JPH0722178B2 - Wafer optical pre-alignment device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical pre-alignment apparatus for semiconductor wafers, such as an ordinary silicon semiconductor wafer or a light transmissive SOS.
The present invention relates to an optical pre-alignment apparatus for various semiconductor wafers such as (silicon on sapphire) wafers.

(Prior Art) In the past, for example, in the alignment of a semiconductor wafer in a wafer prober or the like, the first wafer is transferred and placed on a measurement stage, the alignment is performed, the electrical characteristics are measured as it is, and then the two wafers are aligned. Similarly, the wafers after the eye are sequentially carried on the measurement stage, aligned, and then measured. However, in this method, since wafer alignment and measurement are alternately performed on the same measurement stage,
Since the work efficiency is poor and the throughput cannot be increased, in recent years, wafers are pre-aligned before they are transferred to the measurement stage, and then the wafer is transferred to the measurement stage while maintaining the pre-aligned state. Then, it has become customary to perform alignment and measurement at separate positions in parallel.

As such a semiconductor wafer pre-alignment apparatus, conventionally, there are many ones that mechanically detect an orientation flat (hereinafter simply referred to as an orientation flat) of the semiconductor wafer with a contact member or the like. There has also been an apparatus for performing pre-alignment of a wafer by detecting reflection of light irradiated onto the wafer mounting table and the wafer by a predetermined amount.

(Problems of the prior art) However, in the mechanical pre-alignment by the contact member or the like described above, the alignment accuracy is insufficient, and the contact between the edge or the like and the contact member causes an undesirable state such as friction or dust. There is.

Further, if the capacitance sensor is used to detect the difference in capacitance of the reflected light between the carrier table portion and the wafer portion and pre-alignment is performed,
Although the above problem does not occur, there is a problem in that the device itself using the capacitance sensor becomes very expensive, resulting in a significant increase in cost. Moreover, in the pre-alignment using this capacitance sensor, unlike a normal semiconductor wafer that reflects light, it transmits light, for example, SOS (silicon on sapphire).
In a light-transmitting semiconductor wafer such as a wafer, there is a problem that accurate pre-alignment cannot be performed because light is transmitted and the measured amount of the capacitance sensor is disturbed.

In view of the above problems, the present invention provides a wafer pre-alignment device that can perform extremely accurate pre-alignment on a light-transmitting semiconductor wafer, does not cause a problem such as dust generation, and is relatively inexpensive. With the goal.

(Means for Solving the Problems) The present invention is configured as follows in order to solve the above problems.

That is, in an apparatus that optically detects alignment of a light-transmitting semiconductor wafer to a predetermined position by a light emitting element and a light receiving element, and aligns the irradiation optical axis of the light emitting element with respect to the semiconductor wafer. Then, the edge line of the semiconductor wafer and its eccentricity amount are sensed by utilizing the reflection of the light irradiated obliquely to the edge of the semiconductor wafer.

Further, it is preferable that the light-emitting element provided on one surface of the light-transmitting semiconductor wafer described above receives light by a light-receiving element in which the irradiation optical axis inclined with respect to the semiconductor wafer is arranged in a line.

(Operation) The present invention is configured such that the irradiation by the light emitting element is set to be inclined with respect to the wafer and the edge of the wafer is irradiated as described above. Therefore, the irradiation light that hits the wafer is emitted at the edge portion of the wafer. Almost reflected and very little transmitted.
By utilizing the reflection phenomenon at the edge portion, the edge line of the wafer and the amount of eccentricity can be accurately sensed, and highly accurate and clean pre-alignment of the wafer can be performed.

When light is applied to the semiconductor wafer surface from an oblique direction,
The light is divided into one that is reflected by the wafer surface and one that is refracted and transmitted depending on the incident angle on the wafer surface.

However, when the wafer edge does not enter between the two elements, the entire amount of light traveling from the light emitting element to the light receiving element is received by the light receiving element without being interrupted halfway. Therefore, there is a difference in the amount of light received by the light receiving element depending on whether the wafer edge enters between the quantity elements or not, so that the wafer edge can be detected.

Irradiation by the light emitting element provided on one surface of the semiconductor wafer described above Since the light is received by the light receiving element in which the optical axis inclined with respect to the semiconductor wafer is arranged in a line, the wafer edge is deviated by the eccentric amount of the central position of the light transmissive wafer. The position of the light path to be blocked moves, so that the light path is so wide that the light emitting element cannot capture the position of the light path blocked by the wafer edge at one point.

