Glass composition for production of structured glass elements from alkali-free glasses and structured, alkali-free glass elements

Abstract

The invention relates to an alkali-free glass which is suitable in particular for alkaline etching. The glass has a CaO content of < 7 mol%, a BaO content of less than 1.6 mol% and an SrO content of less than 1.6 mol%. The total content of alkaline earth metal oxides MO in the glass composition is less than 13 mol% and / or the ratio of the calcium oxide content to the total content of alkaline earth metal oxides Ca / ∑MO is < 0.4. In addition, the invention relates to a glass element in plate form having the glass composition, wherein the glass element has a first surface (2) and a second surface (3) opposite the first surface (2), and at least one recess that penetrates at least one of the surfaces (2, 3), wherein the recess extends in a longitudinal direction (L) and a transverse direction (Q) and the longitudinal direction (L) of the recess is in a transverse arrangement to the surface (2, 3) which is penetrated by the recess, wherein the recess takes the form of a channel (15) that extends through the glass element from the first surface (2) through the glass in the direction of the second surface (3) and penetrates at least the first surface (2). The glass element may especially be obtained by alkaline etching processes and is suitable for use in electronic components, for example as interposer.

Description

[0001] Glass composition for the production of structured glass elements from alkali-free glasses and structured, alkali-free glass elements

[0002] Field of the invention

[0003] In general, the invention relates to glass articles with structured glass surfaces. More specifically, the invention relates to an alkali-free glass composition for producing structured, alkali-free glass articles by basic etching in aqueous solutions.

[0004] Description

[0005] In many areas, precise processing is relevant, for example, in the form of structuring transparent, opaque, or non-transparent glass or glass-ceramic elements. Many applications require precise structures in the size range of a few micrometers. Depending on the specific application, the required structures can be recesses, depressions, channels with various cross-sectional shapes, or even freeform shapes. Thus, there is a need for structuring processes that allow for high flexibility in terms of shape, while at the same time allowing for minimal deviations in the dimensions and properties of the resulting structures.

[0006] Various methods for structuring glass are known from the prior art. For example, DE 10 2013 103 370 A1 describes a method for microperforating glass substrates in which the desired structures are obtained through a combination of laser irradiation and a subsequent etching process. In this process, the material in the areas that were previously subjected to laser treatment is removed by an etching process. Structuring methods are also known in which material is removed in an etching process in an acidic, aqueous solution. However, the structuring methods described above predominantly use alkali-containing glasses or pure quartz glass. In alkali-containing glasses, however, leaching of the alkali components can occur or these components exhibit a high degree of mobility.For this reason, alkali-containing glasses are not suitable for use in components in electronic packaging applications or semiconductors, for example, because the high mobility of alkali ions, particularly potassium and lithium ions, can lead to diffusion into other components and thus to contamination. Furthermore, alkali-free glasses exhibit excellent dielectric properties, making them highly important in semiconductor and electronic packaging manufacturing. At the same time, these manufacturing sectors require microstructuring, which can be achieved in particular through microstructuring. Pure quartz glass is unsuitable due to its inappropriate thermal expansion and the complex manufacturing process at very high temperatures.

[0007] However, it has been shown that when etching alkali-free glasses in acidic etching baths such as HF, only very low etching rates can be achieved and the etching process is therefore very inefficient.

[0008] Although an etching process in alkaline etching media is possible, only low etching rates can generally be achieved. Furthermore, alkali-free glasses generally contain higher levels of alkaline earth oxides. However, alkaline earth oxides are problematic during alkaline etching because, in the alkaline pH range, poorly soluble alkaline earth silicates form, which precipitate on the glass surface and form a passivation layer. Thus, the etching process locally stops or is at least significantly slowed down, so that the etching process causes the initially created filaments to expand into channels and the channel walls to deform. Object of the invention

[0009] It is therefore an object of the invention to provide a glass composition that enables the production of structured glass articles or for the processing of alkali-free glasses without the disadvantages described above and enables the production of structures with high dimensional accuracy while simultaneously achieving a high etching rate. A further object of the invention is to provide a structured glass element.

