US3867272A

US3867272A - Electrolytic anticompromise apparatus

Info

Publication number: US3867272A
Application number: US325984A
Authority: US
Inventors: John B Rust; Gary S Smolker
Original assignee: Hughes Aircraft Co
Current assignee: Raytheon Co
Priority date: 1970-06-30
Filing date: 1973-01-23
Publication date: 1975-02-18
Anticipated expiration: 1992-02-18

Abstract

Microelectric devices and circuits, such as are found in semiconductor and hybrid microelectronics, are rendered unrecognizable and are destructed by means of an electrochemical reaction comprising an electrochemical or chemical etching and/or de-plating process.

Description

United States Patent Rust et al.

[ 1 Feb. 18, 1975 [54] ELECTROLYTIC ANTICOMPROMISE 3,418,226 12/1968 Marinace 204/146 APPARATUS 3,483,108 12/1969 Schaefer 1 204/15 3,655,540 4/1972 lrvin 204/146 [75] Inventors: John B. Rust, Malibu; Gary S.

Smolker, Los Angeles, both of Calif. [73] Assignee: Hughes Aircraft Company, Culver Primary EXaml'lerRl Andrews City, Calif. Attorney, Agent, or Firm-James K. Haskell; Lewis B. Sternfels [22] F11ed: Jan. 23, 1973 [21] Appl. No.: 325,984

I 1 'Related US. Application Data ABSTRACT [62] Dlvlsion of Serv No. 51,312, June 30, 1970, Pat. No.

M1croelectr1c dev1ces and circults, such as are found 52 vs. (:1 204/194, 204/263, 204/275 in Scmiccnductcr and hybrid microelectronics arc 51 1m. 01 B0lk 3/00, C23b 3/12 rcndcrcd unrecognizable and are dcstructcd y means 58] Field of Search 204/275, 263, 146, 15, of an electrochemical rcacticn comprising an clcctrc- 204 242 94 1 R chemical or chemical etching and/0r de-plating process.

[56] References Cited UNITED STATES PATENTS 14 Claims, 6 Drawing Figures 2,799,637 7/1957 Williams 204/15 Sou/(c5 r //2 C/lCd/T 0c. Ion A16 Sear/41::

PATENIEU FEB I 81915 SHEEI 10F 2 1 ELECTROLYTIC ANTICOMPROMISE APPARATUS This a division of application Ser. No. 51,312, filed June 30, I970, now U.S. Pat. No. 3,775,274 issued Nov. 27, I973.

The present invention relates to a process and associated apparatus which provides a means for destroying microcircuits or otherwise rendering unrecognizable details of specific circuit patterns and details of circuit device manufacture by means of an electrolytic etching and/or deplating process.

Military electronic equipment such as radars, computers, and communications equipment as well as similar and other commercial apparatus, utilizing electronic devices and circuits which contain classified or trade secret information or technology as to their design, are protectiable insofar as non-friendly persons or competitors cannot obtain such information or technology. The products value is seriously degraded if enemy personnel or competitors are able to obtain a sufficient amount of classified or trade secret information concerning the device parameters and modes of operation to enable the enemy personnel or competitors to develop effective countermeasures or to produce competing products. Such information is generally obtained when the item is stolen, lost in deployment, captured, or purchased on the open market.

In order to prevent such information from falling into the enemys or a competitors hands, several approaches have been taken among which are the use of an explosive to'shatter the device into many pieces and the use of microelectronic anticompromise circuits wherein a destruct mechanism destroys a thin film circuit pattern or a logic network. The first approach does not adequately destroy very small electronic circuits when placed in either hybrid microcircuits, LSI circuits, or MSI circuits whose dimensions are of only a few square inches because of its inability to render unrecognizable microcircuits of such small dimensions even after the microcircuit has been shattered into many small pieces. Regarding consumer items, such an explosive is a safety hazard and, therefore, impractical. The microelectronic technology approach is much less hazardous and has the ability to completely destroy miniscule critical parts without destroying neighboring parts. Furthermore, such an approach enables repair or replacement of inadvertently destroyed microcircuits. It is also possible to obtain destruction of only selected devices such as resistors, capacitors, inductors, diodes, and transistors. Consequently, the microelectronic technology approach is generally preferred.

One such approach utilizes a thermal-chemical reation in which microcircuit elements are destroyed by heat. This method is limited by the temperature rise which is possible to be brought to the elements of the microcircuit. For example, many microelectronic devices are provided with a heat-sink for cooling purposes; also, many electronic circuits are made out of thermally conductive material which will not reach its fusion temperature under any but the most unusual circumstances. For example, the heat of fusion of silicon is approximately 1,400C, which is a difficult temperature to maintain in a microelectronic package. Therefore, the thermal-chemical method is undesirable for many electronic devices. In another approach, an oxidation-reduction reaction occurs only on the surface of the devices and leaves either an oxide or metal residue which could aid in the determination of initial circuit or chemical composition of the component. Therefore, complete destruction is not obtainable.

