# Patent

## Title
Light sensitive switch for semiconductor package tamper detection

## Abstract

Embodiments relate to the detection of semiconductor tampering with a light-sensitive circuit. A tamper detection device for an integrated circuit includes a light-sensitive circuit disposed within a package of an integrated circuit. The light-sensitive circuit closes in response to an exposure to a light source, indicating a tamper condition.

## Background
BACKGROUND
The present invention relates generally to semiconductors, and more specifically, to detectability of semiconductor tampering.
Semiconductor manufacturers may rigorously test a packaged semiconductor component to meet minimal quality standards. During the testing process, the semiconductor component can be marked with its exact part number and quality information on a viewable surface, such as a semiconductor case. Semiconductor manufacturers and end-users may rely on this information to accurately identify the semiconductor component.
However, after the semiconductor component is released into the public domain, tampering may occur. This tampering may include, but is not limited to, an opening of the case of the semiconductor component and/or a modification integrated circuit.
SUMMARY
Embodiments include systems and a method of manufacture for detecting tampering with a semiconductor. According to an embodiment of the present invention, a tamper detection device for an integrated circuit includes a light-sensitive circuit disposed within a package of an integrated circuit, wherein the light-sensitive circuit closes in response to an exposure to a light source, thereby indicating a tamper condition.
According to another embodiment of the present invention, a light-sensitive circuit that includes at least one passive radio-frequency (RF) tag, the light-sensitive circuit closes in response to an exposure to a light source and the RF tag indicates a closure of the light-sensitive circuit.
According to another embodiment of the present invention, a method of forming a tamper detection device for an integrated circuit, comprises depositing a silicon layer on an insulating substrate, forming a patterned hard mask on the silicon layer, etching exposed portions of the silicon layer to form a plurality of silicon planks, removing the hard mask from the plurality of silicon planks, implanting ions defined by photoresist to form at least one PIN junction on the plurality of silicon planks, forming an interconnect layer that electrically connects a plurality of photovoltaic cells, depositing patterned electrodes of a MEMS switch on the interconnect layer, the patterned electrodes include a pull-in electrode and a contact electrode depositing a sacrificial material over the patterned electrodes, forming an arm of the MEMS switch on the sacrificial material, the arm includes a cantilever, etching the sacrificial material from the patterned electrodes, and connecting the MEMS switch with the plurality of photovoltaic cells. The PIN junction has an undoped intrinsic semiconductor region between a p-type semiconductor region and an n-type semiconductor region, and the at least one PIN junction forms a photovoltaic cell.



BRIEF DESCRIPTION OF THE DRAWINGS
The subject matter which is regarded as embodiments is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the embodiments are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
FIG. 1 depicts a semiconductor assembly with a tampering detection device in accordance with an embodiment;
FIG. 2 depicts a light-sensitive circuit in accordance within an embodiment; and
FIG. 3 illustrates a light-sensitive circuit electrically connected to an integrated circuit in accordance with an embodiment;
FIG. 4 illustrates a light-sensitive circuit electrically connected to a radio-frequency identification tag in accordance with an embodiment;
FIG. 5 is a flow diagram illustrating a process for manufacturing the light-sensitive circuit in accordance with an embodiment; and
FIGS. 6A-6I are a series of cross sectional and top views further illustrating a process for manufacturing the light-sensitive circuit in accordance with an embodiment, in which:
FIG. 6A depicts a thin silicon layer deposited on an insulating substrate;
FIG. 6B depicts a silicon dioxide hard mask deposited on the thin silicon layer;
FIG. 6C depicts a hard mask transferred to the thin silicon layer to form silicon planks;
FIG. 6D depicts silicon planks doped to form p-i-n junctions;
FIG. 6E depicts an interconnect layer to electrically connect photovoltaic cells;
FIG. 6F depicts electrodes deposited with a metal;
FIG. 6G depicts a sacrificial material deposited on the electrodes;
FIG. 6H depicts an arm formed on a mounting surface of the sacrificial material; and
FIG. 6I depicts a sacrificial material etch that exposes a space between the arm, the pull-in electrode, and the contact electrode.



