Glass wafer and method for producing same

Abstract

The present invention relates generally to glass wafers for use as interposers. The present invention particularly refers to glass wafers having at least one opening.

Description

[0001] Glass wafer and method for its production

[0002] Field of the invention

[0003] The present invention generally relates to glass wafers, particularly for use as interposers. Further applications include MEMS, glass cores for packaging in assembly and interconnection technology, antenna-in-package concepts for GHz applications, and other similar applications. In particular, the present invention relates to glass wafers comprising at least one opening.

[0004] Background of the invention

[0005] Glass wafers used as interposers and / or suitable for similar applications, for example as MEMS or as glass cores for packaging applications, have at least one opening, preferably several, and are usually metallized.

[0006] For example, it is known to produce such glass wafers by laser treatment followed by an etching step. This method can produce glass wafers with defined openings. Applications include, for example, the industrial production of semiconductors.

[0007] In the context of the present disclosure, a glass wafer is generally understood to mean a glass disk-shaped piece, which may, for example, be round, elliptical, or generally rectangular. In particular, the term "glass wafer" also encompasses glass panels or glass panes.

[0008] Although such glass interposers have been known for some time, certain difficulties still arise in practice, for example, regarding the mechanical stability of these wafers or the durability of metallization on these glass wafers. This also applies, for example, to the metallization within the opening itself.

[0009] A glass wafer must therefore be optimized under the following aspects:

[0010] - Metallizations, such as metallic electrodes, must adhere optimally to the surface of the glass, especially within the opening of the glass wafer,

[0011] - thermal stresses that can arise during signal transmission through contacting in the glass wafer should be as low as possible to ensure long-term stability of the interposer; in particular, tensile stresses on the surfaces must be avoided.

[0012] Finally, it is important that the glass wafer is mechanically stable during the production and use of the semiconductor, in particular that it has good mechanical strength.

[0013] However, the past has shown that there is still room for improvement, particularly with regard to the adhesion strength of a metal layer to glass and the mechanical strength of the glass wafer.

[0014] Glass wafers can generally be made more mechanically stable using various processes. For example, US patent application US 2009 / 0220761 A1 describes a process for chemically tempering glass.

[0015] Furthermore, it is known that laser treatment can lead to a compositional change in a vitreous body. This is described, for example, in US patent application US 2020 / 024188 Al.

[0016] Sun et al. describe in Optical Materials, Volume 108, 2020, that etching of fused silica with KOH is possible and can lead to the formation of a diffusion layer of the etching medium in the surface of the fused silica. This can increase the fused silica's resistance to laser irradiation. Furthermore, there are various studies demonstrating that the mechanical and / or chemical properties of a glass or glass-ceramic can be altered by etching. However, no studies have been conducted on structured glass wafers for use as interposers.

[0017] There is therefore a general need for glass wafers with improved mechanical strength, which at the same time are also designed to be easy to coat, especially in such a way that metallizations adhere well.

[0018] The object of the invention is to provide glass wafers that at least partially mitigate the weaknesses of the prior art. A further object is to provide a method for producing such glass wafers.

[0019] The problem is solved by the subject matter of the independent claims. Preferred and specific embodiments can be found in the dependent claims, the description, and the drawings of the disclosure.

[0020] The present invention therefore relates to a glass wafer comprising at least one opening with a surface having two opposing side surfaces and a circumferential edge surface. The glass encompassed by the glass substrate comprises at least one network former and at least one metal oxide. The at least one opening has a maximum lateral dimension, in particular a diameter, of at most 400 pm, preferably of at most 300 pm, and particularly preferably of at most 200 pm. The maximum lateral boundary is preferably at least 10 pm. The glass wafer has a thickness of at least 10 pm. Advantageously, the thickness of the wafer is limited and amounts to at most 5 mm. Preferred lower limits for the thickness of the wafer are at least 30 pm, for example 50 pm or 100 pm. Preferred upper limits can be 3 mm or 1.5 mm or even only 1 mm.

[0021] It can be provided that the thickness of the glass wafer and the maximum lateral dimension are in a ratio to each other in order to achieve advantageous strengths of the glass wafer. This aspect ratio of the maximum lateral dimension of the opening (e.g., the diameter of the opening) to the thickness of the glass wafer is preferably at least 1:100.

[0022] The leaching depth of metal ions, in particular of alkali metal ions, in particular of lithium, sodium and / or potassium ions, is at least 1.1 times greater in the surface of the at least one opening than the leaching depth on the two side surfaces, preferably 1.5 times greater, particularly preferably 2 times greater, more preferably 5 times greater and most preferably 10 times greater, wherein the leaching depth is preferably at most 15 times greater than on the two side surfaces, which is preferably determined by means of a ToF-SIMS measurement.

