JP5105984B2 - Beam irradiation apparatus and laser annealing method - Google Patents

Description

  The present invention relates to a beam irradiation apparatus that performs processing by irradiating a workpiece with a laser beam, and a laser annealing method that performs annealing.

  Techniques such as RTP (Rapid Thermal Processing), FLA (Flash Lamp Annealing), and LTP (Laser Thermal Processing) are used to activate the implanted impurities in the semiconductor manufacturing process. However, it is difficult for RTP to suppress the diffusion of implanted impurities. Further, since FLA has a long heating time, it is difficult to activate impurities without diffusion. In LTP, if the heating time is extremely short as several tens to several hundreds ns, and the impurity implantation depth is relatively deep as several tens to several hundreds nm, activation is insufficient when processing is performed without melting. There was.

  A technique called LSA (Laser Spike Annealing) has been developed to irradiate a silicon wafer into which impurities are implanted by irradiating a continuous wave laser beam (see, for example, Patent Documents 1 and 2). In LSA, the time for heating the impurity implantation region can only be controlled by the scanning speed of the laser beam, which is insufficient in this respect.

  An invention of double pulse annealing using green light (laser light in the green wavelength region) has been disclosed (see, for example, Patent Documents 3 and 4).

  In addition, “a first laser beam and a second laser beam having a wavelength different from that of the first laser beam are applied to the substrate to heat-treat the substrate or the film on the substrate”. An invention of a method and a manufacturing apparatus is disclosed (for example, see Patent Document 5).

JP 2005-244191 A Japanese Patent Laying-Open No. 2005-210129 JP 2004-152888 A JP 2006-156784 A International Publication No. 2007/015388 Pamphlet

  An object of the present invention is to provide a beam irradiation apparatus capable of performing high-quality processing.

  It is another object of the present invention to provide a laser annealing method capable of performing high-quality annealing.

According to one aspect of the present invention,
First and second laser light sources that emit laser pulses of different wavelengths by external control;
A stage for holding the workpiece,
An optical system for causing laser pulses emitted from the first and second laser light sources to be incident on an object to be processed held on the stage so that both incident areas overlap at least partially;
The pulse width of the laser pulse emitted from the first laser light source is longer than the pulse width of the laser pulse emitted from the second laser light source, and the laser pulse emitted from the first laser light source is the workpiece. before exiting from entering the laser pulses emitted from the second laser light source and a first and second system that controls the laser light source control unit to be incident on the workpiece ,
When the second laser light source receives a trigger signal from the control device, it emits a pulse laser beam,
The control device includes a storage device in which information defining a delay time from generation of the trigger signal to a fall of a pulse laser beam emitted from the first laser light source is stored, and the second laser from the emission start of the laser pulse from the light source, the on time has elapsed by a predetermined delay time by the information stored in the storage means, to the first so that the laser pulse falls emitted from the laser light source, wherein A beam irradiation apparatus for controlling the first and second laser light sources is provided.

According to another aspect of the present invention,
Starting an irradiation of the first laser pulse on the object to be annealed;
Irradiating a region to be irradiated with the first laser pulse with a second laser pulse to heat the annealing object;
Ending irradiation of the first laser pulse after the irradiation end time of the second laser pulse,
When the annealing object has an absorption coefficient at the wavelength of the first laser pulse lower than that at the wavelength of the second laser pulse and is heated by irradiation with the second laser pulse, the annealing is performed. of the object, the absorption coefficient in the wavelength range of the first laser pulse, Ri a higher than before the heating,
There is provided a laser annealing method for controlling the heating time of the annealing target object by controlling the time from the irradiation start time of the second laser pulse to the irradiation end time of the first laser pulse .

  ADVANTAGE OF THE INVENTION According to this invention, the beam irradiation apparatus which can perform a high quality process can be provided.

  In addition, a laser annealing method capable of performing high-quality annealing can be provided.

  FIG. 1 is a schematic diagram illustrating a beam irradiation apparatus according to an embodiment.

  The beam irradiation apparatus according to the embodiment includes laser light sources 10a and 10b that emit pulsed laser beams, shutters 11a and 11b, homogenizers 12a and 12b, folding mirrors 13a to 13c, dichroic mirror 14, mask 15, imaging optical system 16, and XY. A stage 17 and a control device 18 are included. The control device 18 includes a storage device 18a, for example, a memory.

  On the XY stage 17, a silicon wafer 20 as a processing target is held. An n-type or p-type impurity is implanted into the silicon wafer 20. Using the beam irradiation apparatus according to the embodiment, the pulse laser beam emitted from the laser light sources 10a and 10b is incident on the silicon wafer 20 to activate the impurities at the incident position.

