阅读说明：本技术 保护电路及测试结构 (Protection circuit and test structure ) 是由 于奎龙 韩坤 于 2019-08-28 设计创作，主要内容包括：本申请公开了一种保护电路及测试结构。该保护电路包括：晶体管；以及电阻,电阻的第一端连接至晶体管的第二通路端,第二端连接至晶体管的控制端,晶体管的第一通路端和电阻的第二端中的一个用于接收检测电流,晶体管的第一通路端和电阻的第二端中的另一个连接至参考地,其中,当检测电流小于预设电流时,晶体管导通以使检测电流到参考地的电流路径被导通,当检测电流大于/等于预设电流时,晶体管关断以断开电流路径。该保护电路中在检测电流大于/等于预设电流时,关断晶体管,并将检测电流限制在预设电流,实现了大电流的限位保护,避免大电流对测试结构造成的不利影响,提高了测试结构的可靠性。(The application discloses protection circuit and test structure. The protection circuit includes: a transistor; and a resistor, a first end of the resistor is connected to the second path end of the transistor, a second end of the resistor is connected to the control end of the transistor, one of the first path end of the transistor and the second end of the resistor is used for receiving a detection current, and the other of the first path end of the transistor and the second end of the resistor is connected to a reference ground, wherein when the detection current is less than a preset current, the transistor is turned on to enable a current path from the detection current to the reference ground to be turned on, and when the detection current is greater than or equal to the preset current, the transistor is turned off to disconnect the current path. When the detection current is larger than or equal to the preset current, the transistor is turned off, the detection current is limited to the preset current, the high-current limiting protection is realized, the adverse effect of the high current on the test structure is avoided, and the reliability of the test structure is improved.)

1. A protection circuit, comprising:

a transistor; and

a resistor having a first terminal connected to the second path terminal of the transistor and a second terminal connected to the control terminal of the transistor, one of the first path terminal of the transistor and the second terminal of the resistor receiving a detection current, the other of the first path terminal of the transistor and the second terminal of the resistor being connected to a ground reference,

when the detection current is smaller than a preset current, the transistor is turned on to enable a current path from the detection current to the reference ground to be turned on, and when the detection current is larger than or equal to the preset current, the transistor is turned off to disconnect the current path.

2. The protection circuit of claim 1, wherein the detection current is a positive voltage current, a first pass terminal of the transistor receives the detection current, and a second terminal of the resistor is connected to a ground reference.

3. The protection circuit of claim 1, wherein the sense current is a negative current, the second terminal of the resistor receives the sense current, and the first pass terminal of the transistor is connected to a ground reference.

4. The protection circuit according to any one of claims 1 to 3, wherein the transistor is a depletion type NMOS transistor.

5. The protection circuit according to claim 1, wherein the resistor is an adjustable resistor, and a resistance value of the resistor is adjusted according to a magnitude of the preset current.

6. The protection circuit of claim 1, wherein the transistor further has a body electrode for receiving a body voltage for adjusting a threshold voltage of the transistor according to the magnitude of the preset current.

7. The protection circuit of claim 6, further comprising: and the power supply is connected to the body region electrode and is used for providing the body region voltage.

8. A test structure, comprising:

a device under test; and

the protection circuit of any one of claims 1 to 7, connected to the device under test and receiving the detection current provided by the device under test.

9. The test structure of claim 8, wherein the device under test is a capacitor under test, a first terminal of the capacitor under test is connected to a tester, a second terminal of the capacitor under test is connected to a ground reference unit via the protection circuit,

and the preset current of the protection circuit is the current of the capacitor to be tested during breakdown.

10. The test structure of claim 8, wherein the device under test is a transistor under test, a first path terminal of the transistor under test is connected to the tester, a second path terminal and the control terminal are commonly connected to the ground reference unit via the protection circuit,

and the preset current of the protection circuit is the current of the transistor to be tested when the transistor to be tested breaks down.

Technical Field

The present invention relates to the field of integrated circuit technologies, and more particularly, to a protection circuit and a test structure.

Background

Breakdown voltage is an important electrical parameter in integrated circuit manufacturing technology, such as Gate Oxide BV (Gate Oxide BV), MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) breakdown voltage (MOS BVds). Taking a gate dielectric layer as an example, evaluating the pressure resistance of a gate is an important index of the service life of a device, and as a core of a field effect transistor, the reliability of the gate dielectric layer is one of important factors which restrict the reliability of the device and determine whether the device can be produced in mass.

