JP7699561B2 - Semiconductor device manufacturing method and semiconductor manufacturing apparatus - Google Patents

Description

This disclosure relates to a semiconductor device manufacturing method and semiconductor manufacturing apparatus that perform laser annealing.

Conventionally, the following laser annealing device is known. That is, it is equipped with a glass processing stage, and the front surface of a semiconductor wafer is fixed to the wafer mounting surface of the processing stage by suction. Then, while the semiconductor wafer is cooled from the front surface side on the wafer mounting surface, a laser beam is irradiated onto the back side of the semiconductor wafer, and laser annealing is performed.

In such laser annealing devices, if the size of the processing stage, in other words the size of the wafer mounting surface, becomes larger than the size of the semiconductor wafer, there is a concern that vibrations of the device will occur. For this reason, a processing stage smaller than the size of the semiconductor wafer is used. In this case, because the processing stage is responsible for cooling the semiconductor wafer, a difference in the degree of annealing will occur between the outer periphery and the non-outer periphery of the semiconductor wafer that is placed on the wafer mounting surface of the processing stage and subjected to laser annealing.

In laser annealing, the scanning of the laser beam irradiated onto the semiconductor wafer is performed, for example, as follows. That is, if the surface including the back surface of the semiconductor wafer subjected to laser annealing is taken as the XY plane, the laser beam scans in the Y positive direction, shifts the position by one pitch in the X direction at the turning point, then scans in the Y negative direction, shifts the position by one pitch in the X direction again at the turning point, and scans again in the Y positive direction, and this process is repeated.

For example, in Patent Document 1, the power of the laser beam irradiated onto the semiconductor wafer is changed according to the Y-direction position of the scanned laser beam. This is intended to achieve uniform annealing.

JP 2013-74247 A

In the case of the above-mentioned laser beam scanning, non-uniform annealing occurs between the vicinity of the turning point on the outer periphery of the semiconductor wafer and other locations. This is because, near the turning point, the time interval between the laser irradiation in the Y positive direction scan and the laser irradiation in the Y negative direction scan, which is shifted one pitch in the X direction from the Y positive direction scan, is short, and the laser irradiation is performed in a state where the semiconductor wafer is not sufficiently cooled. The technology of Patent Document 1 does not take this into consideration.

The present disclosure aims to provide a semiconductor device manufacturing method and semiconductor manufacturing apparatus that can suppress uneven annealing that occurs between the outer periphery and non-outer periphery of a semiconductor wafer.

In one aspect, the method for manufacturing a semiconductor device according to the present disclosure includes a laser annealing step of irradiating a semiconductor wafer with a laser beam and performing heat treatment of the semiconductor wafer, the laser annealing step includes a step of scanning the laser beam irradiated to the semiconductor wafer, in which the laser beam is scanned in a positive direction of a first direction, shifted by a plurality of pitch positions in a second direction perpendicular to the first direction at a turning point, then scanned in the negative direction of the first direction, shifted by a plurality of pitch positions in the second direction at a turning point again, and then scanned in the positive direction of the first direction, and this is repeated, the pitch being the interval between adjacent scans in the positive direction of the first direction or the negative direction of the first direction in the second direction , and the scanning speed of the laser beam is slower when the laser beam is irradiated to a portion other than the outer periphery of the semiconductor wafer than when the laser beam is irradiated to the outer periphery of the semiconductor wafer .

Moreover, in one aspect, the semiconductor manufacturing apparatus of the present disclosure includes a laser annealing device that irradiates a semiconductor wafer with a laser beam and performs heat treatment of the semiconductor wafer, the laser annealing device includes a scanning mechanism that scans the laser beam irradiated to the semiconductor wafer, and in the scanning, the laser beam is scanned in a positive direction in a first direction, shifted by a plurality of pitch positions in a second direction perpendicular to the first direction at a turning point, then scanned in the negative direction in the first direction, shifted by a plurality of pitch positions in the second direction at a turning point again, and then scanned in the positive direction in the first direction, and this is repeated, the pitch being the interval between adjacent scans in the positive direction of the first direction or the negative direction of the first direction in the second direction, and the scanning speed of the laser beam is slower when the laser beam is irradiated to a portion other than the outer periphery of the semiconductor wafer than when the laser beam is irradiated to the outer periphery of the semiconductor wafer .