Therefore, by arranging the light receiving elements in a line, even if the amount of eccentricity of the central position of the light transmissive wafer increases, it can be detected with a sufficient width.

(Example) Below, the Example of this invention is described according to drawing.

FIG. 1 is a side view showing an embodiment of the pre-alignment apparatus of the present invention. In the figure, reference numeral 1 is a holding portion of the pre-alignment apparatus, and the holding portion 1 is formed in a U-shape at the lower end side thereof. The optical sensor mounting portion 1'is integrally mounted in an inclined state by mounting means such as bolts. The light emitting element 3 is internally provided in the one side collar portion located above the SOS semiconductor wafer (a silicon film is formed on a sapphire substrate) 6 among the hanging portions of the U-shaped optical sensor mounting portion 1 ′. The light receiving element 4 is provided in the optical path from the light emitting element 3 at the corresponding flange position of the other hanging part, and the light emitting elements 3 and 4 constitute the optical sensor 2. The optical axis of the optical sensor 2 is
The irradiation by the light emitting element 3 is set to be inclined with respect to the SOS semiconductor wafer 6 so that the edge of the wafer 6 is irradiated with the light.
It is located at the edge of the SOS semiconductor wafer 6 placed on the sub chuck 5, and specifically, the Z stage on which the Y stage 7 and the sub chuck 5 are formed corresponding to the wafer size.
By moving and stopping the stage 8 to a predetermined position, the optical axis of the optical sensor 2 arranged on the optical sensor mounting portion 1'in the inclined state as described above is positioned at the edge of the SOS semiconductor wafer 6. . The light emitting element 3 of the optical sensor 2 is
For example, a light emitting diode is provided, and the light receiving element 4 is interposed, and the light receiving element 4 is formed of, for example, a photodiode, and the lens is interposed.
Can use any element other than those described above. In this example, the inclination angle of the optical sensor 2 is set so that the incident angle of the sensor light with respect to the edge is about 75 °. However, the light of the optical sensor 2 in which the light emitting / receiving elements 3 and 4 are arranged in an inclined state. The inclination angle of the optical sensor 2 is not particularly limited as long as the axis is located at a part of the outer edge of the SOS semiconductor wafer 6, and the sensor light is incident on the edge of the light transmissive SOS semiconductor wafer 6. When hit, most of the angle is reflected, that is, an angle of about 45 ° or more and less than 90 °, and an appropriate angle can be set according to the light reflection characteristics of the SOS semiconductor wafer 6. This is because the flat surface is a light-transmissive wafer, and the descending edge portion becomes a reflective portion.
S If semiconductor wafers, glass wafers, and other light-transmitting semiconductor wafers are pre-aligned, the light emitted from the optical sensor will also be transmitted through the wafer parts such as IC chips.
As shown in FIG. 12, the output data of the sensor fluctuates and the precision of pre-alignment becomes extremely low, which makes it impossible to carry out the pre-alignment.

In FIG. 1, the light emitting element 3 and the light receiving element 4 of the optical sensor 2 are shown.
Although only one is provided for each, a plurality is provided for each and a plurality of light emitting elements 3 and light receiving elements 4 are arranged in the same circuit according to the wafer size (3, 5, 8 inches, etc.) of the SOS semiconductor wafer 6. Alternatively, the pre-alignment may be performed via the switching control circuit. This alignment can be performed, for example, by observing the change in the photocurrent in the phototransistor due to the total transmission of light at OF of the wafer.

In FIG. 1, reference numeral 9 denotes tweezers for mounting the SOS semiconductor wafer 6 and correcting the eccentricity of the SOS semiconductor wafer 6 in the X direction when the sub chuck 5 is lowered.

In order to perform the wafer pre-alignment using the present invention described above, first, as shown in the flowchart of FIG.
After checking the operations of the light emitting / receiving elements 3, 4, etc., the first sample SOS semiconductor wafer 6 is placed on the sub-chuck 5, the Y stage 7 is moved in the Y direction, and the Z stage 8,
The SOS semiconductor wafer 6 is moved in the Y direction together with the sub chuck 5, then the SOS semiconductor wafer 6 is rotated once, and the edge line of the SOS semiconductor wafer 6 is sensed by the optical sensor 2 to obtain the sensor output shown in FIG. Based on this, ΔS is integrated to calculate the wafer area, the wafer size is checked, the correlation data between the position of the wafer edge and the sensor output is sampled, and tilted with respect to the SOS semiconductor wafer 6 mounted on the sub chuck 5. The Y stage 7 is moved to an ideal position so that the optical axis of the optical sensor 2 arranged in this state is located at the edge of the SOS semiconductor wafer 6, and the initial setting position of the Y stage 7 is determined. As shown in FIG. 6, the correlation data sampled and sampled becomes non-linear as it moves away from the optical axis. Therefore, the data is converted so that the sensor output and the edge position have a linear relationship.
Performs a correlation approximation process.