[0023] Preferably, the glass substrate comprises a glass comprising from 30 wt% to 75 wt% SiO2, preferably up to 65 wt% SiO2.

[0024] Such a design has a number of advantages.

[0025] The glass wafer is generally designed such that it comprises a glass substrate. A glass substrate is understood to be a shaped body made of glass which, apart from shaping, such as cutting, has not yet undergone any finishing and / or further processing steps, such as coating. The wafer can therefore generally be understood as a finished substrate. In this sense, the sides and surfaces of a substrate and a wafer correspond within the scope of the present disclosure. Therefore, if reference is made to a side surface of the glass wafer or an edge surface of the wafer, this also corresponds to the side surface or edge surface of the glass substrate. The glass wafer or the glass substrate is generally disk-shaped or plate-shaped in the present case. The thickness of the glass wafer or-Substrate is therefore its smallest lateral dimension, in particular less than its length and width or, in the case of a round wafer / substrate, its diameter.

[0026] The glass wafer has at least one opening with a maximum lateral dimension of 400 pm at most, preferably 300 pm at most, and particularly preferably 200 pm at most, and depending on the precise design, can also be significantly smaller. The opening can also be generally referred to as a "via."

[0027] The glass which is comprised by the glass substrate and accordingly by the glass wafer is not a single-component glass and accordingly comprises, in addition to a network former, generally metal oxides in particular.

[0028] This is advantageous because it allows for a simple and cost-effective production of the wafer using conventional melting processes, unlike with quartz glass.

[0029] In the surface of the at least one opening, the leaching depth of metal ions, in particular of alkali metal ions, in particular of lithium, sodium and / or potassium ions, is at least 1.1 times greater than the leaching depth on the two side surfaces, preferably 1.5 times greater, particularly preferably 2 times greater, more preferably 5 times greater and most preferably 10 times greater, wherein the leaching depth is preferably at most 15 times greater than on the two side surfaces.

[0030] This surprising design of the glass wafer according to embodiments is very advantageous, as it has been shown that the properties of the glass wafer can be significantly improved in this way. In particular, this design surprisingly makes it possible to improve the mechanical strength of the glass wafer, thus increasing handling and service life.

[0031] The reasons for this are not entirely clear. It is known, as described above, that ion exchange can increase the mechanical strength of a glass, a process known as chemical tempering. However, in this case, ion exchange is not performed; instead, etching occurs. This results in the removal of the entire glass, but the dissolution of the glass network is not homogeneous, so that certain ions, especially metal ions, are also released from the glass network. In other words, the glass network with the network-forming elements remains in a surface area, albeit with a certain depletion of metal ions.

[0032] Surprisingly, it has not only been shown that this can have an advantageous effect on the properties of the glass wafer, for example with regard to the adhesion of metallization subsequently applied to the glass wafer or with regard to the resulting strength. It has also been shown that the leaching in the side surfaces differs from the leaching in the surface of the at least one opening. In particular, it was shown that the leaching depth in the feedthrough is at least 1.1 times greater than the leaching depth on the two side surfaces, preferably 1.5 times greater, particularly preferably 2 times greater, more preferably 5 times greater, and most preferably 10 times greater, wherein the leaching depth is preferably at most 15 times greater than on the two side surfaces of the wafer.

[0033] The reasons for this are not fully understood. However, the inventors assume that it is due to the specific etching process, resulting in different concentration gradients within the narrow opening, leading to the formation of this strong leaching compared to the leaching at the wafer surface. The leaching depth and its different formation on the side surfaces of the wafer compared to the surface of the opening can be determined, in particular, using ToF-SIMS measurements.

[0034] This is particularly advantageous for alkali-containing glasses, where alkali leaching occurs. For example, it has been shown that when using a KOH-containing alkali, sodium ions are preferentially leached, although, as explained above, their leaching differs on the side surfaces and the surface of the via. At the same time, an enrichment of potassium ions can be observed on the wafer surface (see also Figures 8 to 11).

[0035] The inventors suspect similar effects when leaching lithium-containing glass with KOH- and / or NaOH-containing lye. The replacement of glasses containing alkaline earth metal ions, either alternatively or in addition to alkali ions, could also exhibit a similar leaching pattern.

[0036] According to one embodiment, the glass substrate comprises a glass containing from 30 wt.% to 85 wt.% SiO2. A preferred range for the SiO2 content can be from 60 to 84 wt.%. It has been shown that such a glass is particularly advantageously suited for forming a glass wafer according to embodiments.

[0037] According to a further embodiment, the glass wafer is designed such that the breaking strength of the glass wafer is at least 400 MPa and preferably at most 650 MPa and / or that the Weibull modulus of the glass wafer is between 4.2 and 7.1.