The present disclosure provides a semiconductor device manufacturing method and semiconductor manufacturing apparatus that can suppress uneven annealing that occurs between the outer periphery and non-outer periphery of a semiconductor wafer.

4A and 4B are diagrams for explaining laser beam scanning by a scanning mechanism. 10 is a diagram illustrating the length of time until the next irradiation of the laser beam. FIG. 11 is a diagram conceptually showing a configuration of a laser annealing device provided in a semiconductor manufacturing apparatus according to a second embodiment. FIG. FIG. 11 is an explanatory diagram showing scanning of a laser beam according to a first modified example of the first embodiment. 1 is a diagram conceptually showing a configuration of a laser annealing device provided in a semiconductor manufacturing apparatus according to a first embodiment; 6 is a flow chart showing steps of a laser annealing process in a method for manufacturing a semiconductor device using the laser annealing apparatus of FIG. 5 . FIG. 11 is a diagram showing an example of a method for setting the scanning speed of a laser beam. 13 is an explanatory diagram showing scanning of a laser beam according to a second modification of the first embodiment; FIG.

<A. First embodiment>
<A-1. Configuration of semiconductor manufacturing equipment>
FIG. 5 is a diagram conceptually showing the configuration of a laser annealing device provided in the semiconductor manufacturing apparatus according to the first embodiment.

As shown in FIG. 5, the laser annealing device includes a glass stage 1, a stage base 2, a cooling section 3, an adsorption line 4, and a laser oscillator 5.

The glass stage 1 carries a semiconductor wafer 6. The semiconductor wafer 6 is fixed to the carrying surface of the glass stage 1 by suction through the suction line 4. Impurity ions are implanted into the back side of the semiconductor wafer 6. The semiconductor wafer 6 is placed with its front side facing the glass stage 1 so that the back side can be heat-treated (i.e., laser annealing) by irradiation with a laser beam 7 from a laser oscillator 5. The impurity ions implanted into the back side of the semiconductor wafer 6 can be activated by performing the laser annealing. The semiconductor wafer 6 is formed using a semiconductor material made of, for example, Si or SiC.

The stage base 2 supports the glass stage 1 or is formed integrally with the glass stage 1. A cooling unit 3 is attached to the stage base 2, which is in contact with or integral with the glass stage 1, and this cools the semiconductor wafer 6 from the front surface of the semiconductor wafer 6 (i.e., the surface in contact with the mounting surface of the glass stage 1) when performing laser annealing.

<A-2. Manufacturing method of semiconductor device>
Next, a method for manufacturing a semiconductor device according to the first embodiment using the laser annealing apparatus of Fig. 5 will be described. Fig. 6 is a flow chart showing the steps of a laser annealing process in the method for manufacturing a semiconductor device using the laser annealing apparatus of Fig. 5. As shown in Fig. 6, the steps of the laser annealing process include a preparation step S1 and a laser annealing step S2.

In the preparation step S1, a process of ion-injecting impurities into the back side of the semiconductor wafer 6 is performed. Then, the semiconductor wafer 6 is placed on the glass stage 1 and fixed by suction via the suction line 4. At this time, the semiconductor wafer 6 is positioned so that the front surface of the semiconductor wafer 6 faces the mounting surface of the glass stage 1 so that the back side of the semiconductor wafer 6 can be irradiated with a laser beam 7 from a laser oscillator 5 and heat-treated. The impurities ion-injected into the semiconductor wafer 6 are, for example, phosphorus, arsenic, or protons if they are n-type impurities. The injected impurities are activated by the laser annealing step S2, and become, for example, a buffer layer of an IGBT (Insulated-Gate Bipolar Transistor) or a cathode layer of a diode in an IGBT or diode as a semiconductor device.

In the laser annealing step S2, the semiconductor wafer 6 placed on the glass stage 1 is annealed by irradiating it with a laser beam 7 from a laser oscillator 5 while being cooled by a cooling unit 3. The wavelength of the laser beam 7 is, for example, 350 nm to 600 nm. Specifically, for example, the second harmonic of a Nd:YAG laser (the wavelength of the second harmonic is 532 nm), a second harmonic of a solid laser such as an Nd:YLF laser or an Nd:YVO4 laser may be used as the laser beam 7. With a laser with a wavelength band longer than the above, such as a carbon dioxide laser (the wavelength of the carbon dioxide laser is, for example, 9 μm to 10 μm), the activation heat treatment is performed not only on the back surface of the semiconductor wafer 6 but also on the front surface side. Therefore, it is desirable to use a laser with the above wavelength band in terms of the relationship between the depth to be activated and the depth to which heat is not to be transferred.

