Ion beam etching system with etching rate in-situ monitoring function and etching method

Abstract

The invention provides an ion beam etching system with an etching rate in-situ monitoring function and an etching method, the ion beam etching system is provided with an objective table which can deflect by 90 degrees and an electrical test detection element which can move close to or far away from the objective table, and by the etching method, an ion source is not closed, a sample is not taken out, and the etching rate can be accurately measured. The etching depth can be accurately monitored by measuring the surface resistance of the sample in situ, the etching rate can be reduced in time, and the method is more suitable for the tape-out process. According to the ion beam etching system and the etching method, sputter spectrum monitoring is replaced by sample surface resistance detection, so that the test sensitivity is higher, the system cost is lower, the etching precision in magnetic tunnel junction preparation is greatly improved, the sample is prevented from being excessively etched, the thickness of a sample layer can be kept consistent, the resistance distribution is uniform, and the quality of the magnetic tunnel junction is improved. And the high success rate preparation of the SOT-MRAM memory with large capacity and small size is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor etching, and particularly relates to an ion beam etching system and an etching method with an in-situ monitoring function of etching rate. Background Art

[0002] Both spin orbital torque magnetic random access memory (SOT-MRAM) and spin transfer torque magnetic random access memory (STT-MRAM) use current to flip the magnetic layer in the magnetic tunnel junction, thereby realizing the write operation of information. In comparison, SOT-MRAM has more advantages. During the write operation, the current does not flow through the tunneling layer, significantly reducing problems such as device breakdown caused by thermal effects. SOT-MRAM utilizes the spin orbital coupling property of heavy metals such as Pt or Ta to convert current into spin current and uses the spin current to flip the magnetic layer.

[0003] The magnetic tunnel junction is a magnesium oxide insulating layer with a thickness of about 1 - 2 nm inserted between two magnetic thin films. When the direction of one magnetic layer is fixed, the magnetization direction of the other magnetic layer can change with the external field, thereby realizing the parallel or antiparallel arrangement of the magnetization directions between the two magnetic layers. At this time, the junction resistance will respectively appear in a low-resistance state and a high-resistance state, which can correspond to the information "1" and "0". Figure 1 The figure shows a schematic diagram of magnetic tunnel junction storing and processing information, where F polarizer represents the polarization layer (pinned layer), in which the direction of the magnetic moment does not change, insulator represents the insulating layer MgO, F Free represents the free layer, whose magnetic moment direction can point up or down and can be controlled by current. Controlling the magnetic moment direction of the free layer with current corresponds to writing the information "1" and "0" with current. This requires that the current can only flow in the free layer, and the excess polarization layer and insulating layer need to be etched away, leaving only the free layer. Plasma etching systems are widely used in the processing of the magnetic tunnel junction structure in spin orbital torque magnetic random access memory (SOT-MRAM). Chinese Patent Application No. 201510762515 discloses a metal etching device for MRAM preparation, Chinese Patent Application No. 202210959093 discloses an etching device for MRAM memory, and Chinese Patent Application No. 202110697725 discloses an ICP etching device that can clean the deposited reaction products.

[0004] At present, energy spectrometers capable of detecting chemical elements are usually equipped in plasma etching systems to monitor the etching process. For example, since only the free layer contains Ta, once the Ta element is detected by the energy spectrometer, the etching can be stopped. Chinese Patent Application No. 202210203194 discloses a device for judging the etching end point detection by obtaining the spectral signal generated based on the plasma etching sample collected by the spectrometer. Chinese Patent Application No. 202210203197 discloses a device for judging the etching end point detection by analyzing the gas components generated by etching through a mass spectrometer. Although monitoring the etching process through an energy spectrometer can in-situ judge the etching degree and termination timing without stopping the etching, there are still two technical problems that are difficult to overcome: one is that the random error of the remaining thickness of the free layer is relatively high, resulting in a large distribution of resistance, which is not conducive to the development of large-capacity SOT-MRAM memories; the other is that in order to obtain higher detection accuracy of the energy spectrometer, samples with larger sizes must be used, and the samples need to have a specific thin film structure so that enough heavy metal atoms can be sputtered during the etching process for the energy spectrometer to detect. Therefore, there is an urgent need to develop an ion beam etching system that can accurately monitor the etching depth of small-sized samples and then in-situ monitor the etching rate. Summary of the Invention

[0005] In view of this, the present invention aims to provide an ion beam etching system and an etching method with an in-situ monitoring function of etching rate to solve the problems in the prior art that the ion beam etching depth of small-sized samples cannot be accurately monitored in-situ, and the random error of the free layer thickness is relatively high, resulting in a large distribution of resistance.

[0006] To achieve the above object, the technical solution of the present invention is realized as follows:

[0007] In a first aspect, the present invention provides an ion beam etching system with an in-situ monitoring function of etching rate. The ion beam etching system includes a reaction chamber, an ion source, and a stage. A lifting probe is arranged in the reaction chamber for approaching or departing from the stage. A detection element is arranged on one side of the lifting probe inside the reaction chamber, and a high-resistance measuring instrument is connected to the other side of the lifting probe outside the reaction chamber. The detection element and the high-resistance measuring instrument are electrically connected to form a closed loop for measuring the contact resistance when contacting the etching sample.

