JPH0626232B2 - Wafer position alignment method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for aligning a wafer, and more particularly, in a semiconductor manufacturing apparatus, the orientation of the wafer orientation flat and the center position of the wafer are set to a predetermined direction and position. The present invention relates to a wafer position alignment method suitable for alignment.

[Conventional technology]

In the electron beam drawing apparatus, when a circuit pattern is overlaid and drawn on a wafer, the circuit pattern alignment needs to be performed accurately and at high speed. In order to perform the circuit pattern alignment at high speed, first, it is necessary to accurately align the wafer outer shape with the reference position. The wafer aligning device is a device for aligning the outer shape of the wafer. Wafer alignment is performed by aligning the orientation of an orientation flat (hereinafter referred to as an orientation flat) provided to indicate the center position of the wafer and the crystal direction with the reference position. The wafer center position alignment is performed by calculating the amount of deviation (eccentricity amount) between the wafer center and the rotation reference axis center from the wafer outer edge position data. The eccentricity amount is calculated from the result of detecting three or four points of the wafer outer edge position data other than the orientation flat portion, as shown in JP-A-60-81613.

First, the method of detecting three points will be described. The wafer is rotated by 90 ° from the angle at which the orientation flat center is located at the wafer outer edge position detection unit, and the distance ρ from the rotation center to the wafer edge (wafer outer edge position) is detected, and this is designated as a. Subsequently, the wafer is rotated by 90 °, and the similar distance ρ is detected, which are designated as b and c. The amount of eccentricity is calculated by using these a, b, and c.

Next, a method of detecting four points will be described. First, the wafer is rotated by 45 ° from the angle at which the orientation flat center is located at the wafer outer edge position detection unit, and the distance ρ from the rotation center to the wafer edge is detected, and this is designated as a. Subsequently, the wafer is rotated by 90 °, and the same distance ρ is detected, which are designated as b, c, and d. The amount of eccentricity is calculated by using these a, b, c and d.

The eccentricity can be obtained by using any of the above methods.

[Problems to be Solved by the Invention]

In the above-mentioned conventional technique, whether or not the outer edge position data of three or four points necessary for obtaining the eccentricity amount is correct (whether or not the data includes a noise component due to wafer chipping, resist peeling, sub orientation flat, etc.). ) Without judging
The eccentricity amount is obtained assuming that the outer edge position data of three or four points are on the circumference of the wafer. Therefore, when the detected wafer outer edge position has a sub orientation flat, a chip, or resist peeling, an error factor is generated in the outer edge position data, and the matching accuracy is significantly impaired.

It is an object of the present invention to obtain an accurate wafer eccentricity amount even if there is a chip on the outer edge of the wafer, resist peeling, or sub-olifura, and it is possible to always realize highly accurate wafer position alignment.

[Means for Solving the Problems]

