A LASER ETCHING METHOD FOR MEMS PROBES

Abstract

A laser etching method for MEMS probes belongs to the technical field of semiconductor processing and testing; first, the MEMS probe laser etching method performs the parameter calculation to obtain the step angle of the motor according to the etching spacing of the single crystal silicon wafer; then it performs the initial position adjustment to rotate the spiral through-groove plate to the initial position and move the first etching point to the optical axis, and adjust the four-dimensional stage; and then it performs the laser etching and progress judgment; and finally adjusts the four-dimensional stage and the motor, including the downward movement distance, left movement distance and clockwise rotation angle of the four-dimensional stage and the rotation angle of the motor; the MEMS probe laser etching method, combined with the MEMS probe laser etching device, not only has higher etching accuracy, but also continuously adjusts the etching spacing.

Claims

1. A laser etching method for MEMS probes, wherein: it includes the following steps: Step a: Parameter calculation According to the etching spacing d of the single crystal silicon wafer (5), the step angle of the motor (8) is obtained: $=\frac{d}{k}.Math.\frac{l_1}{l_2}.Math.\frac{d_1}{d_2}$ Wherein: k is the coefficient of the spiral line of the spiral through-groove of the first base plate (2-1) with the length/radian dimension; l.sub.1 is the distance from the second base plate (3-1) to the center of the objective lens (4); l.sub.2 is the distance from the upper surface of the single crystal silicon wafer (5) to the center of the objective lens (4); d.sub.1 is the diameter of the pitch circle of the first side edge (2-2); d.sub.2 is the diameter of the pitch circle of the gear (7); Step b: Initial position adjustment Step b1: Rotate the spiral through-groove plate (2) to the initial position, and move the first etching point to the optical axis; Step b2: Four-dimensional stage (6) adjustment: Move upward: $\left(h_1+h_2\right).Math.\frac{\sqrt{l_0^2+l_1^2}-l_1}{\sqrt{l_0^2+l_1^2}}$ Move to the right: $l_0.Math.\frac{l_2}{l_1}+\left(h_1+h_2\right).Math.\frac{l_0}{\sqrt{l_0^2+l_1^2}}$ Rotate counterclockwise: $\arctan \frac{l_0}{l_1}$ Wherein: l.sub.0 is the maximum distance between the spiral line and the center of the first base plate (2-1); h.sub.1 is the thickness of the single crystal silicon wafer (5); h.sub.2 is the distance from the center of the rotation axis of the four-dimensional stage (6) to the upper surface; Step c: Laser etching Light the arc light source (1) until the etching is completed; Step d: Progress judgment Judge whether the current etch line is etched, and if: Yes, the four-dimensional stage (6) moves forward or backward to the next line for etching; No, go to step e; Step e: Four-dimensional stage (6) and motor (8) adjustment Specifically: The four-dimensional stage (6) moves downward:
(h.sub.1+h.sub.2).Math.cos .sub.2d.Math.sin .sub.2(h.sub.1+h.sub.2).Math.cos .sub.1 The four-dimensional stage (6) moves to the left; $\frac{l_2}{\tan {}_1}+\left(h_1+h_2\right).Math.\sin {}_1-\frac{l_2}{\tan {}_2}-\left(h_1+h_2\right).Math.\sin {}_2+d.Math.\cos {}_2$ The four-dimensional stage (6) rotates clockwise:
.sub.1.sub.2 The motor (8) rotates; $\frac{d_1}{d_2}.Math.\frac{l_1}{k}.Math.\left(\tan {}_1-\tan {}_2\right)$ Wherein: .sub.1 is the angle between the light beam and the optical axis at the current etching point; .sub.2 is the angle between the light beam and the optical axis at the next etching point; Return to step c.

2. The laser etching method for MEMS probes according to the claim 1, wherein: it is applied to a MEMS probe laser etching device.