[0008] The stage is provided with a rotating shaft connected to a driving mechanism outside the reaction chamber for driving the stage to deflect between a first angle and a second angle around the axis of the rotating shaft. When the stage is at the first angle position, the etching sample faces the ion source. When the stage is at the second angle position, the etching sample faces the lifting probe.

[0009] Preferably, a movable shielding plate is provided in the reaction chamber. The movable shielding plate includes a connecting portion and a shielding portion. The connecting portion is connected to a driving device of the movable shielding plate outside the reaction chamber. The movable shielding plate rotates between an upper limit position and a lower limit position around a driving axis under the action of the driving device of the movable shielding plate.

[0010] More preferably, when the movable shielding plate reaches the upper limit position, the shielding portion is in a shielding state and is located between the ion source and the stage to shield the bombardment of the etched sample by the ion source. When the movable shielding plate reaches the lower limit position, the shielding portion is in an open state and there is no shielding between the ion source and the stage.

[0011] More preferably, a fixed shielding plate is further provided in the reaction chamber and is located between the movable shielding plate and the lifting probe. The fixed shielding plate is arranged in parallel with the shielding portion of the movable shielding plate to shield the bombardment of the ion source on the probe and the detection element.

[0012] Preferably, the lifting probe moves closer to or away from the stage under the drive of a lifting probe drive device provided outside the reaction chamber.

[0013] Preferably, the detection element includes a first detection element and a second detection element, which are respectively electrically connected to the positive and negative electrodes of the high-resistance measuring instrument. When the first detection element and the second detection element are in contact with the surface of the etched sample at the same time, an electrically connected loop is formed among the first detection element, the second detection element, the etched sample and the high-resistance measuring instrument, so as to detect the contact resistance value of the surface of the etched sample.

[0014] In a second aspect, the present invention further provides a method for etching using the ion beam etching system with an in-situ monitoring function of etching rate as described above, including the following steps:

[0015] S1. Collect the etching duration T and the termination resistance R of the etched sample standard 终止 of

[0016] By means of optical emission spectroscopy, continuously collect the light intensity values of the light emitted by the characteristic elements in the etched layer of the etched sample standard during the etching process. Record the time interval between the start of growth and the start of decline of the light intensity values of the light emitted by the characteristic elements in the etched layer as the etching duration T. Record the contact resistance at the moment when the light intensity value of the light emitted by the characteristic elements in the etched layer starts to decline as the termination resistance R 终止 ; The etched sample standard is the same as the etched sample;

[0017] S2. Complete the conversion between the N ion beam etching working states and the etching rate detection working states of the etched sample

[0018] In the Nth ion beam etching working state, the completion duration is the preset etching time t N After the Nth etching with a duration of t, the ion beam etching working state ends, and the Nth etching rate detection working state is entered; where t N = T×(n - 1) / n N ; T is the etching duration; integer N≥1; integer n>1;

[0019] In the Nth etching rate detection working state, the resistance value R of the etched layer is detected N ; If R N ≥80% of R 终止 , the ion source power is reduced in the next ion beam etching working state; if R N <80% of R 终止 , the ion source power remains unchanged in the next ion beam etching working state; after detecting the resistance value of the etched layer, the next ion beam etching working state is entered;

[0020] S3. End the ion beam etching process for the etched sample

[0021] According to the steps in S2, the N - time conversion between the ion beam etching working state and the etching rate detection working state for the etched sample is completed until R N ≥R 终止 , continue to reduce the ion source power, and after the (N + 1)th etching with a duration of the preset etching time t N+1 , the ion beam etching process ends; where t N+1 = T×1 / n N .

[0022] Preferably, in the ion beam etching working state, the stage faces the ion source, and the etched sample is located on the upper surface of the stage facing the ion source; the movable shielding plate is in the lower limit position and in an open state, enabling the ion source to bombard and etch the etched sample.

[0023] Preferably, in the etching rate detection working state, the stage faces the lifting probe, and the etched sample is located on the upper surface of the stage facing the lifting probe; the movable shielding plate is in the upper limit position and in a shielding state, and the shielding part of the movable shielding plate completely blocks between the ion source and the stage to prevent the ion source from bombarding and etching the etched sample.

[0024] More preferably, in the etching rate detection working state, the lifting probe is driven to move towards the etched sample, so that the detection element contacts the etched sample, and the high - resistance measuring instrument detects the resistance value of the etched layer.