The present invention includes an XY stage movable in X and Y two-axis directions,
A θ stage for vacuum suctioning and rotating a wafer, a rotation angle detector for detecting a rotation angle of the θ stage, and a wafer outer edge position detector for detecting an outer edge position of the wafer are provided.
An eccentric amount of the wafer with respect to the θ stage is detected by using a three-point detection method or a four-point detection method from the result of detecting the wafer outer-edge position at three or four points of the wafer detected by the wafer outer-edge position detector. In the wafer position aligning method of calculating the X-axis component and the Y-axis component of the wafer and correcting the position corresponding to the X-axis component and the Y-axis component by using the XY stage, the wafer outer edge position detector is used. Points obtained by equally dividing the outer edge position of the entire circumference into predetermined rotation angle units (these points are referred to as equal points, and the equal points are the three-point detection method or the four-point detection method described above).
It is detected in relation to the rotation angle of the θ stage by using the point detection method in such a manner that it can become a large number of candidates for 3 or 4 points data, and the whole circumference of the wafer is calculated from these wafer outer edge position data using a calculation means. A distance ρ between the wafer outer edge position at each of the equally divided points and the rotation center of the θ stage is calculated, and the rotation angle A of the θ stage is calculated using this distance calculation data.
The distance ρ _i between the wafer outer edge position corresponding to _i and the rotation center of the θ stage, and the rotation angle A 180 ° apart from the rotation angle A _i.
to _{i + 180 °} calculates the sum of the distances [rho _{i + 180 °} between the center of rotation of the corresponding wafer outer edge position · theta stage, the sum and the wafer diameter r _i of the temporary calculation of wafer diameter r _i of the temporary Is performed at each half point of the wafer, that is, at each equally divided point in which the rotation angle A _i is in the range of 0 ° to 180 °, and the frequency distribution of the diameter r _i of the wafer is created from the result of calculating these diameters r _i. A value is calculated, an average value of data included in the effective range of the mode is calculated, and the calculated value is used as a wafer diameter r for noise component determination, and the three-point detection method or the four-point detection method is executed. In this case, it is determined whether or not the provisional diameter r _i corresponding to the outer edge positions of three or four points on the wafer falls within the allowable range of the diameter r for noise component determination. Three
When the eccentricity amount calculation is performed by the point detection method or the 4-point detection method and the above condition is not satisfied, the θ
The condition determination is performed for three or four points at different outer edge positions by changing the rotation angle of the stage.

[Action]

Equal division points (rotation angle A
i) the distance ρ _i from the rotation center of the θ stage to the wafer outer edge position, and the distance ρ _i from the rotation center of the θ stage on the opposite side (a point 180 ° apart) from the wafer outer edge position
the sum of _{i + 180 °} approximates to the diameter of the wafer.

However, (chipping wafer, Sabuorifura, resist peeling, etc.) noise component if there is, if the sum of the [rho _i and [rho _{i + 180 °} of the point in the noise component is compared with the original wafer diameter of the wafer, error It becomes large, and the above approximate relation is no longer established.

Using 3 or 4 points data with this noise component, 3
Performing the wafer eccentricity calculation by the point detection method and the four-point detection method deteriorates the wafer eccentricity amount and thus the wafer alignment position accuracy.

Focusing on the above points, the present invention prepares a large number of 3 to 4 point data to be candidates for the 3 point detection method or the 4 point detection method (this data is achieved by the above process), 3
When executing the point detection method or the 4-point detection method,
Determined by these detection methods candidate with all three to four points of the outer edge position data temporary diameter _{ri = ρ i + ρ i +} 180 _° The above process should be in and by the process described above r _i is the noise component A noise determination diameter r for determining whether or not the wafer outer edge position is not present is obtained.

As the noise determination diameter r, the average value of the data within the effective range of the mode in the diameter r _i frequency distribution is used.

This is because each of the temporary wafer diameters r _i corresponding to the points equally divided have variations when the wafer is eccentric with respect to the θ stage, and have a large error with respect to the original diameter. There is no noise component because it can be statistically determined that the most frequent diameter is the closest to the original diameter by expressing it as a frequency distribution (normal distribution). This is because it can be regarded as a regular wafer diameter.

Then, the noise component by using the determination diameter r, the process of each point as a three-point or four-point detection method candidate tentative diameter _{r i = ρ i + ρ i} + 180 _° is determined for the diameter r It is possible to determine whether or not it falls within the allowable range, and if this condition is satisfied, the outer edge position data of the candidate point is regarded as reliable without a noise component and the wafer eccentricity amount calculation of the three-point or four-point detection method is performed. Can be executed. Further, the diameter r corresponding to three or four points that should be candidates for each detection method
_{If i} does not satisfy the above condition, the rotation angle of the θ stage is changed until the condition is satisfied, and the condition determination is performed for another outer edge position (candidate) of 3 points or 4 points.