[0038] In other words, according to this embodiment of the wafer, the wafer is designed to be particularly break-resistant.

[0039] According to a preferred embodiment, the glass comprises the following components in wt.% on an oxide basis: B2O3 5 to 25, preferably 8 to 25

[0040] AhCh 0 to 25, preferably 0 to 10.

[0041] According to yet another form, the glass wafer has a roughness of at most 1000 nm on at least one surface, in particular on at least one of the two side surfaces. Preferably, the roughness can be less than 100 nm or even less than 10 nm. According to one embodiment, the roughness is at most 1 nm or even less.

[0042] It has been found that the glasses listed below are particularly suitable for the manufacturing process with laser irradiation, formation, filamentary damage and subsequent etching with merging of widening channels along the filamentary damage.

[0043] According to a first embodiment, the composition comprises the following components in wt.% on an oxide basis:

[0044] The following ranges in wt% on an oxide basis are advantageous:

[0045] A further advantageous embodiment comprises wt.% on an oxide basis:

[0046] A further advantageous embodiment comprises wt.% on an oxide basis:

[0047] A further advantageous embodiment comprises wt.% on an oxide basis:

[0048] Another advantageous embodiment comprises wt.% on an oxide basis:

[0049] For all of the above-mentioned glass compositions, coloring oxides such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, CuO, Cr2O3 may be added if desired. 0-2 wt.% of As2O3, Sb2O3, SnO2, SO3, Cl, F, and / or CeO2 may be added as refining agents, and the total amount of the total composition is 100 wt.% in each case.

[0050] According to a further advantageous embodiment, the glass comprises the following

[0051] Components in wt% on an oxide basis:

[0052] SiO2 30 to 75, preferably 30 to 65

[0053] B2O3 6 to 25, preferably 6 to 10.5

[0054] AI2O3 1 to 15

[0055] Na2Ü 1 to 15, preferably 3 to 15

[0056] K2O 0.5 to 15, preferably 3 to 15

[0057] ZnO 0 to 12

[0058] TiCh 0 to 10, preferably 0.5 to 10

[0059] CaO O to 0.1. According to a further advantageous embodiment, the glass comprises the following components in wt.% on an oxide basis:

[0060] SiO258 to 65

[0061] B2O3 6 to 10.5

[0062] AI2O3 14 to 25

[0063] MgO 0 to 3

[0064] CaO 0 to 9

[0065] BaO 3 to 8

[0066] ZnO 0 to 2.

[0067] It is generally advantageous that the sum of the contents of MgO, CaO and BaO is characterized by being in the range of 0 to 18 wt% or 0 to 10 wt% or 0 to 4 wt%.

[0068] It has proven particularly advantageous for all embodiments if the total alkali content is limited. This means that the sum of Li2O + Na2O + K2O is advantageously less than 15 wt.%, particularly advantageously less than 5 wt.%.

[0069] Advantageous Na2O contents for all embodiments are from 0 to 8 wt.%, in particular from 1 to 5 wt.%. Advantageous K2O contents for all embodiments are from 0 to 8 wt.%, in particular from 0 to 3 wt.%.

[0070] It has been observed, applicable to all embodiments, that it is particularly advantageous if the Li2O content is lower than that of Na2O and / or K2O. This means that Li2O / Na2O <1 and / or Li2O / K2O <1. The glasses mentioned herein are particularly advantageously free of Li2O. Unavoidable impurities, which can usually be in the range of up to 5 ppm, can of course also be present. Surprisingly, it has been found that the wafer according to embodiments of the present disclosure is particularly well suited for connection technology, in particular for providing very high data rates. For this purpose, rather small vias are necessary. Furthermore, it has been shown that through the selective leaching of metal ions, in particular alkali ions, metallizations adhere particularly well to the wafer, especially in the region of the via or the through-opening itself.

[0071] Metallizations, for example comprising or made of Ni, Cr, Ti, Pd, which can also act as adhesion promoters between the glass substrate or wafer and further layers, for example further metal layers, can be applied, for example, electroless plating or galvanically.

[0072] According to a preferred embodiment, the metallization comprises copper, silver, gold, or aluminum. The copper-comprising layer can be applied directly to the glass wafer or to an adhesion-promoting layer, for example, comprising or made of Ni, Cr, Ti, or Pd, which is applied between the glass wafer and the copper-comprising layer. According to a further embodiment, the metallization can consist predominantly, i.e., more than 50 wt.%, or substantially, i.e., more than 90 wt.%, or entirely of copper.

[0073] The excellent adhesion of metallizations can be demonstrated, for example, by performing a scratch test on the surface of a metallized wafer, as explained in more detail below. Another method is the "Tesate test," in which an adhesive strip is applied to the sample and the force required to peel off the adhesive strip and coating is measured.

[0074] The invention also relates to a method.

