WO2016115685A1

WO2016115685A1 - Low cte glass with high uv-transmittance and solarization resistance

Info

Publication number: WO2016115685A1
Application number: PCT/CN2015/071159
Authority: WO
Inventors: Junming Xue; Wenliang PING; Huiyan Fan; Jose Zimmer; Hiroshi Kuroki
Original assignee: Schott Glass Technologies (Suzhou) Co. Ltd.
Priority date: 2015-01-20
Filing date: 2015-01-20
Publication date: 2016-07-28
Also published as: JP6827934B2; CN107108333A; JP2018504356A; TWI667214B; CN107108333B; TW201634418A

Abstract

A low CTE glass with a high UV-transmittance and high solarization resistance, a glass carrier wafer made of the low CTE glass and the use of such a glass carrier wafer. The glass comprises an alkaline metal oxide free composition of 50-75 mol%SiO2, 3-20 mol%Al2O3, 5-20 mol%B2O3, 0-15 mol%MgO, 0-15 mol%CaO, 0-15 mol%SrO, and 0-15 mol%BaO, where MgO+CaO+SrO+BaO amounts to 3 to 25 mol%and the average number of non-bridging oxygen per polyhedron (NBO) is equal or larger than -0.08 and equal or smaller than-0.38, or comprises an alkaline earth metal oxide free composition of 78-85 mol%SiO2, 0-7 mol%Al2O3, 8-15 mol%B2O3, 0-8 mol%Na2O, and 0-5 mol%K2O, where the NBO is equal or larger than -0.25 and equal or smaller than -0.10. The glass carrier wafer has a high UV-transmittance at a wavelength of 248 nm and/or 308 nm, good solarization resistance, a long recycling lifetime and reduced processing cost.

Description

Low CTE glass with high UV-transmittance and solarization resistance

Field of the invention

The present application relates to a low CTE glass with high UV-transmittance and solarization resistance for the use as glass carrier wafer. The invention also concerns a glass carrier wafer made from the low CTE glass and a use thereof as carrier wafer for the processing of a silicon substrate.

Background of the invention

Thinning silicon substrates in order to account for the continuous demand for size reduction of e.g. integrated circuits has become a common process in semiconductor industries. Silicon carrier wafers have been widely used as mechanical carriers for the thinning and back grinding of the silicon substrates in order to facilitate handling of the fragile thinned substrates. The silicon substrate is thereby generally bonded to the carrier wafer by an adhesive. De-bonding of the silicon substrate after processing from the carrier wafer can be achieved by e.g. solvent-release or thermal-release, dependent on the adhesive.

Due to its advantageous properties as e.g. optical transparency for visual inspection and other electro-magnetic radiation based processing technologies, glass has been used as carrier wafer material. In particular, glass carrier wafers allow for a de-bonding method by irradiation with electro-magnetic radiation. The bonding adhesive in this case is sensitive to a certain kind of electro-magnetic radiation and can be irradiated through the transparent wafer in order to reduce or eliminate the adhesive effect (deactivation) . Commonly used adhesives can be typically deactivated by irradiation with UV laser radiation (laser-release) . The UV-laser radiation is usually at wavelengths of 248 nm or 308 nm, but can also be at other wavelengths dependent on the adhesive. In order to achieve a sufficient de-bonding effect, it is generally required that the UV-transmittance at the corresponding wavelength is higher than 20％e.g. at a carrier wafer thickness of 0.5 mm.

A general problem arising during UV laser-release is solarization of the glass carrier wafer i.e. degeneration in transmittance due to the irradiation by the laser radiation. This becomes a particular problem if a glass carrier wafer is repeatedly exposed to the laser radiation. Solarization can thus significantly limit the recycling lifetime of a glass carrier wafer. The use of glass carrier wafers in semiconductor industries therefore also requires glasses with high solarization resistance in order to yield a long recycling lifetime and ultimately reduce processing cost.