Therefore, when the eccentricity amount of the wafer with respect to the θ stage is calculated by the three-point detection method or the four-point detection method, the three or four wafer outer edge positions of the wafer outer edge used for the operation are calculated among a large number of equally divided points. Since a point having no noise component is selected from the three points and the three-point detection method or the four-point detection method is executed, the X-axis component and the Y-axis component of the wafer eccentricity amount can always be calculated accurately.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to FIGS.

FIG. 1 is an overall configuration diagram showing an embodiment of a wafer alignment apparatus to which the present invention is applied.

In FIG. 1, 1 is an XY stage, 2 is a θ stage for vacuum-sucking and rotating a wafer 3, and the XY stage 1 is position-controlled by an X-axis control system 4 and a Y-axis control system 5. , Θ stage 2 includes drive motor 6 and timing belt 7
Is rotated by the rotation axis (in other words, the θ stage 2)
The rotation angle detector 8 for detecting the rotation angle of

The light source 11, the condenser lens 12, the imaging lens 13, and the one-dimensional image sensor (CCD) 14 constitute a wafer outer edge position detector that detects the outer edge position of the wafer 3 on the θ stage 2, and light from the light source 11 is detected. Is condensed by the condenser lens 12, illuminates the outer edge of the wafer 3, and forms an image of the outer edge position of the wafer 3 on the CCD 14 through the imaging lens 13.

In the present embodiment, the wafer 3 is sequentially rotated by a predetermined rotation angle unit by the θ stage 2 and finally rotated once, and the outer edge position of the entire circumference of the wafer is divided into a large number of points at predetermined rotation angles (first point). Rotation angles A ₀ , A ₁ , A ₂ , A ₃ ... An in FIG.
At each point corresponding to
Is detected in relation to the rotation angle of the, and the outer edge position information for each constant angle is taken into the electronic computer 15. This A ₀ ~ A
The equidistant point corresponding to n is 3 of the 3 point detection method or the 4 point detection method.
Or, it is equally divided so that it can be a large number of candidates for four-point data.

At the time when the data for one rotation of the wafer has been acquired, the computer 15 calculates the correction amount necessary for the wafer alignment operation from the wafer outer edge position information according to the flow chart shown in FIG. X-axis control system 4, Y-axis control system 5,
The θ stage 2 is used to align the orientation flat direction of the wafer 3 and the wafer center with a predetermined direction and position. The details of this position alignment will be described later.

FIG. 3 is a diagram showing the relationship between the wafer 3 and the CCD 14,
(A) shows the relationship between the two, and (b) shows the waveform of the outer edge position data for one rotation of the wafer 3. In FIG. 3 (a), O is the rotation center of the θ stage 2, W is the center of the wafer 3, and A ₀ , A ₁ , A ₂ , A ₃ , ... An are the predetermined rotation angles of the θ stage 2. Then, each rotation angle Ai (Ai is A _{0 to} A
The distance ρ between the outer edge position of the wafer 3 and the rotation center O of the θ stage 2 corresponding to n) is calculated by the computer 15 based on the outer edge position detection data of the CCD 14 and the position data of the rotation center O. An example of the relationship between the rotation angle Ai and the outer edge position data (distance ρ) is shown in FIG. 3 (b).

Next, the calculation of the amount of eccentricity (the amount of deviation between the wafer center W and the θ stage rotation center O) necessary for aligning the centers of the wafers 3 is calculated using the flow chart shown in FIG. 2 and FIGS. The details will be described. The amount of eccentricity can be obtained from the outer edge position information of three or four points. The three-point detection method and the four-point detection method themselves are known,
A new method is adopted for the condition determination as to whether or not the outer edge position data of a point includes a noise component.

First, a method of obtaining the amount of eccentricity from the outer edge position information of four points (4
The point detection method) will be described.

