and makes the intensity distribution of the laser beam uniform in the incident area.

  The pulse laser beam emitted from the laser light source 50 is attenuated at a predetermined attenuation rate by the attenuator 51 and then propagates on the silicon wafer 60 via the beam shaping optical system 52, the folding mirror 53, and the focus lens 54. Is done. The incident region of the laser beam on the silicon wafer 60 is, for example, a rectangular shape of 2.5 mm in the X axis direction and 0.3 mm in the Y axis direction.

  The laser annealing apparatus according to the first embodiment also includes a control device 56. The control device 56 controls the emission of the laser beam from the laser light source 50 by giving a current signal to the laser light source 50. The energy of the laser beam emitted can be controlled by the magnitude of the applied current. Further, the attenuation rate of the attenuator 51 can be changed. Further, the operation of the stage 55 is controlled. The incident position of the laser beam on the silicon wafer 60 can be controlled by moving the silicon wafer 60 held on the stage 55 in the X-axis direction and the Y-axis direction.

  The scanning mode of the laser beam on the silicon wafer 60 is as shown in FIG. 1A. By controlling the stage 55 with the control device 56 and moving the silicon wafer 60 in the short axis direction (Y-axis direction) of the rectangular beam cross section on the back side surface of the silicon wafer 60 while irradiating the laser beam, A band-shaped region having a width in the long axis direction (X axis direction) can be annealed. The entire surface of the silicon wafer 60 is annealed by repeating the process of annealing the band-shaped region by shifting the silicon wafer 60 in the major axis direction of the beam cross section. The overlapping ratio of laser beams in the major axis direction and the minor axis direction is, for example, 80%. The shifting direction may be a direction that intersects the minor axis direction of the beam cross section.

  In the laser annealing apparatus according to the first embodiment, the controller 56 causes the laser beam to be incident on the silicon wafer 60 at a pulse energy density that varies depending on the position. Specifically, three or more, for example, three areas are defined on the laser irradiation surface of the silicon wafer 60 along the Y-axis direction (laser beam scanning direction), and the same area has the same pulse energy density. The laser beam is irradiated, and the pulse energy density is varied in at least two or more areas.

  3A to 3E are schematic plan views showing how the area is defined on the silicon wafer 60. FIG. 3A to 3E show an example in which the laser irradiation area on the silicon wafer 60 is divided into three areas 41 to 43. FIG.

FIG. 3A shows 40% of the silicon wafer 60 on the Y axis positive direction side when viewed in the diameter direction parallel to the Y axis (when viewed along a straight line passing through the center of the silicon wafer 60 and parallel to the Y axis). Area 41, area 20% including the center of the silicon wafer 60 belongs to area 42, and area 40% of the silicon wafer 60 on the Y axis negative direction side belongs to area 43. An example in which 43 boundary lines are defined is shown. The controller 56 irradiates the area 42 with a laser beam with a relatively high pulse energy density of ² J / cm ² and the areas 41 and 43 with a relatively low pulse energy density of 1.9 J / cm ^2. Then, the laser light source 50 or the attenuator 51 is controlled so that the laser beam is irradiated.

  For example, when the laser beam is incident on the area 42, the control device 56 gives a relatively large current signal to the laser light source 50, and relatively increases the pulse energy of the emitted laser beam. Further, when a laser beam is incident on the areas 41 and 43, a relatively small current signal is given to the laser light source 50, and the pulse energy of the emitted laser beam is relatively reduced. Alternatively, when the laser beam is incident on the area 42, the attenuation factor of the attenuator 51 may be reduced, and when the laser beam is incident on the areas 41 and 43, the attenuation factor of the attenuator 51 may be increased.

  Using the laser annealing apparatus according to the first embodiment, a laser beam is irradiated with a relatively small pulse energy density in the peripheral regions (areas 41 and 43) on the silicon wafer 60 where the temperature is relatively high during laser annealing. Irradiation is performed to relatively reduce the energy of the laser beam irradiated per unit area (input energy per unit area). Further, the central region (area 42) on the silicon wafer 60 where the temperature is relatively low during laser annealing is irradiated with a laser beam with a relatively large pulse energy density, and the input energy per unit area is relatively set. Make it bigger. By performing laser annealing in this manner, the activation rate of impurities and the uniformity of device characteristics in the surface of the silicon wafer 60 can be increased.