A known method for improving the solarization resistance is adding controlled amounts of CeO₂, Fe₂O₃, TiO₂, SnO₂, As₂O₃, MnO₂ and V₂O₅, but this will block (cut off) the UV-transmittance at a wavelength range of less than 300 nm. For example, the patents or applications, such as EP 0 735 007 B1 (Osram Sylvania Inc.) , US 5,528,107 A (Richard et al.) , US 7,217,673 B2 (Schott AG) , US 7,517,822 B2 (Schott AG) , US 2014/0117294 A (Schott AG) , US 2013/0207058 A (Schott AG) , US 7,951,312 B2 (Schott AG) , US 8,283,269 B2 (Schott AG) , and US 7,535,179 B2 (Schott AG) disclose the above solution. Obviously, glass prepared by this method cannot be used for carrier glass wafer applications due to the low UV-transmittance at a wavelength of 248 nm of less than 10％.

Another method of improving the solarization resistance is not using any UV sensitive agent as mentioned above or increasing the content of BO₃ in the borosilicate glass (see e.g. US 5,547,904 A, Schott AG； US 5,599,753 A, Jenaer Glaswerk GmbH； US 5,610,108 A, Schott Glaswerke) . Thus, in these patents or applications, the borosilicate glass can have as high a UV-transmittance at the wavelength of 248 nm as possible, i.e. much higher than 20％. However, the borosilicate glasses disclosed in these documents are not suitable to be used as carrier glass wafer for silicon back grinding and thinning processes for several reasons. For example, one problem of US 5,547,904 A (Schott AG) is that Li₂O is used in the borosilicate glass, which is not preferred in semiconductor industries since the silicon substrate can be contaminated by lithium ions. The glasses described in US 5,599,753 A (Jenaer Glaswerk GmbH) and US 5,610,108 A (Schott Glaswerke) have a coefficient of thermal expansion (CTE) of 4-6 ppm/K and are therefore not suitable as glass carrier wafers for silicon substrates since the glass used as carrier wafer needs to have a CTE that is sufficiently close to the CTE of silicon in order to avoid cracks or warping during the processing due to unbalanced thermal expansion between carrier wafer and silicon substrate.

Summary of the invention

It is therefore an object of the invention to provide a glass which overcomes the disadvantages of the prior art. In particular, it is an object of the invention to provide a glass with a high UV-transmittance and high solarization resistance, in particular at a wavelength of 248 nm and/or 308 nm, preferably for the use as a glass carrier wafer for silicon substrates in semiconductor industry. It is a further object of the invention to provide a glass that allows for reusable glass carrier wafers in semiconductor industries with a long recycle lifetime and low processing cost. It is a further object of the invention to provide a glass that has a low CTE, in particular a CTE that is close to the CTE of silicon. Moreover, it is an object of the invention to provide a glass carrier wafer and a use thereof in semiconductor industry.

This object is solved by a low CTE glass, a glass carrier wafer, a use and a method as defined in the independent claims. Preferred embodiments are defined in the dependent claims. “Low CTE glass” herein generally refers to a glass with a CTE equal or smaller than 4.0 ppm/K.

In accordance with one aspect of the present invention, a low CTE glass with a high UV-transmittance and high solarization resistance comprises an alkaline metal oxide free composition as follows (in percentage of mole) :

where MgO+CaO+SrO+BaO amounts to 3 to 25 mol-％and the average number of non-bridging oxygen per polyhedron (NBO) is equal or larger than-0.08 and equal or smaller than-0.38.

Considering the structure of glass, the concept of NBO (Non-Bridging Oxygen) is widely used. NBO can be regarded as a parameter reflecting the network structure of a glass resulting from the specific chemical composition. It has surprisingly been found that the network structure indicated by the NBO of the low CTE glasses as described herein influences the optical property, in particular the UV-transmittance. In other words, the UV-transmittance of the low CTE glasses as described herein can be significantly improved by adjusting the NBO content inside the glass.