DETAILED DESCRIPTION
Counterfeit semiconductor components generally do not meet minimal quality standards and may not work properly if installed in commercial or military systems. As counterfeiters become more sophisticated with the creation of components with accurate dimensions and packaging, it is increasingly difficult to detect a counterfeit component by visual inspection. Accordingly, it is important to have a tampering detection system that goes beyond surface aesthetics. A tampering detection system directly tied to existing component hardware is more difficult to duplicate and avoid triggering by a counterfeiter. Also, by tying the tampering detection system to circuit hardware, the level of technical sophistication required by the counterfeiter to avoid detection increases.
FIG. 1 illustrates an exemplary semiconductor assembly 100 with a tamper detection device in accordance with an embodiment. Specifically, in FIG. 1, the semiconductor assembly 100 includes an integrated circuit 102 enclosed in a package 104. Electrical contacts 106 extend from the package 104 and provide an electrical connection with elements of the integrated circuit 102.
In some embodiments, a tamper detection device including light sensitive circuit 108 is disposed within the package 104 of the integrated circuit 102 as shown in FIG. 1. Alternatively, the light sensitive circuit 108 may be electrically isolated from the integrated circuit 102. The light sensitive circuit 108 is covered by the package 104 to limit exposure of the light sensitive circuit 108 to ambient light, for example. In the event that the light sensitive circuit 108 is exposed to a light source due to removal or partial removal of the package 104, (e.g., from tampering, etc.), the light sensitive circuit 108 activates, permanently changing the electrical properties of the light sensitive circuit 108 and/or properties of the integrated circuit 102, thereby indicating a tamper condition. The operation and configurations of the light-sensitive circuit 108 are described in more detail below. FIG. 2 illustrates a light sensitive circuit 108 in accordance with one embodiment. In particular, the light sensitive circuit 108 includes a photovoltaic circuit 202 connected in parallel with a micro-electromechanical system (MEMS) switch 204 and a resistive element 206. The resistive element 206 can be a resistor, a combination of resistors in series or parallel, or any other type of resistive device. The resistive element 206 is optional, but provides an increased output voltage of the light sensitive circuit 108, as described in more detail. The photovoltaic circuit 202 includes a plurality of photovoltaic cells 208 arranged sequentially in a series configuration. Alternatively, the photovoltaic circuit 202 may include a single photovoltaic cell. Although a series configuration of photovoltaic cells 208 is shown, other arrangements of the photovoltaic cells 208 are contemplated by other embodiments.
The photovoltaic circuit 202 includes a plurality of contact pads 210 that electrically connect adjacent photovoltaic cells. Terminating contact pads 212 form nodes of the photovoltaic circuit 202, at the parallel connection of the MEMS switch 204 and the resistive element 206.
When exposed to light source such as sunlight, a lamp, or any other light source, the photovoltaic cells 208 generate an electrical current. A series configuration of the photovoltaic cells 208 increases the open circuit output voltage generated by the photovoltaic circuit 202. The resistive element 206 acts to provide a linear relationship between the electrical current and voltage between the nodes of the photovoltaic circuit 202, increasing sensitivity of the light sensitive circuit 108. The resistive element 206 is configured to generate a voltage across the MEMS switch 204 in response to the current generated by the photovoltaic circuit 202.
Further details of the MEMS switch 204, according to an embodiment, are also shown in FIG. 2. The MEMS switch 204 includes an arm 214 electrically connected to a first node 216 of the light sensitive circuit 108. The arm 214 is mechanically affixed to a base structure 217 at one end thereof, and is suspended at a second end thereof so as to define a cantilever. The MEMS switch 204 further includes a pull-in electrode 218 and a contact electrode 220 affixed to the base structure 217, and are connected to the second node 222 of the photovoltaic circuit 202. Prior to activation of the photovoltaic circuit 202, the arm 214 and the pull-in electrode 218 are separated by a space, which electrically isolates the pull-in electrode 218 and the contact electrode 220 from the arm 214.
The exposure of the photovoltaic cells 208 to a light source causes the photovoltaic cells 208 to generate an electrical current. Accordingly, a voltage differential is also generated across the resistive element 206 and across the MEMS switch 204 upon generation of the electrical current. The first node 216 of the light sensitive circuit is electrically connected to the arm 214, and the second node 222 of the light sensitive circuit 108 is connected to the pull-in electrode 218.
The difference in voltage potential between the arm 214 and the pull-in electrode 218 creates an electrostatic force between the arm 214 and the contact electrode 220. The electrostatic force causes the arm 214 to deflect and come into contact with the contact electrode 220, creating a shorted circuit or wire between the first node and the second node, as shown in FIG. 3. In one embodiment, the force between the pull-in electrode 218 and the arm 214 causes the arm 214 to bend and strike the contact electrode 220. The impact force of the arm 214 with the contact electrode 220 results in a permanent connection between the arm 214 and the contact electrode 220 of the MEMS switch 214, even in the event the source of the light is subsequently removed. Accordingly, the arm 214 and the contact electrode 220 remain electrically connected after exposure of the photovoltaic cells 208 to the light source is discontinued.