  The laser light sources 10a and 10b receive signals sent from the control device 18 and emit pulse laser beams 30a and 30b, respectively. Control by the control device 18 is performed based on control information stored in the storage device 18a.

  The laser light source 10a includes, for example, an Nd: YAG laser oscillator that is a Q-switched laser oscillator and a nonlinear optical element. The pulse laser beam 30a is a second harmonic (green light with a wavelength of 532 nm) of an Nd: YAG laser having a pulse width of several tens to several hundreds ns, for example, 100 ns.

  The laser light source 10b is, for example, a semiconductor laser, and emits a pulse laser beam 30b having a wavelength of 800 nm and a pulse width of several μs to several hundreds μs. The pulse laser beam 30b emitted from the laser light source 10b has a longer wavelength and pulse width than the pulse laser beam 30a emitted from the laser light source 10a. Further, the absorption coefficient of silicon at room temperature (for example, 300 K) at the wavelength of the pulse laser beam 30b is smaller than that of the pulse laser beam 30a. The absorption length of the pulsed laser beam 30a in silicon at room temperature is about 1 μm, while that of the pulsed laser beam 30b is about 10 μm.

Note that an Nd: YAG laser oscillator may be used as the laser light source 10b, and a pulsed laser beam 30b that is a fundamental wave (wavelength: 1064 nm) of the Nd: YAG laser may be emitted. A CO ₂ laser can also be used for the laser light source 10b.

  The pulse laser beams 30a and 30b are opened and closed by a control signal from the control device 18, respectively, are transmitted through shutters 11a and 11b that can switch between transmission and shielding of the incident laser beam, and enter the homogenizers 12a and 12b.

  The pulse laser beams 30a and 30b are shaped in beam cross sections on the homogenization surfaces of the homogenizers 12a and 12b by the homogenizers 12a and 12b, and the beam intensity is made uniform.

  A mask 15 is disposed on the homogenization surfaces of the homogenizers 12a and 12b. The pulse laser beam 30 a is reflected by the folding mirror 13 a, then passes through the dichroic mirror 14 and enters the mask 15. The pulse laser beam 30 b is reflected by the folding mirrors 13 b and 13 c and the dichroic mirror 14 and enters the mask 15.

  The mask 15 includes a light transmitting region and a light shielding region. The pulsed laser beams 30 a and 30 b that have passed through the light transmitting region of the mask 15 enter the same region on the silicon wafer 20 placed on the XY stage 17 via the imaging optical system 16. The imaging optical system 16 transfers the shape of the light transmitting region of the mask 15 onto the silicon wafer 20.

  The XY stage 17 receives the control signal transmitted from the control device 18, moves the held silicon wafer 20 in the in-plane direction, and changes the incident positions of the pulse laser beams 30 a and 30 b on the silicon wafer 20.

  The beam irradiation method according to the embodiment will be described with reference to FIGS.

  FIG. 2A shows an example of the incident timing of the pulse laser beams 30a and 30b incident on the silicon wafer 20. FIG. In the figure, the horizontal axis represents time (time), and the vertical axis represents laser light intensity.

At time _{t 1,} the trigger signal is generated by the controller 18, Nd: sent to the laser light source 10a that includes a YAG laser oscillator. From the laser source 10a In response, the pulse laser beam 30a, for example, a pulse width 100 ns Nd: is second harmonic (green light having a wavelength of 532 nm) is emitted a YAG laser, only during the period from time _{t 1,} the silicon wafer 20 Is irradiated.

From the time _{t 2} immediately after time _{t 1} to time _{t 3,} the control unit 18, a signal is sent to the laser light source 10b including a semiconductor laser. Emitted from the laser light source 10b receives this, pulsed laser beams 30b, for example, a wavelength 800 nm, pulse laser beam 30b of the pulse width of several μs~ several hundred μs is emitted, between the time _{t 2} at time _{t 3,} the silicon wafer 20 Is done. Rising time of the pulse laser beam 30b (extraction start time) is _{t 2,} the fall time is _{t 3.}

In the storage device 18a, control information that defines the time from generation of a trigger signal for emitting the pulse laser beam 30a to the fall of the pulse laser beam 30b, for example, | t ₃ −t ₁ | itself or time t ₁ and time t ₃ is stored. The control device 18 transmits a signal to the laser light sources 10a and 10b based on these pieces of information.

  FIG. 2B is a schematic diagram showing a temperature change of the silicon wafer 20 when the pulsed laser beams 30a and 30b are irradiated onto the silicon wafer 20 in the mode shown in FIG. In the figure, the horizontal axis represents time (time), and the vertical axis represents temperature.

