JP2000349042A - Method and apparatus for manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an impurity concentration profile which is ideal for a rear electrode by a method wherein a semiconductor substrate is irradiated with a laser beam via an optical system, reflected light from the semiconductor substrate is reflected by a mirror and the reflected light is returned to the semiconductor substrate so as to be irradiated. SOLUTION: A laser beam 22 which is output from a laser oscillator 21 is guided, by a mirror 23 24, to a beam homogenizer 25 which makes the spatial intensity distribution of the laser beam 22 uniform, and it irradiates a semiconductor substrate 31, which is arranged on an X-Y table 30, from a synthetic quartz glass window 25 in a chamber 28 via a mirror 26 and an image formation lens 27. In addition, a concave mirror 32 which is fixed to the chamber 28 just above the semiconductor substrate 31 reflected light reflected from the semiconductor substrate 31 so as to irradiate the semiconductor substrate 31. Consequently, the surface of the semiconductor substrate 31 is irradiated with direct light which irradiates the semiconductor substrate via a corner optical system from the laser oscillator 21 and with indirect light which is reflected by the concave mirror 32 in such a way that both the direct light and the indirect light are superposed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device and a technique of a manufacturing apparatus therefor, and more particularly to a method of forming a back surface electrode of a semiconductor device, in which boron or phosphorus is ion-implanted and then a pulse laser beam is irradiated. The present invention relates to a technique of activating an aluminum alloy film to form a collector electrode.

[0002]

2. Description of the Related Art Generally, an IGBT (Insulated)
Gate Bipolar Transistor)
In the case of a power-MOS device, a source / drain electrode is formed on a front surface of a semiconductor substrate, and a collector electrode is formed on a back surface.

For example, in the case of an IGBT, a collector electrode is formed adjacent to a collector electrode of an N-type silicon substrate.
It is necessary to form a P-type layer in which the boron impurity concentration is controlled. The P-type layer is formed by doping boron by an ion implantation method and then activating it. in this case,
Activation can achieve 100% by annealing at about 900 ° C./30 min in an electric furnace or the like, but annealing at about 900 ° C. is performed because the n + source, p + well, and source / drain electrodes are already formed on the surface. Can not.

Therefore, an alloy such as chrome, nickel, or silver is vapor-deposited without ion implantation of boron, and then annealing is performed at about 450 ° C. for 30 minutes to form a P-type layer adjacent to a collector electrode on an N-type silicon substrate. Having a collector electrode.

As another method, boron is ion-implanted, and then the implanted boron is electrically activated by using an instantaneous annealing technique. Instant annealing technology
This technology irradiates the surface of the silicon substrate with radiation such as high-power laser light, electron beam, or flash light to instantaneously anneal the surface layer. It is roughly classified into a continuous wave (CW) method by continuous oscillation and Q There is a pulse method using a switch or the like.

In the instantaneous annealing technique, (1) heating for a short time is possible [CW method: up to ms, pulse method: ns to μ]
s], (2) Local heating is possible [heat treatment area can be controlled], (3) Only the surface layer can be heated [depth of heat treatment can be controlled by radiation wavelength and energy],
(4) High-temperature heating is possible [usually around the melting point of silicon], (5) Short-time cooling is possible [-10 ° C./s cooling rate], and (6) Fast crystal growth rate is obtained ( ~
liquid / solid at m / s).

Usually, as a method of forming a sufficient P-type layer, activation is often performed by instantaneous high-temperature annealing by pulsed laser irradiation. According to this method, the pulse width of the pulse laser is as short as about 20 ns (half width), and only the very surface layer (1 μm to 3 μm) of the substrate can be heated. realizable.

The pulse laser used in this case is a short-pulse high-output XeCl excimer laser or KrF excimer laser.
Excimer laser.

In particular, if a short-wavelength pulse laser is used, the semiconductor thin film can be efficiently annealed without damaging the underlying semiconductor substrate. For example, XeF
(Wavelength 351 nm), XeCl (308 nm), KrF
(248 nm) and an ArF (193 nm) excimer laser can be used. The energy density of the laser is
For example, irradiation is performed at 0.5 to ^2.5 mJ / cm ² .

[0010]

However, in the method of annealing after vapor deposition of an alloy such as chrome, nickel, and silver, since the annealing is performed at about 450 ° C. for 30 minutes, the p-type layer can be sufficiently formed. No, and need to use multiple metals. For this reason, the manufacturing process takes a long time, and a decrease in throughput is inevitable.