  3B, 3C, and 3D, when viewed in the diameter direction parallel to the Y axis, 33%, 25%, and 15% of the silicon wafer 60 on the Y axis positive direction side belong to the area 41, respectively. The 33%, 50%, and 70% regions including the center of the wafer 60 belong to the area 42, and the 33%, 25%, and 15% regions on the negative side of the silicon wafer 60 belong to the area 43. The example which defines the boundary line of the areas 41-43 was shown. Thus, the areas 41 to 43 are defined, the area 42 is irradiated with a laser beam with a relatively large pulse energy density, and the areas 41 and 43 are irradiated with a laser beam with a relatively small pulse energy density. Further, the uniformity of the impurity activation rate in the surface of the silicon wafer 60 can be increased.

  As shown in FIGS. 3A to 3D, the area 42 is defined so that a region of 20% to 70% including the center of the silicon wafer 60 belongs to the area 42 when viewed in the diameter direction parallel to the Y axis. Good.

  In FIG. 3E, when viewed in the diameter direction parallel to the Y axis, 15% of the silicon wafer 60 on the Y axis positive direction side belongs to the area 41, and 60% of the area including the center of the silicon wafer 60 is the area 42. In this example, the boundary lines of the areas 41 to 43 are defined so that 25% of the silicon wafer 60 on the Y-axis negative direction side belongs to the area 43. Thus, the ratio of the silicon wafers 60 belonging to the area 41 and the area 43 may not be equal. However, when the silicon wafer 60 is divided into three regions 41 to 43 as in the embodiment, 15% or more of the silicon wafer 60 on the Y axis positive direction side belongs to the area 41, and the silicon wafer The boundary lines of the areas 41 to 43 are demarcated so that 15% or more of the 60 Y-axis negative direction side belongs to the area 43.

In the first embodiment, the areas 41 and 43 are irradiated with a laser beam with a pulse energy density of 1.9 J / cm ² , and the area 42 is irradiated with a laser beam with a pulse energy density of 2.0 · J / cm ^2. Was irradiated. Here, the pulse energy density of the irradiated laser beam, and consequently the energy input per unit area of the silicon wafer 60 will be considered.

  As described above, when annealing is performed without making a difference in the input energy depending on the position on the silicon wafer 60, the device characteristics at the center and the periphery are less than 1% in terms of sheet resistance. I know that there is a difference. From this, the pulse energy density of the laser beams irradiated to the areas 41 and 43 and the area 42 is, for example, based on the pulse energy density of the laser beam irradiated to the area 42 as a reference. If the pulse energy density is reduced by 1% or more, the uniformity of the impurity activation rate within the surface of the silicon wafer 60 can be increased. Moreover, the effect of improving the uniformity of the impurity activation rate in the surface of the silicon wafer 60 will also be obtained by reducing it by 0.3% or more.

  The surface of the silicon wafer 60 (the laser irradiation region of the silicon wafer 60) can be divided into more than three areas. 4A to 4C are schematic plan views showing how the areas 44 to 48 are defined.

  As shown in FIGS. 4A and 4B, the surface of the silicon wafer 60 can be divided into five regions.

  In FIG. 4A, when viewed in the diametrical direction parallel to the Y-axis, a region of 5% of the silicon wafer 60 on the most Y-axis positive direction side (end on the Y-axis positive direction side) belongs to the area 44 and is adjacent thereto. A 10% region belongs to area 45, a 70% region including the center of silicon wafer 60 belongs to area 46, and a 10% region adjacent to it on the negative Y-axis side belongs to area 47. An example is shown in which the boundary lines of the areas 44 to 48 are defined so that 5% of the area on the Y axis negative direction side (the end on the Y axis negative direction side) belongs to the area 48.

