JP7528396B2 - Laser heat treatment equipment - Google Patents

Description

The present invention relates to a laser heat treatment device for heat-treating wafers.

A laser heat treatment apparatus is known which irradiates a wafer or the like with a laser beam to heat it to a desired temperature and performs a desired process at this heating temperature.
As such laser heating processing apparatus, for example, Patent Document 1 describes an apparatus in which a plurality of laser light source units are provided for the entire surface of a semiconductor substrate, a laser light irradiation device corresponding to the shape of the semiconductor substrate is installed, and a laser is irradiated from this laser light irradiation device to the semiconductor substrate surface; Patent Document 2 describes an apparatus for irradiating a laser beam onto the surface of a semiconductor wafer; Patent Document 3 describes an apparatus for irradiating a semiconductor substrate surface with a plurality of laser lights, each with a uniform intensity distribution, to perform processing; and Patent Document 4 describes an apparatus for irradiating the rear surface of a wafer with infrared laser light, the beam of which has a diameter equal to or greater than the diameter of the wafer.

Here, even if the laser light of the same intensity is irradiated, the wafer is not heated uniformly, and the heating temperature varies depending on the location on the surface of the heated object, which may result in uneven heating. If any processing is performed on the surface of the heated object with uneven heating, the subsequent processing results will also reflect the uneven heating, resulting in uneven processing. In addition, the uneven processing may cause damage or deterioration of the coating, or crystal defects in the wafer itself, resulting in a decrease in yield.
For this reason, the laser heat treatment apparatus is required to heat the wafer uniformly.
In order to solve the problem of uneven processing, the surface of the object to be heated is heated gently, that is, the rate of temperature rise caused by heating is made extremely slow, thereby heating the entire surface of the object to a uniform temperature. However, under such gentle heating conditions, the significance of performing laser heating that can heat the wafer quickly is diminished, and the time required for the entire heating process is lengthened, resulting in poor overall productivity. Therefore, gentle heating using a laser heating treatment device is not a realistic method.

JP 2003-77857 A JP 2014-41909 A JP 2013-55111 A JP 2016-1642 A

The objective is to provide a laser heating processing device that can uniformly heat a wafer.

1. A plurality of arms for supporting the outer periphery of a wafer;
a laser beam irradiation device that irradiates a polygonal laser beam onto a lower surface of the wafer, the polygon having an apex positioned on the lower surface of the arm.
2. The polygon is a regular n-sided polygon (n is 4 to 8),
2. The laser heat treatment apparatus according to 1, wherein the arm supports the wafers at equal intervals.
3. Having a hydrogen gas supply line;
3. The laser heat treatment apparatus according to 1. or 2., characterized in that hydrogen annealing is possible.
4. The laser heat treatment apparatus according to any one of 1 to 3, characterized in that it is for use with wafers having a diameter of 4 inches or less.

The laser heat treatment device of the present invention irradiates the lower surface of the wafer with polygonal laser light whose apex is located on the lower surface of the arm supporting the wafer, and heats the arm simultaneously with the wafer. The laser heat treatment device of the present invention can reduce the temperature difference between the wafer and the arm by heating the arm, thereby suppressing heat escape from the wafer to the arm and greatly reducing heating unevenness over the entire wafer. The laser heat treatment device of the present invention, which irradiates the arms at equal intervals and irradiates infrared laser light in a regular n-gon (n is 4 to 8) whose apex is located on the lower surface of the arm, makes heat escape from the wafer to the arm more uniform, and can heat the outer peripheral edge of the wafer in particular uniformly. The laser heat treatment device of the present invention has very high in-plane uniformity of treatment, so that the outer peripheral edge of the wafer can be used without waste, and can increase yield.
The laser heating processing apparatus of the present invention heats the entire surface of the wafer very uniformly, so that processing irregularities resulting from non-uniform heating are very small, and the apparatus can be suitably used, particularly as a hydrogen annealing processing apparatus.
The laser heat treatment apparatus of the present invention can be particularly suitably used for small-diameter wafers having a diameter of 4 inches or less, which are prone to uneven heating.