After configuring the pre-alignment apparatus in this way, sensor light is irradiated from the light receiving element 3 to the vicinity of the edge of the SOS semiconductor wafer 6 placed on the sub chuck 5, and the wafer is rotated once to sense the edge data. Then, this edge data is converted into data based on the above correlation and taken out as a sensor output as shown in FIG. 4, the eccentricity of the SOS semiconductor wafer 6 is calculated, and the Y stage 7, sub chuck 5 and tweezers 9 are calculated. By moving the eccentricity to correct the eccentricity, the same sensing is performed to determine the OF position, and the OF is positioned at the determined angle.

In order to improve the accuracy when calculating the eccentricity,
The electrical noise component is removed by the autocorrelation calculation.

When pre-aligning the second and subsequent SOS semiconductor wafers 6, the SOS semiconductor wafers 6 placed on the sub-chuck 5 from the beginning unless the wafer size changes.
The optical axis of the optical sensor 2 arranged in an inclined state with respect to
The Y stage 7 is located at the edge of the SOS semiconductor wafer 6 and may be moved to a predetermined position from the beginning so that the edge is irradiated from the light emitting element 3.

FIG. 8 is a block diagram showing an example of a sensor output processing circuit when the sensor output is analyzed by an arithmetic circuit such as a microcomputer. The output current of the photosensor is converted into a voltage by the conversion circuit A. A conversion circuit D performs AD conversion via a low-pass filter B and a sample / hold circuit C, and inputs to the CPU of the microcomputer.

Next, the operation of this embodiment will be described.

The irradiation light that hits the SOS semiconductor wafer 6 is almost reflected by the edge portion of the wafer 6 and only slightly transmits. By utilizing the reflection phenomenon at the edge portion, the edge line and the amount of eccentricity of the SOS semiconductor wafer 6 can be accurately sensed, and the SOS semiconductor wafer 6 can be highly accurately and cleanly pre-aligned.

Although the example of the transmitted light detection type optical pre-alignment apparatus has been described in the above embodiment, the phototransistor may be arranged at a position for receiving the reflected light from the edge portion.

Incidentally, it goes without saying that the wafer pre-alignment apparatus of the present invention can be applied not only to the SOS semiconductor wafer described above, but also to all of light-transmitting wafers such as glass wafers, crystal wafers, and GaAs wafers. It may be applied to a wafer that does not transmit light.

Further, as shown in FIG. 2, the position of the optical path blocked by the wafer edge moves due to the eccentricity of the central position of the light-transmissive wafer, which allows the light receiving element to capture the position of the optical path blocked by the wafer edge at one point. The optical path is so wide that it cannot be done.

Therefore, by arranging the light receiving elements in a line, even if the amount of eccentricity of the central position of the light transmissive wafer increases, it can be detected with a sufficient width.

Next, a second embodiment of the present invention will be described with reference to the drawings.

FIG. 9 is a perspective view showing a pre-alignment apparatus according to a second embodiment of the present invention, FIG. 10 is a partial side view showing the sensing state of the same, and FIG. 11 is a graph showing the sensor output of the same. .

The optical pre-alignment apparatus in this embodiment is basically a Z stage 11 which is interlocked with a Y stage 10 which positions the wafer in the Y direction and which can be raised and lowered as shown in FIGS. 9 and 10. The wafer 13 is placed on the provided sub-chuck 12, the sub-chuck 12 is rotated to rotate the wafer 13 once, and the wafer 13 is placed vertically upward from the light-emitting element 14 of the optical sensor also provided vertically upward on the Z stage 11. Irradiating the sensor light, other than the portion which passes through the sensor slit 14a and is blocked by the wafer 13, that is, the sensor light which passes outside the edge of the wafer 13 is detected by the light receiving element 16 formed vertically downward in the sensor holding portion 15. Then, the detection result of the sensor as shown in FIG. 7 is obtained, the center position of the wafer 13 and the eccentricity amount are calculated, and based on the result, the Y stage 10 is moved to correct the position in the Y direction. And lowering the click 12,
The wafer 13 is placed on the tweezers 17 provided on the Z stage 11 and slid by a predetermined amount to correct the position in the X direction, and further, the sub chuck 11 is rotated by a predetermined angle to prealign the orientation flat of the wafer 13. It constitutes the device.