[0025] The present invention creatively proposes to install an electrical test detection element that can move close to or away from the stage in an ion beam etching system, so that the contact resistance of the sample surface can be measured in-situ without turning off the ion source or removing the sample. According to the inverse proportional relationship between the sample contact resistance and the sample film thickness, combined with the etching method of the present invention, the etching depth and etching rate of the sample surface can be accurately monitored, thereby accurately mastering the spacing between the etched layer and the free layer, and timely making process adjustments such as reducing the etching rate based on this spacing. In addition, in order to cooperate with the normal use of the electrical test detection element, the present invention designs a stage that can be deflected by 90°, and encapsulates the water-cooling circulation pipeline in the rotating shaft that drives the deflection of the stage, so that the water-cooling circulation pipeline can deflect together with the stage. In addition, in order to ensure the accuracy of contact resistance measurement, the present invention also specially designs a set of shielding devices. By using the fixed shielding plate and the movable shielding plate in cooperation, the bombardment of the ion beam on the probe of the electrical detection element and the wafer sample during the in-situ monitoring of the etching rate is effectively shielded. In order to cooperate with the use of the ion beam etching system of the present invention, an etching method is also proposed to accurately judge the etching depth and timely adjust the etching rate to ensure the final etching effect.

[0026] By using the ion beam etching system and etching method proposed by the present invention, the wafer sample is installed on a deflectable stage. When the wafer is facing the ion beam, the wafer can be etched. After etching for a certain time, deflect the stage by 90°, the wafer is facing the electrical test detection element, and slowly move the electrical test detection element close to the stage, then the contact resistance value of the etched sample wafer surface can be obtained through electrical measurement. Since the bottom electrode metal is usually metals such as Ta, Pt, Co, and Ru, and the resistivity difference is very small, it can be considered that the resistance value of the etched sample only depends on the sample film thickness, without considering the type of bottom electrode metal. Therefore, the etching depth and etching rate of the sample surface can be accurately judged through the measured contact resistance value.

[0027] Compared with the prior art, the ion beam etching system and etching method with in-situ monitoring function of etching rate proposed by the present invention have the following advantages:

[0028] (1) The ion beam etching system and etching method of the present invention can in-situ monitor the etching depth and etching rate while performing plasma etching in a vacuum reaction chamber, without turning off the ion source or removing the sample from the vacuum reaction chamber, so that both the plasma etching process and the etching depth monitoring link are completed in the vacuum reaction chamber, which is more suitable for the wafer fabrication process;

[0029] (2) The ion beam etching system and etching method of the present invention greatly improve the etching accuracy in the preparation of magnetic tunnel junctions, accurately monitor the spacing between the etched layer and the free layer, and adjust the ion source power in real time to reduce the etching rate, thereby effectively controlling the remaining thickness of the etched layer. While preventing the free layer from being over-etched, it can also ensure that the thickness of the free layer remains consistent and the resistance distribution is uniform, thus realizing the preparation of large-capacity SOT-MRAM memories;

[0030] (3) The ion beam etching system and etching method of the present invention replace the monitoring of the emission spectral curve of the sputtered material of the free layer by using a more sensitive and accurate detection of the surface contact resistance of the etched layer. It is not only applicable to the etching of wafer-level samples, but can also accurately etch small-size samples. Replacing spectral monitoring with current detection can not only avoid over-etching of the free layer of small-size samples, but also achieve a high success rate in the preparation of small-size SOT-MRAM memories with various required thin film structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0032] Figure 1 is a schematic diagram of the magnetic tunnel junction storing and processing information in the prior art;

[0033] Figure 2 is a schematic structural diagram of the ion beam etching system of the present invention along the X-Y plane in the etching working state;

[0034] Figure 3 is a schematic structural diagram of the ion beam etching system of the present invention along the X-Y plane in the working state of detecting the etching rate;

[0035] Figure 4 is a schematic structural diagram of the ion beam etching system of the present invention along the Y-Z plane in the working state of detecting the etching rate.

[0036] DESCRIPTION OF REFERENCE NUMERALS: 1, reaction chamber; 2, ion source; 3, carrier stage; 4, external fixed cover; 5, movable shielding plate; 51, connecting part; 52, shielding part; 6, movable shielding plate driving device; 7, grid; 8, wafer; 9, upper surface; 10, side surface; 11, rotating shaft; 12, motor; 13, water cooling circulation pipeline; 14, lifting probe; 15, lifting probe driving device; 16, detecting element; 161, first detecting element; 162, second detecting element; 17, high resistance measuring instrument; 18, fixed shielding plate; 19, ion beam. DETAILED DESCRIPTION OF THE INVENTION

[0037] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0038] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "vertical", "horizontal", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0039] In addition, many specific details of the present invention are described below, such as the structure, materials, dimensions, processing techniques and technologies of the device, in order to understand the present invention more clearly. However, as those of ordinary skill in the art can understand, the present invention can be implemented without these specific details. Unless specifically stated below, each part of the device can be made of materials well known to those of ordinary skill in the art, or materials with similar functions developed in the future can be used.