[0075] The method for producing a glass wafer comprising a glass substrate comprising at least one opening, having two opposite side surfaces and a circumferential edge surface, in particular a glass wafer according to an embodiment of the present disclosure, comprises the steps:

[0076] - Providing a disc-shaped glass substrate,

[0077] - Directing a laser beam of an ultrashort pulse laser onto one of the side surfaces of the disc-shaped glass substrate, wherein the laser beam is shaped by means of focusing optics into an elongated focus in the disc-shaped glass substrate, so that the radiated energy of the laser beam generates filamentary damage in the volume of the disc-shaped glass substrate, the longitudinal direction of which is perpendicular to at least one of the side surfaces of the disc-shaped glass substrate, and wherein, to generate filamentary damage, the ultrashort pulse laser radiates a pulse or a pulse packet with at least two consecutive laser pulses,

[0078] - Etching the disc-shaped glass substrate at least in the region in which filament-shaped damages are formed in the disc-shaped glass substrate, in a liquid etching medium, wherein the filament-shaped damages are widened to form channels, wherein the liquid etching medium is or comprises an alkali, preferably a potassium-containing alkali.

[0079] The inventors have discovered that such a procedure, especially etching using a lye, is particularly advantageous.

[0080] It has been shown that metallization applied to the wafer adheres better when etched using an alkali than when etched using an acid.

[0081] Etching with a caustic solution appears to result in fewer metal ions, particularly alkalis and / or alkaline earths, being leached from the glass network. This appears to improve the adhesion of the metallization to the glass. The inventors suspect that this is due to a diffusion process from the glass into the metallization.

[0082] As already explained above, it has been shown that it is possible in this way to obtain a glass wafer in which the leaching in an opening differs significantly from the leaching on the surface of the glass wafer, in particular on the two side surfaces.

[0083] In particular, the leaching depth in the opening is higher than the leaching depth on the surface.

[0084] In other words, leaching appears to be more pronounced in the openings than on the surface of the glass wafer. Nevertheless, it has been shown that very good contact between the metallization and the glass surface is still possible even in the openings.

[0085] Etching with a potassium-containing lye, preferably an aqueous potassium-containing lye, appears to be particularly advantageous here. This results in a particularly advantageous leaching profile, which can prove beneficial in subsequent processing steps in the manufacture of an interposer. Of particular note here is improved adhesion of the metallization to the etched glass surface.

[0086] Preferably, the etching can be carried out at a temperature of at least 110°C, for example at 115°C or 120°C, i.e. with an etching medium which has a temperature of at least 110°C, preferably at least 115°C, preferably of at most 150°C.

[0087] In this way, it seems particularly easy to achieve the special surface structure of the glass wafer.

[0088] Surprisingly, it has been shown that changing the other process parameters is not absolutely necessary to achieve advantageous properties of the glass wafer. In particular, it is not necessary to adjust the laser parameters for generating filaments, which are necessary to later obtain the corresponding openings in the glass wafer, for example, to improve the strength of the glass wafer compared to state-of-the-art glass wafers. Rather, surprisingly, adjusting the etching parameters appears sufficient to achieve improved properties, particularly the temperature of the etching bath.

[0089] According to one embodiment, the glassy material of the disc-shaped glass substrate is removed at a removal rate of less than 5 pm per hour. This appears to be advantageous because a different surface structure appears to form in this way than with higher removal rates. In particular, this method appears to lead to selective removal of the glass substrate, which appears to be advantageous with regard to the mechanical properties of the resulting glass wafer. It also appears to be advantageous with regard to the resulting adhesive strength if a rather slow removal is selected. The inventors suspect that this method leads to more selective removal and the resulting surface structure is correspondingly more favorable, in particular certain substances, such as metal ions, can be leached out to a lesser extent.The inventors suspect that this could possibly result in a kind of "pre-stressing effect" - or alternatively, in comparison to a strong, rapid, comprehensive removal, a less severe weakening of the glass structure could result, which is advantageous in the subsequent handling of the glass wafer.

[0090] According to one embodiment, the etching time is at least 12 hours. Even a slower or longer etching time can lead to a beneficial increase in the mechanical stability of the resulting glass wafer.

[0091] According to one embodiment, the number of pulses of a burst for inducing filamentous damage is at least 2 or at most 7.

[0092] However, it is also possible and may be preferable to create the filament-shaped damage with only one laser pulse and not in the form of a pulse packet.

[0093] According to yet another embodiment, the pulse duration of the laser is in the range of 0.5 ps to 2 ps. According to yet another embodiment, at least one surface is mechanically polished. This is particularly advantageous for achieving a low roughness and can also contribute to a further increase in the mechanical strength of the glass wafer. Particularly preferably, the polishing takes place after etching.