The structure of the network structure can be characterized with four parameters X, Y, Z and R, defined as follows:

X ＝ average number of non-bridging oxygen per polyhedron, i.e. NBO；

Y ＝ average number of bridging oxygen per polyhedron；

Z ＝ total average number of oxygen per polyhedron； and

R ＝ ratio of total number of oxygen to total number of network formers.

R can be deduced from the molar composition of the low CTE glass. The four parameters X, Y, Z and R can be calculated according the following formulas:

R ＝ O_mol/ (Si_mol+Al_mol+B_mol) (1)

Y ＝ 2Z-2R (2)

X ＝ 2R–Z. (3)

For silicates:

Z ＝ 4. (4)

From the formulas (1) , (3) and (4) , it can be concluded that,

X ＝ 2 x O_mol/ (Si_mol+Al_mol+B_mol) -4 (5)

According to this aspect of the invention, the alkaline metal oxide free low CTE glass with NBO equal or larger than-0.08 and equal or smaller than-0.38 can achieve a UV-transmittance higher than 20％at the wavelength of 248 nm, rendering the glass particularly useful in applications as carrier wafers in semiconductor industry.

In a preferred embodiment of this aspect, the alkaline metal oxide free composition comprises SiO₂ in the range from 55 to 70 mol-％, and B₂O₃ in the range from 14-20 mol-％, where preferably the NBO is equal or smaller than-0.38.

In another preferred embodiment of this aspect, the alkaline metal oxide free composition comprises SiO₂ in the range from 65 to 75 mol-％, and B₂O₃ in the range from 5-10 mol-％, where preferably the NBO is equal or larger than-0.08.

In a further preferred embodiment, the alkaline metal oxide free composition comprises MgO in the range from 2-15 mol-％and/or CaO in the range from 0-10 mol-％, in particular 0-5 mol-％, and/or BaO in the range from 0-10 mol-％, in particular 0-5 mol-％.

In accordance with another aspect, the present invention alternatively provides a low CTE glass comprising an alkaline earth metal oxide free composition as follows (in percentage of mole) :

Preferably, the NBO of the alkaline earth metal oxide free composition is equal or larger than-0.25 and equal or smaller than-0.10.

It has surprisingly been found that, according to this aspect of the invention, the alkaline earth metal oxide free low CTE glass can achieve a UV-transmittance higher than 25％at the wavelength of 248 nm, rendering the glass particularly useful in applications as carrier wafers in semiconductor industry. The UV-transmittance can be further increased by adjusting the NBO to a range equal or larger than-0.25 and equal or smaller than-0.10.

In a preferred embodiment of this aspect, the low CTE glass comprising an alkaline earth metal oxide free composition comprises K₂O in the range from 0 to 3 mol-％. In a further preferred embodiment, the alkaline earth metal oxide free composition comprises Na₂O in the range from 0-6 mol-％and more preferably in the range from 1 to 5.5 mol-％.

For the use of the low CTE glass according to present invention in semiconductor industry, the low CTE glass is preferably essentially free of Li₂O in order to prevent contamination of a silicon substrate by lithium ions. “Essentially free” hereby refers to a content of less than 0.01 mol-％.

The low CTE glass of the invention has a UV-transmittance at a wavelength of 248 nm that is equal or larger than 20％, preferably equal or larger than 22％and, in the case of the alkaline earth metal oxide free low CTE glass, equal or larger than 25％. The UV-transmittance at wavelengths larger than 248 nm and smaller than 780 nm thereby is preferably equal or higher than the UV-transmittance at 248 nm. The low CTE glass also has a solarization resistance of lower than 1％loss in transmittance after 100’000 mJ/cm² UV energy dosage at a wavelength of 248 nm irradiated by laser.

In a preferred embodiment, the UV-transmittance at a wavelength of 248 nm can be further improved if the low CTE glass has a content of Fe₂O₃ of less than 0.01 mol-％. Such high purity glasses, however, are expensive but can nevertheless be preferred for a given requirement.

In a preferred embodiment, the low CTE glass has a transition temperature T_g higher than 550℃, preferably higher than 650℃and further preferably higher than 700℃.