In addition, since the wafer surface is frequently contacted with the support during the annealing process, scratches on the wafer surface and a high dust adhesion rate may adversely affect semiconductor characteristics.

Also, in the method of performing activation by instantaneous high-temperature annealing by pulse laser irradiation after boron ion implantation, the reflectance of laser light of the silicon substrate after boron ion implantation is as high as 50%. The loss of the laser light applied to the silicon substrate is large, and the output of the laser oscillator needs to be increased, and the efficiency of the device is not very good.

The present invention has been made based on these circumstances, and when performing activation by instantaneous high-temperature annealing by pulsed laser irradiation in a semiconductor device manufacturing process, the loss of laser light is reduced to reduce the boron activity. And IGB
It is an object of the present invention to provide a method and an apparatus for manufacturing a semiconductor device capable of realizing an ideal concentration profile of an insensitive object for a back electrode such as T, Power-MOS or the like.

[0014]

According to the first aspect of the present invention, in forming a back electrode of a semiconductor substrate, an impurity is ion-implanted into the semiconductor substrate, and the impurity is activated by heat treatment. In the manufacturing method, the heat treatment irradiates the semiconductor substrate with a laser beam emitted from a laser oscillator through an optical system,
A method of manufacturing a semiconductor device, characterized in that light reflected from the semiconductor substrate is reflected by a mirror and returned to the semiconductor substrate for irradiation.

According to the second aspect of the present invention,
The pulse laser emitted from the laser oscillator is XeC
In l excimer laser or KrF excimer laser, the intensity of the laser light is a method of manufacturing a semiconductor device, wherein said at 2.5 J / cm ² or less at 0.5 J / cm ² or more in the semiconductor substrate surface.

According to the third aspect of the present invention,
The mirror has a concave reflecting portion, is provided on an optical axis of laser light emitted from the laser oscillator, and irradiates the semiconductor substrate by passing the pulsed laser light through a hole provided in a central portion. A method for manufacturing a semiconductor device, comprising: reflecting light reflected from the semiconductor substrate on the reflecting surface to the semiconductor substrate.

Further, according to the means of the present invention,
In the apparatus for manufacturing a semiconductor element, in which an impurity is ion-implanted into the semiconductor substrate when the back electrode of the semiconductor substrate is formed and the impurity is activated by a heat treatment unit, the heat treatment unit emits a laser beam emitted from a laser oscillator into an optical system. An irradiating means for irradiating the semiconductor substrate through the semiconductor substrate, and a concave mirror for irradiating reflected light from the semiconductor substrate with a concave mirror surface and returning the reflected light to the semiconductor substrate. It is.

According to the fifth aspect of the present invention,
The concave mirror is an apparatus for manufacturing a semiconductor device, wherein the mirror surface is an aluminum vapor-deposited surface or a dielectric multilayer film surface.

Further, according to the means of the invention of claim 6,
The arrangement of the concave mirror is a position of a focal length of an imaging lens forming the optical system on an optical axis immediately above the semiconductor substrate.

According to the means of the invention of claim 7,
The curvature of the concave mirror is twice as long as the distance from the focal length of the imaging lens to the semiconductor substrate.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

First, main manufacturing steps of a semiconductor device to which the present invention is applied will be described.

FIG. 1 shows an embodiment according to the semiconductor device of the present invention.
It is sectional drawing of the IGBT which shows a form. N-type silicon base
In the surface of the wafer 1 formed of a plate, a high-concentration P-type
P + -type wells with gates
Gate electrode 2, P-type base region 3, N⁺Type emitter region
4. An insulating film 5 is formed. The emitter electrode 6 is
⁺To short-circuit each emitter region and P-type base region
It is provided in.

In the present invention, the back surface of the wafer 1 is
Aluminum or an aluminum alloy doped with boron is used as the material of the collector electrode 7.
A low-concentration P-type layer (P-
Layer 8 is formed, and a good low-resistance ohmic contact is formed.

Next, a method of manufacturing the structure shown in FIG. 1 will be described.
First, the surface of the wafer 1 is formed by using a well-known technique by using a P ⁺ -type well region, a gate electrode 2 on a gate insulating film, a P-type base region 3, an N ⁺ -type emitter region 4, and an insulating film. 5 is formed. Thereafter, aluminum is formed as the emitter electrode 6 to electrically short the N ⁺ -type emitter and the P-type base regions. Until these steps are completed, heat treatment steps for each electrode such as annealing and reflow are appropriately inserted.

