A system for applying an electric potential to a wafer

Abstract

The application provides a system for applying electric potential to a wafer, comprising two metal needles, a pushing mechanism, the two metal needles being arranged at the front end of the pushing mechanism, the pushing mechanism being used for pushing the two metal needles to move linearly so as to be stuck on a wafer to be measured, and a contact state detection module, the contact state detection module comprising an alternating current power supply, a resistor, a voltage acquisition unit and an upper computer, one end of the alternating current power supply being connected with one metal needle, the other end being connected with the other metal needle through the resistor, the voltage acquisition unit being used for monitoring the voltage of the resistor in real time and sending the voltage to the upper computer, the upper computer processing the voltage monitored in real time to obtain the waveform of voltage change, and whether the two metal needles are in good contact with the wafer to be measured being judged according to the waveform of voltage change and the waveform of the alternating current power supply.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wafer measurement technology, in particular to a system for applying electric potential to a wafer. BACKGROUND

[0002] In order to measure certain electrical characteristics of a device, such as breakdown voltage, leakage current or conduction characteristics, different electric potentials need to be applied to the wafer. For example, when testing IGBT or MOSFET, high voltage between drain and source needs to be accurately measured, and changes in wafer backside potential can be used to simulate actual working conditions, or to trigger specific electrical responses, so as to evaluate the performance of the device.

[0003] Materials like silicon may have an oxide layer (SiO2) on the surface in the natural state, or there may still be a contact barrier in the case of high doping. Traditional backside scratching method is commonly used in semiconductor device manufacturing, especially when forming a back electrode contact. This method involves mechanical processing, such as scratching the wafer back with a diamond pen or other hard objects, locally damaging the surface oxide layer or other insulating layer, exposing fresh semiconductor material, so that the metal electrode is in direct contact with the semiconductor, reducing the contact resistance. This method is low in cost and simple in equipment, but may cause mechanical damage to the wafer, affecting the reliability and life of the device, especially for thin wafers or flexible devices. In addition, the uniformity of scratching is difficult to control, which may lead to inconsistent contact resistance, affecting the consistency of device performance. There is also a risk of introducing impurities or contamination, which may affect subsequent process steps.

[0004] Therefore, how to avoid the above problems when applying electric potential to the wafer is the focus of attention of those skilled in the art. SUMMARY

[0005] The purpose of the present application is to provide a system for applying electric potential to a wafer, which can verify the contact quality, avoid damaging the semiconductor device, and realize non-destructive testing.

[0006] In order to achieve the above purpose, the present application provides a system for applying electric potential to a wafer, comprising:

[0007] Two metal needles;

[0008] A pushing mechanism, the two metal needles are arranged at the front end of the pushing mechanism; the pushing mechanism is used to push the two metal needles to move linearly, so as to pierce the wafer to be tested;

[0009] A contact state detection module, the contact state detection module comprises an alternating current power supply, a resistor, a voltage acquisition unit and an upper computer;

[0010] One end of the AC power source is connected to one metal needle, and the other end is connected to another metal needle through the resistor; the voltage acquisition unit is used for monitoring the voltage of the resistor in real time, and sending the voltage to the upper computer; the upper computer processes the voltage monitored in real time to obtain the waveform of voltage change;

[0011] According to the waveform of voltage change and the waveform of AC power source, it is judged whether the two metal needles and the wafer to be measured are in good contact.

[0012] In an optional solution, the system further comprises a chuck; the chuck is used for carrying the wafer to be measured, and the chuck is provided with two through holes; the pushing mechanism is arranged below the chuck, and the two metal needles pass through the through holes and pierce the back surface of the wafer to be measured.

[0013] In an optional solution, the pushing mechanism is a pneumatic cylinder.

[0014] In an optional solution, the pushing mechanism further comprises a buffer mechanism, the buffer mechanism is arranged on the outer periphery of the metal needle, the lower end is fixed to the pushing mechanism, and the upper end is a free end.

[0015] In an optional solution, the buffer mechanism is a spring.

[0016] In an optional solution, the measurement system further comprises a switch; the switch is connected between the resistor and the AC power source.

[0017] In an optional solution, the measurement system further comprises a DC power source; the switch is used for switching to connect the AC power source or the DC power source; when it is judged that the contact is good, the AC power source is disconnected, the DC power source is connected, and an electric potential is applied to the wafer.

[0018] In an optional solution, the voltage acquisition unit is a lock-in amplifier.

