Laser heating apparatus

Abstract

To provide a laser heating apparatus with a fast cooling rate without increasing the size of the device. [Solution] A support that supports the object to be heated and has a channel through which a refrigerant passes, A laser light irradiation device that irradiates the lower surface of the object to be heated through the support, It has, A laser heating apparatus comprising a support made of a material having an absorption rate of 1% or less at the wavelength of the laser when the support is 10 mm thick.

Description

Technical Field

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[0001] The present invention relates to a laser heat treatment apparatus that irradiates an object to be heated with a laser for heating.

Background Art

[0002] As heat treatment methods, methods such as hot plates, lamp heating (radiation), and laser heating are known. Laser heating is excellent in directivity and heating efficiency, and also has a high heating rate and can shorten the time required for heat treatment. Therefore, it is used in soldering of electronic components, semiconductor manufacturing processes, and the like. For example, the present applicants have proposed a laser heat treatment apparatus that irradiates infrared laser light having a beam diameter equal to or larger than the diameter of a wafer onto the back surface of the wafer in Patent Document 1, and in Patent Document 2, a laser heat treatment apparatus having a plurality of arms that support the outer peripheral portion of the wafer and a laser light irradiation device that irradiates polygonal laser light onto the lower surface of the wafer, wherein the apex of the polygon of the laser light is located on the lower surface of the arm.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In heat treatment, after the temperature of the object to be heated has risen, it is generally cooled naturally in the heating chamber or forced air-cooled by flowing gas into the heating chamber, or conveyed onto a cooling plate and cooled. When cooling naturally or by forced air-cooling in the heating chamber, a long time is required to lower the temperature to a temperature at which it can be taken out (about 60°C or lower). Also, when cooling on a cooling plate, a cooling chamber or the like is required, which causes the apparatus to become large-sized. The present invention aims to solve these problems and provides a laser heating apparatus that has a fast cooling rate without increasing the size of the device. [Means for solving the problem]

[0005] The means for solving the problems of the present invention are as follows. 1. A support that supports the object to be heated and has a channel through which a refrigerant flows, A laser light irradiation device that irradiates the lower surface of the object to be heated through the support, It has, A laser heating apparatus characterized in that the support is made of a material whose absorption rate at the wavelength of the laser is 1% or less when the support is 10 mm thick. 2. The laser heating apparatus according to 1, characterized in that the laser is irradiated over the entire lower surface of the object to be heated. 3. The laser heating apparatus according to 1, characterized in that the laser is irradiated only to a portion of the lower surface of the object to be heated. 4. The laser heating apparatus according to any one of claims 1 to 3, characterized in that the reflectance of the laser in the laser incident region of the support is 1% or less. 5. The laser heating apparatus according to any one of claims 1 to 4, characterized in that fine irregularities are formed on at least a portion of the region of the support that supports the object to be heated. [Effects of the Invention]

[0006] The laser heating apparatus of the present invention allows a coolant to flow through a support that holds the object to be heated, thus enabling rapid cooling of the object after heating. The laser heating apparatus of the present invention requires fewer components for cooling, thus suppressing the increase in size and complexity of the apparatus, and is also low-cost. The laser heating apparatus of the present invention irradiates the underside of the object to be heated with a laser through a support, but since the laser is hardly absorbed by the support, the object to be heated can be heated efficiently. In the laser heating apparatus of the present invention, by irradiating only a part of the object to be heated with a laser while flowing a coolant, heating of the laser irradiation area and suppression of temperature rise around the irradiation area can be achieved simultaneously, so that only the irradiation area can be heated with pinpoint accuracy, and the occurrence of thermal damage to components etc. placed around the irradiation area can be prevented. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram of a laser heating apparatus 1, which is a first embodiment of the present invention. [Figure 2] A schematic diagram of a laser heating apparatus 2, which is a second embodiment of the present invention. [Modes for carrying out the invention]

[0008] In this specification, the notation "A to B (where A and B are numerical values)" refers to a numerical range that includes both ends of that range. The laser heating apparatus of the present invention will be described below with reference to the figures. "First Embodiment" Figure 1 shows a schematic diagram of a laser heating apparatus 1, which is a first embodiment of the present invention. The laser heating apparatus 1, which is the first embodiment of the present invention, uses a wafer W as the object to be heated. The laser heating apparatus 1 comprises a support body 11 that supports a wafer W and has a channel P through which a refrigerant C passes, and a laser light irradiation device 12 that irradiates the lower surface of the wafer W with a laser L through the support body 11. Although not shown in the figures, the laser heating apparatus of the present invention may include a chamber, an inert gas supply line such as argon or nitrogen, a hydrogen gas supply line, an oxygen gas supply line, an exhaust line, and various sensors such as a temperature measuring device and a pressure measuring device.

[0009] The support body 11 supports the object to be heated (wafer W in this embodiment) and has a flow path P through which the refrigerant C passes. The support 11 is made of a material with an absorption rate of 1% or less with respect to the wavelength of the laser L used to heat the object to be heated, when the support is 10 mm thick. In the laser heating apparatus of the present invention, the laser L is irradiated onto the lower surface of the object to be heated, passing through the support 11 and the refrigerant C. Because the support 11 is made of a material with an absorption rate of 1% or less, the laser is absorbed less by the support 11, and the object to be heated can be heated efficiently.

