JP7051203B2 - Annealing method and annealing equipment - Google Patents

Description

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

A known activation annealing method is to irradiate a pulsed laser beam while overlapping irradiation regions 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 of the back surface opposite to the irradiation surface of the pulsed laser beam.

Japanese Unexamined Patent Publication No. 2009-283636

The activation rate of the dopant depends on the temperature of the surface layer portion of the semiconductor wafer increased 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 during heating uniform in the plane of the semiconductor wafer. However, due to various variations in the annealing environment, in-plane variations occur in the heating temperature.

An object of the present invention is to provide an annealing method and an annealing apparatus capable of suppressing in-plane variation in temperature during heating.

According to one aspect of the invention
This is an annealing method in which the surface of the object to be annealed is scanned with a pulsed laser beam to perform annealing.
The surface of the object to be annealed was scanned with the pulsed laser beam while overlapping the irradiation areas between the shots of the pulsed laser beam.
If the intensity of the thermal radiant light measured at the location heated by the incident of the pulsed laser beam is higher than the target value, the overlap rate is lower than the current overlap rate, and if it is lower than the target value, the overlap rate is lower than the current overlap rate. An annealing method is provided in which the rate is higher than the current overlap rate .

According to another aspect of the invention
A laser light source that outputs a pulsed laser beam and
A scanning mechanism that scans the surface of the object to be annealed with the pulsed laser beam,
A temperature sensor that measures the intensity of heat radiant light from the annealed object heated by the incident of the pulsed laser beam, and
It has a control device that controls the laser light source and the scanning mechanism to scan the surface of the annealed object with the pulsed laser beam while overlapping the irradiation regions between shots of the pulsed laser beam.
When the intensity of the thermal radiant light measured by the temperature sensor is higher than the target value, the control device lowers the overlap rate to the current overlap rate, and when the intensity is lower than the target value, the overlap rate is currently set to the current overlap rate. An annealing device is provided in which the overlap rate is higher than that of the above.

According to yet another aspect of the invention.
This is an annealing method in which the surface of the object to be annealed is scanned with a pulsed laser beam to perform annealing.
The surface of the object to be annealed was scanned with the pulsed laser beam while overlapping the irradiation areas between the shots of the pulsed laser beam.
In scanning the surface of the object to be annealed, the main scan and the sub scan are repeated to perform annealing.
For each main scan, an annealing method is provided in which the overlap rate is reduced as the distance from the start point of the main scan increases .

According to yet another aspect of the invention.
A laser light source that outputs a pulsed laser beam and
A scanning mechanism that scans the surface of the object to be annealed with the pulsed laser beam,
It has a control device that controls the laser light source and the scanning mechanism to scan the surface of the annealed object with the pulsed laser beam while overlapping the irradiation regions between shots of the pulsed laser beam.
The control device is
In scanning the surface of the object to be annealed, the main scan and the sub scan are repeated to perform annealing.
For each main scan, an annealing device is provided that reduces the overlap rate as the distance from the start point of the main scan increases .

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

FIG. 1 is a schematic view of a laser annealing device according to an embodiment. FIG. 2A is a plan view showing a scanning path for scanning the surface of an object to be annealed with a pulsed laser beam, and FIG. 2B is a diagram showing a positional relationship between shots of an irradiation region of the pulsed laser beam during main scanning. FIG. 2C is a diagram showing the positional relationship between shots in the irradiation region of the pulsed laser beam before and after the sub-scan. FIG. 3 is a diagram 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 annealing temperature in the x-axis direction, and FIG. 4B is a diagram schematically showing the distribution of annealing temperature in the y-axis direction. FIG. 5 is a graph showing the relationship between the pulse energy density of the pulsed laser beam incident on the object to be annealed and the output voltage of the temperature sensor for each overlap rate. FIG. 6A is a flowchart showing a procedure for performing annealing using the annealing device according to the embodiment, and FIG. 6B shows the relationship between the measurement result of the annealing temperature and the amount of change in the overlap rate OVRx in the x-axis direction ΔOVRx. It is a graph which shows an example. 7A and 7B are graphs showing an example of a change in the overlap rate 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 a change in the average value of the overlap rate OVRx for each main scan when annealed 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 device according to an embodiment. The holding table 13 is supported in the chamber 10 by the scanning mechanism 12. 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 action of the vacuum chuck mechanism of the holding table 13 up to the annealing target 30. The object to be annealed 30 is, for example, a semiconductor wafer such as a silicon wafer into which a dopant has been injected. The laser annealing device according to the embodiment performs, for example, activation annealing of a dopant.