1 is a schematic diagram of a laser heat treatment apparatus 1 according to a first embodiment. FIG. 4 is a schematic diagram of an example of a holder. FIG. 4 is a diagram showing an example of a tip shape of an arm. 1A and 1B are schematic diagrams showing a state in which an infrared laser beam is irradiated onto a lower surface of a wafer by a laser heating treatment apparatus 1 according to a first embodiment, as viewed from below and from the side. FIG. 4 is a schematic diagram of a laser heat treatment apparatus 2 according to a second embodiment. 5A and 5B are schematic diagrams showing a state in which the underside of a wafer is irradiated with infrared laser light by a laser heating treatment apparatus 2 according to a second embodiment, as viewed from below and from the side.

The laser heat treatment apparatus (hereinafter also referred to as heat treatment apparatus) of the present invention includes a plurality of arms for supporting the outer periphery of a wafer,
a laser light irradiation device for irradiating a polygonal laser light onto the lower surface of the wafer,
The polygon is characterized by having an apex located on the underside of the arm.

The laser heating processing apparatus of the present invention can perform various processes under known heating conditions that have been performed on wafers. For example, it can perform processes such as impurity activation annealing, oxidation, nitridation, diffusion, CVD processing, hydrogen annealing, and argon annealing. In addition, known conditions such as temperature and time during processing can be adopted.

First Embodiment FIG. 1 shows a schematic diagram of a heat treatment apparatus 1 according to a first embodiment of the present invention.
The heat treatment apparatus 1 has a chamber 11 in which a laser heat treatment is performed, and a holder 12 is fixed in this chamber 11. The holder 12 has six arms 13 provided at equal intervals, and the arms 13 support a wafer W.

The wafer W is not particularly limited as long as it is a circular wafer made of various known materials such as silicon, SiC, III-V compounds, etc., and may be a wafer for known applications such as integrated circuits, MEMS, etc. In addition, the wafer may be unprocessed or processed.
The size of the wafer W is not particularly limited, and may range from 10 mm to 450 mm or more in diameter. Small-diameter wafers have a small volume, and are prone to localized temperature drops due to heat loss. The laser heat treatment device of the present invention can suppress heat loss to the arm, and is therefore suitable for use with small-diameter wafers. For example, the diameter of the wafer W is preferably 4 inches or less, more preferably 3 inches or less, and even more preferably 2 inches or less. The diameter of the wafer W is preferably 0.5 inches (12.5 mm) or more.

The chamber 11 can be selected from among known chambers depending on conditions such as the type of heat treatment and the material and size of the wafer W. The chamber 11 has a gate (not shown) for loading and unloading the wafer W. The chamber 11 is provided with a transmission window 111, and the laser light L irradiated from the laser light irradiating device 14 passes through the transmission window 111 and is irradiated onto the lower surface of the wafer W as a regular hexagon whose apex is located on the lower surface of the arm 13.
The chamber 11 may be provided with a window for visually observing or photographing the state of the wafer W, a measurement window for a radiation thermometer for measuring the temperature of the wafer, etc. Furthermore, the chamber 11 may be connected to piping such as a hydrogen gas supply line, an oxygen gas supply line, an inert gas supply line such as argon or nitrogen, an exhaust line, a pressure measurement sensor, etc., depending on the process to be performed.

The laser light irradiation device 14 includes at least a semiconductor laser oscillator and an optical system for adjusting the shape of the laser light. The laser light generated by the semiconductor laser oscillator is adjusted by the optical system including a plurality of optical elements such as various lenses, such as aspherical lenses and rod lenses, a homogenizer, and an expander, into a uniform laser light L shaped into a regular hexagon whose apex is located on the lower surface of the arm 13, and is then emitted.
The semiconductor laser oscillator may be a continuous oscillation high-power semiconductor laser oscillator or a known pulsed semiconductor laser oscillator. In the present invention, the wavelength of the irradiated laser light is not particularly limited as long as it is capable of heating the wafer, and is preferably 400 nm to 1600 nm (visible light to infrared light), more preferably 780 nm to 1200 nm (infrared light), and even more preferably 800 nm to 1000 nm. The infrared laser light irradiated to the lower surface of the wafer may be a polygon whose apex is located on the lower surface of the arm, and is preferably an n-gon (n is 4 to 8), and more preferably a hexagon. A regular polygon is also preferable.
It is preferable that the laser light L is irradiated perpendicularly to the lower surface of the wafer W, but the lower surface of the wafer W may also be irradiated obliquely within a range in which uniform irradiation is possible.