[0010] From the viewpoint of improving heating efficiency, it is preferable that the reflectivity of the laser L in the incident region of the support 11 is 1% or less. The method for achieving a reflectivity of 1% or less is not particularly limited and can be conventionally known as anti-reflective treatment (AR treatment). This reflectivity is more preferably 0.9% or less, even more preferably 0.8% or less, even more preferably 0.7% or less, even more preferably 0.6% or less, and even more preferably 0.5% or less. It is preferable that the area of ​​the lower surface of the support 11 other than the incident region of the laser L be roughened to scatter the laser L in order to prevent the generation of reflected light and stray light. It is preferable that the support 11 has fine irregularities formed on at least a portion of the area that supports the object to be heated, in order to prevent the object to be heated from sticking to it.

[0011] The material of the support 11 should have an absorption rate of 1% or less with respect to the wavelength of the laser L when the thickness is 10 mm. For example, if the wavelength of the laser is 880 nm, the support material can be synthetic quartz (absorption rate of almost zero%), borosilicate crown glass (absorption rate of almost zero%), etc. Furthermore, refrigerant C may be either a liquid such as water or oil, or a gas such as air, nitrogen, or helium, but a liquid is preferable from the viewpoint of cooling efficiency. In addition, it is preferable that the refrigerant has a low absorption rate with respect to the wavelength of laser L. For example, when the wavelength of the laser is 880 nm, pure water (absorption rate of approximately 6% at a thickness of 10 mm, absorption rate of approximately 3% at a thickness of 5 mm), dry air (absorption rate of almost zero%), helium gas (absorption rate of zero%), etc. can be used.

[0012] The absorption rate of the wavelength of laser L with respect to the thickness of 10 mm of the material of the support is preferably 0.8% or less, more preferably 0.6% or less, still more preferably 0.4% or less, even more preferably 0.2% or less, even more preferably 0.1% or less, even more preferably 0.05% or less, even more preferably 0.02% or less, and even more preferably 0.01% or less.

[0013] The laser light irradiation device 12 includes at least a semiconductor laser oscillator and an optical system for adjusting the shape of the laser. As the semiconductor laser oscillator, a continuous oscillation high-output semiconductor laser oscillator, a known semiconductor laser oscillator that emits pulses, or the like can be adopted. In the present invention, the wavelength of the laser light to be irradiated is not particularly limited as long as it can heat the object to be heated and the absorption rate of the support 11 described above is 1% or less. For example, the range of 400 nm to 1600 nm (visible light to infrared) is preferable, and the range of 780 nm to 1200 nm (infrared) is more preferable. Particularly, when the refrigerant is water, the range of 780 nm to 1000 nm is even more preferable. The laser generated by the semiconductor laser oscillator is adjusted by an optical system including various lenses such as an aspherical lens and a rod lens, and a plurality of optical elements such as a homogenizer and an expander, and is adjusted to a uniform laser L having a desired shape and then emitted. The laser L is preferably irradiated perpendicularly to the lower surface of the wafer W, but can also be irradiated obliquely to the lower surface of the wafer W within a range where uniform irradiation is possible.

[0014] In the laser heat treatment apparatus 1 according to the first embodiment, the laser L is irradiated onto the entire lower surface of the wafer W. As a result, the wafer W is uniformly heated, but the outer peripheral edge portion of the wafer W is likely to be at a lower temperature than the central portion of the wafer W due to heat dissipation. In order to reduce the temperature non-uniformity in the plane of the wafer W, an annular (ring-shaped) laser beam that heats only the outer peripheral edge portion of the wafer W can also be overlapped and irradiated.

[0015] "Cooling in the Laser Heat Treatment Apparatus According to the First Embodiment" In the laser heat treatment apparatus 1 according to the first embodiment, the entire lower surface of the wafer W is irradiated with the laser L, and the entire wafer W is heated. In the laser heat treatment apparatus 1 according to the first embodiment, after the heat treatment is completed, by flowing the refrigerant C, the wafer W can be rapidly cooled down. As a result, the time required for a series of operations including the heat treatment and the loading and unloading of the heated object (wafer W) before and after it can be shortened, and the number of heated objects (wafer W) that can be heat-treated per unit time can be increased. In addition, in order to prevent heat from being transferred from the high-temperature wafer W and prevent the support 11 and the refrigerant C from becoming high-temperature, the refrigerant C can also be flowed during the heat treatment.

[0016] "Second Embodiment" FIG. 2 shows a schematic view of the laser heat treatment apparatus 2 according to the second embodiment of the present invention. In the laser heat treatment apparatus 2 according to the second embodiment, 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 heat treatment apparatus 2 according to the second embodiment of the present invention has the same configuration as the laser heat treatment apparatus 1 according to the first embodiment, except that the laser light irradiation device 22 irradiates the laser L only on a part of the lower surface of the wafer W.

