DE102013016665A1 - Combined wafer fabrication process with ion implantation and temperature-induced stresses - Google Patents

Abstract

The present invention relates to a method for producing solid state layers. The method comprises at least the steps of providing a solid body (2) for splitting off at least one solid layer (4), introducing ions (6) into the solid body (2) to specify a first decoating plane (8) along which the solid layer ( 4) is separated from the solid body (2), the thermal loading of a on the solid body (2) arranged polymer layer (10) for, in particular mechanical, generating stresses in the solid body (2), which is due to the stresses a crack in the solid (2) along the Ablöseebene (8) propagates, which separates the solid state layer (4) from the solid body (2).

Description

The present invention relates to a method for producing solid-state layers according to the subject-matter of claim 1 and to a wafer produced by this method (claim 9).

In many technical areas (eg microelectronics or photovoltaic technology), materials such. As silicon, germanium or sapphire, often in the form of thin slices and plates (so-called wafer) needed. By default, such wafers are currently produced by sawing from an ingot, resulting in relatively large material losses ("kerf-loss"). Since the starting material used is often very expensive, there are strong efforts to produce such wafers with less material and thus more efficient and cost-effective.

For example, in the production of silicon wafers for solar cells, almost 50% of the material used is lost as a "kerf loss" with the currently customary processes. Worldwide, this represents an annual loss of over 2 billion euros. Since the cost of the wafer accounts for the largest share of the cost of the finished solar cell (over 40%), the cost of solar cells could be significantly reduced through improvements in wafer manufacturing.

Particularly attractive for such a wafer production without kerf-loss ("kerf-free wafering") appear methods that do without the conventional sawing and z. B. by using temperature-induced voltages directly thin wafers can split off from a thicker workpiece. These include in particular methods, such as. In PCT / US2008 / 012140 and PCT / EP2009 / 067539 where a polymer layer applied to the workpiece is used to generate these stresses.

The polymer layer has in the mentioned method a compared to the workpiece by about two orders of magnitude higher thermal expansion coefficient. In addition, by utilizing a glass transition, a relatively high modulus of elasticity in the polymer layer can be achieved, so that sufficiently high voltages can be induced in the layer system polymer layer workpiece by cooling in order to enable the removal of wafers from the workpiece.

When a wafer is split off from the workpiece, polymer still adheres to one side of the wafer in each of the methods mentioned. The wafer bends very strongly in the direction of this polymer layer, which makes controlled separation difficult, and z. B. can lead to thickness variations of the split-wafer. In addition, the high curvature makes further processing difficult and may even break the wafer.

When using the methods of the prior art, the wafers produced usually each have larger variations in thickness, wherein the spatial thickness distribution often shows a pattern with fourfold symmetry. The total thickness variation (TTV) over the entire wafer is often greater than 100% of the average wafer thickness (eg, a wafer of, for example, 100 microns average thickness, eg, at its thinnest 50 microns thick and 170 microns thick at its thickest point, has a TTV of 170-50 = 120 microns, which corresponds to a total thickness variation of 120% relative to its mean thickness). Wafers with such large thickness variations are not suitable for many applications. In addition, in the most common fourfold thickness distribution patterns, the regions of greatest variability unfortunately lie in the middle of the wafer where they are most disturbing.

In addition, in the method according to the current state of the art during the fracture propagation during the splitting off, undesired oscillations in the layer systems involved occur, which unfavorably influence the course of the fracture front and in particular can lead to significant thickness fluctuations of the split-off wafer.

In addition, it is difficult in the previous methods to ensure a reproducibly good thermal contact over the entire surface of the polymer layer. Due to the low thermal conductivity of the polymers used, locally insufficient thermal contact can lead to unwanted, significant local temperature deviations in the layer system, which in turn adversely affects the controllability of the generated stress fields and thus the quality of the produced wafers.

An alternative method, which also manages without sawing, is described by the document DE 692 31 328 T2 described. According to this document, H-ions at 150 keV are introduced into a monocrystalline silicon plate by means of an ion implantation. The H ⁺ ions are controlled in the silicon plate introduced so that they come to rest substantially at a defined level within the plate. The dose of the thereby implanted H ⁺ ions is greater than 10 ¹⁶ cm ^-2 , resulting as a result of heating the silicon plate to a temperature of greater than 500 ° C. a coalescence of the introduced ions is effected, resulting in a separation of the plane of the introduced ions adjacent portions of the silicon plate.

This process is very costly and complex, since an extremely expensive and expensive ion gun with appropriate control devices must be provided. Furthermore, the implantation of the ions takes quite a long time due to the high dose. Furthermore, heating the silicon plate requires a high energy input and prevents electrical components that are damaged at such high temperatures from being placed on the silicon plate prior to heating.