When dividing this manner into five regions, the example area 44 and 48, the laser beam is irradiated at a pulse energy density of 1.9J / cm ^2, the area 45 and 47, of 1.95J / cm ² The controller 56 moves the silicon wafer 60 by the stage 55 so that the laser beam is irradiated with a pulse energy density and the area 46 is irradiated with a laser beam with a pulse energy density of 2.0 J / cm ² . Control is performed to synchronize the increase or decrease in the pulse energy of the laser beam emitted from the laser light source 50 or the change in the attenuation factor of the attenuator 51.

  FIG. 4B shows an example in which the boundary lines of the areas 44 to 48 are defined so that 20% of the silicon wafer 60 belongs to the areas 44 to 48 when viewed in the diameter direction parallel to the Y axis. The pulse energy density of the laser beam applied to each of the areas 44 to 48 is equal to, for example, the boundary line defining aspect shown in FIG. 4A.

  4A shows an example in which 70% of the region including the center of the silicon wafer 60 belongs to the area 46, and FIG. 4B shows an example in which 20% of the region including the center of the silicon wafer 60 belongs to the area 46. . Even when the silicon wafer 60 is divided into more than three regions, the region including the center of the silicon wafer 60 is 20% to 70% of the entire silicon wafer 60 when viewed in the diameter direction parallel to the Y axis. .

  In addition, when the silicon wafer 60 is divided into more than three regions, when viewed in the diameter direction parallel to the Y axis, the irradiation is performed on an area that is distant from the center position of the silicon wafer 60 on the Y axis direction side. The pulse energy density of the laser beam is set to be equal to or lower than the pulse energy density of the laser beam that irradiates an area including or close to the center position. Further, as in the case where n is 3, the pulse energy density of the laser beam irradiated to the area 46 to which the center of the silicon wafer 60 belongs and the area 44 on the most Y-axis positive direction side (end on the Y-axis positive direction side). The difference from the pulse energy density of the laser beam irradiated to the area 46 is set to 0.3% or more of the pulse energy density of the laser beam irradiated to the area 46 as a reference. It may be 1% or more. The same applies to the difference in pulse energy density between the area 46 and the area 48 closest to the Y-axis negative direction side (end on the Y-axis negative direction side).

  FIG. 4C shows an example in which the silicon wafer 60 is divided into four regions. In the example shown in this figure, when viewed in the diametrical direction parallel to the Y-axis, 15% of the area of the silicon wafer 60 closest to the Y-axis positive direction side (end on the Y-axis positive direction side) belongs to the area 44. A 35% region adjacent to it belongs to the area 45, and a 35% region adjacent to it in the Y-axis negative direction side belongs to the area 46, and the most negative Y-axis side (Y-axis negative direction side of the silicon wafer 60). An example is shown in which the boundary lines of the areas 44 to 47 are defined so that 15% of the edge portion belongs to the area 47.

  The center position C of the silicon wafer 60 is on the boundary line between the area 45 and the area 46. In such a case, the center position C is considered to belong to both the area 45 and the area 46.

As shown in FIG. 4C, when four regions of areas 44 to 47 are defined on the silicon wafer 60, for example, the areas 45 and 46 are irradiated with a laser beam at a pulse energy density of 2.0 J / cm ^2. The areas 44 and 47 are irradiated with a laser beam at a pulse energy density of 1.9 J / cm ² .

  For example, when the silicon wafer 60 is divided into even-numbered areas and the center position C of the silicon wafer 60 is on the boundary line between the two areas (the center position C belongs to the two areas), the diameter parallel to the Y-axis When viewed in the direction, the total of the regions including the center of the silicon wafer 60 (areas 45 and 46 in FIG. 4C) is 20% to 70%.

  Further, when viewed in the diameter direction parallel to the Y axis, the pulse energy density of the laser beam applied to the area separated in the Y axis direction side with respect to the center position of the silicon wafer 60 includes the center position or the center. It is set to be equal to or lower than the pulse energy density of the laser beam irradiated to the area close to the position. Further, the areas 45 and 46 are irradiated with the difference in pulse energy density between the areas 45 and 46 to which the center of the silicon wafer 60 belongs and the areas 44 and 47 on the most Y-axis direction side (end on the Y-axis direction side). The pulse energy density is set to 0.3% or more of the laser beam. It may be 1% or more.