[0094] Drawings

[0095] The invention is explained in more detail below with reference to the drawings.

[0096] Fig. 1 is a perspective view of a glass wafer according to an embodiment,

[0097] Fig. 2 is a sectional view of a glass wafer according to an embodiment,

[0098] Fig. 3 is a schematic representation of the process for producing a

[0099] Glass wafer according to one embodiment,

[0100] Fig. 4 and 5 show the fracture probabilities of different glass wafers,

[0101] Fig. 6 and 7 ToF-SIMS profiles to illustrate the different leaching of glass wafers depending on the etching medium,

[0102] Fig. 8 to 11 ToF-SIMS profiles to illustrate the different surface structure in the opening and on the side surface of glass wafers according to embodiments,

[0103] Fig. 12 to 15 ToF-SIMS profiles of differently pretreated and metallized

[0104] Glass wafers, as well as

[0105] Fig. 16 to 17 representations of scratch marks on metallized glass wafers. Fig. 1 shows a schematic and not to scale perspective representation of a glass wafer 1 according to one embodiment. The glass wafer 1 comprises a glass substrate (not designated here) comprising at least one opening 7, which in the context of the present disclosure can also be referred to as a "via". The glass substrate or, correspondingly, also the glass wafer 1 comprises two opposite side surfaces 3, 5. The glass wafer 1 or, correspondingly, also the glass substrate comprises a glass comprising at least one network former, preferably SiO2, and at least one metal oxide. The glass is thus formed as a multi-component glass, which offers significant advantages over, for example, pure quartz glass. In particular, the glass is thus amenable to a manufacturing and shaping process in a conventional melting process.

[0106] Fig. 2 shows a sectional view of a glass wafer 1 according to one embodiment. Shown in section here are two openings 7, which are visible as holes 71, 72 on the respective sides 3, 5 of the glass wafer 1. Also shown is the depletion zone 9 caused by the etching process. This is divided into two regions: region 91 formed on both side surfaces 3, 5 of the glass wafer 1 with only a small depletion depth or leaching depth, and region 92 formed in opening 7 with a significantly greater leaching depth.The leaching depth, particularly for metal ions in the region of the opening 7, is at least 1.1 times greater than the leaching depth on the two side surfaces, preferably 1.5 times greater, particularly preferably 2 times greater, more preferably 5 times greater, and most preferably 10 times greater, with the leaching depth preferably being 15 times greater than on the two side surfaces 3, 5 of the glass wafer 1. This can preferably be determined in a ToF-SIMS measurement.

[0107] Fig. 3 shows, in a schematic and not-to-scale representation, an example of a method for producing a glass wafer 1 (not shown here). A glass substrate 2 is provided for this purpose. The sides 3, 5 of the glass substrate 2 correspond to the sides of the subsequent glass wafer 1.

[0108] A laser beam 13 is generated by an ultrashort pulse laser 11 and directed onto the glass substrate 2. The focusing optics 15 form an elongated focus 17 in the disc-shaped glass substrate 2, so that the radiated energy of the laser beam 13 creates a filament-shaped damage 19 in the volume of the disc-shaped glass substrate 2, the longitudinal direction of which is perpendicular to the surface of the glass substrate 2 or to at least one of the two side surfaces 3, 5 of the glass substrate 2.

[0109] This process can be repeated at other locations on the glass substrate. In the further course of the process, an opening is created from the filament-shaped damage 19, which serves as a through-hole in the interposer.

[0110] Fig. 4 shows the strength of glass wafers as a function of the etching medium used or of glass substrates that have undergone a different pretreatment. All measurement data were obtained without openings in the wafers or substrates under consideration. As is common when depicting the strength of brittle materials, the points are plotted in a log-log Weibull diagram. This also applies to Fig. 5.

[0111] Measurement points a) (black solid points) are fracture probabilities for glass substrates that were neither etched nor otherwise pretreated, and thus represent the reference in terms of fracture probability. Points b) (black solid triangles) represent fracture probabilities determined for glass wafers etched with KOH. Points c) (open square standing on its tip) are fracture probabilities for wafers etched with HF. Finally, point d) (square with an inscribed cross) show fracture probabilities for a polished wafer. As can be seen from the fracture probability as a function of the stress acting on the substrate or wafer, there are clear differences here. Accordingly, the wafers etched with KOH demonstrate improved mechanical stability, even compared to completely unetched substrates and especially to samples etched with HF.

[0112] This is particularly true when temperatures of the etching bath, i.e., the alkali used, for example, a KOH-containing alkali, are set at at least 110°C, preferably at least 115°C, for example, 120°C. As explained above, it has been shown that the probability of glass breakage can be significantly influenced by the choice of etching medium and also by its temperature. This can also be demonstrated for the structured substrate, i.e., the resulting glass wafer.

