JPH07221164A - Alignment method of semiconductor wafer and pick up method of semiconductor pellet - Google Patents

Abstract

PURPOSE:To provide the title alignment method of semiconductor wafer capable of automatically computing the gradient angle to be automatically corrected for efficient alignment adjustment of a scribed wafer making an obscure gradient angle. CONSTITUTION:The title alignment method of semiconductor wafer is composed of the two steps as follows i.e., the first step of recognizing and processing the pellet picture images applying the previously prepared square reference pattern to the picture image signals transmitted by photographing plural pellets of the wafers 15 fixed on an XY stage of a semiconductor pellet mounting device by a television camera 17 so as to be stored in a picture image memory as well as the second step of computing the wafer gradient angle according to the processed pellet picture images so that the XY stage may be driven by the results of computation for automatic alignment adjustment to correct the wafer gradient.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment method for aligning a semiconductor wafer and a pickup method for picking up a semiconductor pellet when mounting the semiconductor pellet in an assembly process of a semiconductor device.

[0002]

2. Description of the Related Art Generally, in the process of assembling a semiconductor device, a semiconductor wafer after element formation is scribed on a sheet and divided into individual pellets, and the wafer is stretched (hereinafter, referred to as a scribed sheet). (Referred to as a wafer), the pellet is picked up and mounted on a lead frame or the like.

In this case, the tilt angle of the wafer after scribing and the position of each pellet are ambiguous, and in order to improve the efficiency at the time of picking up, the tilt of the wafer is adjusted to a constant state and the position of the pellet is detected. There is a need.

Therefore, conventionally, when the wafer after scribing is mounted on the XY stage of the pellet mounting apparatus, the tilt of the wafer is manually adjusted by the operator, so that the alignment adjustment time becomes long.

Further, the position of the pellet is detected by performing image recognition processing for each pellet in a fixed direction on the wafer mounted on the XY stage of the pellet mounting apparatus. In this case, if the pellets cannot be detected in the peripheral portion of the wafer, the pickup direction is reversed and the stage is changed, so there is much waste in the movement of the XY stage.
This is leading to a decline in operating rate.

[0006]

As described above, since the conventional semiconductor wafer alignment method is carried out manually by the operator, there is a problem that the adjustment time becomes long. Further, the conventional semiconductor pellet pick-up method has a problem that movement of the XY stage of the pellet mount device is wasteful, leading to a decrease in operating rate.

The present invention has been made to solve the above-mentioned problems. The tilt angle of a scribed wafer mounted on an XY stage of a semiconductor pellet mounting apparatus at an ambiguous tilt angle is automatically adjusted. It is an object of the present invention to provide a semiconductor wafer alignment method that can be calculated dynamically and the tilt can be automatically corrected to improve the efficiency of wafer alignment adjustment.

Further, according to the present invention, when picking up pellets from a wafer after scribing mounted on the XY stage of the semiconductor pellet mounting apparatus, the pickup position can be surely detected even in the peripheral portion of the wafer, and the XY of the pellet mounting apparatus can be detected. An object of the present invention is to provide a method of picking up a semiconductor pellet, which can improve the efficiency of the movement of the stage and further improve the efficiency of pellet mounting.

[0009]

A semiconductor wafer alignment method according to the present invention is a method of stretching a semiconductor wafer, which is scribed on a sheet after formation of semiconductor elements and scribed into individual pellets. Step of mounting on the XY stage of the semiconductor pellet mounting apparatus in the above state, and the level of the analog image signal obtained by photographing a plurality of pellets of the semiconductor wafer on the XY stage with a television camera, based on a certain threshold value. Second, binarization processing is performed to convert into a digital image signal representing light and shade, and a pellet image is subjected to recognition processing using a quadrilateral reference pattern prepared in advance and stored in an image memory.
Step, and calculate the tilt angle of the semiconductor wafer based on the pellet image obtained in the second step,
And a third step for automatically performing alignment adjustment for correcting the inclination of the semiconductor wafer by driving the XY stage based on the calculation result.

