JP2006351659A - Method of manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a semiconductor device by which impurity ions injected into a deep part can be activated. <P>SOLUTION: The method of manufacturing a semiconductor device includes first to third steps, wherein the frontal structure of the semiconductor device is formed on the front side of a wafer 14 in the first step, impurity ions are injected into the wafer 14 from the rear surface in the second step, and a laser light is given to the rear surface of the wafer 14 under the satisfactory conditions of (1) wavelength of 690-900 nm, (2) irradiation time of 10-100 μ sec, and (3) power density of 250-750 kW/cm<SP>2</SP>in the third step. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor device. Specifically, the present invention relates to a technique for activating impurity ions implanted into a wafer.

  The first step of forming the front side structure of the semiconductor device on the front side of the wafer, the second step of implanting impurity ions into the wafer from the back side of the wafer, and the second step by irradiating the back side of the wafer with laser light A manufacturing method of a semiconductor device including a third step of activating impurity ions is known (for example, Patent Document 1).

JP 2003-59856 A

Conventionally, an excimer laser (wavelength: 308 nm), a YAG second harmonic laser (wavelength: 532 nm), a YLF second harmonic laser (wavelength: 527 nm), or the like is used to activate impurity ions. When the wafer is irradiated with these laser beams, since the absorption coefficient of the laser beams by the wafer is high, most of the laser beams are absorbed near the surface of the wafer and do not reach the deep part. The conventional laser beam irradiation technique cannot heat to the deep part and cannot activate the impurity ions implanted into the deep part.
If the power density of the laser is increased in order to activate the impurity ions implanted in the deep part, the vicinity of the wafer surface becomes too hot and melts, resulting in damage to the wafer. Alternatively, the concentration distribution of impurity ions implanted into the wafer in the depth direction changes.
The present invention has been made to solve the problem, and an object of the present invention is to provide a method of manufacturing a semiconductor device capable of activating impurity ions implanted in a deep portion.

The method for manufacturing a semiconductor device of the present invention includes a first step, a second step, and a third step. In the first step, the front side structure of the semiconductor device is formed on the front side of the wafer. In the second step, impurity ions are implanted into the wafer from the back surface of the wafer. In the third step, the back surface of the wafer is irradiated with laser light that satisfies the following conditions. The conditions are (1) the wavelength is 690 to 900 nm, (2) the irradiation time is 10 to 100 μsec, and (3) the power density is 250 to 750 kW / cm ² . Here, the power density is on the back surface of the wafer.
When the back surface of the wafer is irradiated with laser light that satisfies the above-mentioned conditions (1), (2), and (3), the laser light penetrates from the back surface of the wafer to the deep part and can be heated to the deep part of the wafer. it can. Impurity ions implanted in the deep part can be activated. On the other hand, the laser beam does not enter too much from the back surface of the wafer, and the front side structure of the semiconductor device formed on the front side of the wafer is not damaged.

When manufacturing an IGBT, an n-type semiconductor wafer is used, and in the second step, phosphorus ions are implanted at an implantation energy of 500 to 1500 keV and a dose of 5 × 10 ^{12 to} 5 × 10 ¹⁵ / cm ² , and then boron ions are implanted. It is preferable to implant at an energy of 10 to 50 keV and a dose of 1 × 10 ¹³ to 1 × 10 ¹⁴ / cm ² .
By implanting phosphorus ions and boron ions under such conditions, a collector layer can be formed near the back surface of the wafer, and a field stop layer can be formed deeper than that. It is possible to effectively activate phosphorus implanted in the deep part to form the field stop layer.

  According to the present invention, the activation rate of impurity ions implanted into the deep portion can be increased without damaging the wafer of the semiconductor device or without affecting the concentration distribution of impurity ions in the depth direction of the wafer. Can do. At the same time, damage to the front side structure of the semiconductor device formed on the front side of the wafer can be avoided.

The preferred embodiment of this invention is illustrated.
(Form 1)
A semiconductor device manufacturing method, wherein the semiconductor device is an IGBT.