[0010] The object of the invention is already achieved by the subject matter of the independent claims. Advantageous embodiments and further developments are the subject matter of the dependent claims.

[0011] During the structuring process, a glass element is provided, and glass material is removed locally or in selected areas through an etching process. For this purpose, the glass element is brought into contact with an etching solution, at least in the areas to be structured.

[0012] The method provides at least the following steps a) to c): a) providing a glass element b) producing at least one filament-shaped channel using a laser beam from an ultrashort pulse laser, the longitudinal direction of the channel running transversely to the surface of the glass element c) treating the glass element obtained in step b) with a basic etching solution, the glass of the glass element being removed by the etching solution so that the channel produced in step b) is widened to form a recess. The glass composition according to the invention or a glass element with a corresponding glass composition has proven particularly advantageous for use in the etching process described above with regard to the etching rate and very little or even no formation of deposits or coatings on the glass surface.The glass element comprises an alkali-free glass with a CaO content of less than 7 mol%. An alkali-free glass is understood, in particular, to be a glass that contains no alkali oxides, apart from unavoidable traces introduced by the raw materials used. According to one embodiment, the total alkali oxide content in the glass is less than 500 ppm or 0.0005 mol%.

[0013] Because the glass is alkali-free, it is particularly suitable for use in electronic components. In alkali-containing glasses, alkali metal oxides are used primarily to adjust the glass viscosity or softening temperature, whereby the softening temperature can be lowered by adding alkali metal oxides. In alkali-free glasses, the softening temperature is adjusted by the content of alkaline earth metals such as calcium oxide. Thus, a minimum content of alkaline earth metal oxides is usually unavoidable in alkali-free glasses.

[0014] In step b), the glass element is laser filamented. A pulsed ultrashort laser is used to specifically create filaments, for example in the form of fine channels, in the glass element. These filaments can either pass completely through the substrate and thus extend from side surface to side surface, or they can only be connected to one of the surfaces of the side surface. The prerequisite for this process is that the glass element used is transparent to the wavelength of the laser radiation used. This process step is generally called laser filamenting. The basis of this process is also that the laser radiation used creates damage in the glass substrate. This damage forms the point of attack for the subsequent etching process. Accordingly, glasses that respond efficiently to laser irradiation, i.e. that can exhibit a sufficient degree of damage, are advantageous.In step c), which follows step b), the glass element thus structured is brought into contact with a basic etching solution, at least in the areas to be structured. This causes the introduced filaments or structures to expand or enlarge due to the etching process performed in step c).

[0015] When etching alkaline earth-containing glasses with acidic etching solutions, for example, when using HF-containing etching solutions, inhibition generally occurs relatively early in the etching process, so that the etching process proceeds only at very low etching rates. This inhibition is primarily a result of poorly soluble precipitates such as calcium fluoride, which settle on the glass surface and act as a passivation layer. Furthermore, the acid is inactivated. Therefore, the glasses according to the invention are particularly suitable for use in basic etching processes.

[0016] When etching with basic etching media, the high pH value in the exposed areas of the glass element causes the SiCh matrix to dissolve, forming silicates, and thus also to dissolve the remaining glass components in the corresponding area. Unlike with acidic etching, the etching process is not inhibited, or at least not as quickly. This can be explained by the fact that the high pH value of the etching solution causes the silicate dissolved from the glass to exist as a Lewis base and to exhibit high nucleophilicity. Accordingly, the silicate, as the dissolved component, can also act as an attacking nucleophile. As the concentration of silicates increases during the etching process, the effects described above are further amplified.

