JP2019110153A - Annealing method and annealing apparatus - Google Patents

Abstract

To provide an annealing method capable of suppressing the variation in the surface of the temperature at the time of heating.SOLUTION: When annealing is performed by scanning the surface of an object to be annealed with a pulse laser beam, the surface of the object to be annealed is scanned with a pulse laser beam while performing overlapping of an irradiation region between shots of the pulse laser beam. An overlap ratio is changed on the basis of the measurement result of the temperature of a portion heated by the incidence of the pulsed laser beam.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an annealing method and an annealing apparatus.

  There is known an activation annealing method in which a pulsed laser beam is irradiated while the irradiation region is overlapped between shots when activating a dopant injected into a surface layer portion of a semiconductor wafer (Patent Document 1). According to this method, the surface layer portion can be heated to activate the dopant while suppressing the temperature rise on the back surface opposite to the irradiation surface of the pulsed laser beam.

JP, 2009-283636, A

  The activation rate of the dopant depends on the temperature of the surface portion of the semiconductor wafer raised by the irradiation of the pulsed laser beam. In order to perform uniform activation in the plane of the semiconductor wafer, it is preferable to make the temperature at the time of heating uniform in the plane of the semiconductor wafer. However, variations in various annealing environments cause in-plane variations in temperature during heating.

  An object of the present invention is to provide an annealing method and an annealing apparatus capable of suppressing the variation in the surface of the temperature at the time of heating.

According to one aspect of the invention
An annealing method in which a surface of an object to be annealed is scanned by a pulsed laser beam to perform annealing,
Scanning the surface of the object to be annealed with the pulsed laser beam while overlapping irradiation areas between shots of the pulsed laser beam;
An annealing method is provided to change the overlap ratio based on the measurement result of the temperature of the portion heated by the incidence of the pulsed laser beam.

According to another aspect of the invention:
A laser light source for outputting a pulsed laser beam;
A scanning mechanism for scanning the surface of the object to be annealed with the pulsed laser beam;
A temperature sensor for measuring the temperature of the object to be annealed heated by the incidence of the pulsed laser beam;
And a controller configured to scan the surface of the object to be annealed with the pulse laser beam while controlling the laser light source and the scanning mechanism to overlap an irradiation region between shots of the pulse laser beam.
The controller is provided with an annealing device that changes an overlap rate based on a measurement result of temperature by the temperature sensor.

According to yet another aspect of the invention,
An annealing method in which a surface of an object to be annealed is scanned by a pulsed laser beam to perform annealing,
Scanning the surface of the object to be annealed with the pulsed laser beam while overlapping irradiation areas between shots of the pulsed laser beam;
According to another aspect of the present invention, there is provided an annealing method in which an overlap ratio is changed according to a position in the surface of the object to be annealed.

According to yet another aspect of the invention,
A laser light source for outputting a pulsed laser beam;
A scanning mechanism for scanning the surface of the object to be annealed with the pulsed laser beam;
And a controller configured to scan the surface of the object to be annealed with the pulse laser beam while controlling the laser light source and the scanning mechanism to overlap an irradiation region between shots of the pulse laser beam.
The controller may provide an annealer having a function of changing an overlap rate according to a position in the surface of the anneal target.

  It is possible to reduce the variation of the in-plane annealing temperature.

FIG. 1 is a schematic view of a laser annealing apparatus according to an embodiment. FIG. 2A is a plan view showing a scanning path for scanning the surface of the object to be annealed with a pulsed laser beam, and FIG. 2B is a view showing a positional relationship between shots of the irradiation region of the pulsed laser beam when main scanning is performed. FIG. 2C is a view showing the positional relationship between shots of the irradiation area of the pulsed laser beam before and after the sub-scan. FIG. 3 is a view showing the distribution of the annealing temperature when the object to be annealed is actually annealed. FIG. 4A is a diagram schematically showing the distribution of the annealing temperature in the x-axis direction, and FIG. 4B is a diagram schematically showing the distribution of the annealing temperature in the y-axis direction. FIG. 5 is a graph showing the relationship between the pulse energy density of the pulse laser beam to be incident on the object to be annealed and the output voltage of the temperature sensor for each overlap rate. FIG. 6A is a flow chart showing a procedure for performing annealing using the annealing apparatus according to the embodiment, and FIG. 6B shows the relationship between the measurement result of the annealing temperature and the variation ΔOVRx of the overlap rate OVRx in the x-axis direction. It is a graph which shows an example. FIGS. 7A and 7B are graphs showing an example of the change in the overlap ratio OVRx when annealed by the method according to the embodiment shown in FIGS. 1 to 6B. FIG. 8 is a graph showing an example of the change in the average value of the overlap rate OVRx for each main scan when annealing is performed by the method according to the embodiment shown in FIGS. 1 to 6B.

