JP2007123300A - Method for activating impurities, laser annealer, semiconductor device and method for fabricating same - Google Patents

Method for activating impurities, laser annealer, semiconductor device and method for fabricating same Download PDF

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JP2007123300A
JP2007123300A JP2005309308A JP2005309308A JP2007123300A JP 2007123300 A JP2007123300 A JP 2007123300A JP 2005309308 A JP2005309308 A JP 2005309308A JP 2005309308 A JP2005309308 A JP 2005309308A JP 2007123300 A JP2007123300 A JP 2007123300A
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laser
semiconductor substrate
pulse laser
pulse
timing
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Masanori Saito
正典 斉藤
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Toyota Motor Corp
トヨタ自動車株式会社
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<P>PROBLEM TO BE SOLVED: To heat a position deep from the backside of a semiconductor substrate up to ≥950°C while sustaining the intensity of pulse laser per unit area at a level not causing ablation in laser anneal. <P>SOLUTION: The method for activating impurities introduced into a semiconductor substrate 44 comprises; a step for forming a semiconductor region by introducing impurities from the surface of the semiconductor substrate 44; and a step for irradiating a local region on the surface of the semiconductor substrate 44 with a plurality of pulse lasers 22 and 24 using a plurality of laser oscillators 12 and 16. In the irradiation step, a difference is formed between a timing for irradiating the local region with the first pulse laser 22 oscillated by the first laser oscillator 12 and a timing for irradiating the local region with the second pulse laser 24 oscillated by the second laser oscillator 16. The difference is regulated to ≤700 nanoseconds. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for activating impurities introduced into a semiconductor substrate and a laser annealing apparatus used when performing the method. The present invention also relates to a semiconductor device obtained using the impurity activation method and a method for manufacturing the same.

In order to improve various characteristics of a semiconductor device, development of a semiconductor device in which the thickness of the semiconductor device is adjusted to about 100 μm is underway. As an example, a thin plate IGBT (Insulated Gate Bipolar Transistor) is known. The thin plate IGBT includes an n + -type field stop layer and a p + -type collector layer on the back surface portion of the semiconductor substrate. In general, the field stop layer and the collector layer are often laminated. There is also known a collector short type in which field stop layers are dispersedly arranged and a collector layer and a drift layer are partially short-circuited. In this specification, the stacked type will be mainly described. However, the technique disclosed in this specification is also useful for the collector short type. In the field stop layer and the collector layer, phosphorus ions that are n-type impurities are introduced into deep positions from the back surface of the semiconductor substrate, and boron ions that are p-type impurities are introduced into shallow positions, and then heat treatment for activation is performed. Can be formed.

Development of a technique using laser annealing as a heat treatment method of this type has been promoted. Laser annealing often uses a pulse waveform oscillation mode. The pulse laser can increase the intensity per unit area. For this reason, it becomes possible to heat the back surface part of a semiconductor substrate to high temperature by utilizing a pulse laser. For this type of pulse laser, an excimer laser, a YAG second harmonic laser, a YLF second harmonic laser, or the like is often used. These pulse lasers are commonly used because of their large absorption coefficient in the semiconductor substrate.
When laser annealing is used, only the back surface portion of the semiconductor substrate can be selectively heated. For this reason, it can avoid that the aluminum electrode and polyimide layer which are formed in the surface of a semiconductor substrate will be damaged. A method using this type of laser annealing is disclosed in the following patent document.
Japanese Patent Laid-Open No. 10-41244 JP 2000-349042 A JP 2001-509316 A JP 2004-363168 A

For example, in the n + type field stop layer of a thin IGBT, an impurity concentration peak is formed at a deep position of about 0.5 μm from the back surface of the semiconductor substrate, and the formation range is at a deep position of about 1 μm from the back surface of the semiconductor substrate. Often. For this reason, phosphorus ions, which are n-type impurities, are also introduced deep from the back surface of the semiconductor substrate. In order to activate this phosphorus ion highly, it must be heated to 950 ° C. or higher up to a deep position. However, in the current laser annealing, it is difficult to highly activate impurities introduced deep from the back surface of the semiconductor substrate.
A pulse laser such as an excimer laser, a YAG second harmonic laser, or a YLF second harmonic laser is a laser having a relatively short wavelength. For this reason, it is known that these pulse lasers do not reach a deep position from the back surface of the semiconductor substrate. When these pulse lasers are used, a lot of energy is absorbed at a shallow position (approximately a depth of several tens of nm), and the deep position cannot be heated.
Even with these pulse lasers, if the irradiation power is increased (intensity per unit area is increased), it is possible to heat to a deep position by heat conduction. However, when the irradiation power is increased, the temperature at the shallow position excessively rises, causing a problem that sublimation (ablation) occurs on the back surface portion of the semiconductor substrate and is lost. Further, when it is attempted to secure the irradiation amount by increasing the pulse width of the pulse laser, the intensity per unit area of the pulse laser is reduced, and the back surface portion of the semiconductor substrate cannot be heated to a high temperature.