3. The laser etching method for MEMS probes according to the claim 2, wherein: the MEMS probe laser etching device is sequentially provided with an arc light source (1), a spiral through-groove plate (2), a straight through-groove plate (3), an objective lens (4), a single crystal silicon wafer (5), and a four-dimensional stage (6) according to the direction of light propagation; The distance from each point of the arc light source (1) to the center of the objective lens (4) is the same, that is, the shape of the arc light source (1) is a circular arc with the center of the objective lens (4) as the center of the circle; the tangent of each point of the arc light source (1) is perpendicular to the line connecting the point to the center of the objective lens (4); The spiral through-groove plate (2) comprises a first base plate (2-1) with a spiral through-groove and a first side edge (2-2) with a circular cross-section, and the outer surface of the side edge (2-2) is provided with teeth to form a gear structure, and the spiral line of the spiral through-groove satisfies the following relationship:
l()=l.sub.0k Wherein: l.sub.0 is the maximum distance between the spiral line and the center of the first base plate (2-1), and when the distance from the intersection of the spiral through-groove and the straight through-groove to the center of the first base plate (2-1) is the maximum distance, the position of the first base plate (2-1) is defined as the initial position; k is a coefficient with a dimension of length/radian; is a radian; l() represents the distance from the intersection of the spiral through-groove and the straight through-groove to the center of the first base plate (2-1) after the spiral line rotates from the initial position; The straight through-groove plate (3) comprises a second base plate (3-1) with a straight through-groove and a second side edge (3-2) with an annular cross-section, and the diameter of the inner circle of the second side edge (3-2) is larger than the diameter of outer circle of the first side edge (2-2), and the upper surface of the second base plate (3-1) is in close contact with the lower surface of the first base plate (2-1); The upper surface of the single crystal silicon wafer (5) and the second base plate (3-1) are respectively located on the image plane and the object plane of the objective lens (4), and the single crystal silicon wafer (5) can complete four-dimensional motion under the bearing of the four-dimensional stage (6); The four-dimensional stage (6) can complete three-dimensional translation and one-dimensional rotation, and the rotation is performed in the plane determined by the arc light source (1) and the optical axis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0106] FIG. 1 is a schematic view 1 of the MEMS probe laser etching device of the present invention.

[0107] FIG. 2 is a schematic view 1 of the spiral through-groove plate of the MEMS probe laser etching device of the present invention.

[0108] FIG. 3 is a schematic view 1 of the straight through-groove plate of the MEMS probe laser etching device of the present invention.

[0109] FIG. 4 is a schematic view of a pinhole formed after a spiral through-groove plate and a straight through-groove plate are superimposed.

[0110] FIG. 5 is a schematic view of the second base plate.

[0111] FIG. 6 is a schematic view 2 of the MEMS probe laser etching device of the present invention.

[0112] FIG. 7 is a flow chart of the MEMS probe laser etching method of the present invention.

[0113] FIG. 8 is a schematic view of the relative position of components after the first step of the initial position adjustment process is completed.

[0114] FIG. 9 is a relative positional relationship diagram before and after the adjustment of the four-dimensional stage in the second step of the initial position adjustment process.

[0115] FIG. 10 is a relative positional relationship diagram before and after the adjustment of the four-dimensional stage between two adjacent etchings.

[0116] FIG. 11 is a schematic view of an optical focusing structure for the MEMS probe laser etching device of the present invention.

[0117] FIG. 12 is a flow chart of the optical focusing method for the MEMS probe laser etching method of the present invention.

[0118] In the figures: 1 arc light source, 2 spiral through-groove plate, 2-1 first base plate, 2-2 first side edge, 3 straight through-groove plate, 3-1 second base plate, 3-2 second side edge, 4 objective lens, 5 single crystal silicon wafer, 6 four-dimensional stage, 7 gear, 8 motor, 9 controller, 10 prism, 11 image sensor, 21 upper slotted through-groove plate, 31 lower slotted through-groove plate, 51 plane mirror.

SPECIFIC EMBODIMENT

[0119] The specific embodiments of the invention are further described in detail below with reference to the figures.

Specific Embodiment 1

[0120] The following is a specific embodiment of the MEMS probe laser etching device of the present invention.

[0121] The MEMS probe laser etching device of the embodiment with the schematic view shown in FIG. 1, is sequentially provided with an arc light source 1, a spiral through-groove plate 2, a straight through-groove plate 3, an objective lens 4, a single crystal silicon wafer 5, and a four-dimensional stage 6 according to the direction of light propagation;

[0122] The distance from each point of the arc light source 1 to the center of the objective lens 4 is the same, that is, the shape of the arc light source 1 is a circular arc with the center of the objective lens 4 as the center of the circle; the tangent of each point of the arc light source 1 is perpendicular to the line connecting the point to the center of the objective lens 4;