[0017] "Cooling in the Laser Heat Treatment Apparatus According to the Second Embodiment" In the laser heat treatment apparatus 2 according to the second embodiment, the laser L is irradiated only on a part of the lower surface of the wafer W. If the laser L is irradiated without flowing the refrigerant C, heat is transferred from the irradiated area, causing the area surrounding the irradiated area to become hot. The second embodiment, the laser heating apparatus 2, can simultaneously heat the irradiated area and cool the entire surface of the wafer W by irradiating the laser L locally while flowing the refrigerant C. As a result, the second embodiment, the laser heating apparatus 2, can heat only the irradiated area with pinpoint accuracy, preventing thermal damage to the area surrounding the irradiated area. Although the irradiated area is heated (laser irradiation) and cooled simultaneously, this can be achieved by using a high-power laser L to heat the area more than it is cooled.

[0018] The laser heating apparatus described in the first and second embodiments is merely an example, and the laser heating apparatus of the present invention is not limited to these. For example, the object to be heated is not limited to the wafer W, but can be any object. [Examples]

[0019] "Example 1" In the minimal laser heating apparatus described in Patent Document 2, the wafer was supported by being placed on a quartz cell (AS ONE Corporation, Azlab Quartz Cell (2-sided transparent)) instead of being supported by multiple arms. The quartz cell was a rectangular prism shape with a wall thickness of 1.25 mm, dimensions of 12.5 mm x 12.5 mm, and a height of 45 mm, and was filled with pure water. The quartz cell filled with pure water was placed on a holder base, lying on its side with the transparent side facing up and down, and an untreated silicon wafer (250 μm thick) of half an inch size was placed on the top surface of the quartz cell. A semiconductor laser (wavelength 880 nm) was irradiated across the entire underside of the wafer via a support (quartz cell, absorption rate almost zero%) and a coolant (pure water). The temperature of the center of the top surface of the wafer was measured using a radiation thermometer (Japan Sensor Co., Ltd., TMHX-TME0050-0100H002, target size 2 mm in diameter). After raising the temperature to over 300°C, the laser irradiation was stopped, and the number of seconds required to cool down from 300°C to 200°C and from 300°C to 100°C was measured.

[0020] "Comparative Example 1" Using the minimal laser heating device described in Patent Document 2, the number of seconds required to cool the wafer from 300°C to 200°C and from 300°C to 100°C was measured in the same manner as in Example 1, except that the wafer was supported by multiple arms. Comparative Example 1 shows the cooling rate when the wafer is naturally air-cooled. "Comparative Example 2" Except for not filling the cell with pure water as a refrigerant and using an empty quartz cell, the procedure was the same as in Example 1, and the number of seconds required to cool the temperature from 300°C to 200°C and from 300°C to 100°C was measured.

[0021] The results are shown in Table 1. [Table 1]

[0022] The laser heating apparatus of Example 1 of the present invention was able to cool from 300°C to 100°C in less than one second. In Example 1, the refrigerant (pure water) is stagnant, but by circulating the refrigerant, cooling can be accelerated even further. In contrast, the laser heating apparatus of Comparative Example 1, which uses natural air cooling, took 1.7 seconds to cool from 300°C to 200°C and 5.0 seconds to cool from 300°C to 100°C, which were 8.5 times (1.7 / 0.2) and 6.25 times (5.0 / 0.8) those of Example 1, respectively. The laser heating apparatus of Comparative Example 2 took 0.9 seconds to cool from 300°C to 200°C and 6.5 seconds to cool from 300°C to 100°C, which were 4.5 times (0.9 / 0.2) and 8.13 times (6.5 / 0.8) that of Example 1, respectively. Comparative Example 2 took longer to cool from 300°C to 100°C than Comparative Example 1. This is because, in Comparative Example 2, the heat from the wafer was transferred only to the quartz cell, which has a smaller heat capacity, causing the quartz cell in Comparative Example 2 to become hotter than the quartz cell and refrigerant in Comparative Example 1. [Explanation of Symbols]

[0023] 1, 2 Laser heating apparatus 11 Support P channel 12, 22 Laser light irradiation device L Laser W wafer (object to be heated)

Claims

1. A support that supports the object to be heated and has a channel through which a refrigerant flows, A laser light irradiation device that irradiates the lower surface of the object to be heated through the support, It has, A laser heating apparatus characterized in that the support is made of a material whose absorption rate at the wavelength of the laser is 1% or less when the support is 10 mm thick.

2. The laser heating apparatus according to claim 1, characterized in that the laser is irradiated over the entire lower surface of the object to be heated.

3. The laser heating apparatus according to claim 1, characterized in that the laser is irradiated only a portion of the lower surface of the object to be heated.

4. The laser heating apparatus according to any one of claims 1 to 3, characterized in that the reflectance of the laser in the laser incident region of the support is 1% or less.

5. The laser heating apparatus according to any one of claims 1 to 3, characterized in that fine irregularities are formed on at least a portion of the region of the support that supports the object to be heated.

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