METHOD FOR SELECTIVELY CURING A FILM ON A SUBSTRATE.

Abstract

A method is disclosed for rapidly curing a film on a substrate by selective heating causing it to cure from the inside out. This is achieved by illuminating the sample with a light source having a peak wavelength which is mainly absorbed by the underlying substrate and is transparent to the overlying film. Therefore, the substrate will be selectively heated first by direct absorption of the radiation and the film to be cured will in turn be heated by conduction from the substrate. In this way, the film will be hardened starting from the internal interface towards the surface, that is, from the inside to the outside.

Description

TITLE METHOD FOR SELECTIVELY HARDENING A FILM ON A SUBSTRATE, INVENTOR STULTZ TIMOTHY J. PRIORITY1USA PATENT APPLICATION FOR INDUSTRIAL INVENTION 23 MARCH 1990 N. 07 / 499.913 Rome, November 15, 1994 THE MANAGER (ATTILIO RONCACCI) TO THE MINISTRY OF INDUSTRY, TRADE AND CRAFTS CENTRAL PATENT OFFICE - ROME OOMAN^^BRE VETTO FOR INDUSTRIAL INVENTION A. APPLICANT (I) 1) Name L. . Βθ β.Κ StGlìlS, ...Ι..Π_C _____________________...____________________________________________________ Resident L Fremont, Cai.________________________USA__________________________________ 2) Name |_______________________________________________________________________________________ Residence I_____ __________________________________ . __________________________________________________________________________________ MODULE A Code l. J B. REPRESENTATIVE OF APPLICANTS AT THE UCB the FAMES Avv. Carlo and others surname name J coti, taxes LQQ^SmQW , , , , I THE FLAMES-FLAMES of nomination study of belonging L________ eieI of the Four. Fountain | „ u ,3Jici„à l C. ELECTION HOME RECIPIENT I_U£djsopra____ via L……………… ………….-………………………………………………………………………………………………………………………………………………………………………………I C. I C. I_L-IJ.J city ì_ ROME cep LQJUl.S.4 (prov) LSU ι cap (prov) D. TITLE proposed class (sez / cl / scl) iHQV.li jLM AND 0 D 0 P FOR EFFECT AT UARE SELECTIVELY THE HARDENING OF A SUBSTANT SljLUN FILM. I__________________________________________________I E. DESIGNATED INVENTORS surname name τι L Stultz Timothy J?__________ F. PRIORITY type of priority __________________________j ι D.INV. surname name J 4) L nation ΰ organization 1, 1 ......USA ...... 2) L .................. ....................._J L application number j ι 07 / 499.913 J I____ filing date attachment S / R l23 / lQ3 / Ji.1LQ lB LlJ / LlJ / I litigation U G. AUTHORIZED CENTRE FOR COLLECTING MICROORGANISMS CULTURES, name «. SPECIAL NOTES l_ none THE..... THE........ THE................. ADDED DOCUMENTATION N. es Doc. 1) L2 [PRÓvI n. pag. Doc 2) l3 Djfcv 1 / 1 n. tav. Due. 3) LJ □fe'l / i,' Doc. 4) lQ DITI Doc. $) Lt LÈZI 4 ' Odc. 6) Li dis im Ooc 7) ia Eris ι S| payment certificates, total lire lìQ ώ?ι summary with main drawing, description and claims (2 copies required) drawing (2 copies required if cited in the description) letter of assignment, procuie or reference general power of attorney inventor's designation priority documents with translation into Italian authorization or deed of assignment complete name of the applicant 9 | Revenue stamps for patent certificate of 1___________TEN THOUSAND lire COMPLETED ON i2 VlQJ / lIBII . SIGNATURE OF THE APPLICANT(S) CONTINUE / NO LNQ L................. ................................... AUTHENTIC COPY OF THIS ΑΠΟ IS REQUIRED YES / ND S ί ILAw.-C.-F1AMM —tot-t>.-MMENIGHE: Vi. Here PROVINCIAL OFFICE IND. COMM. ART. 01 DEPOSIT MINUTES The Honest Nineteen Hundred L APPLICATION NUMBER NINETY-ONE 1GH! N'2? ROME J mandatory J mandatory fci N. 24$ 3F code the applicant(s) indicated above has / have submitted to me, the undersigned I. MISCELLANEOUS NOTES BY THE AUTHORIZED OFFICER I_____________ .____________________________________________________ THE...................................................... THE DEPOSITOR of the above-mentioned patent. Reg.A TWENTY-FIRST of the month of MARCH J, the day And ROGANTE PROSPEnO A SUMMARY OF THE INVENTION WITH MAIN DRAWING, DESCRIPTION AND CLAIM APPLICATION NUMBER L....................Λ Λ Λ 1 Ù 'T* FILING DATE PATENT NUMBER^ · L ΛΖ l -jL-UU ÀJLJ jO · ISSUE DATE LlJ / LlJ / Ll.1_.lJ D. TITLE I___________METHOD FOR SELECTIVELY HARDENING A________| L..... FILM ON A SUBSTRATE» _________ΣΞΞΞΞ..ΖΖ__ΖΞ_ί'__Ξ_______ _________J l. SUMMARY A method is described for rapidly curing a film on a substrate by selective heating, causing it to harden from the inside out. This is achieved by illuminating the sample with a light source having a peak wavelength that is primarily absorbed by the underlying substrate and is transparent to the overlying film. Therefore, the substrate will be selectively heated first by direct absorption of the radiation, and the film to be cured will in turn be heated by conduction from the substrate. In this way, the film will be cured from the internal interface towards the surface, i.e., from the inside out. M. DISEONO fl G ,AA ι go there Description of the invention entitled: MG0 / ps / 50p METHOD FOR SELECTIVELY CARRYING OUT HARDENING TO OF A FILM ON A SUBSTRATE on behalf of the company PEAK SYSTEMS INC. in Fremont, California (USA) Inventor Mr. Timothy J. Stultz DESCRIPTION The present invention relates to methods for rapidly hardening a film on a substrate by selective heating. An example would be the creation of an insulating layer, such as SiO2, on a standard integrated circuit. The film is applied to the integrated circuit in liquid form. After application, the film must be hardened using heat to transform it into solid form. The hardening process, in general, requires the expulsion of volatile molecules or atoms. Using a conventional oven that heats by convection, this is done at relatively low temperatures for long periods to allow the melting and expulsion of volatiles from the film as it is subjected to hardening. Since materials being heated by convection heat from the outside in, the surface of the film begins to harden. - 2 Aw. C. FIAMMENGHI N* 29 Doti D. DOMÌNlGrtHh - & O Vi» Quattro Fontane, 31 Aw. C. FIAMMINGHI N* 29 Dr. D. DOMENJGKEHI - RAMENGHI N' ZI Yia Qmttro Fintane, 31 -.ROME___ yes before the inside. This inner surface layer prevents the emission or subsequent diffusion of volatile products from the rest of the film that has not yet hardened. Under extreme conditions, the expulsion of volatile products can be prevented and they can agglomerate, forming pockets or empty spaces within the film that reduce the effectiveness of the film itself. This effect occurs more quickly if high temperatures are used. Therefore, it is necessary to treat the films at low temperatures and for long periods to allow the curing process to proceed to the end without degradation