JPS62216318A - Laser annealing apparatus - Google Patents

Abstract

PURPOSE:To stably and uniformly perform a laser annealing by aligning the optical axis of an oscillation tube of a gas laser unit in Y direction perpendicular to X direction reciprocating at high speed to avoid the variation in the output of the laser unit due to an impact generated by the reciprocation of X, Y stages. CONSTITUTION:Since an impact becomes perpendicular to an optical axis of a laser unit 10 when the optical axis of the laser unit 10 is directed to Y direction, it is avoided to vary the position of an oscillation mirror. In other words, the mirror is held by a spring and a micrometer mechanism to be movable in X direction, but sufficiently rigidly supported by bearings in the Y direction, thereby ignoring the variation in the position. Since a distance between the mirrors as to the laser oscillation is not varied even if the position varies, a power value does not alter.

Description

[Detailed Description of the Invention] [Summary] A laser annealing device in which the optical axis direction of the laser device main body is perpendicular to the direction of high-speed movement of the stage to avoid adverse effects on the laser device due to impact.

[Industrial application field]

The present invention relates to an apparatus for converting polycrystalline silicon on a wafer into a single crystal by laser annealing.

[Conventional technology]

The laser recrystallization method uses SOI (Silicon O
n In5ul-ator) structure MOS F[! This is an effective method for producing T. MOSF with SOI structure
Since ET can be used to produce high-speed, highly integrated ICs (integrated circuits) such as 5OI-ICs and three-dimensional ICs, much research and development has been carried out on laser recrystallization methods in recent years.

The laser recrystallization apparatus has a configuration schematically shown in FIG. 1
0 is a gas laser device, 12, 14.16 is a mirror, 18
20 is a focusing lens, and 20 is a silicon wafer which is held by a heating device (actual chuck) 22. 26
is an X stage (X direction moving mechanism), on which a Y stage (Y direction moving mechanism) 24 is attached, and a heating device 22
rides the Y stage.

The wafer 20 is, for example, 400 wafers as shown in FIG. 3(a).
It consists of silicon dioxide SiO2 with a thickness of about 1.0 μm, which is formed by thermally oxidizing the surface of the silicon substrate S I % with a thickness of μm, and polycrystalline silicon poli-3t formed thereon by the CVD method. The laser device 10 is an argon gas laser, and as shown in FIG.
a, and oscillation mirrors 10b and 10c at both ends thereof.

The laser beam 30 emitted from the laser device 10 has a diameter of about 2 fl, is guided by the mirrors 12, 14, and 16 as shown in the figure, is focused by the lens 18 to a diameter of 20 to 100 μm, and is directed onto the wafer 20.
is projected on. When the laser beam is projected onto the wafer, the polycrystalline silicon in the top layer of the wafer, which has already been heated to about 500°C by the heating device 22, immediately melts, causing
As the Y stage 26 and 24 move in the X and Y directions, the polycrystalline silicon layer melts completely as shown in Figure 3 (C1).
Solidification takes place, resulting in single crystallization. This third
Figure (1.2 in C1... is the first time, second time, etc.
. . . shows the regions melted and solidified by movement in the X direction (although this is for illustration purposes only), these are narrow band-shaped regions having a width equal to the diameter of the laser beam. Since this is a full-surface filling process, these band-shaped areas are slightly irregular in shape. Arrows indicate the direction of movement.

[Problem that the invention seeks to solve]

In laser annealing, the wafer is irradiated with a narrow laser beam of 20 μm (the irradiation position is fixed), then the wafer is moved in the X direction, then moved in the Y direction by a minute length, and then moved in the same X direction but in the opposite direction. The wafer is melted and solidified over its entire surface by moving in a zigzag pattern. The above-mentioned micro length in the Y direction is 20 μm or less in this example because the melting and solidifying zones are overlapped, and in order to melt and solidify the entire wafer, the processing will require a long time unless the moving speed is high. .

Therefore, to improve throughput, the scanning speed was set to 30Qw/s.
Since it is a reciprocating motion, the acceleration is 1 to Ion/s2. By the way, the wafer itself is lightweight and has no problem with high speed and high acceleration.
The heating device 22 is heavy and has difficulty in high acceleration. As shown in FIG. 3(d) (el), the heating device 22 consists of an intake/exhaust mechanism for vacuum suctioning the wafer, a heater for heating, and a water cooling mechanism for not heating the X and Y stages, and has a diameter of 6" φ. For wafers, it weighs more than 18 kg.When such a heavy object moves at high speed, the acceleration is, for example, 5 m/
As s2, the impact during the accelerated movement of the X and Y stages is 2.
0Kg・5m/52=10 It becomes ON, causing misalignment or vibration of the mirror and optical system of the laser device, making precise positioning and long-term stable laser irradiation difficult.

As shown in FIG. 3(b), the laser device 10 includes mirrors 10b and 10c for oscillation placed at both ends of an oscillation tube.
The mirror is held down by a spring and pushed from the opposite side with a micrometer to center it at a desired position, so it can be moved in the direction of the optical axis. Therefore, when the above-mentioned impact is applied in the optical axis direction of the laser device, the mirror position changes and the power value changes.

As long as reciprocating laser scanning is used, the occurrence of impact is unavoidable, but the problem is that the impact reduces the output of the laser device, making uniform laser annealing impossible. Therefore, the present invention aims to make this impact as harmless as possible.

[Means for solving problems]

The present invention includes a gas laser device (10), a device (22) placed on an X, Y stage (26, 24) for holding and heating a wafer (20), and an optical system for projecting laser light from the gas laser device onto the wafer. System (12,14°16,18
), while projecting a laser beam and X.