[0040] Figures 2 - 4 This is a schematic structural diagram of the ion beam etching system of the present invention in the etching working state and the working state of detecting the etching rate. As can be Figures 2 - 4 seen, the ion beam etching system of the present invention with an in-situ monitoring function of the etching rate includes: a reaction chamber 1, an ion source 2, and a stage 3. An external fixing cover 4 for fixing the ion source is provided outside the ion source 2. The reaction chamber 1 is a polyhedron structure with a hollow chamber, and a rectangular opening (not shown in the prior art) is provided on one side wall. The size of the rectangular opening meets the standards of the semiconductor SemiS2 certification, and the standard size of the rectangular opening can be adjusted according to the wafers applicable to the system. The opening allows a manipulator to carry the wafer into the reaction chamber. After the manipulator places the wafer on the etching stage, it exits from the opening. Thereafter, the valve installed outside the reaction chamber is closed, making the inside of the reaction chamber in a sealed vacuum state.

[0041] An active shielding plate 5 is provided in the reaction chamber 1. The active shielding plate 5 includes a connecting portion 51 and a shielding portion 52. The connecting portion 51 is connected to an active shielding plate driving device 6 located outside the reaction chamber 1. Under the action of the driving device 6, the active shielding plate 5 rotates between two extreme positions up and down around a driving axis, and the driving axis is substantially parallel to the X direction (i.e., the first direction). The shielding portion 52 is disposed between the grid 7 of the ion source 2 and the stage 3, and its size should be larger than the area of the grid 7. Before the stage 3 and the wafer 8 reach the set positions, the active shielding plate 5 is located at the upper extreme position to be in a shielding state, blocking between the grid 7 of the ion source and the stage 3 to protect the stage 3 and the wafer 8 from being damaged by the ion beam and affecting the finished product quality. However, at this time, the active shielding plate 5 is also directly bombarded by the ion beam at a close distance, and the constituent materials of the active shielding plate 5 itself will also be sputtered out by the ion beam and deposited in large amounts on the insulating cylinder of the ion source and the grid 7 of the ion source. Therefore, in some specific embodiments of the present invention, in order to reduce the active shielding plate material sputtered out by the ion beam from entering the interior of the ion source, reduce the damage to the insulating cylinder and the grid of the ion source, and improve the stability and reliability of the equipment, the shielding portion 52 can also be designed as an inclined surface that slopes away from the ion source, so as to form an acute angle with the Y direction (i.e., the second direction) perpendicular to the X direction. In other specific embodiments, the side of the shielding portion 52 facing the grid 7 can also be designed as a convex surface shape, and the central symmetry axis of the convex surface coincides with the central axis of the ion source. In the above-mentioned various design schemes of the shielding portion 52 in the specific embodiments, when the ion beam is emitted from the grid 7 of the ion source to the surface of the shielding portion 52, the shielding portion 52 can reflect part of the active shielding plate material sputtered out by the ion beam to the area outside the grid 7, thereby greatly reducing the amount of active shielding plate material sputtered out by the ion beam from entering the interior of the ion source, reducing the damage to the insulating cylinder and the grid of the ion source, and improving the stability and reliability of the equipment.

[0042] A stage 3 is arranged in the middle of the reaction chamber 1. A wafer 8 is placed on the upper surface 9 of the stage 3. The side surface 10 of the stage 3 adjacent to the upper surface 9 is connected to the outside of the reaction chamber 1 through a rotating shaft 11. The rotating shaft 11 is arranged along the Z direction (i.e., the third direction) perpendicular to the X-Y plane. The stage 3 can be deflected around the Z direction where the rotating shaft 11 is located under the drive of a motor 12 or other driving mechanisms. The water-cooling circulation pipeline 13 inside the stage 3 is encapsulated inside the rotating shaft 11 and connected to the water-cooling circulation system outside the reaction chamber 1 to ensure that the wafer 8 on the stage 3 always maintains an appropriate temperature. During ion beam etching, the stage 3 is set at a first angular position so that the wafer 8 on the stage 3 is placed facing the ion source along the Y-Z plane, and the ion source is turned on to release an ion beam to etch the wafer 8 placed on the stage 3. During etching rate monitoring, the stage 3 is set at a second angular position so that the wafer 8 on the stage 3 is placed facing the lifting probe 14 along the X-Z plane. The lifting probe 14 can be driven by a lifting probe driving device 15 to move close to the wafer 8 until the detection element 16 on the lifting probe 14 contacts the wafer 8. At this time, the resistance value of the wafer 8 placed on the stage 3 is detected through a high-resistance measuring instrument 17 electrically connected to the detection element 16. According to the corresponding relationship that the etching layer thickness is inversely proportional to the resistance value, the distance between the etching layer and the free layer is obtained, and whether process parameters such as the etching rate need to be adjusted is judged accordingly.

[0043] The high-resistance measuring instrument 17 is arranged outside the reaction chamber 1 for convenient reading of the resistance detection result of the etching layer on the surface of the wafer 8. Its positive and negative electrodes are electrically connected to the first detection element 161 and the second detection element 162 of the detection element 16 respectively, thus forming a closed loop for testing the resistance value of the etching layer on the surface of the wafer 8. The lifting probe driving device 15 is also arranged outside the reaction chamber 1 for convenient control operation and maintenance. The first detection element 161 and the second detection element 162 are preferably needle-shaped metals such as tungsten or stainless steel. In some specific embodiments, other metal conductor materials resistant to plasma etching can also be selected for the first detection element and the second detection element. Since the distance between the two detection elements does not affect the resistance value of the etching layer on the wafer surface detected by the high-resistance measuring instrument, generally, the distance between the first detection element 161 and the second detection element 162 is preferably 3 cm to 8 cm, which can be applicable to the vast majority of ion beam etching systems. Of course, in other specific embodiments, those skilled in the art can also set the distance between the first detection element and the second detection element according to the actual size of the wafer. The high-resistance measuring instrument 17 can be any instrument well-known in the art that can accurately measure high resistance values.