An embodiment according to the manufacturing method of the present invention will be described with reference to the drawings. In the manufacturing method of the present embodiment, as shown in FIG. 1, the collector electrode 20, the p ⁺ -type collector layer 17, the n ⁺ -type field stop layer 16, the n-type substrate (wafer) 14, the p-type body are sequentially arranged from the back side. An IGBT including the layer 15, the n ⁺ -type emitter region 24, the gate electrode 23, the gate insulating film 22, the interlayer insulating film 25, the emitter electrode 27, and the polyimide layer 28 is manufactured.
The collector electrode 20 is formed on the back surface of the p ⁺ type collector layer 17 and is an aluminum electrode. The emitter electrode 27 is formed on the surfaces of the p-type body layer 15 and the n ⁺ -type emitter region 24, and is an aluminum electrode. The emitter electrode 27 is connected to the n ⁺ -type emitter region 24. In a cross section (not shown), ap ⁺ type contact region is formed on the surface of the p type body layer 15. The emitter electrode 27 is also connected to the p-type body layer 15 through a p ⁺ -type contact region. The gate electrode 23 is formed in a trench 21 that reaches the n-type substrate 14 through the n ⁺ -type emitter region 24 and the p-type body layer 15. The gate electrode 23 is disposed in the trench 21 while being covered with the gate insulating film 22. The gate electrode 23 is insulated from the emitter electrode 27 by the interlayer insulating film 25. The gate electrode 23 is electrically connected to the gate voltage signal line in a cross section (not shown). The polyimide layer 28 covers the p-type body layer 15 and the emitter electrode 27.

When the semiconductor 10 is manufactured, an n-type substrate 14 is prepared as shown in FIG. The n-type substrate 14 can be manufactured at low cost using, for example, the CZ method, the MCZ method, the FZ method, or the like. A thick n-type substrate 14 is prepared so that it can be easily handled during the manufacturing process. This is because if the n-type substrate 14 is thin, the n-type substrate 14 is easily destroyed.
Next, as shown in FIG. 3, p-type body layers 15 are formed by implanting p-type impurity ions (specifically, boron ions) into the front surface of the n-type substrate 14. Next, n type impurity ions are implanted to form an n ⁺ type emitter region 24.
Next, a trench 21 that reaches the n-type substrate 14 through the n ⁺ -type emitter region 24 and the p-type body layer 15 is formed using an etching technique such as IRE. Next, the gate insulating film 22 is formed on the inner surface of the trench 21 by thermal oxidation. Next, a gate electrode 23 is formed by growing polycrystalline silicon in the trench 21.
Next, an interlayer insulating film 25 is formed, an emitter electrode 27 is formed, and a polyimide layer 28 is formed. Before forming the emitter electrode 27 and the polyimide layer 28, the implanted impurity ions are activated for heat treatment.
Since the technique for manufacturing the front side structure of the IGBT is known, further description thereof is omitted.

In the state of FIG. 3, the front side structure of the IGBT is completed. Next, as shown in FIG. 4, the thickness of the n-type substrate 14 is reduced by polishing the back side of the n-type substrate 14 or the like. By reducing the thickness of the n-type substrate 14, the on-voltage of the IGBT is reduced.
Next, as shown in FIG. 5, phosphorus (P) 32 is ion-implanted into the n-type substrate 14 from the back surface. The phosphorus implantation conditions are an implantation energy of 500 to 1500 keV and a dose of 5 × 10 ^{12 to} 5 × 10 ¹⁵ / cm ² . Next, as shown in FIG. 6, boron (B) 33 is ion-implanted into the n-type substrate 14 from the back side. Boron implantation conditions are an implantation energy of 10 to 50 keV and a dose of 1 × 10 ¹³ to 1 × 10 ¹⁴ / cm ² . Phosphorus is implanted deep and boron is implanted shallow.
Next, as shown in FIG. 7, laser annealing is performed in which the back surface of the n-type substrate 14 is irradiated with laser light 34 and the back side of the n-type substrate 14 is heated. When laser annealing is performed, the implanted phosphorus 32 and boron 33 are activated, and the n ⁺ field stop layer 16 and the p ⁺ collector layer 17 are formed. Finally, the collector electrode 20 is bonded to the back side of the p ⁺ collector layer 17 to complete the semiconductor device 10 shown in FIG.

As described above, the semiconductor device 10 is activated by laser annealing phosphorus and boron implanted into the n-type substrate 14 to form the n ⁺ field stop layer 16 and the p ⁺ collector layer 17. In that case, it is preferable to irradiate the back surface of the n-type substrate 14 from the semiconductor laser with a laser beam having a wavelength of 690 to 900 nm and a power density of 250 to 750 kW / cm ² for an irradiation time of 10 to 100 μsec. The basis for setting the irradiation conditions will be described in detail below.