As shown in FIG. 5, the laser annealing apparatus is provided with a scanning mechanism 8 for scanning the laser beam 7 irradiated onto the semiconductor wafer 6. The scanning mechanism 8 changes the irradiation position of the laser beam 7 irradiated from the laser oscillator 5 toward the semiconductor wafer 6 on the glass stage 1 with respect to the semiconductor wafer 6 over time. That is, the scanning mechanism 8 scans the irradiation position of the laser beam 7 on the semiconductor wafer 6 on the irradiated surface of the semiconductor wafer 6 (the back surface of the semiconductor wafer 6 in this embodiment). The scanning mechanism 8 may be any mechanism that can change the relative position between the laser beam 7 and the semiconductor wafer 6 over time. For example, the scanning mechanism 8 may move the laser beam 7 irradiated from the laser oscillator 5 over time. Also, for example, the scanning mechanism 8 may move the stage base 2 over time. Furthermore, for example, the scanning mechanism 8 may move both the laser beam 7 and the stage base 2 over time.

Figure 1 is a diagram for explaining the scanning of the laser beam 7 by the scanning mechanism 8. Figure 1 (a) shows a typical conventional scanning, and Figure 1 (b) shows a typical scanning according to the present embodiment. Here, the right direction of the paper is the positive first direction, the left direction of the paper is the negative first direction, and the up-down direction of the paper is the second direction. The scanning in the positive first direction or the negative first direction is also simply called the scanning in the first direction. The interval between adjacent first direction scans in the second direction is set to pitch p. The numbers in the symbols of the first direction scans SC1, SC2, SC3, SC4, and SC5 indicate the order of the scans. Note that between two adjacent first direction scans in the second direction, irradiation may be performed with the laser beam 7 overlapped by n percent. n is a variable parameter that can be set in the laser annealing device.

First, the conventional scanning shown in FIG. 1(a) will be described. In a laser annealing process for performing heat treatment on a semiconductor wafer 6, when scanning a laser beam 7 irradiated onto the semiconductor wafer 6, the laser beam 7 is scanned in a first direction, in the positive direction, shifted by one pitch p in a second direction perpendicular to the first direction at a turning point t, then scanned in the first direction, in the negative direction, shifted by one pitch p in the second direction again at a turning point t, then scanned in the first direction, in the positive direction, and this process is repeated.

In this way, in conventional scanning, one outward (or return) in the first direction and the subsequent return (or outward) in the first direction are always adjacent to each other. That is, the distance in the second direction shifted at the turning point t is always the shortest, one pitch p. Therefore, in conventional scanning, the outer periphery of the semiconductor wafer 6 is over-annealed, and the sheet resistance in the surface of the semiconductor wafer 6 varies between the outer periphery and its inner part. This is because, in the outer periphery of the semiconductor wafer 6 close to the turning point t, after irradiation with the laser beam 7 by one first direction scanning, irradiation with the laser beam 7 by the next first direction scanning is performed shortly after the outer periphery is sufficiently cooled. Figure 2 is a diagram illustrating the length of time until the next irradiation of the laser beam 7 in adjacent first direction scanning. In Figure 2, path 7a shows the scanning path of the laser beam 7 in the vicinity of the turning point t.

Next, scanning according to the present embodiment in FIG. 1(b) will be described. In the laser annealing step S2 for performing heat treatment of the semiconductor wafer 6, when scanning the laser beam 7 irradiated to the semiconductor wafer 6, the laser beam 7 is scanned in the first direction in the positive direction, shifted by a number of pitches x·p in the second direction perpendicular to the first direction at the turning point t, then scanned in the first direction in the negative direction, shifted by a number of pitches x·p in the second direction again at the turning point t, and then scanned in the first direction in the positive direction, and this is repeated. x is an integer and is a variable that may be different for each turn, and is a variable that is set in the laser annealing device, for example. Shifting the position by a number of pitches in the second direction includes shifting the position by a number of pitches in one direction of the second direction and shifting the position by a number of pitches in the other direction of the second direction.