[0017] The glass element or the glass composition has a CaO content of less than 7 mol%, preferably less than 6 mol%. According to one embodiment, the CaO content is in the range from 0.2 mol% to <7 mol%, in particular from 1 mol% to <7 mol% or from 2 to <7 mol%, particularly preferably in the range from 3 to 6 mol%. Potassium ions can form calcium silicate (CaSiCh) during the etching process, which precipitates on the glass surface. This is disadvantageous because it can lead to passivation of the glass surface. Furthermore, the properties of the glass surface are altered by CaSiCh deposits. The CaO content according to the invention reduces this effect, so that the etching process can be carried out at sufficiently high etching rates.

[0018] NaOH or KOH solutions have proven to be particularly suitable as etching media.

[0019] An embodiment of the invention provides that the etching rate in a 6 molar KOH solution at an etching temperature of 100°C is at least 1.0 pm / h, preferably more than 1.0 pm / h.

[0020] Furthermore, in a first alternative, the glass has a ratio of the CaO content to the total content of alkaline earth oxides MO, comprising CaO, MgO, SrO and BaO, for which the following applies:

[0021] CaO / ^MO < 1, preferably in the range 0.4 to < 1.

[0022] This ratio is particularly advantageous because it ensures that the properties required for processing and using the glass, such as lowering the softening temperature and adjusting the thermal expansion coefficient, can be achieved even without the presence of alkali oxides by means of an appropriate content of alkaline earth oxides, and at the same time the content of the oxides of the higher alkaline earth metals, whose silicates have particularly low solubility products, can be kept relatively low in the glass, so that the disadvantages described above do not occur or only occur to a small extent during the etching process.

[0023] Alternatively or in addition to the CaO / MO ratio described above, in a second alternative, the total content of alkaline earth oxides MO in the glass is less than 13 mol%, preferably less than 12 mol%. The alkaline earth oxide content in the glass is preferably in the range of 9 to 12 mol%. It has been found that glasses with this CaO / MO ratio, in particular, can be processed just as efficiently by laser filamentation. Setting this ratio, in particular with the values ​​mentioned, particularly advantageously provides both good processability by laser irradiation and, at the same time, good etchability.

[0024] One embodiment of the invention provides that the barium oxide and / or strontium oxide content in the glass is less than 1.6 mol%. A strontium oxide content of less than 1.4 mol%, preferably less than 1 mol%, has proven particularly advantageous. It is assumed that by limiting the contents of higher alkaline earth metal oxides, it is possible to prevent the very low solubility products of the strontium or barium silicates from being exceeded during the etching process, thus leading to the formation of precipitates and inhibition of the etching process. Surprisingly, however, a barium oxide content of more than 0.7 mol% has proven advantageous. According to one embodiment, the BaO content is therefore in the range >0.7 to <1.6 mol%. Alkali-free borosilicate glasses have proven particularly advantageous. A further aspect of the invention relates to the provision of an alkali-free glass with the following composition in mol%:

[0025] SiO265 - 69.2

[0026] B2O3 9 - 11, preferably 7 - 12,

[0027] AI2O3 10.9 - 12, preferably 11 - 18,

[0028] BaO 0.7 - 1.6, preferably 0.8 - 1.2,

[0029] MgO 3 - 8, preferably 3.4 to 5,

[0030] SrO < 1.6, preferably < 1.4, particularly preferably < 1

[0031] CaO 4 - 7, preferably 5 to 6, CaO+MgO+SrO+BaO 9 - 13, preferably 11 - <12

[0032] £Na2O+K2O+Cs2O < 0.005 and where CaO / Jj CaO+MgO+SrO+BaO < 1, preferably in the range from 0.4 to <1. A further aspect of the invention relates to a plate-shaped glass element made of the alkali-free glass described above, having a first and a second surface arranged opposite the first. The plate-shaped glass element has at least one recess which breaks through at least one of the two surfaces of the glass element. The recess extends over a longitudinal direction (L) and a transverse direction (Q), wherein the longitudinal direction is arranged transversely to the surface of the glass element which is broken through by the recess. The recess is designed as a channel which extends at least from one surface of the glass element through the glass element towards the other surface. According to one embodiment, the recess is arranged as a continuous channel or opening between the first and the second surface of the glass element.

