JP2011187761A - Method for manufacturing semiconductor device, and laser annealing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor device, adapted to suppress an excessive increase in temperature of a back of an irradiation object, and to activate even down to a deep region. <P>SOLUTION: Laser beam incidence to the surface of an irradiation object starts. During the incidence of laser beam on the irradiation object, a physical quantity depending on the surface temperature of a region where the laser beam is incident is measured. It is determined whether the irradiation of laser beam is to be stopped, on the basis of the measured physical quantity. If it is determined that the irradiation of laser beam is to be stopped, irradiation of laser beam is stopped, and after a predetermined standby time elapses, irradiation of laser beam resumed; and if it is determined that the irradiation of laser beam is not to be stopped, irradiation of laser beam is continued. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor device including a step of annealing a target object by irradiating a laser beam and a laser annealing apparatus.

  In the manufacturing process of an insulated gate bipolar transistor (IGBT), a collector is formed on the surface (second surface) opposite to the surface (first surface) on which the gate electrode and emitter are formed. By irradiating the second surface of the semiconductor wafer with the laser beam, the impurity implanted into the collector can be activated.

In order to activate the impurities implanted deep in the semiconductor wafer, the wavelength 690Nm～900nm, irradiation time 10Myuesu～100myuesu, a method of performing laser annealing under the conditions in the power density 250kW ^/ cm ² ~750kW ^/ cm 2 are known ( Patent Document 1). A method of controlling the irradiation time of a laser beam by using a continuous wave laser light source and controlling the beam spot size on the surface of a semiconductor wafer is known (Patent Document 2).

JP 2006-351659 A Japanese Patent No. 4117020

  In the case of activating the impurities implanted in the IGBT collector, it is preferable to activate as deep a region as possible without melting the surface of the semiconductor wafer. In addition, it is preferable to suppress an excessive temperature rise on the surface where the gate electrode or the like is formed (the surface opposite to the surface irradiated with the laser). The conventional laser annealing method cannot sufficiently satisfy both of these requirements.

  An object of the present invention is to provide a method for manufacturing a semiconductor device and a laser annealing apparatus suitable for suppressing an excessive temperature increase on the back surface of an irradiation object and activating a deep region.

According to one aspect of the invention,
Starting the incidence of the laser beam on the surface of the irradiation object;
Measuring a physical quantity depending on a surface temperature of a region where the laser beam is incident during a period in which the laser beam is incident on the irradiation object;
Determining whether to stop the irradiation of the laser beam based on the measured physical quantity; and
If it is determined that the laser beam irradiation is to be stopped, it is determined that the laser beam irradiation is resumed after a certain waiting time has elapsed after the laser beam irradiation is stopped, and the laser beam irradiation is not stopped. In such a case, there is provided a method for manufacturing a semiconductor device including a step of continuing the laser beam irradiation.

According to another aspect of the invention,
A laser light source for emitting a laser beam;
A stage for holding an irradiation object at a position where a laser beam emitted from the laser light source is incident;
A blocking device that switches between a state in which the laser beam emitted from the laser light source reaches the irradiation object held on the stage and a state in which the laser beam is blocked so as not to reach the object;
A measuring device that measures a physical quantity that depends on a surface temperature of the irradiation object at a position where the laser beam is incident;
The blocking device is
Based on the measurement result of the physical quantity by the measurement device, determine whether to stop the irradiation of the laser beam,
When it is determined that the laser beam irradiation is to be stopped, after the laser beam is interrupted, after a certain waiting time has elapsed, the laser beam irradiation is resumed and it is determined not to stop the laser beam irradiation. Provides a laser annealing apparatus for continuing the irradiation of the laser beam.

  By stopping the irradiation of the laser beam, an excessive increase in the surface temperature of the irradiation object can be suppressed. Further, by restarting the laser irradiation after the standby time has elapsed, the thermal energy can reach a deep region.

1 is a schematic view of a laser annealing apparatus according to Example 1. FIG. It is a graph which shows the simulation result of the relationship between the irradiation time until the surface temperature of an irradiation target object becomes 1673K, and a power density. It is a graph which shows the result of having calculated | required with the simulation the relationship between the maximum temperature of the position of 3 micrometers depth when laser irradiation is performed until the surface temperature of an irradiation target object is 1673K, and a power density. It is a graph which shows the result of having calculated | required the relationship between the temperature of the back surface when laser irradiation is performed until the surface temperature of an irradiation target object is 1673K, and elapsed time by simulation. 3 is a flowchart showing a laser annealing method according to Example 1. It is a graph which shows the simulation result of the temperature change at the time of performing laser irradiation by the method by Example 1. 6 is a schematic view of a laser annealing apparatus according to Example 2. FIG. 6 is a flowchart showing a laser annealing method according to Example 2. It is a graph which shows the simulation result of the temperature change at the time of performing laser irradiation by the method by Example 2. FIG. 10 is a flowchart showing a laser annealing method according to Example 3. (11A) and (11B) are plan views showing the positional relationship between the beam spot of the annealing laser beam and the beam spot of the reference laser beam, and (11C) is a plan view showing another example. It is a graph which shows the simulation result of the temperature change at the time of performing laser irradiation by the method by Example 3. It is a graph which shows the relationship between a power density and a scanning speed. It is sectional drawing of IGBT.