In the four-point detection method, as shown in FIG. 5, the wafer is rotated by θ from the angle at which the center of the orientation flat is located at the wafer outer edge position detector, and the wafer outer edge position (rotation position) at the position of the wafer outer edge position detector at that time is rotated. The outer edge position of the angle θ) and the distance ρ between the θ stage rotation centers are set as a, and the following θ + π / 2, θ
The distance ρ corresponding to the outer edge position of + π, θ + 3 / 2π is b,
c and d, the X-axis component and the Y-axis component of the wafer eccentricity amount are calculated from the four-point data a, b, c, and d. [For this calculation, (6) and (7) will be described later. In this embodiment, noise components (wafer chipping, resist peeling, sub orientation flat, etc.) affect the data a, b, c, d at the four points in the four-point detection method. In order to avoid the above, the method for obtaining the diameter of the wafer described with reference to FIG. 4 and the data compression method described with reference to FIG. 5 are used together to select four points having no noise component.

First, a method for obtaining the diameter of the wafer 3 will be described with reference to FIG.

As shown in FIG. 4 (a), the rotation angle Ai of the XY stage 2 (i = 0 to n, but in FIG. 4, Ai after the rotation half-circle angle of 180 degrees of the θ stage is A _{n. / 2} , A _{n / 2 + 1} , A
_{n / 2 + 2} , ..., of which suffix n / 2
Is the rotation angle of 180 °), and the distance data ρ _i (i = 0 to _n ) between the wafer outer edge position and the θ stage rotation center O corresponding to the rotation angle A _{n. / 2} after the distance [rho _i is _{ρ n / 2, ρ n /} 2 + 1, ρ n / 2 + 2, ... are indicated by) and when the diameter r _i of the wafer 3 in the rotation angle a _i is the following equation Can be approximated by

_{r i = ρ i + ρ i} + 180 _° ... (1) ρ _{i + 180 °} of the above formula is equivalent to the FIG. 4 ρ _{n / 2 + i.} Let r _i be a temporary diameter and A _i be A _{0 to} A _{n / 2.}
An example of the result obtained at (θ = 0 ° to 180 °) is shown in FIG. 4 (b). From this result, in order to obtain the diameter r of the wafer 3, the mode (value with a large number of data frequencies) is obtained from the frequency distribution of the diameters, as shown in FIG. 4 (c). By taking out only the data contained in the effective range ± α (α is an arbitrary constant that determines the allowable range of the wafer diameter) from the mode and averaging, the diameter r of the wafer 3 can be approximated by the following equation. .

Here, r _j ; data included in the effective range from the mode m; number of the data Since the diameter r is the closest to the original wafer diameter, it can be considered that there is no noise component. ,
This is used as a diameter for noise component determination, and the compressed data shown below is also used to detect data at four points that do not include noise components, as shown in FIG. 5 (a).

FIG. 5B shows the waveform of the compressed data value of the outer edge position data. The compressed data is data obtained by sequentially comparing adjacent outer edge positions with respect to the deviation of the distance ρ at each point of A _{0 to} An on the entire circumference of the wafer. Each of the adjacent outer edge position (distance ρ) data is − L ₁ / N, L ₂ / N (N,
L ₁ and L ₂ are obtained by multiplying a weight function of an arbitrary constant which can distinguish the noise component and the outer edge position data, and adding the result. The calculation result is an integer, and the part after the decimal point is truncated.

Hereinafter, a method of selecting four points in the four-point detection method based on the obtained diameter r and compressed data will be described.

First, the distance between the rotation center O of the θ stage 2 and the outer edge position of the wafer 3 corresponding to the rotation angle θ is a. Below, θ + π
Data corresponding to / 2, θ + π, and θ + 3 / 2π are b, c, and d, respectively. The following condition judgments are made for a, b, c and d.

r−β ≦ a + c ≦ r + β (3) r-β ≦ b + d ≦ r + β (4) a (θ) = b (θ + π / 2) = c (θ + π) = d (θ + 3 / 2π) 0 (5) Where β is an arbitrary constant that determines the allowable range of the diameter a (θ) to d (θ + 3 / 2π); rotation angle θ (rotation angle Ai)
The rotation angle satisfying all the conditions above the compressed data value corresponding to is detected from the range of θ = A _{0 to} A _n . The X-axis component e and the Y-axis component f of the eccentricity are determined by the following equations based on the four points of data a, b, c, d detected as described above.

