METHOD FOR RAPID ANNEALING OF A STACK OF THIN LAYERS CONTAINING AN INDIUM OVERLAY

Abstract

A heat treatment process includes irradiating a substrate including a glass sheet coated on one of its faces with a stack of thin layers, under an atmosphere containing oxygen (O.sub.2), with electromagnetic radiation having a wavelength comprised between 500 and 2000 nm, the electromagnetic radiation being emitted by an emitter device placed facing the stack of thin layers, a relative movement being created between the emitter device and the substrate, so as to raise the stack of thin layers to a temperature at least equal to 300 C. for a brief duration shorter than one second, wherein the last layer of the stack, making contact with the atmosphere, called the overcoat, is a metal layer of indium or of an indium-based alloy.

Claims

1. A heat treatment process comprising irradiating a substrate comprising a transparent sheet coated on one of its faces with a stack of thin layers, under an atmosphere containing oxygen (O.sub.2), with electromagnetic radiation having a wavelength comprised between 500 and 2000 nm, said electromagnetic radiation being emitted by an emitter device placed facing the stack of thin layers, a relative movement being created between said emitter device and said substrate, so as to raise the stack of thin layers to a temperature at least equal to 300 C. for a brief duration shorter than one second, wherein a last layer of the stack, making contact with the atmosphere, forming an overcoat, is a metal layer of indium or of an indium-based alloy.

2. The process as claimed in claim 1, wherein a mass per unit area of the overcoat, expressed as the mass of metal atoms per unit area, is comprised between 1 and 30 g/cm.sup.2.

3. The process as claimed in claim 1, wherein the overcoat is a layer of an indium-based alloy containing more than 70% indium atoms relative to the total amount of metal atoms in the alloy.

4. The process as claimed in claim 1, wherein the overcoat is a layer of an indium-tin alloy (InSn).

5. The process as claimed in claim 1, wherein the stack of thin layers comprises at least one electrically conductive layer other than the overcoat making contact with the atmosphere, the electrically conductive layer being a metal layer or a layer of a transparent conductive oxide.

6. The process as claimed in claim 5, wherein the stack of thin layers is a low-emissivity stack comprising at least one metal layer that reflects infrared radiation between two dielectric layers.

7. The process as claimed in claim 1, wherein the penultimate layer of the stack of thin layers, which corresponds to the layer located directly under the overcoat making contact with the atmosphere, is a layer of indium tin oxide (ITO).

8. The process as claimed in claim 5, wherein the heat treatment leads to a decrease in the sheet resistance and/or the emissivity of the stack of thin layers of at least 15%.

9. The process as claimed in claim 1, wherein the electromagnetic radiation is laser radiation.

10. The process as claimed in claim 9, wherein the wavelength of the laser radiation is comprised between 900 and 1100 nm.

11. The process as claimed in claim 10, wherein the laser radiation is a laser beam focused on a plane of the overcoat in the form of a laser line simultaneously irradiating all or some of a width of the substrate.

12. The process as claimed in claim 1, wherein the device that emits the electromagnetic radiation is a flash lamp.

13. A substrate for the implementation of a process as claimed in claim 1, comprising a transparent sheet coated on one of its faces with a stack of thin layers, wherein a last layer of the stack, making contact with the atmosphere, forming an overcoat, is a layer of indium or of an indium-based alloy.

14. A substrate obtainable with a process as claimed in claim 1, comprising an untempered glass sheet coated on one of its faces with a stack of thin layers comprising a thin silver layer between two thin dielectric layers, wherein a last layer of the stack of thin layers, making contact with the atmosphere, is a layer of indium oxide or indium tin oxide (ITO) with a mass per unit area, expressed as the mass of metal atoms per unit area, comprised between 1 and 30 g/cm.sup.2.

15. The substrate as claimed in claim 14, wherein the layer of indium oxide or indium tin oxide (ITO) has a surface relief with a variance (Ra), determined by atomic force microscopy (AFM), comprised between 1 and 5 nm, most of the elements of the relief having a parabolic peak shape.

