Disclosure of Invention
The invention aims to provide a method and equipment for testing minority carrier lifetime of a silicon wafer, which can accurately determine minority carrier lifetime of the silicon wafer, thereby accurately reflecting quality of the wafer.
In order to achieve the above object, in one aspect, the present invention provides a method for testing minority carrier lifetime of a silicon wafer, comprising the steps of:
S10, performing heat treatment on the silicon wafer to enable the front surface and the back surface of the silicon wafer to grow uniform thin oxide films;
s20, carrying out charge deposition on the front side and the back side of the silicon wafer;
s30, rotating the silicon wafer according to a set rotation angle theta;
s40, carrying out charge deposition on the front side and the back side of the rotated silicon wafer;
S50, repeatedly executing the steps S30 and S40, wherein the repetition number is greater than or equal to 1;
s60, obtaining the minority carrier lifetime of the silicon wafer after charge deposition.
Preferably, in S10, the heat treatment of the silicon wafer includes:
S101, placing the silicon wafer into a heating cavity of heat treatment equipment;
S102, introducing oxygen into a heating cavity of the heat treatment equipment, and heating to 700-950 ℃ at a speed of 50-100 ℃ per second;
s103, preserving heat for 3-25 minutes;
S104, stopping oxygen supply, then introducing nitrogen into the heating cavity of the heat treatment equipment, and cooling to 70-90 ℃ at a speed of 20-90 ℃ per minute.
Preferably, the thickness of the thin oxide film formed on the front side and the back side of the silicon wafer is 2-8nm.
Preferably, in S30, the rotation angle θ of the silicon wafer is 20-40 degrees.
Preferably, in S30, the rotating silicon wafer includes:
S301, clamping the silicon wafer by a manipulator, and placing the silicon wafer in a rotating device;
s302, the rotating device rotates the silicon wafer according to a rotation angle theta;
S303, clamping the silicon wafer by a manipulator, and returning the silicon wafer to the charge deposition position.
Preferably, in S30, the rotating silicon wafer includes:
S304, judging the rotation angle of the silicon wafer; if the silicon wafer has rotated by θ degrees, then S40 is performed; if the silicon wafer is not rotated, S301 is performed.
Preferably, the judging the rotation angle of the silicon wafer is judged according to a Notch on the silicon wafer.
Compared with the prior art, the method for testing the minority carrier lifetime of the silicon wafer provided by the invention has the advantages that the silicon wafer is subjected to heat treatment, so that the uniform thin oxide films are grown on the front side and the back side of the silicon wafer, and in the process of carrying out charge deposition on the silicon wafer, the silicon wafer is rotated for multiple times according to a set angle, so that the interference on the charge deposition uniformity (such as the interference of a supporting point in the charge deposition process of the silicon wafer) during the charge deposition of the silicon wafer can be reduced, the minority carrier lifetime value can be accurately measured, and a tester can accurately analyze the quality of the wafer according to a test result. Therefore, the method for testing the minority carrier lifetime of the silicon wafer can accurately determine the minority carrier lifetime of the silicon wafer, thereby accurately reflecting the quality of the wafer.
On the other hand, the invention also provides equipment for testing the minority carrier lifetime of the silicon wafer, which comprises a heat treatment device, a charge deposition device, a rotating device, a silicon wafer minority carrier lifetime measuring device and a conveying device, wherein the heat treatment device can carry out heat treatment on the silicon wafer so as to enable the front side and the back side of the silicon wafer to grow uniform thin oxide films, the charge deposition device can carry out charge deposition on the front side and the back side of the silicon wafer after heat treatment, and the rotating device can rotate the silicon wafer; the transport device transports the silicon wafer between the charge deposition device and the rotation device.
Preferably, the charge deposition device comprises a silicon wafer positioning platform and an electrode discharger, the silicon wafer positioning platform comprises a positioning ring and at least two supporting points fixed on the positioning ring, the positioning ring is U-shaped, the silicon wafer can be placed in the positioning ring and supported on the supporting points, and the electrode discharger can perform charge deposition on the front side and the back side of the silicon wafer placed in the positioning ring.
Preferably, the charge deposition device comprises a silicon wafer rotation angle detection element, and the silicon wafer rotation angle detection element detects the rotation angle of the silicon wafer according to a Notch on the silicon wafer.
The device for testing the minority carrier lifetime of the silicon wafer has the same technical advantages as the method for testing the minority carrier lifetime of the silicon wafer in the prior art, and is not described herein.