[Example 1]
FIG. 1 shows a schematic diagram of a laser annealing apparatus according to the first embodiment. The laser light source 10 emits a continuous wave laser beam. For the laser light source 10, for example, a semiconductor laser is used. The oscillation wavelength is, for example, 808 nm. A semiconductor laser having an oscillation wavelength in the range of 650 nm to 850 nm may be used. An irradiation object 60 is held on the stage 35. The irradiation object 60 is, for example, a silicon wafer after an impurity is implanted and before activation annealing is performed. Laser annealing is performed when the laser beam is incident on the irradiation object 60. The laser beam emitted from the laser light source 10 is referred to as “annealing laser beam”.

  The laser beam emitted from the laser light source 10 enters the irradiation target 60 via the blocking device 20, the beam shaping optical system 25, the homogenizing optical element 26, the folding mirror 30, and the lens 31.

  The blocking device 20 includes a control device 21, an electro-optic element 22, a beam splitter 23, and a beam damper 24. The laser beam emitted from the laser light source 10 enters the beam splitter 23 via the electro-optic element 22. For example, a Pockels cell is used as the electro-optic element 22. The beam splitter 23 transmits the P component of the incident laser beam and reflects the S component. The laser beam reflected by the beam splitter 23 enters the beam damper 24. The laser beam transmitted through the beam splitter 23 exits from the blocking device 20 and enters the beam shaping optical system 25.

  The control device 21 can control the electro-optic element 22 to change the polarization direction of the laser beam, and can switch the state of only the S component and the state of only the P component with respect to the beam splitter 23. In a state where the laser beam is only the S component, the laser beam enters a beam damper 24 and is cut off. When the laser beam is only the P component, the laser beam enters a beam shaping optical system 25 and enters a transmission state. Instead of the electro-optic element 22 and the beam splitter 23, an acousto-optic element (AOM) may be used.

  The beam shaping optical system 25 shapes the beam cross section of the laser beam. For the beam shaping optical system 25, for example, a beam expander is used. The laser beam whose beam section has been shaped by the beam shaping optical system 25 enters the uniformizing optical element 26. The uniformizing optical element 26 uniformizes the light intensity distribution in the beam cross section of the laser beam. For the uniformizing optical element 26, for example, a diffractive optical element (DOE), an array lens, a fly-eye lens, or the like is used.

  The laser beam transmitted through the homogenizing optical element 26 is reflected by the folding mirror 30 and enters the irradiation object 60 via the lens 31. The central beam of the laser beam incident on the irradiation target 60 is perpendicular to the surface of the irradiation target 60. The positions of the uniformizing optical element 26, the lens 31, and the stage 35 are adjusted with respect to the traveling direction of the laser beam so that the light intensity distribution is uniform on the surface of the irradiation target 60 held on the stage 35.

  The reference light source 40 emits a reference laser beam. For the reference light source 40, for example, a HeNe laser having a wavelength of 633 nm is used. Note that a laser in the near-infrared region having an oscillation wavelength of visible light or a wavelength of 1 μm or less may be used. The reference laser beam is reflected by the folding mirror 41 and obliquely enters the irradiation object 60. The beam spot of the reference laser beam on the surface of the irradiation object 60 is included or partially overlaps with the beam spot of the annealing laser beam. A preferred positional relationship between the beam spots will be described later.

  A part of the reference laser beam that has entered the irradiation target 60 is reflected by the surface of the irradiation target 60, is reflected by the folding mirror 42, and enters the reference light detector 43. For the reference light detector 43, for example, a photodiode is used. The intensity data of the reflected light detected by the reference light detector 43 is input to the control device 21.

  A part of the black body radiation from a specific position in the beam spot of the annealing laser beam on the surface of the irradiation object 60 is collected by the condenser lens 50 and enters the black body radiation detector 51. . Black body radiation intensity data detected by the black body radiation detector 51 is input to the control device 21. The control device 21 controls the electro-optical element 22 based on at least one of reflected light intensity data and blackbody radiation intensity data.

  Since black body radiation is radiated from the surface of the irradiation object 60 into a space with a solid angle of 2π steradians, there is little black body radiation incident on the condenser lens 50. Therefore, it is preferable to use a detector having a multiplication function such as an avalanche photodiode (APD) or a photomultiplier tube (PMT) as the black body radiation detector 51. In order not to be affected by the scattered light of the annealing laser beam, the black body radiation detector 51 is disposed in the dark room, and the black body radiation detector 51 is disposed in the dark room with an optical fiber. It is preferable to transmit up to.

  The scanning mechanism 36 moves the stage 35 in the X axis direction and the Y axis direction parallel to the surface of the irradiation target 60. By moving the stage 35 while irradiating the annealing laser beam, the surface of the irradiation object 60 can be scanned with the laser beam. For example, let the X-axis direction and the Y-axis direction be the main scanning direction and the sub-scanning direction, respectively.