[0044] A fixed shielding plate 18 is arranged in the reaction chamber 1. The fixed shielding plate 18 is arranged in parallel with the shielding part 52 of the movable shielding plate 5, and is located between the movable shielding plate 5 and the lifting probe 14. The fixed shielding plate 18 can completely shield the lifting probe 14 and the detection element 16 during ion beam etching, reducing the damage to the lifting probe 14 and the detection element 16 caused by ion beam bombardment, and ensuring the accurate and effective detection accuracy of the lifting probe 14 and the detection element 16. The fixed shielding plate 18 can be selected to have as large a size as possible without affecting the free deflection of the stage 3 and the normal loading and unloading of the wafer 8 from the reaction chamber 1, so as to avoid the bombardment of the ion beam on the probe 14 and the detection element 16 to the greatest extent, ensuring that the detection element 16 accurately measures the etching layer resistance value on the basis of normal conduction. Thus, the ion beam etching system of the present invention can accurately detect the etching depth with nanometer-level accuracy, and then adjust the etching rate with the highest accuracy.

[0045] For a more comprehensive and clear description of the etching method using the ion beam etching system with in-situ monitoring function of etching rate of the present invention, the following embodiments will be combined with the attached Figures 2 - 4 Specifically describe the etching method.

[0046] Embodiment 1

[0047] Figure 2 It is a schematic structural diagram of the ion beam etching system of the present invention along the X-Y plane in the etching working state. As Figure 2 shown, in the ion beam etching working state, the stage 3 faces the ion source 2, and the wafer 8 is located on the upper surface 9 of the stage 3 facing the ion source 2. The movable shielding plate 5 is in the open state at the lower limit position, and the ion beam 19 is emitted from the grid 7 of the ion source 2 to bombard the wafer 8, and the etching of the wafer 8 is started. According to the process requirements, after a preset etching time, the etching of the wafer 8 is stopped. At this time, it enters the working state of detecting the etching rate.

[0048] The above-mentioned preset etching time can be determined by collecting the emission spectrum curve generated by the chemical changes of different dielectric layers during plasma etching to determine the plasma etching process and then collected. In this embodiment, taking the etching process of the MgO insulating layer as an example, through optical emission spectroscopy, the continuous change of the light intensity value of the light emitted by the characteristic elements of the MgO insulating layer of the etched sample standard during etching is collected. According to the properties of the Mg element and the element emission spectrum database, in the etching gas environment, the Mg element atoms emit light with a wavelength of 285.2 nm. When the light intensity value of this wavelength increases sharply, it indicates that the concentration of the Mg element is increasing sharply, indicating that the etching of the MgO insulating layer has begun; when the light intensity value of this wavelength drops sharply, it indicates that the concentration of the Mg element drops sharply, indicating that the MgO insulating layer is almost completely etched. Thus, the acquisition of the etching state information of the etched layer is completed. The time interval between the moment when the light intensity value of the light emitted by the Mg element starts to increase and the moment when it starts to decrease is recorded as the etching duration T, and the contact resistance at the moment when the light intensity value of the light emitted by the Mg element starts to decrease is measured and recorded as the termination resistance R 终止 . After measurement, the termination resistance R of the MgO insulating layer in the etched sample standard 终止 is 9.635 Ω / cm 2 .

[0049] During the entire etching process of the etched sample, it may go through N conversions between the ion beam etching working state and the detection of the etching rate working state. The preset etching time t1 of the first ion beam etching working state = T×(n - 1) / n, and the preset etching time t2 of the second ion beam etching working state = T×(n - 1) / n 2 , the preset etching time t3 of the third ion beam etching working state = T×(n - 1) / n 3 , and so on. The preset etching time t of the Nth ion beam etching working state N = T×(n - 1) / n N , where T is the etching duration, the integer N≥1, and the integer n>1. According to the efficiency requirements of the etching process, if it is necessary to complete the etching process as efficiently as possible, n can be selected as a relatively large integer. For example, n is set as an integer not less than 10; if the efficiency requirement for the etching process is not high and the etching accuracy requirement is higher, n can be set as an integer less than 10.

[0050] In the Nth detection of the etching rate working state, the etched layer resistance value R is detected N ; if R N ≥80% of R 终止 , then the ion source power is reduced in the next ion beam etching working state; if R N <R 终止If it is 80% of the above, the ion source power remains unchanged in the next ion beam etching working state; after completing the detection of the etched layer resistance value, enter the next ion beam etching working state.