  By increasing the number of divided areas and adjusting the pulse energy density of the laser beam applied to each area, the temperature of the silicon wafer 60 can be finely controlled and the uniformity can be further increased.

  FIG. 5A is a schematic view showing a laser annealing apparatus according to the second embodiment. The laser annealing apparatus according to the second embodiment includes, for example, a laser light source 89 that emits a second harmonic of an Nd: YAG laser at a repetition frequency of 3 kHz, a stage 95 that holds the silicon wafers 60a to 60f, and a laser light source 89. A propagation optical system that propagates the emitted laser beam onto the silicon wafers 60 a to 60 f held on the stage 95 is included.

  The stage 95 includes a base 70, a θ stage 72, a chuck plate 73, and a drive mechanism 71. The θ stage 72 is disposed on the base 70, and the chuck plate 73 is disposed on the θ stage 72, for example, parallel to the horizontal plane (XY plane). The drive mechanism 71 includes, for example, a motor and a bearing, and rotates the θ stage 72 and the chuck plate 73 fixedly disposed on the θ stage 72 around a rotation axis l parallel to the Z axis. The rotation direction is counterclockwise when, for example, the θ stage 72 is viewed from the positive direction of the Z axis. The chuck plate 73 can suck and hold the silicon wafers 60a to 60f. The silicon wafers 60a to 60f are objects to be annealed similar to the silicon wafer 60 in the first embodiment.

  Similar to the laser annealing apparatus according to the first embodiment, the propagation optical system includes an attenuator 90, a beam shaping optical system 91, a folding mirror 92, and a focus lens 93. The beam shaping optical system 91, the folding mirror 92, and the focus lens 93 are fixedly disposed inside the lens barrel 94.

  The laser annealing apparatus according to the second embodiment further includes a support 85, a base 86, a Y stage 88, guides 87a and 87b, and a drive mechanism 87c.

  The base 86 is supported at a constant height by the support 85. A Y stage 88 is held on the base 86 so as to be movable along the Y-axis direction. The Y stage 88 is provided with a drive mechanism 87c including, for example, a motor, a ball screw, and a bearing. Further, guides 87 a and 87 b are installed between the base 86 and the Y stage 88. The Y stage 88 is movable in the Y-axis direction along the guides 87a and 87b by the drive mechanism 87c.

  On the Y stage 88, a laser light source 89 and a propagation optical system are arranged. Note that the lens barrel 94 only needs to be movable together with the Y stage 88, and the laser light source 89 and the attenuator 90 may not be disposed on the Y stage 88.

  FIG. 5B shows a plan view of the chuck plate 73. The chuck plate 73 has, for example, a circular shape when viewed from the positive direction of the Z axis. The center of the circle is on the rotation axis l of the θ stage 72. On the chuck plate 73, positions (wafer mounting positions 73a to 73f) for mounting a circular silicon wafer are defined. The wafer placement positions 73a to 73f are, for example, circular, and the silicon wafers 60a to 60f are placed at the placement positions 73a to 73f. The center positions of the mounting positions 73a to 73f (center positions of the silicon wafers 60a to 60f) are equidistant from the center of the chuck plate 73, and a regular hexagon is formed by connecting the centers of the mounting positions 73a to 73f. The

  The pulse laser beam emitted from the laser light source 89 is placed on the wafer placement positions 73 a to 73 f via the attenuator 90, the beam shaping optical system 91, the folding mirror 92, and the focus lens 93, and is rotated by the θ stage 72. is propagated onto the silicon wafers 60a-60f that are rotated around l. The incident region of the laser beam on the silicon wafers 60a to 60f is, for example, a rectangular shape of 2.5 mm in the rotational radius direction and 0.3 mm in the rotational circumferential direction.

  The laser annealing apparatus according to the second embodiment also includes a control device 96. The control device 96 controls the emission timing of the pulse laser beam from the laser light source 89, the pulse energy of the emitted laser beam, and the attenuation factor of the attenuator 90, as with the control device 56 in the first embodiment. Further, the movement of the silicon wafers 60 a to 60 f in the rotation direction by the θ stage 72 and the movement of the lens barrel 94 by the Y stage 88 are controlled.