That is, when a pulse laser such as an excimer laser, a YAG second harmonic laser, or a YLF second harmonic laser is used, (1) the intensity per unit area of the pulse laser is such that sublimation (ablation) does not occur. (2) It is difficult to simultaneously achieve both of (2) securing an irradiation amount necessary to heat the semiconductor substrate from the back surface to a deep position at 950 ° C. or higher. Therefore, in order to efficiently activate the field stop layer of the thin IGBT, a laser annealing technique that realizes both simultaneously is desired.
This type of problem is not limited to thin IGBTs, and is common to semiconductor devices in which a highly active semiconductor region is desired to be formed at a deep position. Development of a useful activation method for these semiconductor devices is also desired.
An object of the present invention is to provide an impurity activation method that solves the above-described problems, and a laser annealing apparatus that is used when performing the activation method. Another object of the present invention is to provide a semiconductor device obtained by the activation method and a manufacturing method thereof.

The present invention is characterized in that laser annealing is performed using a plurality of laser oscillators. The intensity per unit area of the pulse laser oscillated from each laser oscillator is maintained at such a level that the surface of the semiconductor substrate does not undergo sublimation (ablation). Furthermore, a time difference is formed between the timings when the pulse lasers oscillated by the individual laser oscillators irradiate the local region on the surface of the semiconductor substrate. Thereby, it is possible to ensure a substantial irradiation time while maintaining the intensity of the pulse laser smaller than a predetermined size. Since the substantial irradiation time can be secured for a long time, a large amount of laser annealing can be secured, and the heat can be heated to a deep position by heat conduction. According to the present invention, it is possible to secure an irradiation amount necessary for heating to a deep position while avoiding sublimation (ablation) of the surface of the semiconductor substrate.
Here, the “time difference between timings” refers to a time difference generated between the two when compared with a characteristic time point of the pulse waveform of the pulse laser. For example, the time difference between the two when the pulse waveform rises (starting time) as a reference may be used, or the time difference between the two when the pulse waveform peak value is used as a reference may be used.

The present invention can be embodied in a method for activating impurities introduced into a semiconductor substrate. The activation method of the present invention includes a step of introducing impurities from the surface of the semiconductor substrate, and a step of irradiating a plurality of pulse lasers on a local region of the surface of the semiconductor substrate using a plurality of laser oscillators. In the irradiation process of the present invention, a time difference is set between the timing when the pulse laser oscillated by one laser oscillator irradiates the local region and the timing when the pulse laser oscillated by another laser oscillator irradiates the local region. It is characterized by having.
According to the above activation method, the intensity per unit area of the pulse laser oscillated from each laser oscillator can be maintained at such a level that the surface of the semiconductor substrate does not undergo sublimation (ablation). Furthermore, a time difference is formed between the timings when the pulse lasers oscillated by the individual laser oscillators irradiate the local region on the surface of the semiconductor substrate. For this reason, it is possible to lengthen the total irradiation time of each pulse laser while maintaining the intensity of the pulse laser at such a level that the surface of the semiconductor substrate does not cause sublimation.
According to the activation method of the present invention, it is possible to secure an irradiation amount necessary for heating to a deep position while avoiding sublimation (ablation) of the surface of the semiconductor substrate.

In the irradiation step of the present invention, it is preferable that the time difference set between the timings when the pulse laser from the laser oscillator irradiates the local region is adjusted to 700 nanoseconds or less. Under this condition, it is preferable that the laser oscillator irradiates a pulse laser having a half width of 10 to 200 nanoseconds. A pulse laser having a half width of 10 to 200 nanoseconds can be oscillated using, for example, an excimer laser, a YAG second harmonic laser, or a YLF second harmonic laser.
When the irradiation step is performed by the above method, the timings at which the respective pulse lasers irradiate the surface of the semiconductor substrate can be brought close to each other. For this reason, since the other pulse laser can be irradiated before the heating effect by one pulse laser disappears, it is possible to ensure a substantial irradiation time. Note that if the time difference formed between the timings of pulse laser irradiation exceeds 700 nanoseconds, the timings of irradiation of the respective pulse lasers are separated, so that a synergistic effect by bringing the pulse lasers close to each other cannot be obtained. .