Detailed Description
The principles and features of the present invention are described below with reference to the drawings, the examples are illustrated for the purpose of illustrating the invention and are not to be construed as limiting the scope of the invention.
In the prior art, due to the problem of uniformity of charge deposition on the surface of a silicon wafer when charge deposition is performed, the measured minority carrier lifetime of the silicon wafer has deviation, so that the quality of the wafer cannot be accurately judged.
In order to solve the above problems, the method for testing minority carrier lifetime of a silicon wafer provided by the invention, as shown in fig. 1, comprises the following steps:
S10, performing heat treatment on the silicon wafer to enable the front side and the back side of the silicon wafer to grow uniform thin oxide films. In the present embodiment, the silicon wafer is heat-treated by various conventional heat treatment apparatuses, such as a high-temperature diffusion furnace. After the heat treatment of the silicon wafer, the thickness of the thin oxide film obtained on the front and back sides of the silicon wafer is preferably 2 nm to 8 nm.
The step of forming a uniform thin oxide film on the front and back surfaces of the silicon wafer by the heat treatment apparatus preferably employs the steps of:
S101, placing the silicon wafer into a heating cavity of heat treatment equipment; when the silicon wafer is placed in the heating cavity of the heat treatment equipment, the silicon wafer to be heat treated can be placed on the wafer boat by the manipulator, and then the wafer boat is placed in the heating cavity of the heat treatment equipment. When the silicon wafer is placed on the wafer boat, in order to improve the thickness uniformity of the thin oxide film formed on the surface of the silicon wafer, baffle plates are required to be placed in clamping grooves at the upper end and the lower end of the wafer boat so as to stabilize the air flow in the heating cavity and balance the temperature in the furnace.
S102, introducing oxygen into a heating cavity of the heat treatment equipment, and heating to 700-950 ℃ at a speed of 50-100 ℃ per second; specifically, firstly, oxygen is introduced into heat treatment equipment through an oxygen pipe, oxygen transportation is kept, and the furnace temperature is rapidly increased from room temperature to 700-950 ℃, and the heating speed is 50-100 ℃ per second. Preferably, after the oxygen is introduced, the temperature in the heating chamber is rapidly increased to 800 degrees celsius at a ramp rate of 75 degrees celsius per second.
S103, preserving heat for 3-25 minutes; preferably, the incubation time is 10 minutes.
S104, stopping oxygen supply, then introducing nitrogen into the heating cavity of the heat treatment equipment, and cooling to 70-90 ℃ at a speed of 20-90 ℃ per minute. Specifically, the oxygen transmission of the oxygen pipe of the heat treatment equipment is cut off, then the nitrogen pipe is opened, nitrogen is introduced into the heating cavity of the heat treatment equipment, and the temperature in the heating cavity is reduced to 70-90 ℃ at the speed of 20-90 ℃ per minute. Preferably, after the nitrogen gas is introduced, the temperature in the heating chamber is reduced to 70 degrees celsius at a rate of 45 degrees celsius per minute.
S20, carrying out charge deposition on the front side and the back side of the silicon wafer. The charge deposition of the silicon wafer with thin oxide films formed on the front and back sides can be performed by using the existing charge deposition equipment, such as a WT2500 series test equipment. The silicon wafer may be transferred into the charge deposition chamber of the charge deposition apparatus by a robot after the wafer is cooled to room temperature (e.g., 25 ℃).
S30, rotating the silicon wafer according to a set rotation angle theta; specifically, after the silicon wafer is clamped by the manipulator, the manipulator is controlled to rotate the silicon wafer by an angle of theta, and then the silicon wafer is placed at a charge deposition position of the charge deposition cavity; the silicon wafer can also be rotated by a rotating device, and preferably, the method comprises the following steps of S301, clamping the silicon wafer by a manipulator, and placing the silicon wafer in the rotating device; s302, the rotating device rotates the silicon wafer according to a rotation angle theta; s303, clamping the silicon wafer by a manipulator, and returning the silicon wafer to the charge deposition position. The rotating device can adopt the existing device capable of realizing the rotation of the silicon wafer.
Wherein the rotation angle θ is such that when the silicon wafer is placed in the charge deposition position after rotation, the contact position of the silicon wafer with the support of the silicon wafer deposition position is different from the contact position of the silicon wafer with the support before being rotated. The rotation angle theta of the silicon wafer is preferably 20-40 degrees.