In the present example, the light-emitting element 14 uses an infrared LED, and the light-receiving element 16 uses a photodiode with an optical filter.However, the light-emitting element 14 is not limited to this. The light receiving element can be selected.

Further, FIG. 13 is a schematic diagram showing the relationship between the light passing through the sensor slit 14a and the light receiving portion 16 and the wafer 13.
The light from 1 passes through the sensor slit 14a having a width of 1 mm and a length of 20 mm, and is received by the light receiving element 16 except for the portion d blocked by the wafer 13. In this case, as shown in FIG.
Are arranged side by side, and the light emitting element 14 is changed corresponding to each wafer size such as 3 ″, 3.5 ″, 4 ″, 5 ″, 6 ″, and the like, so that a function corresponding to the wafer size is provided.

The procedure of pre-alignment by the pre-alignment apparatus of the second embodiment described above is shown in the flow chart of FIG.

That is, first, initialization is performed to check the initial setting of the LED as the light emitting element 14, the photodiode light receiving sensor as the light receiving element 16, the operating unit such as the A / D converter. This unit check setting value model
Shown in Figure 15. In the sampling of the figure, the movement amount (Ga
The relational expression of (in) and the amount of change (shift) is expressed as follows, for example.

Next, the first pre-alignment wafer 13 is placed on the sub chuck 12 at the pre-alignment position, and the resolution calculation for sensing (Gain × 1, shift = 0) is performed.
In this case, as shown in FIG. 16, if the length per bit is L ₀ , The measured value L ₀ = ((n ₀ +1 mm) −n ₀ ) / Nd−Nd + 1. Note that this resolution calculation is not necessary when pre-aligning the second and subsequent wafers 13 of the same model.

Here, the rotation of the wafer is started to collect and smooth the data. Data is collected as shown in FIG. 17. For example, the data is collected under the following conditions.

Sampling interval Data / 0.9 ° Number of data 360 ° / 0.9 ° = 400 pieces Sampling time 4800μs / data Total sampling time 4800 × 400 = 1.92s In addition, noise removal and smoothing of the data sampled in this way are performed at equal intervals. The true signal is extracted by a polynomial fitting method that fits the polynomial with a least square error to a range of sampled data points.

Here, based on this smoothed data, the presence or absence of eccentricity of the wafer and the amount of eccentricity are calculated as follows, for example.

In FIG. 18, ′ indicates the eccentric position of the wafer 13, is the center position, θ is the rotation correction amount, and L is the movement correction amount. Here, the calculation of the eccentricity is such that the true circle center is on the vertical bisector of the straight line connecting the two points on the circumference, and the intersection point with the vertical bisector of another line segment is the circle. Using the principle of being the center of each, each calculation is performed from the collected data. Then, as shown in FIG. 19, after collecting and smoothing the data, an arbitrary point A and the point A
The difference in the data of point B facing 180 ° is within ± 500 μm (| A-
If B | ≦ 500 μm), then the orientation flat alignment step is started assuming that the center of the wafer has come out. When the data difference exceeds ± 500 μm, the eccentricity of the wafer 13 is corrected according to the eccentricity amount. That is, the wafer is rotated to align the θ direction, then the sub chuck 12 is lowered, the wafer 13 is placed on the tweezers 17, and the tweezers are set.
After the X-direction alignment is performed by the movement of 17, the sub-chuck 12 is moved up, and the data collection is performed again.
This repetition is repeated until the amount of eccentricity becomes | AB | ≦ 500 μm.

Next, when the amount of eccentricity is within the above range, orientation flat calculation and orientation flat position adjustment are performed. A specific calculation formula for orientation flat calculation in this example will be described with reference to FIGS. 20 to 22.

As shown in FIG. 20, it is assumed that the orientation flat of the wafer starts from and ends with. Converting this to the X, Y Cartesian coordinates and expressing it as data sampling,
It becomes like the figure. At this time, the estimated curve is a quadratic curve y = ax ² + bx + c. The unknowns a, b, and c are estimated from the data using the least squares method. That is, the formula y = ax
The coefficients a, b, and c of the formula are determined so that the sum of squares of the difference between the calculated value Y of y by ² + bx + c and the actual data y is minimized. Difference between actual data and calculated value Y εi = yi−Yi = yi− (ax ² + bx + c) Sum of squared deviations To minimize S, the equation is Solve the simultaneous equations as. That is, nc + bΣXi + aΣ ▲ X ² _i ▼ = Σyi cΣXi + bΣ ▲ X ² _i ▼ + aΣ ▲ ³ _i ▼ = ΣXiyi cΣ ▲ X ² _i ▼ + bΣ ▲ X ³ _i ▼ + a Σ ▲ X ⁴ _i ▼ = Σ ▼ X ² _i ▼ yi Is solved to find the coefficients a, b, and c.

