TWI667214B - Low cte glass with high uv-transmittance and solarization resistance - Google Patents

Abstract

The invention provides a low thermal expansion coefficient glass with high ultraviolet transmittance and high light resistance, which includes components without alkali metal oxides: 50-75 mole% SiO ₂ and 3-20 mole% Al ₂ O ₃ , 5-20 mol% B ₂ O ₃ , 0-15 mol% MgO, 0-15 mol% CaO, 0-15 mol% SrO, and 0-15 mol% BaO Where MgO + CaO + SrO + BaO is equal to 3 to 25 mole%, and the average number of non-bridged oxygen (NBO) of each polyhedron is equal to or greater than -0.08 or equal to or less than -0.38. The invention further provides a component of an alkaline-earth-free metal oxide: 75-85 mole% SiO ₂ , 0-7 mole% Al ₂ O ₃ , 8-15 mole% B ₂ O ₃ , 0- 8 mole% Na ₂ O and 0-5 mole% K ₂ O, wherein the number of non-bridged oxygen (NBO) is preferably equal to or greater than -0.25 and equal to or less than -0.10. The invention also provides a glass carrier wafer and use thereof. The glass carrier wafer has high ultraviolet transmittance at a wavelength of 248 nm and / or 308 nm, good light resistance, long cycle life and reduced processing cost.

Description

Low thermal expansion glass with high UV transmittance and high light resistance

The invention relates to a low coefficient of thermal expansion (CTE) glass used as a glass carrier wafer with high ultraviolet transmittance and light resistance. The invention also relates to a glass carrier wafer made of the low CTE glass and its use as a carrier wafer in the processing of a silicon substrate.

Making silicon substrates thin in order to meet ongoing demand for, for example, the reduction in size of integrated circuits has become a common process in the semiconductor industry. Silicon carrier wafers have been widely used as mechanical carriers for thinning and back-grinding silicon substrates to facilitate the processing of fragile thinned substrates. The silicon substrate is thus usually bonded to the carrier wafer by an adhesive. Depending on the adhesive, the debonding of the silicon substrate from the carrier wafer after processing can be achieved by, for example, solvent release or heat release.

Due to its advantageous properties, such as optical transparency for visual inspection and other electromagnetic radiation-based processing technologies, glass has been used as a carrier wafer material. In particular, the glass carrier wafer allows for delamination by irradiation of electromagnetic radiation. Sticky method. In this case, the adhesive is sensitive to certain types of electromagnetic radiation and can be irradiated through a transparent wafer to reduce or eliminate the effect of the adhesive (deactivation). Commonly used adhesives can usually be inactivated by irradiation with ultraviolet laser light (laser release). Ultraviolet laser light radiation is usually at a wavelength of 248 nm or 308 nm, but other wavelengths can be used depending on the adhesive. In order to achieve a sufficient debonding effect, it is generally required that, for example, at a thickness of a carrier wafer of 0.5 mm, the ultraviolet transmittance at the corresponding wavelength is higher than 20%.

A common problem that arises during the release of ultraviolet lasers is the solarization of glass carrier wafers, that is, the transmittance deteriorates due to the irradiation by laser light radiation. This is a particular problem if the glass carrier wafer is repeatedly exposed to laser light radiation. Exposure can therefore significantly limit the cycle life of the glass carrier wafer. Therefore, the use of glass carrier wafers in the semiconductor industry also requires glasses with high solarization resistance to produce long cycle life and ultimately reduced processing costs.

A known method for improving lightfastness is to add controlled amounts of CeO ₂ , Fe ₂ O ₃ , TiO ₂ , SnO ₂ , As ₂ O ₃ , MnO ₂ and V ₂ O ₅ , but this will prevent (cut off) the Ultraviolet transmittance in a wavelength range of less than 300 nm. For example, such as EP 0 735 007 B1 (Osram Silvenia), US 5,528,107 A (Richard, etc.), 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) These patents or applications disclose the above schemes. Obviously, the glass prepared by this method cannot be used for glass carrier wafers due to the low ultraviolet transmittance of less than 10% at a wavelength of 248 nm.