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

The laser light source 20 receives a command from the control device 40 and outputs a pulsed laser beam for annealing. As the laser light source 20, for example, a laser diode having 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 passes through the annealing object 30. 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 region on the surface of the object to be annealed 30 and make the beam profile uniform.

The thermal radiant light emitted from the object to be annealed 30 passes through the laser transmission window 11, is reflected by the dichroic mirror 22 via the lens 23, and is further incident on the temperature sensor 25 via the lens 24. The dichroic mirror 22 reflects thermal radiation in a wavelength range of 1 μm or more. The temperature sensor 25 measures the intensity of thermal radiant light in a specific wavelength range. The intensity of thermal radiation depends on the temperature of the object to be annealed 30. 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 lens 23 and the lens 24 form an image on the surface of the object to be annealed 30 on the light receiving surface of the temperature sensor 25. As a result, the intensity of the thermal radiant light emitted from the surface region of the annealing target 30 having a conjugate relationship with the light receiving surface of the temperature sensor 25 is measured. The surface area to be measured is set so as to be included in the irradiation area of the laser beam, for example.

The control device 40 controls the scanning mechanism 12 to move the annealed object 30 held on the holding table 13 in a two-dimensional direction in the horizontal plane. Further, the laser light source 20 is controlled to output a pulsed laser beam from the laser light source 20 based on the current position information of the holding table 13. 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 result is stored in the storage device 41 in association with the position in the plane of the annealing target 30.

As an example, a time change in the intensity of thermal radiation can be obtained for each shot of the pulsed laser beam. The detection result stored in the storage device 41 is, for example, the peak value or the integrated value of the intensity of the thermal radiation light for each shot of the pulsed laser beam. The temperature obtained from the peak value or the integrated value of the intensity of thermal radiation is referred to as the "annealing temperature". The control device 40 outputs information on the intensity distribution of thermal radiation light (distribution of annealing temperature) 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 orthogonal coordinate system is defined in which the surface (laser irradiation surface) of the object to be annealed 30 is the xy plane and the normal direction of the surface is the positive direction of the z axis. By repeating the main scanning and the sub-scanning with the x-axis direction as the main scanning direction and the y-axis direction as the sub-scanning direction, almost the entire surface of the annealing target 30 is scanned by the pulsed laser beam.

FIG. 2B is a diagram showing the positional relationship between shots of the irradiation region 31 of the pulsed laser beam during the main scan. The irradiation region 31 has a substantially rectangular planar shape long in the y-axis direction. In FIG. 2B, the irradiation area 31a of the immediately preceding shot is shown by a broken line, and the irradiation area 31 of the shot immediately after that is shown by a solid line. The dimension (width) of the irradiation region 31 in the x-axis direction is represented by Wx. The dimension in the x-axis direction of the overlapping portion of the irradiation regions 31a and 31 of two consecutive shots is represented by Wov. The overlap rate OVRx of the irradiation area during the main scan,
OVRx = Wov / Wx
Is defined as.

FIG. 2C is a diagram showing the positional relationship between shots of the irradiation region 31 of the pulsed laser beam before and after the sub-scan. The irradiation area 31b immediately before the sub-scanning is shown by a broken line, and the irradiation area 31 after the sub-scanning is shown by a solid line. The dimension (length) of the irradiation region 31 in the y-axis direction is represented by Ly. The dimension in the y-axis direction of the overlapped portion between the irradiation regions 31b and 31 before and after one sub-scan is represented by Lov. The overlap rate OVRy of the irradiation area at the time of sub-scanning,
OVRy = Lov / Ly
Is defined as.

Before explaining the examples, the result of the evaluation experiment in which annealing was performed with a constant overlap rate will be described.

FIG. 3 is a diagram showing the distribution of the annealing temperature measured when the annealing target 30 was actually annealed. In FIG. 3, the region where the annealing temperature is higher is represented by making the shade of gray lighter. The radial and concentric regions with low annealing temperature appear because the planar shape of the adsorption groove provided on the holding table 13 (FIG. 1) is reflected. Further, a region having a low annealing temperature appears corresponding to the four locations where the lift pins are arranged. Except for special conditions of the base such as the groove for suction and the lift pin, vertical stripes parallel to the x-axis direction (main scanning direction) appear. Further, 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 diagram schematically showing the distribution of annealing temperature in the x-axis direction. Focusing on the linear region parallel to the x-axis scanned in one main scan, the annealing temperature is relatively higher in a part of the region 32 on the start point side of the scan than in the remaining region 33 on the end point side. It has become. In FIG. 4A, a region having a relatively high annealing temperature is hatched with a relatively low density, and a region having a relatively low annealing temperature is hatched with a relatively high density. In FIG. 4A, the boundary between the region 32 where the annealing temperature was high and the region 33 where the annealing temperature was low is clearly shown, but in reality, the boundary between the two is not clear and the annealing temperature is in the x-axis direction. It is gradually changing to.

