Wafer inspection pre-alignment system and method

Abstract

The application relates to the technical field of chip detection processing equipment, and discloses a wafer detection pre-alignment system, which comprises a precision motion unit, an optical detection unit, a vacuum unit and a drive control unit arranged on a rack. The vacuum unit realizes vacuum adsorption of a wafer. The vacuum unit is arranged on the precision motion unit. The optical detection unit is located on one side of the precision motion unit. The drive control unit controls the precision motion unit to drive the vacuum unit to send the wafer to the optical detection unit for detection. The motion of the precision motion unit comprises XYZ-axis direction motion and C-axis rotation of the vacuum unit. The application further discloses a corresponding pre-alignment method. The application adopts the differential principle to carry out detection, is easy to distinguish, has high alignment precision, good stability and strong applicability.

Description

Technical Field

[0001] This invention relates to the field of chip inspection and processing equipment technology, and in particular to a wafer inspection pre-alignment system and method. Background Technology

[0002] As the core of the electronics and information industry, integrated circuits (ICs) have been developing rapidly driven by market demand and have become a strategic industry affecting national economic, political, and defense security. With the continuous improvement of IC integration levels, the semiconductor manufacturing industry has increasingly higher requirements for wafer size specifications and processing precision. Wafer sizes are becoming larger, materials are becoming more diverse, and processing precision has reached the nanometer level.

[0003] Semiconductor manufacturing involves processes such as grinding, polishing, coating, photolithography, etching, oxidation, dicing, and packaging. Each process requires obtaining the wafer's position and orientation beforehand, a process known as wafer pre-alignment. While a wafer pre-alignment system is an auxiliary system in semiconductor manufacturing equipment, it integrates technologies from multiple disciplines, including mechanics, electronics, optics, software, and algorithms. The accuracy and efficiency of the wafer pre-alignment system directly affect the yield and productivity of semiconductor manufacturing. Therefore, developing miniaturized, integrated, high-precision, and high-efficiency wafer pre-alignment systems has significant practical importance and application value.

[0004] Wafer pre-alignment systems have evolved through two stages: mechanical and optical pre-alignment. Mechanical pre-alignment is entirely dependent on the precision of the mechanical structure, resulting in relatively low alignment accuracy. Optical pre-alignment is currently more widely used, utilizing optical sensors to detect the wafer's edges and employing specific algorithms to determine the wafer's center position and notch orientation. Analysis of existing products on the market reveals the following shortcomings:

[0005] 1. Poor accuracy:

[0006] Currently, pre-alignment systems on the market typically use stepper motors for driving and only use linear array optical sensors on one side of the wafer for visual inspection, which limits accuracy.

[0007] 2. Low efficiency:

[0008] For example, the θ-R type pre-alignment system contains three degrees of freedom: Y, Z, and θ. Since the alignment of the wafer center can only be performed along one horizontal axis, it suffers from complex calculations and low efficiency.

[0009] 3. Poor applicability:

[0010] Although semiconductor manufacturing demands increasingly larger wafer sizes, the complexity and immaturity of large-size wafer processes mean that wafer sizes remain diverse, with common sizes including 4-inch, 6-inch, 8-inch, and 12-inch wafers. At the same time, the variety of semiconductor materials necessitates that wafer pre-alignment systems be applicable to opaque, semi-transparent, and transparent wafers simultaneously.

[0011] Products on the market generally specify a particular scope of application, and different modules need to be selected to achieve the desired effect for wafers of different sizes. Summary of the Invention

[0012] The purpose of this invention is to solve the above-mentioned problems and provide a wafer inspection pre-alignment system and method that uses the differential principle for detection, which is easy to distinguish, has high alignment accuracy, good stability, and strong applicability.

[0013] The technical solution adopted in this invention is:

[0014] A wafer inspection pre-alignment system is characterized by comprising a precision motion unit, an optical inspection unit, a vacuum unit, and a drive and control unit mounted on a rack. The vacuum unit performs vacuum adsorption on the wafer and is mounted on the precision motion unit. The optical inspection unit is located on one side of the precision motion unit. The drive and control unit controls the precision motion unit to drive the vacuum unit to deliver the wafer to the optical inspection unit for inspection. The motion of the precision motion unit includes movement in the XYZ axis direction and driving the vacuum unit to rotate along the C-axis.