According to the method of picking up semiconductor pellets of the present invention, a semiconductor wafer, which is scribed on a sheet after the formation of semiconductor elements and scribed into individual pellets, is subjected to the semiconductor operation while the sheet is stretched. The first step of mounting on the XY stage of the pellet mount device, and the binarization processing of the level of the analog image signal obtained by photographing a plurality of pellets of the semiconductor wafer on the XY stage with a television camera, based on a certain threshold value. And convert it to a digital image signal that expresses light and shade,
A second step of recognizing and storing a pellet image in an image memory using a quadrilateral reference pattern prepared in advance, and calculating the tilt angle of the semiconductor wafer based on the pellet image obtained in the second step. The third step of automatically performing alignment adjustment for correcting the tilt of the semiconductor wafer by driving the XY stage based on the calculation result, and moving the position of the reference image to four points on the outer circumference of the wafer. A fourth step of detecting coordinate values and automatically calculating the center position and radius of the semiconductor wafer based on the coordinate values; and, after the completion of the fourth step, moving the XY stage to pick up a semiconductor pellet. While setting the start position, referring to the center position of the semiconductor wafer, the calculation result of the radius and a plurality of reference images prepared in advance Characterized by comprising a fifth step of sequentially advances the pickup process of the conductor pellets.

[0011]

The alignment adjustment can be automated for the scribed wafer mounted on the XY stage of the semiconductor pellet mounter at an ambiguous tilt angle.

As a result, the efficiency of alignment adjustment can be improved, and continuous operation of the semiconductor pellet mounting apparatus having a mechanism for automatically loading wafers on the XY stage (automatic loading mechanism for a plurality of wafers) becomes possible. Become.

Further, since the pickup process of the semiconductor pellet is advanced while referring to the calculation result of the center position and the radius of the semiconductor wafer, the pickup position can be surely detected even in the peripheral portion of the wafer, and the movement of the XY stage of the pellet mounting apparatus can be performed. The efficiency of pellet mounting can be improved, and the efficiency of pellet mounting can be improved.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a perspective view schematically showing an example of a pellet mount device used for carrying out a semiconductor wafer alignment method and a semiconductor pellet pickup method of the present invention during a semiconductor device assembly process.

In this pellet mounter, 10
Is an XY stage, 11 is a pulse motor for driving the XY stage in the X direction in the horizontal plane, 12 is a pulse motor for driving the XY stage in the Y direction in the horizontal plane, 1
3 is a pulse motor for driving the XY stage in the rotation direction θ in the horizontal plane, and 14 is a motor drive circuit for driving each of the pulse motors.

Reference numeral 15 denotes a semiconductor wafer which is scribed in a state of being attached to a sheet after element formation and divided into individual pellets, and the sheet is stretched and the above-mentioned X is formed.
It is mounted on the Y stage.

Reference numeral 16 is a light source for illuminating the wafer 15 obliquely from above, and 17 is an industrial television camera installed above the central portion of the wafer 15 for imaging a plurality of pellets of the wafer and its peripheral portion. Reference numeral 18 denotes a camera control device (for example, solid-state camera; CCD camera) for controlling the CCD camera 12.

An image processing device 19 converts an analog image signal of an image obtained by the CCD camera 17 into a digital signal, stores the digital signal in an image memory, and processes the stored data. . Reference numeral 20 denotes an image monitor device for monitoring the image supplied from the image processing device.

Reference numeral 21 denotes a pellet pick-up device for picking up a pellet group of the wafer in a predetermined order and mounting it on a lead frame or the like after the semiconductor wafer on the XY stage 10 is aligned.

The image processing apparatus 19 includes a computer system and has processing means as described below. (1) Means for pre-storing a digital image signal for displaying a square reference image indicating a reference position on the monitor screen in an image memory.

(2) Means for storing in the image memory the pellet image obtained by binarizing the analog image signal obtained by picking up the image of the semiconductor wafer 15 with the CCD camera 17 and converting the analog image signal into a digital signal representing light and shade.

