CN118081513B - A piezoelectric array driven film active stress control polishing device and method - Google Patents

Abstract

The present invention relates to a piezoelectric array driven thin film active stress regulation grinding and polishing device and method, belonging to the field of ultra-precision polishing, the device comprises: a stress regulation unit, a processing unit, a control unit and a thin film workpiece; the stress regulation unit comprises an array piezoelectric platform and a common positive electrode, the array piezoelectric platform is composed of a plurality of piezoelectric ceramic motion platforms distributed according to an array, and the common positive electrode is arranged above the array piezoelectric platform; the thin film workpiece comprises a bottom substrate and an upper thin film, and the thin film workpiece is fixed on the common positive electrode through an adhesive layer; the processing unit is located above the thin film workpiece and is used for processing the thin film workpiece; the control unit is used for controlling the processing unit to move in the X, Y and Z axis directions, and for outputting corresponding voltages to each piezoelectric ceramic motion platform, during processing, the tensile and compressive stresses of the workpiece can be adjusted through the stress regulation unit, and controllable ultra-precision grinding and polishing can be achieved.

Description

A piezoelectric array driven film active stress control polishing device and method

Technical Field

The present invention belongs to the field of ultra-precision polishing, and in particular relates to a thin film active stress regulation and polishing device and method driven by a piezoelectric array.

Background technique

Thin films are generally coated on substrates to achieve high performance such as wear resistance or chemical corrosion resistance; for example, silicon wafers coated with silicon nitride films are widely used in microelectronics, optoelectronics and other fields; for such components, due to their difficult processing and easy damage, it is a considerable challenge to achieve controllable processing and high surface integrity, reduce the occurrence of sub-surface damage, and thus achieve designed performance.

At present, the traditional grinding and polishing processing methods of thin film workpieces remove materials by combining mechanical force with chemical modification, such as ultra-precision cutting, ion beam polishing, magnetorheological polishing, chemical mechanical polishing and other polishing methods. Although these processing methods have the processing accuracy of sub-nanometer surface roughness, the material removal of ultra-precision grinding and polishing requires more precision. In the initial stage of processing, the residual stress generated by the workpiece in the previous process will affect the processing results of ultra-precision grinding and polishing. At the same time, sub-surface damage is inevitable in the processing process, and the means to suppress the generation of sub-surface damage are relatively simple.

For the initial residual stress, the traditional processing method is to let the material stand still before processing to let the stress dissipate naturally. This method has a low impact on the surface result, but the regulation cycle is long. In order to promote the processing of hard and brittle materials, in addition to simple contact and chemical reactions, scholars are also exploring the application rules of multi-energy field superposition in the processing process. A feasible method is to superimpose "energy" during the processing, such as using magnetic assistance in cutting or electric assistance in forming. However, these methods are limited by the characteristics of the material. Lasers are usually used to soften materials to achieve high removal rates, but they will inevitably bring about an increase in residual stress and/or cracks caused by laser shock. Heat treatment methods can alleviate this situation and achieve surface strengthening, but these processes cannot be simply integrated into the production line. Some scholars have tried to use grinding heat to achieve the processing of hard and brittle materials, although they have noticed that the superposition of thermal effects may cause undesirable surface changes, such as cracks or white etching areas. In addition, most research work only focuses on studying the response of bulk materials under a single compressive load. When it comes to thin film specimens, the situation may be much more complicated, because thin film specimens can easily deform in different directions, resulting in more serious fractures or nano-scale defects under the surface. The clamping and stretching regulation method is obviously not suitable for thin film specimens.

Summary of the invention

The purpose of the present invention is to provide a piezoelectric array driven thin film active stress control grinding and polishing device and method to solve the problems that in the existing thin film workpiece grinding and polishing process, the residual stress of the thin film workpiece will affect the ultra-precision grinding and polishing results and cause sub-surface damage, and the existing methods for eliminating residual stress have long control cycles, cause undesirable surface changes, and are not suitable for thin film workpieces.