Also, in Fig. 21, it is considered that the orientation flat center is where the slope is 0. Therefore, when the curve y = ax ² + bx + c is differentiated, y '= 2ax + b = 0 ∴X = -b / 2a Thus, the point X ₀ is the orientation flat center.

In this way, when the alignment of the orientation flat of the wafer is completed, the pre-alignment of the wafer is completed, and the wafer is conveyed to the measurement stage (not shown) while maintaining its position.

As for the sensor output processing circuit and the like in the second embodiment, the same circuit as that of the embodiment of FIG. 1 shown in FIG. 8 may be used, and other portions which do not particularly need to be changed may have the same configuration.

Further, in each of the above-described embodiments, the pre-alignment apparatus has been described by taking the case where the wafer is provided with the orientation flat as an example, but the present invention is such that the notch portion is provided on the circumference of the wafer, for example. It goes without saying that it can be applied to cases.

EFFECTS OF THE INVENTION As is apparent from the above, according to the present invention, in an apparatus for optically detecting and aligning alignment of a wafer at a predetermined position with a light emitting element and a light receiving element, irradiation by the light emitting element is performed. The edge of the wafer is set to be inclined with respect to the wafer and the edge of the wafer is irradiated, so the edge line of the wafer and the amount of eccentricity can be detected extremely accurately. It is possible to perform high-precision pre-alignment even with the above wafer.

In addition, a light emitting element is arranged in a line on one surface of the front and back surfaces of the wafer, and a light receiving element is arranged in a line on the other surface of the wafer. Since the orientation flat of the wafer is positioned, the eccentricity and the like can be detected relatively inexpensively and accurately, and highly accurate prealignment can be performed.

[Brief description of drawings]

FIG. 1 is a side view showing an embodiment of the pre-alignment apparatus of the present invention, FIG. 2 is a sensing principle diagram of the same as above, FIG. 3 is a flowchart of pre-alignment of the above, and FIG. Graph, FIG. 5 is a sensor output waveform diagram when checking the wafer size in the same as above, FIG. 6 is a sensor data diagram showing the correlation between the sensor output and the edge position in the above, and FIG. FIG. 8 and FIG. 8 are block diagrams showing an example of the sensor output processing circuit in the above embodiment, and FIG. 9 is a perspective view showing an optical pre-alignment apparatus according to the second embodiment of the present invention. FIG. 11 is a partial side view showing the sensing state of the same as above, FIG. 11 is a graph showing the sensor output of the same as above, FIG. 12 is a graph showing the sensor output of the same as above for a transparent wafer, and FIG. Slit and sensor Schematic diagram showing the relationship with the light receiving part,
FIG. 14 is a flow chart of pre-alignment according to the second embodiment, FIG. 15 is an initial set data diagram of unit check, FIG. 16 is a schematic diagram showing a relationship between theoretical value and actual measured value of resolution calculation, and FIG. Is a flow chart of sampling and sampling of wafer eccentricity data, FIGS. 18 and 19 are schematic diagrams showing wafer eccentricity calculation, and FIGS. 20 and 22 are schematic diagrams for wafer orientation flat calculation, respectively. 1,15 …… Sensor holding part, 1 ′ …… Optical sensor mounting part, 2
...... Light sensor, 3,14 ...... Light emitting element, 4,16 ...... Light receiving element,
5,12 …… Sub chuck, 6,13 …… Wafer, 7,10 …… Y stage, 8,11 …… Z stage, 14a …… Sensor slit, 17 …… Tweezers.

Claims (2)

[Claims] 1. An apparatus for optically aligning a light-transmitting semiconductor wafer to a predetermined position by optically detecting the alignment with a light emitting element and a light receiving element, and irradiating an optical axis of the light emitting element with respect to the semiconductor wafer. The optical characteristics of the wafer are characterized in that the edge line of the semiconductor wafer and the amount of eccentricity thereof are sensed by using the reflection of light that is obliquely applied to the edge of the semiconductor wafer to set the tilted state. Pre-alignment device. 2. A light-receiving element having a linearly arranged irradiation optical axis with respect to the semiconductor wafer by the light-emitting element provided on one surface of the light-transmitting semiconductor wafer. 1. An optical pre-alignment apparatus for a wafer according to 1.