Another way to improve lightfastness is to not use any UV sensitizers as described above or to increase the content of BO ₃ in borosilicate glass (see for example US 5,547,904 A, SCHOTT AG; US 5,599,753 A, Jenaer Glaswerk Ltd .; US 5,610,108 A, SCHOTT Glass). Therefore, in these patents or applications, the borosilicate glass can have as high an ultraviolet transmittance as possible at a wavelength of 248 nm, that is, much higher than 20%. However, the borosilicate glass disclosed in these documents is not suitable for use as a carrier glass wafer for back grinding and thinning processing of silicon for several reasons. For example, a problem with US 5,547,904 A (Schott AG) is that Li ₂ O is used for borosilicate glass, which is not preferred in the semiconductor industry because silicon substrates can be contaminated with lithium ions. The coefficient of thermal expansion (CTE) of the glass described in US 5,599,753 A (Jenaer Glaswerk Co., Ltd.) and US 5,610,108 A (Schott glass) is 4-6 ppm / K, so it is not suitable as a glass carrier wafer for silicon substrates, because The glass used as the carrier wafer needs to have a CTE that is very close to the CTE of silicon in order to avoid cracks or warpage caused by unbalanced thermal expansion between the carrier wafer and the silicon substrate during processing.

It is therefore an object of the present invention to provide a glass which overcomes the disadvantages of the prior art. In particular, it is an object of the present invention to provide a special In particular, glass having high ultraviolet transmittance and high light resistance at a wavelength of 248 nm and / or 308 nm is preferably used as a glass carrier wafer for a silicon substrate in the semiconductor industry. Another object of the present invention is to provide a glass that allows reusable glass carrier wafers in the semiconductor industry, which has a long cycle life and low processing costs. Another object of the present invention is to provide a glass having a low CTE, especially a CTE having a CTE close to that of silicon. Furthermore, it is an object of the present invention to provide a glass carrier wafer and its use in the semiconductor industry.

This object is solved by low CTE glass, glass carrier wafers, uses and methods as defined in the independent claims. Preferred embodiments are defined in the dependent claims. "Low CTE glass" herein generally refers to glass with a CTE equal to or less than 4.0 ppm / K.

According to one aspect of the present invention, a low CTE glass having high ultraviolet transmittance and high light fastness contains the following alkali-free metal oxide component (in mole percentage): 50-75 mole% SiO ₂ , 3 -20 mol% Al ₂ O ₃ , 5-20 mol% B ₂ O ₃ , 0-15 mol% MgO, 0-15 mol% CaO, 0-15 mol% SrO, And 0-15 mole% BaO, where MgO + CaO + SrO + BaO is equal to 3-25 mole% and the average number of non-bridged oxygen (NBO) of each polyhedron is equal to or greater than -0.08 or equal to or less than -0.38 .

Considering the structure of glass, the concept of NBO (non-bridged oxygen) is widely used. NBO can be regarded as a parameter reflecting the network structure of glass caused by a specific chemical composition. It has been surprisingly found that the network structure shown by the NBO of the low CTE glass described herein affects the optical characteristics, especially the ultraviolet transmittance. In other words, the UV transmission of the low CTE glass described herein The rate can be significantly increased by adjusting the NBO content inside the glass.

The structure of the network structure can be expressed by four parameters X, Y, Z, and R defined as follows.

X = non-bridged oxygen per polyhedron, which is the average number of NBOs.

Y = average number of bridged oxygen for each polyhedron.

Z = total average of oxygen per polyhedron.

R = ratio of the total number of oxygen to the total number of network forming agents.

R can be deduced from the Mohr component of the low CTE glass. The four parameters X, Y, Z, and R can be calculated according to the following formula.

R = O _mol / (Si _mol + Al _mol + B _mol ) Formula (1)

Y = 2Z-2R formula (2)

X = 2R-Z formula (3)

For silicate, Z = 4 Formula (4)

From equations (1), (3), and (4), the following conclusions can be drawn.

X = 2 x O _mol / (Si _mol + Al _mol + B _mol ) -4 Formula (5)

According to this aspect of the present invention, a low CTE glass having an alkali-free metal oxide of NBO equal to or greater than -0.08 or equal to or less than -0.38 can achieve an ultraviolet transmittance of more than 20% at a wavelength of 248 nm, This makes the glass particularly useful in the application of carrier wafers in the semiconductor industry.

In a preferred embodiment of this aspect, the alkali-free metal oxide-containing component comprises SiO ₂ in the range of 55-70 mole% and B ₂ O ₃ in the range of 14-20 mole%, with NBO being preferred. Equal to or less than -0.38.