It is thus the object of the present invention to provide a method for producing solid-state layers, which enables the cost-effective production of solid-state plates or wafers with a uniform thickness, in particular with a TTV of less than 120 micrometers.

The aforementioned object is achieved by a method according to claim 1 for producing solid-state layers. This method according to the invention preferably comprises at least the following steps: provision of a solid for splitting off at least one solid-state layer, introduction of ions into the solid for predetermining a first decoupling plane along which the solid-state layer can be separated from the solid, arranging a receiving layer for holding the solid-state layer on the solid, thermally exposing the receiving layer to, in particular mechanical, generating stresses in the solid body, wherein the tensions propagate a crack in the solid body along the first release plane, which separates the solid state layer from the solid state.

This solution is advantageous because it is less susceptible to solid state layer generation based solely on implantation of ions due to shorter bombardment times, i. H. a significantly shorter use of an ion gun, or a significantly lower number of implanted ions is much cheaper, faster and more energy efficient. Furthermore, more solids from different materials can be divided into solid layers with this method, since the process temperature is significantly lower. Another advantage of the invention is that, due to the implanted ions, the release plane or a defect layer can be generated in the solid body through which the crack propagates during the crack propagation, which results in the realization of very small TTVs, in particular less than 100 micrometers or less than 80 microns or less than 60 microns or less than 40 microns or less than 20 microns or less than 10 microns or less than 5 microns, especially 4, 3, 2, 1 microns. The ion implantation thus creates a kind of perforation in the interior of the solid, along which the crack propagation takes place or along which the solid-state layer is separated from the solid.

Further advantageous embodiments are the subject of the following description and / or the dependent claims.

According to a preferred embodiment of the present invention, the solid body is arranged to be held on a holding layer, wherein the holding layer is arranged on a first flat surface portion of the solid, wherein the first planar surface portion of the solid body is spaced from a second planar area portion of the solid, wherein the second planar area fraction, the polymer layer is arranged. This embodiment is advantageous since the solid body is arranged at least in sections and preferably completely between the holding layer and the polymer layer, whereby the stresses for crack generation or crack propagation into the solid body can be introduced by means of one of these layers or by means of both layers.

At least or exactly one radiation source is provided according to a further preferred embodiment of the present invention for providing the ions to be introduced into the solid, wherein the radiation source is oriented such that the ions emitted by it penetrate into the solid. The radiation source is preferably used to provide H ⁺ ions or noble gas ions, such as. As the substances helium, neon, krypton and xenon, wherein the ions of the remaining unspecified noble gases can also be used. Furthermore, it is conceivable that the ions of the aforementioned substances and / or other substances are used separately or combined or used simultaneously or successively.

The radiation source is adjusted in accordance with a further preferred embodiment of the present invention such that the ions emitted by it penetrate into the solid body to produce the release plane to a defined depth, in particular <100 μm. Preferably, the Ablöseebene spaced parallel to an outer and preferably flat surface of the solid is formed. Preferably, the release plane is less than 100 microns, and preferably less than 50 microns, and more preferably less than or equal to 20, 10, 5, or 2 microns spaced from the planar surface of the solid within the solid.

The solid is subjected to a predetermined dose of ions according to another preferred embodiment of the present invention, wherein the predetermined dose is less than or equal to 5 + 10 ¹⁶ cm ^-2 , less than 5 + 10 ¹⁵ cm ^-2 or less than 10 ¹⁵ cm ^-2 or less than 10 ¹⁴ cm ^-2 or less than 10 ¹³ cm ^-2 . This embodiment is advantageous because defects are generated within the solid due to the low dose, which cause an advantageous crack guidance, but the implantation time is relatively short and the energy to be used is relatively low.

According to a further preferred embodiment of the present invention, the solid body is heated in such a way that coalescence of the ions introduced into the solid body is prevented. Coalescence generally refers to the confluence of colloidal particles. In this case, colloids are particles or ions which are finely distributed in the dispersion medium (solid). This embodiment is advantageous because not only temperature-stable solid, but also temperature-critical solids or solids with temperature-critical components such. B. electronic components that are damaged at temperatures greater than 50 ° C or greater than 100 ° C or greater than 200 ° C or greater than 300 ° C or greater than 400 ° C or greater than 500 ° C, can be processed.

According to a further preferred embodiment of the present invention, the solid has silicon and / or gallium and / or a ceramic material and the receiving layer preferably consists of a polymer layer, wherein the polymer layer and / or the holding layer at least partially and preferably completely or more than 75 % consist of polydimethylsiloxanes (PDMS), wherein the holding layer is disposed on an at least partially planar surface of a stabilizing device, which consists at least partially of at least one metal. The stabilizing device is preferably a plate, in particular a plate comprising or consisting of aluminum. This embodiment is advantageous because the solid state is defined or held by the stabilization device and the holding layer, as a result of which the stresses can be generated very accurately in the solid.