  Next, with reference to FIG. 2 to FIG. 4, preferable annealing conditions for performing activation annealing of a semiconductor wafer, for example, a silicon wafer will be described. The melting point of silicon is 1687K. When annealing the IGBT collector, the annealing should be performed under the condition that the temperature on the front side where the gate electrode, the emitter, etc. are formed does not increase excessively and is activated as deep as possible from the back surface. preferable.

  An ultraviolet laser such as an excimer laser is absorbed by the extreme surface of the semiconductor wafer, and is not suitable for annealing to activate to a deep position. Further, when the wavelength is in the far infrared region, the absorption coefficient of the semiconductor wafer is low, so that it is not suitable for annealing. For activation annealing of the IGBT collector, it is preferable to use a laser having a wavelength of 650 nm to 850 nm.

FIG. 2 shows a simulation result of the relationship between the power density of the laser beam on the surface of the semiconductor wafer and the irradiation time until the surface temperature rises to 1673 K, which is slightly lower than the melting point of the semiconductor wafer. The horizontal axis represents the power density in the unit “kW / cm ² ”, and the vertical axis represents the irradiation time in the unit “μs”. The wavelength of the laser beam was 800 nm, and the semiconductor wafer material was silicon. As the power density increases, the irradiation time until the surface temperature reaches 1673K is shortened.

FIG. 3 shows the maximum temperature reached at a depth of 3 μm from the surface on the laser irradiation side in the simulation of FIG. The horizontal axis represents the power density in the unit “kW / cm ² ”, and the vertical axis represents the maximum attained temperature in the unit “K”. Under any irradiation condition, the maximum temperature reached on the surface is 1673K, but the maximum temperature reached at a depth of 3 μm varies depending on the power density. As the power density increases, the maximum temperature reached tends to decrease.

  As shown in FIG. 2, when the power density is increased, the irradiation time is shortened, so that the vicinity of the surface of the semiconductor wafer is rapidly heated. Thereby, the temperature rise width inside the semiconductor wafer is reduced, and the time during which the temperature is kept high is shortened. It can be seen that when the power density increases, it is difficult to activate deep region impurities under the condition that the surface is not melted.

  FIG. 4 shows a simulation result of the relationship between the elapsed time from the start of laser irradiation and the temperature of the back surface of the semiconductor wafer (surface opposite to the surface irradiated with laser). The horizontal axis represents the elapsed time in the unit “μs”, and the vertical axis represents the back surface temperature in the unit “K”. The numerical value attached to each curve indicates the power density of the laser beam on the surface of the semiconductor wafer. The laser irradiation was stopped when the surface temperature of the semiconductor wafer reached 1673K. As boundary conditions, the thickness of the semiconductor wafer was set to 100 μm, and the back surface was insulative.

  As the power density decreases, the temperature reached on the back surface of the semiconductor wafer increases. This is because when the power density is lowered, the irradiation time becomes longer as shown in FIG. 2, so that the total energy input to the semiconductor wafer is increased.

  In order to increase the activation depth, it is required to perform annealing at a high temperature for a long time. In order to perform annealing at a high temperature for a long time, it is preferable to lower the power density from the results shown in FIGS. However, as shown in FIG. 4, when the power density is lowered, the back surface temperature of the semiconductor wafer is greatly increased. The configuration of the back surface of the semiconductor wafer, that is, the surface side of the IGBT, restricts the temperature increase range allowed during laser annealing. When the allowable temperature rise is large, deep region impurities can be activated by laser annealing at a low power density.

On the other hand, when the allowable temperature rise is small, it is necessary to anneal at a high power density, and it becomes difficult to increase the activation depth. As shown in FIG. 4, when the power density is less than 150 kW / cm ² , the increase in the back surface temperature of the semiconductor wafer becomes too large. Therefore, it is understood that the power density is preferably 150 kW / cm ² or more.

The upper limit of the preferred value of the power density depends on the target value of the activation depth. When the power density exceeds 1 MW / cm ² , the order is about the same as that in the annealing method using a pulse laser, and it becomes difficult to perform activation under non-melting conditions. Therefore, the power density is preferably 1 MW / cm ² or less.

In general, it is desirable that the maximum temperature reached on the back surface of the semiconductor wafer be 600K or less. For this reason, it is preferable from the simulation result of FIG. 4 that the power density is 250 kW / cm ² or more. Moreover, when the target value of the activation depth is set to about 3 μm, it is preferable that the maximum temperature reached at the position of the depth of 3 μm exceeds 1000 ° C. (1273 K). Therefore, from the simulation results of FIG. 3, the power density is preferably 500 kW / cm ² or less.

  FIG. 5 shows a flowchart of the laser annealing method according to the first embodiment. In the first embodiment, a step-and-repeat method is adopted. That is, the irradiation object 60 is stopped and the annealing laser beam is irradiated. When the annealing of the irradiation position is completed, the laser irradiation is stopped (the laser beam is interrupted), and the irradiation object 60 is moved. Thereafter, the irradiation object 60 is stopped and a new region is irradiated with the annealing laser beam. In this way, the irradiation of the laser beam and the movement of the irradiation target 60 with the irradiation target 60 stationary are alternately repeated.