The breakdown voltage test usually uses a semiconductor parameter tester (SMU) to perform a voltage Ramp test on a semiconductor test structure, when breakdown occurs, a large current passes through the test structure, and the tester determines the breakdown voltage when breakdown occurs by monitoring the current and limits the current within a certain range, and the test structure is, for example, a Gate oxide capacitor (Gate oxide) test structure or a field effect transistor (fet) test structure. However, breakdown in the test structure occurs very quickly, in many cases exceeding the response speed of the tester, and the tester cannot limit the current to a certain range, resulting in thermal breakdown and burning out of the test structure.

It is desirable to further improve the test structure to improve the reliability of the test structure.

Disclosure of Invention

In view of the foregoing problems, an object of the present invention is to provide a protection circuit and a test structure, wherein when a detection current is greater than or equal to a preset current, a transistor is turned off, and the detection current is limited to the preset current, so that a high-current limit protection is implemented, an adverse effect of the high current on the test structure is avoided, and reliability of the test structure is improved.

According to an aspect of the present invention, there is provided a protection circuit including: a transistor; and a resistor, a first end of the resistor is connected to a second path end of the transistor, a second end of the resistor is connected to a control end of the transistor, one of the first path end of the transistor and the second end of the resistor is used for receiving a detection current, and the other of the first path end of the transistor and the second end of the resistor is connected to a reference ground, wherein when the detection current is less than a preset current, the transistor is turned on to enable a current path from the detection current to the reference ground to be turned on, and when the detection current is greater than or equal to the preset current, the transistor is turned off to disconnect the current path.

Preferably, the detection current is a positive voltage current, a first path end of the transistor receives the detection current, and a second end of the resistor is connected to a reference ground.

Preferably, the detection current is a negative voltage current, the second terminal of the resistor receives the detection current, and the first path terminal of the transistor is connected to a ground reference.

Preferably, the transistor is a depletion type NMOS transistor.

Preferably, the resistor is an adjustable resistor, and the resistance value of the resistor is adjusted according to the magnitude of the preset current.

Preferably, the transistor further has a body electrode for receiving a body voltage, and the body voltage is used for adjusting the threshold voltage of the transistor according to the magnitude of the preset current.

Preferably, the method further comprises the following steps: and the power supply is connected to the body region electrode and is used for providing the body region voltage.

According to another aspect of the present invention, there is provided a test structure comprising: a device under test; and the protection circuit is connected to the device to be tested and receives the detection current provided by the device to be tested.

Preferably, the device to be tested is a capacitor to be tested, a first end of the capacitor to be tested is connected to the tester, a second end of the capacitor to be tested is connected to the reference ground unit through the protection circuit, and the preset current of the protection circuit is the current of the capacitor to be tested when the capacitor to be tested breaks down.

Preferably, the device to be tested is a transistor to be tested, a first path end of the transistor to be tested is connected to the tester, and a second path end and the control end of the transistor to be tested are connected to the reference ground unit through the protection circuit, wherein the preset current of the protection circuit is the current of the transistor to be tested when the transistor to be tested breaks down.

According to the protection circuit and the test structure provided by the invention, the resistance partial pressure of the protection circuit is related to the received detection current, when the detection current is increased, the resistance partial pressure is increased to control the on and off of the transistor, so that when the detection current is greater than or equal to the preset current, the resistance partial pressure is greater than or equal to the threshold voltage of the transistor, the transistor is turned off and limits the detection current to the preset current, the detection current is not increased continuously, the limit protection of large current is realized, the adverse effect of the large current on the test structure is avoided, and the reliability of the test structure is improved.

Furthermore, the protection circuit has simple structure, high reaction speed and small interference to the original circuit; furthermore, in the integrated circuit manufacturing process, the protection circuit can be realized by adopting the existing transistor and resistor in the circuit, and an additional process for manufacturing the protection circuit is not needed, so that the cost is saved.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

FIGS. 1 and 2 respectively show schematic diagrams of a conventional test structure;

FIG. 3 illustrates a current-voltage characteristic of a conventional test structure;

FIGS. 4 and 5 show the thermal breakdown voltage current characteristic curves of a conventional test structure, respectively;

FIGS. 6a and 6b show schematic diagrams of a protection circuit according to an embodiment of the invention;

FIG. 7a shows a schematic diagram of a test structure according to a first embodiment of the invention;

FIG. 7b shows a current-voltage characteristic of a test structure according to a first embodiment of the invention;

FIG. 8a shows a schematic view of a test structure according to a second embodiment of the present invention;

fig. 8b shows a current-voltage characteristic of a test structure according to a second embodiment of the invention.