In order to solve the above technical problems, the technical solution provided by the present invention is:

The present invention relates to a thin film active stress regulation and polishing device driven by a piezoelectric array, which comprises a stress regulation unit, a processing unit, a control unit and a thin film workpiece; the stress regulation unit comprises an array piezoelectric platform and a common positive electrode, the array piezoelectric platform is composed of a plurality of piezoelectric ceramic motion platforms distributed according to an array, and the common positive electrode is arranged above the array piezoelectric platform; the thin film workpiece comprises a bottom substrate and an upper thin film, and the thin film workpiece is fixed on the common positive electrode through an adhesive layer; the processing unit is located above the thin film workpiece and is used for processing the thin film workpiece; the control unit is used for controlling the processing unit to move in the X, Y and Z axis directions, and for outputting corresponding voltages to each piezoelectric ceramic motion platform.

Preferably, the processing unit comprises a processing tool and a motion platform, the motion platform is used to clamp the processing tool and drive the processing tool along the X, Y and Z axis directions, and the processing tool adopts a polishing disc or an air bag for grinding and polishing the thin film workpiece.

Preferably, the control unit comprises a computer, a motion controller and a piezoelectric drive controller;

The motion controller is used to drive the motion platform so that the processing tool moves along a set path;

The piezoelectric drive controller is provided with a plurality of output ports, each of which is connected to a corresponding piezoelectric ceramic motion platform and is used to output a corresponding voltage value to each piezoelectric ceramic motion platform;

The computer is used to set the voltage value of each output port on the piezoelectric drive controller and the movement path of the processing tool.

Preferably, the output port of the piezoelectric drive controller outputs a positive voltage or a negative voltage;

When the output port outputs a positive voltage, the corresponding piezoelectric ceramic motion platform bulges upward, exerting tensile stress on the surface of the film workpiece;

When the output port outputs a negative voltage, the corresponding piezoelectric ceramic motion platform is recessed downward, exerting compressive stress on the surface of the thin film workpiece.

Preferably, the maximum voltage setting value of the piezoelectric ceramic motion platform decreases from the edge to the center of the array.

Preferably, the stiffness of the thin film workpiece is not greater than the allowable stiffness of the piezoelectric ceramic motion platform.

The present invention also relates to a polishing method using the thin film active stress regulation polishing device driven by the piezoelectric array, which comprises the following steps:

S1. Detect stress distribution on the surface of the thin film workpiece to obtain the initial residual stress of the thin film workpiece itself;

S2. Setting target material removal and sub-surface damage;

S3. Based on the set target material removal and subsurface damage, combined with the initial residual stress of the thin film workpiece itself, set the target prestress distribution of the entire surface of the thin film workpiece, and calculate the voltage value of each piezoelectric ceramic motion platform based on the target prestress distribution;

S4. The control unit outputs a corresponding voltage to each piezoelectric ceramic motion platform according to the calculated voltage value, so that the array piezoelectric platform produces a controllable deformation, and drives the thin film workpiece to deform under the action of the adhesive layer;

S5. The control unit drives the processing unit to grind and polish the surface of the thin film workpiece.

Preferably, the calculation formula for the target prestress distribution on the entire surface of the thin film workpiece in S3 is:

(1),

Wherein, σf is _the target surface prestress, E and v are the Young's modulus and Poisson's ratio of the substrate respectively, Ts is the thickness of the substrate, Tf is the thickness of the film; ρ ( r ) is the radius of curvature of any point on the surface with coordinate r where the workpiece _is displaced and bent by the piezoelectric ceramic motion platform.

Preferably, the calculation formula of the displacement and voltage of each piezoelectric ceramic motion platform in S3 is:

(2),

(3),

Wherein, L ( r ) is the displacement of any point with coordinate r within the maximum radius affected by the piezoelectric ceramic motion platform, L ( r )' and L ( r )" are the first-order derivative and second-order derivative of L ( r ), respectively, KA is the coupling stiffness between the piezoelectric ceramic motion platform and the thin film workpiece, _K1 is the proportionality coefficient between the piezoelectric ceramic motion platform and the input voltage and the output load, V is the input voltage of the piezoelectric ceramic _motion platform, R is the maximum radius affected by the piezoelectric ceramic motion platform, r is the coordinate of any point within the maximum radius affected by the piezoelectric ceramic motion platform, , x is the horizontal coordinate of any point within the maximum radius affected by the piezoelectric ceramic motion platform, and y is the vertical coordinate of any point within the maximum radius affected by the piezoelectric ceramic motion platform.