First, in step SA1, the stage 35 is moved so that the annealing laser beam is incident on the target position of the irradiation object 60. Thereafter, irradiation of the annealing laser beam is started while the stage 35 is stationary. The power density on the surface of the irradiation target 60 is, for example, 400 kW / cm ² .

  In step SA2, it is determined whether or not a prescribed irradiation time has elapsed since the irradiation start time. The prescribed irradiation time is determined in advance by performing various evaluation experiments, and is stored in the control device 21. The prescribed irradiation time is, for example, 53 μs.

  In step SA3, a physical quantity depending on the surface temperature of the irradiation object 60 is measured. As a physical quantity that depends on the surface temperature, the intensity of the reflected light detected by the reference light detector 43 can be employed. When an extremely shallow region on the surface of the irradiation object 60 is melted and enters a liquid phase state, the reflectance increases. By measuring the intensity of the reflected light, it is possible to detect that an extremely shallow region on the surface of the irradiation object 60 has melted.

  Further, the black body radiation intensity detected by the black body radiation detector 51 may be adopted as a physical quantity that depends on the surface temperature. By measuring the black body radiation intensity, the surface temperature of the irradiation object 60 can be calculated. A method for calculating the surface temperature of the processing object 60 from the black body radiation intensity is described in JP-A-2008-116269.

  In step SA4, it is determined whether or not the physical quantity depending on the surface temperature is equal to or greater than a threshold value. In this threshold value, the physical quantity is set to a value corresponding to the upper limit value of the temperature allowable range. When the intensity of reflected light is adopted as a physical quantity that depends on the surface temperature, the intensity between the intensity of the reflected light in the solid phase and the intensity of the reflected light in the liquid phase is used as a threshold value. Good. This threshold value is stored in the control device 21. When the measured intensity of the reflected light is equal to or higher than this threshold value, it is considered that an extremely shallow region on the surface of the irradiation object 60 has melted.

  When black body radiation intensity is adopted as a physical quantity depending on the surface temperature, the black body radiation intensity from the surface of the object 60 to be processed or a temperature slightly lower than the melting point may be used as the threshold value. For example, this threshold value is set to be equal to the black body radiation intensity when the surface temperature is 1673K.

  Note that both the measurement result of the reflected light intensity and the measurement result of the black body radiation intensity may be used as determination conditions.

  If it is determined that the physical quantity depending on the surface temperature is equal to or greater than the threshold value, the laser beam irradiation is stopped in step SA5. Specifically, the laser beam is blocked by controlling the electro-optic element 22. Thereafter, in step SA6, after waiting for a certain time, the process returns to step SA1 to resume laser irradiation. This standby time is set to a time for which the surface temperature decreases to a certain temperature (for example, 1273 K), for example. This time may be obtained in advance by simulation or actual evaluation experiment.

  If it is determined in step SA4 that the physical quantity depending on the surface temperature is less than the threshold value, the process returns to step SA2 without stopping the laser beam irradiation.

  If it is determined in step SA2 that the specified irradiation time has elapsed from the start of irradiation, laser irradiation is stopped in step SA7. The “irradiation start time” means not the time when irradiation is resumed in step SA1 via step SA6 but the time when laser irradiation is first started after the stage 35 is stopped.

  After stopping laser irradiation in step SA7, in step SA8, it is determined whether or not irradiation of the entire irradiation object 60 has been completed. When the irradiation of the entire area is completed, the annealing process is terminated. If irradiation of the entire area has not been completed, the stage 35 is moved and then stopped at step SA9. Thereafter, the process returns to step SA1, and laser irradiation to a new area is started. Note that it is preferable that the region where laser irradiation has already been completed and the region where laser irradiation is to be performed next overlap with each other.

  FIG. 6 shows a simulation result of a temperature change during laser irradiation while the stage 35 is stationary, that is, from step SA1 to step SA7 in FIG. The horizontal axis represents elapsed time in the unit “μs”, and the vertical axis represents temperature in the unit “K”. The solid line in FIG. 6 indicates the surface temperature, and the dotted line indicates the temperature at a depth of 3 μm. A broken line indicates the temperature of the back surface when the thickness of the processing object 60 is 100 μm. In addition, it was assumed that the back surface of the process target object 60 is a heat insulation state. The object to be irradiated was a silicon wafer, and the wavelength of the annealing laser beam was 800 nm.

At time 0, laser irradiation is started. Surface temperature rises by laser irradiation. At time t _1, the temperature-dependent physical quantity is equal to or greater than the threshold value, the laser irradiation is stopped (step SA5). For this reason, the surface temperature starts to fall. Wait until time t2 (step SA6), and resume laser irradiation at time t2 (step SA1). Until time t3, laser irradiation is stopped 14 times in step SA5. When the prescribed irradiation time has elapsed at time t3, laser irradiation is stopped (step SA7).