In a further preferred embodiment, the low CTE glass has a coefficient of thermal expansion (CTE) equal or larger than 2.0 ppm/K and equal or less than 4.0 ppm/K. Preferably, the CTE of the glass is close to the CTE of the silicon substrate (about 3 ppm/K) in order to avoid warps or cracks that can occur due to a mismatch of CTE between glass carrier wafer and silicon substrate.

In a preferred embodiment, the low CTE glass of the present invention is provided as a glass wafer, in particular with a thickness in the range from 0.05 mm to 1.2 mm, preferably in the range from 0.1 mm to 0.7 mm. The thicknesses can in particular be equal or smaller than 1.2 mm, equal or smaller than 0.7 mm, equal or smaller than 0.5 mm, equal or smaller than 0.25 mm, equal or smaller than 0.1 mm, or equal or smaller than 0.05 mm. Other preferred selected thicknesses are 100 μm, 200 μm, 250 μm, 400 μm, 500 μm, 550 μm, 700 μm or 1000 μm. Surface dimensions of the glass wafer preferably are approximately 15 cm, 20 cm or 30 cm, or preferably approximately 6” , 8” or 12” . The shape of the glass wafer can be rectangular or circular as well as elliptical. Other shapes and dimensions can also be applied if the specific application so requires.

Based on the above description, the glass carrier wafer made of the present low CTE glass can have a high UV-transmittance at a wavelength of 248 nm, i.e. a UV-transmittance larger than 20％, a good solarization resistance, i.e. less than 1％loss in transmittance after 100’000 mJ/cm² UV energy dosage by laser irradiation at 248 nm wavelength, and a long recycling lifetime, i.e. at least 500 cycles without significant degradation.

The invention further concerns a bonded article, including a glass carrier wafer made form a low CTE glass according to the invention and a silicon substrate bonded thereto. The silicon substrate is preferably bonded to the glass carrier wafer by an adhesive, which can preferentially be deactivated by irradiation with UV-radiation, in particular by laser-radiation at a wavelength of preferably 248 nm or alternatively 308 nm. Deactivation hereby means that the adhesive force of the adhesive layer can be sufficiently reduced or eliminated by irradiation with UV-radiation for the de-bonding of the silicon substrate from the glass carrier wafer.

The glass carrier wafer according to the invention is preferably used as a carrier wafer for the processing of a silicon substrate, in particular during thinning and/or back grinding of the silicon substrate. During the use, the silicon substrate preferably adheres to the glass carrier wafer, in particular by means of an adhesive layer, and is handled via the glass carrier wafer during processing.

The present low CTE glass shows that, in a further aspect of the invention, a method for providing a low CTE glass including SiO₂, Al₂O₃, and B₂O₃ with a high UV-transmittance and high solarization resistance is provided, comprising altering a given low CTE glass composition by adjusting the NBO number in order to increase a UV-transmittance, in particular increase a UV-transmittance to more than 20％, at a given wavelength, in particular at a wavelength of 248 nm and/or 308 nm, wherein the NBO number is defined as NBO ＝ 2 x O_mol/ (Si_mol+Al_mol+B_mol) –4. The person skilled in the art can immediately gather from the present disclosure how, starting from a given low CTE glass composition, a high UV-transmittance can be achieved with limited effort by adjusting the NBO number.

Brief description of the drawings

The invention is described in more detail in the following by way of exemplary embodiments and with reference to the accompanying drawings. The same reference numerals are used to designate the same or corresponding elements in the drawings. The drawings show:

Fig. 1: a sectional view of a bonded article with a glass carrier waver processed by laser irradiation during a de-bonding process；

Fig. 2: UV transmittance at a wavelength of 248 nm in relation to the NBO for exemplary embodiments；

Fig. 3: a diagram of spectral transmittance for several glass compositions；

Fig. 4: a comparative example of the UV-transmittance between high purity (low Fe₂O₃ content) glass according to a preferred embodiment of the invention and a commercial grade glass.

Detailed description

The objects, features and advantages of the invention are illustrated in more detail by the examples and embodiments as described in the following with reference to the accompanying drawings.

