Method for measuring wafer to be measured by four-probe measuring instrument and four-probe measuring system

Abstract

The invention provides a method for measuring a wafer to be measured through a four-probe measuring instrument and a four-probe measuring system. The method comprises the steps that the wafer is placed on a testing platform; the probes of the four-probe measuring instrument are in physical contact with the surface of the wafer; irradiating the contact surface of the probe and the wafer by using laser; and applying current to two probes of the four-probe measuring instrument, and measuring the voltage drop between the other two probes. According to the invention, a semiconductor is irradiated by laser, electrons are transited to a conduction band, holes are generated, and electron-hole pairs are formed, so that the contact characteristic is improved, good ohmic contact can be formed between the probe and the surface of a silicon wafer to be measured, and the stability of silicon wafer measurement is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor detection, and in particular 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] The four-probe measuring instrument is a special instrument for measuring the resistivity and sheet resistance of semiconductor materials. It is used to measure the resistivity of rod-shaped and block-shaped semiconductor materials (including thick and thin slices) and the sheet resistance of the diffusion layer, ion implantation layer, and epitaxial layer on the silicon wafer. The instrument has the characteristics of high measurement accuracy, high sensitivity, good stability, wide measurement range, compact structure, and the measurement results are directly displayed in digital form, which is easy to use.

[0003] Due to the material properties of IIIV and IIVI compound semiconductors, SiC, gallium nitride, etc., it is difficult for the probe to form a good ohmic contact with the surface to be measured when using four-probe measurement, which makes it difficult to apply the traditional four-probe method in the preparation process of these semiconductors. The reasons why the above materials are difficult to form ohmic contact include 1. Complex band structure: These semiconductor materials usually have a more complex band structure, which is different from common silicon materials. This makes it difficult to match the electronic state and band at the contact interface, and it is difficult to achieve an ideal ohmic contact. For example, the band structure of gallium nitride has a high electron affinity and a wide bandgap, which makes it difficult to find a suitable metal material to form a low-resistance ohmic contact when in contact with metals. 2. Surface state influence: There are often a large number of surface states on the surface of compound semiconductors, which will capture carriers and affect the electrical properties of the contact interface. The surface state can form a 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 high electron affinity and wide bandgap width, which makes it relatively easy for them to form a depletion layer at the surface. The formation of the depletion layer is related to factors such as the surface state of the semiconductor, impurity concentration, and external conditions. 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 for the probe to form a good ohmic contact with the surface to be measured when using a four-probe measurement.

[0005] Therefore, how to make the probe and the surface of the wafer under test form a good ohmic contact is a problem that needs to be solved at present. Summary of the invention

[0006] The purpose 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 contact and improve the stability of silicon wafer measurement.

[0007] In order to achieve the above object, the present invention provides a method for measuring a wafer to be tested using a four-probe measuring instrument, comprising:

[0008] placing the wafer on a test platform;

[0009] Probes of the four-probe measuring instrument are brought into physical contact with a surface of a wafer;

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

[0011] Current is applied to two of the needles of the four-probe meter, and the voltage drop between the other two needles is measured.

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

[0013] In an optional solution, when the contact surface between the probe and the wafer is irradiated with laser, the laser spot covers the entire contact area between the four probes and the wafer.

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

[0015] Four-probe measuring instrument;

[0016] A laser emitter, which is arranged on the frame of the four-probe measuring instrument and can be raised and lowered simultaneously with the probes of the four-probe measuring instrument;

[0017] The host computer, control denoising module and preamplifier are connected in sequence;

[0018] The host computer sends an acquisition command to the control denoising module and controls the switching frequency of the laser transmitter;

[0019] The control denoising module controls the operation of the preamplifier according to the acquisition 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 acquisition 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 operates it with the switching frequency of the laser transmitter to suppress noise that is out of frequency or out of phase with the switching frequency of the laser transmitter, and then converts the voltage signal into a digital signal and sends it to the host computer.

[0022] In an optional solution, the control denoising module is a phase-locked amplifier.

[0023] In an optional solution, 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 measurement instrument during measurement; the soft breakdown circuit structure includes:

[0024] A capacitor, one end of which is grounded, and the other end of which 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 charging branches connected in parallel, each of the charging branches includes a first switch that controls the connection or disconnection of the current branch; the electric energy provided by each charging branch is different;

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

[0027] In an optional solution, each of the charging branches includes a voltage source, a negative terminal of the voltage source is grounded, a 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 optional solution, each of the charging branches includes a current source, a negative terminal of the current source is grounded, a 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 connected between the positive and negative terminals of the current source; the current sources of different charging branches provide different currents.

[0029] In an optional solution, the charging circuit includes:

[0030] transformer;

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

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

[0033] In an optional solution, the discharge 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 discharge branches are connected to the other end of the resistor.

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

[0038] The present invention uses laser to irradiate semiconductor to make electrons jump to the conduction band and generate holes at the same time to form electron-hole pairs, thereby improving contact characteristics, making the probe and the surface of the silicon wafer to be measured form good ohmic contact, and improving the stability of silicon wafer measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, in which like reference numerals generally represent like components.