FIG. 8 shows the result of simulating the relationship of the laser absorption intensity (W / cm ³ ) (vertical axis) to the depth (μm) (horizontal axis) from the irradiated surface for each wavelength of laser light used for laser annealing. ing. Here, the irradiation surface is the back surface of the n-type substrate 14. The laser absorption intensity means the amount of heat absorbed by the n-type substrate 14 (silicon) per unit volume. The higher the laser absorption intensity, the higher the temperature of the absorption site. Laser light with a wavelength of 308 nm is emitted from an excimer laser. The laser beam having a wavelength of 532 nm is emitted from the YAG second harmonic laser. The laser beam having a wavelength of 527 nm is emitted from the YLF second harmonic laser. Laser beams having wavelengths of 690 nm, 808 nm, and 940 nm are emitted from a semiconductor laser made of a III-V group compound (for example, AlGaAs).

The phosphorus implanted into the n-type substrate 14 to form the n ⁺ field stop layer 16 has a peak concentration at a depth of about 1 μm. For this reason, phosphorous cannot be activated satisfactorily unless the laser absorption intensity is increased to a depth deeper than 1 μm. However, when irradiated with an excimer laser (308 nm), the laser absorption intensity can be secured only to a very shallow portion on the back side of the n-type substrate 14. When YAG second harmonic laser (532 nm) or YLF second harmonic laser (527 nm) is irradiated, laser absorption intensity can be secured even at a depth of 1 μm. However, when irradiated with a YAG second harmonic laser or a YLF second harmonic laser, the laser absorption intensity rapidly decreases from the back surface to a depth of 1 μm. Therefore, when laser annealing is performed so that the back surface of the n-type substrate 14 is not melted, the portion having a depth of 1 μm does not reach the temperature necessary for activation. For this reason, even if laser annealing is performed with the YAG second harmonic or the YLF second harmonic, the implanted phosphorus and boron are not activated well (the activation rate is lowered). In contrast, when irradiated with a semiconductor laser (690 nm, 808 nm, 940 nm), the laser absorption intensity at a depth of 1 μm can be secured and the laser absorption intensity changes rapidly along the depth direction. There is nothing to do. Therefore, by performing laser annealing with laser light having a wavelength of 690 nm, 808 nm, and 940 nm obtained from a semiconductor laser, the implanted phosphorus and boron are activated well with the back surface of the n-type substrate 14 not melted. be able to.

FIG. 9 shows the result of measuring the light transmittance (%) (vertical axis) in silicon having a thickness of 100 μm with respect to the wavelength (nm) of light (horizontal axis). The light transmittance is a ratio of the intensity of transmitted light to the intensity of irradiated light. As is clear from FIG. 9, when the wavelength of light exceeds 900 nm, the transmittance of silicon increases rapidly. For this reason, when laser annealing is performed with a laser beam having a wavelength of 900 nm or more, the surface side of the semiconductor device 10 becomes a high temperature (for example, 450 ° C. or more), and the emitter electrode 27 formed of aluminum melts or a polyimide layer 28 is carbonized. Therefore, from the viewpoint of suppressing the transmittance, the wavelength of the laser light emitted from the semiconductor laser needs to be 900 nm or less.
From the laser absorption intensity shown in FIG. 8 and the transmittance shown in FIG. 9, it is confirmed that the wavelength of the laser light emitted from the semiconductor laser is preferably 690 to 900 nm.

FIG. 10 shows the result of simulating the relationship of the temperature (° C.) (vertical axis) of the n-type substrate 14 to the irradiation time (μs) (horizontal axis) of the semiconductor laser for each depth from the back surface of the n-type substrate 14. Show. In order to activate the n ⁺ field stop layer 16 and the p ⁺ collector layer 17 satisfactorily, it is necessary to heat the portion of the n-type substrate 14 into which phosphorus and boron are implanted to about 950 ° C. As is apparent from FIG. 10, the temperature of the n-type substrate 14 at each depth when the irradiation time is in the range of 10 to 100 μm for each of the irradiation surface, the depth of 0.5 μm, and the depth of 1 μm. Becomes a value close to 950 ° C. At a depth of 0.5 μm and a depth of 1 μm, the temperature does not increase when the irradiation time is 10 μs or less. The irradiation time needs to be 10 μs or more. When the irradiation time is 100 μs or more, the temperature at a position of 100 μm depth (near the surface of the semiconductor device 10) exceeds 450 ° C. If the temperature at a depth of 100 μm (near the surface of the semiconductor device 10) exceeds 450 ° C., the aluminum emitter electrode 27 may melt and the polyimide layer 28 may be carbonized. The irradiation time needs to be 100 μs or less. The irradiation time of the semiconductor laser is preferably 10 to 100 μs.