Detailed Description

The invention will be described in more detail below with reference to the accompanying drawings. Like elements in the various figures are denoted by like reference numerals. For purposes of clarity, the various features in the drawings are not necessarily drawn to scale. In addition, certain well known components may not be shown.

In the manufacturing process of the semiconductor device, a semiconductor parameter tester SMU is adopted to carry out a voltage Ramp test on a semiconductor test structure so as to obtain the breakdown voltage of the device. As shown in fig. 1 and 2, conventional test structure 101 includes a gate dielectric capacitance test structure C0, test structure 102 includes a field effect transistor test structure Q0, semiconductor parametric tester SMU is connected to one end of test structure 101/102, and the other end of test structure 101/102 is connected to a ground reference unit GNDU. As shown in fig. 3, when a breakdown occurs, a large current may pass through the test structure 101/102, and the tester SMU monitors the detection current to determine the breakdown voltage when the breakdown occurs and limit the detection current to the predetermined current Icomp. However, breakdown in test structure 101/102 occurs very quickly, in many cases exceeding the response speed of tester SMU, which cannot limit the sense current to the preset current Icomp, resulting in overheating of test structure 101/102 and burning out. As shown in fig. 4 and 5, thermal breakdown of test structures 101 and 102 occurs and causes many adverse effects. For example, the thermal effect of the large current can damage the test structure and the interconnection metal thereof, which is not beneficial to the subsequent failure analysis to obtain effective information; the sudden change of the detection current can affect the stability of the bias voltage, and in the parallel test, the interference is caused to a plurality of tests which are performed in parallel; detecting current surges can cause interference between multiple test structures using a common pad (common pad).

The inventors of the present application have noticed the above-mentioned problem affecting the reliability of the test structure, and thus propose a further improved protection circuit and test structure.

The present invention may be embodied in various forms, some examples of which are described below.

Fig. 6a and 6b show schematic diagrams of a protection circuit according to an embodiment of the invention.

As shown in fig. 6a and 6b, the protection circuit includes a transistor Q1 and a resistor R1, and is used for receiving the detection current and switching off the circuit when the detection current is greater than or equal to the preset current, so as to realize the large current limit protection. A first terminal of the resistor R1 is connected to the second path terminal of the transistor Q1, a second terminal of the resistor R1 is connected to the control terminal of the transistor Q1, one of the first path terminal of the transistor Q1 and the second terminal of the resistor R1 is used for receiving the detection current, and the other of the first path terminal of the transistor Q1 and the second terminal of the resistor R1 is connected to the ground reference. The transistor Q1 and the resistor R1 adopt different connection modes according to the fact that the detected current is positive voltage current or negative voltage current.

When the detected current is a positive voltage current, the transistor Q1 and the resistor R1 are connected as shown in fig. 6 a. The transistor Q1 has a first terminal coupled to the sensing current, a second terminal coupled to the first terminal of the resistor R1, a control terminal coupled to the second terminal of the resistor R1, and a second terminal of the resistor R1 coupled to ground. Preferably, a body voltage Vb is applied to the body of transistor Q1 to adjust the threshold voltage of transistor Q1.

When the detected current is a negative voltage current, the transistor Q1 and the resistor R1 are connected as shown in fig. 6 b. The first terminal of the resistor R1 is connected to the second path terminal of the transistor Q1, the second terminal of the resistor R1 is connected to the control terminal of the transistor Q1, the second terminal of the resistor R1 is used for receiving the detection current, and the first path terminal of the transistor Q1 is connected to the ground reference. Preferably, a body voltage Vb is applied to the body of transistor Q1 to adjust the threshold voltage of transistor Q1.

Preferably, the transistor Q1 is a depletion NMOS transistor, the first path terminal of the transistor Q1 is a drain, the second path terminal is a source, and the control terminal is a gate.

In this embodiment, the predetermined current Icomp is the maximum current allowed by the protection circuit, for example, when the protection circuit is applied to a test structure of a capacitor or a transistor, the predetermined current Icomp is the corresponding current when the test structure breaks down.

In this embodiment, the product of the preset current Icomp and the resistance of the resistor R1 has a certain relationship with the threshold voltage of the transistor Q1, and the threshold voltage of the transistor Q1 can be controlled according to the magnitude of the body voltage Vb, so that the preset current Icomp of the protection circuit can be adjusted by adjusting the magnitude of the body voltage Vb and the resistor R1, and the specific parameters of the preset current Icomp can meet the following conditions. The resistor R1 is preferably an adjustable resistor, and the size of the resistor R1 is adjusted according to the preset current Icomp of the protection circuit.