[0033] According to one embodiment, at least one wall of the recess of the glass element has a plurality of dome-shaped depressions. Such dome-shaped structures are obtained in particular by etching processes using basic etching solutions. According to one embodiment, the glass element is manufactured or can be manufactured by a process comprising the steps of laser filamentation and subsequent etching with a basic, aqueous etching solution.

[0034] In a further development of the invention, the glass element has a plurality of openings that are directly adjacent to one another, forming an edge. The edge forms an outer edge that surrounds at least parts of the glass element. Alternatively or additionally, the glass element has an edge formed by a plurality of openings that forms an inner edge of the glass element that at least partially surrounds the recess.

[0035] The plate-shaped glass elements are particularly suitable for use in electronic components, preferably as spacers. Such electronic components can be used, in particular, as components for the hermetic packaging of electro-optical functionalities, as components for camera imaging modules, or as components in semiconductor manufacturing. Detailed description

[0036] The invention is explained in more detail below with reference to Figures 1 to 3 and exemplary embodiments. They show:

[0037] Fig. 1 Schematic representation of the generation of damage in the glass element by a laser;

[0038] Fig. 2 Schematic representation of a glass element with multiple damages;

[0039] Fig. 3 Schematic representation of an etching process of the glass element

[0040] Fig. 1 schematically shows a glass element 1 with a first 2 and a second 3 surface, and a thickness D. The first surface 2 is arranged opposite, and in particular preferably plane-parallel to, the second surface 3. The glass element 1 further extends in a longitudinal direction L and a transverse direction Q. Preferably, the glass element 1 also has at least one side surface 4, which ideally surrounds the glass element 1 and whose height corresponds to the thickness D of the glass element 1. Ideally, the thickness D of the glass element 1 and the height of the side surface 4 extend in the longitudinal direction L. The first 2 and second 3 surfaces can further extend in the transverse direction.

[0041] Furthermore, Fig. 1 shows step b) of the method according to the invention according to one embodiment. Here, damage, in particular channels 15 or channel-shaped damage 15, is generated in the volume of the glass element 1 by a laser 101, preferably an ultrashort pulse laser 101. For this purpose, the laser beam 100 is focused by means of a focusing optics 102, for example a lens or a lens system, and directed onto a surface 2, 3, preferably the first surface 2 of the glass element 1. By focusing, in particular a prolonged focusing of the laser beam 100 onto an area within the volume of the glass element 1, the energy radiated by the laser beam 100 ensures that filament-shaped damage is generated, which, for example, widens the damage into a channel 15 through multiple laser pulses, for example in the form of a pulse packet.

[0042] Preferably, in step b), as shown in Figure 2, a plurality of channels 15 are produced in further steps, which are ideally arranged next to one another in such a way that a plurality of channels 15 results in a perforation, and this perforation or this plurality of channels forms outlines of a structure 16. Ideally, a structure 16 produced in this way corresponds to the shape of a recess to be produced. In other words, a spacing and a number of channels 15 are selected such that outlines of recesses to be produced are formed. In other words, a spacing and a number of channels 15 are selected such that outlines of recesses to be produced are formed.

[0043] Fig. 3 schematically illustrates step c) of the method according to one exemplary embodiment. The glass element 1 is detachably arranged on holders 50. The glass element 1 can simply rest on the holders 50 or be fixed to them. Preferably, certain areas of the holders 50 serve to cover or shield defined areas of the glass element 1.