[0113] Fig. 5 shows the fracture probabilities as a function of the stress applied to a wafer for two different types of wafers. Points a) (open circles) show the fracture probabilities for a glass wafer, obtained from a 1 mm thick wafer with openings with a diameter of 50 pm. Etching was carried out using HF. In contrast, points b) (open triangle upright on its vertex) show fracture probabilities for a 1 mm thick wafer etched with KOH and with openings with a diameter of 10 pm.

[0114] The characteristic strength, o c , as well as the Weibull modulus for these samples are summarized in the following table, with the confidence interval given in parentheses:

[0115] The characteristic value and the Weibull modulus are the two parameters of a Weibull distribution. The strengths of brittle materials are usually described by Weibull distributions. The characteristic strength is then one of the two parameters that define the distribution.

[0116] As can be seen from these data, the data for the characteristic strength and Weibull modulus depend on the etching process. In this case, it results in glass wafers etched using an alkali, in this case KOH, exhibiting greater strength.

[0117] It can be shown that samples etched using HF exhibit a significantly increased leaching and depletion of metal ions, especially alkali metal ions such as sodium and potassium ions, relative to etching using a caustic such as KOH.

[0118] This is illustrated by way of example in Figures 6 and 7, which show ToF-SIMS profiles of glass wafers etched using HF (filled circles) and KOH (open circles), respectively. It is clearly evident that the KOH-etched samples are less depleted of metal ions, in this case sodium and potassium ions, than glass wafers etched using HF.

[0119] The inventors hypothesize that this reduced depletion of the surface zone of a glass wafer leads to the observed improved strength. It is generally believed that sodium depletion in a surface zone increases the propagation of cracks in a glass. A sodium-depleted surface layer has a lower density compared to non-sodium-depleted glass, which should lead to the development of tensile stresses at the surface. This, in turn, should lead to an increased likelihood of crack initiation and growth, ultimately resulting in failure by fracture.

[0120] Every etching process also intrinsically leads to leaching and a depletion of metal ions, for example sodium ions. However, the precise formation of this depletion zone appears to be critical, especially for structured substrates or wafers with openings. The inventors suspect that this could be related to the laser structuring process, because the laser treatment initially induces microcracks in the substrate / wafer. In this case, however, etching initially has a more advantageous effect, because the etching and the associated material removal initially eliminate such microcracks and prevent further crack propagation. However, as observed and explained, HF or acid etching obviously leads to a significantly greater depletion of metal ions, which somewhat reduces this positive effect.Alkaline etching offers advantages here because it results in less leaching of metal ions, especially sodium, which better supports the minimization of crack propagation. The inventors suspect that the general correlations of sodium depletion, which lead to an increased probability of fracture, apply not only to sodium but to metal ions in general. Therefore, the overall improvement in the mechanical strength of the structured glass wafers compared to prior art wafers could be attributed to the overall reduced leaching compared to known wafers.

[0121] The inventors suspect that this could be due to the mechanism of acid etching, for example, with HF, which initially involves adsorption of the fluorine anion on the glass surface, leaching of metal ions, particularly alkali and / or alkaline earth ions, creating a porous layer on the glass surface, followed by rapid rupture of Si-O-Si or XO-Si bonds (where X stands for another network former, such as aluminum or boron). The inventors suspect that, in the case of alkaline etching, in contrast, a more uniform removal rate results, which weakens the bonds by the network formers less. In this way, the surface chemistry of the glass is kept more intact than with etching with an acid such as HF.Although this has the advantage of a faster process, it obviously has significant disadvantages with regard to the resulting product, such as reduced mechanical strength.

[0122] Interestingly, this reduced surface leaching has also been shown to have advantages when considering subsequent processing steps. For example, metal ions can adhere better to the glass wafer, presumably due to interdiffusion of metal ions into subsequently applied metallizations.

[0123] The differences in the leaching depth between the side surfaces and the surfaces in the opening are shown in Figs. 8 to 11. Here, ToF-SIMS profiles of metal ions are shown, namely in Figures 8 and 9 of sodium ions and in Figures

[0124] 10 and 11 of potassium ions. It is clearly visible that for sodium ions, when leached with KOH-containing lye, the leaching is stronger inside the opening (Fig. 9) than at the side surface (Fig. 8). Fig. 10 (side surface) and

[0125] 11 (inside the opening) show an enrichment of potassium ions in the near-surface area.

[0126] Figures 12 to 17 illustrate the difference between prior art glass wafers and those according to embodiments of the present disclosure. The glass wafers have been metallized in each case because this most clearly demonstrates the difference in the glass wafers and the type of pretreatment, and this corresponds to the application.

