Use of high-power laser radiation for stress crack separation of bodies made of semiconductor materials and equipment for this purpose

Abstract

Use of laser radiation for stress crack cutting of bodies made of semiconductor materials, characterized in that continuous laser radiation of a laser with a wavelength between 1,000 nm and 1,100 nm, a two-dimensional Gaussian beam distribution formed by an F-Theta optic and guided by a galvo or polygon mirror scanner, an effective diameter that does not cause melting of the semiconductor material and an applied power of 200 W to 20,000 W is used for stress crack cutting with a cutting speed of over 550 mm / s.

Description

[0001] The invention relates to uses of high-power laser radiation for stress crack separation of bodies made of semiconductor materials and devices for stress crack separation of bodies made of semiconductor materials.

[0002] The generation of stress cracks by heating and subsequent cooling is well known.

[0003] The publication DE 10 2004 024 475 A1 describes a method and device for separating semiconductor materials. A ytterbium fiber laser with a wavelength of 1120 nm and a power of up to 200 W, operated in continuous wave mode, is used to create the cracks. To separate thick materials, the laser beam must be passed over the interface multiple times.

[0004] The publication by O. Haupt, "Ablation-free separation of crystalline silicon with continuous laser radiation," Reports from the LZH, Volume 03 / 2009, describes the stress crack separation of semiconductor materials. A maximum cutting speed of 550 mm / s is specified for the separation of a 220 µm thick wafer. Only straight cuts were performed.

[0005] The publication by P. Romero*, N. Otero, I. Coto, C. Leira, A. Gonzáleza: Experimental study of diode laser cutting of silicon by means of water-assisted thermally driven separation mechanism, Physics Procedia 41 (2013), 610-619, describes a stress cracking process for a 200 µm thick wafer, specifying a maximum cutting speed of 170 mm / s. Curved cuts were also performed. However, this required pretreatment with a liquid.

[0006] Document US 2011 / 0244659 A1 discloses a method for cutting a semiconductor wafer by creating a crack within the wafer. The method comprises irradiating a laser beam onto a surface of the wafer and converging the laser beam to form a focal point, thereby creating a focal volume defined by the focal point and a boundary of the laser beam within the wafer. The energy contained in the focal volume causes the wafer located at the edge of the focal volume to contract faster than the wafer located within the focal volume, thereby creating a crack in the wafer.

[0007] The publication EXNER, H. et al., High Speed ​​Laser Micro Processing Using High Brilliance Continuous Wave Laser Radiation, in: JLMN-Journal of Laser Micro / Nanoengineering, 2012, pp. 115 - 121, ISSN 1880-0688, discusses laser microprocessing using a high-power single-mode continuous wave fiber laser in combination with a galvanometer scanner and a polygon scanning system.

[0008] The solutions in these publications show only very limited cutting speeds.

[0009] The invention defined in claim 1 is based on the object of separating bodies made of semiconductor materials simply and quickly by stress cracking.

[0010] This problem is solved with the features listed in patent claim 1.

[0011] The use of high-power laser radiation and the devices are characterized by the rapid separation of bodies made of semiconductor materials. For high-speed stress crack separation of bodies made of semiconductor materials, either continuous laser radiation from a laser with a wavelength between 1,000 nm and 1,100 nm, an at least one-dimensional, nearly Gaussian or Bessel-shaped beam distribution, an effective width that does not cause melting of the semiconductor material, and an applied power of 200 to 20,000 W, or pulsed laser radiation from a laser with a wavelength between 800 nm and 1,100 nm, a one-dimensional, nearly Gaussian or Bessel-shaped beam distribution, an effective width of the laser radiation that does not cause melting of the semiconductor material, and an applied pulse power of 1,000 to 1,000,000 W is used.

[0012] The absorption of laser radiation, combined with a resulting temperature increase, generates thermo-mechanical stresses in the body made of semiconductor material. If a critical stress is exceeded, these stresses lead to cracking in the body. This phenomenon can be used for the targeted separation of the body as thermally induced stress separation or stress crack separation. Surprisingly, it has been shown that the use of high-power laser radiation can also achieve high cutting speeds that are significantly greater than those of conventional methods. With conventional methods, cutting speeds of up to 550 mm / s have been achieved. In contrast, when using the high-power laser radiation listed with a laser power of, for example, 3,000 W, cutting speeds of up to 15,000 mm / s could be achieved. An end to the scaling could not be determined.