[0040] Figure 1 A schematic diagram of the structure of a four-probe measurement system in one embodiment of the present invention is shown.

[0041] Figure 2 A schematic diagram showing an inversion area on the wafer surface without laser irradiation in another embodiment of the present invention is shown.

[0042] Figure 3 A schematic diagram showing an inversion area on the surface of a wafer when laser irradiation is performed in another embodiment of the present invention.

[0043] Figure 4 Another embodiment of the present invention is to perform laser irradiation (laser wavelength ratio Figure 3 Schematic diagram of the inversion zone on the wafer surface when the wavelength is long.

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

[0045] Figure 6 A schematic diagram showing a soft breakdown circuit structure in another embodiment of the present invention is shown.

[0046] Figure 7 A schematic diagram showing a soft breakdown circuit structure in another embodiment of the present invention is shown. DETAILED DESCRIPTION

[0047] The present invention is 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 become clearer. However, it should be noted that the concept of the technical solution of the present invention can be implemented in a variety of different forms and is not limited to the specific embodiments described herein. The drawings are all in a very simplified form and are not in precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0048] It should be understood that when an element or layer is referred to as being "on, adjacent to, connected to or coupled to other elements or layers, it may be directly on, adjacent to, connected to or coupled to other elements or layers, or there may be intervening elements or layers. In contrast, when an element is referred to as being "directly on, directly adjacent to, directly connected to or directly coupled to other elements or layers, there may be 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. Therefore, without departing from the teachings of the present invention, the first element, component, region, layer or part discussed below may be represented as a second element, component, region, layer or part.

[0049] Spatially relative terms such as "under," "below," "below," "under," "above," "above," etc., may be used herein for ease of description to describe the relationship of an element or feature shown in the figures to other elements or features. It should be understood that in addition to the orientations shown in the figures, the spatially relative terms are intended to include different orientations of the device in use and operation. For example, if the device in the accompanying drawings is flipped, then the elements or features described as "under other elements" or "under" or "under" will be oriented as "on" the other elements or features. Therefore, the exemplary terms "under" and "under" may include both upper and lower orientations. The device may be oriented otherwise (rotated 90 degrees or other orientations) and the spatial descriptors used herein are interpreted accordingly.

[0050] The purpose of the terms used herein is only to describe specific embodiments and is not intended to be limiting of the present invention. When used herein, the singular forms "one", "an" and "said / the" are also intended to include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "consisting of" and / or "comprising", when used in this specification, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0051] Example 1

[0052] Reference Figure 1 , this embodiment provides a four-probe measurement system, including:

[0053] Four-probe measuring instrument;

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

[0055] The upper computer 1, the control denoising module 2 and the preamplifier 3 are connected in sequence;

[0056] The host computer 1 sends an acquisition command to the control denoising module 2 and controls the switching frequency of the laser transmitter 6;

[0057] The control denoising module 2 controls the preamplifier 3 to work according to the acquisition instruction of the host computer 1;

[0058] The preamplifier 3 is connected to the probes 4 of the four-probe measuring instrument, and is used to apply current to two of the probes according to the acquisition 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 operates it with the switching frequency of the laser transmitter 6 to suppress the noise that is out of frequency or out of phase with the switching frequency of the laser transmitter 6, and then converts the voltage signal into a digital signal and sends it to the host computer 1.

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

[0061] Example 2

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

[0063] placing the wafer on a test platform;

[0064] Probes of the four-probe measuring instrument are brought into physical contact with a surface of a wafer;

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

[0066] Current is applied to two of the needles of the four-probe meter, and the voltage drop between the other two needles is measured.

[0067] In this embodiment, when the contact surface between the probe and the wafer is irradiated with laser, the laser is irradiated at a set frequency or continuously irradiated. When the contact surface between the probe and the wafer is irradiated 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] Based on the measured current and voltage values, the sheet resistance of the wafer surface can be calculated using the corresponding formula. In order to improve the accuracy of the measurement, multiple measurements are usually performed at different locations on the wafer surface and the average value is taken.

[0069] Reference Figures 2 to 4 The reason why the probe and the wafer can form an ohmic contact by using laser to irradiate the wafer in Embodiment 1 and Embodiment 2 is:

[0070] When laser irradiates semiconductor, the atoms in the semiconductor absorb the energy of laser. This energy will cause the electrons in the atoms to jump from low energy state to high energy state. In semiconductor, there are conduction band and valence band. Normally, electrons are in the valence band, and there are almost no electrons in the conduction band. When the electron absorbs enough energy, it can jump to the conduction band and become a free electron. At the same time, a hole will be left in the valence band, which can be regarded as a particle with 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, turning the original poor contact measurement into an ohmic contact that is easy to measure resistance with four probes. The energy and wavelength of the laser will affect the efficiency and number of carrier generation. Therefore, the choice of laser should be based on the characteristics of the material being measured. Based on current experimental data, lasers with wavelengths between 200nm and 300nm are suitable for most third-generation semiconductors or wide bandgap semiconductors and high-resistance epitaxy.