Compared with the prior art, the beneficial technical effects of the present invention are as follows:

1. The piezoelectric array driven thin film active stress control grinding and polishing device involved in the present invention includes a stress control unit and a control unit. The stress control unit includes an array piezoelectric platform and a common positive electrode. The array piezoelectric platform is composed of a number of piezoelectric ceramic motion platforms distributed according to the array. The common positive electrode is arranged above the array piezoelectric platform. The control unit outputs a corresponding voltage to each piezoelectric ceramic motion platform. Before processing the thin film workpiece, a stress distribution detection is first performed to obtain the residual stress distribution of the thin film workpiece itself. Based on the residual stress distribution, different voltages are output to each piezoelectric ceramic motion platform through the control unit to achieve a balance between the tensile and compressive stresses of the workpiece, thereby reducing the influence of the residual stress of the thin film workpiece itself on the processing results of ultra-precision grinding and polishing.

2. The piezoelectric array-driven thin film active stress control grinding and polishing device involved in the present invention includes, in addition to a stress control unit and a control unit, a processing unit. The control unit is also used to control the movement of the processing unit in the X, Y and Z axis directions. During processing, the target material removal and sub-surface damage conditions can be set, and the piezoelectric ceramic motion platform can be automatically adjusted to achieve precise application of full-domain prestress. While ensuring that sub-surface damage is suppressed, the optimal processing parameters are optimized to achieve controllable ultra-precision grinding and polishing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the structure of a thin film active stress control polishing device driven by a piezoelectric array;

FIG2 is a schematic diagram of the deformation and film stress distribution of the piezoelectric ceramic motion platform when positive and negative voltages are applied;

FIG3 is a graph showing the changes in the material removal rate and stress removal threshold of a thin film workpiece under different stress distributions;

FIG4 is a schematic diagram of a machining process for removing uneven surface of a thin film workpiece;

FIG. 5 is a schematic diagram of a machining process in which the removal target is uniform machining of the surface of a thin film workpiece.

Among them, 101 is a motion platform, 102 is a processing tool, 103 is a motion controller, 104 is a computer, 105 is a piezoelectric drive controller, 106 is a piezoelectric ceramic motion platform, 107 is a common positive electrode, 108 is an adhesive layer, 109 is a substrate, and 110 is a film.

Detailed ways

The technical scheme of the present invention is further specifically described below through specific embodiments. The embodiments are for the purpose of explaining the present invention, not for limiting the present invention. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

Example 1

Referring to FIG. 1 , the present invention relates to a piezoelectric array driven thin film active stress control grinding and polishing device including a stress control unit, a processing unit, a control unit and a thin film workpiece. The stress control unit includes an array piezoelectric platform and a common positive electrode 107. The array piezoelectric platform is composed of a plurality of piezoelectric ceramic motion platforms 106 distributed in an array. The common positive electrode 107 is arranged above the array piezoelectric platform. The thin film workpiece includes a bottom substrate 109 and an upper film 110. The thin film workpiece is fixed on the common positive electrode 107 through an adhesive layer 108. The processing unit is located above the thin film workpiece. The processing unit includes a processing tool 102 and a motion platform 101. The motion platform 101 is used to clamp the processing tool 102 and drive the processing tool 102 along the X, Y and Z axis directions. The processing tool 102 uses a polishing disc or an air bag for grinding and polishing the thin film workpiece. The control unit includes a computer 104, a motion controller 103 and a piezoelectric drive controller 105. The motion controller 103 is used to drive the motion platform 101 so that the processing tool 102 moves along a set path; a plurality of output ports are arranged on the piezoelectric drive controller 105, each output port is connected to a corresponding piezoelectric ceramic motion platform 106, and is used to output a corresponding voltage value to each piezoelectric ceramic motion platform 106; the computer 104 is used to set the voltage value of each output port on the piezoelectric drive controller 105, and the computer 104 is also used to set the motion path of the processing tool 102.