In the irradiation step of the present invention, it is preferable that the time difference set between the timings when the pulse laser from the laser oscillator irradiates the local region is adjusted to be equal to or greater than the half-value width of the pulse laser. Under this condition, it is preferable that the laser oscillator emits a pulsed laser.
If a time difference of more than half-value width is formed between the timing of irradiation by a pulse laser oscillated by one laser oscillator and the timing of irradiation by a pulse laser oscillated by another laser oscillator, the total intensity will be a predetermined value. It is possible to obtain the effect of extending the total irradiation time while maintaining smaller than that.

In the irradiation step of the present invention, a plurality of laser oscillators may irradiate a pulse laser having the same frequency, or a plurality of laser oscillators may irradiate a pulse laser having a different frequency.
When pulse lasers having the same frequency are used, the time difference between the timings of irradiation by the pulse laser is kept constant for each pulse, so that control becomes easy and good results can be obtained.

  In the irradiation step of the present invention, it is preferable to irradiate such that a part of the pulse waveform of the pulse laser oscillated by one laser oscillator and a part of the pulse waveform of the pulse laser oscillated by another laser oscillator overlap. If it is adjusted so that part of the pulse waveform of the pulse laser overlaps, the heating effect of one pulse laser and the heating effect of the other pulse laser can be obtained synergistically, and the total irradiation time becomes longer An effect can be obtained predominately.

The irradiation step of the present invention, the total intensity of the pulsed laser is at 0.5 J / cm 2 or more, which is preferably and adjusted to 2.5 J / cm 2 or less. If the total intensity of the pulse laser is adjusted to 0.5 J / cm 2 or more, it becomes possible to heat the semiconductor substrate from the surface to a deep position to 950 ° C. or more by heat conduction. Furthermore, when the total intensity of the pulse laser is adjusted to 2.5 J / cm 2 or less, the phenomenon of sublimation (ablation) on the surface of the semiconductor substrate can be avoided.

When silicon is used as the main material of the semiconductor substrate, in the irradiation process of the present invention, the pulse laser is used under the condition that the temperature of the surface of the semiconductor substrate is higher than the melting temperature of silicon and lower than the sublimation temperature of silicon. Is preferably irradiated.
Thereby, it can recrystallize, after making the surface part of a semiconductor substrate into a molten state. For this reason, the surface part of a semiconductor substrate can be made into a state with few crystal defects.

The laser annealing apparatus created in the present invention includes a first oscillator, a second oscillator, an optical axis of a pulse laser oscillated by the first oscillator, and an optical axis of a pulse laser oscillated by the second oscillator on the surface of the irradiated substrate. Optical axis adjusting means for matching in the local region is provided. The laser annealing apparatus of the present invention further forms a time difference between the timing at which the pulse laser oscillated by the first oscillator irradiates the local region and the timing at which the pulse laser oscillated by the second oscillator irradiates the local region. Timing adjustment means is provided.
The timing adjusting means may adjust the timing at which the laser oscillator oscillates based on a pre-programmed command, or adjust the distance by providing a distance difference in the optical axis path of the pulse laser from each laser oscillator. There may be.

The timing adjustment means may be means for forming a time difference between the timing at which the first laser oscillator oscillates the pulse laser and the timing at which the second laser oscillator oscillates the pulse laser.
In this case, the distance between the optical axis path of the pulse laser from the first laser oscillator and the optical axis path of the pulse laser from the second laser oscillator can be designed to be substantially the same. The timing at which each laser oscillator oscillates a pulse laser is adjusted.

The activation method created in the present invention is useful when used in a method of manufacturing an IGBT (Insulated Gate Bipolar Transistor).
In this case, the manufacturing method includes a step of introducing a first conductivity type impurity at a deep position from the back surface of the semiconductor substrate to form a field stop region, and a second conductivity type impurity at a shallow position from the back surface of the semiconductor substrate. Forming a collector region, and irradiating a plurality of pulse lasers to a local region on the back surface of the semiconductor substrate using a plurality of laser oscillators. In the manufacturing method of the present invention, a time difference is set between the timing when a pulse laser oscillated by one laser oscillator irradiates the local region and the timing when a pulse laser oscillated by another laser oscillator irradiates the local region. It is characterized by having.
The field stop region of the IGBT is formed at a deep position from the back surface of the semiconductor substrate, and development of a technique for efficiently activating the field stop region has been desired. When the activation method of the present invention is used, a well-activated field stop region can be formed, so that the characteristics of the IGBT can be remarkably improved.