In another preferred embodiment of this aspect, the alkali-free metal oxide-containing component comprises SiO ₂ in a range of 65-75 mole% and B ₂ O ₃ in a range of 5-10 mole%, where NBO is more than Good is equal to or greater than -0.08.

In another preferred embodiment, the alkali-free metal oxide-containing component comprises MgO in the range of 2-15-mol% and / or 0-10 mole%, especially in the range of 0-5 mole%. CaO and / or BaO in the range of 0-10 mole%, especially in the range of 0-5 mole%.

According to another aspect, the present invention optionally provides a low-CTE glass comprising the following components (in mole percentages) of an alkaline-earth-free metal oxide: 78-85 mole% SiO ₂ , 0-7 mole Ear ₂ % Al ₂ O ₃ , 8-15 moles B ₂ O ₃ , 0-8 moles Na ₂ O, and 0-5 moles K ₂ O.

Preferably, the NBO of the component of the alkaline-earth-free metal oxide is equal to or greater than -0.25 and equal to or less than -0.10.

It has been surprisingly found that, according to this aspect of the invention, low CTE glass without alkaline earth metal oxides can achieve a UV transmittance higher than 25% at a wavelength of 248 nm, making glass a carrier in the semiconductor industry It is particularly useful in wafer applications. By adjusting the NBO to be equal to or larger than -0.25 and equal to or smaller than -0.10, the ultraviolet transmittance can be further improved.

In a preferred embodiment of this aspect, the low-CTE glass including a component of an alkaline-earth-free metal oxide contains K ₂ O in the range of 0 to 3 mole%. In another preferred embodiment, the alkaline earth metal oxide-free component comprises Na ₂ O in the range of 0-6 mole%, more preferably in the range of 1-5.5 mole%.

For the use of the low CTE glass according to the present invention in the semiconductor industry, the low CTE glass preferably does not substantially contain Li ₂ O to prevent the silicon substrate from being contaminated by lithium ions. By "substantially free" is here meant a content of less than 0.01 mole%.

The low CTE glass of the present invention has an ultraviolet transmittance equal to or greater than 20%, preferably equal to or greater than 22% at a wavelength of 248 nm, and is equal to or greater than 25 in the case of the low CTE glass having no alkaline earth metal oxide. %. The ultraviolet transmittance at a wavelength greater than 248 nm and less than 780 nm is therefore preferably equal to or greater than the ultraviolet transmittance at 248 nm. Low CTE glass also has a lightfastness of less than 1% after transmission of 100,000 mJ / cm ² of ultraviolet energy by laser light at a wavelength of 248 nm.

In a preferred embodiment, if the low CTE glass has a Fe ₂ O ₃ content of less than 0.01 mole%, the ultraviolet transmittance at a wavelength of 248 nm can be further increased. However, such high purity glasses are expensive, but can still be better for a given requirement.

In a preferred embodiment, the low CTE glass has a transition temperature (Tg) above 550 ° C, preferably above 650 ° C and more preferably above 700 ° C.

In another preferred embodiment, the coefficient of thermal expansion (CTE) of the low CTE glass is equal to or greater than 2.0 ppm / K and equal to 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 warping and cracking that may occur due to a mismatch in the coefficient of thermal expansion between the glass carrier wafer and the silicon substrate.

In a preferred embodiment, the low CTE glass of the present invention is provided as a glass wafer, with a thickness in the range of 0.05 to 1.2 mm, preferably 0.1 mm. Glass wafers in the range of 0.7 mm. The thickness may be, in particular, 1.2 mm or less, 0.7 mm or less, 0.5 mm or less, 0.25 mm or less, 0.1 mm or less, or 0.05 mm or less. Other preferred thicknesses are 100 μm, 200 μm, 250 μm, 400 μm, 500 μm, 550 μm, 700 μm, or 1000 μm. The surface size of the glass wafer is preferably about 15 cm, 20 cm, 30 cm, or preferably about 6 ", 8", or 12 ". The shape of the glass wafer can be rectangular or circular and oval. If required for a particular application , Other shapes and sizes can also be used.

Based on the above description, the glass carrier wafer made of the low CTE glass of the present invention can have a high ultraviolet transmittance at a wavelength of 248 nanometers, that is, the ultraviolet transmittance is greater than 20%; good light resistance, that is, at 248 nanometers The transmission loss of ultraviolet energy of 100,000 mJ / cm ² through laser light at a wavelength of meters is less than 1%; and a long cycle life, that is, at least 500 cycles without significant degradation.