The reason why the annealing temperature is high in the region 32 on the start point side of the main scan is that the influence of heating (heat storage effect) at the time of the main scan immediately before the sub scan remains. As described above, focusing on the region scanned in one main scan, it was confirmed that temperature unevenness occurs in the x-axis direction.

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

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

In the embodiment described below, this temperature unevenness is reduced by changing the overlap rate during the main scan.

FIG. 5 is a graph showing the relationship between the energy density per pulse (pulse energy density) of the pulsed laser beam incident on the annealing target 30 and the output voltage of the temperature sensor 25 (FIG. 1) for each overlap rate. Is. The horizontal axis represents the 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 to be annealed 30.

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

From the results shown in FIG. 5, it can be seen 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 rate OVRx of the irradiation region between the current shot and the next shot based on the measurement result of the annealing temperature by irradiation of one shot of the pulsed laser beam. ..

FIG. 6A is a flowchart showing a procedure for performing annealing using the annealing device 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 in the holding table 13 (FIG. 1), and the movement of the holding table 13 is started (step S1). For example, during the period of one main scan, the holding table 13 (FIG. 2A) is moved in the x-axis direction at a substantially constant velocity.

It is determined whether or not the annealing target 30 has moved to the irradiation start position (step S2), and when the object has moved 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 terminated (step S4).

The control device 40 reads the output voltage from the temperature sensor 25 and acquires information on the annealing temperature (step S5). The control device 40 performs feedback control using the overlap rate OVRx as an operation amount so that the measurement result of the annealing temperature approaches the target value Tt. For example, the control device 40 has an overlap rate OVRx in the x-axis direction between the irradiation region of the immediately preceding shot and the irradiation region of the next shot so that the annealing temperature approaches the target value Tt based on the measurement result of the annealing temperature. Is 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 amount of change ΔOVRx in the overlap rate OVRx. When the measurement result of the annealing temperature matches the target value Tt, the change amount ΔOVRx of the overlap rate OVRx is 0, and the current overlap rate OVRx 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 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. To. That is, when the measurement result of the annealing temperature is higher than the target value, the overlap rate OVRx is set lower than the current overlap rate OVRx, and when the measurement result of the annealing temperature is lower than the target value, the overlap rate OVRx is set. The overlap rate is higher than the current OVRx. In either case, the larger the deviation from the target value Tt to the measurement result of the annealing temperature, the larger the absolute value of the amount of change ΔOVRx.

After determining the overlap rate OVRx, the object to be annealed waits for the output of the pulsed laser beam until the object 30 reaches the 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, a pulse laser beam is irradiated for one shot (step S3). After that, steps S4 to S3 are repeatedly executed until the processing is completed.

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

In the embodiment, the overlap rate OVRx is adjusted so that the annealing temperature approaches the target value Tt based on the measurement result of the annealing temperature, so that the in-plane uniformity of the annealing temperature can be improved. This makes it possible to increase the in-plane uniformity of the activation rate of the dopant.

Further, in the embodiment, the power and the pulse width of the pulsed laser beam output from the laser light source 20 (FIG. 1) are not changed, and the annealing temperature is adjusted by changing the overlap rate OVRx, so that the power and the pulse width are adjusted. It is possible to adjust the annealing temperature even 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 this embodiment, the overlap rate OVRx is changed depending on the position of the annealing target 30 in the surface. For example, when annealing is performed at a constant overlap rate OVRx, the overlap rate OVRx is set low in a region where the annealing temperature tends to increase.

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

7A and 7B are graphs showing an example of a change in the overlap rate OVRx when annealed by the method according to the embodiment shown in FIGS. 1 to 6B. When the overlap rate OVRx is constant, the annealing temperature becomes relatively high in the vicinity of the start point of the main scan, as shown in FIG. 4A. When the above embodiment is applied, the annealing temperature is set to the target value Tt in both the case of main scanning in the positive direction of the x-axis (FIG. 7A) and the case of main scanning in the negative direction of the x-axis (FIG. 7B). The overlap rate OVRx is controlled to increase as the irradiation position of the pulsed 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 pulsed laser beam moves away from the start point of the main scan.

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

Therefore, in order to make the annealing temperature uniform in the y-axis direction, the average value of the overlap rate OVRx in the vicinity of both ends in the y-axis direction may be lower than the average value of the overlap rate OVRx inside. ..

