JP7523960B2 - Laser processing method, control device for laser processing device, and laser processing device - Google Patents

Description

The present invention relates to a laser processing method, a control device for a laser processing device, and a laser processing device.

Laser annealing is used for activation annealing of dopants ion-implanted into semiconductor wafers. Many laser annealing devices use a line beam as the laser beam for annealing (see Patent Document 1, etc.). A line beam refers to a laser beam in which the beam spot on the surface of the semiconductor wafer to be annealed is an elongated (linear) beam spot that is long in one direction. By moving the beam spot on the surface of the semiconductor wafer in the width direction perpendicular to the longitudinal direction, the desired region of the semiconductor wafer is annealed.

JP 2011-119297 A

When annealing is performed using a conventional laser annealing device, the annealing effect may vary along the longitudinal direction of the beam spot. For example, when activation annealing is performed on dopants ion-implanted in a semiconductor wafer, the activation rate varies along the longitudinal direction of the beam spot.

The object of the present invention is to provide a laser processing method, a control device for a laser processing device, and a laser processing device that can suppress the variation in the annealing effect in the longitudinal direction of a long beam spot.

According to one aspect of the present invention,
A laser beam is irradiated onto the surface of the object under conditions in which a beam spot that is elongated in one direction is formed on the surface of the object and has an intensity distribution in which the intensity increases from the center toward the end in the longitudinal direction ;
There is provided a laser processing method in which the beam spot is moved relative to the object in a width direction of the beam spot, and the shape of the intensity distribution of the beam spot is changed according to the moving speed of the beam spot relative to the object .

According to another aspect of the invention,
A control device for controlling a laser processing device that forms a beam spot having a shape elongated in one direction on a surface of an object and moves the beam spot relative to the object,
an input section for inputting laser processing conditions;
a control unit that controls the laser processing device based on the laser processing conditions input from the input unit,
A control device is provided in which, when the moving speed of the beam spot relative to the object is given as the laser processing condition, the control unit controls the laser processing device to generate an intensity distribution in which the intensity increases from the center to the ends in the longitudinal direction of the beam spot, and the ratio of the intensity at the ends to the intensity at the center in the longitudinal direction is set to a value corresponding to the moving speed of the beam spot.

According to yet another aspect of the present invention,
a beam expander that changes the beam diameter of the laser beam;
a diffractive optical element on which the laser beam that has passed through the beam expander is incident and which forms a beam spot having a shape that is elongated in one direction on a surface of an object;
The beam expander changes a beam diameter at an incident position on the diffractive optical element,
The diffractive optical element produces an intensity distribution in which the intensity increases from the center to the ends in the longitudinal direction of the beam spot when the beam diameter of the laser beam at the incident position becomes larger than a specified size, and a laser processing device is provided having the characteristic that as the beam diameter of the laser beam at the incident position becomes larger, the ratio of the intensity at the ends to the intensity at the longitudinal center becomes larger.

By adjusting the intensity distribution of the beam spot in the longitudinal direction as described above, it is possible to suppress variation in the annealing effect in the longitudinal direction.

FIG. 1 is a block diagram of a control device according to an embodiment, and a schematic perspective view of a laser processing device that is an object to be controlled by the control device. FIG. 2 is a schematic diagram showing the movement history of a beam spot on the surface of a semiconductor wafer. 3A to 3C are schematic perspective views showing the positional relationship between a diffractive optical element and a laser beam incident on the diffractive optical element, and FIG. 3D is a graph showing the longitudinal intensity distribution of the beam spot when laser beams with beam diameters _D1 , _D2 , and _D3 are incident on the diffractive optical element. 4A and 4B are graphs showing the intensity distribution of the beam spot and the distribution of the maximum temperature reached on the surface of the semiconductor wafer. FIG. 5 is a graph showing the distribution of the maximum temperature reached on the surface of the semiconductor wafer for each moving speed of the beam spot. FIG. 6 is a graph showing the relationship between the moving speed of the beam spot, the beam diameter of the laser beam incident on the diffractive optical element, and the intensity distribution in the longitudinal direction of the beam spot. FIG. 7 is a flow chart showing the procedure of the laser annealing method according to the embodiment. 8A and 8B are diagrams showing a schematic view of a region annealed by two main scans of a beam spot.