At time t ₁ , the pulsed laser beam 30 a having a large room temperature silicon absorption coefficient and an absorption length of about 1 μm is irradiated onto the silicon wafer 20 and absorbed in the vicinity of the surface of the silicon wafer 20. As a result, the temperature of the silicon wafer 20 is increased. Rises rapidly, for example, to about 1400 ° C.

Subsequently, the silicon wafer 20 is irradiated with the pulse laser beam 30b. The absorption coefficient of silicon at about 1400 ° C. at the wavelength of the pulsed laser beam 30b is larger than the absorption coefficient of silicon at room temperature. Since the pulse laser beam 30b is absorbed in the vicinity of the surface of the silicon wafer 20, the temperature drop of the silicon wafer 20 is suppressed, and the silicon wafer 20 is irradiated with the irradiation time of the pulse laser beam 30b (pulse width | t ₃ of the pulse laser beam 30b). -t ₂ |) it is only heated.

  FIG. 2C shows another example of the incident timing of the pulse laser beams 30a and 30b incident on the silicon wafer 20. In the figure, the horizontal axis represents time (time), and the vertical axis represents laser light intensity.

This figure shows a case where the oscillation timing (time t ₁ ) of the laser light source 10 a is delayed and the laser light source 10 b is oscillated during the oscillation (time t ₂ to time t ₃ ).

  FIG. 2D is a schematic view showing a temperature change of the silicon wafer 20 when the pulsed laser beams 30a and 30b are irradiated onto the silicon wafer 20 in the mode shown in FIG. In the figure, the horizontal axis represents time (time), and the vertical axis represents temperature.

The time t ₂ as a starting point, a small pulse laser beam 30b is the absorption coefficient at room temperature of the silicon is irradiated on the silicon wafer 20. Since the absorption length of the pulse laser beam 30b in silicon is as long as about 10 μm, the temperature rise near the surface of the silicon wafer 20 is moderate.

While the pulse laser beam 30b is irradiated on the silicon wafer 20 (time t ₂ to time t ₃ ), the pulse laser beam 30a is irradiated on the silicon wafer 20 at time t ₁ .

  Since the pulse laser beam 30a has a large absorption coefficient of silicon at room temperature, it is absorbed in the vicinity of the surface of the silicon wafer 20, and the temperature of the silicon wafer 20 is rapidly increased to, for example, about 1400 ° C.

The absorption coefficient of silicon at about 1400 ° C. at the wavelength of the pulsed laser beam 30b is large. Thus after time t _1, the pulsed laser beam 30b is irradiated on the silicon wafer 20 is absorbed near the surface of the silicon wafer 20.

Accordingly, the temperature drop of the silicon wafer 20 is suppressed, the silicon wafer 20, the time _{t 1} after the pulsed laser beam 30b irradiation time _(| t 3 _-t 1 |) is only heated.

  In the beam irradiation method according to the embodiment, the heating time of the silicon wafer can be controlled by the pulse width of the laser beam and the oscillation timing of the incident laser pulse. For this reason, it becomes possible to set the heating time of the silicon wafer almost arbitrarily. Therefore, according to a given condition, for example, even when the impurity is activated at a relatively deep position of the silicon wafer, optimal annealing can be performed while suppressing the diffusion of the impurity.

  An example of impurity activation (laser annealing) performed using the beam irradiation method will be given.

As as impurities, As was ion-implanted into the silicon wafer at an energy of 200 keV and a dose of 1E + 14 ions / cm ² . On this silicon wafer, a second harmonic (green light with a wavelength of 532 nm) of an Nd: YAG laser with a pulse width of 100 ns is used as the pulse laser beam 30a, and a semiconductor laser with a wavelength of 808 nm is used as the pulse laser beam 30b. Impurity activation (laser annealing) was performed by irradiation with a pulse width of 100 μs.

  Both of the pulse laser beams 30a and 30b were oscillated at a frequency of 1 kHz, and shaped so as to have a long shape with a major axis direction of 6 mm and a minor axis direction of 0.1 mm on the silicon irradiation surface. The feed speed of the XY stage was adjusted to 10 mm / s so that the pulsed laser beams 30a and 30b were irradiated with a 90% overlap rate in the minor axis direction. The overlap ratio in the major axis direction was 66.7%, and the feed was 2 mm / line.

The energy density of the pulse laser beams 30a and 30b was set within a range where the silicon wafer did not melt. 50 μs after the start of irradiation with the pulsed laser beam 30b, the pulsed laser beam 30a was made incident on the silicon wafer. Therefore, when t ₁ to t ₃ in FIG. 2C are used, | t ₃ −t ₁ | (heating time) and | t ₁ −t ₂ | are both 50 μs.

  No diffusion of impurities was observed in the annealed silicon wafer, and no defects or the like were observed. The implanted dopant was activated, indicating a sufficiently low sheet resistance value.