The present invention avoids these and other problems by utilization of an electrolytic reaction by etching and/or electrochemical de-plating which does not depend upon temperature melting or fusing effects for destruction of the microcircuit and is not limited only to superficial destruction. Briefly, the present invention utilizes an electrolyte in solution which is in contact with or is caused to come into contact with the microcircuit or microcircuits or the circuit patterns thereof to be destructed. The electrolyte alone etches the microcircuit but, when the microcircuit is made the anode, upon supply of direct current, acid is formed at the anode in a nascent, highly active state. The substrate is rapidly oxidized and moves into solution along with any ions formed from the electronic devices, components and circuit connections and patterns.

An object of the present invention provides for an apparatus for destructing microelectronics circuits and devices.

Another object of the present invention is the provision of a method for destructing microelectronic circuits and devices.

Another object is the provision of an apparatus and method for destructing microelectronic circuits by electrochemical and/or de-plating means.

Another object of the present invention is to provide an apparatus and method for destroying the identity of microelectronic circuits.

Other aims and objects as well as a more complete understanding of the present invention will appear from the following explanation of exemplary embodiments and the accompanying drawings thereof, in which:

FIG. 1 schematically illustrates a first embodiment of the present invention for packaging a destruct apparatus prior to use thereof;

FIG. 2 shows the embodiment of FIG. 1 subsequent to initiation of the destruct mechanism;

FIG. 3 depicts the first embodiment of FIGS. 1 and 2 after destruct has been accomplished;

FIG. 4 schematically shows a second embodiment of the present invention;

FIG. 5 depicts a third embodiment of the present invention; and

FIG. 6 shows a fourth embodiment of the present invention utilizing fuzing means to initiate the supply of electrolytic solution to a microelectronic circuit.

Accordingly, with reference to FIGS. 1-3, a microcircuit 10 is included in or placed on a substrate 12 of silicon or germanium or the like. Device 10 and sub strate 12 are packaged within an enclosure 14 into which a cathode 16 and an anode 18 are provided and sealed. A source of direct current power 20 is secured to the anode and cathode. An encapsulated salt 22 comprising an electrolyte is positioned above the microcircuit and substrate and separated therefrom by some barrier, such as a pyrotechnic metal shield 24 which is to be removed when destruct is to be initiated. A solvent 26 is placed above the salt and separated therefrom by a divider 28 in order to prevent premature formation of an electrolytic solution formed from the combination of solvent 26 and salt 22. In order to insure that the solution, when formed, will come into contact with the microcircuit and substrate, a volume expander 30 is included within enclosure 14 and separated from a solvent and salt by a barrier 32, which may be made self-removing by means such as a pyrotechnic element.

Upon removal of

barriers

24, 28 and 32, the solvent and salt combine to form an electrolytic solution 34 which is thrust upon the microcircuit by expander 30, as shown in FIG. 2. Upon supply of current from source 20, acid in a nascent, highly active state forms at microcircuit and substrate 12 to cause oxidation and formation of ions therefrom which subsequently are dissolved in the solution in order to completely destroy and make unrecognizable the circuit and components therein. The result is shown in FIG. 3.

Referring now to FIG. 4, which depicts a second embodiment of the present invention, a microcircuit 40 is shown positioned upon a flat pack 42 both of which are sealed within an enclosure 44. A cathode 46 and an anode 48 which extend into and are sealed within the enclosure, are secured to a direct current source of power 50. For convenience, the separate packaging of the solvent and salt have been omitted from this figure, since they may be packaged in a manner similar to that depicted in FIG. 1. Therefore, FIG. 4 shows an electrolytic solution 52 already in contact with microcircuit and flat pack 42 as thrust thereagainst by a volume expander 54 through means of a deformable diaphragm 56. A wire 58 is shown connecting the anode to microcircuit 40 although the anode may be directly connected thereto. As described above, upon supply of power from source 50, the microcircuit is destroyed by electrochemical de-plating reactions.

Both FIGS. l and 4 show a volume expander, whose function is to ensure that the electrolyte will contact the microcircuit regardless of the gravity field, whether zero or not, and the physical attitude of the apparatus.

A third embodiment of the present invention is depicted in FIG. 5 wherein a circuit 60 to be destructed is positioned within an enclosure 62 sealed by means of a lid 64. A cathode 66 and an anode 68 extend within the package and are secured to a direct current source of power 70. A wire 72 connects the anode to circuit 60. In this embodiment, an electrolytic solution'74 is stored within a container 76 under pressure. Container 76 is coupled to the circuit package by a conduit 78 which is fitted within cover 64 and sealed from circuit 60 by a breakable diaphragm 80. This conduit may consist of a short path from container 76 to lid 64 allowing a pickaback configuration for container and device. Upon breaking of diaphragm 80, solution 74 flows from a container 76 into contact with circuit 60 through conduit 78 for destruct of the circuit upon supply of power from source 70.