[0123] The spiral through-groove plate 2 with the schematic view shown in FIG. 2 comprises a first base plate 2-1 with a spiral through-groove and a first side edge 2-2 with a circular cross-section, and the outer surface of the side edge 2-2 is provided with teeth to form a gear structure, and the spiral line of the spiral through-groove satisfies the following relationship:

l()=l.sub.0k [0124] Wherein: l.sub.0 is the maximum distance between the spiral line and the center of the first base plate 2-1, and when the distance from the intersection of the spiral through-groove and the straight through-groove to the center of the first base plate 2-1 is the maximum distance, the position of the first base plate 2-1 is defined as the initial position; k is a coefficient with a dimension of length/radian; is a radian; l() represents the distance from the intersection of the spiral through-groove and the straight through-groove to the center of the first base plate 2-1 after the spiral line rotates from the initial position; [0125] The straight through-groove plate 3 with the schematic view shown in FIG. 3 comprises a second base plate 3-1 with a straight through-groove and a second side edge 3-2 with an annular cross-section, and the diameter of the inner circle of the second side edge 3-2 is larger than the diameter of outer circle of the first side edge 2-2, and the upper surface of the second base plate 3-1 is in close contact with the lower surface of the first base plate 2-1; [0126] The schematic view of a pinhole formed after a spiral through-groove plate 2 and a straight through-groove plate 3 are superimposed is shown in FIG. 4; [0127] The upper surface of the single crystal silicon wafer 5 and the second base plate 3-1 are respectively located on the image plane and the object plane of the objective lens 4, and the single crystal silicon wafer 5 can complete four-dimensional motion under the bearing of the four-dimensional stage 6; [0128] The four-dimensional stage 6 can complete three-dimensional translation and one-dimensional rotation, and the rotation is performed in the plane determined by the arc light source 1 and the optical axis.

Specific Embodiment 2

[0129] The following is a specific embodiment of the MEMS probe laser etching device of the present invention.

[0130] For the EMS probe laser etching device of the embodiment, it is further defined on the basis of the specific embodiment 1: a scraper is arranged around the straight through-groove of the second base plate 3-1, and a plurality of annular grooves concentric with the second base plate 3-1 are arranged on the upper surface of the second base plate 3-1 and the annular grooves start from and end at the scraper around the straight through-groove; the upper surface of the second base plate 3-1 is also provided with a straight groove in the radial direction, the annular groove and the straight groove are cross-connected, and the annular groove and the straight groove are filled with lubricating oil as shown in FIG. 5, and the lubricating oil is added dropwise between the first side edge 2-2 and the second side edge 3-2.

Specific Embodiment 3

[0131] The following is a specific embodiment of the MEMS probe laser etching device of the present invention.

[0132] For the EMS probe laser etching device of the embodiment, it is further defined on the basis of the specific embodiment 1 and the specific embodiment 2: In the structure of the MEMS probe laser etching device as shown in FIG. 6, the first side edge 2-2 is externally meshed with a gear 7, and the gear is controlled to rotate by a motor 8, and the motor 8 is connected to a controller 9, and the controller 9 is connected to a four-dimensional stage 6.

Specific Embodiment 4

[0133] The following is a specific embodiment of the MEMS probe laser etching device of the present invention.

[0134] For the EMS probe laser etching device of the embodiment, it is further defined on the basis of the specific embodiment 3: a transmission structure is formed between the first side edge 2-2 and the gear 7.

Specific Embodiment 5

[0135] The following is a specific embodiment of the pinhole structure for the MEMS probe laser etching device of the present invention.

[0136] The pinhole structure for MEMS probe laser etching device of the embodiment comprises a spiral through-groove plate 2 and straight through-groove plate 3;

[0137] The spiral through-groove plate 2 with the schematic view shown in FIG. 2 comprises a first base plate 2-1 with a spiral through-groove and a first side edge 2-2 with a circular cross-section, and the outer surface of the side edge 2-2 is provided with teeth to form a gear structure, and the spiral line of the spiral through-groove satisfies the following relationship:

l()=l.sub.0k [0138] Wherein: l.sub.0 is the maximum distance between the spiral line and the center of the first base plate 2-1, and when the distance from the intersection of the spiral through-groove and the straight through-groove to the center of the first base plate 2-1 is the maximum distance, the position of the first base plate 2-1 is defined as the initial position; k is a coefficient with a dimension of length/radian; is a radian; l() represents the distance from the intersection of the spiral through-groove and the straight through-groove to the center of the first base plate 2-1 after the spiral line rotates from the initial position; [0139] The straight through-groove plate 3 with the schematic view shown in FIG. 3 comprises a second base plate 3-1 with a straight through-groove and a second side edge 3-2 with an annular cross-section, and the diameter of the inner circle of the second side edge 3-2 is larger than the diameter of outer circle of the first side edge 2-2, and the upper surface of the second base plate 3-1 is in close contact with the lower surface of the first base plate 2-1; [0140] The schematic view of a pinhole formed after a spiral through-groove plate 2 and a straight through-groove plate 3 are superimposed is shown in FIG. 4; [0141] A scraper is arranged around the straight through-groove of the second base plate 3-1, and a plurality of annular grooves concentric with the second base plate 3-1 are arranged on the upper surface of the second base plate 3-1 and the annular grooves start from and end at the scraper around the straight through-groove; the upper surface of the second base plate 3-1 is also provided with a straight groove in the radial direction, the annular groove and the straight groove are cross-connected, and the annular groove and the straight groove are filled with lubricating oil as shown in FIG. 5, and the lubricating oil is added dropwise between the first side edge 2-2 and the second side edge 3-2.

Specific Embodiment 6

[0142] The following is a specific embodiment of the MEMS probe laser etching method of the present invention.

[0143] The MEMS probe laser etching method of the present invention is applied to the MEMS probe laser etching device of the specific embodiments 1, 2, 3 or 4.

[0144] The laser etching method for MEMS probes as shown in flow chart of the FIG. 7 includes the following steps: [0145] Step a: Parameter calculation [0146] According to the etching spacing d of the single crystal silicon wafer 5, the step angle of the motor 8 is obtained:

[00009]$=\frac{d}{k}.Math.\frac{l_1}{l_2}.Math.\frac{d_1}{d_2}$ [0147] Wherein: [0148] k is the coefficient of the spiral line of the spiral through-groove of the first base plate 2-1 with the length/radian dimension; [0149] l.sub.1 is the distance from the second base plate 3-1 to the center of the objective lens 4; [0150] l.sub.2 is the distance from the upper surface of the single crystal silicon wafer 5 to the center of the objective lens 4; [0151] d.sub.1 is the diameter of the pitch circle of the first side edge 2-2; [0152] d.sub.2 is the diameter of the pitch circle of the gear 7; [0153] Step b: Initial position adjustment [0154] Step b1: Rotate the spiral through-groove plate 2 to the initial position, and move the first etching point to the optical axis, as shown in FIG. 8; [0155] Step b2: Four-dimensional stage 6 adjustment: [0156] Move upward:

[00010]$\left(h_1+h_2\right).Math.\frac{\sqrt{l_0^2+l_1^2}-l_1}{\sqrt{l_0^2+l_1^2}}$ [0157] Move to the right:

[00011]$l_0.Math.\frac{l_2}{l_1}+\left(h_1+h_2\right).Math.\frac{l_0}{\sqrt{l_0^2+l_1^2}}$ [0158] Rotate counterclockwise:

[00012]$\arctan \frac{l_0}{l_1}$ [0159] Wherein: [0160] l.sub.0 is the maximum distance between the spiral line and the center of the first base plate 2-1; [0161] h.sub.1 is the thickness of the single crystal silicon wafer 5; [0162] h.sub.2 is the distance from the center of the rotation axis of the four-dimensional stage 6 to the upper surface; [0163] The relative positional relationship of four-dimensional stage 6 before and after adjustment is shown in FIG. 9; [0164] Step c: Laser etching [0165] Light the arc light source 1 until the etching is completed; [0166] Step d: Progress judgment [0167] Judge whether the current etch line is etched, and if: [0168] Yes, the four-dimensional stage 6 moves forward or backward to the next line for etching; [0169] No, go to step e; [0170] Step e: Four-dimensional stage 6 and motor 8 adjustment [0171] Specifically: [0172] The four-dimensional stage 6 moves downward:

(h.sub.1+h.sub.2).Math.cos .sub.2d.Math.sin .sub.2(h.sub.1+h.sub.2).Math.cos .sub.1 [0173] The four-dimensional stage 6 moves to the left;

[00013]$\frac{l_2}{\tan {}_1}+\left(h_1+h_2\right).Math.\sin {}_1-\frac{l_2}{\tan {}_2}-\left(h_1+h_2\right).Math.\sin {}_2+d.Math.\cos {}_2$ [0174] The four-dimensional stage 6 rotates clockwise:

.sub.1.sub.2 [0175] The motor 8 rotates;

[00014]$\frac{d_1}{d_2}.Math.\frac{l_1}{k}.Math.\left(\tan {}_1-\tan {}_2\right)$ [0176] Wherein: [0177] .sub.1 is the angle between the light beam and the optical axis at the current etching point; [0178] .sub.2 is the angle between the light beam and the optical axis at the next etching point; [0179] The relative positional relationship diagram before and after the adjustment of the four-dimensional stage between two adjacent etchings is shown in FIG. 10; [0180] Return to step c.

Specific Embodiment 7

[0181] The following is a specific embodiment of the MEMS probe laser etching motor and four-dimensional stage driving method of the present invention.

[0182] The MEMS probe laser etching motor and four-dimensional stage driving method of the present invention is applied to the MEMS probe laser etching device of the specific embodiments 1, 2, 3 or 4.

[0183] With the MEMS probe laser etching motor and a four-dimensional stage driving method, the step angle of the motor 8, the upward or downward movement distance, the left or right movement distance, and the clockwise or counterclockwise rotation angle of the four-dimensional stage 6 are obtained from the etching spacing d of a single crystal silicon wafer 5.

Specific Embodiment 8

[0184] The following is a specific embodiment of the MEMS probe laser etching motor and four-dimensional stage driving method of the present invention.

[0185] The MEMS probe laser etching motor and four-dimensional stage driving method of the present invention is applied to the MEMS probe laser etching device of the specific embodiments 1, 2, 3 or 4; it's further defined on the basis of the specific embodiment 6:

[0186] The etching spacing of the single crystal silicon wafer is d, then:

[0187] The step angle of the motor 8 is:

[00015]$=\frac{d}{k}.Math.\frac{l_1}{l_2}.Math.\frac{d_1}{d_2}$

[0188] The four-dimensional stage 6 moves upward or downward:

(h.sub.1+h.sub.2).Math.cos .sub.2d.Math.sin .sub.2(h.sub.1+h.sub.2).Math.cos .sub.1

[0189] The four-dimensional stage 6 moves to the left or to the right:

[00016]$\frac{l_2}{\tan {}_1}+\left(h_1+h_2\right).Math.\sin {}_1-\frac{l_2}{\tan {}_2}-\left(h_1+h_2\right).Math.\sin {}_2+d.Math.\cos {}_2$

[0190] The four-dimensional stage 6 rotates clockwise or counterclockwise:

.sub.1.sub.2 [0191] Wherein: [0192] k is the coefficient of the spiral line of the spiral through-groove of the first base plate 2-1 with the length/radian dimension; [0193] l.sub.1 is the distance from the second base plate 3-1 to the center of the objective lens 4; [0194] l.sub.2 is the distance from the upper surface of the single crystal silicon wafer 5 to the center of the objective lens 4;

[0195] d.sub.1 is the diameter of the pitch circle of the first side edge 2-2;

[0196] d.sub.2 is the diameter of the pitch circle of the gear 7;

[0197] h.sub.1 is the thickness of the single crystal silicon wafer 5;

[0198] h.sub.2 is the distance from the center of the rotation axis of the four-dimensional stage 6 to the upper surface; [0199] .sub.1 is the angle between the light beam and the optical axis at the current etching point; [0200] .sub.2 is the angle between the light beam and the optical axis at the next etching point; [0201] The relative positional relationship diagram before and after the adjustment of the four-dimensional stage between two adjacent etchings is shown in FIG. 10; [0202] The movement direction and rotation direction of the four-dimensional stage 6 are determined by the rotation direction of the motor 8.

Specific Embodiment 9

[0203] The following is a specific embodiment of the optical focusing structure for the MEMS probe laser etching device of the present invention.