An annealing apparatus and an annealing method according to an embodiment will be described with reference to FIGS. 1 to 6B.
FIG. 1 is a schematic view of a laser annealing apparatus according to an embodiment. A holding table 13 is supported by the scanning mechanism 12 in the chamber 10. The scanning mechanism 12 can move the holding table 13 in the horizontal plane in response to a command from the control device 40. The scanning mechanism 12 includes an encoder, and position information representing the current position of the holding table 13 is read from the encoder into the control device 40.

  The object to be annealed 30 is held on the holding table 13 via the chuck plate 14. The holding table 13 includes a vacuum chuck mechanism, and the chuck plate 14 has a plurality of through holes for exerting the function of the vacuum chuck mechanism of the holding table 13 to the object 30 to be annealed. The annealing target 30 is, for example, a semiconductor wafer such as a silicon wafer in which a dopant is implanted. The laser annealing apparatus according to the embodiment performs, for example, activation annealing of a dopant.

  The holding table 13 is formed of, for example, a metal such as aluminum. For the chuck plate 14, a material harder than the material of the holding table 13, for example, a ceramic or the like is used. The chuck plate 14 is disposed and used between the holding table 13 and the object 30 to be annealed, for example, in order to obtain high surface accuracy.

  The laser light source 20 receives a command from the controller 40 and outputs a pulse laser beam for annealing. As the laser light source 20, for example, a laser diode with an oscillation wavelength of about 800 nm is used. The pulsed laser beam output from the laser light source 20 passes through the transmission optical system 21, the dichroic mirror 22, and the lens 23, passes through the laser transmission window 11 provided on the top plate of the chamber 10, and is transmitted to the annealing target 30. It will be incident. The dichroic mirror 22 transmits a laser beam for annealing. The transmission optical system 21 includes, for example, a beam homogenizer, a lens, a mirror, and the like. The beam homogenizer and the lens 23 shape the irradiation area on the surface of the object to be annealed 30 to make the beam profile uniform.

  The thermal radiation light emitted from the object 30 to be annealed passes through the laser transmission window 11, passes through the lens 23, is reflected by the dichroic mirror 22, and enters the temperature sensor 25 through the lens 24. The dichroic mirror 22 reflects thermal radiation light in a wavelength range of 1 μm or more. The temperature sensor 25 measures the intensity of thermal radiation light in a specific wavelength range. The intensity of the thermal radiation depends on the temperature of the object 30 to be annealed. The measurement result of the thermal radiation light by the temperature sensor 25 is input to the control device 40 as a voltage value.

  The lenses 23 and 24 focus the surface of the object to be annealed 30 on the light receiving surface of the temperature sensor 25. Thereby, the intensity of the thermal radiation emitted from the region of the surface of the object to be annealed 30 which has a conjugate relationship with the light receiving surface of the temperature sensor 25 is measured. The surface area to be measured is set, for example, to be included inside the irradiation area of the laser beam.

  The control device 40 controls the scanning mechanism 12 to move the annealing target 30 held by the holding table 13 in a two-dimensional direction in the horizontal plane. Furthermore, based on the current position information of the holding table 13, the laser light source 20 is controlled to output a pulse laser beam from the laser light source 20. Further, the control device 40 acquires the detection result of the temperature sensor 25 in synchronization with each shot of the pulsed laser beam output from the laser light source 20. The acquired detection results are stored in the storage device 41 in association with the in-plane position of the annealing target 30.