In accordance with a further preferred embodiment of the present invention, the stresses in the solid body can be adjusted or generated such that the crack initiation and / or the crack propagation can be controlled to produce a defined topography of the surface resulting in the crack plane. The stresses are thus preferably in different areas of the solid preferably at least temporarily differently strong generated. This embodiment is advantageous since the topography of the generated or separated solid-state layer can be advantageously influenced or influenced by controlling the crack initiation and / or the crack progression.

The solid preferably comprises a material or a material combination of one of the main groups 3, 4 and 5 of the Periodic Table of the Elements, such as. Si, SiC, SiGe, Ge, GaAs, InP, GaN, Al 2 O 3 (sapphire), AlN. Particularly preferably, the solid has a combination of elements occurring in the third and fifth group of the periodic table. Conceivable materials or material combinations are z. B. gallium arsenide, silicon, silicon carbide, etc. Furthermore, the solid may have a ceramic (eg., Al2O3 - alumina) or consist of a ceramic, preferred ceramics are z. Perovskite ceramics (such as Pb, O, Ti / Zr containing ceramics) in general, and lead magnesium niobates, barium titanate, lithium titanate, yttrium aluminum garnet, especially yttrium aluminum garnet crystals for solid state laser applications , SAW ceramics (surface acoustic wave), such. As lithium niobate, gallium orthophosphate, quartz, calcium titanate, etc. in particular. The solid body thus preferably has a semiconductor material or a ceramic material or particularly preferably the solid body consists of at least one semiconductor material or a ceramic material. It is also conceivable that the solid has a transparent material or partially made of a transparent material, such. B. sapphire, consists or is made. Other materials that come here as a solid material alone or in combination with another material in question are, for. "Wide band gap" materials, InAlSb, high temperature superconductors, especially rare earth cuprates (eg YBa2Cu3O7).

The stresses for detaching the solid-state layer are generated by the solid body by the thermal loading of the receiving layer arranged on the solid, in particular a polymer layer, in accordance with a further preferred embodiment of the present invention. The thermal application preferably represents a cooling of the receiving layer or polymer layer to or below the ambient temperature and preferably below 10 ° C. and more preferably below 0 ° C. and more preferably below -10 ° C. The cooling of the polymer layer is most preferably such that at least a part of the polymer layer, which preferably consists of PDMS, undergoes a glass transition. The cooling can be a cooling to below -100 ° C, the z. B. by means of liquid nitrogen is effected. This embodiment is advantageous because the polymer layer contracts as a function of the temperature change and / or undergoes a gas transfer and transfers the resulting forces to the solid, whereby mechanical stresses can be generated in the solid, which lead to the initiation of a crack and / or crack propagation, wherein the crack first propagates along the first release plane for splitting off the solid-state layer.

The invention further relates to a wafer which is produced by a method according to one of claims 1 to 8.

Furthermore, the subjects of the publications PCT / US2008 / 012140 and PCT / EP2009 / 067539 fully incorporated by reference into the subject matter of the present application. Likewise, the objects of all other filed on the filing date of the present patent application by the Applicant also filed and related to the field of producing solid state layers further patent applications are made in full the subject of the present patent application.

Further advantages, objects and characteristics of the present invention will be explained with reference to the following description of appended drawings, in which the wafer production according to the invention is shown by way of example. Components or elements of the wafer production according to the invention, which in the figures at least essentially coincide with respect to their function, may hereby be identified by the same reference symbols, these components or elements not having to be numbered or explained in all figures.

Individual or all representations of the figures described below are preferably to be regarded as construction drawings, d. H. the dimensions, proportions, functional relationships and / or arrangements resulting from the figure or figures preferably correspond exactly or preferably substantially to those of the device according to the invention or of the product according to the invention.

Show:

1a a schematic structure for implanting ions in a solid state;

1b a schematic representation of a layer arrangement prior to the separation of a solid layer of a solid;

1c a schematic representation of a layer arrangement after the separation of a solid layer of a solid.

In 1a is a solid 2 or a substrate shown in the region of a radiation source 18 , in particular an ion gun, is arranged. The solid 2 preferably has a first planar surface portion 14 and a second planar area portion 16 on, wherein the first planar surface portion 14 preferably substantially or exactly parallel to the second planar area fraction 16 is aligned. The first flat area fraction 14 and the second planar area fraction 16 preferably limit the solids 2 in a Y-direction, which is preferably oriented vertically or vertically. The flat area proportions 14 and 16 preferably extend in each case in an XZ plane, wherein the XZ plane is preferably oriented horizontally. Furthermore, it can be seen from this illustration that the radiation source 18 Steels or ions 6 on the solid 2 radiates. The ions 6 Depending on the configuration defined penetrate deep into the solid 2 and remain in the respective position. As a rule, the ions arrange themselves at different depths within the solid in the sense of the Gaussian bell curve. As detachment level 8th or defined configuration is preferably considered the plane in which the largest ion density is recorded according to the Gaussian bell curve.