[0015] Furthermore, the maximum travel distance of the precision motion unit in the Y-axis direction is greater than 150mm.

[0016] Furthermore, the wafer has a diameter of ф50~ф300mm.

[0017] Furthermore, the optical detection unit includes a wafer space and a light source, a collimating lens, a first filter, and a first optical sensor disposed above the wafer space. The first optical sensor is located above the wafer and receives reflected light from the wafer.

[0018] Furthermore, the first optical sensor is located on the upper side of the wafer space, and a beam splitter is disposed below the collimating lens, which sends the reflected light to the first optical sensor.

[0019] Furthermore, a second filter and a second optical sensor are disposed below the wafer space. The optical sensor is located below the wafer space, and the pixel order of the first optical sensor and the second optical sensor is reversed.

[0020] A wafer inspection pre-alignment method, characterized by comprising the following steps:

[0021] Step 1: System initialization and reset;

[0022] Step 2: The robotic arm places the wafer onto the vacuum unit;

[0023] Step 3: The precision motion unit delivers the wafer to the position of the optical inspection unit;

[0024] Step 4: After the optical detection unit detects the wafer, the vacuum unit adsorbs and fixes the wafer;

[0025] Step 5: The C-axis rotates 360°, and the optical detection unit collects the wafer edge position and notch position signals and sends them to the drive and control unit;

[0026] Step 6: Calculate the quadrant in which the wafer center is located and its offset from the C-axis center on the X and Y axes;

[0027] Step 7: The vacuum unit releases the wafer, the Z-axis moves upward, and the wafer detaches from the vacuum unit;

[0028] Step 8: Adjust the offsets of the X and Y axes to make the wafer concentric with the C axis;

[0029] Step 9: The Z-axis moves downwards, and the vacuum unit adsorbs the wafer;

[0030] Step 10: The C-axis rotates 360°, and the optical detection unit collects the wafer edge position and notch position signals and sends them to the drive and control unit;

[0031] Step 11: Calculate the quadrant in which the center of the gap is located;

[0032] Step 12: Based on the quadrant where the center of the notch is located, rotate the C-axis by the required angle to complete the notch positioning;

[0033] Step 13: The vacuum unit releases the wafer, and the robotic arm removes the wafer.

[0034] The beneficial effects of this invention are:

[0035] (1) Amplification is achieved through the differential principle, making the signal easier to identify and acquire;

[0036] (2) It avoids common-mode error, has strong anti-interference ability, and good EMC performance;

[0037] (3) It has strong applicability and can be applied to wafers with diameters of ф50 to ф300.

[0038] (4) The positioning accuracy is greatly improved compared with traditional mechanical or optical modes;

[0039] (5) Applicable to wafers of various transparent and non-transparent materials;

[0040] (6) It can meet the pre-alignment requirements of wafers for nanoscale processes such as photolithography, etching, and testing. Attached Figure Description

[0041] Appendix Figure 1 This is a schematic diagram of the pre-alignment system of the present invention;

[0042] Appendix Figure 2 This is a schematic diagram of the pre-alignment system workstation transformation;

[0043] Appendix Figure 3 This is a schematic diagram of the optical detection unit.

[0044] Appendix Figure 4 This is a schematic diagram of the photosensitive optical path of the first optical sensor;

[0045] Appendix Figure 5 This is a schematic diagram of the signal output of the first optical sensor;

[0046] Appendix Figure 6 This is a schematic diagram of the photosensitive optical path of the second optical sensor;

[0047] Appendix Figure 7 This is a schematic diagram of the signal output of the second optical sensor;

[0048] Appendix Figure 8 This is a flowchart of the pre-alignment method;

[0049] Appendix Figure 9 This is a schematic diagram illustrating the movement patterns of points on the edge transition zone;

[0050] Appendix Figure 10 This is a schematic diagram comparing single-ended signals and differential signals. Detailed Implementation

[0051] The specific embodiments of the wafer inspection pre-alignment system and method of the present invention will be described in detail below with reference to the accompanying drawings.