(3) Means for displaying the reference image and pellet image stored in the image memory on the monitor screen. (4) Data processing is performed on the digital image signal of the pellet image based on the digital image signal of the reference image to calculate the wafer tilt angle, the outer peripheral position, the center position, and the radius,
Means for controlling the motor drive circuit 14 based on the result to control the XY stage 10 to a predetermined position in the horizontal plane.

FIG. 2 is a flow chart showing the flow of processing in the first embodiment of the semiconductor wafer alignment method and semiconductor pellet pick-up method of the present invention. 3 to 15 are diagrams for explaining the display image on the monitor screen or the processing contents at each stage of the processing of FIG.

Next, an example of a semiconductor wafer alignment method and a semiconductor pellet pickup method will be described with reference to FIGS. Step S
In No. 1, the semiconductor wafer 15 in the state of being scribed on a sheet after being formed with semiconductor elements and divided into individual pellets is mounted on the XY stage 10 of the semiconductor pellet mounting apparatus with the sheet being stretched. In this case, each pellet of the wafer is arranged in an ambiguous state in the X direction and the Y direction.

In step S2, the plurality of pellets of the semiconductor wafer 15 on the XY stage 10 are subjected to C under oblique illumination.
The level of the analog signal of the image captured by the CD camera 17 is binarized with a certain threshold value as a reference to be converted into a digital signal representing the light and shade, and a pellet image formed of this digital signal is subjected to recognition processing to obtain an image. Store in memory.

At this time, as a pellet image recognition processing method, for example, Japanese Patent Application No. 56-238 filed by the applicant of the present application.
No. 68 (Japanese Patent Laid-Open No. 57-137978), the correlation coefficient between the input data and the reference data prepared in advance is calculated as disclosed in “Pattern detection apparatus”, and the reference data is calculated from the calculated output. The input data having the best pattern match is determined. Details of this pattern detection device will be described later.

In step S3, the reference image and pellet image stored in the image memory are displayed on the monitor screen, and as shown in FIG. The position of the reference image R is adjusted so that the center of the individual pellet image 15a and the center of the reference image R coincide with each other. The coordinate position of the first corner of the reference image R on the monitor screen after this position adjustment is represented by X ₀ , Y ₀ (unit is pixel).

In step S4, the XY stage 10 is controlled to move in the X direction of the pellet arrangement direction by one pellet pitch (stored in advance),
At the position after moving by one pellet pitch, as shown in FIG. 4, the position of the reference image R is again adjusted so that the centers of four vertically and horizontally adjacent pellet images 15a coincide with the center of the reference image R. adjust. The coordinate position of the first corner of the reference image R on the monitor screen after this position adjustment is set to X ₁ , Y
Expressed as ₁ (unit is pixel).

In step S5, the Chebyshev approximation formula shown below is used to automatically calculate the tilt angle θ between one pellet in the X direction of the pellet arrangement direction (see FIG. 5). Automatically detect the rotational position of the position).

Θ [rad] = arctan (ΔX / ΔY) arctan (X) = C ₁ · X + C ₃ · X ³ + C ₅ · X ⁵ + C
₇ · X ⁷ However, −1 <X <1 C ₁ = 0.999215 C ₃ = −0.321198 C ₅ = 0.146277 C ₇ = −0.038997.

In step S6, the XY stage 10 is driven based on the tilt angle θ obtained in step S5, and the tilt of the wafer 15 is automatically corrected so that θ becomes zero.
In step S7, as shown in FIG.
0 is controlled to be moved by n pellet pitches (previously stored) in the X direction of the pellet arrangement direction, the position of the reference image R is recognized, and the reference on the monitor screen subjected to the recognition processing is recognized. The coordinate position of the image R is represented by X ₂ and Y ₂ .

In step S8, the coordinate positions X ₁ , Y
The tilt angle θ of the wafer 15 is automatically calculated based on ₁ and X ₂ , Y ₂ and the number of moved pixels (the number of pixels), and the tilt of the wafer 15 is automatically corrected based on the calculation result.

As described above, the calculation of the tilt angle θ between two points and the tilt correction processing based on the calculation result are sequentially performed on a plurality of sets of two points having different combinations.
The alignment adjustment of 0 is completed.