The present invention also relates to a bonded article including a glass carrier wafer made of a low CTE glass according to the present invention and a silicon substrate bonded thereto. The silicon substrate is preferably adhered to the glass carrier wafer through an adhesive, which can be deactivated by irradiating UV radiation, especially by laser light radiation at a wavelength of preferably 248 nm or 308 nm. Deactivation here means that the adhesive force of the adhesive layer can be sufficiently reduced or eliminated by irradiating UV radiation, so as to debond the silicon substrate from the glass carrier wafer.

The glass carrier wafer according to the present invention is preferably used as a carrier crystal for the processing of silicon substrates, particularly during the thinning and / or backside grinding of the silicon substrates. sheet. During use, the silicon substrate is preferably adhered to a glass carrier wafer, especially through an adhesive layer, and handled via the glass carrier wafer during processing.

The low CTE glass of the present invention shows that, in yet another aspect of the present invention, a method for providing a low CTE glass with high ultraviolet transmittance and high light resistance is provided, the low CTE glass includes SiO _2. Al ₂ O ₃ and B ₂ O ₃ , the method comprising: changing a given low CTE glass component by adjusting the NBO number in order to increase the ultraviolet light at a given wavelength, in particular a wavelength of 248 nm and / or 308 nm The transmittance, especially the ultraviolet transmittance is increased to more than 20%, where the NBO number is defined as NBO = 2 x O _mol / (Si _mol + Al _mol + B _mol ) -4. Those with ordinary knowledge in the technical field to which this case belongs can immediately know from the present disclosure how to start with a given low CTE glass component and achieve a high ultraviolet transmittance by adjusting the NBO number with limited efforts.

1‧‧‧Combined products

2‧‧‧ glass carrier wafer

3‧‧‧ silicon substrate

4‧‧‧Adhesive layer

5‧‧‧laser

6‧‧‧ destination area

The present invention will be further described below with reference to schematic embodiments and drawings. The same reference numerals are used in the drawings to indicate the same or corresponding elements.

FIG. 1 is a cross-sectional view of a bonded product having a glass carrier member treated by laser irradiation during a debonding process.

FIG. 2 is the ultraviolet transmittance of the exemplary embodiment at a wavelength of 248 nm with respect to NBO.

FIG. 3 is a graph of the spectral transmittance of a plurality of glass compositions.

4 is a comparative example of the ultraviolet transmittance between a high-purity (low Fe ₂ O ₃ content) glass and a commercial-grade glass according to a preferred embodiment of the present invention.

The objects, features, and advantages of the present invention will be illustrated in more detail through examples and embodiments described below with reference to the drawings.

FIG. 1 schematically illustrates a bonded article including a glass carrier wafer 2 during a debonding process released by laser. The bonded product 1 includes a glass carrier wafer 2 and a silicon substrate 3 made of glass according to the present invention, which are bonded together by an adhesive layer 4 which can be deactivated by irradiation of electromagnetic radiation. In this example, the adhesive layer 4 can be deactivated by UV radiation at a wavelength of 248 nm, so that the adhesive force is reduced or eliminated, so that the silicon substrate 3 can be debonded. This debonding (laser release) is achieved by irradiating the adhesive layer 4 with the laser 5 through the glass carrier wafer 2. In a typical process, a wafer is mounted on a computer controlled (CNC) controlled platform (not shown) and moved under a stationary laser (beam) 5. Processing details depend on the performance of the laser and mobile platform. For example, a 248 nm laser 5 with a maximum pulse energy of 800 mJ operates at a pulse repetition rate of 30 Hz and defocuss to provide 200 mJ / cm ² on a destination area 6 having a size of 1.01 mm x 1.01 mm. The low CTE glass / silicon bonded product 1 moves below the pulsed light beam (laser 5) at 30 mm / sec so that the pulses overlap by 10 μm. Under these conditions, the glass carrier wafer 2 was cleanly debonded from the silicon substrate 3 at a rate of 20 cm2 / minute.

Table 1 below shows some general parameters of the debonding process. As can be seen from Table 1, the glass carrier wafer 2 can withstand at least 500 cycles without significant loss of ultraviolet transmittance, that is, having high light resistance. The glass carrier wafer 2 according to the present invention can withstand radiation of at least 100,000 mJ / cm ² at a wavelength of 248 nanometers from an ultraviolet laser, and the drop in transmittance at this wavelength is much less than 1%.