When the activation method created in the present invention is used, a novel and novel IGBT can be obtained. The IGBT created in the present invention includes a first conductivity type field stop region formed deep from the back surface of the semiconductor substrate and a second conductivity type collector region formed shallow from the back surface of the semiconductor substrate. It has. The field stop region is formed at a position deeper than 0.5 μm from the back surface of the semiconductor substrate. The collector region includes a region where the impurity concentration is uniform from the back surface of the semiconductor substrate toward the deep portion.
In the case where a field stop region formed at a position deeper than 0.5 μm from the back surface of the semiconductor substrate is provided, the laser annealing according to the prior art cannot be sufficiently activated. In addition, when trying to activate the deep field stop region by the conventional technique, sublimation (ablation) occurs in the shallow collector region, and the collector region is lost.
The IGBT obtained using the activation method created in the present invention realizes that the field stop region is well activated by heat conduction, and further realizes recrystallization in the molten state of the collector region. For this reason, a region where the impurity concentration is uniformly distributed from the back surface of the semiconductor substrate to the deep portion is formed in the collector region. That is, a combination of a field stop region formed at a position deeper than 0.5 μm and a collector region having a region where the impurity concentration is uniformly distributed from the back surface to the deep portion of the semiconductor substrate is It is a new and novel structure created by the invention.

  When the impurity activation method of the present invention is used, a substantial irradiation time of the laser pulse can be secured for a long time, so that a large amount of laser annealing can be secured. For this reason, it can heat to the deep position from the surface or back surface of a semiconductor substrate by heat conduction. According to the present invention, it is possible to secure an irradiation amount necessary for heating to a deep position while avoiding the phenomenon of sublimation (ablation) of the surface of the semiconductor substrate.

The features of the present invention are listed.
(First Embodiment) As the laser oscillator, an excimer laser, a YAG second harmonic laser, a YLF second harmonic laser, or the like can be used.
(2nd form) It is desirable for substantial irradiation time to be 50 nanoseconds or more.
(Third Embodiment) The “plurality of laser oscillators” of the present invention is not limited to the case of using two laser oscillators. The “plurality of laser oscillators” includes a case where three or more laser oscillators are used.
(4th form) A laser oscillator with a short wavelength and a laser oscillator with a long wavelength can also be utilized for a laser oscillator. A shallow position of the semiconductor substrate is heated by a laser oscillator having a short wavelength, and a deep position of the semiconductor substrate is heated by a laser oscillator having a long wavelength. By combining both features, it is possible to efficiently heat a deep position of the semiconductor substrate while suppressing excessive heating of the surface of the semiconductor substrate.

Hereinafter, embodiments will be described in detail with reference to the drawings. First, basic features of the present embodiment will be schematically described with reference to FIGS.
FIG. 1 shows the configuration of the laser annealing apparatus 10. The configuration and operating conditions of the laser annealing apparatus 10 described here are also applied to the IGBT manufacturing method described later.
The laser annealing apparatus 10 includes a first oscillator 12, a second oscillator 16, an optical axis adjustment unit 30, and a timing adjustment unit 14.
Each of the first oscillator 12 and the second oscillator 16 is a type that oscillates the YAG second harmonic. The first oscillator 12 oscillates the first pulse laser 22. The second oscillator 16 oscillates the second pulse laser 24. The half width of the first pulse laser 22 and the second pulse laser 24 is about 100 nanoseconds (nsec), and the frequency is adjusted to 1 kHz.
The optical axis adjusting unit 30 includes a first lens 32 and a second lens 34. The first lens 32 adjusts the optical axis of the first pulse laser 22. The second lens 34 adjusts the optical axis of the second pulse laser 24. The optical axis adjusting means 30 matches the optical axis of the first pulse laser 22 and the optical axis of the second pulse laser 24 in a local region on the surface of the semiconductor substrate 44 (semiconductor wafer). The semiconductor substrate 44 is placed on the XY stage 42.
The timing adjustment unit 14 inputs a control signal to the first laser oscillator 12 via the first signal line 13. Further, the timing adjusting unit 14 inputs a control signal to the second laser oscillator 16 through the second signal line 15. The timing adjusting unit 14 forms a time difference between the timing at which the first pulse laser 22 irradiates the local region on the surface of the semiconductor substrate 44 and the timing at which the second pulse laser 24 irradiates the local region. In the laser annealing apparatus 10, the distance difference between the optical axis distance of the first pulse laser 22 and the optical axis distance of the second pulse laser 24 can be substantially ignored. Therefore, the time difference between the timing at which the first pulse laser 22 and the second pulse laser 24 irradiate the local region of the surface of the semiconductor substrate 44 is different from the timing at which the first laser oscillator 12 oscillates the first pulse laser 22 and the second laser. The oscillator 16 is formed based on a time difference between timings at which the second pulse laser 24 is oscillated. That is, the timing adjusting unit 14 makes the oscillation timings of the first pulse laser 22 and the second pulse laser 24 different from each other based on the half width and frequency. The timing adjustment unit 14 adjusts the timing so that the second laser oscillator 16 oscillates the second pulse laser 24 so that the second laser oscillator 16 oscillates with a delay from the timing when the first laser oscillator 12 oscillates the first pulse laser 22. Yes. The timing adjusting means 14 outputs a control signal via the first signal line 13 and the second signal line 15 to adjust the timing at which the first laser oscillator 12 and the second laser oscillator 16 oscillate.