The laser processing device and laser processing method according to one embodiment will be described with reference to Figures 1 to 8B.

Figure 1 is a block diagram of a control device 55 according to an embodiment, and a schematic perspective view of a laser processing device 60 that is controlled by the control device 55.

First, the configuration of the laser processing device 60 will be described. The laser light source 10 outputs a pulsed laser beam. A solid-state laser, a gas laser, a laser diode, or the like can be used as the laser light source 10. The pulsed laser beam output from the laser light source 10 passes through a beam expander 11, folding mirrors 13, 14, and 15, and a diffractive optical element 16 and is incident on the surface of a semiconductor wafer 20, which is the object to be annealed.

The semiconductor wafer 20 is held by a wafer chuck 18 supported by a moving mechanism 17. The moving mechanism 17 moves the wafer chuck 18 in two directions in a horizontal plane, thereby moving the semiconductor wafer 20 in two directions. For example, an XY stage is used as the moving mechanism 17.

The beam expander 11 adjusts the beam size (diameter of the beam cross section) at the position where the laser beam is incident on the diffractive optical element 16. The diffractive optical element 16 forms a beam spot on the surface of the semiconductor wafer 20 that has an elongated shape that is long in one direction and a predetermined intensity distribution.

Next, the control device 55 will be described. The control device 55 includes a control unit 50 and an input unit 51. A user inputs laser processing conditions from the input unit 51. The control unit 50 controls the laser light source 10, the beam expander 11, and the moving mechanism 17 based on the input laser processing conditions. For example, the control unit 50 moves the semiconductor wafer 20 in the width direction of the beam spot while irradiating the semiconductor wafer 20 with a pulsed laser beam. This causes the beam spot to move in the width direction relative to the surface of the semiconductor wafer 20. The laser processing conditions input by the user from the input unit 51 include, for example, the pulse repetition frequency of the pulsed laser beam, the laser power, the moving speed of the beam spot, etc.

The process of moving the beam spot relative to the semiconductor wafer 20 in its width direction is called main scanning, and the process of moving it relative to the semiconductor wafer 20 in its length direction is called sub-scanning. By repeating main scanning and sub-scanning, it is possible to anneal almost the entire surface of the semiconductor wafer 20.

Next, referring to Figure 2, we will explain the movement of the beam spot on the surface of the semiconductor wafer 20.

Figure 2 is a schematic diagram showing the movement history of the beam spot 30 on the surface of the semiconductor wafer 20 (Figure 1). An xyz Cartesian coordinate system is defined in which the longitudinal direction of the beam spot 30 is the y direction, the width direction is the x direction, and the normal direction to the surface of the semiconductor wafer 20 is the z direction. The longitudinal dimension of the beam spot 30 is denoted as L, and the width direction is denoted as W. When the beam spot 30 is moved in the x direction (main scanning), the beam spot 30 is moved so that two consecutive shots of the beam spot 30 partially overlap.

The dimension in the x direction of the area where the beam spots 30 of two consecutive shots overlap is denoted as Wov. Wov/W is called the overlap ratio R.

Next, the diffractive optical element 16, the beam diameter of the incident laser beam, and the longitudinal intensity distribution of the beam spot 30 (Figure 2) will be described with reference to Figures 3A to 3D.

3A to 3C are schematic perspective views showing the positional relationship between the diffractive optical element 16 and a laser beam 31 incident on the diffractive optical element 16. The laser beam 31 is incident on the diffractive optical element 16. The laser beam 31 is a Gaussian beam. FIG. 3B shows a state in which the laser beam 31 is incident on the diffractive optical element 16 according to the design specifications. The design specifications of the diffractive optical element 16 specify the wavelength of the laser beam and the beam diameter _D2 at the position of incidence of the laser beam on the diffractive optical element 16. In this specification, the beam diameter at the position of incidence of the laser beam on the diffractive optical element 16 may be simply referred to as the "beam diameter".

Fig. 3A shows a state where a laser beam ₃₁ having a beam diameter D1 smaller than the design beam diameter _D2 is incident. Fig. 3C shows a state where a laser beam ₃₁ having a beam diameter _D3 larger than the design beam diameter D2 is incident. The spread angle of the laser beam 31 in Figs. 3A to 3C is the same.

