Method for a four-probe measuring instrument to measure a wafer under test and four-probe measuring system

Abstract

The present invention provides a method for a four-probe measuring instrument to measure a wafer to be measured and a four-probe measuring system. The method includes: placing the wafer on a test platform; physically contacting the probes of the four-probe measuring instrument with the surface of the wafer; irradiating the contact surface between the probes and the wafer with a laser; applying a current to two of the needles of the four-probe measuring instrument and measuring the voltage drop between the other two needles. By irradiating the semiconductor with a laser, the present invention causes electrons to transition to the conduction band, simultaneously generates holes, and forms electron-hole pairs, thereby improving the contact characteristics, enabling good ohmic contact to be formed between the probes and the surface of the silicon wafer to be measured, and improving the stability of silicon wafer measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor detection, and particularly relates to a method for measuring a wafer to be measured by a four-probe measuring instrument and a four-probe measuring system. Background Art

[0002] A four-probe measuring instrument is a special instrument for measuring the resistivity and sheet resistance of semiconductor materials, and is used to measure the resistivity of rod-shaped and block-shaped semiconductor materials (including thick wafers and thin wafers) and the sheet resistance of diffusion layers, ion implantation layers, and epitaxial layers on silicon wafers. The instrument has the characteristics of high measurement accuracy, high sensitivity, good stability, wide measurement range, and compact structure, and the measurement results are directly displayed digitally, making it convenient to use.

[0003] For group III-V, group II-VI compound semiconductors, SiC, gallium nitride, etc., due to material characteristics, it is difficult to form good ohmic contacts between the probes and the surface to be measured during four-probe measurement, resulting in the difficulty of applying the traditional four-probe method in the manufacturing processes of these semiconductors. The reasons for the difficulty in forming ohmic contacts for the above materials include: 1. Complex energy band structure: These semiconductor materials usually have a relatively complex energy band structure, different from common silicon materials. This makes it difficult to match the electron states and energy bands at the contact interface, and it is difficult to achieve an ideal ohmic contact. For example, gallium nitride has a high electron affinity and a wide bandgap in its energy band structure, resulting in difficulty in finding a suitable metal material to form a low-resistance ohmic contact when contacting with metals. 2. Influence of surface states: There are often a large number of surface states on the surface of compound semiconductors. These surface states can capture carriers and affect the electrical properties of the contact interface. The surface states can form a potential barrier at the contact interface, hindering the transmission of carriers, thereby increasing the contact resistance and making it difficult to form an ohmic contact.

[0004] Wide-bandgap semiconductors usually have a relatively high electron affinity and a wide bandgap, which makes it relatively easy to form a depletion layer on their surfaces. The formation of the depletion layer is related to factors such as the surface states, impurity concentration, and external conditions of the semiconductor. In wide-bandgap semiconductors, the presence of surface states may lead to a decrease in the carrier concentration near the surface, thereby forming a depletion layer. It is also difficult to form good ohmic contacts between the probes and the surface to be measured during four-probe measurement.

[0005] Therefore, how to make the probes and the surface of the wafer to be measured form good ohmic contacts is a problem that needs to be solved currently. Summary of the Invention

[0006] The object of the present invention is to provide a method for measuring a wafer to be measured by a four-probe measuring instrument and a four-probe measuring system, which can make the probes and the surface of the silicon wafer to be measured form good ohmic contacts and improve the stability of silicon wafer measurement.

[0007] To achieve the above object, the present invention provides a method for measuring a wafer to be measured by a four-probe measuring instrument, including:

[0008] Placing the wafer on a test platform;

[0009] Physically contacting the probes of the four-probe measuring instrument with the wafer surface;

[0010] Irradiating the contact surface between the probe and the wafer with a laser;

[0011] Applying current to two of the needles of the four-probe measuring instrument and measuring the voltage drop between the other two needles.

[0012] In an alternative embodiment, when irradiating the contact surface between the probe and the wafer with a laser, the laser is irradiated at a set frequency or continuously irradiated.