[0013] For this purpose, the device comprises a single-mode laser with a continuous laser radiation, a device that shapes the laser radiation and a device that guides the shaped laser radiation.

[0014] The continuous laser radiation has a wavelength between 1,000 nm and 1,100 nm, a focus diameter that does not cause melting of the semiconductor material, and an applied power between 200 and 20,000 W. The device guiding the laser radiation over the surface of the body made of semiconductor material is arranged in the beam path downstream of the single-mode laser. Further downstream of this is the device shaping the laser radiation in the form of a cylindrical lens for laser radiation with a one-dimensional, nearly Gaussian beam distribution, a focusing optic for laser radiation with a two-dimensional, nearly Gaussian beam distribution, an F-theta optic for laser radiation with a two-dimensional, nearly Gaussian beam distribution, a prism lens for laser radiation with a one-dimensional, nearly Bessel-shaped beam distribution, or an axicon for laser radiation with a two-dimensional, nearly Bessel-shaped beam distribution.

[0015] The device that guides the laser radiation is, for example, a well-known galvo or polygon mirror scanner.

[0016] Alternatively, a high-power pulsed laser can be used for cutting. This involves using laser radiation with a wavelength between 800 nm and 1,100 nm, a one-dimensional, nearly Gaussian or Bessel-shaped beam distribution, an effective width of the laser radiation that does not cause melting of the semiconductor material, and an applied pulse power between 1,000 W and 1,000,000 W for stress crack cutting of bodies made of semiconductor materials at extremely high speeds.

[0017] In the beam path after the single-mode laser there is the device that shapes the laser radiation in the form of a cylindrical lens for laser radiation with a one-dimensional, almost Gaussian beam distribution or a prism lens for laser radiation with a one-dimensional, almost Bessel-shaped beam distribution.

[0018] The separation takes place across the entire width of the body with a laser pulse.

[0019] The shaped and guided, or simply shaped, laser beam can thus be advantageously used for cutting without pretreatment of the body, so that no prior damage is caused. Further pretreatment with water or other liquids is also unnecessary. Using these laser beams, no waste is generated during cutting.

[0020] Advantageous embodiments of the invention are specified in patent claims 2 to 8.

[0021] According to the embodiment of patent claim 2, the laser radiation of a one- or two-dimensional monomode laser is used for stress crack cutting. A one-dimensional monomode laser can be, for example, a diode laser with a linear beam or a pulsed rod laser with a shaped linear beam. The two-dimensional monomode laser is preferably a disk or fiber laser.

[0022] For stress crack separation, a laser radiation with a one-dimensional, almost Gaussian beam distribution shaped by a cylindrical lens is used.

[0023] For stress crack cutting, a laser beam with a two-dimensional, nearly Gaussian beam distribution shaped by a focusing optic or an F-Theta optic is used.

[0024] For stress crack cutting, laser radiation with a one-dimensional, almost Bessel-shaped beam distribution formed by a prism lens is used.

[0025] For stress crack cutting, laser radiation with a two-dimensional, almost Bessel-shaped beam distribution formed by an axicon is used.

[0026] According to the embodiment of patent claim 6, the laser radiation is used for stress crack separation of bodies made of doped silicon as semiconductor material, wherein the silicon is polycrystalline or monocrystalline and the body is polished or unpolished.

[0027] Advantageously, the laser radiation according to the embodiment of patent claim 7 is used for stress crack separation of panes as bodies.

[0028] According to the embodiment of patent claim 8, the laser radiation is used to separate the body from stress cracks with a freely definable and thus arbitrary cutting geometry and resulting contour.

[0029] Embodiments of the invention are described in more detail below.

[0030] A device for stress crack separation of bodies made of semiconductor materials essentially consists of a single-mode laser and a device guiding the laser radiation over the surface of the body made of semiconductor material in the beam path after the single-mode laser.

[0031] In embodiments, the device comprises a device shaping the laser radiation in the beam path after the single-mode laser and the device guiding the laser radiation over the surface of the body made of the semiconductor material.