Example A

In one aspect, the present invention provides a low CTE glass with high ultraviolet transmittance and high light fastness, which includes the following composition (in mole percentage) without alkali metal oxide: SiO ₂ 50-75 mole% , Al2O ₃ 3-20 mole%, B ₂ O ₃ 5-20 mole%, MgO 0-15 mole%, CaO 0-15 mole%, SrO 0-15 mole%, BaO 0-15 mole ear%.

Wherein MgO + CaO + SrO + BaO is equal to 3-25 mole% and the average number of non-bridged oxygen (NBO) is equal to or greater than -0.08 or equal to or less than -0.38.

Table 2 listed below shows 8 samples (Nos. 1-5, 13-15) and 7 comparisons according to this aspect of the invention of an alkali metal oxide-free low CTE glass (Example A) Sample (No. 6-12).

As can be seen from Table 2, the number of NBOs (samples 6-12) in the range of -0.38 to -0.08 resulted in an ultraviolet transmittance of less than 20% at a wavelength of 248 nm (see also Figure 2). Therefore, the low CTE glass of the comparative sample is not suitable as a carrier glass due to its low ultraviolet transmittance at a wavelength of 248 nm. However, samples No. 1-5 with NBO in the range of -0.53 to -0.38 (rounded) and samples No. 13-15 with NBO in the range of -0.08 to 0.02 (rounded), that is, NBO number equal to or greater than -0.08 Or equal to or less than -0.38, the ultraviolet transmittance at a wavelength of 248nm is higher than 20%. 4th The abnormally high UV transmittance of the No. sample is due to the abnormal influence of the specific BaO content.

Fig. 3 shows a graph of the spectral transmittance of several glass compositions according to the first aspect of the present invention in a wavelength range of 200 nm to 350 nm. The thin dotted line corresponds to sample No. 11 and serves as a reference for the glass composition according to the present invention. The dotted line corresponds to sample No. 13 which has an NBO number of -0.08. The solid line corresponds to sample No. 15, which has an NBO number of 0.01 (see Table 2). As is apparent from the figure, the glass components Nos. 13 and 15 according to the present invention have enhanced ultraviolet transmittance compared to the glass sample No. 11. In particular, the transmittance at wavelengths of 248 nm and 308 nm is also increased, making the glass composition particularly suitable for applications such as glass carrier wafers.

The dashed line shows a glass sample with the same composition as the sample No. 11 in which a high-purity raw material was used, that is, a low Fe ₂ O ₃ content (see also FIG. 4). It is immediately obvious that the use of such a high-purity material greatly improves the ultraviolet transmittance, and especially not only in addition to the increase caused by adjusting the NBO number, making the glass suitable for use as a glass carrier wafer application.

Example B

According to another aspect, the present invention optionally provides a low-CTE glass comprising the following components (in mole percentages) of an alkaline-earth-free metal oxide: SiO ₂ 78-85 mole%, Al ₂ O ₃ 0 -7 Molar%, B ₂ O ₃ 8-15 Molar%, Na ₂ O 0-8 Molar%, K ₂ O 0-5 Molar%.

Preferably, the NBO is equal to or larger than -0.25 and equal to or smaller than -0.10.

Table 3 listed below shows the parameters of five samples (Nos. 16-20) of the alkaline-earth-free metal oxide glass according to this aspect of the invention (Example B).

The NBO number of all the samples of the alkaline-earth-free metal oxide glass according to Table 3 (ie, samples Nos. 16-20) was -0.25 to -0.10. The UV transmission at the corresponding 248 nm wavelength of all samples was significantly higher than 20%.

All samples of Examples A and B were prepared to a thickness of 0.5 mm. The coefficient of thermal expansion (CTE) of all samples according to the invention (Nos. 1-5 and 13-20) is greater than 2.0 ppm / K and less than 4.0 ppm / K, which is very close to that of silicon used for conventional purposes (about 3 ppm) / K). The low CTE glass is preferably substantially free of Li ₂ O.

From Tables 2 and 3, the UV transmittance at 248 nm of the samples Nos. 1-5 and 13-20 was greater than 20%. The UV transmittance of samples 16-20 was even greater than 27%.