The output port of the piezoelectric drive controller 105 outputs a positive voltage or a negative voltage. When the output port outputs a positive voltage, the corresponding piezoelectric ceramic motion platform 106 bulges upward, applying tensile stress to the surface of the thin film workpiece. When the output port outputs a negative voltage, the corresponding piezoelectric ceramic motion platform 106 is concave downward, applying compressive stress to the surface of the thin film workpiece, as shown in FIG2. Under the same processing parameters (same force Fg ), tensile stress will increase the material removal rate, that is, the depth δw increases, and the stress removal threshold is reduced, which is manifested as cracks in the processing area; compressive stress will reduce the material removal rate, that is, the depth δw decreases, but the stress removal threshold is increased, which is manifested as no cracks in the processing area, thereby suppressing sub-surface damage and improving workpiece performance, as shown in FIG3. In order to ensure that the thin film workpiece will not collapse, plastic deformation, etc. due to deformation, the maximum voltage setting value of the piezoelectric ceramic motion platform 106 decreases from the edge to the center of the array, and the stiffness of the thin film workpiece is not greater than the allowable stiffness of the piezoelectric ceramic motion platform 106.

Example 2

Referring to FIG. 4 , this embodiment relates to a polishing method of a thin film active stress regulation polishing device driven by a piezoelectric array as described in Embodiment 1, which comprises the following steps:

S1. Detect stress distribution on the surface of the thin film workpiece to obtain the initial residual stress of the thin film workpiece itself;

S2. Setting the target material removal and sub-surface damage, the target material removal is uneven removal;

S3. Based on the set target material removal and sub-surface damage, combined with the initial residual stress of the thin film workpiece itself, the target prestress distribution of the entire surface of the thin film workpiece is set. The calculation formula of the prestress distribution of the entire surface of the thin film workpiece is:

(1),

Wherein, σf is _the target surface prestress, E and v are the Young's modulus and Poisson's ratio of the substrate respectively, Ts is the thickness of the substrate, Tf is the thickness of the film; ρ ( r ) is the radius of curvature of any point on the surface with coordinate r where the workpiece _is displaced and bent by the piezoelectric ceramic motion platform;

The displacement distribution is calculated based on the target prestress distribution, and then the voltage value of each piezoelectric ceramic motion platform 106 is calculated. The calculation formula is:

(2),

(3),

Among them, L ( r ) is the displacement of any point with coordinate r within the maximum radius affected by the piezoelectric ceramic motion platform, L ( r )' and L ( r )" are the first-order derivative and second-order derivative of L ( r ), respectively, KA is the coupling stiffness between the piezoelectric ceramic motion platform and the thin film workpiece, _K1 is the proportionality coefficient between the piezoelectric ceramic motion platform and the input voltage and the output load, V is the input voltage of the piezoelectric ceramic motion _platform , R is the maximum radius affected by the piezoelectric ceramic motion platform, r is the coordinate of any point within the maximum radius affected by the piezoelectric ceramic motion platform, , x is the horizontal coordinate of any point within the maximum radius affected by the piezoelectric ceramic motion platform, y is the vertical coordinate of any point within the maximum radius affected by the piezoelectric ceramic motion platform;

Combining formula (1) to formula (3), the voltage value V of each piezoelectric ceramic motion platform can be calculated by setting the global surface target prestress distribution.

S4. The computer 104 transmits the calculated voltage value of each piezoelectric ceramic motion platform 106 to the piezoelectric drive controller 105, and the piezoelectric drive controller 105 outputs a corresponding voltage to each piezoelectric ceramic motion platform 106 according to the calculated voltage value, so that the array piezoelectric platform produces a controllable deformation, and drives the thin film workpiece to deform under the action of the adhesive layer, so that the prestress condition on the surface of the thin film workpiece meets the target prestress distribution;

S5. The computer calculates the processing parameters of the processing unit based on the stress value on the surface of the thin film workpiece, including the pressing depth, pressing force, running speed, running trajectory, etc., and sends the processing parameters to the motion controller. The motion controller drives the motion platform 101 and drives the processing tool 102 to grind and polish the surface of the thin film workpiece.