FIG. 2 shows how the first pulse laser 22 and the second pulse laser 24 scan the surface of the semiconductor substrate 44. A plurality of chip patterns 46 are formed in the semiconductor substrate 44. The first pulse laser 22 and the second pulse laser 24 meander and continuously irradiate while traversing a plurality of chip patterns 46. The irradiation positions of the first pulse laser 22 and the second pulse laser 24 are fixed, and scanning of the pulse laser is performed by moving the XY stage 42.
The speed (scanning speed) at which the XY stage 42 moves is determined based on a predetermined overlap rate. The overlap rate of this embodiment is 67%. Therefore, as will be described later, a double pulse in which the first laser pulse 22 and the second laser pulse 24 are combined is irradiated to the same portion three times. By ensuring an overlap ratio of 50% or more, unevenness of the semiconductor region formed on the surface of the semiconductor substrate 44 can be suppressed.

FIG. 3 shows temporal changes in the pulse waveform of the first pulse laser 22 and the pulse waveform of the second pulse laser 24.
The second pulse laser 24 oscillates with respect to the first pulse laser 22 with a delay substantially equal to the half-value width T10. For this reason, a part of the pulse waveform of the first pulse laser 22 and a part of the pulse waveform of the second pulse laser 24 overlap. For this reason, a double pulse laser in which the first pulse laser 22 and the second pulse laser 24 are combined is formed. If a part of the pulse waveforms of the first pulse laser 22 and the second pulse laser 24 overlap, the substantial irradiation time T20 (in this specification, the sum of the half width and the half width is referred to as the irradiation time) becomes longer. . For this reason, while the heating effect with respect to the semiconductor substrate 44 by the 1st pulse laser 22 is maintained, the heating effect with respect to the semiconductor substrate 44 by the 2nd pulse laser 24 can be added. In order to obtain a synergistic heating effect of the heating effect of the first pulse laser 22 and the heating effect of the second pulse laser 24, the delay time of the second pulse laser 24 is adjusted to 700 nanoseconds or less. Is desirable. Thereby, the timing which the 1st pulse laser 22 and the 2nd pulse laser 24 irradiate can be made to adjoin. For this reason, since the 2nd pulse laser 24 is irradiated before the heating effect by the 1st pulse laser 22 lose | disappears, the substantial irradiation time T20 can be ensured long. Further, when a delay of half width T10 or more is secured, even if the intensities of the first pulse laser 22 and the second pulse laser 24 are summed, the total intensity is the peak intensity of each of the pulse lasers 22 and 24. Is not exceeded.
Therefore, if the time difference provided between the first pulse laser 22 and the second pulse laser 24 is not less than the half-value width T10 and is adjusted to 700 nanoseconds or less, the total intensity becomes smaller than a predetermined value. While maintaining, the effect of lengthening the total irradiation time T20 can be obtained.