Still another embodiment is shown in FIG. 6 for destruction of a circuit 90, which is contained within an enclosure 92 having a lide 94. In a manner similarly described above, a cathode 96 and an anode 98 connected to a source of power 100 extend within the FIG. 6 package. A wire 102 connects the anode with the circuit. In this embodiment, an electrolytic solution 104 such as an acid for etching or de-plating is contained within an ampoule 106 and placed atop lid 94. A squib cap 108 is placed around the ampoule and enclosed electrolytic solution and sealed to lid 94. A shaped charge 110 contained within a portion 110 of cap 108 is connected to an ignition source 112 and is disposed above squib 108 which is provided with a specific configuration 114 in order to provide a shaped charge. Upon energization of ignition source 112, the shaped charge explodes and punctures both ampoule 106 and lid 94 to force the electrolytic solution into contact with circuit 90. Electrochemical de-plating of the circuit occurs when current is supplied from source 100.

As stated above, the electrolytic process herein de scribed proceeds by means of the dissolution of the microcircuit in electrolyte solutions. This process consists of the oxidation of the microcircuit, such as a silicon semiconductor, from a low oxidation state to some higher state which is soluble in the electrolytic solution. This oxidation is coupled with the reduction of species in the system. In the dissolution of a silicon semiconductor in electrolytic solution, the metal is oxidized to ions. Oxidation of metal and reduction of electrolyte occur at corresponding anodes and cathodes. At steady state, the rate of anodic and cathodic reaction is equal to the overall dissolution rate. The oxidation and reduction rates are proportional to the current flow through the anode-cathode circuit.

The preferred electrolytic etchant means for attacking silicon, silicon nitride and silicon dioxide are hydrofluoric acid and mixtures of hydrofluoric acid with nitric acid. These etchants are modified with acetic acid, phosphoric acid, ammonium fluoride, etc., to achieve enhanced results for good chemical reactions, for chemical milling and etching.

In order to obtain rapid and complete eradication of dopants, dopant patterns and interconnections in a microcircuit, it is preferred to utilize salts which will give the desired acid or combination of acids at the anode surface of the microcircuit. Such salts include sodium fluoride, potassium fluoride, ammonium fluoride, lithium fluoride, the combination of potassium fluoride and potassium phosphate, lithium fluoride combined with lithium nitrate, sodium fluoride combined with sodium nitrate, potassium fluoride combined with potassium nitrate, lithium fluoride combined with lithium phosphate, sodium fluoride combined with sodium phosphate, lithium phosphate, lithium orthophosphate, etc. Because the effect of electrolytic etching processes is generally different and more active than chemical etching processes, mixed electrolytes are able to enhance activity. Therefore, sodium chlorate, potassium chlorate, etc., may be substituted for the nitrates, sodium persulphate, ammonium persulphate, etc., in conjunction with the fluoride. Added salts may be provided such as sodium acetate, sodium phosphate, and the like.

The electrolytic processes separate the ions in the electrolyte which, when in aqueous solution, form an acid at the anode and an alkali at the cathode. In order to prevent mixing and rapid neutralization, it is desirable to slow the diffusion by making the electrolyte viscous with polymeric additives, such as hydroxyethyl cellulose, polyvinyl alcohol, polyvinyl pyrollidone, and deacetylated chitin salt, and/or to surround the cathode with a porous structure such as a porous ceramic shell or a regenerated cellulose membrane, so as to confine the alkali released at the cathode.

Although the invention has been described with reference to particular embodiments thereof, it should be realized that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. An anticompromise apparatus, for destruction of the identity and usefulness of an otherwise operable electronic microcircuit comprising:

a source of direct current electrical power having an anode and a cathode, said anode coupled to the microcircuit;

means coupled to the microcircuit for containing a solution of electrolyte in isolation from the microcircuit and from said cathode, said solution including a composition capable of electro-de-plating at least portions of the microcircuit upon supply of the power from said source to said solution; and

means coupled to said containing means for placing said solution in contact with the microcircuit and for effecting an electrical circuit including said source, said solution and the microcircuit for the destruction of at least the portions of the microcircuit in a nonselective uncontrolled manner whereby identification and recognition of at least the portions is frustrated.

2. An apparatus as in claim 1 wherein said electrolyte is selected from the salts consisting of the fluorides of sodium, potassium, ammonia, and lithium singly and in combination with the nitrates, phosphates, chlorates, persulfates, and acetates of sodium, potassium, lithium and ammonia.