[0019] In an optional solution, the method for judging whether the two metal needles and the wafer to be measured are in good contact according to the waveform of voltage change and the waveform of AC power source comprises:

[0020] If the phase difference between the measured waveform of voltage change and the waveform of AC power source is between 85° and 95°, and the phase of the measured waveform of voltage change is ahead, it is determined that the contact is poor;

[0021] If the phase difference between the measured waveform of voltage change and the waveform of AC power source is between -5° and +5°, it is determined that the contact is good.

[0022] The beneficial effects of the present application are:

[0023] The present application uses a pushing mechanism to make the metal needle tip penetrate the wafer oxide layer and make point contact with the semiconductor body of the wafer to be tested, avoiding mechanical damage to the wafer and damage to the semiconductor device by the scraping method. The contact state detection module can detect the contact quality between the two metal needles and the wafer to be tested, so as to ensure that the metal needle and the wafer to be tested form a good ohmic contact. BRIEF DESCRIPTION OF DRAWINGS

[0024] The above and other objects, features and advantages of the present application will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which like reference characters refer to like parts throughout the different views of the drawings.

[0025] Figure 1 The hardware structure diagram of the system for applying potential to the wafer in an embodiment of the present application.

[0026] Figure 2 The structure diagram of the metal needle penetrating the oxide layer (such as SiO2) on the back surface of the wafer and forming contact with the semiconductor body (such as silicon substrate) in an embodiment of the present application.

[0027] Figure 3 The structure diagram of the metal needle not penetrating the oxide layer (such as SiO2) on the back surface of the wafer and not forming contact with the semiconductor body (such as silicon substrate) in an embodiment of the present application.

[0028] Figure 4 The circuit connection diagram of the system for applying potential to the wafer in an embodiment of the present application.

[0029] Figure 5 The circuit diagram when the metal needle does not contact the semiconductor body during contact state detection in an embodiment of the present application.

[0030] Figure 6 The circuit diagram when the metal needle contacts the semiconductor body during contact state detection in an embodiment of the present application.

[0031] Figure 7 The voltage waveform diagram obtained when the metal needle contacts the semiconductor body in an embodiment of the present application.

[0032] Figure 8 The voltage waveform diagram obtained when the metal needle does not contact the semiconductor body in an embodiment of the present application.

[0033] REFERENCE NUMERALS:

[0034] 1-metal needle; 2-spring; 3-chuck; 4-through hole; 5-semiconductor body; 51-oxide layer; 6-air cylinder. DETAILED DESCRIPTION

[0035] The present application will be further described with reference to the drawings and specific examples. The advantages and features of the present application will become apparent from the following description of the preferred embodiments and from the claims. It is to be understood, however, that the application can assume various alternative shapes and embodiments, and that the application is not limited to the specific examples described hereinafter. The drawings are not to precise scale and are only used to facilitate an easy understanding of the present application.

[0036] It should be understood that when an element or layer is referred to as being "on", "adjacent", "connected to" or "coupled to" another element or layer, it can be directly on, adjacent, connected or coupled to the other element or layer, or one or more intervening elements or layers can be present. In contrast, when an element is referred to as being "directly on", "directly adjacent", "directly connected to", or "directly coupled to" another element or layer, then there are no intervening elements or layers present. It will be understood that, although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present application.

[0037] Spatially relative terms, such as "beneath", "below", "lower", "under", "above", "upper" and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use and / or operation in addition to the orientations depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" or "over" the other elements or features. Thus, the exemplary term "below" can encompass both an orientation of above and below. The device can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0038] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising", when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein the term "and / or" includes any and all combinations of associated items.

[0039] Embodiments

[0040] Reference Figures 1 to 8 The present embodiments provide a system for applying an electric potential to a wafer, comprising:

[0041] Two metal needles 1;

[0042] A pushing mechanism, the two metal needles 1 are arranged at the front end of the pushing mechanism; the pushing mechanism is used to push the two metal needles 1 to move linearly, so as to pierce into the wafer to be tested (the wafer to be tested includes a semiconductor body 5 and an oxide layer 51 on the surface);

[0043] A contact state detection module, the contact state detection module includes: an alternating current power supply V S , a resistor R, a voltage acquisition unit and an upper computer;

[0044] One end of the alternating current power supply V S is connected to one metal needle 1, and the other end is connected to the other metal needle 1 through the resistor R; the voltage acquisition unit is used to monitor the voltage of the resistor R in real time, and send the voltage to the upper computer; the upper computer processes the voltage monitored in real time to obtain the waveform of the voltage change; according to the waveform of the voltage change and the waveform of the alternating current power supply, it is judged whether the two metal needles are in good contact with the wafer to be tested.