[0052] See appendix Figure 1 The wafer inspection pre-alignment system includes a precision motion unit 10, an optical inspection unit 11, a vacuum unit 12, and a drive and control unit 13 mounted on a rack. The vacuum unit 12 performs vacuum adsorption on the wafer and is mounted on the precision motion unit 10. The optical inspection unit 11 is located on one side of the precision motion unit 10. The drive and control unit 13 controls the precision motion unit 10 to drive the vacuum unit 12 to deliver the wafer to the optical inspection unit 11 for inspection. The motion of the precision motion unit 10 includes movement in the XYZ axis direction and rotation of the vacuum unit along the C axis.

[0053] The system comprises an optical inspection unit 11 for detecting wafer edge contour data, and a precision motion unit 10 for adjusting wafer center eccentricity and notch direction. The precision motion unit 10 includes four motion axes (X, Y, Z, and C) and is a θ-XY type pre-alignment system. A vacuum unit 12 is used for wafer adsorption and release. A drive and control unit 13 receives, processes, and transmits data from the optical inspection unit, and controls the precision motion unit 10. The drive and control unit 13 uses a multi-axis motion control card integrated into the system and is connected to host computer software for control.

[0054] See appendix Figure 2 After amplifying the Y-axis motion stroke of the precision motion unit, according to the principle of workstation transformation, let the radii of the large and small wafers be R1 and R2 respectively, then: ΔY = R1 - R2. Further, ΔY max = R1 max -R2 min .

[0055] Assuming the wafer diameter is a maximum of 300mm and a minimum of 50mm, then ΔY max = R1 max -R2 min =300 / 2-50 / 2=125 (mm). When the Y-axis travel is greater than 150mm, the wafer pre-alignment system described in the patent can be applied to wafers with diameters from ф50 to ф300.

[0056] See appendix Figure 3 The optical detection unit is structured as follows: a point light source 1, a lens 2, an aperture 4, a beam splitter 5, and a first filter 6 are arranged on one side of wafer 7 (the upper side in the diagram), and a second filter 8 is arranged on the other side of wafer 7 (the lower side in the diagram). Simultaneously, a first optical sensor 3 and a second optical sensor 9 are respectively arranged on both sides of the wafer 7 under test (the upper and lower sides in the diagram) for light reception and signal conversion; the pixel order of the two sensors is exactly reversed.

[0057] See appendix Figure 4 The light-sensing path of the first optical sensor is as follows: the light beam emitted by the point light source 1 is collimated by the lens 2, and then passes through the beam splitter 5 and the first filter 6 in sequence after being limited by the aperture 4. At this time, the part of the light beam blocked by the wafer 7 will be reflected back, and then pass through the first filter 6 again. After being reflected by the beam splitter prism, it illuminates the first optical sensor 3.

[0058] The photosensitive area of ​​the first optical sensor 3 is the part of the light beam reflected by the wafer 7, and its output signal is shown in the attached figure. Figure 5 As shown (taking a linear array optical sensor as an example).

[0059] See appendix Figure 6The optical path of the second optical sensor is as follows: the light beam emitted by point light source 1 is collimated by lens 2, and then passes through the beam splitter 5 and the first filter 6 in sequence after being limited by aperture 4. At this time, the light beam can be split into two parts. One part of the light is projected into wafer 7, then passes through the second filter 8, and finally illuminates the second optical sensor 9. The other part of the light that is not blocked by wafer 7 will directly pass through the second filter 8 and then illuminate the second optical sensor 9.

[0060] The photosensitive area of ​​the second optical sensor 9 has two parts: one part is the light beam projected onto the wafer 7, and the other part is the light beam not blocked by the wafer 7. Its output signal is shown in the attached figure. Figure 7 As shown (taking a linear array optical sensor as an example).

[0061] See appendix Figure 5 , 7 ,T a The corresponding beam of light is partially reflected due to being blocked by wafer 7, T b The corresponding beam is the portion of light incident on wafer 7. Sa and Sb are both edge transition zones. Qa is the unsensitized portion of the first optical sensor, and Qb corresponds to the beam that is not blocked by wafer 7.

[0062] analyze Figure 5 and Figure 7 According to relevant optical theories, the edge transition zone S a With S b Center point H a With H b This refers to the theoretical wafer outline position. Since the pixel order of the first optical sensor and the second optical sensor is exactly reversed, then H... a Point and H b The motion of the point follows the exact opposite pattern; furthermore, H a Point and H b A point can represent two contour points on a wafer that are 180° apart.