3. An apparatus as in claim 1 wherein said electrolyte is selected from the group consisting of the nitro and fluoro compounds capable of forming nitro and fluoro acids.

4. An apparatus as in claim 1 wherein said solution includes additives for inhibiting neutralization of acids and alkalis formed in said solution.

5. An apparatus as in claim 1 further including a porous structure surrounding said cathode.

6. An apparatus as in claim 1 further including additives in said solution for making said solution viscous.

7. An electronic microcircuit destruct apparatus comprising means for containing an acid medium in isolation from a microcircuit and from portions thereof, and means for nonselectively placing said acid medium in flooded contact with the microcircuit and the portions thereof and for electrolytically destroying the identity of at least the portions in an uncontrolled non-selective manner when the contact is made.

8. An apparatus as in claim 7 wherein said destroying means includes a source of electrical power coupled in series with said acid medium and the microcircuit for creating the acid medium in a nascent, highly active state and for electrochemically removing at least the portions of the microcircuit.

9. An apparatus as in claim 8 wherein the microcircuit comprises a substrate, electronic devices, and circuit connections and wherein said source of electrical power includes a source of direct current energy coupled at its positive terminal to the microcircuit for oxidizing the substrate into an electrolyte soluble state and for oxidizing metal of the devices and the circuit interconnections to ions.

10. An apparatus for destructing semiconductor devices and circuit patterns comprising:

an enclosure for enclosing the devices and the circuit patterns; means for containing a source of electrolyte in isolation from the devices and the patterns; and

means for supplying said electrolyte to the devices and the patterns into non-selective contact therewith and for electrolytically destructing the contacted devices and the patterns.

11. An apparatus as in claim 10 wherein said source of electrolyte includes separate packages of an electrolytic solvent and salts and wherein said electrolyte supplying means includes means for enabling dissolution of said salts and solvent in solution for flow of said solution into the contact with the devices and the patterns.

12. An apparatus as in claim 11 wherein said dissolution means includes fuse means for partially removing said packages.

13. An apparatus as in claim 10 further including:

a source of direct current energy having a cathode disposed within said enclosure for contact with said electrolyte and means for connecting the devices and the patterns to said source at the positive terminal thereof.

14. An apparatus as in claim 10 wherein said containing means includes a package surrounding said electrolyte.

Claims

1. AN ANTICOMPROMISE APPARATUS FOR DESTRUCTION OF THE IDENTITY AND USEFULNESS OF AN OTHERWISE OPERABLE ELECTRONIC MICROCIRCUIT COMPRISING: A SOURCE OF DIRECT CURRENT ELECTRICAL POWER HAING AN ANODE AND A CATHODE, SAID ANODE COUPLED TO THE MICROCIRCUIT; MEANS COUPLED TO THE MICROCIRCUIT FOR CONTAINING A SOLUTION OF ELECTROLYTE IN ISOLATION FROM THE MICROCIRCUIT AND FROM SAID CATHODE, SAID SOLUTION INCLUDING A COMPOSITION CAPABLE OF ELECTRO-DE-PLATING AT LEAST PORTIONS OF THE MICROCIRCUIT UPON SUPPLY OF THE POWER FROM SAID SOURCE TO SAID SOLUTION; AND MEANS COUPLED TO SAID CONTAINING MEANS FOR PLACING SAID SOLUTION IN CONTACT WITH THE MICROCIRCUIT AND FOR EFFECTING AN ELECTRICAL CIRCUIT INCLUDING SAID SOURCE, SAID SOLUTION AND THE MICROCIRCUIT FOR THE DESTRUCTION OF AT LEAST THE PORTION OF THE MICROCIRCUIT IN A NONSELECTIVE UNCONTROLLED MANNER WHEREBY IDENTIFICATION AND RECOGNITION OF AT LEAST THE PORTION IS FRUCTRATED.

7. An electronic microcircuit destruct apparatus comprising means for containing an acid medium in isolation from a microcircuit and from portions thereof, and means for non-selectively placing said acid medium in flooded contact with the microcircuit and the portions thereof and for electrolytically destroying the identity of at least the portions in an uncontrolled non-selective manner when the contact is made.

10. An apparatus for destructing semiconductor devices and circuit patterns comprising: an enclosure for enclosing the devices and the circuit patterns; means for containing a source of electrolyte in isolation from the devices and the patterns; and means for supplying said electrolyte to the devices and the patterns into non-selective contact therewith and for electrolytically destructing the contacted devices and the patterns.

13. An apparatus as in claim 10 further including: a source of direct current energy having a cathode disposed within said enclosure for contact with said electrolyte and means for connecting the devices and the patterns to said source at the positive terminal thereof.