Method and device for producing planar modifications in solid bodies

Abstract

A method for creating modifications in a solid-state material is described, wherein a crack guidance region for guiding a crack for separating a solid-state layer from the solid-state material is predetermined by the modifications. The method includes: moving the solid-state material relative to a laser processing system; successively emitting a plurality of laser beams from the laser processing system to the solid-state material to create at least one modification within the solid-state material; and continuously adjusting the laser processing system for defined focusing of the plurality of laser beams and/or for adjustment of energy of the plurality of laser beams as a function of at least one parameter.

Claims

1. A method for creating modifications in a solid-state material, wherein a crack guidance region for guiding a crack for separating a solid-state layer from the solid-state material is predetermined by the modifications, the method comprising: moving the solid-state material relative to a laser processing system; successively emitting a plurality of laser beams from the laser processing system to the solid-state material to create at least one modification within the solid-state material; and continuously adjusting the laser processing system for defined focusing of the plurality of laser beams and/or for adjustment of energy of the plurality of laser beams as a function of at least one parameter, wherein the at least one parameter for adjusting the laser processing system includes a degree of doping of the solid-state material at a predetermined location or in a predetermined region.

2. The method of claim 1, further comprising: processing distance data regarding a distance parameter for adjusting the laser processing system, wherein the distance parameter represents a distance with respect to the laser processing system, wherein the plurality of laser beams is introduced into the solid-state material at a point in time of creation of the at least one modification, and wherein the distance data is detected by means of a sensor device.

3. The method of claim 1, further comprising: determining the degree of doping by analysis of backscattered light with an inelastic (Raman) scattering, the backscattered light having a different wavelength or a different wavelength range than incident light defined for triggering the backscattering, wherein the backscattered light is backscattered from the predefined location or from the predetermined region.

4. The method of claim 1, further comprising: determining the degree of doping by an eddy current measurement, wherein differences in conductivity are determined in the solid-state material.

5. The method of claim 1, further comprising: determining the degree of doping by ellipsometric measurement.

6. The method of claim 5, wherein the ellipsometric measurement is based on optical transmission of the solid-state material.

7. The method of claim 1, further comprising: determining the degree of doping by Mller matrix ellipsometry with rear side reflection.

8. The method of claim 1, further comprising: determining the degree of doping by a transmission measurement that is calibrated optically.

9. The method of claim 8, wherein the optical calibration is performed by a Hall measurement and a 4-point measurement.

10. The method of claim 8, further comprising: determining a doping/number of free charge carriers in the solid-state material by the transmission measurement.

Description

(1) Additional advantages, goals and properties of the present invention will now be explained on the basis of the following description of the accompanying drawings, which illustrate devices according to the invention as examples. Elements of the devices according to the invention and methods which correspond at least essentially with regard to their function in the figures can be characterized with the same reference numerals herein, such that these components and/or elements need not be labeled with reference numerals in all the figures or explained. The invention will now be described in greater detail below purely as an example on the basis of the accompanying figures.

(2) The drawings show:

(3) FIG. 1 an example of a laser processing system according to the invention;

(4) FIG. 2a an example of a device according to the invention;

(5) FIG. 2b the processing of a polymer layer arranged on the solid state using a functional fluid;

(6) FIG. 3a an exemplary diagram of a surface profile of a solid state and the refractive indices of this surface profile;

(7) FIG. 3b several diagrams of surface profiles;

(8) FIG. 4a several diagrams of the changes in control positions of the laser head; and

(9) FIG. 4b two curves representing profiles of different modification distributions and

(10) FIG. 5a a schematic drawing of a Raman instrument, such as that preferably used according to the invention, in particular such as that which is a preferred component of the device according to the invention;

(11) FIG. 5b various exemplary vibration states of the lattice vibrations of SiC;

(12) FIGS. 6a and 6b two diagrams illustrating doping concentrations in a solid state;

(13) FIG. 7a a feed-forward process according to the invention, and

(14) FIG. 7b a feedback process according to the invention.

(15) FIG. 1 shows an laser processing system 8 according to the invention, such as that preferred in the method according to the invention and the device 30 according to the invention for creating modifications 2 in a solid state 1.