16. The process as claimed in claim 1, wherein the transparent sheet is a glass sheet.

17. The process as claimed in claim 1, wherein the brief duration is shorter than 0.1 second.

18. The process as claimed in claim 2, wherein the mass per unit area of the overcoat, expressed as the mass of metal atoms per unit area, is comprised between 3 and 25 g/cm.sup.2.

19. The process as claimed in claim 3, wherein the overcoat is a layer of an indium-based alloy containing more than 80% indium atoms relative to the total amount of metal atoms in the alloy.

20. The process as claimed in claim 4, wherein the indium-tin alloy (InSn) contains about 90% indium atoms and 10% tin atoms.

21. The process as claimed in claim 6, wherein the at least one metal layer is a silver layer.

22. The process as claimed in claim 8, wherein the heat treatment leads to a decrease in the sheet resistance and/or the emissivity of the stack of thin layers of at least 20%.

23. The process as claimed in claim 10, wherein the wavelength of the laser radiation is comprised between 950 and 1050 nm.

24. The process as claimed in claim 11, wherein the laser line simultaneously irradiates all of the width of the substrate.

Description

EXAMPLE 1

[0085] A thin ITO film of a thickness of about 23 nm is deposited by magnetron cathode sputtering of a ceramic target onto a 2 mm thick sheet of Planilux glass.

[0086] On two series of samples of this glass sheet, the following metal overcoats are then respectively deposited: [0087] a 4 nm layer made of titanium (comparative example) and [0088] a layer of (90/10) InSn (example according to the invention) having an equivalent thickness of about 5 nm.

[0089] Before heat treatment, the two series of samples have a sheet resistance (R.sub.) of about 400 ohms/ and a light absorbance of about 20%.

[0090] The two series of samples are subjected to a laser anneal by means of a diode-pumped laser emitting laser radiation in the form of a line focused on the coating to be annealed: [0091] wavelength of the radiation: 915+980 nm [0092] power per unit length: 49 W/mm [0093] width of the line in the focal plane: 45 m [0094] length of the line: 30 cm

[0095] The samples are run at various speeds under this laser device, then the absorbance of the visible light and the decrease in the value of P.sub. are measured in percent relative to the initial value.

[0096] The results are collated in table 1 below

TABLE-US-00001 TABLE 1 Overcoat made of Overcoat made of InSn titanium (according to the (comparative) invention) Absorbance Decrease Absorbance Decrease Run speed (%) in R.sub. (%) (%) in R.sub. (%) 2 m/min 1 69 3 m/min 1.5 62 1.5 69 4 m/min 2 58 2 68 6 m/min 4 52 5 65

[0097] It will be noted that the increases in conductivity obtained with the InSn overcoat according to the invention are larger than those obtained with the overcoat made of titanium according to the prior art. The increase in conductivity obtained for a sample according to the invention at a speed of 6 m/min is thus higher (65%) than that obtained at a speed of 3 m/min only for a sample with a titanium overcoat (62%).

[0098] These results show that an overcoat made of titanium, oxidizing into TiO.sub.2, may advantageously be replaced by an overcoat made of InSn that gives, after oxidation, ITO.

[0099] The samples according to the invention thus have a single ITO layer and are advantageously exempt of an overcoat made of high-index TiO.sub.2 that is liable to unfavorably modify the solar gain of a glazing.

EXAMPLE 2

[0100] All the trials were carried out on a glazing formed by a sheet of Planiclear glass bearing on one of its faces a low-E stack made up of the following layers in succession:

[0101] Si.sub.3N.sub.4 (30 nm)

[0102] TiO.sub.2 (12 nm)

[0103] ZnO (4 nm)

[0104] Ti (0.4 nm)

[0105] Ag (13.5 nm)

[0106] ZnO (4 nm)

[0107] TiO.sub.2 (24 nm)

[0108] Planiclear (4 mm)

[0109] Four samples that differed in the absorbing overcoat deposited by magnetron sputtering before laser treatment are prepared.