In a semiconductor manufacturing apparatus in which a Y stage reciprocates a wafer at high speed in the X direction while advancing it in the Y direction to monocrystallize a polycrystalline silicon layer on the wafer surface, the optical axis of the oscillation tube of a gas laser device is It is characterized by being aligned in the Y direction, which is orthogonal to the X direction.

[Effect]

In laser annealing, the laser beam position is fixed and
, High-speed reciprocation of the wafer in the X direction by the Y stage,
A small step is made in the Y direction, which generates a strong impact force in the X direction. Therefore, as shown in FIG. 2, if the optical axis of the laser device 10 (the optical axis of the oscillation tube) is set in the Y direction, the impact will be in a direction perpendicular to the optical axis, thereby avoiding positional fluctuations of the oscillation mirror. be done. That is, the oscillation mirror is held by a spring and a micrometer mechanism and is movable in the X direction, but is supported sufficiently firmly in the Y direction by bearings, etc., so that positional fluctuations can be ignored. Furthermore, even if there is a positional change, there is no change in the distance between the mirrors involved in laser oscillation (in this case, the distance between the mirrors is that in the Y direction, and the positional change is in the X direction, so they are unrelated to each other), so power value fluctuations etc. will not occur.

〔Example〕

In the present invention, in the laser annealing apparatus shown in FIG. 1, if the optical axis of the laser device 10 is in the horizontal direction, the moving direction of the Y stage is in the horizontal direction that coincides with the optical axis direction of the laser device,
The direction of movement of the X stage is the direction perpendicular to the plane of the paper, which is perpendicular to this direction. This avoids positional fluctuations of the oscillation mirror.

Since there is also a Z direction in the direction orthogonal to the X direction in which it reciprocates at high speed, it is conceivable to place the laser device 10 vertically in FIG. However, in a gas laser device for laser annealing, the oscillation tube has a total length of 2 m and is a double tube, with the inner tube being a vacuum (filled with argon gas) and the space between the outer tube and the inner tube being a passage for cooling water. , the weight including the magnet for shrinking the plasma is 65 kg. Making something like this vertical is tricky and I don't see any examples of that. At most, there are some examples of diagonal arrangement for the purpose of saving space.

The laser device 10 has legs 10d and 10e mounted on a pedestal 28.
It is fixed by fitting it into the stopper.

One of the X and Y scans in laser annealing may be performed by moving the laser beam itself using a rotating or vibrating mirror, and if the high-speed reciprocating movement is performed by deflecting the laser beam, the above-mentioned impact will not occur. , the movement of laser light involves complications. That is, the portion of the laser beam projected onto the wafer in FIG. 1 is as shown in FIG.
is a gicchroic mirror that reflects only the argon laser beam, on which ordinary light is projected by a system of a light source and a half mirror, and the light point of the ordinary light projected onto the wafer 20 through the lens 18 is transmitted to the trinocular tube. View through the observation window and move the lens 18 up and down to make the diameter of the light spot a desired diameter. This also adjusts the light spot of the argon laser light on the wafer. Since such a system is attached and laser annealing is performed by performing X and Y scanning with a laser beam spot of a desired diameter with slight overlap, it is difficult to deflect the laser beam.

Note that when the laser beam is deflected by the mirror 16, the angle of incidence of the laser beam on the lens 18 changes, causing problems such as the need to increase the size of the lens and shift of the focal position. Regarding this point, the lens 18 can be moved according to the movement of the mirror 16 so that the focal position is always on the wafer surface, but the mirror 16 is equipped with a rotation mechanism for articulating the laser beam spot position on the wafer 20. Therefore, the above operation is difficult to perform.

Laser annealing is not performed on the entire surface of the wafer;
Scribing lines and bonding band portions of each chip are not performed. When a portion that is not to be laser annealed in the Y direction is reached, that portion is skipped and the process proceeds to the next step, thereby reducing processing time. Some ICs are a mixture of bulk FETs and Sol PETs, and in such ICs, a bulk FET is formed by opening a window in the surface insulating film of the silicon substrate, diffusing the source and drain, and forming a gate insulating film and gate electrode. Since polycrystalline silicon is formed on the surface insulating film, the single crystal is made into a single crystal by laser annealing, and an FET is formed on the single crystal, the area to be subjected to laser annealing is considerably limited. For portions that are not to be laser annealed, the laser light is blocked by a shutter.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to avoid fluctuations in the output of the laser device due to the impact caused by the reciprocating motion of the X and Y stages, and to perform stable and uniform laser annealing, which is extremely effective.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a laser annealing apparatus, FIG. 2 is an explanatory diagram of the principle of the present invention, and FIGS. 3 and 4 are detailed explanatory diagrams of each part. In FIG. 1, 10 is a gas laser device, 22 is a heating device, 20
is a wafer, and 12, 14, 16.18 is an optical system.

Claims (1)

[Claims] Gas laser device (10) and X, Y stage (26, 2
4) includes a device (22) for holding and heating the wafer (20) placed on the wafer, and an optical system (12, 14, 16, 18) for projecting laser light from the gas laser device onto the wafer;
While projecting a laser beam, the wafer is advanced in the Y direction while being reciprocated at high speed in the X direction using the X and Y stages.
A laser annealing device for single-crystallizing a polycrystalline silicon layer on a wafer surface, characterized in that the optical axis of the oscillation tube of the gas laser device is aligned in the Y direction that is orthogonal to the X direction in which the high speed reciprocation occurs. Annealing equipment.