[0013] In an alternative embodiment, when irradiating the contact surface between the probe and the wafer with a laser, the laser spot covers the entire area where the four probes contact the wafer.

[0014] The present invention also provides a four-probe measurement system, including:

[0015] A four-probe measuring instrument;

[0016] A laser emitter, disposed on the frame of the four-probe measuring instrument, capable of lifting and lowering simultaneously with the probes of the four-probe measuring instrument;

[0017] A host computer, a control denoising module, and a preamplifier connected in sequence;

[0018] The host computer sends a collection command to the control denoising module and controls the switching frequency of the laser emitter;

[0019] The control denoising module controls the operation of the preamplifier according to the collection instruction of the host computer;

[0020] The preamplifier is connected to the probes of the four-probe measuring instrument, and is used to apply current to two of the probes according to the collection instruction, and receive the voltage drop of the other two probes; and transmit the voltage signal to the control denoising module;

[0021] The control denoising module amplifies the voltage signal and performs an operation with the switching frequency of the laser emitter to suppress noise that is not of the same frequency or in-phase as the switching frequency of the laser emitter, and then converts the voltage signal into a digital signal and sends it to the host computer.

[0022] In an alternative embodiment, the control denoising module is a lock-in amplifier.

[0023] In an alternative embodiment, the four-probe measurement system further includes a soft breakdown circuit structure, which is connected to the four-probe measuring instrument during measurement; the soft breakdown circuit structure includes:

[0024] A capacitor, one end of the capacitor is grounded, and the other end is connected to a charging circuit and a discharging circuit;

[0025] The charging circuit is used to charge the capacitor; the charging circuit includes a plurality of parallel charging branches, and each charging branch includes a first switch for controlling the connection or disconnection of the current branch; the electric energy provided by each charging branch is different;

[0026] The discharging circuit is used to discharge the capacitor; the discharging circuit includes four parallel discharging branches, each discharging branch is connected to a probe of the four-probe measuring instrument, and each discharging branch includes a second switch for controlling the connection or disconnection of the current branch.

[0027] In an alternative embodiment, each charging branch includes a voltage source, the negative terminal of the voltage source is grounded, the positive terminal is connected to a resistor, the other end of the resistor is connected to the first switch, and the other end of the first switch is connected to the capacitor; the voltage sources of different charging branches provide different voltages.

[0028] In an alternative embodiment, each charging branch includes a current source, the negative terminal of the current source is grounded, the positive terminal is connected to a first resistor, the other end of the first resistor is connected to the first switch, the other end of the first switch is connected to the capacitor, and a second resistor is also connected between the positive terminal and the negative terminal of the current source; the current sources of different charging branches provide different currents.

[0029] In an alternative embodiment, the charging circuit includes:

[0030] A transformer;

[0031] A plurality of series-connected voltage-dividing resistors, connected between the transformer and the reference ground;

[0032] A plurality of the charging branches are connected between different voltage-dividing resistors.

[0033] In an alternative embodiment, the discharging circuit includes:

[0034] A control switch, connected to the capacitor;

[0035] A resistor, connected to the other end of the control switch;

[0036] The four parallel discharging branches are connected to the other end of the resistor.

[0037] The beneficial effects of the present invention are as follows:

[0038] In the present invention, a semiconductor is irradiated with a laser to cause electrons to transition to the conduction band, while holes are generated simultaneously, forming electron-hole pairs, thereby improving the contact characteristics, enabling a good ohmic contact to be formed between the probe and the surface of the silicon wafer to be measured, and improving the stability of silicon wafer measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] By describing the exemplary embodiments of the present invention in more detail in conjunction with the accompanying drawings, the above and other objects, features, and advantages of the present invention will become more apparent. In the exemplary embodiments of the present invention, the same reference numerals generally represent the same components.

[0040] Figure 1 FIG. shows a schematic structural diagram of a four-probe measurement system in an embodiment of the present invention.