In 1b is shown a multilayer arrangement wherein the solid 2 the detachment level 8th includes and in the area of the first flat area fraction 14 with a holding layer 12 is provided, which in turn preferred by a further layer 20 is superimposed, with the further layer 20 preferably a stabilizing device, in particular a metal plate, is. At the second planar surface portion 16 of the solid 2 is preferably a polymer layer 10 arranged. The receiving layer or polymer layer 10 and / or the holding layer 12 are preferably at least partially, and most preferably entirely of PDMS.

In 1c is shown a state after a crack initiation and subsequent cracking. The solid state layer 4 adheres to the polymer layer 10 and is from the remainder of the solid 2 spaced or spaced.

The present invention thus relates to a method for producing solid-state layers. The method comprises at least the steps of providing a solid 2 for splitting off at least one solid-state layer 4 , the introduction of ions 6 in the solid state 2 for specifying a first detachment level 8th , along which the solid-state layer 4 from the solid 2 is separated, the thermal impingement of a on the solid 2 arranged polymer layer 10 for, in particular mechanical, generating stresses in the solid 2 , whereby the tensions cause a crack in the solid 2 along the detachment level 8th spreads out the solid-state layer 4 from the solid 2 separates.

LIST OF REFERENCE NUMBERS

2

solid

4

Solid layer

6

ions

8th

transfer level

10

polymer layer

12

holding layer

14

first plane area fraction

16

second plane area fraction

18

radiation source

20

stabilizing device

X

first direction

Y

second direction

Z

third direction

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2008/012140 [0004, 0026]
• EP 2009/067539 [0004, 0026]
• DE 69231328 T2 [0010]

Claims (9)

Method for producing solid-state layers, comprising at least the steps of: providing a solid ( 2 ) for splitting off at least one solid-state layer ( 4 ), Introduction of ions ( 6 ) in the solid state ( 2 ) for specifying a first detachment level ( 8th ), along which the solid state layer ( 4 ) from the solid state ( 2 ) is detachable, arranging a recording layer ( 10 ) for holding the solid state layer ( 4 ) on the solid ( 2 ), thermal loading of the recording layer ( 10 ) for, in particular mechanical, generating stresses in the solid ( 2 ), whereby due to the stresses a crack in the solid ( 2 ) along the first release plane ( 8th ) spreading the solid state layer ( 4 ) of the solid ( 2 ) separates. Method according to claim 1, characterized in that a radiation source ( 18 ) for providing in the solid state ( 2 ) ions to be introduced ( 6 ) is provided, wherein the radiation source ( 18 ) is oriented such that the ions emitted by it ( 6 ) in the solid state ( 2 ). Method according to claim 2, characterized in that the radiation source ( 18 ) is set such that the ions emitted by it ( 6 ) for generating the detachment level ( 8th ) to a defined depth, in particular <100 μm, into the solid ( 2 ). Method according to one of the preceding claims, characterized in that the solid state ( 2 ) with a predetermined dose of ions ( 6 ), the predetermined dose being less than 5 + 10 ¹⁶ cm ^-2 . Method according to one of the preceding claims, characterized in that the solid state ( 2 ) is tempered such that a coalescence in the solid ( 2 ) introduced ions ( 6 ) is prevented. Method according to one of the preceding claims, characterized in that the solid state ( 2 ) for holding on a holding layer ( 12 ), wherein the holding layer ( 12 ) at a first planar surface portion ( 14 ) of the solid ( 2 ), wherein the first planar surface portion ( 14 ) of the solid ( 2 ) of a second planar surface portion ( 16 ) of the solid ( 2 ), wherein at the second planar surface portion ( 16 ) the polymer layer ( 10 ) is arranged. Method according to claim 6, characterized in that the solid ( 2 ) Silicon and / or gallium and / or a ceramic material and the receiving layer as a polymer layer ( 10 ), wherein polymer layer and / or the holding layer ( 12 ) consist at least partially of PDMS, the holding layer ( 12 ) at an at least partially planar surface of a stabilization device ( 20 ) is arranged, which consists at least partially of at least one metal. Method according to one of the preceding claims, characterized in that the stresses in the solid state ( 2 ) are adjusted to control crack initiation and / or crack propagation to produce a defined topography of the surface resulting in the crack plane. Wafer produced by a process according to one of claims 1 to 8.

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