The attachment of the contact electrode 220 with the arm 214 of the MEMS switch 204 is facilitated by a roughened surface on the arm 214 and/or the contact electrode 220. The roughened surface(s) act to provide an additional bonding capability for the arm 214 and the contact electrode 220. The arm 214, the pull-in electrode 218 and the contact electrode 220 can be made of aluminum or any other suitable conductive material.
Referring to FIG. 3 with continuing reference to FIG. 2, FIG. 3 further illustrates a light-sensitive circuit 108 electrically connected to the integrated circuit 102. In this embodiment, the integrated circuit 102 is electrically connected to at least one node of the light-sensitive circuit 108. Light exposure induces a current in the light-sensitive circuit 108, causing the MEMS switch 204 of the light-sensitive circuit 108 to close. Because of the electrical connection with the integrated circuit 102, operating parameters of the integrated circuit 102 are changed. For example, the conductive path formed by the MEMS switch 204 of the light-sensitive circuit 108 may short-circuit a component of the integrated circuit 102, inhibiting or disabling the operation of the integrated circuit 102.
FIG. 4 illustrates a light-sensitive circuit 400 electrically isolated from the integrated circuit 402 and packaged within the semiconductor device 404. In this embodiment, the removal of the package 406 and/or exposure of the light-sensitive circuit 400 to ambient light, for example, causes a short-circuit in the light sensitive circuit 400. Although the light-sensitive circuit 400 is electrically isolated from the integrated circuit 402, the light-sensitive circuit 400 can be electrically connected to a passive radio-frequency tag 408, for example. The passive radio-frequency tag 408 may indicate to that exposure to a light source has occurred and that the light-sensitive circuit 400 has activated (i.e., a switch has closed). A user may detect the change with any suitable radio-frequency analysis tool, allowing the user to leave the package 406 in place while a determination of semiconductor integrity is performed.
Referring now to both FIG. 5 and the accompanying views of FIGS. 6A-6J, FIG. 5 is a flow diagram that illustrates a method of manufacture of the light-sensitive circuit in accordance with one embodiment. At block 501, with reference to FIG. 6A, a thin silicon layer 551 (e.g. 10 nm to 10 μm) is formed on an insulating substrate 552 to begin a process of forming the photovoltaic cells. The thin silicon layer 551 may be deposited by at least one of a silicon spalling technique, poly-silicon deposition with annealing, or a direct silicon on insulator wafer.
At block 502, a silicon dioxide hard mask deposition is performed and a silicon dioxide hard mask 553 is deposited as shown in FIG. 6B. The silicon dioxide hard mask 553 provides a protective surface on the thin silicon layer 551 during a subtractive etching process. In this embodiment, the silicon dioxide hard mask 553 is formed and then selectively patterned on a top surface of the thin silicon layer 551.
At block 503 and as shown in FIG. 6C, a silicon RIE (reactive ion etching) etch is performed to transfer the hard mask pattern into the silicon layer 551, thereby defining silicon planks 554 on the insulating substrate 552 that correspond to the pattern of the silicon dioxide hard mask 553. Following the etching process of block 503, the silicon dioxide hard mask 553 is removed through reactive ion etch or wet etch, for example. Then, as shown in block 504 of FIG. 5 and the top view of FIG. 6D, the silicon planks 554 are subject to a doping process so as to form p-i-n junctions. For example, ion implantation of phosphorous (n+) at one end of the plank and boron (p+) at the opposite end of the plank can be implemented with sequential photoresist and/or hard mask steps to form a p-i-n junction having an undoped intrinsic region 555, an N+ region 556 and a P+ region 557. At block 505 as shown by FIG. 6E, an interconnect layer 559 is formed to electrically the photovoltaic cells. The interconnect layer 559 may be formed by depositing and patterning a titanium/gold alloy or a chromium/gold alloy, for example. In addition to connecting the silicon planks, the interconnect layer 558 may include at least two pads formed for connection with the MEMS switch and other components of the light-sensitive circuit.
At block 506 and as shown in FIG. 6F, electrodes 560 are deposited and patterned using aluminum, for example. The electrodes 560 connect the MEMS switch with the at least one pad of the photovoltaic cells. In one embodiment, the electrodes 506 include a contact electrode and a pull-in electrode. Optionally, at block 507, argon atoms are bombarded on the surfaces of the electrodes, to roughen the electrodes and improve adhesion upon contact of the arm with the contact electrode, for example. At block 508 and as shown in FIG. 6G, a sacrificial material 561, for example parylene, is deposited on the electrodes 560 and the space surrounding the electrodes 560. The parylene 561 forms a mounting surface on which an arm 562 is formed as shown in FIG. 6H. At block 509, aluminum can be deposited and patterned to form the arm 562 of the MEMS switch. In one embodiment, the arm 562 is a cantilever that bends in response to an applied voltage. At block 510, an oxygen-plasma etch is performed to remove the parylene 561 and expose a space between the arm 562, the pull-electrode, and the contact electrode as shown in FIG. 6J. At block 511, MEMS electrodes are connected to the photovoltaic cells in a light-controlled environment. The control of light is avoids triggering the MEMS switch (e.g., activating the making contact with the arm and the contact electrode).
The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