Figure 1 schematically shows a bonded article including a glass carrier wafer 2 during a de-bonding process by laser-release. A bonded article 1 comprises a glass carrier wafer 2 made from a glass according to the invention and a silicon substrate 3 which are bonded together by an adhesive layer 4 that can be deactivated by irradiation of electro-magnetic radiation. In the present example, the adhesive layer 4 can be deactivated by UV-radiation at a wavelength of 248 nm such that the adhesive force is reduced or eliminated allowing for the de-bonding of the silicon substrate 3. The de-bonding (laser-release) is accomplished by irradiating the adhesive layer 4 by a laser 5 through the glass carrier wafer 2. In a typical process, the wafer is mounted on a computer numerical control (CNC) controlled stage (not shown) and is moved beneath the stationary laser beam 5. The process details depend on the capabilities of laser and of the moving stage. As an example, the 248 nm laser 5 with maximum pulse energy of 800 mJ is run at 30 Hz pulse repetition rate and is defocused to deliver 200 mJ/cm² over a target area 6 with size 1.01 mm x 1.01 mm. The low CTE glass/silicon bonded article 1 is moved beneath the pulsed beam 5 at 30 mm/sec, so that pulses overlap by 10 μm. Under these conditions, the glass carrier wafer 2 was cleanly de-bonded from the silicon substrate 3 at a rate of 20 cm²/min.

Table 1 below shows some general parameters of the de-bonding process. From table 1, it can be seen that the glass carrier wafer 2 can bear at least 500 recycles without significant loss in UV-transmittance i.e. has a high solarization resistance. The glass carrier wafer 2 according to the invention can bear at least 100’000 mJ/cm² irradiation at wavelength of 248 nm from UV laser with a degradation of the transmittance at this wavelength of much less than 1％.

Parameter	Value
Parameter	Value	Focus point:	1.01mm x 1.01mm
Moving speed		Focus point:	1.01mm x 1.01mm
Moving speed		30 mm/sec
Defocused UV energy dosage		30 mm/sec	200 mJ/cm²
Defocused UV energy dosage	UV energy dosage after 10 recycles	2000 mJ/cm²	200 mJ/cm²
UV energy dosage after 20 recycles	UV energy dosage after 10 recycles	2000 mJ/cm²	4000 mJ/cm²
UV energy dosage after 20 recycles	UV energy dosage after 50 recycles	10000 mJ/cm²	4000 mJ/cm²
UV energy dosage after 100 recycles	UV energy dosage after 50 recycles	10000 mJ/cm²	20000 mJ/cm²
UV energy dosage after 100 recycles	UV energy dosage after 500 recycles	100000 mJ/cm²	20000 mJ/cm²

Table 1: General parameters of the de-bonding process

Examples A

In one aspect, the present application provides a low CTE glass with a high UV-transmittance and high solarization resistance, which comprises an alkaline metal oxide free composition as follows (in mol-％) :

where MgO+CaO+SrO+BaO amounts to 3 to 25 mol-％and the average number of NBO is equal or larger than-0.08 and equal or smaller than-0.38.

Table 2 listed below shows eight samples according to this aspect of the invention (No. 1-5, 13-15) and seven comparative samples (No. 6-12) of alkaline metal oxide free low CTE glasses (examples A) .

Table 2: Parameters of 15 samples of a low CTE glass (examples A)

From table 2, it can be seen that an NBO number in the range from-0.38 to-0.08 (samples No. 6-12) results in a UV-transmittance at the wavelength of 248 nm lower than 20％ (see also Fig. 2) . The low CTE glasses of the comparative samples are therefore not suitable as carrier glasses due to the low UV-transmittance at a wavelength of 248 nm. However, samples No. 1-5 in the NBO range from (rounded) -0.53 to-0.38 and samples No. 13-15 in the NBO range from (rounded) -0.08 to 0.02, i.e. the NBO number is equal or larger than-0.08 or equal or smaller than-0.38, have a UV-transmittance at a wavelength of 248 nm that is higher than 20％. The exceptionally high UV-transmittance of sample No. 4 is due to an abnormal effect of the specific BaO content.