[0072] In general, the principle of generating carriers by laser irradiation of semiconductors is to provide energy to make electrons jump to the conduction band, while generating holes to form electron-hole pairs, thereby improving contact characteristics and achieving stable four-probe measurement.

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

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

[0075] The charging circuit is used to charge the capacitor; the charging circuit includes a plurality of charging branches connected in parallel, each of the charging branches includes a first switch that controls the connection or disconnection of the current branch; the electric energy provided by each charging branch is different;

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

[0077] Specifically, refer to Figure 5The charging circuit is used to charge the capacitor C. The charging circuit includes a plurality of charging branches connected in parallel. 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 plurality of 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 are 15V, 10V, 5V and 0.1V respectively. Multiple charging branches can be set to provide different voltages to adapt to more silicon wafers with different properties to be measured.

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

[0079] There are many types of charging circuits, see Figure 6 , 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 R1 is connected to the first switch (the first switches of the four branches are S1, S2, S3, and Sn respectively), the other end of the first switch is connected to the capacitor C, and 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] Reference Figure 7 The charging circuit includes: a transformer T; a plurality of voltage-dividing resistors connected in series, connected between the transformer T and a reference ground; and a plurality of charging branches connected between different voltage-dividing resistors. The voltage can be boosted to a set voltage value (such as 100V) by the transformer T, and then divided by the voltage-dividing resistors connected in series, so that each charging branch has a different voltage value.

[0081] According to the properties of the wafer to be tested, this embodiment selects a charging branch with suitable energy to charge the capacitor, and then discharges the capacitor. The silicon wafer is soft-punctured by the probe, so that the probe and the surface of the silicon wafer to be tested can form a good ohmic contact, thereby improving the stability of the silicon wafer measurement. The energy for charging the capacitor is 1 / 2CU 2, soft breakdown of the silicon wafer by capacitor discharge will not cause harm to the silicon wafer. If power is directly applied, it may cause harm to the silicon wafer. There can be many forms of capacitor charging circuits and discharge circuits, as long as they can charge and discharge the capacitor.

[0082] Example 3

[0083] This embodiment provides a method for measuring a silicon wafer to be tested using a four-probe measuring instrument, comprising:

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

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

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

[0087] Repeat the above steps until all four probes complete a capacitor discharge process;

[0088] Then the silicon wafer is measured by the four-probe measuring instrument.

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

[0090] In this embodiment, before measuring the silicon wafer, the silicon wafer is first soft-punctured so that a good ohmic contact is formed between the probe and the surface of the silicon wafer to be measured, thereby improving the stability of the 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 tested, and the method of Embodiment 1 is applicable to the case where there is no oxide layer on the silicon wafer to be tested.

[0092] The above description is only a description of the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention. Any changes or modifications made by a person skilled in the art in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.

Claims

1. A method for measuring a wafer to be tested using a four-probe measuring instrument, characterized in that: include: placing the wafer on a test platform; Probes of the four-probe measuring instrument are brought into physical contact with a surface of a wafer; irradiating the contact surface between the probe and the wafer with a laser; Current is applied to two of the needles of the four-probe meter, and the voltage drop between the other two needles is measured.

2. The method for measuring a wafer to be tested by a four-probe measuring instrument as claimed in claim 1, characterized in that: When the contact surface between the probe and the wafer is irradiated with laser, the laser is irradiated at a set frequency or continuously.

3. The method for measuring a wafer to be tested by a four-probe measuring instrument as claimed in claim 1, characterized in that: When the contact surface between the probes and the wafer is irradiated with laser, the laser spot covers the entire contact area between the four probes and the wafer.

4. A four-probe measurement system, characterized in that: include: Four-probe measuring instrument; A laser emitter, which is arranged on the frame of the four-probe measuring instrument and can be raised and lowered simultaneously with the probes of the four-probe measuring instrument; The host computer, control denoising module and preamplifier are connected in sequence; The host computer sends an acquisition command to the control denoising module and controls the switching frequency of the laser transmitter; The control denoising module controls the operation of the preamplifier according to the acquisition instruction of the host computer; 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 acquisition instruction, and receive the voltage drops of the other two probes; and transmitting the voltage signal to the control denoising module; The control denoising module amplifies the voltage signal and operates it with the switching frequency of the laser transmitter to suppress noise that is out of frequency or out of phase with the switching frequency of the laser transmitter, and then converts the voltage signal into a digital signal and sends it to the host computer.

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

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

7. The four-probe measurement system according to claim 6, characterized in that: Each of the charging branches includes a voltage source, a negative terminal of the voltage source is grounded, a 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, characterized in that: Each of the charging branches includes a current source, a negative terminal of the current source is grounded, a 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 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 comprises: transformer; A plurality of voltage-dividing resistors connected in series, connected between the transformer and a 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, characterized in that: The discharge circuit comprises: A control switch connected to the capacitor; a resistor connected to the other end of the control switch; The four parallel discharge branches are connected to the other end of the resistor.

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