[0041] Figure 2 FIG. shows a schematic diagram of an inversion region on the surface of a wafer without laser irradiation in another embodiment of the present invention.

[0042] Figure 3 FIG. shows a schematic diagram of an inversion region on the surface of a wafer under laser irradiation in another embodiment of the present invention.

[0043] Figure 4 FIG. shows a situation where laser irradiation (the wavelength of the laser is longer than the wavelength in Figure 3 ) is performed on the surface of a wafer, and a schematic diagram of the inversion region on the surface of the wafer.

[0044] Figure 5 FIG. shows a schematic diagram of a soft breakdown circuit structure in an embodiment of the present invention.

[0045] Figure 6 FIG. shows a schematic diagram of a soft breakdown circuit structure in another embodiment of the present invention.

[0046] Figure 7 FIG. shows a schematic diagram of a soft breakdown circuit structure in another embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. According to the following description and drawings, the advantages and features of the present invention will be clearer. However, it should be noted that the concept of the technical solution of the present invention can be implemented in various different forms and is not limited to the specific embodiments described herein. The drawings are all in a very simplified form and use non-precise scales, only for the purpose of conveniently and clearly assisting in explaining the embodiments of the present invention.

[0048] It should be understood that when an element or layer is referred to as "on", "adjacent to", "connected to", or "coupled to" another element or layer, it can be directly on, adjacent to, connected or coupled to the other element or layer, or there may be intervening elements or layers. In contrast, when an element is referred to as "directly on", "directly adjacent to", "directly connected to", or "directly coupled to" another element or layer, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers, and / or parts, these elements, components, regions, layers, and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or part from another element, component, region, layer, or part. Thus, without departing from the teachings of the present invention, the first element, component, region, layer, or part discussed below may be denoted as the second element, component, region, layer, or part.

[0049] Spatial relationship terms such as "under", "below", "lower", "beneath", "above", "upper", etc. are used herein for convenience in describing the relationship of one element or feature shown in the figures to other elements or features. It should be understood that, in addition to the orientation shown in the figures, spatial relationship terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figures is flipped, then an element or feature described as "under" or "beneath" or "below" other elements or features will be oriented "above" the other elements or features. Thus, the exemplary terms "under" and "below" can include both an upper and a lower orientation. The device may be otherwise oriented (rotated 90 degrees or other orientations) and the spatial descriptors used herein are to be interpreted accordingly.

[0050] The purpose of the terms used herein is only to describe specific embodiments and is not a limitation of the present invention. As used herein, the singular forms "a", "an", and "the" are also intended to include the plural forms unless the context clearly dictates otherwise. It should also be understood that the terms "comprising" and / or "including", when used in this specification, specify the presence of the 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. As used herein, the term "and / or" includes any and all combinations of the associated listed items.

[0051] Embodiment 1

[0052] Referring to Figure 1 , this embodiment provides a four-probe measurement system, comprising:

[0053] A four-probe measuring instrument;

[0054] A laser emitter 6 is arranged on the frame 5 of the four-probe measuring instrument and can be lifted and lowered simultaneously with the probe 4 of the four-probe measuring instrument;

[0055] An upper computer 1, a control denoising module 2, and a preamplifier 3 connected in sequence;

[0056] The upper computer 1 sends a collection command to the control denoising module 2 and controls the switching frequency of the laser emitter 6;

[0057] The control denoising module 2 controls the operation of the preamplifier 3 according to the collection instruction of the upper computer 1;

[0058] The preamplifier 3 is connected to the probe 4 of the four-probe measuring instrument, and is used to apply current to two of the probes according to the collection instruction, and receive the voltage drop of the other two probes; and transmit the voltage signal to the control denoising module 2;

[0059] The control denoising module 2 amplifies the voltage signal and performs an operation with the switching frequency of the laser emitter 6 to suppress noise that is not of the same frequency or in-phase as the switching frequency of the laser emitter 6, and then converts the voltage signal into a digital signal and sends it to the upper computer 1.