FIG. 4 shows a temperature distribution along the depth direction of the semiconductor substrate 44 when the laser annealing apparatus 10 is used. Reference numeral 94 is a comparative example in which the semiconductor substrate is irradiated using only the first laser oscillator 12.
As indicated by reference numeral 94, when irradiation is performed using only the first laser oscillator 12, a large amount of energy is absorbed at a shallow position (approximately a depth of several tens of nm), and the temperature distribution is steep along the depth direction. To change. For this reason, when irradiation is performed using only the first laser oscillator 12, when attempting to achieve 950 ° C. necessary for activation at a deep position (for example, 1 μm), the temperature at the shallow position rises excessively, and the semiconductor substrate 44. There is a problem that the temperature of the surface becomes higher than the ablation point.
On the other hand, as indicated by reference numeral 44, when the first laser oscillator 12 and the second laser oscillator 14 are used in combination, the temperature distribution becomes gentle along the depth direction. For this reason, it is possible to increase the temperature at a deep position while suppressing the temperature of the surface of the semiconductor substrate 44. This is because, while maintaining the intensity per unit area of the first pulse laser 22 and the second pulse laser 24 to be small, the irradiation amount of the laser annealing can be secured large by securing the substantial irradiation time T20. It is. Since a large irradiation amount of laser annealing can be secured, the temperature at a deep position can be increased by heat conduction.
Therefore, if the irradiation power is appropriately adjusted, a position 1 μm deep from the surface of the semiconductor substrate 44 can be heated to 950 ° C. or higher. Even in this case, the temperature of the surface of the semiconductor substrate 44 is maintained lower than the ablation point (about 2000 ° C.). Further, in the case of reference numeral 44, the temperature of the surface of the semiconductor substrate 44 exceeds 1420 ° C., which is the melting temperature of silicon. Therefore, the surface portion of the semiconductor substrate 44 undergoes recrystallization when it is cooled after being melted by laser annealing. For this reason, a state with few crystal defects is obtained on the surface portion of the semiconductor substrate 44. In order to adjust the temperature of the surface of the semiconductor substrate 44 within the range of the ablation point from 1420 ° C. while heating the deep position of 1 μm from the surface of the semiconductor substrate 44 to a high temperature up to 950 ° C. or more, a substantial irradiation time It is desirable to adjust T20 (in this specification, the sum of the full width at half maximum and the full width at half maximum is referred to as irradiation time) to 50 nanoseconds or more.

(Manufacturing method of IGBT)
Next, an IGBT manufacturing method will be described with reference to FIGS. In particular, the method for forming the field stop layer and the collector layer will be mainly described.
In FIG. 5, the principal part sectional drawing of the manufacturing process of IGBT100 is shown typically. The IGBT 100 is formed using an n-type silicon single crystal wafer (CZ, MCZ, FZ). The IGBT 100 includes a p-type body layer 54 formed on the n -type drift layer 52 and an n + -type source region 62 formed on the surface portion of the body layer 54. The body layer 54 and the source region 62 can be formed on the surface portion of the drift layer 52 using an ion implantation technique. The drift layer 52 and the body layer 54 are collectively referred to as a semiconductor substrate 50.
The IGBT 100 includes a trench gate electrode 58. The trench gate electrode 58 is opposed to the body layer 54 that separates the source region 62 and the drift layer 52 via the gate insulating film 56. The gate insulating film 56 can be formed by forming a trench from the surface of the body layer 54 and then thermally oxidizing the inner wall of the trench. The trench gate electrode 58 can be formed by filling the trench covered with the gate insulating film 56 with polysilicon. Impurities are introduced into the polysilicon of the trench gate electrode 58 at a high concentration, which is substantially a conductor.
A source electrode 66 that is electrically connected to the source region 62 is formed on the surface of the semiconductor substrate 50. The source electrode 66 and the trench gate electrode 58 are electrically separated by the interlayer insulating film 64. A polyimide layer 68 is further formed on the surface of the body layer 54. The polyimide layer 68 covers the source electrode 66 and is provided for passivation (protective film) of the source electrode 66 and the like.

Next, as shown in FIG. 6, the drift layer 52 of the IGBT 100 is polished from the back surface side, and the semiconductor substrate 50 is adjusted to a thickness of about 100 to 150 μm.
Next, as shown in FIG. 7, phosphorus ions 76 a that are n-type impurities are introduced from a back surface of the drift layer 52 to a deep position, and boron ions 74 a that are p-type impurities are introduced to a shallow position. The implantation conditions of phosphorus ions 76a are such that the implantation energy is 400 KeV and the dose is adjusted to 1 × 10 13 cm −2 . The implantation conditions of the boron ions 74a are such that the implantation energy is 10 to 20 KeV and the dose amount is adjusted to 5 × 10 13 to 1 × 10 14 cm −2 . As shown in FIG. 10, in the introduction concentration distribution 76 a of phosphorus ions, an impurity concentration peak is formed at a deep position of about 0.5 μm from the back surface of the semiconductor substrate 50, and the formation range is about 1 μm from the back surface of the semiconductor substrate 50. It has reached a deep position.