[0110] Sample 1 (comparative): 2 nm of TiO.sub.2

[0111] Sample 2 (comparative): 3 nm Sn.sub.xZn.sub.(1-x) (x=0.35)

[0112] Sample 3 (according to the invention): 2.8 nm InSn

[0113] Sample 4 (according to the invention): 8.4 nm InSn

[0114] The four samples were subjected to a heat treatment by a laser line of a power per unit length of 25 W/mm (wavelength 915 nm and 980 nm; width of the line in the focal plane 45 m, length of the line 30 cm). Table 2 below indicates the run speeds of the substrates, the visible absorption before and after laser treatment and the sheet resistance before and after laser treatment.

TABLE-US-00002 TABLE 2 Run Visibility speed Absorption (%) R.sub. (ohms/) of the Sample (m/min) Before After Before After raying 1 (comparative) 3 8.5 5.7 2.61 2.04 3.5 2 (comparative) 5 23.1 6.1 2.66 2.03 2.0 3 (invention) 5 19.3 5.4 2.69 2.19 1.25 4 (invention) 15 32.0 5.8 2.61 2.05 1.0

[0115] It will be observed that the four samples have, after heat treatment, absorption and sheet resistance values that are approximately equivalent. For sample 4 bearing an 8.4 nm absorbing layer made of InSn these results have however been obtainable with a treatment speed three times higher than that used for the absorbing layer of SnZn of the prior art (sample 2).

[0116] Moreover, it may clearly be seen in the last column of the table that the raying of the samples treated according to the invention is significantly less visible than that of the comparative samples.

[0117] The visibility of the raying is evaluated by an operator with the naked eye according to the following marking scheme: [0118] a grade of 1 is attributed when no nonuniformity is perceptible to the eye, [0119] a grade of 2 is attributed when localized nonuniformities, limited to certain zones of the sample, are perceptible to the eye under bright diffuse illumination (>800 lux), [0120] a grade of 3 is attributed when localized nonuniformities limited to certain zones of the sample are perceptible to the eye under standard illumination (<500 lux), and [0121] a grade of 4 is attributed when nonuniformities extending over all the surface of the sample are perceptible to the eye under standard illumination (<500 lux).

EXAMPLE 3

[0122] Two series of Planitherm type samples are prepared that differ in the absorbing overcoat used:

[0123] Series 1 (according to the invention): InSn 8.4 nm

[0124] Series 2 (comparative): SnZn 5 nm

[0125] The light absorption of the two series of samples before laser treatment is about 35%.

[0126] The samples of each series are subjected to a heat treatment, at various run speeds, under a laser line having the same characteristics as in the example 2.

[0127] FIG. 1 shows the variation in the absorption of the visible light (in %) of the samples after laser treatment as a function of the run speed of the substrate.

[0128] It will be noted that at low run speeds (less than 10 m/minute) the light absorption of the samples of the two series is approximately equivalent (about 5-10%). As the run speed increases, the absorption difference between the two series is accentuated: the samples according to the invention preserve a relatively low absorption (lower than 10%) even at high run speeds (30 m/minute), whereas for the samples using an overcoat of SnZn, the absorption increases greatly with run speed.

[0129] FIG. 2 shows the variation in the increase in conductivity after heat treatment as a function of the run speed of the substrate. The increase in conductivity is defined as the difference between the initial R.sub. (before heat treatment) and the final R.sub. (after heat treatment) divided by the initial R.sub..

Increase (%)=(RinitialRfinal)/Rinitial

[0130] It will be noted that at low run speeds, up to about 15 meters per minute, the increase in conductivity is approximately equivalent for the two series of samples, about 20%. In contrast, at a run speed of 30 meters per minute, the increase in conductivity after heat treatment is two times greater for samples bearing an InSn overcoat according to the invention than those bearing a comparative SnZn overcoat.