  The control device 96 rotates the silicon wafers 60a to 60f around the rotation axis 1 by the θ stage 72, thereby changing the incident position of the laser beam on the silicon wafers 60a to 60f in a direction parallel to the rotation direction (the rotation direction). Move in the opposite direction.

  FIG. 6 is a schematic view showing a scanning mode of the laser beam on the silicon wafers 60a to 60f. For example, the laser beam is first applied to the end regions of the silicon wafers 60 a to 60 f farthest from the center of the chuck plate 73. In this drawing, the laser beam incident area at the start of laser annealing is indicated by the symbol L. With the θ stage 72, the chuck plate 73 holding the silicon wafers 60a to 60f is rotated once around the rotation axis l, so that the end portions of the silicon wafers 60a to 60f that are farthest from the center of the chuck plate 73 are A band-shaped region having the width in the major axis direction (rotating radius direction) of the beam cross section can be annealed along the rotating circumferential direction. The overlapping rate of laser pulses is, for example, 80% in the rotation circumferential direction.

  When the position on the chuck plate 73 other than the silicon wafers 60a to 60f is arranged at the position of the laser beam incident region L with the rotation, the control device 96 stops the signal applied to the laser light source 89. Then, the emission of the laser beam from the laser light source 89 is stopped.

  The controller 96 rotates the silicon wafers 60a to 60f around the rotation axis 1 by the θ stage 72, and then moves the Y stage 88 in the Y axis positive direction (long axis direction of the beam cross section), for example, 0.5 mm. Move. The lens barrel 94 moves 0.5 mm in the Y-axis positive direction, and the laser beam incident area L also moves 0.5 mm in the Y-axis positive direction. While irradiating the laser beam, the silicon wafers 60a to 60f are rotated once around the rotation axis l, and then the process of moving the laser beam incident region L in the direction of the rotation radius is repeated, whereby the silicon wafers 60a to 60f are repeated. Each of the surfaces is annealed.

  In the second embodiment, similarly to the first embodiment, the laser beam is emitted with the same pulse energy density in the same area for three or more areas defined on the laser irradiation surfaces of the silicon wafers 60a to 60f. Irradiate and vary the pulse energy density in at least two or more areas.

  FIG. 6 shows an example in which areas 77 to 79 are defined on each of the silicon wafers 60a to 60f. Each of the areas 77 to 79 is in one direction orthogonal to the direction parallel to the rotation direction of the θ stage 72 and the chuck plate 73. In the example shown in the figure, the center of the chuck plate 73 and the wafer mounting positions 73a to 73f are arranged. It is demarcated along the direction orthogonal to the extending direction (rotating radial direction) of the straight line connecting the centers. That is, the boundary lines of the areas 77 to 79 on each of the silicon wafers 60a to 60f are defined in parallel with a straight line connecting the center of the chuck plate 73 and the centers of the silicon wafers 60a to 60f. The center positions of the wafer mounting positions 73a to 73f (the center positions of the silicon wafers 60a to 60f) do not belong to the end areas 77 and 79 in the direction orthogonal to the one direction orthogonal to the direction parallel to the rotation direction. Belongs to area 78, which is Note that the boundary lines of the silicon wafers 60a to 60f are defined in such a manner that the silicon wafers 60a to 60f are divided into three regions (areas 77 to 79) when viewed along a direction parallel to the rotation direction. The defining aspect of the areas 77 to 79 shown in the figure is an example of such an area defining aspect.

Also in the second embodiment, similarly to the first embodiment, the areas 77 and 79 are irradiated with a laser beam at a pulse energy density of 1.9 J / cm ² , and the area 78 is 2.0 J / cm ^2. The laser beam is irradiated with a pulse energy density of cm ² .

  Even when the laser annealing apparatus according to the second embodiment is used, the activation rate of impurities and the uniformity of device characteristics in the surfaces of the silicon wafers 60a to 60f can be increased. The difference in pulse energy density between areas, the number of area divisions, the boundary demarcation positions of the areas, and the like are the same as those in the first embodiment.