Next, laser annealing is performed toward the back surface of the semiconductor substrate 50. This laser annealing is performed using the laser annealing apparatus 10 described above. The configuration and operating conditions of the laser annealing apparatus 10 are the same as those described above.
FIG. 11 shows a concentration distribution 76a of phosphorus ions and a concentration distribution 76 of activated phosphorus that has been activated. The introduction concentration distribution 76a of phosphorus ions was calculated using a secondary ion mass spectrometry system (SIMS). The concentration distribution 76 of activated phosphorus was calculated using the spread resistance (SR). Reference numeral 94 is a comparative example in which only the first laser oscillator 12 is used, and shows the concentration distribution of activated phosphorus.
It can be seen that the activated phosphorus concentration distribution 76 of this example is substantially activated to a deep position along the phosphorus ion introduction concentration distribution 76a. When the activation rate (= SR integral value ÷ SIMS integral value × 100) is calculated, the activation rate of this example up to a depth of 1.0 μm is 70%, and the comparative example of reference numeral 94 is 2%. Met. It was confirmed that the activation rate of the present example was remarkably improved as compared with that of the comparative example.

Furthermore, in this embodiment, the activation of the boron ions 74a introduced into the shallow position of the semiconductor substrate 50 has a unique feature.
FIG. 12 schematically shows the impurity concentration distribution of the activated boron 74 along the depth direction from the back surface of the semiconductor substrate 50.
In the present embodiment, the back surface portion of the semiconductor substrate 50 is heated to 1420 ° C. or higher, which is the melting temperature of silicon. However, it has not been heated to such a high temperature that sublimation (ablation) occurs. For this reason, the back surface portion of the semiconductor substrate 50 is not lost by sublimation, and recrystallization occurs after passing through a molten state. Therefore, the crystal defects on the back surface portion of the semiconductor substrate 50 are recovered, and a state with few crystal defects is obtained.
Further, according to the laser annealing of this embodiment, there is an advantage that the impurity concentration of the collector layer 74 is formed uniformly. As shown by reference numeral 80 in FIG. 12, when a conventional technique such as lamp annealing is used, the distribution of the impurity concentration in the collector layer varies along the depth direction, and the impurity concentration in the surface portion of the semiconductor substrate is large. It has decreased (see 80 in the figure). The reduction of the surface portion is reduced by about 2/3 with respect to the peak value. On the other hand, the collector layer 74 of the present embodiment can have a region where the impurity concentration is uniform from the back surface of the semiconductor substrate 50 toward the deep portion by experiencing the molten state. Thereby, the contact property with respect to the collector electrode and the hole injection efficiency are improved, and an IGBT having a low on-voltage can be obtained.
Next, as shown in FIG. 9, the collector electrode 72 is formed by vapor-depositing aluminum on the back surface of the collector layer 74, whereby the IGBT 100 can be obtained.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

The structure of a laser annealing apparatus is shown. A mode that a pulse laser scans a semiconductor substrate is shown. The waveform of a 1st laser pulse and the waveform of a 2nd laser pulse are shown. The temperature distribution of the back surface part of a semiconductor substrate is shown. The manufacturing process of IGBT is shown (1). The manufacturing process of IGBT is shown (2). The manufacturing process of IGBT is shown (3). The manufacturing process of IGBT is shown (4). The manufacturing process of IGBT is shown (5). The distribution of phosphorus ions and boron ions introduced into the back surface portion of the semiconductor substrate is shown. The distribution of activated phosphorus on the back surface portion of the semiconductor substrate is shown. The distribution of activated boron on the back surface portion of the semiconductor substrate is shown.

Explanation of symbols

10: laser annealing device 12: first laser oscillator 13: first signal line 14: timing control means 15: second signal line 16: second laser oscillator 22: first laser pulse 24: second laser pulse 30: optical axis Adjustment means 32: first lens 34: second lens 42: XY stage 44: semiconductor substrate

Claims (17)