Further, S304, judging the rotation angle of the silicon wafer; if the silicon wafer has rotated by θ degrees, then S40 is performed; if the silicon wafer is not rotated, S301 is performed. The method for judging the rotation angle of the silicon wafer can be to detect by arranging a position sensor, and preferably, the position sensor can judge the rotation angle of the silicon wafer according to a Notch on the silicon wafer.
S40, carrying out charge deposition on the front side and the back side of the rotated silicon wafer; the manner of charge deposition is the same as that of charge deposition in step S20.
S50, repeatedly executing the steps S30 and S40, wherein the repetition number is greater than or equal to 1; the repeated execution of the steps S30 and S40 means that after the step S40 is completed to perform charge deposition on the silicon wafer, the step S30 is executed again to rotate the silicon wafer and the step S40 is executed to perform charge deposition on the silicon wafer, that is, the silicon wafer is rotated to perform charge deposition on the silicon wafer. For example, steps S30 and S40 are repeated twice, that is, after the silicon wafer is rotated and subjected to charge deposition, the silicon wafer is rotated again and subjected to charge deposition.
Wherein the time for each charge deposition on the front and back sides of the wafer is typically 30 seconds to 2 minutes. The number of times of repeatedly executing the steps S30 and S40 is determined according to the electric charge deposited on the surface of the silicon wafer when electric charge deposition is carried out each time, the total amount of electric charge deposited on the surface of the silicon wafer is generally 2000-4000 nanometers, and the oxide film can be broken down when the electric charge deposited on the surface of the silicon wafer is too much. It should be understood by those skilled in the art that the number of times of repeating steps S30 and S40 should be limited to not breakdown the thin oxide film on the silicon wafer.
S60, obtaining the minority carrier lifetime of the silicon wafer after charge deposition. The minority carrier lifetime of the silicon wafer after charge deposition is mainly realized by a microwave photoconductive decay method (mu-PCD). The microwave photoconductive decay method is to irradiate the surface of the silicon wafer with pulse laser with the width greater than the forbidden band of silicon, and the generated hole-electron can increase the photoconductivity, and the photoconductivity decays exponentially with the withdrawal of the laser, and the change of the photoconductivity is detected by the change of the microwave reflection intensity, so that the minority carrier lifetime is obtained. In particular, silicon wafer minority carrier lifetime can be obtained by existing μ -PCD detection equipment (e.g., WT2500 series equipment).
According to the method for testing the minority carrier lifetime of the silicon wafer, provided by the embodiment, through heat treatment of the silicon wafer, the uniform thin oxide films are grown on the front side and the back side of the silicon wafer, and in the process of carrying out charge deposition on the silicon wafer, the silicon wafer is rotated for multiple times according to the set angle, so that interference of supporting points in the charge deposition process of the silicon wafer can be reduced, the situation that the charge deposition cannot be carried out on the supporting points of the silicon wafer is avoided, meanwhile, interference of the specificity of the movement track of the electrode discharger on the charge deposition of the silicon wafer can be reduced, the minority carrier lifetime value can be accurately measured, and a tester can accurately analyze the quality of the wafer according to a test result.
Similar to the technical conception of the method for testing the minority carrier lifetime of the silicon wafer provided by the embodiment, the invention also provides equipment for testing the minority carrier lifetime of the silicon wafer, which comprises a heat treatment device, a charge deposition device, a rotation device, a silicon wafer minority carrier lifetime measuring device and a conveying device.
The heat treatment device can carry out heat treatment on the silicon wafer, so that the front and back surfaces of the silicon wafer grow uniformly thin oxide films. The heat treatment device can be selected from various existing heat treatment equipment, such as a high-temperature diffusion furnace.
The charge deposition device can perform charge deposition on the front side and the back side of the silicon wafer after heat treatment. The charge deposition device can select the existing charge deposition equipment to deposit the charges on the silicon wafer, for example, the WT2500 series test equipment is used for depositing the charges on the silicon wafer.
In one embodiment of the invention, the charge deposition apparatus includes a silicon wafer positioning stage and an electrode discharger. As shown in fig. 2, the silicon wafer positioning platform comprises a positioning ring 1 and at least two supporting points 2 fixed on the positioning ring, the positioning ring 1 is in a U shape, and the silicon wafer can be placed in the positioning ring 1 and supported on the supporting points 2. The diameter of the inner hole at the right end of the positioning ring 1 is slightly larger than the outer diameter of the silicon wafer, meanwhile, the supporting point 2 is positioned in the inner hole of the positioning ring 1, and when the silicon wafer is placed in the inner hole of the positioning ring 1, the supporting point 2 can support the silicon wafer. Wherein the number of fulcrums 2 is preferably 3.