A radiation thermometer 15 is provided outside the chamber 11 and is directed obliquely toward the lower surface of the wafer W. The radiation thermometer 15 measures the temperature of the lower surface of the wafer W through a transmission window 111, but a heat ray transmission window separate from the transmission window 111 may also be provided.
The transparent window 111 and the heat ray transparent window must be made of a material having high infrared transmittance, such as quartz, _BaF2 , _MgF2 , _CaF2 , sapphire, ZnSe, glass, etc., and when the pressure inside the chamber is reduced, a material having mechanical strength can be selected.

The radiation thermometer 15 may be a known type, and one or more may be installed. When only one radiation thermometer 15 is installed, for example, the temperature of the center of the lower surface or the center of the upper surface of the wafer W can be measured. By sequentially changing the orientation of one radiation thermometer 15, it is possible to obtain measurement results of the temperature distribution at multiple locations on the wafer W. When multiple radiation thermometers 15 are installed, it is possible to simultaneously measure the temperatures of multiple locations, such as the center and outer periphery of the lower surface of the wafer W, and the center and outer periphery of the upper surface of the wafer W. Furthermore, if necessary, the intensity of the laser light L can be adjusted by performing feedback control such as PID control based on the measurement values from one or more radiation thermometers 15 and the target temperature so that the temperature of the lower surface of the wafer W becomes uniform and reaches the target temperature.

(holder)
A schematic diagram of an example of a holder is shown in FIG.
The holder 12 has a circular opening 121 in the approximate center that is larger than the diameter of the wafer W, and six arms 13 are formed at equal intervals extending from the edge of the opening 121 toward the center. The holder 12 also has a notch 122 formed therein through which a transfer arm passes when transferring the wafer, as described below. The holder 12 is fixed in the chamber 11 by screw holes.
In the present invention, the material of the holder and the arm is not particularly limited, but it is preferable that the material is resistant to thermal expansion and has excellent heat resistance and thermal shock resistance. Examples of such materials include quartz, sapphire, alumina, zirconia, silicon nitride, silicon carbide, silicon, SiC-coated graphite, etc., and quartz is preferable. In the present invention, the arm may be formed integrally with the holder, or may be formed separately and then fixed to the holder by welding or the like. When formed separately, it is preferable that the arm and the holder are made of the same material.

(Placement of Wafer)
The wafer W is transferred into the chamber 11 by an arbitrary transfer device through a gate (not shown), and placed on the arm 13. In the laser heating processing device 1 of the first embodiment, the wafer W is transferred while being placed on a transfer arm (not shown), but since the transfer arm passes through the notch 122 of the holder 12 and does not come into contact with the holder 12, the wafer W is placed on the arm 13 by moving the transfer arm on which the wafer W is placed from above to below the holder 12.

FIG. 3 shows an example of the shape of the tip of the arm.
The arm 13 has a flat portion 131 that supports a wafer at its tip, and an inclined portion 132 that is continuous from the flat portion 131 and inclined upward toward the outside. Since the arm 13 has the flat portion 131 and the inclined portion 132, even if the position of the wafer W is slightly shifted, the wafer W slides down the inclined portion 132 and is accurately supported at a predetermined position (flat portion 131) of the arm 13. The inclined portion 132 can prevent the wafer W from moving on the arm 13. In order to make it easy for the wafer W to slide down the inclined portion 132, the inclination (θ in FIG. 3) of the inclined portion 132 is preferably 35° or more, more preferably 40° or more, and even more preferably 45° or more. The length of the inclined portion 132 in the wafer surface direction is preferably 3% or more of the wafer diameter, more preferably 5% or more.