The low CTE glass according to the present invention has a light resistance with a loss of transmittance much less than 1% after an ultraviolet energy amount of 100,000 mJ / cm ² under a laser of 248 nm. As can be obtained from Table 3 and Table 2, at 500 cycles, each cycle of energy usage after laser irradiation 200mJ / cm ² (corresponding to a total amount of ultraviolet energy 100,000mJ / cm ²⁾ is, according to the present All samples of the invention (i.e., Nos. 1-5 and 13-20) had a transmission loss of less than 1% at 248 nm. Therefore, the low CTE glass according to the present invention has excellent light resistance, which prolongs the cycle life and reduces the processing cost.

Figure 4 shows a comparison of the spectral transmittance between high purity and commercial grade of the same glass component. The glass used in FIG. 4 corresponds to the glass of Sample No. 11. Here, "high purity" means that the Fe ₂ O ₃ content is very low compared to comparable glass of a conventional commodity. In the present invention, the Fe ₂ O ₃ content of the high-purity glass is less than 0.01 mole%.

The experimental data in FIG. 4 shows that the ultraviolet transmittance of the high-purity component is about 51% and the commercial-grade component is only about 10% (refer to FIG. 4). Similarly, the high-purity component has a UV transmittance of 88% at a wavelength of 308 nm and a commercial grade component of only 61%. The UV transmittance of commercial-grade glass can therefore be significantly improved by using high-purity raw materials. As shown in the example in Figure 4, the use of high purity materials generally significantly improves the UV transmission of glass, even glass that does not form part of the invention. Obviously, when using high-purity raw materials, the glass of the present invention will achieve corresponding improvements.

Due to the excellent properties of the low CTE glass according to the present invention, the carrier glass wafer made from it can achieve high ultraviolet transmittance at 248nm and / or 308nm, good light resistance, long cycle life and thereby reduce Processing costs.

The terminology used for the disclosure and description of the invention herein is for the purpose of describing particular aspects only and does not limit the invention in any way. In addition, throughout the present specification and the scope of the patent application, the word "including" and other forms of the word, such as "including" and "including", include, but are not limited to, not intended to exclude, for example, other additives or ingredients, Unless explicitly stated.

Claims (24)