Figure 3 shows a diagram of the spectral transmittance of several glass compositions according to the first aspect of the invention in the wavelength range from 200 nm to 350 nm. The fine dotted line corresponds to sample No. 11 and serves as a benchmark for the glass compositions according to the invention. The dash-dotted line corresponds to sample No. 13 having an NBO number of-0.08. The continuous line corresponds to sample No. 15 having an NBO number of 0.01 (see table 2) . As becomes obvious from the diagram, the glass compositions No. 13 and 15 according to the invention have an enhanced UV-transmittance as compared to the glass sample No. 11. In particular, the transmittance at the wavelengths 248 nm and also 308 nm are enhanced, rendering the glass composition particularly suited for the application as glass carrier wafer.

The dashed line shows a glass sample with the same composition as sample No. 11 where high purity raw materials, i.e. low Fe₂O₃ contents, are used (see also Fig. 4) . It becomes immediately obvious that the use of such high purity materials strongly enhances the UV-transmittance which, in particular but not only in addition to the enhancement resulting from the adjusted NBO number, renders the glass suitable for application as glass carrier wafer.

Examples B

In another aspect, the present invention alternatively provides a low CTE glass comprising an alkaline earth metal oxide free composition as follows (in mol-％) :

The NBO is preferably equal or larger than-0.25 and equal or smaller than-0.10.

Table 3 listed below shows parameters of five samples (No. 16-20) of an alkaline earth metal oxide free glass according to this aspect of the invention (examples B) .

Table 3: Parameters of 5 samples of a low CTE glass (examples B)

The number of NBO for alkaline earth metal oxide free glasses according to table 3 lies in the range from-0.25 to-0.10 for all samples (i.e. samples No. 16-20) . The corresponding UV-transmittance at a wavelength of 248 nm is significantly higher than 20％for all samples.

All samples of examples A and B have been prepared with a thickness of 0.5 mm. All samples according to the invention (No. 1-5 and 13-20) have a coefficient of thermal expansion (CTE) larger than 2.0 ppm/K and less than 4.0 ppm/K, which is sufficiently close to the CTE of silicon (about 3 ppm/K) for general purposes. The low CTE glass is preferably essentially free of Li₂O.

From tables 2 and 3, the UV-transmittance at 248 nm for samples No. 1-5 and 13-20 is larger than 20％. The UV-transmittance for samples No. 16-20 is even larger than 27％.

The low CTE glasses according to the invention have a high solarization resistance resulting in a loss in transmittance after 100’000 mJ/cm² UV energy dosage at 248 nm laser of much less than 1％. As can be gathered from table 2 and 3, the loss in transmittance at 248 nm after 500 cycles of laser irradiation with an energy dosage of 200 mJ/cm² per cycle (corresponding to an UV energy dosage of 100’000 mJ/cm² in total) is much less than 1％for all samples according to the invention (i.e. No. 1-5 and 13-20) . Therefore, the low CTE glass according to the invention has an excellent solarization resistance which extends recycling lifetime and reduces processing cost.

Figure 4 shows a comparison of spectral transmittance between high purity and commercially available versions of the same glass composition. The glass used in figure 4 is the glass corresponding to sample No. 11. Herein, “high purity” refers to a very low content of Fe₂O₃ as compared to the generally available comparable commercial glasses. In the present invention, high purity glasses have a Fe₂O₃ content of less than 0.01 mol-％.

The experimental data in Fig. 4 shows that the UV-transmittance is approx. 51％for the high purity composition and only approx. 10％for the commercial grade composition (see Fig. 4) . Similarly, the UV-transmittance at a wavelength of 308 nm is 88％for the high purity composition and only 61％for the commercial grade composition. UV-transmittance of commercial grade glasses can therefore be significantly improved by using high purity raw materials. As the example of Fig. 4 shows, the use of high purity materials generally significantly improves the UV-transmittance of glasses, even glasses that do not form part of the invention. It is of course evident that corresponding improvements will be achieved with the glasses of the invention when using high purity raw materials.