## Claims

1. A tamper detection device for an integrated circuit, comprising:
a light-sensitive circuit disposed within a package of an integrated circuit, wherein the light-sensitive circuit closes in response to an exposure to a light source, thereby indicating a tamper condition;
wherein the light-sensitive circuit comprises a photovoltaic circuit connected in parallel with a micro-electromechanical system (MEMS) switch; and
wherein the light-sensitive circuit further comprises a resistive element connected in parallel with the MEMS switch and the photovoltaic circuit, the resistive element is configured to generate a voltage across the MEMS switch in response to a current generated by the photovoltaic circuit.

2. The tamper detection device for an integrated circuit of claim 1, wherein at least a partial removal of the package exposes the light-sensitive circuit to the light source.

3. The tamper detection device for an integrated circuit of claim 1, wherein the photovoltaic circuit comprises a plurality of photovoltaic cells arranged in series, the photovoltaic cells configured to generate the current in response to exposure of light from the light source.

4. The tamper detection device for an integrated circuit of claim 3, wherein the MEMS switch comprises an arm electrically connected to a first node of the photovoltaic circuit, a pull-in electrode and a contact electrode connected to a second node of the photovoltaic circuit, the arm and the pull-in electrode are separated by a space.

5. The tamper detection device for an integrated circuit of claim 4, wherein the voltage generated by the photovoltaic circuit causes the light-sensitive circuit to close by causing the arm to electrically connect with the contact electrode, wherein the arm and the contact electrode remain electrically connected after exposure of the photovoltaic circuit to the light source is discontinued.

6. The tamper detection device for an integrated circuit of claim 4, wherein the arm, the contact electrode and the pull-in electrode are made of aluminum, the contact electrode and the arm include roughened surfaces, wherein the arm electrically connects with the contact electrode by deflecting.