FIG. 11 shows the relationship of the temperature (° C.) (vertical axis) of the n-type substrate 14 to the power density (kW / cm ² ) (horizontal axis) irradiated by the semiconductor laser for each depth from the back surface of the n-type substrate 14. It is the result of having simulated. The wavelength of the laser beam irradiated by the semiconductor laser is 808 nm. In FIG. 11, the difference between the irradiation surface (the back surface of the n-type substrate 14) and the depth of 1 μm is extremely small, and thus both are shown by one line. The power density is on the irradiation surface of the n-type substrate 14. As is clear from FIG. 11, the temperature is about 950 ° C. in the power density range of 250 to 750 kW / cm ² for the irradiation surface and the depth of 1 μm. For a depth of 100 μm, the temperature suddenly increases when the power density exceeds 500 kW / cm ² and reaches 300 ° C. at 750 kW / cm ² . Although not shown in FIG. 11, the temperature of the portion having a depth of 100 μm tends to be higher when the power density is 750 kW / cm ² or more. The depth of 100 μm corresponds to the vicinity of the surface of the semiconductor element 10. In the vicinity of the surface of the semiconductor element 10, an aluminum emitter electrode 27 and a polyimide layer 28 which are easily affected by heat are disposed, and it is not preferable that the temperature is increased. Therefore, the back surface of the n-type substrate 14 and the temperature of 1 μm in depth become a value around 950 ° C. that activates the n ⁺ field stop layer 16 and the p ⁺ collector layer 17 well, and the surface of the n-type substrate 14 The power density is preferably set to 250 to 750 kW / cm ² so that the vicinity does not become so hot.

FIG. 12 shows the carrier concentration (atoms / cm ³ ) relative to the depth (μm) (horizontal axis) from the back surface of the n-type substrate 14 when phosphorus is implanted and when the implanted phosphorus is activated by a laser. ) (Vertical axis) is a result of actual measurement. For comparison, activation by a laser was performed using a YLF second harmonic laser and an excimer laser conventionally used and a semiconductor laser according to this embodiment for comparison. The n-type substrate 14 is manufactured by the CZ method and has a thickness of 100 μm. Phosphorus was implanted with an implantation energy of 1000 keV and a dose of 1 × 10 ¹³ cm ² . The semiconductor laser was irradiated at a wavelength of 808 nm, an irradiation time of 10 μsec, and a power density of 400 kW / cm ² . The YLF second harmonic laser was irradiated at a wavelength of 527 nm, an irradiation time of 200 nsec, and a power density of 20 MW / cm ² . The excimer laser was irradiated at a wavelength of 308 nm, an irradiation time of 50 nsec, and a power density of 40 MW / cm ² . The activation rate was calculated by “SR integral value / SIMS integral value × 100”.
As is clear from FIG. 12, when activation was performed by irradiation from a YLF second harmonic laser, an activation rate as low as 5% was obtained. When activation was performed by irradiation from an excimer laser, the activation rate was 30%. When irradiated from the semiconductor laser which is the technology of the present invention, a high activation rate of 70% could be achieved.

FIG. 13 shows the impurity concentration with respect to the depth (μm) (horizontal axis) from the back surface of the n-type substrate 14 when boron is implanted and when activated by the YLF second harmonic laser and the semiconductor laser. This is a result of actually measuring a profile of atoms / cm ³ ) (vertical axis).
As is apparent from FIG. 13, when the YLF second harmonic laser beam is irradiated, the profile greatly changes from the state in which boron is implanted. On the other hand, when irradiated with a semiconductor laser, the profile remains almost as it is implanted. Therefore, it is easy to obtain an intended concentration distribution profile by irradiating with a semiconductor laser.