[0044] To etch the glass element 1, it is held in the basic etching solution 200 by means of the holders 50. In the embodiment shown in Fig. 3, the glass element 1 is immersed in the etching solution 200 in the etching tank 202. The etching solution 200 used is a basic etching solution that can be stirred using a stirrer 60. Reference numeral 70 denotes etched surface areas of the glass element. Table 1 shows the glass compositions of the various embodiments 1 to 3 in mol% as well as the etching rates in pm / h. For this purpose, the glasses were etched with a 6 molar aqueous KOH solution at a temperature of 100°C for 22 hours. The etching rates were determined by determining the glass weight before and after the etching process.

[0045] Table 1: Glass compositions and etching rates of the working examples 1 - 3

[0046] The "Deposition" line indicates whether a white coating is visible to the naked eye on the etched areas after an etching time of 22 hours. Table 1 clearly shows that all of the exemplary embodiments 1 to 3 can be alkali etched at relatively high etching rates of more than 1 pm / h without a visible coating forming on the etched surfaces. The glass compositions according to the exemplary embodiments 1 to 3 are adjusted with regard to their total content of alkaline earth oxides as well as with regard to the content of the various alkaline earth oxides MgO, CaO, SrO and BaO such that the formation of sparingly soluble alkaline earth silicates can be avoided or at least significantly reduced, so that neither an inhibition of the etching process nor a coating formation occurs. The solubility product of the respective alkaline earth silicate decreases with increasing atomic number of the corresponding alkaline earth silicate.Therefore, it is advantageous if a relatively large proportion of the alkaline earth metal oxides in the glass are present as calcium oxide. This is described by the CaO / JjMO ratio. In Examples 1 to 3, this ranges from >0.44 to <1. In Examples 1 and 2, the total content of alkaline earth metal oxides is also below 12 mol%. At the same time, in Examples 1 to 3, the CaO content is below 7 mol%.

[0047] Through the interaction and proportions of the glass components described above, precipitation of alkaline earth metal silicates, and thus inhibition of the etching process and the formation of deposits on the glass surface, can be avoided or at least significantly reduced. Therefore, the glass can be etched with alkaline etching solutions at comparatively high etching rates. The relevance of the individual glass components and their proportions in the glass composition to the etching behavior can be demonstrated using Comparative Examples 4 to 15 presented in Tables 2 and 3. Comparative Examples 4 to 15 were etched under the same conditions as the exemplary embodiments shown in Table 1.

[0048] Table 2. Comparative Examples 4 to 9. Comparative Examples 4 to 7 illustrate the relevance of a low CaO content to etching performance. While the comparative examples have a total alkaline earth metal oxide content of less than 12 mol% and a CaO / J / MO ratio of more than 0.44, the CaO content is above 7 mol%. Comparative Examples 4 to 7 exhibit a low etch rate of less than 1 pm / h and a visible coating on the glass surface.

[0049] Furthermore, the influence of the SrO content on the etching behavior can be demonstrated using Comparative Examples 9, 10, and 13. Although Comparative Example 9 is comparable to the working examples in terms of the total alkaline earth oxide content, the CaO content, and the CaO / ^MO ratio, Comparative Example 9 has an SrO content of more than 1.6 mol%. The etching rate here is only 0.89 pm / h, and a visible deposit was formed. The same applies to Comparative Examples 10 and 13, which are shown in Table 3.

[0050] Table 3: Comparative examples 10 to 15

[0051] Comparative examples 14 and 15 illustrate the influence of BaO content on deposit formation and etching rates during the etching process. Excessively high BaO content leads to deposit formation.

Claims

Patent claims 1. Alkali-free glass, particularly suitable for laser filamentation and alkaline etching, wherein the glass composition has a CaO content of <7 mol%, a BaO content of less than 1.6 mol% and a SrO content of less than 1.6 mol% and wherein the total content of alkaline earth oxides MO in the glass composition is less than 13 mol% and / or the ratio of the calcium oxide content to the total content of alkaline earth oxides Ca / ^MO> 0.

4.

2. Glass according to the preceding claim, wherein the total content of alkaline earth oxides MO in the glass composition is less than 12 mol% and / or the ratio of the calcium oxide content to the total content of alkaline earth oxides Ca / ^MO is in the range from >0.4 to <1.