In this way, according to the scanning of this embodiment, the outward (or return) path in one first direction and the subsequent return (or outward) path in one first direction are not adjacent to each other. That is, the distance in the second direction shifted at the turning point t is a plurality of pitches x·p. Therefore, according to the scanning of this embodiment, the outer periphery of the semiconductor wafer 6 is prevented from being over-annealed, and the occurrence of variations in the sheet resistance in the surface of the semiconductor wafer 6 between the outer periphery and its inner part is prevented. This is because, in the outer periphery of the semiconductor wafer 6 close to the turning point t, after the laser beam 7 is irradiated by the scanning of one first direction, time is ensured for cooling, and then the laser beam 7 is irradiated by the scanning of another first direction adjacent to the scanning of the one first direction.

The semiconductor device manufacturing method and semiconductor manufacturing apparatus according to this embodiment are particularly effective when the area of the semiconductor wafer 6 mounting surface of the glass stage 1 placed on the stage base 2 having the cooling section 3 is smaller than the area of the semiconductor wafer 6, making it difficult to cool the outer periphery of the semiconductor wafer 6.

The laser beam 7 is preferably irradiated perpendicularly to the semiconductor wafer 6. Alternatively, the laser beam 7 is preferably irradiated perpendicularly to the glass stage 1. This is because the depth to which heat is transferred in the semiconductor wafer 6 is more likely to be uniform and the thermal profile is more likely to be uniform when the laser beam 7 is irradiated perpendicularly to the semiconductor wafer 6 than when the laser beam 7 is irradiated obliquely to the semiconductor wafer 6. Even when the irradiation power of the laser beam 7 is changed during scanning, as in the modified example described below, perpendicular incidence is more preferable than oblique incidence, which allows for a stable heat treatment temperature and suppresses unevenness in the heat treatment by laser annealing between the outer periphery and the non-outer periphery of the semiconductor wafer 6. Here, perpendicular refers not only to the case where the angle between the surface and the line is strictly 90 degrees, but also to the case where the angle is 85 degrees or more.

<A-3. Modification 1>
4 is an explanatory diagram showing scanning of the laser beam 7 according to the first modification. In the first modification, as shown in FIG. 4, the scanning speed of the laser beam 7 by the scanning mechanism 8 is high when the laser beam 7 is irradiated to the outer periphery of the semiconductor wafer 6, and is low when the laser beam 7 is irradiated to the other part of the semiconductor wafer 6. That is, the scanning speed of the laser beam 7 is slower when the laser beam 7 is irradiated to the other part of the semiconductor wafer 6 than when the laser beam 7 is irradiated to the other part of the semiconductor wafer 6. By changing the scanning speed of the laser beam 7 by the scanning mechanism 8 between the outer periphery and the other part according to the sheet resistance distribution of the semiconductor wafer 6 between the outer periphery and the other part, which is grasped in advance, it is possible to suppress non-uniformity of annealing.

For example, if the sheet resistance of the semiconductor wafer 6 other than the outer periphery is high as determined in advance, the scanning speed is slowed down when the laser beam 7 is irradiated to the outer periphery of the semiconductor wafer 6, and if the sheet resistance of the outer periphery is low as determined in advance, the scanning speed is increased when the laser beam 7 is irradiated to the outer periphery of the semiconductor wafer 6. For example, if the sheet resistance is higher outside the outer periphery than outside the outer periphery as shown in FIG. 7 when the scanning speed of the laser beam 7 is constant, that is, when the scanning speed of the laser beam 7 is the same between the outer periphery and the outer periphery, the sheet resistance is uniformed by scanning the laser beam 7 faster in the outer periphery than outside the outer periphery, as shown in FIG. 7.

The change in the scanning speed of the laser beam 7 is not limited to the two-step change described above, but may be a multiple-step change of three or more steps.