(16) The laser processing system 8 here has at least one laser bean source 32, in particular with focus marking. The laser beam source 32 may specifically be a coaxial light source with focus marking. The beams of light 10 generated by the laser beam source 32 are preferably directed on a predetermined path from the laser beam source 32 to a focus device 44 or an adjusting device 44 for adjusting the size of the focus and the position of the focus in the solid state 1. The adjusting device 44 here may preferably be a fine-focusing device, in particular for focusing in Z direction or in the direction of the laser beam. The adjusting device 44 may preferably be designed as a piezo fine-focusing device. The laser beams 10 that pass through the adjusting device 44 preferably pass through a microscope with a long working distance 46. The laser beam is preferably adapted and/or adjusted and/or modified especially preferably by the microscope with the long working distance 46 and the adjusting device 44 in such a way that the modification 2 is created in the predefined location. For example, it is conceivable here for modification 2 to be created at a location which deviates less than 5 m and preferably less than 2 m and especially preferably less than 1 m from the predefined location or is at a distance therefrom. The adjusting device 44 is preferably controlled by a control system 14, wherein the control system 14 preferably calculates and/or determines and/or uses the position and orientation of the solid state 1 with respect to the laser processing system 8 or the distance of the current surface portion into which the laser beam is to be introduced, relative to the laser processing system 8 and the local refractive index or the average refractive index of the solid-state material and the depth of processing of the solid state 1 at the respective location for the adjustment of the laser processing system 8, in particular at least the adjusting device 44. The control system 14 can detect and/or receive the required data in real time through corresponding sensor systems and/or sensor means, which are thus connected to communicate. Alternatively however it is also conceivable for an analysis of the surface over which the laser beams 10 penetrate into the solid state 1 to create the modifications 2 to be performed and/or carried out for one or both of the refractive index and processing depth parameters prior to the start of processing. These parameters can then be stored and/or entered into a memory device, i.e., a data memory 12, in the form of corresponding location-dependent data. The data memory 12 here may be a variable medium, in particular a memory card or a permanently installed memory as part of the laser processing system 8.

(17) Alternatively, however, it is also conceivable for the data memory 12 to be set up outside of the laser processing system 8 and to be connectable at least temporarily so that it can communicate with the laser processing system 8. Additionally or alternatively, work sequences or changes in the work sequence can be preselected for the control system 14 by a user 52. Furthermore, it is also conceivable for the data memory 12 to be embodied as a component of the control system 14. Additionally or alternatively, distance data can be detected by means of a sensor system 16 regarding the distance between the predetermined surface points on the solid state and the laser processing system 8. This distance data is preferably also supplied to the control system 14 for processing.

(18) In addition, it is conceivable for the laser beam processing system 8 to have a camera 34, in particular a coaxial focus camera. The camera 34 is preferably arranged in the direction of the beam path of the laser beams 10 emitted by the laser processing system 8. It is also conceivable here for an optical element 36, in particular a partially transparent mirror, to be arranged in the optical field of the camera 34. The laser beams 10 are preferably fed into the optical field of the camera through the optical element 34.

(19) In addition, it is conceivable that an additional optical element 38 and/or a diffractive optical element, in particular a beam splitter 38 is provided. A portion of the laser beam 10 can be deflected and/or separated from the main beam here by the beam splitter 38. Furthermore the separated and/or deflected portion of the laser beam can be modified by an optional spherical aberration compensation 40 and/or by an optional beam widening 42.

(20) Furthermore, reference numeral 48 denotes a fluid-providing device 48 that is preferably provided, in particular for supplying a cooling fluid. A temperature control, in particular cooling, of the solid state 1 and/or of the microscope can preferably be induced by means of the fluid supply system 48.

(21) Reference numeral 50 denotes a refractive index determination means which can preferably also analyze transparent and reflective surfaces. The refractive index is preferably determined by using the refractive index determination means 50 prior to creation of the modification. Alternatively, it is also conceivable here for the refractive index to be determined on another installation and for the data thereby detected to be supplied to the existing laser processing system 18 by data transfer.

(22) The dotted lines illustrated in FIG. 1 with an arrow preferably characterize data and/or signal transmissions.

(23) FIG. 2a shows schematically a preferred arrangement of the device components, namely the laser processing system 8, the receiving device 18 and the drive and/or traversing device 22 of the device 30. It can be seen that the solid state 1 according to this arrangement is preferably situated between the receiving device 18 and the laser processing system 8. The solid state 1 is preferably glued to the receiving device 18, but it is also conceivable for it to be pressed thereto.