Due the excellent properties of the low CTE glasses according to the invention, the carrier glass wafer made thereof can achieve a high UV-transmittance at wavelength of 248 nm and/or 308 nm, good solarization resistance, long recycling lifetime and, hence, reduced processing cost.

The terminology used herein for the disclosure and description of the invention is for the purpose of describing particular aspects only and does not limit the invention in any way. Moreover, throughout the description and claims of the present invention, the word “comprise” and other forms of the word, such as “comprising” and “comprises” , means including but not limited to and is not intended to exclude, for example, other additives, or components, unless explicitly declared otherwise.

Claims

A low CTE glass with a high UV-transmittance and high solarization resistance comprising an alkaline metal oxide free composition in percentage of mole:

SiO₂ 50-75,

Al₂O₃ 3-20,

B₂O₃ 5-20,

MgO 0-15,

CaO 0-15,

SrO 0-15,

BaO 0-15,

where MgO+CaO+SrO+BaO amounts to 3 to 25 mol-％ and the average number of non-bridging oxygen per polyhedron (NBO) is equal or larger than-0.08 or equal or smaller than -0.38； or

an alkaline earth metal oxide free composition in percentage of mole:

SiO₂ 78-85,

Al₂O₃ 0-7,

B₂O₃ 8-15,

Na₂O 0-8,

K₂O 0-5,

where preferably the NBO is equal or larger than -0.25 and equal or smaller than -0.10；

wherein the NBO is defined as NBO ＝ 2 x O_mol/ (Si_mol+Al_mol+B_mol) -4.
The low CTE glass according to Claim 1, wherein the glass is essentially free of Li₂O.
The low CTE glass according to any one of Claims 1 or 2, wherein the UV-transmittance at 248 nm is larger than 20％, preferably larger than 22％.
The low CTE glass according to any one of Claims 1-3, wherein the glass has a solarization resistance which is lower than 1％ loss in transmittance after 100’ 000 mJ/cm² UV energy dosage irradiated by a laser at 248 nm wavelength.
The low CTE glass according to any one of Claims 1-4, wherein the content of Fe₂O₃ is less than 0.01 mol-％
The low CTE glass according to any one of Claims 1-5, wherein the glass has a transition temperature T_g higher than 550℃, preferably higher than 650℃, further preferably higher than 700℃.
The low CTE glass according to any one of Claims 1-6, wherein the coefficient of thermal expansion (CTE) is larger than 2.0 ppm/K and less than 4.0 ppm/K.
The low CTE glass according to any one of Claims 1-7, wherein the glass has a thickness in the range from 0.05 mm to 1.2 mm, preferably from 0.1 mm to 0.7 mm.
A glass carrier wafer made of the low CTE glass according to any one of Claims 1-8.
Bonded article including a glass carrier wafer according to Claim 9 and a silicon substrate bonded thereto, in particular by an adhesive, wherein preferably the adhesive can be deactivated by irradiation with UV-radiation, in particular by laser-radiation at a wavelength of 248 nm.
Use of a glass carrier wafer according to Claim 9 as a carrier wafer for the processing of a silicon substrate, in particular during thinning and/or back grinding of the silicon substrate.
Use according to Claim 11, wherein the silicon substrate adheres to the glass carrier wafer, in particular by means of an adhesive layer, and is handled via the glass carrier wafer during processing.
Method for providing a low CTE glass including at least SiO₂, Al₂O₃, and B₂O₃ with a high UV-transmittance and high solarization resistance comprising altering a given low CTE glass composition by adjusting the NBO number in order to increase a UV-transmittance, in particular increase a UV-transmittance to more than 20％, at a given wavelength, in particular at a wavelength of 248 nm and/or 308 nm, wherein the NBO number is defined as NBO ＝ 2 x O_mol/ (Si_mol+Al_mol+B_mol) –4.