Example 3

5, this embodiment relates to a polishing method of a thin film active stress regulation polishing device driven by a piezoelectric array as described in Embodiment 1, which comprises the following steps:

S1. Detect stress distribution on the surface of the thin film workpiece to obtain the initial residual stress of the thin film workpiece itself;

S2. Setting the target material removal and sub-surface damage, the target material removal is uniform removal;

S3. Based on the set target material removal and sub-surface damage, combined with the initial residual stress of the thin film workpiece itself, the target prestress distribution of the entire surface of the thin film workpiece is set. In this embodiment, the target prestress distribution of the entire surface of the thin film workpiece is no apparent stress or a uniform apparent stress distribution. The calculation formula for the prestress distribution of the entire surface of the thin film workpiece is:

(1),

Wherein, σf is _the target surface prestress, E and v are the Young's modulus and Poisson's ratio of the substrate respectively, Ts is the thickness of the substrate, Tf is the thickness of the film; ρ ( r ) is the radius of curvature of any point on the surface with coordinate r where the workpiece _is displaced and bent by the piezoelectric ceramic motion platform;

The displacement distribution is calculated based on the target prestress distribution, and then the voltage value of each piezoelectric ceramic motion platform 106 is calculated. The calculation formula is:

(2),

(3),

Among them, L ( r ) is the displacement of any point with coordinate r within the maximum radius affected by the piezoelectric ceramic motion platform, L ( r )' and L ( r )" are the first-order derivative and second-order derivative of L ( r ), respectively, KA is the coupling stiffness between the piezoelectric ceramic motion platform and the thin film workpiece, _K1 is the proportionality coefficient between the piezoelectric ceramic motion platform and the input voltage and the output load, V is the input voltage of the piezoelectric ceramic motion _platform , R is the maximum radius affected by the piezoelectric ceramic motion platform, r is the coordinate of any point within the maximum radius affected by the piezoelectric ceramic motion platform, , x is the horizontal coordinate of any point within the maximum radius affected by the piezoelectric ceramic motion platform, y is the vertical coordinate of any point within the maximum radius affected by the piezoelectric ceramic motion platform;

Combining formula (1) to formula (3), the voltage value V of each piezoelectric ceramic motion platform can be calculated by setting the global surface target prestress distribution.

S4. The computer 104 transmits the calculated voltage value of each piezoelectric ceramic motion platform 106 to the piezoelectric drive controller 105, and the piezoelectric drive controller 105 outputs a corresponding voltage to each piezoelectric ceramic motion platform 106 according to the calculated voltage value, so that the array piezoelectric platform produces a controllable deformation, and drives the thin film workpiece to deform under the action of the adhesive layer to balance the surface stress of the thin film workpiece, so that the surface of the thin film workpiece is stress-free or has uniform stress, as shown in FIG5 ;

S5. The computer calculates the processing parameters of the processing unit based on the stress value on the surface of the thin film workpiece, including the pressing depth, pressing force, running speed, running trajectory, etc., and sends the processing parameters to the motion controller. The motion controller drives the motion platform 101 and drives the processing tool 102 to grind and polish the surface of the thin film workpiece.

This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims (8)