In the subsequent steps, recognition processing is performed on the pellets of the wafer whose rotational position has been corrected as described above. At this time, as an initial setting, the position of the reference image R is automatically adjusted so that the centers of the four pellet images 15a adjacent to each other vertically and horizontally in the center of the wafer coincide with the center of the reference image R.

In step S9, the center position and radius of the wafer 15 are calculated. In this case, the position of the reference image is moved in the order shown by the arrow in FIG. 9 by using the initial position of the CCD camera 12 and the value of the wafer diameter in the state before the sheet is stretched, which is prepared in advance. Four
Points P1, P2, P3 and P4 are detected.

At this time, when the position of the reference image is moved from one of the above four points to the next point, since the preset wafer diameter value is used, the movement destination of the position of the reference image R is the wafer. It cannot be predicted whether it is inside or outside.

Therefore, taking the case of moving the position of the reference image from the center point P0 to the point P1 in the wafer 15 shown in FIG. 9 as an example, if the pellet image is recognized at the point P1, it is possible to perform recognition processing. In this case, the operation of recognizing the pellet image by moving the wafer outward by one pellet pitch is repeated until the recognition processing becomes impossible. Then, the position where the recognition process is finally possible is determined to be the outer peripheral edge of the wafer, and the result (coordinates) is stored. The flow of changes in the pellet image 15a at this time is, for example, as shown in FIGS.
Shown in order.

On the other hand, the pellet image 1 at the point P1
When the recognition processing of 5a is impossible, the operation of moving the inside of the wafer 15 by one pellet pitch and performing the recognition processing of the pellet image 15a is repeated until the recognition processing becomes possible. Then, the position where the recognition process is finally possible is determined to be the outer peripheral edge of the wafer, and the result (coordinates) is stored. The flow of changes in the pellet image 15a at this time is shown in a reverse order of the order of FIGS. 7 and 8.

In this way, the four points P1, P2,
P3 and P4 are detected and four combinations of three points (P1, P2, P3), (P1, P2, P4) of these four points,
Regarding (P1, P3, P4) and (P3, P2, P4), the center coordinates (X ₀ , Y) of the wafer as shown in FIG.
₀ ) and the radius r are calculated by the following equations.

Y ₀ = (K ₂ −K ₁ ) / (N ₂ −N ₁ ) X ₀ = K ₂ −N ₂ · Y ₀ r = {(X ₃ −X ₀ ) ² + (Y ₃ −Y ₀ ) ^{2} 1/2} _{where, K 1 = {(X 2} -X 1) (X 2 + X 1) + (Y 2 -Y
_{1) (Y 2 + Y 1} )} / 2 (X 2 -X 1) K 2 = {(X 3 -X 1) (X 3 + X 1) + (Y 3 -Y
_{1) (Y 3 + Y 1} )} / 2 (X 3 -X 1) N 2 = (Y 3 -Y 1) / (X 3 -X 1) N 1 = (Y 2 -Y 1) / (X 2 -X ₁ ) In the above formula, the calculated value of the radius r is maximum 3
Calculated using the coordinate value of the combination of points, and the center coordinate (X
₀ , Y ₀ ) is calculated by adopting the coordinate values of the three points adopted in the calculation of the radius r.

Next, in step S10, semiconductor pellets are picked up. As an initial setting of this pickup processing, as shown in FIG. 11, the XY stage is moved diagonally (for example, −X direction, Y direction) by a half pellet pitch from the position immediately after the processing of calculating the center position and radius of the wafer. To the pickup start position.

Further, in the pickup process, as shown in FIG. 12, reference image data necessary for displaying the five reference images A to E each having a rectangular shape are stored in the image memory in advance. In this case, the reference image A is position detection, the reference images A, B, and C are bevel detection, and the reference image E
Is referred to for detecting a defective mark.