The electrode discharger can deposit charges on the front side and the back side of the silicon wafer placed in the positioning ring. The potential difference is formed between the silicon chip supported by the supporting point 2 and the electrode discharger, the silicon chip is placed on the supporting point 2, the electrode discharger moves to deposit charges on the front surface of the silicon chip according to a fixed line track (for example, a parallel line), then the electrode discharger moves to the back surface of the silicon chip, and the deposited charges are also moved on the back surface of the silicon chip according to the fixed line track, so that the charge deposition on the front surface and the back surface of the silicon chip is realized. The movement of the electrode discharger can be achieved using existing movement means, such as a robot. The number of the electrode dischargers can be two, and charge deposition can be carried out on the front side and the back side of the silicon wafer through the two electrode dischargers respectively.
The charge deposition is carried out on the front side and the back side of the monocrystalline silicon wafer, and the existence of the supporting point 2 inevitably blocks the supporting point position of the monocrystalline silicon wafer, so that the electric charge cannot be deposited in the area, the minority carrier lifetime of the supporting point part is obviously reduced, and a tester cannot accurately analyze the quality of the wafer according to a test result. The apparatus of the present invention thus comprises a rotation device for rotating the wafer.
The rotating device can adopt the structure that the silicon wafer can rotate in the prior art, preferably, the rotating device can comprise a bracket, a rotating piece rotatably installed on the bracket and a stepping motor used for driving the rotating piece to rotate, the rotating piece is disc-shaped and is provided with a notch, so that a manipulator for clamping the silicon wafer can conveniently place the silicon wafer on the rotating piece, and the rotating piece can be rotationally connected with the bracket through a slewing bearing. When the rotating device is used for rotating the silicon wafer, the silicon wafer is firstly placed on the rotating piece through the mechanical arm, then the stepping motor is controlled to enable the rotating piece to rotate for a set angle, the silicon wafer placed on the rotating piece rotates along with the same angle, then the mechanical arm is used for clamping the silicon wafer through a notch at the edge of the rotating piece, and then the silicon wafer is conveyed to the charge deposition device.
Further preferably, the charge deposition apparatus further comprises a silicon wafer rotation angle detection element. The silicon wafer rotation angle detection element can be a position sensor, and detects the rotation angle of the silicon wafer through a Notch on the silicon wafer. Specifically, the silicon wafer rotation angle detection element detects the position of the Notch on the silicon wafer, and judges the rotation angle of the silicon wafer according to the difference between the detected Notch positions of two adjacent times.
The transport device transports the silicon wafer between the charge deposition device and the rotation device. The conveying device can adopt various existing manipulators for clamping the silicon wafers. When the silicon wafer subjected to heat treatment by the heat treatment device is conveyed to the charge deposition device, a mechanical arm can be adopted to realize conveying. The silicon chip minority carrier lifetime measuring device can be realized by the existing mu-PCD detecting equipment. Wherein the silicon wafer minority carrier lifetime measuring device and the charge deposition device can share the same silicon wafer positioning platform.
In the invention, the charge deposition device, the rotation device and the silicon wafer minority carrier lifetime measurement device can be arranged in one shell. In view of the fact that the heat treatment device may have an influence on other devices during operation, the heat treatment device and the charge deposition device, the rotation device and the silicon wafer minority carrier lifetime measurement device may be respectively located in two different housings in order to make the whole apparatus simpler.
According to the method and the device for testing the minority carrier lifetime of the silicon wafer, provided by the invention, the silicon wafer is subjected to multiple rotations and charge deposition, so that the charge deposition without dead zones is uniformly realized on the front side and the back side of the silicon wafer, the whole silicon wafer is ensured to be fully passivated, and the area with low minority carrier lifetime cannot occur due to the problem of testing equipment, so that the minority carrier lifetime value can be accurately measured, and a tester can accurately analyze the quality of the wafer according to the testing result.
In the description of the present invention, it should be understood that the directions or positional relationships indicated by the terms "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, are merely for convenience of description and simplification of the description, and are not indicative or implying that the apparatus in question must have a specific orientation, be constructed and operated in a specific orientation, and are not to be construed as limiting the present invention.
Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present invention, the meaning of "plurality" is two or more unless specifically defined otherwise.
In the present invention, unless explicitly specified and limited otherwise, the terms "mounted," "disposed," "connected," and the like are to be construed broadly, and may be, for example, fixedly attached, detachably attached, or integrally formed, or may have intermediate parts. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.
While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the invention.