  FIG. 7 is a schematic plan view showing another defining aspect of the areas 77 to 79. In the example shown in FIG. 6, the areas 77 to 79 are defined along a direction orthogonal to one direction orthogonal to the direction parallel to the rotation direction of the θ stage 72 and the chuck plate 73, but in the example shown in FIG. 7. Areas 77 to 79 are defined along a direction parallel to the rotation direction.

    Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto.

  For example, in the embodiment, laser annealing for activating impurities added to a silicon wafer is performed using a pulsed laser beam, but a continuous wave laser beam can also be used.

In the example, the second harmonic of the Nd: YAG laser was emitted at a repetition frequency of 3 kHz and made incident on the silicon wafer at an overlap rate of 80% in both the scanning direction and the step direction. The area including the center position of the silicon wafer was irradiated with a laser beam at a pulse energy density of 2.0 J / cm ² . A semiconductor laser with a wavelength of 808 nm may be used, the repetition frequency may be 1 kHz, and the overlap rate may be 50%. For example, an area including the center position of the silicon wafer is irradiated with a laser beam at a pulse energy density of 4.0 J / cm ² . It should be noted that the overlap ratio may be 50% or more in both the scanning direction and the step direction when using the second harmonic of the solid laser or when using the semiconductor laser.

  It will be apparent to those skilled in the art that other various modifications, improvements, combinations, and the like are possible.

41 to 48 Area 50 Laser light source 51 Attenuator 52 Beam shaping optical system 53 Folding mirror 54 Focus lens 55 Stage 56 Control device 60, 60a to 60f Silicon wafer 70 Base 71 Drive mechanism 72 θ stage 73 Chuck plates 73a to 73f Wafer mounting positions 77 to 79 Area 85 Column 86 Base 87a, 87b Guide 87c Drive mechanism 88 Y stage 89 Laser light source 90 Attenuator 91 Beam shaping optical system 92 Folding mirror 93 Focus lens 94 Lens barrel 95 Stage

Claims (6)

A laser light source for emitting a laser beam;
A stage for holding the semiconductor substrate and moving it in a direction parallel to the first direction;
A propagation optical system for propagating a laser beam emitted from the laser light source onto a semiconductor substrate held by the stage;
When n is an integer of 3 or more, the laser light source is emitted to n small regions defined when viewed along the first direction on the semiconductor substrate held on the stage. While scanning a laser beam on the semiconductor substrate in a direction parallel to the first direction, a small area of the n small regions to which the center of the semiconductor substrate belongs is injected per unit area. When the laser beam is incident so that the energy becomes the first value and viewed along a direction parallel to the first direction, the energy input per unit area is applied to the small region at the end. A laser annealing apparatus including: a control device that causes a laser beam to be incident so that the second value is smaller than the first value.   The laser annealing apparatus according to claim 1, wherein a difference between the first value and the second value is 0.3% or more of the first value.   The small region to which the center of the semiconductor substrate belongs is set to 20% to 70% of the semiconductor substrate when viewed along a straight line passing through the center of the semiconductor substrate and parallel to the first direction. The laser annealing apparatus described in 1. (A) When n is an integer greater than or equal to 3, when viewed along the first direction on the semiconductor substrate, n small regions are defined, and a laser beam is projected on the semiconductor substrate on the first substrate. While scanning in a direction parallel to the direction, a laser beam is applied to the small region to which the center of the semiconductor substrate belongs among the n small regions so that the energy input per unit area becomes a first value. When incident and viewed along a direction parallel to the first direction, the energy input per unit area is set to a second value smaller than the first value in the small region at the end. And a step of making a laser beam incident on,
(B) the step of aligning the incident position of the laser beam with the second direction intersecting the first direction;
(C) A laser annealing method including a step of repeating the step (a) after the step (b).   The laser annealing method according to claim 4, wherein a difference between the first value and the second value is 0.3% or more of the first value.   The small region to which the center of the semiconductor substrate belongs is set to 20% to 70% of the semiconductor substrate when viewed along a straight line passing through the center of the semiconductor substrate and parallel to the first direction. The laser annealing method described in 1.

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