When the pellet pick-up process proceeds, the wafer radius is not exceeded when moving to the next pellet pick-up position while referring to the information on the center position and radius of the wafer 15 calculated as described above. The pickup process is performed in the order shown by the arrow in FIG. 13, for example. In this case, the pickup advancing direction within the pellet array is automatically U-turned at the outer peripheral portion of the wafer, and the end of pickup for the pellet group is automatically determined.

FIG. 14 is a block diagram showing an example of the "pattern detecting device". This pattern detection device
A first cutout circuit 31 which cuts out a part of the two-dimensional pattern input data 30 having shades, partial data P (X) cut out by the first cutout circuit, and a partial reference data storage circuit which is prepared in advance. A first correlation coefficient calculation circuit 32 that calculates a correlation coefficient f (X) from the partial reference data R (X) stored in 33 as shown in the following equation (1).
And a first determination circuit 34 for determining the input data having the pattern that most matches the partial reference data from the output of the first correlation coefficient calculation circuit.

In FIG. 14, the input data 30
Has M pieces of data in the X direction and N pieces of data in the Y direction. A part of the input data 30, for example, the data P (X + 0, Y + 0) of the point P (X, Y) to the point P (X + m, Y + 0). Up to m data, from point P (X + 0, Y + 1) to point P
M data up to (X + m, Y + 1), and so on,
From point P (X + 0, Y + i) to point P (X + m, Y + i)
(However, m = n data groups each consisting of m data up to i = 3, ..., N) are cut out as partial data P (X) as shown in the following formula.

[0046]

[Equation 1]

However, K is the integration range, and f (X) is +
It takes a value in the range of 1 to 0 and has a value of +1 when the degree of coincidence (similarity) is maximum. FIG. 15 is a block diagram showing a modification of the pattern detection device of FIG.

Compared to the pattern detecting device shown in FIG. 14, this pattern detecting device further includes the input data 3
A data reduction circuit 41 for obtaining an average value of 0 and reducing the input data, a second cutout circuit 43 for cutting out a part of the data 42 reduced by the data reduction circuit and outputting the reduced partial data, and a second cutout circuit 43 A second phase relationship in which the correlation coefficient between the reduced partial data cut out by the second cutting circuit and the reduced reference data prepared in advance and stored in the reduced reference data storage circuit 45 is calculated by the equation (1). It is characterized by comprising a number calculation circuit 44 and a second judgment circuit 46 for controlling the cut-out position of the first cut-out circuit 31 in accordance with the calculation result of the second correlation coefficient calculation circuit. .

[0049]

As described above, according to the present invention, the tilt angle is automatically calculated for the scribed wafer mounted on the XY stage of the semiconductor pellet mounting apparatus at an ambiguous tilt angle. Thus, it is possible to provide a semiconductor wafer alignment method capable of automatically correcting the inclination and improving the efficiency of wafer alignment adjustment.

Further, according to the present invention, when picking up pellets from the scribed wafer mounted on the XY stage of the semiconductor pellet mounting apparatus, the pickup position can be reliably detected even in the peripheral portion of the wafer, and the pellet mounting apparatus can be detected. It is possible to provide a method for picking up a semiconductor pellet that can improve the efficiency of movement of the XY stage, and further improve the efficiency of pellet mounting.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing an example of a pellet mount device used for carrying out a semiconductor wafer alignment method and a semiconductor pellet pickup method of the present invention.

FIG. 2 is a flowchart showing a processing flow in a first embodiment of a semiconductor wafer alignment method and a semiconductor pellet pickup method of the present invention.

FIG. 3 is a diagram showing an example of a display image on a monitor screen in step S3 in FIG.

FIG. 4 is a diagram showing an example of a display image on a monitor screen in step S4 in FIG.

FIG. 5 is a diagram showing the content of a wafer tilt correction process in step S5 in FIG.

6 is a diagram showing an example of a display image on the monitor screen in step S7 in FIG.

FIG. 7 is a diagram showing an example of a display image on a monitor screen when the center position and radius of the wafer are calculated in step S9 in FIG.

FIG. 8 is a diagram showing another example of the display image on the monitor screen when the center position and radius of the wafer are calculated in step S9 in FIG.