[0032] In the following examples, uses and facilities are explained in more detail.

[0033] In a first embodiment, a single-mode laser with a laser power of 3,000 W is used to separate a wafer, a body made of polycrystalline silicon with a thickness of 200 µm. A galvo scanner guiding the laser radiation over the surface of the body at a speed of 15,000 mm / s and an F-theta optic with a focal length of 500 mm and a defocus of 60 mm, resulting in an effective diameter of 2 mm, are arranged in sequence in the beam path of the single-mode laser.

[0034] In a second embodiment, a single-mode laser with a laser power of 6,000 W is used to separate a body in the form of a wafer made of monocrystalline silicon with a thickness of 200 µm. A polygonal mirror scanner, the device that guides the laser radiation across the surface of the wafer made of semiconductor material at a speed of 30,000 mm / s, and a cylindrical lens or prism lens, the device that shapes the laser radiation, are arranged in sequence in the beam path of the single-mode laser. To achieve straight separation gaps, the wafer is mounted on a linearly guided and driven holder.

[0035] In a third embodiment, a known continuous roll-to-roll system uses a single-mode laser with a laser power of 1,000 W to separate a body from a thin silicon foil with a thickness of less than 60 µm. F-theta optics and a galvo scanner are used to create cutouts for components from the foil. For longitudinal sections, focusing optics and a stationary laser beam can be used. For cross-sections, an inclined cylindrical lens and a galvo scanner, a polygon mirror scanner, or F-theta optics and a galvo scanner can be used. The angle of inclination results from the ratio of transport speed to separation speed.

[0036] In a fourth embodiment, a pulsed laser with single-mode beam quality with a pulse power of 3,000 W and a pulse energy of 30 J is used to separate a body in the form of a wafer made of polycrystalline silicon with a thickness of 200 µm. Located in the laser beam path is an inclined cylindrical lens with a length of 200 mm, a focal length of 500 mm, and a defocus of 60 mm, resulting in an effective length of 200 m and an effective width of 2 mm. The beam is not moved. The wafer is mounted on a holder coupled to at least one drive for continuous wafer transport. This allows continuous straight cuts up to 200 mm long to be produced with one laser pulse each.

[0037] In a fifth embodiment, a single-mode laser with a laser power of 3,000 W is used to separate a body in the form of a wafer made of monocrystalline silicon with a thickness of 200 µm. A galvoscanner is arranged in the beam path of the single-mode laser as the device that guides the laser radiation across the surface of the wafer made of semiconductor material at a speed of 15,000 mm / s, and an F-theta optic with a focal length of 500 mm and a defocus of 60 mm, resulting in an effective diameter of 2 mm, is arranged as a device that shapes the laser radiation. This allows the creation of separating cuts of almost any shape, in particular curved lines and circular sections. Jagged lines can be created up to a material-dependent critical angle for the jags. Widths of the separated structures of less than 1 mm are feasible.

Claims

[1] Use of laser radiation for stress crack separation of bodies made of semiconductor materials, characterized by that for stress crack cutting with a cutting speed of over 550 mm / s, continuous laser radiation from a laser with a wavelength between 1,000 nm and 1,100 nm, a two-dimensional Gaussian beam distribution, shaped by an F-theta optic and guided by a galvo or polygon mirror scanner, an effective diameter that does not cause melting of the semiconductor material and an applied power of 200 W to 20,000 W is used. [2] Use according to claim 1, characterized by that the laser radiation of a one- or two-dimensional monomode beam distributed laser is used for stress crack separation. [3] Use according to one of the preceding claims, wherein the separation speed is at least 1000 mm / s. [4] Use according to one of the preceding claims, wherein the power to be applied is at least 1000 W. [5] Use according to one of the preceding claims, wherein the effective diameter is approximately 2 mm. [6] Use according to claim 1, characterized by that the laser radiation is used for stress crack separation of bodies made of doped silicon as a semiconductor material, wherein the silicon is polycrystalline or monocrystalline and the body is polished or unpolished. [7] Use according to claim 6, characterized by that the laser radiation is used to separate stress cracks in discs as a body. [8] Use according to claim 1, characterized by that the laser radiation is used to cut the body to create stress cracks with a freely definable and therefore arbitrary cutting geometry.