  From time 0 to time t3, the temperature at the depth of 3 μm repeats rising and falling following the surface temperature. While the rise and fall are repeated, the time average temperature at the position of 3 μm in depth shows a rising tendency. The temperature at the depth of 100 μm does not repeat rising and falling, and gradually increases with time.

  Thus, by stopping the laser irradiation when the physical quantity depending on the surface temperature reaches a threshold value corresponding to the upper limit value of the temperature range, the temperature at a deep position is increased without melting the surface. be able to. This makes it possible to activate deep regions.

  In the first embodiment, the standby time in Step SA6 is calculated in advance by simulation by calculating the time until the surface temperature falls to a certain reference temperature, for example, 1273K. However, if the elapsed time from the start of laser irradiation becomes longer, the average temperature of the irradiation object becomes higher, and the time for lowering to the reference temperature also becomes longer. The waiting time may be fixed to a time obtained by calculation by simulation under a specific temperature condition. Further, the standby time may be gradually increased as the average temperature of the processing object increases. However, it is difficult to measure the average temperature of the irradiation object during laser irradiation. For this reason, the standby time is preferably set in advance as a function of the elapsed time from the start of irradiation.

  In the first embodiment, the reference laser beam is obliquely incident on the irradiation target 60. However, the reference laser beam may be vertically incident on the annealing laser beam. In the case of perpendicular incidence, for example, a dichroic mirror may be disposed between the folding mirror 30 and the lens 31 in FIG. 1, and the reference laser beam may be superimposed on the annealing laser beam path. The dichroic mirror transmits the annealing laser beam and reflects the reference laser beam. The reference laser beam reflected by the irradiation object 60 propagates in the direction opposite to the incident path and is reflected by the dichroic mirror. By inserting a beam splitter and a quarter-wave plate between the dichroic mirror and the reference light source 40, the path of the reflected light can be branched from the path of the incident light. A reference light detector 43 is arranged on the reflected light path after branching.

  When the path of the laser beam for reference is superimposed on the path of the laser beam for annealing, the lens 31 is subjected to antireflection processing in two wavelength regions of the laser beam for annealing and the laser beam for reference. It is preferable to use one that has been designed to be erased.

  In the configuration in which the reference laser beam is incident obliquely, the incident position of the reference laser beam also changes when the height of the surface of the irradiation target 60 changes. For this reason, the position of the optical system of the reference laser beam must be readjusted. In the configuration in which the path of the reference laser beam is superimposed on the path of the annealing laser beam, this readjustment is not necessary.

  The intensity of the reflected light and the black body radiation intensity measured in Example 1 are both physical quantities that depend on the surface temperature of the irradiation object 60. In addition to the intensity of reflected light and the black body radiation intensity, other physical quantities that depend on the surface temperature may be measured. For example, the surface temperature can be calculated by measuring the extinction coefficient.

[Example 2]
FIG. 7 shows a schematic diagram of a laser annealing apparatus according to the second embodiment. In the second embodiment, a half-wave plate 22A is used instead of the electro-optical element 22 shown in FIG. The half-wave plate 22 </ b> A is displaced by the control device 21 in the rotation direction around the central ray of the laser beam. By rotating the half-wave plate 22A, the ratio of the S component and the P component with respect to the beam splitter 23 can be changed. As a result, the power of the laser beam that passes through the beam splitter 23 changes. As described above, the control device 21, the half-wave plate 22A, the beam splitter 23, and the beam damper 24 function as the power adjustment device 20A. Other configurations are the same as those of the laser annealing apparatus according to the first embodiment shown in FIG.

FIG. 8 shows a flowchart of the laser annealing method according to the second embodiment. Hereinafter, the description will be made focusing on differences from the flowchart of the laser annealing method according to the first embodiment shown in FIG. First, in step SB0, the power density of the annealing laser beam on the surface of the irradiation object 60 is initialized. Specifically, the position in the rotation direction of the half-wave plate 22A is set to the initial state. As an example, the initial value of the power density is 400 kW / cm ² .

  Steps SA1 to SA4 and steps SA7 to SA9 are common to the method of the first embodiment. If it is determined in step SA4 that the temperature-dependent physical quantity is greater than or equal to the threshold value, the power density of the annealing laser beam is reduced in step SB5. Specifically, the ratio of the P component is reduced by changing the position of the half-wave plate 22A in the rotational direction. By reducing the power density, an increase in the surface temperature can be suppressed, an excessive increase in the surface temperature, and a surface melting can be suppressed. After reducing the power density, the process returns to step SA2. That is, laser irradiation is continued under the condition where the power density is lowered.

  FIG. 9 shows a simulation result of the temperature change during the laser irradiation with the stage 35 stationary, that is, from step SB0 to step SA7 in FIG. The horizontal axis represents elapsed time in the unit “μs”, and the vertical axis represents temperature in the unit “K”. A thick solid line and a thick broken line in FIG. Thin solid line. The thin broken lines indicate the surface temperature, the temperature at a depth of 1 μm, the temperature at a depth of 2 μm, and the temperature at a depth of 3 μm, respectively. The long broken line indicates the temperature of the back surface when the thickness of the processing object 60 is 100 μm. In addition, it was assumed that the back surface of the process target object 60 is a heat insulation state. The irradiation object 60 was a silicon wafer, and the wavelength of the annealing laser beam was 800 nm.