The number of arms 13 is not particularly limited as long as it can stably hold the wafer W, but is preferably between four and eight, and most preferably six. The installation locations of the arms 13 are also not particularly limited as long as it can stably hold the wafer W, but it is preferable to install them at the vertices of a regular polygon. By arranging the arms 13 in this manner, the wafer W can be supported accurately and stably at a predetermined position, and the heat escape from the wafer W to the arms 13, described below, can be made uniform, reducing uneven heating of the wafer W.

(Laser light irradiation)
The state when the laser heating apparatus 1 irradiates the lower surface of the wafer W with the laser light L will be described with reference to Fig. 4. Fig. 4(A) is a schematic view seen from below, and Fig. 4(B) is a schematic view seen from the side.
The laser heating processing apparatus 1 irradiates the underside of a wafer W supported by six arms 13 arranged at equal intervals with a regular hexagonal laser beam L whose apexes are located on the undersides of the arms 13 .
The laser heating processing apparatus 1 irradiates the regular hexagonal laser light L with its apex positioned on the lower surface of the arm 13, thereby heating not only the wafer W but also the portion of the arm 13 irradiated with the laser light (the portion adjacent to the wafer W). When the portion of the arm 13 adjacent to the wafer W is heated, the temperature difference between the wafer W and the arm 13 is reduced, so that the amount of heat escaping from the wafer W to the arm 13 can be reduced. At this time, in order to heat the arm 13 more efficiently, a metal film, a metal oxide film, a silicon nitride film, or a silicon carbide film can be formed by deposition processing or the like on the upper surface, lower surface, side surface, or one or more parts inside the arm 13.

In the portion of the wafer W supported by the arm 13, the laser light L passes through the arm 13 (flat portion 131) before reaching the wafer W. The portion of the wafer W supported by the arm 13 is irradiated with the laser light L that has passed through the arm 13 (flat portion 131), and is therefore slightly less likely to be heated than other portions directly irradiated with the laser light L. It is preferable that the arm 13 not block the laser light L irradiated from below as much as possible, and the area of the flat portion 131 is preferably 1 mm ² or less, more preferably 0.5 mm ² or less, even more preferably 0.2 mm ² or less, and most preferably 0.1 mm ² or less. If the area of the flat portion 131 is narrowed, the wafer W is more likely to fall, so the area of the flat portion 131 is preferably 0.01 mm ² or more, more preferably 0.02 mm ² or more, and more preferably 0.03 mm ² or more. Moreover, the thickness of the flat portion 131 is preferably 0.5 mm or less, more preferably 0.4 mm or less, and even more preferably 0.3 mm or less.

The cross-sectional area of the arm 13 in the wafer radial direction and the vertical plane is preferably as small as possible. The wafer W may be heated to 1000° C. or more by laser heating, but since heat escapes from the heated high-temperature wafer W to the arm 13, the part of the wafer W supported by the arm 13 and its surrounding area may become lower in temperature than other parts of the wafer W. By reducing the cross-sectional area of the arm 13 in the wafer radial direction and the vertical plane, the amount of heat escaping from the wafer W to the arm 13 can be reduced. The cross-sectional area of the arm 13 in the wafer radial direction and the vertical plane is preferably 2 mm ² or less, more preferably 1.5 mm ² or less, even more preferably 1 mm ² or less, and most preferably 0.5 mm ² or less. If the cross-sectional area of the arm 13 in the wafer radial direction and the vertical plane becomes narrow, the arm 13 becomes more likely to break, so this cross-sectional area is preferably 0.05 mm ² or more, more preferably 0.1 mm ² or more, and more preferably 0.2 mm ² or more.