[0060] In this embodiment, the control denoising module 2 is a lock-in amplifier.

[0061] Embodiment 2

[0062] This embodiment provides a method for a four-probe measuring instrument to measure a wafer to be measured, including:

[0063] Placing the wafer on the test platform;

[0064] Making physical contact between the probe of the four-probe measuring instrument and the surface of the wafer;

[0065] Irradiating the contact surface between the probe and the wafer with laser;

[0066] Applying current to two of the needles of the four-probe measuring instrument and measuring the voltage drop between the other two needles.

[0067] In this embodiment, when irradiating the contact surface between the probe and the wafer with laser, the laser irradiates according to a set frequency or continuously irradiates. When irradiating the contact surface between the probe and the wafer with laser, the laser spot covers the entire area where the four probes contact the wafer. In this embodiment, the spot area is 50 mm2.

[0068] According to the measured current and voltage values, the sheet resistance of the wafer surface can be calculated using the corresponding formula. To improve the measurement accuracy, multiple measurements are usually taken at different positions on the wafer surface and the average value is taken.

[0069] Referring to Figures 2 to 4 , in Example 1 and Example 2, laser irradiation is used on the wafer. The reason why an ohmic contact can be formed between the probe and the wafer is as follows:

[0070] When a semiconductor is irradiated with laser, the atoms in the semiconductor will absorb the energy of the laser. This energy will cause the electrons in the atoms to transition from a low energy state to a high energy state. In a semiconductor, there are a conduction band and a valence band. Usually, electrons are in the valence band, and there are almost no electrons in the conduction band. When an electron absorbs enough energy, it can transition to the conduction band and become a free electron. At the same time, a hole will be left in the valence band, and the hole can be regarded as a particle with a positive charge. In this way, electron-hole pairs, that is, carriers, are generated.

[0071] These carriers can move freely in the semiconductor, thus conducting electricity, making the original poorly contacted measurement become an ohmic contact that is easy for four-probe resistance measurement. Factors such as the energy and wavelength of the laser will affect the generation efficiency and quantity of carriers. Therefore, the selection of the laser should be based on the characteristics of the material to be measured. Based on the current experimental data, lasers with wavelengths between 200 nm and 300 nm are suitable for most third-generation semiconductors or wide-bandgap semiconductors and high-resistivity epitaxy.

[0072] Generally speaking, the principle of laser irradiation of a semiconductor to generate carriers is to provide energy to cause electrons to transition to the conduction band, and at the same time generate holes, forming electron-hole pairs, thereby improving the contact characteristics and realizing stable four-probe measurement.

[0073] In this embodiment, the four-probe measurement system further includes a soft breakdown circuit structure. The soft breakdown circuit structure is used to connect the four-probe measuring instrument during measurement. The soft breakdown circuit structure includes:

[0074] A capacitor, one end of the capacitor is grounded, and the other end is connected to a charging circuit and a discharging circuit;

[0075] The charging circuit is used to charge the capacitor; the charging circuit includes multiple parallel charging branches, and each charging branch contains a first switch for controlling the connection or disconnection of the current branch; the electric energy provided by each charging branch is different;

[0076] The discharging circuit is used to discharge the capacitor; the discharging circuit includes four parallel discharging branches, and each discharging branch is connected to a probe of the four-probe measuring instrument. Each discharging branch contains a second switch for controlling the connection or disconnection of the current branch.

[0077] Specifically, referring to Figure 5, the charging circuit is used to charge the capacitor C. The charging circuit includes multiple parallel charging branches. Each of the charging branches includes a voltage source. The negative terminal of the voltage source is grounded, and the positive terminal is connected to a resistor R1. The other end of the resistor R1 is connected to the first switch (the first switches of the multiple branches are S1, S2, S3, Sn respectively), and the other end of the first switch is connected to the capacitor C; the voltage sources of different charging branches provide different voltages. Figure 5 The voltages provided by the four voltage sources in Figure 5 are 15V, 10V, 5V, and 0.1V respectively. Multiple charging branches can be set to provide different voltages to adapt to more silicon wafers to be measured with different properties.