of the properties desired from the film. The present invention relates to a process for rapidly hardening a film on a substrate by selective heating, causing it to harden from the inside out, resulting in luminescence; THE: I expose the sample to a light source having a peak wavelength that is mainly absorbed by the underlying substrate because the overlying film is transparent to light. Therefore, the substrate ι # * will be selectively heated first by direct absorption of the radiation and the film to be cured v, b . will in turn be heated by conduction from the substrate. (, , In this way, the film will harden from the interface,'i Λ. . ' ( internal towards the surface, that is, from the inside towards the outside. In one embodiment, the substrate is silicon and the film is a dielectric insulator initially in liquid form, e.g., spin-on-glass (SOQ). The light source is a gas discharge lamp filled primarily with xenon that has a peak emission at a wavelength that is absorbed by silicon because SOQ is transparent at that wavelength. A process utilizing the present invention can completely cure a film in seconds or minutes, as opposed to prior art processes which typically take hours. Furthermore, due to the inside-out curing mode, more complete film curing and the elimination of undesirable volatiles can be achieved. For a better understanding of the nature and advantages of the present invention, reference is made to the following description made in relation to the accompanying drawings, in which: Fig. 1A schematically represents a film on a substrate which is cured according to the present invention; Aw. C. FIAMMENGHI N* 29 !>jit F>.DOM^KSiETT· - KAMMENGKL· H* 27 Via Quattro 3t - ROME Fig. 1B is a temperature versus time diagram showing a typical two-step process utilizing the present invention; Figs. 2A and 2B are front and side views, respectively, of an embodiment of the present invention utilizing total substrate illumination; Fig.3 illustrates the embodiment of Fig.2A with a heat sink; FIGS. 4A and 4B are front and side views, respectively, of an embodiment of the present invention in which a scanning light line is moved on the substrate; and FIG. 5 shows the embodiment of FIG. 4A with a heat sink. Fig. 1A shows a light source 10 illuminating a film 12 and a substrate 14. Impurities 13 present in the film 12 are shown moving toward the surface during a curing process. The light source 10 is chosen to emit radiation having a wavelength that is absorbed by the substrate 14 but not by the film. 12.As the substrate 14 heats up, the film 12 also heats up by thermal conduction, with heating starting from the interface between the film 12 and the substrate t,, f, the ' Ί * l4. By heating from the inside out, rather than from the outside in, preliminary hardening from the outside, i.e. the formation of a crust, which could trap volatile atoms, is avoided. An example of the light source is described in U.S. Patent 4,820,906, which is incorporated herein by reference. In one embodiment, the light source is a long-arc gas discharge lamp filled primarily with xenon, and the substrate 14 is silicon. The energy of the xenon at its peak emission wavelength is greater than the bandgap energy of silicon and, therefore, will be absorbed by the silicon substrate. The energy of the xenon is less than the bandgap energy of the film 12, which may be spin-applied glass (SOG), for example, so it will not be absorbed. A chamber that can be used to hold the δ sample is illustrated in the U.S. patent. No. 4,755,654 which is incorporated herein by reference. A tray of inert material is used to hold a large number of samples in one embodiment. Fig.1B is the diagram of a typical procedure Z, ·; ; «1. I ' L ϊ : · I r v- ? In using the present invention, the sample is first heated to a relatively low initial temperature (typically 400-600°C, i.e., 240.4-315.5°C) typically for 5-30 seconds. Using this rather low temperature allows for a temperature gradient extending from the substrate through the film. A much higher temperature would heat substantially the entire film so rapidly that the gradient between the interface with the substrate and the outside of the film would not be sufficient to prevent the trapping of volatile atoms. After this initial relatively low temperature stage, the temperature can typically be increased to 900-1000°F (482.2-537.7°C) to complete the curing process after the volatile atoms have had a chance to escape. Typically this second stage lasts 2-20 seconds. Figs. 2A and 2B are front and side views, respectively, of the structure shown in more detail in the above-cited US patent. Sample 16, which consists of the film and the substrate, is placed under the light source 18. A reflector located above the light source focuses the light on sample 16. A pyrometer 22 located below sample 16 detects the infrared light. Aw. C. FIAMMENGHI N* 29 Dr. D. D0MEH!GtìEH5 - Ν' 27 Vie Quattro Fontane, 31 - ROME . emitted by the sample when it is heated and provides a retraction signal to the light source control devices. Fig. 3 shows a similar structure with the addition of a heat sink 24. In the center of the heat sink 24 a through hole 26 is provided, through which the pyrometer 22 can see the sample 16. In one embodiment the heat sink is made of metal and is water cooled. Since the substrate 14 is in contact with the heat sink, this will further help to keep the substrate cool while still allowing the film 12 to heat up. Figs. 4A and 4B are front and side views, respectively, of an alternative embodiment in which a light source 28 and a pyrometer 30 are moved into alignment with respect to the sample 16. The light source 28 and the pyrometer 30 could remain stationary while the sample 16 is moved into the space between them. Alternatively, the sample 16 could remain stationary while the light source 28 and pyrometer 30 are moved. A scan line defined by lines 32 illuminates a portion of the sample 16 with each pass. A longitudinal slit 31 allows light to pass to the pyrometer. 30. Fig.5 shows the embodiment of Fig.4A Aw. C. FIAMMENGHI N· 29 tot. ¢. WMB8GHSTTI - FXWGHJ N* 27 Vi» Quattro Fenfane, 31 - ROME with the addition of a heat sink 34. The latter has a longitudinal slit to allow the pyrometer 30 to see the sample 16 at all times during relative motion. As will be clear to those skilled in the art, this The invention may be practiced in other specific forms without departing from the spirit or essential features thereof. For example, instead of a single lamp, a series of lamps could be used. Therefore, the description of the preferred embodiment of the invention is to be construed only as illustrative but not as limiting the scope of the invention which is defined in the following claims.