[0127] The metallized glass wafers are, for example, glass wafers obtained using a prior art process, in this case HF etching, as well as according to the present disclosure. Metallization was carried out at 100°C in each case, with an adhesion-promoting layer, one of chromium and one of titanium, being applied first, followed by copper metallization. The starting deposition temperature was 100°C. The adhesion strength can generally be improved at a higher deposition temperature, so that the beneficial effect of etching is preferably evident at this lower temperature. Generally, however, deposition temperatures of up to 400°C or even higher are possible for metallization.

[0128] Figs. 12 and 13 show the ToF-SIMS profiles of wafers metallized at 100°C with chromium as an adhesion-promoting layer between glass and copper. As can be seen, the levels of sodium (Fig. 12) and potassium (Fig. 13) in the glass, i.e., in the bulk region of the metallized glass wafer, are identical in each case. However, differences arise with regard to the content of sodium and potassium (represented by the signal of the singly positively charged ions of sodium and potassium, respectively). The level of sodium and potassium is higher in the copper metallization area after etching with KOH than after etching with HF. The inventors suspect that this is due to the fact that the lower leaching of the glass surface by treatment with KOH allows the corresponding metal ion to diffuse more quickly into the metallization, thus ensuring overall better adhesion.Since this effect of the leaching depth is even more pronounced in the surfaces of the opening, the inventors assume that the metallization adheres even better in the opening itself than is already the case in the area of ​​the side surfaces of the wafer.

[0129] The corresponding picture is shown in Figs. 14 and 15 with regard to the use of an adhesion-promoting titanium layer between the glass surface and the copper layer. Here, too, the levels of sodium (Fig. 14) and potassium (Fig. 15) in the glass, i.e., in the bulk area of ​​the metallized glass wafer, are identical. However, differences also arise with regard to the content of sodium and potassium (represented in each case by the signal of the singly positively charged ions of sodium and potassium, respectively). The level of sodium and potassium is higher in the area of ​​the copper metallization after etching with KOH than after etching with HF. The inventors suspect that this is due to the fact that the lower leaching of the glass surface by treatment with KOH allows the corresponding metal ion to diffuse more quickly into the metallization, thus ensuring overall better adhesion.Since this effect of the leaching depth is even more pronounced in the surfaces of the opening, the inventors assume that the metallization adheres even better in the opening itself than is already the case in the area of ​​the side surfaces of the wafer.

[0130] Finally, Figures 16 and 17 show scratch marks on differently etched glass wafers, which were subsequently metallized. Titanium was used as an adhesion-promoting layer.

[0131] The scratch resistance of metallization is generally determined by the Knoop scratch test, which is a standard procedure for determining the scratch resistance and adhesion strength of metallizations in the coating and metallization industry. This test involves applying a diamond tip to the surface of the coating to be tested and moving this tip along a path at a constant speed. The force acting on the tip can be constant or continuously increased along the test path. For the samples shown in Figures 16 and 17, the force was continuously increased along a test path. The corresponding forces are indicated in the respective figures. The load at which the coating fails is noted.Failure of the coating occurs when initial cracks appear in the coating next to the scratch itself, which can then often lead to scalloping or even spalling. The load at which failure due to cracking occurs is determined by visual inspection under a microscope. This load is also referred to as the "critical load" (LC).

[0132] Figure 16 shows a metallization process in which the glass wafer was etched using KOH. Subsequently, a titanium adhesion-promoting layer was applied, followed by a copper layer. The temperature during metallization was 100°C because, as already explained above, this represents the more critical case.

[0133] The figure in Fig. 16 shows:

[0134] - 0.03 N and 1 N (5 mm) no delamination (a, b)

[0135] - IN and 2 N (5 mm) no delamination (c, d)

[0136] - 2 N and 3 N (5 mm) no delamination (e, f) - 3 N and 4 N (5 mm) no delamination (g, h)

[0137] In comparison, Fig. 17 shows the scratch trace for a metallized glass wafer, which was metallized like the glass wafer in Fig. 16, but the glass wafer was etched using HF. Fig. 17 shows:

[0138] - 0.03 N and 1 N (5 mm) no delamination (a, b)

[0139] - IN and 2 N (5 mm) no delamination (c, d)

[0140] - 2 N and 3 N (5 mm) delamination in 1 of 2 measurements from a critical force of approx. 2.9 N (e, f) - 3 N and 4 N (5 mm) delamination in 1 of 2 measurements from a critical force of 3 N (g, h).

[0141] As stated, the adhesion of metallizations is better for glass wafers etched by means of a basic etch according to embodiments.