However, u and v are shown by the following equations.

u = (d−b) / 2 v = (c−a) / 2 (7) Next, there is no rotation angle θ that satisfies the determination conditions represented by the equations (3), (4), and (5). The eccentricity amount detection (the eccentricity amount is detected by the data of three points) in this case will be described with reference to FIG. Data corresponding to the rotation angle θ = A _i is defined as a _i, and θ +
Data corresponding to π / 2 and θ + 3 / 2π are referred to as b _i and d _i , respectively. Also in this case, the above (3), (4), (5)
Although the conditional judgment of the expression is used, the expression (3) is expressed by r−β ≦ 2a _i.
≦ r + β, Expression (4) is determined as r−β ≦ b _i + d _i ≦ r + β.

When the above condition is satisfied, the equation (7) is transformed into the following equation (Fig. 6 (a)).

u = (d _i −b _i ) / 2 v = (r−2 a _i ) / 2 (8) where r: Wafer diameter detected by the above method (8) is applied to (6) Therefore, the amount of eccentricity can be detected from the data of three points.

Note that r _i = ρ _i + ρ _{i + 180 °} (a + in the four-point detection method)
c, b + d, in the three-point detection method, 2a _i , b _i + d _i ) is determined in the condition (3), (4) or this variation in the case of determining whether or not the condition 2a _i , b _i + d _i ) falls within the allowable range of the diameter r for noise component determination Using the format is sufficient and the compressed data method may be omitted. In the above embodiment, the compressed data method is used in combination with the condition determination taken into consideration.

Also, the 4-point detection method or the 3-point detection method is not limited to once,
By changing the rotation angle of the θ stage, all four values in the range of θ = A _{0 to} An (the entire circumference of the wafer) satisfying the above-mentioned condition determination are set.
The maximum frequency of the X-axis component and the Y-axis component is detected from the obtained frequency distribution of the wafer eccentricity [FIG. 5 (b)], and the effective range ± γ ₁ , γ is calculated from the maximum frequency. ₂ (γ ₁ and γ ₂ are arbitrary constants that can be allowed as the eccentricity of the X-axis component and the Y-axis component, respectively)
The eccentricity amount may be obtained from the average value. This amount of eccentricity can be determined by the following equation.

Here, e _j ; the data included in the effective range ± γ ₁ from the mode K; the number of the data f _j ; the data included in the effective range ± γ ₂ from the mode 1; the number of the data Orientation detection of the orientation flat Is performed by recognizing the both ends of the orientation flat from the characteristics of the orientation flat portion (change in data width and polarity) using the waveform of the compressed data value described above, and setting the center as the orientation flat center.

〔The invention's effect〕

As described above, according to the present invention, when the wafer eccentricity amount is calculated by the three-point or four-point detection method, even if a noise component such as a chip on the outer periphery of the wafer, resist peeling, or sub orientation flat exists, the noise 3 point data with components, 4
Since the appropriate 3 point data or 4 point data is selected while avoiding the point data, there is an effect that an accurate wafer eccentricity amount can be obtained and the position of the wafer center can always be aligned with high accuracy.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of a wafer alignment apparatus to which the present invention is applied, FIG. 2 is a flow chart showing an embodiment of a program in the computer of FIG. 1, and FIG. Explanatory drawing of relation of one-dimensional image sensor, 4th
FIG. 5 is an explanatory diagram of a wafer diameter detection method, FIG. 5 is an explanatory diagram of an eccentricity detection method based on 4-point data, and FIG. 6 is an explanatory diagram of an eccentricity detection method based on 3-point data. 1 ... XY stage, 2 ... θ stage, 3 ... Wafer, 4 ... X-axis control system, 5 ... Y-axis control system, 6 ... Drive motor, 7 ... Timing belt, 8 ... Rotation angle detector, 11, 12, 13, 14 ... Wafer outer edge position detector (light source, condenser lens, imaging lens, one-dimensional image sensor), 15 ... Electronic computer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoichi Fujikura 882 Igemo, Katsuta-shi, Ibaraki Hitachi factory Ltd. Naka factory (56) References JP-A-60-81613 (JP, A) JP-A-54- 585 (JP, A)