[0078] The discharging circuit includes four parallel discharging branches. Each discharging branch is connected to a probe of the four-probe measuring instrument. Each of the discharging branches includes a second switch (the second switches on the four discharging branches are SP1, SP2, SP3, SP4 respectively) for controlling the connection or disconnection of the current branch. Specifically, in this embodiment, the discharging circuit includes: a control switch Son connected to the capacitor C; a resistor R connected to the other end of the control switch Son; and the four parallel discharging branches are connected to the other end of the resistor R.

[0079] The form of the charging circuit can be various. Refer to Figure 6 , each charging branch includes a current source. The negative terminal of the current source is grounded, and the positive terminal is connected to a first resistor. The other end of the first resistor R1 is connected to the first switch (the first switches of the four branches are S1, S2, S3, Sn respectively), and the other end of the first switch is connected to the capacitor C. A second resistor R2 is also connected between the positive and negative terminals of the current source; the current sources of different charging branches provide different currents (the currents provided by the four current sources are 100mA, 10mA, 1mA, and 0.01A respectively).

[0080] Refer to Figure 7 , the charging circuit includes: a transformer T; multiple series-connected voltage-dividing resistors connected between the transformer T and the reference ground; and multiple charging branches are connected between different voltage-dividing resistors. It can be boosted to a set voltage value (such as 100V) through the transformer T, and then voltage division is performed through the series-connected voltage-dividing resistors so that each charging branch has a different voltage value.

[0081] In this embodiment, according to the properties of the wafer to be measured, a charging branch with suitable energy is selected to charge the capacitor, and then the capacitor is discharged. The silicon wafer is soft-breakdown through the probe, which can form a good ohmic contact between the probe and the surface of the silicon wafer to be measured and improve the stability of silicon wafer measurement. The energy for charging the capacitor is 1 / 2CU 2, soft breakdown of the silicon wafer is performed by means of capacitor discharge, which will not cause harm to the silicon wafer. If power is directly applied, it may cause harm to the silicon wafer. The forms of the charging circuit and the discharging circuit of the capacitor can be various, as long as the capacitor can be charged and discharged.

[0082] Embodiment 3

[0083] This embodiment provides a method for measuring a silicon wafer to be measured by a four-probe measuring instrument, including:

[0084] Connect the soft breakdown circuit structure to the four-probe measuring instrument in a circuit;

[0085] Place the four probes of the four-probe measuring instrument on the silicon wafer to be measured;

[0086] According to the properties of the silicon wafer to be measured, select one of the charging branches of the charging circuit to charge the capacitor, and then select one of the discharging branches to discharge the capacitor;

[0087] Repeat the above steps until each of the four probes has completed a process of capacitor discharge;

[0088] Then measure the silicon wafer through the four-probe measuring instrument.

[0089] Generally, when measuring a silicon wafer, the same charging branch can be used for the four charging processes. Multiple charging branches are used to adapt to different silicon wafers.

[0090] Before measuring the silicon wafer in this embodiment, soft breakdown of the silicon wafer is first performed to form a good ohmic contact between the probe and the surface of the silicon wafer to be measured, improving the stability of silicon wafer measurement.

[0091] The method of this embodiment is applicable to the case where there is an oxide layer on the silicon wafer to be measured, and the method of Embodiment 1 is applicable to the case where there is no oxide layer on the silicon wafer to be measured.

[0092] The above description is only a description of the preferred embodiments of the present invention, and does not limit the scope of the present invention in any way. Any changes and modifications made by those of ordinary skill in the art of the present invention according to the above disclosure are within the protection scope of the claims.