[0142] List of reference symbols

Claims

Patent claims 1. A glass wafer comprising a glass substrate comprising at least one opening with a surface having two opposing side surfaces and a circumferential edge surface, wherein the glass substrate comprises a glass comprising a network former and at least one metal oxide, wherein the at least one opening has a maximum lateral dimension, in particular a diameter, of at most 400 μm, preferably of at most 300 μm and particularly preferably of at most 200 μm, wherein the glass wafer has a thickness of at least 10 μm, wherein in the surface of the at least one opening, the leaching depth of alkali metal ions, in particular of lithium and / or sodium ions, is at least a factor of 1.1 greater than the leaching depth on the two side surfaces, preferably a factor of 1.5 greater, particularly preferably a factor of 2 greater, more preferably a factor of 5 greater and most preferably a factor of 10 greater,wherein the leaching depth is preferably at most 15 times greater than on the two side surfaces, preferably determined in a ToF-SIMS measurement, and wherein the glass substrate preferably comprises a glass comprising 30 wt.% to 85 wt.% SiO2, preferably from 60 to 84 wt.% SiO2.

2. Glass wafer, in particular according to claim 1, comprising a glass substrate comprising at least one opening with a surface having two opposite side surfaces and a circumferential edge surface, wherein the glass substrate comprises a glass comprising a network former and at least one metal oxide, wherein the at least one opening has a maximum lateral dimension, in particular a diameter, of at most 400 pm, preferably of at most 300 pm and particularly preferably of at most 200 pm, wherein the glass wafer has a thickness of at least 10 pm, wherein in the surface of the at least one opening the leaching depth of metal ions, in particular alkali metal ions, in particular potassium and / or sodium ions, is at least by a factor of 1.1 greater than the leaching depth on the two side surfaces, preferably by a factor of 1.5 larger, particularly preferably by a factor of 2 larger, more preferably by a factor of 5 larger and very particularly preferably by a factor of 10 larger, wherein preferably the leaching depth is at most 15 times greater than on the two side surfaces, preferably determined in a ToF-SIMS measurement, wherein preferably the characteristic strength of the glass wafer is at least 400 MPa and preferably at most 650 MPa and / or wherein the Weibull modulus of the glass wafer is between 4.2 and 7.

1.

3. A glass wafer according to any one of claims 1 or 2, wherein the glass comprises the following components in wt.% on an oxide basis: B2O3 5 to 25, preferably 8 to 25 AI2O3 0 to 25, preferably 0 to 10.

4. Glass wafer according to one of claims 1 to 3, wherein the glass wafer has on at least one surface, in particular on at least one of the two side surfaces, a roughness of at most 1000 nm, preferably of less than 100 nm or even less than 10 nm, in particular of at most 1 nm or even less.

5. A glass wafer according to any one of claims 1 to 4, wherein the glass comprises the following components in wt.% on an oxide basis: preferably with Li2Ü + Na2Ü + K2O from 0 to <15 wt.%, particularly preferably with Li2Ü / Na2Ü < 1 and / or with IÜ2O / K2O <1.

6. A glass wafer according to any one of claims 1 to 5, wherein the glass comprises the following components in wt.% on an oxide basis:

7. Glass wafer according to one of claims 1 to 6, comprising a metallization in at least one region of at least one side surface and / or at least one region of the surface of the opening.

8. A method for producing a glass wafer comprising a glass substrate comprising at least one opening, having two opposite side surfaces and a circumferential edge surface, in particular a glass wafer according to one of claims 1 to 6, comprising the steps: - Providing a disc-shaped glass substrate, - Directing a laser beam of an ultrashort pulse laser onto one of the side surfaces of the disc-shaped glass substrate, wherein the laser beam is shaped by means of focusing optics into an elongated focus in the disc-shaped glass substrate, so that the radiated energy of the laser beam generates filamentary damage in the volume of the disc-shaped glass substrate, the longitudinal direction of which is perpendicular to at least one of the side surfaces of the disc-shaped glass substrate, and wherein, to generate filamentary damage, the ultrashort pulse laser radiates a pulse or a pulse packet with at least two consecutive laser pulses, - Etching the disc-shaped glass substrate at least in the area in which filament-shaped damages are formed in the disc-shaped glass substrate, in a liquid etching medium, wherein the filament-shaped damages form channels be expanded, wherein the liquid etching medium is or comprises an alkali, preferably a potassium-containing alkali.

9. Method according to claim 8, characterized by at least one of the following features: - the glassy material of the disc-shaped glass substrate is removed at a removal rate of less than 5 pm per hour and / or - the etching time is at least 12 hours and / or - the etching medium has a temperature of at least 110°C and preferably of at most 150°C and / or - the number of pulses in a burst to induce filamentous damage is at least 2 or at most 7 and / or - the pulse duration of the laser is in the range of 0.5 ps to 2 ps, - mechanical polishing of at least one surface takes place.

10. Glass wafer, preferably glass wafer according to one of claims 1 to 7, produced or producible by a process according to one of claims 8 or 9.

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