LOW MELTING TEMPERATURE GLASS FOR USE OVER ALUMINIUM INTERCONNECTS OF AN INTEGRATED CIRCUIT STRUCTURE

Abstract: A low temperature insulation glass for use in semiconductor devices comprises a mixture of germanium dioxide, silicon dioxide and phosphorus pentoxide. In the preferred embodiment, the glass comprises a mixture of about 45% to 50% silicon dioxide (SiO₂), about 50% to 45% of germanium dioxide (GeO₂) and about 5% of phosphorus pentoxide (P₂O₅), by weight.

Description: LOW MELTING TEMPERATURE GLASS FOR USE OVER ALUMINIUM {JMINTERCONNECTS OF AN INTEGRATED CIRCUIT STRUCTURE BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates to integrated circuits and in particular to such circuits wherein a glass film with a smooth surface is provided on the integrated ciurcuit over the interconnect structure on the integrated circuit. This invention is particularly useful when the interconnect structure is aluminum or an alloy of aluminum. DESCRIPTION OF THE PRIOR ART The use of glass film overlying aluminum interconnections on integrated circuits is well known. Unfortunately, because prior art glass films melt at a temperature significantly above that of the aluminum, once such a glass film is formed, the topography of the surface of the glass film is permanently fixed. Accordingly, should it be desired to smooth the glass film to allow a second level of interconnects to be formed over the glass film, the underlying aluminum melts. To avoid this problem, first level interconnects are often formed of some material other than aluminum selected to have a melting temperature above that of the insulating glass formed over the interconnect leads. This often raises the impedance of the interconnects and slows the circuit. SUMMARY OF THE INVENTION It is a general object of this invention to provide a glass composition which has a melting point below that of aluminum. This and other objects are attained, in accordance with one aspect of the invention by a low temperature insulation glass for use in semiconductor devices, said insulating glass comprising a mixture of from 30% to 70% siO2, 30% to 708 of GeO2 and 2% to 10% of P205 by weight. Another aspect of the invention includes an integrated circuit comprising: a semiconductor material; insulation formed on said semiconductor material: interconnect leads comprising aluminum formed on said insulation and selectively brought into contact with the underlying semiconductor material through openings in said insulation; and a glass layer formed on said interconnect leads, said glass layer comprising a mixture of germanium, silicon, oxygen and phosphorus. DETAILED DESCRIPTION OF THE INVENTION The glass of this invention comprises a mixture of silicon, germanium,' oxygen, and phosphorus. The composition prefereably is in the range of approximately 30-70% SiO2, 30-70* GeO2, and 2-108 P205, by weight. Of course, the actual percentages of each consitituent are such that the total of the weight percentages of all the constituents is 100%. -By selecting the composition to be in these ranges, the melting or softening temperature of the glass is brought low enough such that the surface of the glass can be reflowed without damaging the aluminum interconnects formed beneath the glass. The preferred range of constituents is 45-50% SiO2: 50-45% GeO2: 5%-P205. In accordance with this invention, the use of a high pressure, as disclosed in co-pending application serial number 243,990 (filed on the same day as this invention on an invention of Reda Razouk entitled "Method of Inducing Flow or Densification of rhosphosilicate Glass for Integrated Circuits" and assigned to Fairchild Camera and Instrument Corporation, the assignee of this application), can be used to further lower the melting temperature of the glass. The use of pressure to accelerate flow is desirable since the temperature window between the highest temperature to which the aluminum interconnect can be heated without damage (typically about S400C but in general dependant upon the aluminum alloy used) and the highest temperature used in subsequent processing is small. The glass softening point should be kept high enough to avoid softening of the glass during later processing for alloy cycles or die attach. For this reason the natural flow of glass is made to take place at a temperature quite close to that of the melting of aluminum alloys. In another approach using temperature pulse techniques involving lasers, a temperature difference between the glass and the underlying interconnect material can be sustained and the glass can be selectively reflowed at a localized temperature somewhat higher than the melting temperature of the aluminum alloy without damaging the underlying alloy interconnect structure. The glass used- here is similar in its properties to phosphosilicate glasses commonly used in the prior art but flows at a much lower temperature. While the prior art phosphosilicate glass flowed, it did so at a temperature much too high to allow it to be used over aluminum or organic dielectrics such as polyimide (which tends to absorb water). The above description is exemplary only and other embodiments of this invention will be obvious to those skilled in the semiconductor glass arts in view of this disclosure.

Claims: WHAT IS CLAIMED IS: 1. A low temperature insulation glass for use in semiconductor devices, said insulating glass being comprised by a mixture of from 30% to 70% siO2, 30% to 70% of GeO2 and 2% to 10% of P205, by weight. 2. Structure as in Claim 1 wherein said glass comprises a mixture of about 45% to 50% SiO2, about 50% to 45% of GeO2 and about 5% of P2O5,. by weight. 3. An integrated circuit comprising: a semiconductor material; insulation formed on said semiconductor material: interconnect leads comprising aluminum formed on said insulation and selectively brought into contact with the underlying semiconductor material through openings in said insulation; and characterized by a glass layer formed on said interconnect leads, said glass layer comprising a mixture of germanium, silicon, oxygen and phosphorus. 4. Structure as in Claim 3 characterized in that said glass layer has a substantially smooth surface. 5. Structure as in Claim 3 or 4 characterized in that said glass layer comrpises a mixture of from 30% to 70% SiO2, 30% to 70% of GeO2 and 2% to 10% of P205, by weight. 6. Structure as in Claim 5 characterized in that said glass layer comprises a mixture of about 45% to 50% SiO2, about 50% to 45% of GeO2 and about 5% of P205, by weight.

Inventors: LEHRER, WILLIAM I., PIERCE, JOHN M.
Applicants: FAIRCHILD CAMERA & INSTRUMENT CORPORATION
Application year: 1982
Main classification: C03C3
IPC codes: C03C4, H01L21, H01L23, H05K1, H05K3, C03C3