  1. A method of activating impurities introduced into a semiconductor substrate,
    Introducing impurities from the surface of the semiconductor substrate;
    A step of irradiating a plurality of pulse lasers using a plurality of laser oscillators on a local region of the surface of the semiconductor substrate;
    In the irradiation step, a time difference is set between the timing at which the pulse laser oscillated by one laser oscillator irradiates the local region and the timing at which the pulse laser oscillated by another laser oscillator irradiates the local region. An activation method characterized by the above.
  2.   2. The activation method according to claim 1, wherein in the irradiation step, a pulse laser having a half width of 10 to 200 nanoseconds is irradiated on the condition that the time difference is 700 nanoseconds or less.
  3.   3. The activation method according to claim 1, wherein in the irradiation step, the pulse laser is irradiated under a condition that the time difference is not less than a half width of the pulse laser.
  4.   4. The activation method according to claim 1, wherein in the irradiation step, a plurality of laser oscillators irradiate a pulse laser having the same frequency.
  5.   In the irradiation step, irradiation is performed such that a part of a pulse waveform of a pulse laser oscillated by one laser oscillator and a part of a pulse waveform of a pulse laser oscillated by another laser oscillator overlap. The activation method in any one of claim | item 1 -4.
  6. Wherein in the irradiation step, or the activation method according to claim 1 to 5, the total intensity of the pulsed laser, characterized in that it is adjusted to 0.5J / cm 2 ~2.5J / cm 2 .
  7. Silicon is used as the main material of the semiconductor substrate,
    7. The pulse laser irradiation is performed in the irradiation step under a condition that the temperature of the surface of the semiconductor substrate is equal to or higher than the melting temperature of silicon and lower than the sublimation temperature of silicon. Activation method.
  8. A laser annealing device used when activating impurities introduced into a semiconductor substrate,
    A first laser oscillator;
    A second laser oscillator;
    Optical axis adjusting means for causing the optical axis of the pulse laser oscillated by the first laser oscillator and the optical axis of the pulse laser oscillated by the second laser oscillator to coincide with each other in a local region of the surface of the irradiated substrate;
    There is provided timing adjustment means for forming a time difference between the timing at which the pulse laser oscillated by the first laser oscillator irradiates the local region and the timing at which the pulse laser oscillated by the second laser oscillator irradiates the local region. A laser annealing apparatus characterized by that.
  9.   9. The laser annealing according to claim 8, wherein the timing adjusting means is means for forming a time difference between the timing at which the first laser oscillator oscillates the pulse laser and the timing at which the second laser oscillator oscillates the pulse laser. apparatus.
  10. It is a manufacturing method of IGBT (Insulated Gate Bipolar Transistor),
    A step of introducing a first conductivity type impurity into a deep position from the back surface of the semiconductor substrate to form a field stop region;
    Introducing a second conductivity type impurity into a shallow position from the back surface of the semiconductor substrate to form a collector region;
    A step of irradiating a plurality of pulsed lasers using a plurality of laser oscillators on a local region on the back surface of the semiconductor substrate;
    In the irradiation step, a time difference is set between the timing at which the pulse laser oscillated by one laser oscillator irradiates the local region and the timing at which the pulse laser oscillated by another laser oscillator irradiates the local region. The manufacturing method characterized by the above-mentioned.
  11.   11. The manufacturing method according to claim 10, wherein, in the irradiation step, a pulse laser having a half width of 10 to 200 nanoseconds is irradiated on the condition that the time difference is 700 nanoseconds or less.
  12.   12. The manufacturing method according to claim 10, wherein in the irradiation step, the pulse laser is irradiated under a condition that the time difference is equal to or greater than a half width of the pulse laser.
  13.   The manufacturing method according to claim 10, wherein in the irradiation step, a plurality of laser oscillators irradiate a pulse laser having the same frequency.
  14.   In the irradiation step, irradiation is performed such that a part of a pulse waveform of a pulse laser oscillated by one laser oscillator overlaps a part of a pulse waveform of a pulse laser oscillated by another laser oscillator. The manufacturing method in any one of claim | item 10-13.
  15. Wherein in the irradiation step, any of the method according to claim 10 to 14 the total intensity of the pulsed laser, characterized in that it is adjusted to 0.5J / cm 2 ~2.5J / cm 2 .
  16. Silicon is used as the main material of the semiconductor substrate,
    16. The pulse laser irradiation is performed in the irradiation step under a condition that the temperature of the back surface of the semiconductor substrate is higher than or equal to the melting temperature of silicon and lower than the sublimation temperature of silicon. Manufacturing method.
  17. IGBT (Insulated Gate Bipolar Transistor)
    A first conductivity type field stop region formed deep from the back surface of the semiconductor substrate;
    A second conductivity type collector region formed at a shallow position from the back surface of the semiconductor substrate;
    At least a part of the field stop region is formed at a position deeper than 0.5 μm from the back surface of the semiconductor substrate,
    The IGBT is characterized in that the collector region includes a region where the impurity concentration is uniformly distributed from the back surface of the semiconductor substrate toward the deep portion.
JP2005309308A 2005-10-25 2005-10-25 Method for activating impurities, laser annealer, semiconductor device and method for fabricating same Pending JP2007123300A (en)

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