After the process of forming the front surface of the wafer 1, the process of forming the rear surface of the wafer 1 which is important in the present invention is started. This will be described with reference to FIGS. Boron ions are implanted into the back surface of the wafer 1 (FIG. 2A). IE13 to IE15 atoms / cm
^2, and the acceleration voltage is 50 KeV. Then wafer 1
Is irradiated with a laser to activate the ion-implanted boron (FIG. 2B). As a result, a low-concentration P-type layer (P-type layer) 8 is formed in the wafer 1. Thereafter, aluminum or a laminated metal (V / Nc / Au) is deposited by sputtering or the like to form a collector electrode (FIG. 2).
(C)).

FIG. 3 is a characteristic curve showing an impurity concentration profile in the collector region of FIG. 2C using the present invention. In the present invention, by irradiating the laser beam to the back surface of the wafer 1, the influence is given only to the back surface of the wafer 1,
It is possible to suppress the application to the surface of the wafer 1.

It should be noted that the manufacturing method of the present invention exerts the same effect as described above even when employed in a light-trigger type thyristor, a reverse element type GTO thyristor, and the like.

Next, the laser annealing apparatus of the present invention used in the above steps will be described.

FIG. 4 is a block diagram of a laser annealing apparatus according to the present invention. That is, mirrors 23 and 24, a homogenizer 25, a mirror 26, an imaging lens 27, and a chamber 28 are sequentially provided in front of the laser oscillator 21 on the optical axis according to the path of the laser light 22. Chamber 28
A window 29 made of synthetic quartz glass is formed in a ceiling portion facing the image forming lens 27, a concave mirror 32 is provided below the inside of the chamber 28, and an XY table 30 provided therebelow. In FIG. 1, a semiconductor substrate 31 to be processed is placed with its back surface facing upward. The surface of the semiconductor substrate 31 is protected by a protective tape and is in contact with the XY table 30. The laser oscillator 21 is connected to a computer 34 via a controller 33.

The repetition frequency of laser oscillation is 200
Hz or 300 Hz, the laser irradiation beam size to the semiconductor substrate 31 is a square beam of 1 mm 5 mm square, and the entire surface of the semiconductor substrate 31 of 5 inches, 6 inches or 8 inches is overlapped by 100 μm to 200 μm with an XY table. Scan by 30. The operation of the XY table 30 and the control of the laser oscillator 21 at that time are performed by the computer 34 and the controller 33.

The concave mirror 32 has a hole diameter φ500 μm-5
A hole 36 mm is provided. The mirror surface is formed by depositing aluminum or using a quartz substrate on which a dielectric multilayer film such as magnesium fluoride (MgF ₂ ) is formed.

With these configurations, the laser light 22 output from the laser oscillator 21 is reflected by the mirrors 23 and 24.
The laser light 22 is guided to a beam homogenizer 25 for making the spatial intensity distribution uniform, and is reflected by a mirror 26 and an imaging lens 27.
A semiconductor substrate 31 arranged on an XY table 30 is irradiated from a window 29 made of synthetic quartz glass into a chamber 28 equipped with vacuum evacuation equipment.

The chamber 2 directly above the semiconductor substrate 31
The concave mirror 32 fixed to 8 irradiates the semiconductor substrate 31 with the light reflected from the semiconductor substrate 31 being reflected by the concave mirror 32. Therefore, both the direct light irradiated from the laser oscillator 21 via the angular optical system and the indirect light reflected by the concave mirror 32 are irradiated on the upper surface of the semiconductor substrate 31 in a superimposed manner.

FIG. 5 is an explanatory diagram showing the relationship between the imaging lens 27 and the concave mirror 32. N of the imaging lens 27
Let α be the angle of incidence determined by A, f be the distance to the focus point, and a be the distance from the focus point to the semiconductor substrate 31. The position of the concave mirror 32 is such that the center of the concave surface is the laser beam 2.
This is the position of the focal point of No. 2. The curvature R of the reflection surface of the concave mirror 32 is twice as long as the distance a from the converging point to the semiconductor substrate 31. The size of the concave mirror 32 is D, and the size of the imaging lens 27 is N
Determined by the angle α determined by A, D = 2 × 2a ×
tanα.

When the NA of the imaging lens 27 is 0.2 and the diameter d of the laser incident light on the imaging lens 27 is 30 mm, the distance f from the imaging lens 27 to the focal point is f =
(D / 2) / tan (sin- ¹ 0.2) ≒ 73.48
mm, and the distance a from the focal point to the semiconductor substrate 31 is a = 1.25 mm when the imaging magnification is 1/6,
From the curvature R of the concave mirror 32 = 2 × a, R ≒ 24.49 m
m.