[0204] The optical focusing structure for the MEMS probe laser etching device of the embodiment is based on the MEMS probe laser etching device of the specific embodiment 1, 2, 3 or 4. In the MEMS probe laser etching device, the spiral through-groove plate 2 is replaced by the upper-slotted through-groove plate 21, and the straight through-groove plate 3 is replaced by the lower-slotted through-groove plate 31, the single crystal silicon wafer 5 is replaced with a plane mirror 51 of the same thickness, the thickness of the upper-slotted through-groove plate 21 is the same as that of the first base plate 2-1 of the spiral through-groove plate 2, the thickness of the lower-slotted through-groove plate 31 is the same as that of the second base plate 3-1 of the straight through-groove plate 3, the thickness of the plane mirror 51 is the same as that of the single crystal silicon wafer 5, and the upper surface of the upper-slotted through-groove plate 21 is in close contact with the lower-slotted through-groove plate 31; a prism 10 is arranged between the lower-slotted through-groove plate 31 and the objective lens 4, and an image sensor 11 is arranged on the side edge of the prism 10. Along the direction of the optical axis, the distance from the lower surface of the lower-slotted through-groove plate 31 to the prism 10 is the same as the distance from the image surface of the image sensor 11 to the prism 10, with the schematic view shown in FIG. 11. It should be noted that FIG. 11 is based on the MEMS probe laser etching device shown in FIG. 1.

Specific Embodiment 10

[0205] The following is a specific embodiment of the optical focusing method for the MEMS probe laser etching device of the present invention.

[0206] The optical focusing method for the MEMS probe laser etching device of the embodiment 9 is applied to the optical focusing structure for the MEMS probe laser etching device of the specific embodiment 9.

[0207] The optical focusing method for MEMS probe laser etching device as shown in the flow chart of FIG. 12 includes the following steps: [0208] Step a: Replace and add the components [0209] Replacement: In the MEMS probe laser etching device, the spiral through-groove plate 2 is replaced by the upper-slotted through-groove plate 21, and the straight through-groove plate 3 is replaced by the lower-slotted through-groove plate 31, and the single crystal silicon wafer 5 is replaced with a plane mirror 51; [0210] Addition: A prism 10 is arranged between the lower-slotted through-groove plate 31 and the objective lens 4, and an image sensor 11 is arranged on the side edge of the prism 10. Along the direction of the optical axis, the distance from the highest point of the arc light source 1 to the prism 10 is the same as the distance from the image surface of the image sensor 11 to the prism [0211] Step b: Data acquisition [0212] The four-dimensional stage 6 moves upward and downward the full range for one cycle, and obtains a series of focused and defocused spot images on the image sensor 11, and records the mapping relationship between the position of the four-dimensional stage 6 in the upward and downward direction and the image; [0213] Step c: Data processing [0214] The spot diameter is obtained according to the focused and defocused spot images on the image sensor 11, and the mapping relationship between the position of the four-dimensional stage 6 in the upward and downward direction and the spot diameter is established; [0215] Step d: Complete the calibration [0216] Determine the minimum value of the spot diameter, and determine the position of the four-dimensional stage 6 in the upward and downward direction corresponding to the minimum value according to the mapping relationship between the position of the four-dimensional stage 6 in the upward and downward direction and the spot diameter, and move the four-dimensional stage 6 to the position.

Specific Embodiment 11

[0217] The following is a specific embodiment of the optical focusing method for the MEMS probe laser etching device of the present invention.

[0218] The optical focusing method for the MEMS probe laser etching device of the embodiment is further defined on the basis of the specific embodiment 10: In step c, the spot diameter is obtained according to the focused and defocused spot images obtained by the image sensor 11. It can be achieved by the following method: By setting a grayscale threshold, pixels in the spot image with a grayscale lower than the grayscale threshold are set to 0, and pixels greater than the grayscale threshold are set to 255. Then, the processed image is fitted circumferentially to synthesize a circular spot, and the diameter of the circular spot is determined.

Specific Embodiment 12

[0219] The following is a specific embodiment of the optical focusing method for the MEMS probe laser etching device of the present invention.

[0220] The optical focusing method for the MEMS probe laser etching device of the embodiment is further defined on the basis of the specific embodiment 10: In step c, the spot diameter is obtained according to the focused and defocused spot images obtained by the image sensor 11. It can be achieved by the following method: In both the focused and defocused spot images, a fixed area with the center of the light spot as the center is selected, the sum of the grayscale values of all pixels within the fixed area is calculated and the reciprocal of the calculated results is used as the spot diameter.

[0221] Finally, it should be noted that the technical features in all the above specific embodiments can be permuted and combined as long as they are not contradictory. Those skilled in the art can exhaust every permutation and combination according to the mathematical knowledge of permutation and combination learned in high school. The results after all the permutations and combinations should be understood as being disclosed by this application.