  At time 0, laser irradiation is started (step SA1). When the temperature-dependent physical quantity exceeds the threshold value at time t1, the power density is reduced (step SB5). The thermal energy flowing from the surface to a deep region becomes larger than the thermal energy input by laser irradiation, and the surface temperature starts to decrease. When thermal energy propagates in the depth direction, the temperature distribution in the depth direction becomes gentle. When the thermal energy flowing from the surface to the deep region becomes smaller than the thermal energy input by laser irradiation, the surface temperature starts to rise again.

Each time the temperature-dependent physical quantity exceeds the threshold, the power density is decreased. For example, the power density is decreased in the order of 400 kW / cm ² , 300 kW / cm ² , 240 kW / cm ² , and 195 kW / cm ² . These suitable values of power density can be calculated in advance by simulation. Each power density described above is set such that the threshold value of the temperature-dependent physical quantity is a value corresponding to 1600K, and the minimum value of the surface temperature after the power density is reduced is 1560K.

  When the prescribed irradiation time has elapsed at time t2, laser irradiation is stopped (step SA7). After time t2, the surface temperature decreases.

  The temperature at a position having a depth of 1 μm from the surface follows the change in the surface temperature well. As it becomes deeper from the surface, the tendency to follow the change in the surface temperature decreases, and the temperature change becomes gentler. In the period from the irradiation start time to time t2, the temperature as a whole shows an upward trend although there is a short vertical movement at any depth.

  Blackbody radiation intensity L (λ, T) is

It is expressed. Here, λ is a wavelength, T is a temperature, and c ₁ and c ₂ are constants. Constant _{c 2} is a 0.0144m · K. The temperatures of 1600K and 1560K are only about 2.5%, but the black body radiation intensity at 1600K is 1.29 times the black body radiation intensity at 1560K. For this reason, it is possible to detect with sufficient accuracy that the surface temperature once lowered to 1560K has risen to 1600K.

  In the second embodiment, compared with the temperature change in the first embodiment shown in FIG. 6, the surface temperature and the temperature change in the extremely shallow region are gentle. Since the surface temperature does not fluctuate up and down, annealing can be performed more efficiently.

[Example 3]
FIG. 10 shows a flowchart of the laser annealing method according to the third embodiment. In Example 1 and Example 2, laser irradiation was performed with the irradiation object stationary, but in Example 3, laser irradiation was performed while moving the irradiation object. Hereinafter, description will be made focusing on differences from the laser annealing method according to the first embodiment.

  First, in step SC0, the movement of the irradiation object 60 in the row direction is started. Specifically, the scanning mechanism 36 is controlled to start the movement of the stage 35 in the X-axis direction. When the moving speed reaches the target speed, laser irradiation is started in step SA1.

  In step SC2, it is determined whether or not scanning for one row is completed. If the scanning for one row is not completed, the temperature-dependent physical quantity is measured in step SA3. The processing from step SA3 to SA6 is the same as that in the first embodiment. That is, one line of scanning is performed while repeating the stop and restart of laser irradiation.

  If it is determined in step SC2 that the scanning for one row has been completed, laser irradiation is stopped in step SA7. Thereafter, in step SC8, the movement in the row direction is stopped. In step SC9, it is determined whether or not scanning of all rows has been completed. When the scanning of all rows is completed, the laser annealing process is terminated. If there is an unscanned row, the stage is moved by one row (sub scanning is performed) in step SC10, and the process returns to step SC0 to start main scanning of the unscanned row.

  FIG. 11A shows the positional relationship between the beam spot of the annealing laser beam and the beam spot of the reference laser beam. The beam spot 61 of the annealing laser beam is, for example, a rectangle that is long in the Y-axis direction. The dimension in the X-axis direction (hereinafter referred to as “beam width”) Wx is, for example, 50 μm. When the beam spot 61 of the annealing laser beam moves in the positive direction of the X axis (the stage 35 moves in the negative direction of the X axis with respect to the path of the annealing laser beam), the beam spot of the reference laser beam 45 is arranged at a position in contact with the rear edge (edge on the negative side of the X axis) of the beam spot 61 of the annealing laser beam with respect to the traveling direction (main scanning direction). The shape of the beam spot 45 is, for example, a circle having a diameter of 10 μm.

  As shown in FIG. 11B, even when the moving direction of the beam spot 61 of the annealing laser beam is the negative direction of the X axis, the beam spot 45 of the reference laser beam is rearward with respect to the traveling direction (main scanning direction). It is arranged at a position in contact with the side edge (edge on the positive side of the X axis). That is, when the moving direction of the beam spot 61 is reversed, the relative positional relationship between the beam spot 61 and the beam spot 45 changes.

  By arranging the beam spot 45 of the reference laser beam at a position in contact with the rear edge of the beam spot 61 of the annealing laser beam in the scanning direction, the molten state at the highest surface temperature in the beam spot 61 is obtained. Can be detected.