The area of the portion of the laser light L that is not irradiated to the wafer W and arm 13 is preferably small. The portion of the laser light L that is not irradiated to the wafer W and arm 13 is a wasted portion that does not contribute to heating the wafer W and arm 13, and may heat up unexpected parts of the device, causing malfunctions, etc. For this reason, the diameter of the inscribed circle of the polygon of the laser light L is preferably 1.2 times or less, more preferably 1.1 times or less, and even more preferably 1.05 times or less, the diameter of the wafer W. Note that the regular hexagonal laser light L naturally includes the wafer W, and the diameter of the inscribed circle is 1.0 times or more the diameter of the wafer W.

Second Embodiment FIG. 5 shows a schematic diagram of a laser heat treatment device 2 according to a second embodiment of the present invention.
In a laser heat treatment apparatus 2 according to a second embodiment shown in FIG. 5, the same members as those in the laser heat treatment apparatus 1 according to the first embodiment are denoted by the same reference numerals.
The laser heating treatment device 2 of the second embodiment has a laser light irradiation device 24a that irradiates a regular hexagonal laser light La whose apex is located on the lower surface of the arm 13, and a laser light irradiation device 24b that irradiates an annular (ring-shaped) laser light Lb that irradiates only the outer peripheral edge of the wafer W. A hydrogen gas supply line 26 and an exhaust line 27 are connected to the chamber 11. Note that, depending on the process to be performed, the chamber 11 can be connected to pipes such as an oxygen gas supply line, an inert gas supply line such as argon or nitrogen, and a pressure measurement sensor.

The two laser beams La and Lb emitted from the laser beam irradiation devices 24a and 24b, respectively, are superimposed as one laser beam using a bandpass filter 28 that transmits light of a specific wavelength but reflects light of other wavelengths, and are irradiated onto the underside of the wafer W. Note that while FIG. 5 shows a configuration in which the regular hexagonal laser beam La is reflected by the bandpass filter 28 and the annular laser beam Lb is transmitted through the bandpass filter 28, the reverse may also be true.

When two laser beams are combined into one laser beam by the bandpass filter 28, it is preferable that the wavelength of one laser beam differs from the wavelength of the other laser beam by 30 nm or more, for example, 880 nm and 940 nm. Note that dichroic mirrors, shortpass filters, etc. can also be used as materials that have the same effect as bandpass filters. Laser beams from one laser light source can also be split by a beam splitter or the like, and then shaped by separate optical systems before being superimposed into one laser beam.

The laser heating processing device 2 has a radiation thermometer 25a that measures the temperature of the center of the underside of the wafer W, and a radiation thermometer 25b that measures the temperature of the outer periphery of the underside of the wafer W. The radiation thermometers 25a and 25b simultaneously measure the temperatures of the center and outer periphery of the underside of the wafer W, and based on the measured values of either or both of the radiation thermometers and the target temperature, feedback control such as PID control is performed so that the temperature of the underside of the wafer W becomes uniform and reaches the target temperature, and the intensity of either or both of the laser beams La and Lb can be adjusted. The laser heating processing device 2 can perform more precise temperature control by adjusting the intensity of the two laser beams. The radiation thermometers can also be installed to measure the temperature of the top surface of the wafer W, or can be installed to measure the temperatures of both the top and bottom surfaces of the wafer W.

(Infrared laser light irradiation)
The state when the laser beams La and Lb are irradiated onto the lower surface of the wafer W by the laser heating processing apparatus 2 will be described with reference to Fig. 6. Fig. 6(A) is a schematic view seen from below, and Fig. 6(B) is a schematic view seen from the side.

The laser light La has a regular hexagonal shape with uniform intensity over its irradiation area, and the laser light Lb has a circular ring shape corresponding to the area equivalent to the outer periphery of the wafer W. The laser light La and the laser light Lb are combined, and the resulting single beam of laser light is irradiated onto the bottom surface of the wafer W.
The regular hexagonal laser light La is similar to the laser light L in the first embodiment.
The means for obtaining the annular laser light Lb is not particularly limited, and can be obtained by combining known optical elements. For example, a beam of laser light whose cross section is shaped into an annular shape can be obtained by combining an axicon convex lens and an axicon concave lens. Furthermore, a diffractive optical element (DOE) can be employed to shape the laser light. The laser light Lb only needs to be irradiated onto the outer peripheral edge of the wafer, and the outer diameter of the laser light Lb may be equal to or larger than the diameter of the wafer W. However, it is preferable that the area of the portion of the laser light Lb that is not irradiated onto the wafer W and the arm 13 is small, and the outer diameter of the laser light Lb is preferably 1.3 times or less, more preferably 1.2 times or less, and even more preferably 1.15 times or less, of the diameter of the wafer W.