3. Glass according to one of the preceding claims, wherein the CaO content is in the range of 2 to < 7 mol%, preferably in the range of 3 to 6 mol%.

4. Glass according to one of the preceding claims, wherein the glass is a borosilicate glass and preferably has the following composition in mol%: SiO265 - 69.2 B2O3 9 - 11, preferably 7 - 12, Al2O3 10.9 - 12, preferably 11 - 18, BaO 0.7 - 1.6, preferably 0.8 - 1.4, MgO 3 - 8, preferably 3.4 to 5, SrO < 1.6 CaO 4 - 7, preferably 5 to 6, ^CaO+MgO+SrO+BaO 9 - 13, preferably 11 - <12 £Na2O+K2O+Cs2O < 0.005 and where CaO / Ä CaO+MgO+SrO+BaO > 0.4, preferably 0.4 to <1.

5. Use of a glass according to one of the preceding claims in a method for modifying a surface (2, 3) of a plate-shaped glass element (1) having a first surface (2) and a second surface (3) arranged opposite the first (2), as well as at least one recess which breaks through at least one of the surfaces (2, 3), wherein the recess extends in a longitudinal direction (L) and a transverse direction (Q) and the longitudinal direction (L) of the recess is arranged transversely to the surface (2, 3) which is broken through by the recess, wherein the method comprises at least the following steps a) to c): a) providing a plate-shaped glass element having a first and a second surface b) generating at least one filament-shaped channel (15) in the glass element by means of a laser beam (100) of an ultrashort pulse laser (101),wherein the longitudinal direction (L) of the channel (15) runs transversely to the surface of the glass element (1), and c) the surface (2, 3) of the glass element, which is penetrated by the channel (15), is exposed to an aqueous, basic etching medium (200) which removes the glass of the glass element at a removal rate r, wherein the channel (15) is widened by the etching medium so that a recess is formed.

6. Method according to the preceding claim, wherein an aqueous KOH solution with a concentration of 6 mol / l is used as the etching medium, the etching temperature is 100°C and the removal rate is at least 1 pm / h, preferably greater than 1 pm / h.

7. Plate-shaped glass element with a glass composition according to one of the preceding claims 1 to 4, in particular producible by the method according to one of the preceding claims 1 to 8, wherein the glass element has a first Surface (2) and a second surface (3) arranged opposite the first (2), and at least one recess which breaks through at least one of the surfaces (2, 3), wherein the recess extends in a longitudinal direction (L) and a transverse direction (Q) and the longitudinal direction (L) of the recess is arranged transversely to the surface (2, 3) which is broken through by the recess, wherein the recess is designed as a channel (15) which extends through the glass element from the first surface (2) through the glass in the direction of the second surface (3) and breaks through at least the first surface (2).

8. Plate-shaped glass element (1) according to the preceding claim, wherein at least one wall of the recess has a plurality of dome-shaped depressions.

9. Plate-shaped glass element (1) according to one of the two preceding claims, wherein the recess is formed as a channel (15) which extends through the glass element (1) from the first surface (2) to the second surface (3) and breaks through both surfaces (2, 3) 10. Plate-shaped glass element according to the preceding claim, wherein the glass element has a plurality of openings which extend through the glass element (1) from the first surface (2) to the second surface (3) and which are directly adjacent to one another, so that an edge (40) is formed which forms an outer edge of the glass element (1) which at least partially surrounds the glass element (1) or an inner edge of the glass element which at least partially surrounds the recess.

11. Use of a glass element according to one of the preceding claims 7 to 10 in an electronic component, in particular for rewiring semiconductor components, in particular interposers.

12. Electronic component, in particular as a component for the hermetic packaging of electro-optical functionalities, microfluidic cells, pressure sensors and / or camera imaging modules, comprising a glass element (1) according to one of the preceding claims 7 to 10.

Images