3D is a graph showing the longitudinal intensity distribution of the beam spot 30 (FIG. 2) when the laser beams having beam diameters _D1 , _D2 , and _D3 are incident on the diffractive optical element 16. The horizontal axis represents the longitudinal position of the beam spot 30, and the vertical axis represents the intensity. The dashed line _D1 , thin solid line _D2 , and thick solid line _D3 in the graph of FIG. 3D show the intensity distribution when the beam diameter of the laser beam incident on the diffractive optical element 16 is _D1 (FIG. 3A), _D2 (FIG. 3B), and _D3 (FIG. 3C), respectively. When the beam diameter is the design specification beam diameter _D2 , the diffractive optical element 16 is designed so that the longitudinal intensity distribution is approximately constant (flat).

When the beam diameter becomes _D1 , _which is smaller than the design beam diameter _{D2, the intensity decreases from the center toward the end in the longitudinal direction. Conversely, when the beam diameter becomes D3 ,} which is larger than the design beam diameter D2, the intensity increases from the center toward the end in the longitudinal direction. In this way, when the beam diameter of the laser beam incident on the diffractive optical element 16 is changed, the intensity distribution in the longitudinal direction of the beam spot 30 on the surface of the semiconductor wafer 20 changes. The diffractive optical element 16 used in this embodiment has a characteristic that the ratio of the intensity at the end to the intensity at the longitudinal center increases as the beam diameter increases.

The intensity distribution in the width direction of the beam spot 30 is, for example, flat-top.

Next, referring to Figures 4A and 4B, the relationship between the longitudinal intensity distribution of the beam spot 30 when a pulsed laser beam is incident on the semiconductor wafer 20 to perform annealing, and the maximum temperature reached on the surface of the semiconductor wafer 20 will be described. During the period when one laser pulse of the pulsed laser beam is incident, the surface temperature rises over time, and when the laser pulse falls, the surface temperature falls over time. The maximum temperature reached corresponds to the surface temperature at the time when the laser pulse falls.

Figures 4A and 4B are graphs showing the intensity distribution in the longitudinal direction of the beam spot 30 and the distribution of the maximum temperature reached on the surface of the semiconductor wafer 20. The upper graphs in each of Figures 4A and 4B show the intensity distribution in the longitudinal direction of the beam spot 30, and the lower graphs show the distribution of the maximum temperature reached on the surface of the semiconductor wafer 20.

As shown in FIG. 4A, when the intensity distribution is flat, the maximum temperature gradually decreases from the center to the end in the longitudinal direction of the beam spot 30. As shown in FIG. 4B, when the shape of the intensity distribution is adjusted under the condition that the intensity increases from the center to the end, the distribution of the maximum temperature becomes almost flat in the longitudinal direction of the beam spot 30. The shape of the distribution of the maximum temperature changes depending on the intensity distribution in the longitudinal direction of the beam spot 30. In order to make the annealing effect in the longitudinal direction of the beam spot 30 uniform, it is preferable to make the distribution of the maximum temperature in the longitudinal direction close to flat.

Next, the relationship between the movement speed of the beam spot 30 and the distribution of the maximum temperature reached on the surface of the semiconductor wafer 20 will be explained with reference to FIG.

5 is a graph showing the distribution of the maximum temperature reached on the surface of the semiconductor wafer 20 for each moving speed of the beam spot 30. The horizontal axis represents the longitudinal position of the beam spot 30, and the vertical axis represents the maximum temperature reached on the surface. The solid and dashed lines in the graph show the distribution of the maximum temperature reached when the moving speeds of the beam spot 30 are _v1 and _v2 , respectively. Here, the moving speed _v1 is faster than the moving speed _v2 . Note that the intensity distribution in the longitudinal direction of the beam spot 30 is the same when the moving speed is _v1 and when the moving speed is _v2 .

When the intensity distribution is approximately flat when the moving speed is _v1 , when the moving speed is changed to _v2 , which is slower than _v1 , the maximum temperature decreases from the center toward both ends in the longitudinal direction of the beam spot 30. As the moving speed becomes slower, the amount of decrease in the maximum temperature at both ends relative to the maximum temperature at the center increases.