(24) FIG. 2b shows an arrangement after creation of the modifications 2 and/or after complete creation of the crack guidance region 4. According to this illustration, a receiving layer or polymer layer 26 is arranged and/or formed on the surface 24 of the solid state 1, through which the laser beams 10 penetrate into the solid state 1. In addition a functional fluid source is characterized by the device 54 which outputs the functional fluid 56. The functional fluid 56 is preferably liquid nitrogen. Thus the receiving layer 26 is cooled by the functional fluid 56 to a temperature below 20 C., in particular to a temperature below 10 C. or to a temperature below 0 C. or to a temperature below the glass transition temperature of the polymer material of the receiving layer 26. High mechanical stresses are created by the cooling of the receiving layer 26, causing a crack to propagate along the crack guidance region 4. FIG. 3a shows, merely as an example, the relationship between a surface profile of a solid state 1 and the refractive index of the solid-state material. The values shown on the horizontal axis are in units of m.

(25) FIG. 3b shows examples of deviations of the material to be lasered (surface profile and lateral variations in the refractive index) as well as the laser focus position (no AF: without autofocus, the surface profile is written into the material in inverse ratio, increased by the refractive index, while a standard AF reverses this inversion so that the surface profile is transmitted with an n-fold gain; nAF: this takes into the account the refractive index of the substrate and/or the refractive index as a fixed factor so that the surface profile is thereby transmitted 1:1 into the material. AAF: knowledge of the average refractive index of the substrate and the target depth, the desired advanced autofocus function can write a precisely horizontal plane into the material).

(26) FIG. 4a shows merely as an example various control positions of the laser focus. The values indicated on the horizontal axis are given in units of m. Thus, the waveform can be determined as a control input variable for the position of the laser head in various cases:

(27) nAF (n-aware AF): the outer focus guide variable of the surface for correcting the average refractive index (n) of the surface. Thus the surface deviation can be transmitted 1:1 into the volume. Therefore, theoretically, the wafer to be split off will not have any fluctuations in thickness (TTV). However, the topography and thus the poor planarity are maintained both for the wafer and for the remaining ingot.

(28) AAF (advanced AF): to correct the autofocus guide variable of the surface with knowledge of the average refractive index of the surface and the correction plane of the surface. It is thus possible to prepare a flat laser plane that prepares the semiconductor crystal to be very flat for additional splits with an inexpensive polishing step. However, the wafer that is split off is flat on one side immediately after the split but has a greater thickness deviation.

(29) AnAF (Advanced n-aware AF): to correct the autofocus guide variable of the surface with knowledge of the local refractive index of the surface and the correction plane of the surface. Thus, a flat laser plane, which prepares the semiconductor crystal to be very flat for additional splits with an inexpensive polishing step, is possible even with heterogeneous samples with prior knowledge.

(30) The present invention thus relates to a method for creating modifications in a solid state, wherein a crack guidance region for guiding a crack for separation of a solid-state component, in particular a solid-state layer from the solid state is predefined by the modification. The method according to the invention here preferably comprises at least the following steps:

(31) Moving the solid state relative to a laser processing system, creating in succession a plurality of laser beams by means of the laser processing system for creating at least one modification, wherein the laser processing system is adjusted for defined focusing of the laser beams continuously as a function of a plurality of parameters, in particular at least two parameters. A planar microfocus for multiphoton material processing in the volume is preferably made possible by the method according to the invention.

(32) FIG. 5a shows a Raman instrument 58. The Raman instrument 58 shown here has a laser 60 for emitting laser rays. The laser rays are preferably sent by means of at least one optical fiber 61 for excitation preferably through a lens and preferably focused by this lens 64 in particular being focused in the solid state. This radiation is at least partially scattered, wherein light components having the same wavelength as the radiation emitted by the laser are preferably filtered out by means of a filter device and/or an exciting filter 62. The other radiation components are then sent to a spectrograph 68 and detected by means of a camera system, in particular a CCD detector 70 and processed and/or analyzed by a control system 14, 72, in particular a computer.

(33) Thus atomic vibrations in the crystal are excited preferably by an external laser or especially preferably by an additional laser. The vibrations are generated by light scattering on crystal atoms, which leads to observable scattered light, which has a photon energy that is altered by the amount of the vibration energy. When there are multiple excitable vibrations, multiple peaks also appear in the spectrum of the scattered light. Then using a spectrometer (grating spectrometer), the resulting Raman scattering spectrum can be investigated in greater detail (so-called Raman spectroscopy). In this method, the local conditions in the crystal are imposed on the individual Raman lines in their shape, and it is possible to deduce the degree of doping by analyzing the shape of the Raman line.