A glass with low thermal expansion coefficient, which has high ultraviolet transmittance and high light resistance, and contains the following alkali-free metal oxide components (in mole percentage): 50-75 mole% SiO ₂ ; 3-20 mole 1% Mo ₂ Al ₂ O ₃ , but does not contain more than 12 mol% Al ₂ O ₃ ; 5-20 Mo% B ₂ O ₃ ; 0-15 Molar MgO; 0-15 Molar% CaO; 0-15 mol% SrO; and 0-15 mol% BaO; where the number of non-bridged oxygen (NBO) is defined as: NBO = 2 x O _mol / (Si _mol + Al _mol + B _mol )- 4 Among the components of the aforementioned alkali-free metal oxide, MgO + CaO + SrO + BaO is equal to 3-25 mol% and the average number of the non-bridged oxygen (NBO) number of each polyhedron is equal to or greater than -0.08 or equal to or less than -0.38. A low coefficient of thermal expansion glass, which has high ultraviolet transmittance and high light resistance, and contains the following alkaline earth metal oxide-free composition (in mole percentage): 78-85 mole% SiO ₂ ; 0-7 Mole% of Al ₂ O ₃ ; 8-15 Mole% of B ₂ O ₃ ; 0-8 Mole% of Na ₂ O; and 0-5 Mole% of K ₂ O; where non-bridged oxygen is defined ( The number of NBO) is: NBO = 2 x O _mol / (Si _mol + Al _mol + B _mol ) -4 In the foregoing alkaline earth metal oxide-free composition, the non-bridged oxygen (NBO) number is equal to or greater than -0.25 and equal to or greater than Less than -0.10. The low thermal expansion coefficient glass according to claim 1 or 2, wherein the low thermal expansion coefficient glass is substantially free of Li ₂ O. The low thermal expansion coefficient glass according to claim 1 or 2, wherein the ultraviolet transmittance at 248 nm is greater than 20%. The low thermal expansion coefficient glass according to claim 4, wherein the ultraviolet transmittance at 248 nm is greater than 22%. The low coefficient of thermal expansion glass as described in claim 1 or 2, wherein the low coefficient of thermal expansion glass has a transmission loss of less than 1% after radiating ultraviolet energy of 100,000 mJ / cm ² through laser light at a wavelength of 248 nm. Lightfastness. The low thermal expansion coefficient glass according to claim 1 or 2, wherein the content of Fe ₂ O ₃ is less than 0.01 mole%. The low thermal expansion coefficient glass according to claim 1 or 2, wherein the low thermal expansion coefficient glass has a transition temperature T _g higher than 550 ° C. The low thermal expansion coefficient glass according to claim 8, wherein the low thermal expansion coefficient glass has a transition temperature T _g higher than 650 ° C. The low thermal expansion coefficient glass according to claim 8, wherein the low thermal expansion coefficient glass has a transition temperature T _g higher than 700 ° C. The low thermal expansion coefficient glass according to claim 1 or 2, wherein the thermal expansion coefficient is greater than 2.0 ppm / K and less than 4.0 ppm / K. The low thermal expansion coefficient glass according to claim 1 or 2, wherein the thickness of the low thermal expansion coefficient glass is in a range of 0.05 to 1.2 mm. The low thermal expansion coefficient glass according to claim 12, wherein the thickness of the low thermal expansion coefficient glass is in a range of 0.1 to 0.7 mm. A glass carrier wafer made of the low thermal expansion coefficient glass according to any one of claims 1 to 13. A bonded product comprising the glass carrier wafer according to claim 14 and a silicon substrate adhered thereto by an adhesive, and the adhesive can be deactivated by irradiating UV radiation. The bonded article according to claim 15, wherein the adhesive is deactivated by laser light radiation at a wavelength of 248 nm. One application is the use of the glass carrier wafer made of the low thermal expansion coefficient glass described in claim 14 for the processing of a silicon substrate. The use according to claim 17, which is the use of the glass carrier wafer in a carrier wafer during thinning of the silicon substrate and / or during backside polishing. The use as recited in claim 17, wherein the silicon substrate is adhered to the glass carrier wafer, and is operated via the glass carrier wafer during processing. The use according to claim 19, wherein the silicon substrate is adhered to the glass carrier wafer through an adhesive layer. A method for providing a low coefficient of thermal expansion glass having high ultraviolet transmittance and high light resistance, the low coefficient of thermal expansion glass including the following alkali-free metal oxide components (in mole percentages): 50-75 moles % SiO ₂ ; 3-20 Molar% Al ₂ O ₃ , but does not contain more than 12 Molar Al ₂ O ₃ ; 5-20 Molar% B ₂ O ₃ ; 0-15 Molar% MgO; 0-15 mole% CaO; 0-15 mole% SrO; and 0-15 mole% BaO; the method includes: changing a given low thermal expansion by adjusting the number of non-bridged oxygen (NBO) Coefficient glass component in order to increase the UV transmittance at a given wavelength; among the aforementioned alkali-free metal oxide components, MgO + CaO + SrO + BaO is equal to 3-25 mole% and the non-bridged oxygen of each polyhedron The average number of (NBO) numbers is adjusted to be equal to or greater than -0.08 or equal to or less than -0.38; where the non-bridged oxygen (NBO) number is defined as NBO = 2 x O _mol / (Si _mol + Al _mol + B _mol ) -4 . A method for providing a low thermal expansion coefficient glass having high ultraviolet transmittance and high light resistance, the low thermal expansion coefficient glass comprising the following composition (in mole percentage) of an alkaline earth metal oxide: 78-85 Mo Mol% SiO ₂ ; 0-7 mol% Al ₂ O ₃ ; 8-15 mol% B ₂ O ₃ ; 0-8 mol% Na ₂ O; and 0-5 mol% K ₂ O; the method includes: changing a given low thermal expansion coefficient glass component by adjusting a non-bridged oxygen (NBO) number so as to improve ultraviolet transmittance at a given wavelength; in the aforementioned alkaline earth metal oxide-free composition , The number of non-bridged oxygen (NBO) is equal to or greater than -0.25 and equal to or less than -0.10; wherein the number of non-bridged oxygen (NBO) is defined as NBO = 2 x O _mol / (Si _mol + Al _mol + B _mol ) -4. A method for providing a low thermal expansion coefficient glass having high ultraviolet transmittance and high light resistance as described in claim 21 or 22, wherein the given wavelength is a wavelength of 248 nm and / or 308 nm. The method for providing a low thermal expansion coefficient glass having high ultraviolet transmittance and high light resistance as described in claim 21 or 22, wherein the ultraviolet transmittance is increased to increase the ultraviolet transmittance to 20% or more.