Claims (3)

[Claims] 1. An XY stage movable in X and Y two-axis directions, a θ stage for vacuum-sucking and rotating a wafer, a rotation angle detector for detecting a rotation angle of the θ stage, and an outer edge of the wafer. A wafer outer edge position detector for detecting a position, and a three-point detection method or four-point detection based on the result of detecting the wafer outer edge position at three or four points of the wafer detected by the wafer outer edge position detector. Position adjustment for calculating the X-axis component and the Y-axis component of the eccentricity of the wafer with respect to the θ stage by using the method and correcting the position corresponding to the X-axis component and the Y-axis component using the XY stage. In the method, the wafer outer edge position detector is used to equally divide the outer edge position of the entire circumference of the wafer into predetermined rotation angle units (these points are called equal dividing points, and the equal dividing points are the three-point detection method). Or there is no 3-point detection method However, it is equally divided so that it can become a large number of candidates for four-point data) and is detected in relation to the rotation angle of the θ stage. The distance ρ between the wafer outer edge position and the θ stage rotation center at a point is calculated, and the distance ρ between the wafer outer edge position and the θ stage rotation center corresponding to the rotation angle A _i of the θ stage is calculated using this distance calculation data.
_i and a rotation angle A 180 degrees apart from the rotation angle A _i
to _{i + 180 °} calculates the sum of the distances [rho _{i + 180 °} between the center of rotation of the corresponding wafer outer edge position · theta stage, the sum and the wafer diameter r _i of the temporary calculation of wafer diameter r _i of the temporary Is performed at each half point of the wafer, that is, at each equally divided point in which the rotation angle A _i is in the range of 0 ° to 180 °, and the frequency distribution of the diameter r _i of the wafer is created from the result of calculating these diameters r _i. A value is calculated, an average value of data included in the effective range of the mode is calculated, and the calculated value is used as a wafer diameter r for noise component determination.
When performing the three-point detection method or the four-point detection method,
It is judged whether or not the temporary diameter r _i corresponding to the outer edge positions of three or four points on the wafer falls within an allowable range of the noise component judging diameter r, and if the condition is satisfied, the three-point detecting method or When the eccentricity amount is calculated by the four-point detection method and the above condition is not satisfied, the rotation angle of the θ stage is changed until the condition is satisfied, and the condition determination is performed for three or four different outer edge positions. A wafer position matching method characterized by the above. 2. When calculating the amount of eccentricity of the wafer with respect to the .theta. Stage in claim 1, first, temporary positions corresponding to the four outer edge positions of the wafer used in the four-point detection method are calculated. If a condition is determined whether the diameter r _i falls within the allowable range of the noise component determination diameter r, and if this condition determination is made at all equal points on the entire circumference of the wafer, the condition is not satisfied. A wafer position matching method, wherein an eccentricity amount calculation is performed by the three-point detection method instead of the four-point detection method. 3. The method according to claim 1 or 2, wherein the three-point detection method or the four-point detection method is applied to the entire circumference of the wafer satisfying the condition determination by changing the rotation angle of the θ stage. Is executed at each of the equal points to create a frequency distribution of the X-axis component and the Y-axis component of the wafer eccentricity amount, and from the average value of the data included in the effective range of the mode in this frequency distribution, A wafer position matching method for calculating the X-axis component and the Y-axis component.