<A-4. Modification 2>
8 is an explanatory diagram showing scanning of the laser beam 7 according to the second modification. As shown in FIG. 8, the power of the laser beam 7 scanned by the scanning mechanism 8 is low when the laser beam 7 is irradiated to the outer periphery of the semiconductor wafer 6, and is high when the laser beam 7 is irradiated to the other part of the semiconductor wafer 6. That is, the power of the scanned laser beam 7 is higher when the laser beam 7 is irradiated to the other part of the semiconductor wafer 6 than when the laser beam 7 is irradiated to the other part of the semiconductor wafer 6. By changing the power of the laser beam 7 when irradiating the outer periphery and when irradiating the other part of the semiconductor wafer 6 according to the sheet resistance distribution of the outer periphery and the other part of the semiconductor wafer 6 that is grasped in advance, it is possible to suppress non-uniformity in annealing.

For example, if the sheet resistance of the semiconductor wafer 6 other than the outer periphery is high as determined in advance, the power is increased when the laser beam 7 is irradiated to the other part of the semiconductor wafer 6 other than the outer periphery, and if the sheet resistance of the semiconductor wafer 6 other than the outer periphery is low as determined in advance, the power is decreased when the laser beam 7 is irradiated to the outer periphery of the semiconductor wafer 6.

It is desirable to change the power during scanning without stopping the scanning of the laser beam 7, which can improve throughput. Note that the change in power of the laser beam 7 is not limited to the two-step change described above, but may be a multiple-step change of three or more steps. In addition, it is also possible to combine variants 1 and 2 and change both the scanning speed and the power.

<B. Second embodiment>
Fig. 3(b) is a conceptual diagram showing the configuration of a laser annealing apparatus provided in a semiconductor manufacturing apparatus according to embodiment 2. The difference from the laser annealing apparatus of Fig. 5 according to embodiment 1 is that, instead of the scanning mechanism 8 of Fig. 5, a rotary movement mechanism 9 is provided as a scanning mechanism for scanning a laser beam 7 in Fig. 3(b). Since the other configurations are the same, a description of the same components will be omitted.

The rotational movement mechanism 9, which serves as a scanning mechanism for scanning the laser beam 7, is disposed under the stage base 2 and scans the laser beam 7. In this embodiment, for example, the irradiation position of the laser beam 7 is fixed. The rotational movement mechanism 9 rotates the stage base 2 about its central axis and moves it in the in-plane direction of the semiconductor wafer 6 (i.e., in the direction indicated by the dashed arrow 9a). As a result, the semiconductor wafer 6 placed on the glass stage 1 also moves in the direction indicated by the dashed arrow 9a while rotating about its central axis while being irradiated with the laser beam 7. As a result, as shown in FIG. 3(a), the laser beam 7 follows the path 7b and is scanned in a spiral shape from the outer periphery of the semiconductor wafer 6 to the center.

Compared to the first embodiment, the laser beam 7 can be scanned in a spiral pattern to perform heat treatment without reversing the scanning direction of the laser beam 7 at each turning point, improving throughput. Also, at the outer periphery of the semiconductor wafer 6, the distance of rotational movement from one irradiation position by the laser beam 7 to the adjacent next irradiation position is long, and after irradiation with the laser beam 7 is performed at the outer periphery of the semiconductor wafer 6, the next irradiation with the laser beam 7 is performed after the outer periphery is sufficiently cooled. As a result, over-annealing at the outer periphery of the semiconductor wafer 6 is suppressed, and the occurrence of variations in the sheet resistance within the surface of the semiconductor wafer 6 between the outer periphery and its inside is suppressed.

The configuration described in the first or second modification of the first embodiment may be combined with the second embodiment. In this case, the scanning speed or power of the laser beam 7 needs to be changed only once, for example, at a specific point in the spiral scanning path 7b. Since the number of changes is small, throughput is improved.

The semiconductor wafer 6 is, for example, circular and has a diameter of 6 to 12 inches. This embodiment is effective for larger semiconductor wafers such as 12 inches, where improving throughput is more important.

In the first embodiment, the number of times the process of reversing the scanning direction of the laser beam 7 increases as the diameter of the semiconductor wafer increases, but in the present embodiment, the process of reversing the scanning direction of the laser beam 7 is not necessary, so this embodiment is more effective for semiconductor wafers with larger diameters.