In this embodiment, when the detection current received by the transistor Q1 is smaller than the preset current Icomp, the divided voltage of the resistor R1 is smaller than the absolute value of the threshold voltage of the transistor Q1, the transistor Q1 is turned on, and the detection current normally flows through the transistor Q1 and the resistor R1; when the detection current received by the transistor Q1 is greater than/equal to the preset current Icomp, the divided voltage of the resistor R1 is greater than/equal to the absolute value of the threshold voltage of the transistor Q1, the transistor Q1 is turned off, and thus the detection current is limited to the preset current Icomp.

Taking the detected current as a positive voltage current as an example, the protection circuit receives the positive voltage current, and when the divided voltage of the resistor R1 is smaller than the absolute value of the threshold voltage of the transistor Q1, the protection circuit is turned on and provides a current path from the positive voltage current to the reference ground; when the divided voltage of the resistor R1 is greater than/equal to the absolute value of the threshold voltage of the transistor Q1, the protection circuit turns off and opens the current path of the positive voltage current to the reference ground, so that the detection current is limited to a current such that the divided voltage of the resistor R1 is greater than the absolute value of the threshold voltage of the transistor Q1.

Given that the normal size of the detection current received by the protection circuit is Ibd, when the detection current received by the protection circuit is greater than/equal to the preset current Icomp, the protection circuit turns off and disconnects the current path from the detection current to the reference ground, so that the size of the detection current does not exceed the preset current Icomp, and the parameter design requirement of the protection circuit is as follows: ibd R1 < Vcritical1, wherein Vcritical1 is the maximum value of the divided voltage of the resistor R1, the divided voltage of the resistor R1 cannot be too large to avoid damaging the resistor R1 and the transistor Q1, and the Vcritical1 is 0.1V for example; ibd R1 < | Vt |, where the threshold voltage of the transistor Q1 is Vt, and under normal conditions, the resistor R1 divides the voltage to be less than the threshold voltage Vt, so as to ensure that the transistor is turned on before the detection current reaches the preset current Icomp; when the drain current Id of the transistor Q1 is equal to Ibd, Vds < Vcritical2 is required to ensure that the transistor voltage division cannot be too large, Vcritical2 is, for example, 0.1V, wherein the drain-source voltage Vds can be adjusted by adjusting the width (width) of the transistor Q1; icomp R1 ≧ Vt |, to ensure that when the sense current increases to Icomp, transistor Q1 turns off and limits the sense current magnitude to Icomp.

For example, if Ibd is 0.1mA, Vt is-1V, Vcritical1 is Vcritical2 is 0.1V, Icomp is 20mA, a resistance R1 with a resistance value of 100ohm is selected, where Ibd R1 is 0.1mA and 100ohm is 10mV, and Ibd R1 < Vcritical1 is satisfied; ibd R1 ═ 0.1mA ═ 100ohm ═ 10mV, meeting Ibd R1 < | Vt |; as can be seen from the current-voltage characteristics of the transistor Q1 under a certain width, when Id is 0.1mA, the drain-source voltage Vds is about 70mV, and Vds < Vcritical2 is satisfied; icomp R1 ≧ 20mA ≧ 100ohm ═ 2V, satisfying Icomp R1 ≧ Vt |. In the embodiment, when the detection current received by the protection circuit is less than 20mA, the protection circuit is normally turned on, and when the detection current received by the protection circuit is greater than or equal to 20mA, the protection circuit is turned off and limits the detection current to 20 mA.

Fig. 7a and 7b show a schematic diagram and a current-voltage characteristic, respectively, of a test structure according to a first embodiment of the invention.

As shown in fig. 7a, the test structure 110 includes a device under test, which is a capacitor under test C1, and a protection circuit 111.

The capacitor to be tested C1 has a first terminal connected to the first tester SMU1 and a second terminal connected to the reference ground via a protection circuit, and the capacitor to be tested C1 is, for example, a gate dielectric capacitor.