[0063] See appendix Figure 8The method and steps for pre-alignment using a pre-alignment system are as follows: After system startup, the system is initialized, and the host computer software returns the X, Y, Z, and C axes to zero. A robotic arm places the wafer on the wafer support platform of the vacuum unit, triggering an optical sensor to detect whether the wafer has been delivered into the optical detection unit. Once the wafer is confirmed to be in the designated position, the vacuum unit holds and fixes it in place. The C-axis is driven to rotate 360°, and the optical detection unit acquires the wafer's edge and notch positions, sending the signals to the control card of the drive and control unit. The control card's A / D module converts the received analog signals into digital signals and transmits them to the host computer software. The host computer software uses a circle fitting algorithm to calculate the quadrant where the wafer's center is located, as well as its offset from the C-axis center on the X and Y axes. Simultaneously, the vacuum unit releases the wafer, driving the Z-axis upwards, and the wafer detaches from the vacuum unit.

[0064] Then, based on the quadrant where the wafer center is located and the offsets from the C-axis center on the X and Y axes, the precision motion unit drives the X and Y axes to move, making the wafer concentric with the C-axis and completing wafer centering. After completion, the Z-axis moves downward, and the wafer descends to the vacuum unit, where it is adsorbed.

[0065] At this point, the C-axis is rotated 360°, and the optical detection unit acquires the wafer edge position and notch position. The host computer software calculates the quadrant where the notch position is located. Based on this quadrant information, the C-axis rotates the wafer to the corresponding angle, completing the notch positioning. After completion, the vacuum unit releases the wafer, and the robotic arm removes it. This completes one pre-alignment.

[0066] After the host computer controls the precision motion unit to return to zero, it performs the pre-alignment operation for the next wafer.

[0067] See appendix Figure 8 , for H a Point and H b The motion law of the point is as follows: point O is the center of wafer rotation, O´ is the initial position (θ=0) of the wafer center, O" is the center of the wafer after rotating by an angle θ, and Δr is the wafer eccentricity.

[0068] H a Switch between CD, H b Transform between AB, CH a With BH b The change follows the law of the cosine function, and its expression when considering system noise is:

[0069] CH a =ξΔr·cos(θ+π+φ)+Δr+k+f(x)

[0070] =-ξΔr·cos(θ+φ)+Δr+k+f(x);

[0071] BH b =ξΔr·cos(θ+φ)+Δr+k+f(x)

[0072] ξ: Random noise factor; φ: Phase difference;

[0073] k: White noise; f(x): Common-mode noise;

[0074] When θ=0, CH a =-ξΔr·cosφ+Δr+k+f(x1);

[0075] BH b =ξΔr·cosφ+Δr+k+f(x1)

[0076] When θ=π, CH a =ξΔr·cosφ+Δr+k+f(x2);

[0077] CH a =-ξΔr·cosφ+Δr+k+f(x2);

[0078] The following conclusions can be drawn from analyzing the first optical sensor or the second optical sensor in isolation:

[0079] 2Δr=|2ξΔr·cosφ+ f(x2)-f(x1)|

[0080] Further results were obtained:

[0081] Δr(1-ξcosφ)=[f(x2)-f(x1)] / 2 or

[0082] Δr(1+ξcosφ)=[f(x1)-f(x2)] / 2

[0083] It is evident that common-mode error is introduced when analyzing the signals of the first or second optical sensor separately. Furthermore, due to the presence of common-mode error, ξ and φ cannot be accurately calibrated.

[0084] Through append Figure 8 The process and appendix Figure 9 By comprehensively analyzing the signals from the first optical sensor and the second optical sensor, we can obtain:

[0085] OH a =OC+CH a =OC-ξΔr·cos(θ+φ)+Δr+k+f(x);

[0086] OH b =OB+BH b =OC+ξΔr·cos(θ+φ)+Δr+k+f(x);

[0087] Thus, we can obtain two signals of equal magnitude but opposite direction (OH). a OH b (the length change), i.e., the differential signal.

[0088] Further, we obtain: OH b -OH a =2ξΔr•cos(θ+φ;

[0089] By calibrating ξ and φ, and based on the measured OH... b With OH a Δr can then be calculated (note that the relative position of the optical sensor and the rotation center O point also needs to be calibrated).