  As shown in FIG. 11C, the beam spot 45 of the reference laser beam may be arranged so as to straddle in the width direction (main scanning direction) from one edge to the other edge of the beam spot 61 of the annealing laser beam. Good. When melting starts in a part of the area in the beam spot 45, the average reflectance in the beam spot 45 increases, so that the intensity of the reflected light increases. Accordingly, it is possible to detect that melting has started in the vicinity of the rear edge in the scanning direction. In this case, even if the scanning direction is reversed, it is not necessary to move the position of the beam spot 45 of the reference laser beam.

  When measuring the intensity of the black body radiation, as in the case shown in FIGS. 11A and 11B, the black body radiation from the position in contact with the rear edge of the beam spot 61 of the annealing laser beam in the scanning direction. Detect light.

FIG. 12 shows the simulation result of the temperature change at the point where the beam spot of the annealing laser beam passes among the surface of the irradiation object 60 (hereinafter, referred to as the point of interest). The horizontal axis represents elapsed time in the unit “μs”, and the vertical axis represents temperature in the unit “K”. The power density on the surface of the irradiation object 60 was 400 kW / cm ² , the beam width Wx was 50 μm, and the scanning speed was 650 mm / s. The time for the beam spot of the annealing laser beam to pass through the point of interest is about 77 μs. The irradiation object 60 was a silicon wafer, and the wavelength of the annealing laser beam was 800 nm.

  At time 0, the front edge of the beam spot in the scanning direction reaches the point of interest. When the temperature on the rear side in the scanning direction in the beam spot of the annealing laser beam reaches the upper limit value, the laser irradiation is stopped (step SA5). After a certain waiting time has elapsed, laser irradiation is resumed (step SA1). The temperature of the point of interest increases during laser irradiation, and the point of interest decreases while laser irradiation is stopped. In a longer time range, the temperature of the point of interest shows an upward trend. When 77 μs has elapsed from the start of irradiation, the beam spot deviates from the point of interest. Thereafter, the surface temperature of the point of interest decreases.

  The simulation result of the activation depth when annealing was performed under the conditions shown in FIG. 12 was 2 μm.

  In Example 3, the temperature-dependent physical quantity of the highest temperature portion in the beam spot of the annealing laser beam is measured. Furthermore, laser irradiation is stopped and restarted based on this temperature-dependent physical quantity. For this reason, the excessive temperature rise of the surface of an irradiation target object and melting of the surface can be suppressed.

FIG. 13 shows the calculation result of the condition that the edge of the beam spot in the scanning direction on the rear side coincides with the target point when the surface temperature of the target point reaches 1673K. The horizontal axis represents the power density in the unit “kW / cm ² ”, and the vertical axis represents the scanning speed in the unit “m / s”. The beam width Wx was 50 μm.

As the power density increases, the rate of increase in surface temperature increases. In order to prevent the surface temperature from exceeding 1673K, the scanning speed must be increased. For example, when the power density is 400 kW / cm ² , the scanning speed must be 4 m / s or more in order to prevent melting of the surface. When the scanning speed increases, a space for acceleration until the stage 35 reaches a constant speed and a space for deceleration until the stage stops must be secured. For this reason, an apparatus will enlarge.

On the other hand, in the method according to the third embodiment, as shown in FIG. 12, annealing can be performed with a power density of 400 kW / cm ² and a scanning speed of 650 mm / s. Thus, since the scanning speed can be reduced, the space for acceleration and deceleration can be reduced. Thereby, the enlargement of an apparatus can be suppressed.

  In the third embodiment, laser irradiation is stopped in step SA5 in FIG. 10, but the power density may be reduced instead of completely stopping the irradiation. In this case, in step SA1, the power density may be returned to the initial state.

  FIG. 14 is a schematic diagram of a cross section of an IGBT to which the laser annealing method according to the first to third embodiments is applied. An IGBT is manufactured by forming an emitter and a gate on one surface of an n-type semiconductor substrate and forming a collector on the other surface. The structure of the surface on which the emitter and the gate are formed is manufactured in the same process as a general MOSFET manufacturing process. For example, as shown in FIG. 14, by arranging a p-type base region 74, an n-type emitter region 75, a gate electrode 81, a gate insulating film 82, and an emitter electrode 80, current at a voltage between the gate and the emitter can be obtained. ON / OFF control can be performed.