The outer shape D of the concave mirror 32 is D = 2 ×
D = 10 mm from 2a × tan α. With this concave mirror 32, the energy loss of the laser beam 22 was reduced from 50% to about 25%.

As described above, according to the present invention, in order to reduce the 50% reflectance loss of the laser light 22, the reflected light of the irradiated laser light 22 is again applied to the semiconductor substrate 3.
A concave mirror 32 that reflects light toward the mirror 1 is provided directly above the semiconductor substrate 31. The concave mirror 32 has a hole 36 for allowing the pulsed laser light 22 to pass therethrough, and the size thereof is φ500 μm.
The incident NA of the pulsed laser beam 22 for irradiating the semiconductor substrate 31 is set to 0.2 or less, the reflection surface of the concave mirror 32 is an Al vapor-deposited film or a dielectric multilayer film, and the arrangement position is the substrate position. From the focal length of the imaging lens 27. As a result, about 25% of the 50% reflected from the semiconductor substrate 31 is re-irradiated to the semiconductor substrate 31, and the loss of the laser beam 22 can be reduced from 50% to about 25%. became.

Therefore, it is possible to activate boron while reducing the loss of the laser beam 22, and the IGBT, P
It is possible to realize an ideal concentration profile of the intact substance for the back electrode of the lower-MOS.

[0040]

According to the present invention, it is possible to obtain a method and an apparatus for manufacturing a semiconductor device in which the energy loss of laser light is greatly reduced and an ideal impurity concentration profile is realized for the back electrode of the semiconductor substrate.

[Brief description of the drawings]

FIG. 1 shows an embodiment of a semiconductor device according to the present invention.
Sectional drawing of GBT.

FIGS. 2A to 2C are partial cross-sectional views sequentially showing a process of forming a back surface of a wafer 1 which is important in the present invention.

FIG. 3 is a characteristic diagram showing an impurity concentration profile in the collector electrode of FIG. 2 (c).

FIG. 4 is a configuration diagram of a laser annealing apparatus of the present invention.

FIG. 5 is an explanatory diagram showing a relationship between an imaging lens and a concave mirror of the laser annealing apparatus of the present invention.

[Explanation of symbols]

1 wafer, 2 gate electrodes 2, 3P base region, 4N +
Emitter region, 5 insulating film, 6 emitter electrode, 7 collector electrode, 8 low-concentration P-type layer, 21 laser oscillator, 27 imaging lens, 28 chamber, 32 concave mirror

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 29/78 658A

Claims (7)

[Claims] 1. A method for manufacturing a semiconductor device, wherein an impurity is ion-implanted into the semiconductor substrate when a back electrode of the semiconductor substrate is formed, and the impurity is activated by heat treatment. And irradiating the semiconductor substrate with the light through an optical system, and reflecting the reflected light from the semiconductor substrate with a mirror and irradiating the semiconductor substrate with the reflected light. 2. A pulse laser emitted from the laser oscillator is an XeCl excimer laser or a KrF excimer laser, and the intensity of the laser light is 0.1 mm on the semiconductor substrate surface.
The method as claimed in claim 1, wherein the at 5 J / cm ² or more and 2.5 J / cm ² or less. 3. The mirror has a concave reflecting portion, is provided on an optical axis of laser light emitted from the laser oscillator, and allows the pulsed laser light to pass through a hole formed in a central portion. 2. The method according to claim 1, further comprising irradiating the semiconductor substrate, and reflecting light reflected from the semiconductor substrate on the reflection surface to the semiconductor substrate. 4. An apparatus for manufacturing a semiconductor device, wherein an impurity is ion-implanted into the semiconductor substrate when a back electrode of the semiconductor substrate is formed, and the impurity is activated by a heat treatment means, wherein the heat treatment means emits light from a laser oscillator. Irradiating means for irradiating the semiconductor substrate with laser light via an optical system, and a concave mirror for reflecting light reflected from the semiconductor substrate on a concave mirror surface and irradiating the semiconductor substrate with the reflected light. Semiconductor device manufacturing equipment. 5. The semiconductor device manufacturing apparatus according to claim 4, wherein said concave mirror has a mirror surface which is an aluminum evaporation surface or a dielectric multilayer film surface. 6. An arrangement position of said concave mirror is a position of a focal length of an imaging lens forming said optical system on an optical axis immediately above said semiconductor substrate. Semiconductor device manufacturing equipment. 7. The apparatus according to claim 6, wherein the curvature of the concave mirror has a value twice as long as a distance from a focal length of the imaging lens to the semiconductor substrate.