[0045] Specifically, in the present embodiment, the pushing mechanism is a gas cylinder 6. The gas cylinder 6 is moved by compressed air to push the metal needle 1 to move through the oxide layer 51 (such as SiO2) of the wafer and try to form an electrical contact with the semiconductor body 5 (such as a silicon substrate). There are two states, one is that the metal needle 1 pierces through the oxide layer 51 and successfully forms an ohmic contact with the semiconductor body 5 (refer to Figure 6 , the ohmic contact is manifested as forming a resistor R1), and the other is that one or two metal needles 1 do not pierce through the oxide layer 51, and the semiconductor body 5 and the metal needle 1 form a capacitor through the oxide layer 51 (refer to Figure 5 , the poor contact is manifested as forming a capacitor C).

[0046] In this embodiment, the voltage acquisition unit is a lock-in amplifier, which is used to monitor the current characteristics of the circuit. In this embodiment, the voltage Vr measured on the resistance R represents the current. The alternating voltage is a sine wave with a frequency of 500 Hz and a peak value of 640 mV. Figure 7 and Figure 8 The blue curve in the middle is the waveform of the alternating power supply, and the green curve is the waveform of the voltage Vr change of the resistance R. According to the waveform of the voltage change and the waveform of the alternating power supply, the method for determining whether the two metal needles are in good contact with the wafer to be tested includes: if the phase of the measured voltage change waveform (i.e. the phase of the voltage Vr of the resistance R, which is also the phase of the current) is about 90° different from the phase of the alternating power supply (that is, the phase difference is between 85° and 95°), and the phase of the measured voltage change waveform leads, it is determined that the contact is poor (see Figure 8 ); if the phase of the measured voltage change waveform is close to 0° different from the phase of the alternating power supply (that is, the phase difference is between -5° and 5°), it is determined that the contact is good (see Figure 7 ). Because the current i(t) = C × dv(t) / dt on the capacitor, if v(t) = sin(ωt + θ), then i(t) = L × cos(ωt + θ), so the current on the capacitor leads the alternating voltage by 90° phase.

[0047] Referring to Figure 3 , Figure 5 and Figure 8 , the metal needle 1 does not penetrate the oxide layer 51 or does not make sufficient contact with the semiconductor body 5, and a capacitor C is formed between the semiconductor body 5 and the metal needle through the oxide layer 51. At this time, the current is mainly dominated by the capacitive impedance, which is characterized by a phase that leads the power supply voltage and a low amplitude (related to the capacitance value). Referring to Figure 2 , Figure 6 and Figure 7 , the metal needle 1 successfully penetrates the oxide layer 51 and forms a direct electrical contact with the semiconductor body 5, establishing a resistive path ( Figure 6 ). The current is dominated by the resistance, and the amplitude increases significantly, and the phase is consistent with the power supply voltage (pure resistance characteristic).

[0048] In this embodiment, the system further includes a chuck 3; the chuck 3 is used to carry the wafer to be tested, and the chuck 3 uses the suction force of the vacuum groove to fix the position of the wafer to ensure the stability of the wafer during the test. The chuck 3 is provided with two through holes 4; the pushing mechanism is arranged below the chuck 3, and the two metal needles 1 pass through the through holes 4 and pierce the back of the wafer to be tested. In other embodiments, the wafer can also be pierced from the front of the wafer from top to bottom.

[0049] In the embodiment, the cylinder 6 further comprises a buffer mechanism, which is arranged at the outer periphery of the metal needle 1, with the lower end fixed to the cylinder 6 and the upper end being a free end. The buffer mechanism functions to buffer the pressure of the cylinder. In the embodiment, the buffer mechanism is a spring 2. When the cylinder 6 moves, the free end of the spring 2 contacts the bottom surface of the chuck, thereby buffering the pressure.

[0050] The measurement system further comprises a switch K, which is connected between the resistor R and the alternating current power supply Vs. The measurement system further comprises a direct current power supply V. The switch K is used to switch to connect the alternating current power supply Vs or the direct current power supply V. When it is determined that the contact is good, the alternating current power supply Vs is disconnected, and the direct current power supply V is connected to apply an electric potential to the wafer.