As already described, the irradiation time of the semiconductor laser is preferably 10 to 100 μs. Hereinafter, a technique for adjusting the irradiation time will be described.
As shown in FIG. 14, when adjusting the irradiation time of the laser light irradiated by the semiconductor laser, the wafer 51 is set on the stage 50. As shown in FIG. 15, a plurality of n-type substrates 14 (the state shown in FIG. 6) that has been manufactured up to the stage where phosphorus and boron are implanted on the back side are arranged on the wafer 51 with the back side facing upward. Has been. As shown in FIG. 14, the stage 50 is driven by a driving device (not shown) and moves in the x direction and the y direction (that is, the horizontal direction). A semiconductor laser source 52 is provided above the stage 50.
The semiconductor laser source 52 continuously irradiates the wafer 51 on the stage 50 with the laser beam 53. The laser beam 53 forms a laser spot on the wafer 51. As the stage 50 moves, the laser spot travels on the wafer 51 accordingly. An arrow 54 in FIG. 15 illustrates a path along which the laser spot travels on the wafer 51.

FIG. 16 illustrates a state in which a laser spot 56 is formed by irradiating the n-type substrate 14 arranged in a row on the wafer 51 with the laser beam 53. The laser spot 53 is rectangular. For example, it is assumed that the length A in the short direction of the laser spot 56 is 50 μm, and the irradiation time required for the n-type substrate 14 is 10 μsec. In that case, the irradiation time can be adjusted to 10 μsec (50 μm / 5 μsec) by advancing the laser spot 56 in the direction indicated by the arrow 58 at 5 μm / μsec.
Laser light 53 can also be irradiated intermittently from the semiconductor laser source 52. In this case, as shown in FIG. 17, by stopping the stage 50, the laser spot 56 is formed at the position B continuously for a predetermined time (for example, 100 μsec). Then, with the irradiation of the laser beam 53 interrupted, the stage 50 is moved so that the laser spot 56 can irradiate the position C, and then the laser beam 53 is irradiated. The irradiation time can be adjusted by repeatedly irradiating and interrupting the laser beam and moving the stage 50 accordingly.

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.
In addition, the technical elements described in the present specification or 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 illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

FIG. 14 is a cross-sectional view of a semiconductor device. Sectional drawing in the state in the middle of manufacture of a semiconductor device. Sectional drawing in the state in the middle of manufacture of a semiconductor device. Sectional drawing in the state in the middle of manufacture of a semiconductor device. Sectional drawing in the state in the middle of manufacture of a semiconductor device. Sectional drawing in the state in the middle of manufacture of a semiconductor device. Sectional drawing in the state in the middle of manufacture of a semiconductor device. The graph which shows the relationship between the depth from an irradiation surface, and laser absorption intensity. The graph which shows the relationship between the wavelength of a laser, and the transmittance | permeability of a silicon | silicone. The graph which shows the relationship between the irradiation time of a laser, and the temperature of an n-type board | substrate. The graph which shows the relationship between the power density of a laser, and the temperature of an n-type board | substrate. The graph which shows the relationship between the depth of an n-type board | substrate, and carrier concentration. The graph which shows the relationship between the depth of an n-type board | substrate, and carrier concentration. The perspective view in the state where the semiconductor laser source is irradiating the wafer with laser light. The figure explaining the path | route which a laser spot advances on a wafer. The figure explaining the state which a laser spot advances continuously on a wafer. The figure explaining the state in which a laser spot advances in a step shape on a wafer.

Explanation of symbols

10: Semiconductor device 14: n-type substrate 15: p-type body layer 16: n ⁺ field stop layer 17: p ⁺ collector layer 20: back surface aluminum electrode 21: trench 22: insulating film 23: gate electrode 24: n ⁺ type emitter Region 25: Interlayer insulating film 27: Emitter electrode 28: Polyimide layer 32: Phosphorous 33: Boron 34: Laser beam 50: Stage 51: Wafer 52: Semiconductor laser source 53: Laser beam 54: Travel path 58: Arrow

Claims (2)

A first step of forming the front side structure of the semiconductor device on the front side of the wafer;
A second step of implanting impurity ions into the wafer from the backside of the wafer;
Laser light that satisfies the following conditions (1), (2), and (3) on the back surface of the wafer:
(1) Wavelength: 690 to 900 nm,
(2) Irradiation time: 10 to 100 μsec,
(3) Power density: 250 to 750 kW / cm ² ,
And a third step of irradiating the semiconductor device. The wafer is an n-type semiconductor,
In the second step, phosphorus ions are implanted with an implantation energy of 500 to 1500 keV and a dose of 5 × 10 ^{12 to} 5 × 10 ¹⁵ / cm ² , and then boron ions are implanted with an implantation energy of 10 to 50 keV and a dose of 1 × 10 ¹³ to 1 ×. The method for manufacturing a semiconductor device according to claim 1, wherein implantation is performed at 10 ¹⁴ / cm ² .

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