1. A piezoelectric array driven thin film active stress control grinding and polishing method, which is implemented by a piezoelectric array driven thin film active stress control grinding and polishing device, the device comprising a stress control unit, a processing unit, a control unit and a thin film workpiece; the stress control unit comprises an array piezoelectric platform and a common positive electrode, the array piezoelectric platform is composed of a plurality of piezoelectric ceramic motion platforms distributed in an array, and the common positive electrode is arranged above the array piezoelectric platform; the thin film workpiece comprises a bottom substrate and an upper thin film, and the thin film workpiece is fixed on the common positive electrode through an adhesive layer; the processing unit is located above the thin film workpiece and is used to process the thin film workpiece; the control unit is used to control the processing unit to move in the X, Y and Z axis directions, and is used to output corresponding voltages to each piezoelectric ceramic motion platform, and is characterized in that it comprises the following steps: S1. Detect stress distribution on the surface of the thin film workpiece to obtain the initial residual stress of the thin film workpiece itself; S2. Setting target material removal and sub-surface damage; S3. Based on the set target material removal and subsurface damage, combined with the initial residual stress of the thin film workpiece itself, set the target prestress distribution of the entire surface of the thin film workpiece, and calculate the voltage value of each piezoelectric ceramic motion platform based on the target prestress distribution; S4. The control unit outputs a corresponding voltage to each piezoelectric ceramic motion platform according to the calculated voltage value, so that the array piezoelectric platform produces a controllable deformation, and drives the thin film workpiece to deform under the action of the adhesive layer; S5. The control unit drives the processing unit to grind and polish the surface of the thin film workpiece. 2. The piezoelectric array driven thin film active stress control polishing method according to claim 1, characterized in that: the control unit in S4 outputs a positive voltage or a negative voltage; When the output port outputs a positive voltage, the corresponding piezoelectric ceramic motion platform bulges upward, exerting tensile stress on the surface of the film workpiece; When the output port outputs a negative voltage, the corresponding piezoelectric ceramic motion platform is recessed downward, exerting compressive stress on the surface of the thin film workpiece. 3. The piezoelectric array driven thin film active stress control polishing method according to claim 1 is characterized in that: the calculation formula of the target prestress distribution of the entire surface of the thin film workpiece in S3 is: (1), Wherein, σf is _the target surface prestress, E and v are the Young's modulus and Poisson's ratio of the substrate respectively, Ts is the thickness of the substrate, Tf is the thickness of the film; ρ ( r ) is the radius of curvature of any point on the surface with coordinate r where the workpiece _is displaced and bent by the piezoelectric ceramic motion platform. 4. The piezoelectric array driven thin film active stress control polishing method according to claim 3 is characterized in that: the calculation formula of the displacement and voltage of each piezoelectric ceramic motion platform in S3 is: (2), (3), Wherein, L ( r ) is the displacement of any point with coordinate r within the maximum radius affected by the piezoelectric ceramic motion platform, L ( r )' and L ( r )" are the first-order derivative and second-order derivative of L ( r ), respectively, KA is the coupling stiffness between the piezoelectric ceramic motion platform and the thin film workpiece, _K1 is the proportionality coefficient between the piezoelectric ceramic motion platform and the input voltage and the output load, V is the input voltage of the piezoelectric ceramic _motion platform, R is the maximum radius affected by the piezoelectric ceramic motion platform, r is the coordinate of any point within the maximum radius affected by the piezoelectric ceramic motion platform, , x is the horizontal coordinate of any point within the maximum radius affected by the piezoelectric ceramic motion platform, and y is the vertical coordinate of any point within the maximum radius affected by the piezoelectric ceramic motion platform. 5. The piezoelectric array driven thin film active stress control grinding and polishing method according to claim 1 is characterized in that: the processing unit in S5 includes a processing tool and a motion platform, the motion platform is used to clamp the processing tool and drive the processing tool along the X, Y and Z axis directions, and the processing tool adopts a polishing disk or an air bag for grinding and polishing the thin film workpiece. 6. The piezoelectric array driven thin film active stress control polishing method according to claim 1, characterized in that: the control unit comprises a computer, a motion controller and a piezoelectric drive controller; The motion controller is used to drive the motion platform so that the processing tool moves along a set path; The piezoelectric drive controller is provided with a plurality of output ports, each of which is connected to a corresponding piezoelectric ceramic motion platform and is used to output a corresponding voltage value to each piezoelectric ceramic motion platform; The computer is used to set the voltage value of each output port on the piezoelectric drive controller and the movement path of the processing tool. 7. The piezoelectric array driven thin film active stress control polishing method according to claim 1 is characterized in that: the maximum voltage setting value of the piezoelectric ceramic motion platform in S4 decreases from the edge to the center of the array. 8. The piezoelectric array driven thin film active stress control grinding and polishing method according to claim 1, characterized in that the stiffness of the thin film workpiece is not greater than the allowable stiffness of the piezoelectric ceramic motion platform.