  As an example, for each shot of a pulsed laser beam, a temporal change in the intensity of thermal radiation is obtained. The detection result stored in the storage device 41 is, for example, a peak value or an integral value of the intensity of the thermal emission light for each shot of the pulse laser beam. The temperature obtained from the peak value or integral value of the thermal radiation light intensity is referred to as the "annealing temperature". The control device 40 outputs information of the intensity distribution (distribution of the annealing temperature) of the thermal radiation light in the surface of the object to be annealed 30 to the output device 42 as an image, a graph or a numerical value.

  FIG. 2A is a plan view showing a scanning path for scanning the surface of the object to be annealed 30 with a pulsed laser beam. An xyz Cartesian coordinate system is defined in which the surface (laser irradiation surface) of the object to be annealed 30 is an xy plane and the normal direction of the surface is a positive direction of the z axis. With the x-axis direction as the main scanning direction and the y-axis direction as the sub-scanning direction, the main scanning and the sub-scanning are repeated to scan almost the entire surface of the object to be annealed 30 with the pulse laser beam.

FIG. 2B is a view showing the positional relationship between shots of the irradiation region 31 of the pulsed laser beam during the main scanning. The irradiation area 31 has a substantially rectangular planar shape elongated in the y-axis direction. In FIG. 2B, the irradiation area 31a of the immediately preceding shot is indicated by a broken line, and the irradiation area 31 of the shot immediately thereafter is indicated by a solid line. The dimension (width) in the x-axis direction of the irradiation area 31 is represented by Wx. The dimension in the x-axis direction of the overlapping part of the irradiation areas 31a and 31 of two consecutive shots is represented by Wov. The overlap rate OVRx of the irradiation area at the time of main scanning is
OVRx = Wov / Wx
Define as

FIG. 2C is a diagram showing the positional relationship between shots of the irradiation area 31 of the pulsed laser beam before and after the sub-scan. The irradiation area 31b immediately before the sub scanning is indicated by a broken line, and the irradiation area 31 after the sub scanning is indicated by a solid line. The dimension (length) in the y-axis direction of the irradiation area 31 is represented by Ly. The dimension in the y-axis direction of the overlapping portion of the irradiation areas 31 b and 31 before and after one sub-scan is represented by Lov. Overlap ratio OVRy of the irradiation area at the time of sub scanning,
OVRy = Lov / Ly
Define as

  Before describing the examples, the results of evaluation experiments in which annealing is performed at a constant overlap rate will be described.

  FIG. 3 is a view showing the distribution of the annealing temperature measured when the object to be annealed 30 is actually annealed. In FIG. 3, the gray level is lighter in the region where the annealing temperature is higher. The regions where the annealing temperature is low appear radially and concentrically because the planar shape of the suction groove provided on the holding table 13 (FIG. 1) is reflected. Furthermore, regions with low annealing temperatures appear corresponding to the four locations where the lift pins are disposed. Vertical stripes appear parallel to the x-axis direction (main scanning direction), considering special conditions of the substrate such as the suction grooves and lift pins. Furthermore, it can be seen that the annealing temperature tends to be higher in the vicinity of both ends in the y-axis direction (sub scanning direction) than in the inner region.

  FIG. 4A is a view schematically showing the distribution of the annealing temperature in the x-axis direction. Focusing on a linear region parallel to the x axis scanned by one main scan, the annealing temperature is relatively higher in a partial region 32 on the start point side of the scan than the remaining region 33 on the end point side It has become. In FIG. 4A, the area with relatively high annealing temperature is hatched with a relatively low density, and the area with relatively low annealing temperature is hatched with a relatively high density. Although FIG. 4A clearly shows the boundary between the region 32 where the annealing temperature is high and the region 33 where the annealing temperature is low, the boundary between the two is not clear in practice, and the annealing temperature is in the x-axis direction. Is gradually changing.

  The annealing temperature increases in the area 32 on the starting point side of the main scan because the influence of heat (heat storage effect) at the time of the main scan immediately before the sub-scan is left. As described above, it was confirmed that temperature unevenness occurs in the x-axis direction, focusing on the area scanned by one main scan.