Claims

1. A method for a four-probe measuring instrument to measure a wafer to be measured, characterized in that, Comprising: Placing a wafer on a test platform; Making physical contact between the probes of the four-probe measuring instrument and the wafer surface; Irradiating the contact surface between the probes and the wafer with a laser, causing electrons to transition to the conduction band, simultaneously generating holes, forming electron-hole pairs, thereby improving the contact characteristics; Applying a current to two of the needles of the four-probe measuring instrument and measuring the voltage drop between the other two needles.

2. The method for measuring a wafer to be measured by the four-probe measuring instrument according to claim 1, characterized in that, When irradiating the contact surface between the probes and the wafer with a laser, the laser irradiates according to a set frequency or continuously irradiates.

3. The method for measuring a wafer to be measured by the four-probe measuring instrument according to claim 1, wherein, When irradiating the contact surface between the probes and the wafer with a laser, the laser spot covers the entire area where the four probes contact the wafer.

4. A four-probe measurement system, characterized in that, Comprising: A four-probe measuring instrument; A laser emitter, arranged on the frame of the four-probe measuring instrument, capable of lifting and lowering simultaneously with the probes of the four-probe measuring instrument; An upper computer, a control denoising module, and a preamplifier connected in sequence; The upper computer sends a collection command to the control denoising module and controls the switching frequency of the laser emitter; The control denoising module controls the operation of the preamplifier according to the collection instruction of the upper computer; The preamplifier is connected to the probes of the four-probe measuring instrument, and is used to apply a current to two of the probes according to the collection instruction and receive the voltage drop of the other two probes; And transmitting the voltage signal to the control denoising module; The control denoising module amplifies the voltage signal and performs an operation with the switching frequency of the laser emitter, suppresses the noise that is not of the same frequency or in-phase as the switching frequency of the laser emitter, and then converts the voltage signal into a digital signal and sends it to the upper computer; When measuring, irradiate the contact surface between the probes and the wafer with a laser, causing electrons to transition to the conduction band, simultaneously generating holes, forming electron-hole pairs, thereby improving the contact characteristics.

5. The four-probe measurement system according to claim 4, wherein, The control denoising module is a lock-in amplifier.

6. The four-probe measurement system according to claim 4, wherein The four-probe measurement system further includes a soft breakdown circuit structure, and the soft breakdown circuit structure is used to be connected to the four-probe measuring instrument during measurement; The soft breakdown circuit structure includes: A capacitor, one end of the capacitor is grounded, and the other end is connected to a charging circuit and a discharging circuit; The charging circuit is used to charge the capacitor; the charging circuit includes multiple parallel charging branches, and each charging branch includes a first switch for controlling the connection or disconnection of the current branch; the electrical energy provided by each charging branch is different; The discharging circuit is used to discharge the capacitor; the discharging circuit includes four parallel discharging branches, and each discharging branch is connected to a probe of the four-probe measuring instrument, and each discharging branch includes a second switch for controlling the connection or disconnection of the current branch.

7. The four-probe measurement system according to claim 6, wherein, Each charging branch includes a voltage source, the negative terminal of the voltage source is grounded, the positive terminal is connected to a resistor, the other end of the resistor is connected to the first switch, and the other end of the first switch is connected to the capacitor; the voltage sources of different charging branches provide different voltages.

8. The four-probe measurement system according to claim 6, wherein, Each of the charging branches includes a current source, the negative terminal of the current source is grounded, the positive terminal is connected to a first resistor, the other end of the first resistor is connected to the first switch, the other end of the first switch is connected to the capacitor, and a second resistor is also connected between the positive and negative terminals of the current source; the current sources of different charging branches provide different currents.

9. The four-probe measurement system according to claim 6, characterized in that, The charging circuit includes: A transformer; A plurality of series-connected voltage-dividing resistors connected between the transformer and the reference ground; A plurality of the charging branches are connected between different voltage-dividing resistors.

10. The four-probe measurement system according to claim 6, wherein The discharging circuit includes: A control switch connected to the capacitor; A resistor connected to the other end of the control switch; The four parallel discharging branches are connected to the other end of the resistor.

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