  As a comparative example, impurity activation is performed by applying a double pulse of a second harmonic (green light with a wavelength of 532 nm) of an Nd: YAG laser having a pulse width of 100 ns to a silicon wafer into which As is ion-implanted with the above-described energy and dose. Laser annealing) was performed.

  In the comparative example, the second laser pulse of the second harmonic of the Nd: YAG laser was irradiated 300 ns after irradiation of the first laser pulse of the second harmonic of the Nd: YAG laser. The oscillation frequencies of the first and second laser pulses, the beam size on the silicon irradiation surface, the overlap ratio in the minor axis and major axis directions were the same as in the above example. Also in the comparative example, the energy density of the pulse laser beam was set within a range where the silicon wafer did not melt.

  Diffusion of impurities was not observed in the annealed silicon wafer, but defect recovery was insufficient. The sheet resistance value was high, and the dopant was not sufficiently activated.

  As mentioned above, although this invention was demonstrated along the Example, this invention is not restrict | limited to these.

  For example, in the beam irradiation apparatus according to the embodiment, the pulse laser beams 30a and 30b emitted from the laser light sources 10a and 10b are incident on the different homogenizers 12a and 12b, but can also be incident on the same homogenizer.

  In the beam irradiation apparatus according to the embodiment, the pulse laser beams 30a and 30b are incident on the same mask and the imaging optical system, but may be incident on different masks and the imaging optical system.

  Further, the pulse laser beams 30a and 30b may be incident so that the incident areas of the laser beams 30a and 30b overlap at least partially.

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

  It can be suitably used for semiconductor activation annealing. It can also be used for silicon crystallization of SOI (Silicon on Insulator).

It is the schematic which shows the beam irradiation apparatus by an Example. (A)-(D) are the figures for demonstrating the beam irradiation method by an Example.

Explanation of symbols

10a, 10b Laser light sources 11a, 11b Shutters 12a, 12b Homogenizers 13a-13c Folding mirror 14 Dichroic mirror 15 Mask 16 Imaging optical system 17 XY stage 18 Controller 18a Storage device 20 Silicon wafers 30a, 30b Pulse laser beam

Claims (7)

First and second laser light sources that emit laser pulses of different wavelengths by external control;
A stage for holding the workpiece,
An optical system for causing laser pulses emitted from the first and second laser light sources to be incident on an object to be processed held on the stage so that both incident areas overlap at least partially;
The pulse width of the laser pulse emitted from the first laser light source is longer than the pulse width of the laser pulse emitted from the second laser light source, and the laser pulse emitted from the first laser light source is the workpiece. before exiting from entering the laser pulses emitted from the second laser light source and a first and second system that controls the laser light source control unit to be incident on the workpiece ,
When the second laser light source receives a trigger signal from the control device, it emits a pulse laser beam,
The control device includes a storage device in which information defining a delay time from generation of the trigger signal to a fall of a pulse laser beam emitted from the first laser light source is stored, and the second laser The first laser light source falls so that the laser pulse emitted from the first laser light source falls after the delay time defined by the information stored in the storage means has elapsed since the start of the emission of the laser pulse from the light source. A beam irradiation apparatus for controlling the first and second laser light sources.   2. The beam irradiation apparatus according to claim 1, wherein an absorption coefficient of silicon of 300 K at a wavelength of a laser pulse emitted from the second laser light source is larger than that of a laser pulse emitted from the first laser light source.   The beam irradiation apparatus according to claim 1 or 2, wherein the laser pulse emitted from the second laser light source has a shorter wavelength than the laser pulse emitted from the first laser light source.   The said 1st laser light source receives the signal given from the outside, and radiate | emits said 1st laser pulse by the variable 1st pulse width according to this signal. The beam irradiation apparatus described in 1.   The beam irradiation apparatus according to claim 1, wherein the second laser light source includes a Q-switch laser oscillator. Starting an irradiation of the first laser pulse on the object to be annealed;
Irradiating a region to be irradiated with the first laser pulse with a second laser pulse to heat the annealing object;
Ending irradiation of the first laser pulse after the irradiation end time of the second laser pulse,
When the annealing object has an absorption coefficient at the wavelength of the first laser pulse lower than that at the wavelength of the second laser pulse and is heated by irradiation with the second laser pulse, the annealing is performed. of the object, the absorption coefficient in the wavelength range of the first laser pulse, Ri a higher than before the heating,
A laser annealing method for controlling a heating time of the object to be annealed by controlling a time from an irradiation start point of the second laser pulse to an end point of irradiation of the first laser pulse .   The laser annealing method according to claim 6, wherein the second laser pulse has a shorter wavelength than the first laser pulse.

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