  FIG. 4B is a view schematically showing the distribution of the annealing temperature in the y-axis direction. FIG. 4B shows the distribution of the average value in the x-axis direction of the annealing temperature of a linear region parallel to the x-axis scanned by one main scan. The average annealing temperature of the regions 34 near both ends in the y-axis direction (sub scanning direction) tends to be higher than the average annealing temperature of the regions inside thereof. In FIG. 4B, hatching with a relatively low density is attached to a region in which the average value of the annealing temperature is relatively high, and hatching in a relatively high density is attached to a region in which the average value of the annealing temperature is relatively low. doing. Although FIG. 4B clearly shows the boundary between the region 34 where the average value of the annealing temperature is high and the region 35 where the average value of the annealing temperature is low, the boundary between the two is not clear in practice. The average value of the annealing temperature gradually changes in the y-axis direction.

  The average value of the annealing temperature is relatively high in the region 34 near the both ends in the y-axis direction because the temperature decrease in the region 34 due to the propagation of heat in the in-plane direction is small. As described above, it was confirmed that unevenness occurs in the average value of the annealing temperature also in the y-axis direction.

  In the embodiment described below, the temperature non-uniformity is reduced by changing the overlap rate during main scanning.

FIG. 5 is a graph showing the relationship between the energy density per pulse (pulse energy density) of a pulse laser beam to be incident on the object to be annealed 30 and the output voltage of the temperature sensor 25 (FIG. 1) for each overlap ratio. It is. The horizontal axis represents pulse energy density in the unit “J / cm ² ”, and the vertical axis represents the output voltage of the temperature sensor 25 in the unit “mV”. The output voltage of the temperature sensor 25 depends on the annealing temperature of the object 30 to be annealed.

  The star voltage, circle symbol, square symbol, and triangle symbol in the graph of FIG. 5 represent the output voltage when the overlap rate OVRx in the x-axis direction is 0%, 50%, 67%, and 80%, respectively. Indicates the measured value. It can be seen that as the pulse energy density is increased, the annealing temperature is increased. Also, it can be seen that, under the condition that the pulse energy density is constant, the annealing temperature becomes higher as the overlap rate OVRx becomes higher.

  From the results shown in FIG. 5, it is understood that the annealing temperature can be controlled by adjusting the overlap rate OVRx in the x-axis direction. In the embodiment, the annealing temperature is adjusted by changing the overlap ratio OVRx of the irradiation area between the current shot and the next shot based on the measurement result of the annealing temperature by the irradiation of one shot of the pulsed laser beam. .

  FIG. 6A is a flowchart showing a procedure for performing annealing using the annealing apparatus according to the embodiment. Each procedure shown in the flowchart is executed by the control device 40 (FIG. 1) controlling the scanning mechanism 12 and the laser light source 20.

  First, the object to be annealed 30 is held on the holding table 13 (FIG. 1), and the movement of the holding table 13 is started (step S1). For example, the holding table 13 (FIG. 2A) is moved in the x-axis direction at substantially the same speed during one main scanning period.

  It is determined whether or not the annealing target 30 has moved to the irradiation start position (step S2), and when moving to the irradiation start position, a pulse laser beam is irradiated for one shot (step S3). When the entire area of the object to be annealed 30 is annealed, the process is ended (step S4).

  The controller 40 reads the output voltage from the temperature sensor 25 and acquires information on the annealing temperature (step S5). The controller 40 performs feedback control so that the measurement result of the annealing temperature approaches the target value Tt, with the overlap rate OVRx as an operation amount. For example, based on the measurement result of the annealing temperature, the controller 40 sets the overlap rate OVRx in the x-axis direction between the irradiation area of the immediately preceding shot and the irradiation area of the next shot so that the annealing temperature approaches the target value Tt. Are determined (step S6).

  FIG. 6B is a graph showing an example of the relationship between the measurement result of the annealing temperature and the change amount ΔOVRx of the overlap rate OVRx in the x-axis direction. The horizontal axis represents the measurement result of the annealing temperature, and the vertical axis represents the change amount ΔOVRx of the overlap rate OVRx. When the measurement result of the annealing temperature matches the target value Tt, the change amount ΔOBRx of the overlap ratio OVRx is 0, and the overlap ratio OVRx at the present time is maintained.