The protection circuit 111 comprises a transistor Q1 and a resistor R1, and is used for receiving the detection current, providing a current path from the capacitor C1 to be detected to the reference ground, and cutting off the circuit when the detection current is too large, so as to realize large-current limit protection. The first pass end of the transistor Q1 is connected to the second end of the capacitor C1 to be measured, the second pass end is connected to the first end of the resistor R1, the second end of the resistor R1 is connected to the control end of the transistor Q1, and the second end of the resistor R1 is further connected to the ground reference unit GNDU. By adjusting the parameters of the transistor Q1 and the resistor R1, the preset current Icomp of the protection circuit 111 can be adjusted.

Preferably, the body electrode of transistor Q1 is connected to a power supply, such as second tester SMU2, and second tester SMU2 can adjust the threshold voltage of transistor Q1 by adjusting the voltage applied to the body of transistor Q1.

As shown in fig. 7b, in this embodiment, the first tester SMU1 provides a test voltage to the capacitor to be tested C1, when the test voltage is less than the breakdown voltage of the capacitor to be tested C1, the detected current value received by the transistor Q1 is small, the divided voltage of the resistor R1 is less than the absolute value of the threshold voltage of the transistor Q1, the transistor Q1 is turned on, and a current path between the capacitor to be tested C1 and the reference ground is provided; when the test voltage is greater than or equal to the breakdown voltage of the capacitor to be tested C1, the detection current value received by the transistor Q1 reaches the preset current Icomp of the protection circuit, the divided voltage of the resistor R1 is greater than or equal to the absolute value of the threshold voltage of the transistor Q1, the transistor Q1 is turned off, and the current path between the capacitor to be tested C1 and the reference ground is disconnected, so that the detection current is limited to the preset current Icomp.

It should be understood that this embodiment only shows the case when the detected current of the capacitor to be measured is a positive voltage current, and when the detected current of the capacitor to be measured is a negative voltage current, the current protection of the capacitor to be measured can be implemented by using the protection circuit shown in fig. 6b to be connected in series with the capacitor to be measured.

Fig. 8a and 8b show a schematic diagram and a current-voltage characteristic, respectively, of a test structure according to a second embodiment of the invention.

As shown in fig. 8a, the test structure 120 includes a device under test, which is a transistor under test Q2, and a protection circuit 121.

The first pass terminal of the transistor Q2 under test is connected to the first tester SMU1, the second pass terminal and the control terminal are connected to the ground reference through the protection circuit, and the body electrode of the transistor Q2 under test may be connected to the ground reference or the test power supply for performing the corresponding test.

The protection circuit 121 includes a transistor Q1 and a resistor R1, and is configured to receive the detection current, provide a current path from the transistor Q2 to be tested to the reference ground, and cut off the circuit when the detection current is too large, so as to implement large current limit protection. The first path end of the transistor Q1 is connected to the second path end of the transistor Q2 to be tested, the second path end of the transistor Q1 is connected to the first end of the resistor R1, the second end of the resistor R1 is connected to the control end of the transistor Q1, and the second end of the resistor R1 is further connected to the reference ground unit GNDU. By adjusting the parameters of the transistor Q1 and the resistor R1, the preset current Icomp of the protection circuit 121 can be adjusted.

Preferably, the body electrode of transistor Q1 is connected to a power supply, such as second tester SMU2, and second tester SMU2 can adjust the threshold voltage of transistor Q1 by adjusting the voltage applied to the body of transistor Q1.

As shown in fig. 8b, in this embodiment, the first tester SMU1 provides a test voltage to the transistor Q2 under test, when the test voltage is less than the breakdown voltage of the transistor Q2 under test, the detected current value received by the transistor Q1 is small, the divided voltage of the resistor R1 is less than the absolute value of the threshold voltage of the transistor Q1, the transistor Q1 is turned on, and a current path between the transistor Q2 under test and the reference ground is provided; when the test voltage is greater than or equal to the breakdown voltage of the transistor Q2 to be tested, the detection current value received by the transistor Q1 reaches the preset current Icomp of the protection circuit, the divided voltage of the resistor R1 is greater than or equal to the absolute value of the threshold voltage of the transistor Q1, the transistor Q1 is turned off, and the current path between the transistor Q2 to be tested and the reference ground is disconnected, so that the detection current is limited to the preset current Icomp.

It should be understood that this embodiment only shows the case when the detected current of the transistor to be tested is a positive voltage current, and when the detected current of the transistor to be tested is a negative voltage current, the current protection of the transistor to be tested can be realized by using the protection circuit shown in fig. 6b to be connected in series with the transistor to be tested.

While embodiments in accordance with the invention have been described above, these embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments described. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The invention is limited only by the claims and their full scope and equivalents.