As shown in Figures 4A, 4B, and 5, the distribution of maximum temperature on the surface depends on the intensity distribution in the longitudinal direction of the beam spot 30 and the movement speed of the beam spot 30. By adjusting the movement speed of the beam spot 30 and the intensity distribution in the longitudinal direction of the beam spot 30, the distribution of maximum temperature can be made closer to flat. As shown in Figure 3D, the intensity distribution in the longitudinal direction of the beam spot 30 depends on the beam diameter of the laser beam incident on the diffractive optical element 16. Therefore, by adjusting the movement speed of the beam spot 30 and the beam diameter of the laser beam, the distribution of maximum temperature can be made closer to flat.

Next, with reference to FIG. 6, the relationship between the movement speed of the beam spot 30, the beam diameter of the laser beam incident on the diffractive optical element 16, and the intensity distribution in the longitudinal direction of the beam spot 30 will be described.

6 is a graph showing the relationship between the moving speed of the beam spot 30, the beam diameter of the laser beam incident on the diffractive optical element 16, and the intensity distribution in the longitudinal direction of the beam spot 30. The horizontal axis represents the moving speed of the beam spot 30, and the vertical axis represents the beam diameter of the laser beam incident on the diffractive optical element 16. The solid line in the graph shows the condition under which the intensity distribution in the longitudinal direction of the beam spot becomes flat. In the region to the upper right of the solid line, the intensity at both ends of the beam spot is higher than the intensity at the center, as shown by the thick solid line _D3 in FIG. 3D. In the region to the lower left of the solid line, the intensity at both ends of the beam spot is lower than the intensity at the center, as shown by the dashed line _D1 in FIG. 3D.

Next, the laser annealing method according to this embodiment will be described with reference to FIG.
7 is a flow chart showing the procedure of the laser annealing method according to the embodiment. When a user inputs the moving speed of the beam spot 30 from the input unit 51 (FIG. 1), the control unit 50 (FIG. 1) acquires the input value of the moving speed (step S1). The control unit 50 controls the beam expander 11 (FIG. 1) according to the input value of the moving speed of the beam spot 30 to adjust the beam diameter of the laser beam incident on the diffractive optical element 16 (step S2).

The control unit 50 controls the beam expander 11 to adjust the beam diameter, and then controls the laser light source 10 and the movement mechanism 17 to perform annealing (step S3).

Next, a method for adjusting the beam diameter will be described. The relationship between the movement speed and the beam diameter for flattening the intensity distribution in the longitudinal direction of the beam spot 30 (the relationship shown by the solid line in Figure 6) is stored in advance in the control unit 50. The control unit 50 determines the beam diameter for flattening the intensity distribution from this relationship and the input value of the movement speed. Once the beam diameter is determined, the control unit 50 controls the beam expander 11 to achieve the determined beam diameter.

Next, the excellent effects of the above embodiment will be described.
In the above embodiment, since the intensity is increased from the center toward the end in the longitudinal direction of the beam spot 30, the distribution of the maximum temperature reached on the surface of the semiconductor wafer 20 can be made closer to flat in the longitudinal direction of the beam spot 30 compared to the case where the intensity distribution is flat. This makes it possible to make the annealing effect closer to uniform. When performing activation annealing of dopants, it makes it possible to make the activation rate closer to uniform.

In addition, by controlling the beam expander 11 (Figure 1) to change the beam diameter, the shape of the intensity distribution in the longitudinal direction of the beam spot 30 can be easily changed. For example, in the above embodiment, the shape of the intensity distribution of the beam spot 30 is changed by adjusting the beam diameter according to the movement speed of the beam spot 30. This makes it possible to make the distribution of the maximum attained temperature for each movement speed closer to flat, even when annealing is performed under conditions where the movement speed of the beam spot 30 is different.

Next, another excellent effect of the above embodiment will be described with reference to FIGS. 8A and 8B.
8A and 8B are diagrams showing regions annealed by two main scans of the beam spot 30. Region 41 is annealed by one main scan in the x direction, and region 42 is annealed by the next main scan after the sub-scan in the y direction. In Fig. 8A and 8B, region 41 is hatched with diagonal slanting downward to the right, and region 42 is hatched with diagonal slanting downward to the right at a lower density than the hatching of region 41.