Claims

CLAIMS 1. A method for selectively heating a film on a substrate, characterized in that it comprises the following steps: choosing the substrate and the film to have different light absorption characteristics; and illuminating the film and the substrate with a light source having a peak wavelength that is substantially absorbed by the substrate and substantially not absorbed by the film.

2. Process according to claim 1, caratAw. C. FIAMMENGHI N' 29 tot D. ΜΜΕΙββΗΕΠ! - PAaSSSSHI lf ZI Via Quattro Fante neg 31 - ROMA characterized by the fact that the substrate is silicon and the film is a liquid-based dielectric.

3. Process according to claim 2, characterised in that the dielectric is glass.

4. The process of claim 2, further comprising: illuminating the film and substrate with a first light intensity to produce a first temperature for a first period of time; and subsequently illuminating the film and substrate with a second light intensity, greater than the first intensity, to heat the film and substrate to a second temperature, greater than the first temperature, for a second period of time.

5. Product made with the process of claim 1. 10 AoUa. k)o . Ρ A ©.so hcM* VJo. Q / l 7J Oco 15 38 E 91 KmdJ· AW Iff} 1538E91 Àw. c. FlXtóMEKiÓHI N· 29 boti. D. WMEMIGHEnf FIAMMENGHI Ν' tJ vi· Qvtttr· 31 · IQMA ÌU'. Λ· ?'Ί °ι-ι * 'Ρ 1538C9I ro F / G, 4A. Aw. C. FIAZ M. t>, POMENIGHETTI ^AMMENGHI ΚίΤ VI* Quallr· foelen·, 31 - IOMA I538 C9 I 1538E91 Aw. C. FIAmMENBHÌ 7n· 29 Oct. D. DOMENIGHETTI - ^AMMENGHI N* 27 VU Quittn Fuck a·. 31 .ROME