In addition, in Modification 1 or Modification 2 of Embodiment 1, the larger the diameter of the semiconductor wafer, the more the number of times the irradiation speed or power of the laser beam 7 is changed. However, when the configuration described in Modification 1 or Modification 2 of Embodiment 1 is combined with this embodiment, the number of times the irradiation speed or power of the laser beam 7 is changed does not need to be increased even if the diameter of the semiconductor wafer increases. Therefore, the configuration in which the configuration described in Modification 1 or Modification 2 of Embodiment 1 is combined with this embodiment is more effective for semiconductor wafers with larger diameters.

The embodiments can be freely combined, modified, or omitted as appropriate.

1 Glass stage, 2 Stage base, 3 Cooling section, 4 Adsorption line, 5 Laser oscillator, 6 Semiconductor wafer, 7 Laser beam, 8 Scanning mechanism, 9 Rotational movement mechanism.

Claims (5)

A laser annealing step of irradiating a semiconductor wafer with a laser beam to perform a heat treatment of the semiconductor wafer,
The laser annealing step includes:
Scanning the laser beam irradiated onto the semiconductor wafer,
In the scanning, the laser beam is scanned in a positive direction of a first direction, shifted by a plurality of pitch positions in a second direction perpendicular to the first direction at a turning point, scanned in a negative direction of the first direction, shifted by a plurality of pitch positions in the second direction at a turning point again, and then scanned in the positive direction of the first direction, and this is repeated;
the pitch is an interval between adjacent scans in the positive direction of the first direction or the negative direction of the first direction in the second direction,
a scanning speed of the laser beam is slower when the laser beam is irradiated to a portion other than the outer periphery of the semiconductor wafer than when the laser beam is irradiated to the outer periphery of the semiconductor wafer;
A method for manufacturing a semiconductor device. A laser annealing step of irradiating a semiconductor wafer with a laser beam to perform a heat treatment of the semiconductor wafer,
The laser annealing step includes:
Scanning the laser beam irradiated onto the semiconductor wafer,
In the scanning, the laser beam is scanned in a spiral manner from the outer periphery to the center of the semiconductor wafer ,
under the assumption that the scanning speed of the laser beam is the same for the outer periphery of the semiconductor wafer and the other part, when the sheet resistance of the other part of the semiconductor wafer is higher than the sheet resistance of the outer periphery, the scanning speed of the laser beam is slower when the laser beam is irradiated to the other part of the semiconductor wafer than when the laser beam is irradiated to the outer periphery of the semiconductor wafer;
A method for manufacturing a semiconductor device. 3. The method for manufacturing a semiconductor device according to claim 1, further comprising the steps of:
The laser beam is irradiated perpendicularly to the semiconductor wafer.
A method for manufacturing a semiconductor device. a laser annealing device that irradiates a semiconductor wafer with a laser beam and performs heat treatment on the semiconductor wafer;
The laser annealing apparatus is
a scanning mechanism for scanning the laser beam irradiated onto the semiconductor wafer,
In the scanning, the laser beam is scanned in a positive direction of a first direction, shifted by a plurality of pitch positions in a second direction perpendicular to the first direction at a turning point, scanned in a negative direction of the first direction, shifted by a plurality of pitch positions in the second direction at a turning point again, and then scanned in the positive direction of the first direction, and this is repeated;
the pitch is an interval between adjacent scans in the positive direction of the first direction or the negative direction of the first direction in the second direction,
a scanning speed of the laser beam is slower when the laser beam is irradiated to a portion other than the outer periphery of the semiconductor wafer than when the laser beam is irradiated to the outer periphery of the semiconductor wafer;
Semiconductor manufacturing equipment. a laser annealing device that irradiates a semiconductor wafer with a laser beam and performs heat treatment on the semiconductor wafer;
The laser annealing apparatus is
a scanning mechanism for scanning the laser beam irradiated onto the semiconductor wafer,
In the scanning, the laser beam is scanned in a spiral manner from the outer periphery to the center of the semiconductor wafer ,
under the assumption that the scanning speed of the laser beam is the same for the outer periphery of the semiconductor wafer and the other part, when the sheet resistance of the other part of the semiconductor wafer is higher than the sheet resistance of the outer periphery, the scanning speed of the laser beam is slower when the laser beam is irradiated to the other part of the semiconductor wafer than when the laser beam is irradiated to the outer periphery of the semiconductor wafer;
Semiconductor manufacturing equipment.

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