[0051] Complete the conversion between the N ion beam etching working states and the detection etching rate working states for the etched sample according to the above steps until R in the Nth detection etching rate working state N ≥R 终止 At this point, it can be judged that the etched layer is almost completely etched. To ensure that the etched layer is completely etched, continue to reduce the ion source power and complete the (N + 1)th etching with a duration of the preset etching time t N+1 After the (N + 1)th etching, where t N+1 = T×1 / n N to end the entire ion beam etching process for the etched sample.

[0052] In this embodiment, the continuous change of the spectral intensity of the Mg element wavelength in the etched sample standard sample is collected by optical emission spectroscopy. Starting from the moment when the spectral intensity of the Mg element wavelength increases sharply and ending at the moment when the spectral intensity of the Mg element wavelength drops sharply, the etching duration T of the MgO insulating layer is 3 minutes. In this embodiment, the integer n is set to 3, so the preset etching time t1 in the first ion beam etching working state is 2 minutes. Therefore, in this embodiment, in the first ion beam etching working state, after completing the first etching for 2 minutes, stop etching the etched sample, and at this time enter the first detection etching rate working state.

[0053] Figure 3 It is a schematic structural diagram of the ion beam etching system of the present invention along the X - Y plane in the detection etching rate working state. Figure 4 It is a schematic structural diagram of the ion beam etching system of the present invention along the Y - Z plane in the detection etching rate working state. As Figures 3 - 4 shown, in the detection etching rate working state, the movable shielding plate driving device 6 controls the movable shielding plate 5 to rotate around the driving axis (X direction), so that the movable shielding plate 5 rotates to the upper limit position and is in the shielding state. At this time, the shielding part 52 of the movable shielding plate 5 completely blocks between the grid 7 of the ion source and the stage 3, thereby forming protection for the stage 3 and the wafer 8 to prevent the ion beam 19 from continuing to bombard and etch the wafer 8.

[0054] The rotating shaft 11 is driven to rotate by the motor 12, and the stage 3 is controlled to deflect by 90° around the axis of the rotating shaft 11 (Z direction), so that the wafer 8 on the stage 3 faces the lifting probe 14. At this time, the upper surface 9 of the stage 3 is substantially perpendicular to the Y direction. The lifting probe driving device 15 is used to control the lifting probe 14 to move towards the wafer 8 at an extremely slow speed, so that the detecting element 16 gradually approaches and contacts the wafer 8. When the first detecting element 161 and the second detecting element 162 contact the wafer 8 instantaneously, the pointer of the high-resistance measuring instrument 17 will deflect immediately. Therefore, when observing the deflection of the pointer of the high-resistance measuring instrument 17, the lifting probe driving device 15 is immediately stopped to prevent the first detecting element and the second detecting element from squeezing the wafer 8 and causing damage to the wafer.

[0055] Whether in the ion beam etching working state or in the detecting etching rate working state, the lifting probe 14 and the detecting element 16 are always under the shielding protection of the fixed shielding plate 18, thus effectively preventing the reduction of the resistance detection accuracy between the first detecting element 161 and the second detecting element 162 and the calculation error of the etching thickness caused by the ion beam bombardment on the lifting probe 14 and the detecting element 16. In addition, by encapsulating the water-cooling circulation pipeline 13 inside the stage 3 in the rotating shaft 11 and connecting it to the water-cooling circulation system outside the reaction chamber 1, the wafer 8 is always maintained at an appropriate temperature under the action of circulating water cooling, preventing the wafer from being damaged due to the high temperature generated by the ion beam etching. In this embodiment, the materials of the first detecting element 161 and the second detecting element 162 are both tungsten, the distance between the first detecting element and the second detecting element is 5 cm, and they are respectively electrically connected to the high-resistance measuring instrument 17 (Keithley 6517B high-resistance meter) outside the reaction chamber 1, thus forming a closed loop for testing the resistance value.

[0056] In this embodiment, in the first detecting etching rate working state, the etching layer resistance value R1 detected by the Keithley 6517B high-resistance meter is 7.569 Ω / cm 2 , and R1 is 78.6% of the termination resistance R 终止 , which is significantly less than the termination resistance R 终止 , indicating that the remaining thickness of the MgO insulating layer is still relatively large, and there is still a certain safety distance between the MgO insulating layer and the free layer. The ion beam etching of the surface of the etched sample can continue according to the current ion source power.