[0051] When the wafer needs to be tested, the wafer is placed on the chuck, the alternating current power supply is connected through the switch K, and the waveform of the voltage change of the resistor R is obtained on the upper computer. By comparing with the waveform of the alternating current power supply, it can be determined whether the metal needle and the wafer form an ohmic contact. If not, the pushing mechanism is pushed again until the metal needle and the wafer form an ohmic contact. At this time, the alternating current power supply is disconnected, and the direct current power supply is connected to start the required test on the wafer.

[0052] In the embodiment, the pushing mechanism is used to make the metal needle tip penetrate the oxide layer of the wafer and point-contact the semiconductor body of the wafer to be tested, thereby avoiding mechanical damage to the wafer and damage to the semiconductor device by the scraping method. The contact state detection module can detect the contact quality between the two metal needles and the wafer to be tested. Specifically, by means of the current response characteristics of the time-varying voltage, the capacitive coupling (poor contact) and the resistance contact (good contact) can be accurately distinguished, so that the metal needle and the wafer to be tested can form a good ohmic contact.

[0053] The micro alternating current signal is used to avoid damage to the semiconductor device, and the capacitive coupling principle is used to realize non-destructive testing. It is suitable for automatic test equipment, and the metal needle pressure or position can be dynamically adjusted to optimize the contact effect, so as to realize efficient and automatic wafer electrical contact detection.

[0054] The above description is only a description of the preferred embodiment of the present application, and does not limit the scope of the present application. Any modification or modification made by a person skilled in the art according to the above disclosure is within the protection scope of the claims.

Claims

1. A system for applying a potential to a wafer, characterized in that, include: Two metal needles; A pushing mechanism is provided, wherein the two metal needles are disposed at the front end of the pushing mechanism; the pushing mechanism is used to push the two metal needles to move linearly, thereby piercing the wafer under test; the wafer under test includes a semiconductor body and an oxide layer on its surface; A contact state detection module, comprising: an AC power supply, a resistor, a voltage acquisition unit, and a host computer; One end of the AC power supply is connected to a metal needle, and the other end is connected to another metal needle through the resistor; the voltage acquisition unit is used to monitor the voltage of the resistor in real time and send the voltage to the host computer; the host computer processes the real-time monitored voltage to obtain the waveform of the voltage change; Based on the waveform of the voltage change and the waveform of the AC power supply, determine whether the two metal needles are in good contact with the wafer under test. When a test is required on a wafer, the pushing mechanism drives a metal needle to penetrate the oxide layer of the wafer and attempt to form an electrical contact with the semiconductor body. If no electrical contact is formed, the pushing mechanism is pushed again until the metal needle forms an ohmic contact with the wafer.

2. The system for applying a potential to a wafer as described in claim 1, characterized in that, The system also includes a chuck; the chuck is used to carry the wafer to be tested, and the chuck has two through holes; the pushing mechanism is located below the chuck, and the two metal needles pass through the through holes and are inserted into the back of the wafer to be tested.

3. The system for applying a potential to a wafer as described in claim 1, characterized in that, The actuation mechanism is a cylinder.

4. The system for applying a potential to a wafer as described in claim 1, characterized in that, The pushing mechanism also includes a buffer mechanism, which is disposed on the outer periphery of the metal needle, with its lower end fixed to the pushing mechanism and its upper end being a free end.

5. The system for applying a potential to a wafer as described in claim 4, characterized in that, The buffer mechanism is a spring.

6. The system for applying a potential to a wafer as described in claim 1, characterized in that, The system also includes a switch; the switch is connected between the resistor and the AC power supply.

7. The system for applying a potential to a wafer as described in claim 6, characterized in that, The system also includes a DC power supply; the switch is used to switch between the AC power supply and the DC power supply; when it is determined that the contact is good, the AC power supply is disconnected and the DC power supply is connected to apply a potential to the wafer.

8. The system for applying a potential to a wafer as described in claim 1, characterized in that, The voltage acquisition unit is a lock-in amplifier.

9. The system for applying a potential to a wafer as described in claim 1, characterized in that, Based on the waveforms of the voltage change and the AC power supply, methods for determining whether the two metal needles are in good contact with the wafer under test include: If the phase difference between the measured voltage change waveform and the AC power supply is between 85° and 95°, and the phase of the measured voltage change waveform is ahead, then it is determined to be a poor contact. If the phase difference between the measured voltage change waveform and the phase difference of the AC power supply is between -5° and +5°, then the contact is considered good.

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