Here, only the top and bottom surfaces of the wafer W are exposed in the center, but the sides as well as the top and bottom are exposed in the outer periphery. Therefore, the temperature of the wafer W tends to decrease from the center toward the outer periphery. This tendency becomes more pronounced as the heating temperature increases and as the amount of gas supply (exhaust) increases. In particular, when the wafer W is heat-treated in a gas atmosphere, the heated wafer W loses heat to the surrounding gas, and the outer periphery tends to become cooler than the center.

The laser light La has a uniform intensity over its irradiation area. The laser light Lb, in combination with the laser light La, makes the intensity of the laser light irradiated to the outer peripheral portion of the wafer W stronger than that of the center portion. By irradiating the circular (ring-shaped) laser light Lb that irradiates only the outer peripheral portion of the wafer W, it is possible to prevent the temperature of the outer peripheral portion of the wafer W from dropping more than that of the center portion, especially during high-temperature heating or heating in a gas atmosphere. That is, the laser light Lb supplies an amount of heat equivalent to the amount of heat dissipated by the outer peripheral portion of the wafer W more than the center portion of the wafer when only the laser light La is irradiated, and by superimposing the circular laser light Lb on the laser light La with uniform intensity and irradiating the wafer W with the laser light La, the heat dissipated from the outer peripheral portion of the wafer W can be compensated for, resulting in uniform heating. In the laser heating processing device of the present invention, the intensities of the two laser lights La and Lb can be adjusted within a range in which this object can be achieved.

(Hydrogen annealing)
The laser heating treatment apparatus 2 of the second embodiment can perform hydrogen annealing by supplying hydrogen gas from the hydrogen gas supply line 26, exhausting the gas from the exhaust line 27, and heating the wafer W to 700° C. or higher while reducing the pressure inside the chamber 11 to approximately 50 kPa or less.
In addition, hydrogen annealing causes silicon atoms to move in a direction that minimizes surface energy even at temperatures below the melting point of silicon (1414° C.). Therefore, when hydrogen annealing is performed on a silicon wafer, the surface is smoothed, the surface is flattened, and the corners are rounded.

The laser heat treatment devices 1 and 2, which are the first and second embodiments described above, are examples of the laser heat treatment device of the present invention, and the laser heat treatment device of the present invention can include various modifications, changes, and improvements to each of the disclosed elements (including the elements described in the claims, specification, and drawings) within the scope of its technical concept. Furthermore, various combinations, substitutions, and selections of each of the disclosed elements are possible within the scope of the claims of the present invention.

W wafer

Reference Signs List 1 Heat treatment device according to the first embodiment 11 Chamber 111 Transmission window 12 Holder 121 Opening 122 Notch 13 Arm 131 Flat portion 132 Inclined portion 14 Laser light irradiation device L Regular hexagonal laser light 15 Radiation thermometer

2 Heat treatment device 24a, b according to the second embodiment Laser light irradiation device La Regular hexagonal laser light Lb Ring-shaped laser light 25a, b Radiation thermometer 26 Hydrogen gas supply line 27 Exhaust line 28 Bandpass filter

Claims (3)

a plurality of arms for supporting the outer periphery of the wafer;
a laser light irradiation device for irradiating a polygonal laser light onto the lower surface of the wafer;
the arm supports the wafer at equal intervals;
The polygon is a regular n-sided polygon (n is 4 or more and 8 or less), and a vertex is located on a lower surface of the arm. A hydrogen gas supply line is provided.
2. The laser heat treatment apparatus according to claim 1, wherein hydrogen annealing is possible. 3. The laser heat treatment apparatus according to claim 1, which is for use with wafers having a diameter of 4 inches or less.