(34) FIG. 5b shows how possible lattice vibrations appear in SiC, wherein these modes are predetermined by crystal symmetry and directions and may also be excited at the same time. The views shown here have one direction along the crystal axis A. Atomic vibrations here are possible only in certain directions, the directions being predetermined by the symmetry of the crystal.

(35) FIG. 6a shows a detail of a Raman diagram of a 4H-silicon carbide solid state doped with nitrogen (example of a Raman spectrum on doped SiC). The shape of the LO(PC) mode is used here for measuring the dopant concentration and is fitted. Bottom panel: fitting residual.

(36) FIG. 6b shows a smaller detail of the Raman spectrum.

(37) As shown here, this yields a direct method for determining the dopant concentration with Raman measurements from a measurement of the shape and subsequent fitting to the LO(PC) mode.

(38) In general, the goal is thus, by adjusting the laser parameters, to adjust the optimum (least possible, shortest possible) path of cracking in the material which will still lead to successful separation due to crack propagation but will otherwise minimize or reduce all loss of material (including that in grinding operations).

(39) FIG. 7a and FIG. 7b show two possibilities for lifting a single wafer from the boule/ingot.

(40) According to FIG. 7a this is embodied as a feed-forward loop and according to FIG. 7b it is embodied as a feedback loop.

(41) In feed-forward, the distribution before the laser process is characterized and then used to calculate a map and/or treatment instructions and/or parameter adjustments, in particular as a function of location, for laser process, in particular for creation of the modification. Feed-forward is preferably carried out on the ingot/boule.

(42) Alternatively, as illustrated in FIG. 7b, a feedback loop may be implemented, so that the resulting wafer is characterized after each separation step and then serves as a template for the next.

(43) Depending on the material and the doping, different adjustments can thus be made during the laser process.

(44) With the SiC material, different adjustments in the laser parameters can be made at different depths as a function of the doping. This can lead to the functions also shown below with the boundary conditions listed below:

(45) Depth 180 m, pulse duration 3 ns, numerical aperture 0.4

(46) Low doping: 7 J-21 mOhmcm

(47) High doping: 8 J-16 mOhmcm

(48) Depth 350 m, pulse duration 3 ns, numerical aperture 0.4

(49) Low doping: 9.5 J-21 mOhmcm

(50) High doping: 12 J-16 mOhmcm

(51) Formula for a Depth of 180 m:

(52) E energy in J

(53) E0 offset energy at the lowest doping

(54) K energy scaling factor

(55) R measured degree of doping

(56) B basic degree of doping (21 mOhmcm)
E=E0+(BR)*K
where
K=1/(2116) J/mOhmcm=0.2 J/mOhmcm
E0=7 J
B=21 mOhmcm
Example: measured degree of doping of 19 mOhmcm: E=7.4 J
Formula for 350 m Depth:
E energy in J
E0 offset energy at the lowest doping
K energy scaling factor
R measured degree of doping
B basic degree of doping (21 mOhmcm)
E=E0+(BR)*K
where
K=2.5/(2116) J/mOhmcm=0.5 J/mOhmcm
E0=9.5 iJ
B=21 mOhmcm
Example: measured degree of doping of 19 mOhmcm: E=10.5 J

(57) TABLE-US-00001 List of Reference Numerals 1 solid state 2 modification 4 crack guidance region 6 solid-state portion 8 laser processing system 10 laser beam 12 data memory device 14 control system 16 sensor device 18 receiving device 20 axis of rotation 22 drive device 24 surface of the solid-state portion to be separated 26 receiving layer 30 device 32 laser beam source 34 camera 36 optical element 38 beam splitter 40 spherical aberration compensation means 42 beam expander 44 adjusting device 46 microscope with a long working distance 48 fluid source 50 refractive index determination means 52 user 54 functional fluid source 56 functional fluid 58 Raman instrument 60 laser 61 optical fiber for excitation 62 excitation filter 64 lens 68 spectrograph 70 CCD detector 72 analysis and/or processing system or control system 14 74 inspection 76 adjusting of laser parameters and/or machine parameters and generating spatially resolved treatment instructions and/or a spatially resolved treatment map 78 laser process (generating modifications) 80 separation step, in particular by means of crack propagation and crack guidance 82 surface treatment