In the example shown in FIG. 8A, the distance over which beam spot 30 is sub-scanned in the y direction is approximately equal to or slightly shorter than the longitudinal dimension L of beam spot 30. In contrast, in the example shown in FIG. 8B, the distance over which beam spot 30 is sub-scanned in the y direction is approximately 2/3 of the longitudinal dimension L of beam spot 30. In the example shown in FIG. 8A, there is only a small overlap between region 41 and region 42. In the example shown in FIG. 8B, the y direction dimension of the area where region 41 and region 42 overlap is approximately 1/3 of length L.

If the intensity distribution in the longitudinal direction of the beam spot 30 is not flat, the overlap between regions 41 and 42 must be increased as shown in FIG. 8B in order to make the annealing effect in the y direction uniform. In contrast, in the above embodiment, the intensity distribution in the longitudinal direction of the beam spot 30 can be made almost flat, so that the annealing effect in the y direction can be made uniform even if the overlap between regions 41 and 42 is reduced as shown in FIG. 8A.

This allows the distance over which the beam spot 30 is sub-scanned to be increased while maintaining uniformity of the annealing effect in the y direction. This allows the number of times the beam spot 30 is main-scanned when annealing the semiconductor wafer 20 to be reduced.

Next, a modification of the above embodiment will be described.
In the above embodiment, a diffractive optical element is used to shape the beam spot 30 and adjust the intensity distribution, but other beam shaping optical systems may be used. For example, an array lens in which a plurality of cylindrical lenses are combined and a condenser lens may be used.

In the above embodiment, the dopants ion-implanted into the semiconductor wafer 20 are activated, but the laser processing apparatus according to the above embodiment can also be applied to laser processing other than activation annealing. For example, it can also be applied to annealing for crystallizing a semiconductor thin film formed on a substrate.

It goes without saying that each embodiment is merely an example, and that partial substitution or combination of the configurations shown in different embodiments is possible. Similar effects resulting from similar configurations in multiple embodiments are not mentioned one after the other for each embodiment. Furthermore, the present invention is not limited to the above-described embodiments. For example, it will be obvious to those skilled in the art that various modifications, improvements, combinations, etc. are possible.

REFERENCE SIGNS LIST 10 Laser light source 11 Beam expander 13, 14, 15 Folding mirror 16 Diffractive optical element 17 Moving mechanism 18 Wafer chuck 20 Semiconductor wafer 30 Beam spot 31 Laser beam 41, 42 Area annealed in first main scan 50 Control unit 51 Input unit 55 Control device 60 Laser processing device

Claims (4)

A laser beam is irradiated onto the surface of the object under conditions in which a beam spot that is elongated in one direction is formed on the surface of the object and has an intensity distribution in which the intensity increases from the center toward the end in the longitudinal direction ;
A laser processing method in which the beam spot is moved relative to the object in a width direction of the beam spot, and the shape of the intensity distribution of the beam spot is changed according to the moving speed of the beam spot relative to the object . A control device for controlling a laser processing device that forms a beam spot having a shape elongated in one direction on a surface of an object and moves the beam spot relative to the object,
an input section for inputting laser processing conditions;
a control unit that controls the laser processing device based on the laser processing conditions input from the input unit,
When the moving speed of the beam spot relative to the object is given as the laser processing condition, the control unit controls the laser processing device to generate an intensity distribution in which the intensity increases from the center to the ends in the longitudinal direction of the beam spot, and sets the ratio of the intensity at the ends to the intensity at the center in the longitudinal direction to a value corresponding to the moving speed of the beam spot. the laser processing device includes a beam expander and a diffractive optical element onto which the laser beam that has passed through the beam expander is incident;
3. The control device according to claim 2, wherein the control unit controls the beam expander to change the beam diameter at the incident position on the diffractive optical element, thereby changing the shape of the intensity distribution in which the intensity increases from the center to the end of the beam spot in the longitudinal direction. a beam expander that changes the beam diameter of the laser beam;
a diffractive optical element on which the laser beam that has passed through the beam expander is incident and which forms a beam spot having a shape that is elongated in one direction on a surface of an object;
The beam expander changes a beam diameter at an incident position on the diffractive optical element,
The diffractive optical element generates an intensity distribution in which the intensity increases from the center to the ends in the longitudinal direction of the beam spot when the beam diameter of the laser beam at the incident position becomes larger than a specified size, and has a characteristic in which the ratio of the intensity at the ends to the intensity at the longitudinal center increases as the beam diameter of the laser beam at the incident position becomes larger.

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