  When the measurement result of the annealing temperature is higher than the target value, the change amount ΔOVRx of the overlap rate OVRx is made negative, and when the measurement result of the annealing temperature is lower than the target value, the change amount ΔOVRx of the overlap rate OVRx is positive Make it That is, when the measurement result of the annealing temperature is higher than the target value, the overlap ratio OVRx is made lower than the current overlap ratio OVRx, and when the measurement result of the annealing temperature is lower than the target value, the overlap ratio OVRx is set. Make it higher than the current overlap rate OVRx. In any case, as the deviation from the target value Tt to the measurement result of the annealing temperature is larger, the absolute value of the change amount ΔOVRx is made larger.

  After the overlap rate OVRx is determined, the output of the pulse laser beam is awaited until the annealing target 30 comes to a position where the next shot is irradiated at the determined overlap rate OVRx (step S7). When the object to be annealed 30 moves to a predetermined position, the pulse laser beam is irradiated for one shot (step S3). Thereafter, steps S4 to S3 are repeatedly executed until the processing is completed.

  Next, excellent effects obtained by adopting the annealing method using the annealing apparatus according to the above embodiment will be described.

  In the embodiment, since the overlap ratio OVRx is adjusted based on the measurement result of the annealing temperature so that the annealing temperature approaches the target value Tt, the in-plane uniformity of the annealing temperature can be enhanced. Thereby, the in-plane uniformity of the activation rate of the dopant can be enhanced.

  Further, in the embodiment, the power and the pulse width of the pulse laser beam output from the laser light source 20 (FIG. 1) are not changed but the overlap temperature OVRx is changed to adjust the annealing temperature. The annealing temperature can also be adjusted when using a laser oscillator that is difficult to change.

  Next, an annealing apparatus and an annealing method according to another embodiment will be described with reference to FIGS. 7A to 8. In the present embodiment, the overlap rate OVRx is changed according to the position in the surface of the object 30 to be annealed. For example, when annealing is performed at a constant overlap rate OVRx, the overlap rate OVRx is set to a lower value in a region where the annealing temperature tends to increase.

  Next, how the overlap rate OVRx should be changed according to the position in the surface of the object to be annealed 30 will be described.

  FIGS. 7A and 7B are graphs showing an example of the change in the overlap ratio OVRx when annealed by the method according to the embodiment shown in FIGS. 1 to 6B. When the overlap rate OVRx is fixed, as shown in FIG. 4A, the annealing temperature becomes relatively high near the start of the main scan. When the above embodiment is applied, the annealing temperature is set to the target value Tt in both the main scanning in the positive direction of the x axis (FIG. 7A) and the main scanning in the negative direction of the x axis (FIG. 7B). In order to approach to the above, control is performed to increase the overlap ratio OVRx as the irradiation position of the pulse laser beam moves away from the start point of the main scan.

  Therefore, in order to make the annealing temperature uniform in one main scan, the overlap rate OVRx may be increased as the irradiation position of the pulse laser beam is farther from the start of the main scan.

  FIG. 8 is a graph showing an example of the change in the average value of the overlap rate OVRx for each main scan when annealing is performed by the method according to the embodiment shown in FIGS. 1 to 6B. When the overlap rate OVRx is constant, as shown in FIG. 4B, the annealing temperature becomes relatively high near both ends in the y-axis direction. By applying the embodiment shown in FIGS. 1 to 6B, in order to bring the annealing temperature closer to the target value Tt, control is performed to relatively lower the overlap rate OVRx near both ends in the y-axis direction.

  Therefore, in order to make the annealing temperature uniform in the y-axis direction, the average value of the overlap ratio OVRx in the vicinity of both ends in the y-axis direction should be lower than the average value of the overlap ratio OVRx in the inner side .

  The preferable relationship between the position in the surface of the object to be annealed 30 and the overlap ratio OVRx can be determined by changing the overlap ratio OVRx and performing a plurality of evaluation experiments. A preferable relationship between the position in the surface of the object to be annealed 30 and the overlap ratio OVRx is stored in the storage device 41 in advance. The controller 40 changes the overlap rate OVRx based on this preferable relationship.