[0090] Therefore, it is evident that comprehensive analysis of the differential signals from the first and second optical sensors can eliminate common-mode errors and accurately calibrate ξ and φ, resulting in higher precision. The differential signals generated by the first and second optical sensors avoid common-mode errors, exhibit strong anti-interference capabilities, and demonstrate good EMC performance.

[0091] See appendix Figure 10 By comprehensively analyzing the differential signals from the first and second optical sensors, common-mode errors can be eliminated, and ξ and φ can be accurately calibrated, thus achieving higher accuracy. This is demonstrated by comparing the differential signal generated by the pair of optical sensors in the figure with the single-ended signal output by a single optical sensor. b CH a A single-ended signal with varying length is differentially divided to double its amplitude, resulting in greater signal energy and making it easier to identify and acquire.

[0092] The first optical sensor receives the light reflected from the wafer, and the second optical sensor receives the light projected onto the wafer and the light not blocked by the wafer. That is, both the light reflected and transmitted by the wafer can be effectively received. Therefore, the wafer pre-alignment system described in this patent is applicable to wafers of transparent, semi-transparent and non-transparent semiconductor materials of all generations.

[0093] The relevant parameters of the wafer pre-alignment system based on the differential principle described in this patent are shown in the table below:

[0094] index numerical values unit Wafer center positioning accuracy ±0.025 mm Wafer notch positioning accuracy ±0.04 ° Positioning time 2 s Applicable wafer diameter ф50~ф300 mm Applicable wafer materials Transparent, translucent, opaque -

[0095] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A wafer inspection pre-alignment system, characterized in that: The system includes a precision motion unit, an optical detection unit, a vacuum unit, and a drive and control unit mounted on a rack. The vacuum unit performs vacuum adsorption on the wafer and is mounted on the precision motion unit. The optical detection unit is located to one side of the precision motion unit. The drive and control unit controls the precision motion unit to drive the vacuum unit to deliver the wafer to the optical detection unit for detection. The motion of the precision motion unit includes movement along the XYZ axes and rotation of the vacuum unit along the C-axis. The optical detection unit includes a wafer space and a light source, a collimating lens, a first filter, and a first optical sensor positioned above the wafer space. The first optical sensor is located above the wafer and receives reflected light from the wafer. The first optical sensor is located on the side above the wafer space. A beam splitter is positioned below the collimating lens and sends reflected light to the first optical sensor. A second filter and a second optical sensor are positioned below the wafer space. The first and second optical sensors have reversed pixel order. The differential signals of the first and second optical sensors are analyzed to eliminate common-mode errors.

2. The wafer inspection pre-alignment system according to claim 1, characterized in that: The maximum travel distance of the precision motion unit in the Y-axis direction is greater than 150mm.

3. The wafer inspection pre-alignment system according to claim 2, characterized in that: The wafer has a diameter of ф50 to ф300 mm.

4. A wafer inspection pre-alignment method, using the wafer inspection pre-alignment system as described in any one of claims 1 to 3, characterized in that: Includes the following steps: Step 1: System initialization and reset; Step 2: The robotic arm places the wafer onto the vacuum unit; Step 3: The precision motion unit delivers the wafer to the position of the optical inspection unit; Step 4: After the optical detection unit detects the wafer, the vacuum unit adsorbs and fixes the wafer; Step 5: The C-axis rotates 360°, and the optical detection unit collects the wafer edge position and notch position signals and sends them to the drive and control unit; Step 6: Calculate the quadrant in which the wafer center is located and its offset from the C-axis center on the X and Y axes; Step 7: The vacuum unit releases the wafer, the Z-axis moves upward, and the wafer detaches from the vacuum unit; Step 8: Adjust the offsets of the X and Y axes to make the wafer concentric with the C axis; Step 9: The Z-axis moves downwards, and the vacuum unit adsorbs the wafer; Step 10: The C-axis rotates 360°, and the optical detection unit collects the wafer edge position and notch position signals and sends them to the drive and control unit; Step 11: Calculate the quadrant in which the center of the gap is located; Step 12: Based on the quadrant where the center of the notch is located, rotate the C-axis by the required angle to complete the notch positioning; Step 13: The vacuum unit releases the wafer, and the robotic arm removes the wafer.

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