[0057] Since the resistivity of the bottom electrode containing metals such as Ta, Pt, Co or Ru differs little, it can be considered that the contact resistance value of the etching layer is only related to the film thickness of the etching layer, and the type of metal does not need to be considered. In addition, according to the inverse proportional relationship between the contact resistance value of the etching layer and the film thickness of the etching layer, when the measured resistance value is smaller, much smaller than the termination resistance R 终止When it indicates that the film thickness of the etching layer is relatively large, at this time, there is still a certain distance between the etching layer and the free layer, and the ion beam bombardment can continue at the original etching rate; when the measured resistance value is larger and approaches the termination resistance R 终止 When it indicates that the film thickness of the etching layer is already very small, at this time, the etching layer is very close to the free layer, and the ion beam bombardment should be carried out at a lower etching rate. Accordingly, the etching rate is adjusted in a timely manner to accurately complete the subsequent etching work. By detecting the contact resistance of the etching layer, the present invention can quantitatively monitor the etching process in the preparation of MRAM, with higher precision than grasping the spectral curve by a mass spectrometer in the prior art. Thus, the etching process can be accurately monitored to ensure that the etching process stops when the etching layer is completely etched away to reach the free layer, avoiding the redundant bombardment of the free layer by the ion beam due to over-etching of the etching layer, and at the same time ensuring the uniformity of the free layer thickness on the surface of the etched sample after etching, greatly reducing the random error of the remaining thickness of the free layer. When using the optical emission spectroscopy method, when the mass spectrometer captures the metal spectrum sputtered from the free layer, it indicates that the ion beam has bombarded the free layer for a period of time, and at this time, over-etching of the etching layer may have occurred. In addition, due to the detection accuracy of the high-resistance measuring instrument for the resistance value being much higher than that of the mass spectrometer for the spectral curve, therefore, even when etching on the surface of a very small wafer, no matter what kind of film with a layered structure needs to be etched, the ion beam etching system of the present invention can accurately complete the etching process.

[0058] After completing the measurement of the resistance value of the etching layer, the first detection of the etching rate working state is ended, and the second ion beam etching working state is continued. The lifting probe driving device 15 is used to control the lifting probe 14 to move away from the wafer 8 to the upper limit position, and the motor 12 is used to drive the rotation shaft 11 to rotate, controlling the stage 3 to deflect 90° around the axis (Z direction) of the rotation shaft 11, so that the wafer 8 on the stage 3 faces the ion source direction. At this time, the upper surface 9 of the stage 3 is basically perpendicular to the X direction. The movable shielding plate driving device 6 is used to control the movable shielding plate 5 to rotate around the driving axis (X direction), so that the movable shielding plate 5 is located at the lower limit position and is in an open state, and the ion beam 19 is emitted from the grid 7 of the ion source 2 to bombard the wafer 8, and the wafer 8 is continuously etched. Thus, the conversion from the first ion beam etching working state to the first detection of the etching rate working state and then into the second ion beam etching working state is completed, and the second ion beam etching working state is entered.

[0059] In the second ion beam etching working state, the preset etching time t2 is calculated according to t2 = 3×(3 - 1) / 3 2Calculation shows that the second etching is completed in 0.667 minutes under the working state of the second ion beam etching. The specific operation of the ion beam etching system is exactly the same as the foregoing operation and will not be elaborated here. In the working state of detecting the etching rate for the second time, the detected resistance value R2 of the etched layer is 9.122 Ω / cm 2 , which has reached 94.7% of the termination resistance R 终止 . This indicates that the remaining thickness of the MgO insulating layer is already close to the free layer, and the etching rate should be reduced to prevent over-etching of the etched layer. Generally, when the detected resistance value of the etched layer has reached 80% of the termination resistance, the etching rate should be decreased. Accordingly, the ion source power can be reduced to 75% of the original power, ending the working state of detecting the etching rate for the second time and entering the third ion beam etching working state for the third etching.

[0060] In the third ion beam etching working state, the preset etching time t3 is calculated according to t3 = 3×(3 - 1) / 3 3 Calculation shows that the third etching is completed in 0.222 minutes under the working state of the third ion beam etching. The specific operation of the ion beam etching system is exactly the same as the foregoing operation and will not be elaborated here. In the working state of detecting the etching rate for the third time, the detected resistance value R3 of the etched layer is 9.784 Ω / cm 2 , which has reached the termination resistance R 终止 , indicating that the MgO insulating layer has been etched completely. To ensure that the MgO insulating layer has indeed been etched completely, the ion source power is reduced to 25% of the original power, ending the working state of detecting the etching rate for the third time and performing the last etching.

[0061] In the last ion beam etching working state, the preset etching time t4 is calculated according to t4 = T×1 / 3 3 Calculation shows that the fourth etching is completed in 0.111 minutes under the working state of the last ion beam etching. The specific operation of the ion beam etching system is exactly the same as the foregoing operation and will not be elaborated here. After the fourth etching is completed, the entire etching process of the etched sample can be ended. At this time, it can be ensured that the MgO insulating layer has been completely etched away. At the same time, since the ion source power of the fourth etching has been reduced to 25% of the original power, it can be ensured that the free layer has not been over-etched by the ion beam, and the thickness of the free layer on the surface of the etched sample is uniform. Thus, the etching process of the MgO insulating layer in the etched sample has been completely completed.