FIG. 9 is a diagram shown for explaining the wafer outer periphery detection processing when calculating the center position and radius of the wafer in step S9 in FIG. 2;

FIG. 10 is a diagram for explaining the calculation processing of the center position and radius of the wafer in step S9 in FIG.

FIG. 11 is a diagram showing an example of a display image on the monitor screen when the pickup start position is set for performing the pellet pickup process in step S10 in FIG.

FIG. 12 is a diagram showing an example of a display image on the monitor screen when the pellet pickup process is performed in step S10 in FIG.

FIG. 13 is a view showing an example of the order of pellet pickup processing in step S10 in FIG.

FIG. 14 is a block diagram showing an example of a pattern detection device used to perform pellet image recognition processing in step S2 in FIG.

15 is a block diagram showing another example of the pattern detection device of FIG.

[Explanation of symbols]

10 ... XY stage, 14 ... Motor drive circuit, 15 ... Semiconductor wafer, 16 ... Light source, 17 ... CCD camera, 18 ...
Camera control device, 19 ... Image processing device, 20 ... Image monitor device, 21 ... Pellet pickup device.

Claims (5)

[Claims] 1. A method for mounting a semiconductor wafer, which is scribed on a sheet after forming a semiconductor element and divided into individual pellets, on an XY stage of a semiconductor pellet mounting apparatus with the sheet stretched. 1 step, the level of an analog image signal obtained by photographing a plurality of pellets of a semiconductor wafer on the XY stage with a television camera is binarized with a certain threshold value as a reference, and converted into a digital image signal representing light and shade. Then, the second step of recognizing and storing the pellet image in the image memory by using the rectangular standard pattern prepared in advance, and the tilt angle of the semiconductor wafer based on the pellet image obtained in the second step. The tilt of the semiconductor wafer is calculated by driving the XY stage based on the calculation result. Alignment method of a semiconductor wafer, characterized by comprising a third step of performing an alignment adjustment positive automatically. 2. The method of aligning a semiconductor wafer according to claim 1, wherein, when the alignment adjustment is performed, a process of correcting an inclination between two points on the semiconductor wafer is performed on a plurality of pairs of two different combinations. A method for aligning a semiconductor wafer, which is performed sequentially. 3. The semiconductor wafer alignment method according to claim 1, wherein when the pellet image is recognized, a correlation coefficient between input data and reference data prepared in advance is calculated, and the reference data is calculated from the calculation output. And a method for aligning a semiconductor wafer, characterized in that input data whose pattern is most matched is determined. 4. A semiconductor wafer, which is scribed in a state of being stuck to a sheet after formation of a semiconductor element and divided into individual pellets, is mounted on an XY stage of a semiconductor pellet mounting apparatus in a state of stretching the sheet. 1 step, the level of an analog image signal obtained by photographing a plurality of pellets of a semiconductor wafer on the XY stage with a television camera is binarized with a certain threshold value as a reference, and converted into a digital image signal representing light and shade. Then, the second step of recognizing and storing the pellet image in the image memory by using the rectangular standard pattern prepared in advance, and the tilt angle of the semiconductor wafer based on the pellet image obtained in the second step. The tilt of the semiconductor wafer is calculated by driving the XY stage based on the calculation result. A third step of automatically performing a correct alignment adjustment, moving the position of the reference image to detect coordinate values of four points on the outer periphery of the wafer, and based on the coordinate values, the center position and radius of the semiconductor wafer. And a fourth step of automatically calculating, and after the completion of the fourth step, the XY stage is moved to set the pickup start position of the semiconductor pellet,
A fifth step of sequentially advancing the pickup process of the semiconductor pellets with reference to the calculation result of the center position and radius of the semiconductor wafer and a plurality of previously prepared reference images. Pick-up method. 5. The method of picking up a semiconductor pellet according to claim 4, wherein a pickup moving direction in the semiconductor pellet array is automatically set at the outer peripheral portion of the semiconductor wafer by using a calculation result of the center position and the radius of the semiconductor wafer. A method for picking up a semiconductor pellet, which is characterized in that a U-turn is selectively made.