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

Also in this embodiment, the annealing temperature can be made uniform with respect to the in-plane. Further, when the pulse repetition frequency of the pulsed laser beam output from the laser light source 20 is kept constant and annealed, the overlap ratio OVRx near the start point for each main scan shown in FIGS. 7A and 7B is relatively low. In, the moving speed of the annealing target 30 can be increased. Therefore, the effect of shortening the annealing time can be obtained as compared with the case where the region near the start point of the main scan is equalized to the overlap rate OVRx on the inner inner portion and the end point side and annealed.

It goes without saying that each of the above embodiments is exemplary and the configurations shown in different examples can be partially replaced or combined. Similar actions and effects due to the same configuration of a plurality of examples will not be mentioned sequentially for each example. Furthermore, the present invention is not limited to the above-mentioned examples. For example, it will be obvious to those skilled in the art that various changes, improvements, combinations, etc. are possible.

10 Chamber 11 Laser transmission window 12 Scanning mechanism 13 Holding table 14 Chuck plate 20 Laser light source 21 Transmission optical system 22 Dycroic mirror 23, 24 Lens 25 Temperature sensor 30 Annealing object 31 Irradiation area 31a Irradiation area 31b of the previous shot Before sub-scanning Irradiation area during the main scan 32 Area on the start point side of the main scan 33 Area other than the area on the start point side of the main scan 34 Area near both ends in the sub-scan direction 35 Area inside the area near both ends in the sub-scan direction 40 Control Device 41 Storage device 42 Output device

Claims (10)

This is an annealing method in which the surface of the object to be annealed is scanned with a pulsed laser beam to perform annealing.
The surface of the object to be annealed was scanned with the pulsed laser beam while overlapping the irradiation areas between the shots of the pulsed laser beam.
If the intensity of the thermal radiant light measured at the location heated by the incident of the pulsed laser beam is higher than the target value, the overlap rate is lower than the current overlap rate, and if it is lower than the target value, the overlap rate is lower than the current overlap rate. An annealing method that makes the rate higher than the current overlap rate . The annealing method according to claim 1, wherein the overlap rate is changed so that the intensity of the heat radiant light measured at the portion heated by the incident of the pulsed laser beam approaches the target value. In the procedure of changing the overlap rate based on the intensity of the thermal radiant light measured for the portion heated by the incident of the pulsed laser beam , this shot and the present shot are based on the measurement result of the portion heated by one shot. The annealing method according to claim 1 or 2, wherein the overlap rate of the irradiation region with the next shot is changed. A laser light source that outputs a pulsed laser beam and
A scanning mechanism that scans the surface of the object to be annealed with the pulsed laser beam,
A temperature sensor that measures the intensity of heat radiant light from the annealed object heated by the incident of the pulsed laser beam, and
It has a control device that controls the laser light source and the scanning mechanism to scan the surface of the annealed object with the pulsed laser beam while overlapping the irradiation regions between shots of the pulsed laser beam.
When the intensity of the thermal radiant light measured by the temperature sensor is higher than the target value, the control device lowers the overlap rate to the current overlap rate, and when the intensity is lower than the target value, the overlap rate is currently set to the current overlap rate. Annealing device that makes the overlap rate higher than that of . The annealing device according to claim 4, wherein the control device changes the overlap rate so that the intensity of the thermal radiant light measured by the temperature sensor approaches the target value. Claim 4 or 5 in which the control device changes the overlap rate of the irradiation region between the current shot and the next shot based on the measurement result by the temperature sensor at the portion heated by one shot. The annealing device described in. This is an annealing method in which the surface of the object to be annealed is scanned with a pulsed laser beam to perform annealing.
The surface of the object to be annealed was scanned with the pulsed laser beam while overlapping the irradiation areas between the shots of the pulsed laser beam.
In scanning the surface of the object to be annealed, the main scan and the sub scan are repeated to perform annealing.
An annealing method in which the overlap rate decreases as the distance from the start point of the main scan increases for each main scan . 7. Claim 7 to make the average value of the overlap rate when the main scan is performed on a certain region including both ends of the annealed object in the sub-scanning direction smaller than the average value of the overlap rate when the main scan is performed inside the region. The annealing method described in. A laser light source that outputs a pulsed laser beam and
A scanning mechanism that scans the surface of the object to be annealed with the pulsed laser beam,
It has a control device that controls the laser light source and the scanning mechanism to scan the surface of the annealed object with the pulsed laser beam while overlapping the irradiation regions between shots of the pulsed laser beam.
The control device is
In scanning the surface of the object to be annealed, the main scan and the sub scan are repeated to perform annealing.
An annealing device that reduces the overlap rate for each main scan as it moves away from the start point of the main scan . The control device sets the average value of the overlap rate when the main scan is performed on a certain region including both ends of the annealed object in the sub-scanning direction from the average value of the overlap rate when the main scan is performed inside the region. The annealing device according to claim 9 .

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