[0062] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An ion beam etching system with an in-situ monitoring function of etching rate, the ion beam etching system comprising a reaction chamber (1), an ion source (2) and a stage (3), characterized in that: A lifting probe (14) is arranged in the reaction chamber (1) for approaching or departing from the stage (3); a detection element (16) is arranged on one side of the lifting probe (14) inside the reaction chamber (1), and a high-resistance measuring instrument (17) is connected to one side of the lifting probe (14) outside the reaction chamber (1). The detection element (16) is electrically connected to the high-resistance measuring instrument (17) to form a closed loop for measuring contact resistance when contacting an etched sample; The stage (3) is provided with a rotating shaft (11) connected to a driving mechanism outside the reaction chamber (1) for driving the stage (3) to deflect between a first angle and a second angle around the axis of the rotating shaft (11); when the stage (3) is at the first angle position, the etched sample faces the ion source (2); when the stage (3) is at the second angle position, the etched sample faces the lifting probe (14).

2. The ion beam etching system according to claim 1, wherein: An active shielding plate (5) is arranged in the reaction chamber (1), and the active shielding plate (5) comprises a connecting portion (51) and a shielding portion (52); the connecting portion (51) is connected to an active shielding plate driving device (6) outside the reaction chamber (1), and the active shielding plate (5) rotates between an upper limit position and a lower limit position around a driving axis under the action of the active shielding plate driving device (6).

3. The ion beam etching system according to claim 2, wherein: When the active shielding plate (5) reaches the upper limit position, the shielding portion (52) is in a shielding state, which is located between the ion source (2) and the stage (3) to shield the bombardment of the ion source (2) on the etched sample; when the active shielding plate (5) reaches the lower limit position, the shielding portion (52) is in an open state, and there is no shielding between the ion source (2) and the stage (3).

4. The ion beam etching system according to claim 2, wherein: A fixed shielding plate (18) is further arranged in the reaction chamber (1), which is located between the active shielding plate (5) and the lifting probe (14), and the fixed shielding plate (18) is arranged in parallel with the shielding portion (52) of the active shielding plate (5) to shield the bombardment of the ion source (2) on the probe (14) and the detection element (16).

5. The ion beam etching system according to claim 1, characterized in that: The lifting probe (14) moves closer to or farther away from the stage (3) under the drive of a lifting probe driving device (15) arranged outside the reaction chamber (1).

6. The ion beam etching system according to claim 1, wherein: The detection element (16) comprises a first detection element (161) and a second detection element (162), which are electrically connected to the positive and negative electrodes of the high-resistance measuring instrument (17) respectively.

7. A method for etching using the ion beam etching system with an in-situ monitoring function of etching rate according to any one of claims 1-6, characterized in that: The method comprises the following steps: S1. Collect the etching duration T and the termination resistance R of the etched sample standard 终止 sample By means of optical emission spectrometry, the continuous change of the light intensity value of the wavelength emitted by the characteristic elements in the etched layer of the etched sample standard is collected during the etching process. The time interval between the moment when the light intensity value of the wavelength emitted by the characteristic elements in the etched layer starts to increase and the moment when it starts to decrease is recorded as the etching duration T; the contact resistance at the moment when the light intensity value of the wavelength emitted by the characteristic elements in the etched layer starts to decrease is recorded as the termination resistance R 终止 ; the etched sample standard is the same as the etched sample; S2. Complete the conversion between the N times of ion beam etching working states and the detection etching rate working states for the etched sample Under the Nth ion beam etching working state, the completion duration is the preset etching time t N After the Nth etching with a duration of N , the ion beam etching working state is ended, and the Nth etching rate detection working state is entered; where t N = T×(n - 1) / n N ; T is the etching duration; integer N ≥ 1; integer n > 1; Under the working state of detecting the etching rate for the Nth time, detect the resistance value R of the etched layer N ; If R N ≥ 80% of R 终止 , then reduce the ion source power in the next ion beam etching working state; if R N < 80% of R 终止 , then keep the ion source power unchanged in the next ion beam etching working state; after completing the detection of the resistance value of the etched layer, enter the next ion beam etching working state; S3. End the ion beam etching process for the etched sample Complete the conversion between the N working states of ion beam etching and the working state of detecting the etching rate for the etched sample according to the step S2 until R in the working state of detecting the etching rate for the Nth time N ≥R 终止 , continue to reduce the ion source power, and after completing the (N + 1)th etching with a duration of the preset etching time t N+1 , end the ion beam etching process; where t N+1 = T×1 / n N .

8. The method according to claim 7, wherein: In the ion beam etching working state, the stage (3) faces the ion source (2), and the etched sample is located on the upper surface (9) of the stage (3) facing the ion source (2); the movable shielding plate (5) is in the lower limit position and in an open state, enabling the ion source (2) to bombard and etch the etched sample.

9. The method according to claim 7, characterized in that: In the working state of detecting the etching rate, the stage (3) faces the lifting probe (14), and the etched sample is located on the upper surface (9) of the stage (3) facing the lifting probe (14); the movable shielding plate (5) is in the upper limit position and in a shielding state, and the shielding portion (52) of the movable shielding plate (5) completely blocks between the ion source (2) and the stage (3) to prevent the ion source (2) from bombarding and etching the etched sample.

10. The method according to claim 9, wherein: In the working state of detecting the etching rate, drive the lifting probe (14) to move towards the etched sample, so that the detection element (16) contacts the etched sample, and the high-resistance measuring instrument (17) detects the resistance value of the etched layer.

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