  A p-type collector layer 73 is formed on the opposite surface of the semiconductor substrate 71. If necessary, an n-type buffer layer 72 may be formed between the collector layer 73 and the semiconductor substrate 71. The collector layer 73 and the buffer layer 72 are formed by implanting boron and phosphorus as impurities, respectively, and performing activation annealing. For this activation annealing, the methods according to the above-described Examples 1 to 3 are applied. A collector electrode 83 is formed on the surface of the collector layer 73 after the activation annealing.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. 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 Laser light source 20 Blocking device 20A Power adjustment device 21 Control device 22 Electro-optical element 22A Half-wave plate 23 Beam splitter 24 Beam damper 25 Beam shaping optical system 26 Uniformation optical system 30 Folding mirror 31 Lens 35 Stage 36 Scan mechanism 40 Reference light source 41, 42 Folding mirror 43 Reference light detector 45 Beam spot 50 of reference laser beam Condensing lens 51 Black body radiation detector 60 Irradiation target 61 Beam spot 70 of annealing laser beam Silicon substrate 71 n ⁻ type region 72 Buffer layer 73 Collector layer 74 Base region 75 Emitter region 80 Emitter electrode 81 Gate electrode 82 Gate insulating film 83 Collector electrode

Claims (9)

Starting the incidence of the laser beam on the surface of the irradiation object;
Measuring a physical quantity depending on a surface temperature of a region where the laser beam is incident during a period in which the laser beam is incident on the irradiation object;
Determining whether to stop the irradiation of the laser beam based on the measured physical quantity; and
If it is determined that the laser beam irradiation is to be stopped, it is determined that the laser beam irradiation is resumed after a certain waiting time has elapsed after the laser beam irradiation is stopped, and the laser beam irradiation is not stopped. If so, a method of manufacturing a semiconductor device, comprising: continuing the laser beam irradiation.   2. The manufacturing of a semiconductor device according to claim 1, wherein in the determining step, when it is detected that the physical quantity exceeds a threshold value corresponding to an upper limit value of an allowable temperature range, it is determined that the irradiation of the laser beam is stopped. Method. A laser light source for emitting a laser beam;
A stage for holding an irradiation object at a position where a laser beam emitted from the laser light source is incident;
A blocking device that switches between a state in which the laser beam emitted from the laser light source reaches the irradiation object held on the stage and a state in which the laser beam is blocked so as not to reach the object;
A measuring device that measures a physical quantity that depends on a surface temperature of the irradiation object at a position where the laser beam is incident;
The blocking device is
Based on the measurement result of the physical quantity by the measurement device, determine whether to stop the irradiation of the laser beam,
When it is determined that the laser beam irradiation is to be stopped, after the laser beam is interrupted, after a certain waiting time has elapsed, the laser beam irradiation is resumed and it is determined not to stop the laser beam irradiation. Is a laser annealing apparatus for continuing the irradiation of the laser beam. Further, a scanning mechanism is provided that moves one of the laser beam path and the irradiation object relative to the other so that the incident position of the laser beam moves on the surface of the irradiation object held on the stage. And
The measuring device measures the physical quantity during a period in which one of the path of the laser beam and the irradiation object is moving with respect to the other by the scanning mechanism,
The cutoff device determines whether or not to stop the irradiation of the laser beam during a period in which one of the path of the laser beam and the irradiation object is moving with respect to the other by the scanning mechanism. Item 4. The laser annealing apparatus according to Item 3. Starting the incidence of the laser beam on the surface of the irradiation object;
Measuring a physical quantity depending on a surface temperature of a region where the laser beam is incident during a period in which the laser beam is incident on the irradiation object;
Determining whether to reduce the power density of the laser beam on the surface of the irradiation object based on the measured physical quantity; and
When it is determined that the power density of the laser beam is to be reduced, the power density of the laser beam is reduced. When it is determined that the power density of the laser beam is not reduced, the laser beam is irradiated. A method for manufacturing a semiconductor device, comprising a step of continuing as it is.   The semiconductor device according to claim 5, wherein in the determination step, when it is detected that the physical quantity exceeds a threshold value corresponding to an upper limit value of a temperature allowable range, it is determined that the power density of the laser beam is reduced. Manufacturing method. A laser light source for emitting a laser beam;
A stage for holding an irradiation object at a position where a laser beam emitted from the laser light source is incident;
A power adjustment device configured to be able to change the power density of the laser beam on the surface of the irradiation object held on the stage;
A measuring device that measures a physical quantity that depends on a surface temperature of the irradiation object at a position where the laser beam is incident;
The power adjustment device is:
Based on the measurement result of the physical quantity by the measurement device, determine whether to reduce the power density,
When it is determined that the power density is to be reduced, the power density of the laser beam on the surface of the irradiation object is reduced, and when it is determined that the power density is not reduced, the irradiation of the laser beam is continued as it is. Laser annealing equipment. Starting movement of the irradiation object relative to the path of the laser beam;
Starting the irradiation of the laser beam;
Measuring a physical quantity depending on a surface temperature of the irradiation object in a region where the laser beam is incident;
Determining whether to stop the irradiation of the laser beam based on the measured physical quantity; and
If it is determined that the irradiation of the laser beam is to be stopped, after the irradiation of the laser beam to the irradiation object is stopped, the irradiation of the laser beam is resumed after a certain waiting time has elapsed, and the laser beam And a step of continuing the laser beam irradiation as it is when it is determined not to stop the irradiation of the semiconductor device.   9. The semiconductor device according to claim 8, wherein, in the determining step, when it is detected that the physical quantity exceeds a threshold value corresponding to an upper limit value of an allowable temperature range, it is determined that the laser beam irradiation is stopped. Production method.