  Also in this embodiment, it is possible to make the annealing temperature uniform in the plane. When annealing is performed with the pulse repetition frequency of the pulse laser beam output from the laser light source 20 constant, the region where the overlap rate OVRx near the start point of each main scan shown in FIGS. 7A and 7B is relatively low. , The moving speed of the object to be annealed 30 can be increased. Therefore, the annealing time can be shortened compared to the case where annealing is performed with the area near the starting point of the main scanning equal to the overlap ratio OVRx on the inner back and end points.

  It goes without saying that the above-described embodiments are exemplification, and partial replacement or combination of the configurations shown in the different embodiments is possible. Similar advantages and effects resulting from similar configurations of the multiple embodiments will not be sequentially described in each embodiment. Furthermore, the invention is not limited to the embodiments described above. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

DESCRIPTION OF SYMBOLS 10 chamber 11 laser transmission window 12 scanning mechanism 13 holding table 14 chuck plate 20 laser light source 21 transmission optical system 22 dichroic mirror 23, 24 lens 25 temperature sensor 30 annealing object 31 irradiation area 31 a shot area immediately before irradiation area 31 b before sub scanning Irradiated area 32 at the time of main scan 32 area of start side of main scan 33 area other than the area of start side of main scan 34 area near both ends in the sub scanning direction 35 area 40 inside the area near both ends in the sub scanning direction Device 41 Storage device 42 Output device

Claims (10)

An annealing method in which a surface of an object to be annealed is scanned by a pulsed laser beam to perform annealing,
Scanning the surface of the object to be annealed with the pulsed laser beam while overlapping irradiation areas between shots of the pulsed laser beam;
The annealing method which changes an overlap rate based on the measurement result of the temperature of the location heated by the incident of the said pulsed laser beam.   The annealing method according to claim 1, wherein the overlap rate is changed such that the measurement result of the temperature of the object to be annealed approaches a target value. A laser light source for outputting a pulsed laser beam;
A scanning mechanism for scanning the surface of the object to be annealed with the pulsed laser beam;
A temperature sensor for measuring the temperature of the object to be annealed heated by the incidence of the pulsed laser beam;
And a controller configured to scan the surface of the object to be annealed with the pulse laser beam while controlling the laser light source and the scanning mechanism to overlap an irradiation region between shots of the pulse laser beam.
The controller according to claim 1, wherein the controller changes an overlap rate based on a measurement result of temperature by the temperature sensor.   The annealing apparatus according to claim 3, wherein the controller changes the overlap rate such that the measurement result of the temperature measured by the temperature sensor approaches a target value. An annealing method in which a surface of an object to be annealed is scanned by a pulsed laser beam to perform annealing,
Scanning the surface of the object to be annealed with the pulsed laser beam while overlapping irradiation areas between shots of the pulsed laser beam;
The annealing method which changes the overlap rate according to the position in the surface of the said annealing object. In the scanning of the surface of the object to be annealed, annealing is performed by repeating main scanning and sub scanning.
6. The annealing method according to claim 5, wherein the overlap rate is decreased as the distance from the start of the main scan is increased for each main scan.   The average value of the overlap rate when main scanning a certain region including both ends of the object to be annealed in the sub-scanning direction is made smaller than the average value of the overlap ratio when main scanning inside the region. Or the annealing method as described in 6. A laser light source for outputting a pulsed laser beam;
A scanning mechanism for scanning the surface of the object to be annealed with the pulsed laser beam;
And a controller configured to scan the surface of the object to be annealed with the pulse laser beam while controlling the laser light source and the scanning mechanism to overlap an irradiation region between shots of the pulse laser beam.
The controller is an annealing apparatus having a function of changing an overlap rate depending on a position in the surface of the object to be annealed. The controller is
In the scanning of the surface of the object to be annealed, annealing is performed by repeating main scanning and sub scanning.
9. The annealing apparatus according to claim 8, wherein for each main scan, the overlap rate is decreased as the distance from the start of the main scan is increased.   The control device is configured to calculate an average value of overlap rates when main scanning a certain area including both ends of the object to be annealed with respect to the sub scanning direction from an average value of overlap rates when main scanning inside the area. The annealing apparatus according to claim 8 or 9, wherein the size is reduced.