JP2010135836A - Method and apparatus of overlaying wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that position alignment of electrodes joining on an entire wafer surface with high accuracy is insufficiently accurate with conventional methods when a wafer size gets larger than conventional ones as the position alignment in joining mutual electrodes is important when wafers having a plurality of semiconductor devices are stacked to improve density of a chip and achieve high-speed drive. <P>SOLUTION: An alignment mark on one of wafers is measured by a reference microscope. For the other wafer, positional relationship between the alignment mark on the wafer and a reference mark on a holder is measured, and then the reference mark is detected by a measurement microscope (whose positional relationship with the reference microscope is known). As a result, the positional relationship between the alignment mark on the wafer and the reference microscope can be known via the reference mark. By moving the wafers to align their positions to overlay, highly accurate position alignment is possible. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a superposition method in a semiconductor wafer laminating process, and more particularly to a superposition method centering on alignment technology used for a process of laminating a wafer on which a high-definition semiconductor device is formed, and superposition for the same. The present invention relates to an aligning device.

In recent years, portable electronic devices such as mobile phones, notebook computers, portable audio devices, and digital cameras have made remarkable progress. Along with this, in addition to improving the performance of the chip itself as well as the performance of the chip itself, improvements in the chip mounting technology are also required, especially from the viewpoint of reducing the chip mounting area and driving the semiconductor device at high speed. There is a need for improved packaging technology.
In order to reduce the chip mounting area, stacking chips is used to increase the amount of mounted chips without increasing the mounting area, thereby reducing the effective mounting area. For example, Patent Literature 1 (JP 2001-257307), Patent Literature 2 (2002-050735), and Patent Literature 3 (JP 2000-349228) disclose such techniques. The first one is based on a wire bond system in which a chip and a chip or a chip and a mounting substrate are connected by a wire. The second one is based on a flip chip method in which a chip and a chip or a chip and a mounting substrate are connected via a micro bump provided on the back surface of the chip. In the third method, a chip and a chip or a chip and a mounting substrate are connected using both a wire bond method and a flip chip method.

  In order to increase the driving speed of a semiconductor device, a method realized by reducing the thickness of the chip and using a through electrode is effective. For example, Patent Document 4 (Japanese Patent Laid-Open No. 2000-208702) shows an example in which the thickness is mounted in units of microns.

  The wire bonding method requires a large occupied area larger than the occupied area of the semiconductor bare chip itself in order to stretch the wire around the semiconductor bare chip, and takes a long time because the wires are stretched one by one. On the other hand, in the flip-chip method, since the connection is made by the micro bump formed on the back surface of the semiconductor bare chip, the area for connection is not particularly required, and the area necessary for mounting the semiconductor bare chip is the semiconductor bare chip. It can be almost equal to its own area. Further, since one surface can have all the bumps, connection to the wiring board can be performed in a lump. Accordingly, the flip chip method is the most suitable method for minimizing the electronic equipment and shortening the construction period by minimizing the occupation area necessary for mounting the semiconductor bare chip to achieve high density mounting.

  In addition to the improvement of the chip-mounting substrate and the connection method between the chip and the chip, as a means of reducing the manufacturing cost, a rewiring layer or the like is formed before separating the wafer on which the semiconductor chip is formed into individual chips. Connection bumps are formed, and in some cases, sealing with resin is performed. A semiconductor device in which processing at the wafer level is effective is a semiconductor device having a high manufacturing yield and a small number of pins, and has many advantages particularly in the production of memory. (NIKKEI MICRODEVICE February 2000, page 56 and NIKKEI ELECTRONICS 2003.9.1 P.127).

  On the other hand, development of a manufacturing apparatus for manufacturing such a semiconductor device has also been earnestly performed. For example, Non-Patent Document 1 introduces an apparatus for aligning and bonding wafers to be bonded. (P. Lindner et al .: 2002 Electronic Component and Technology Conference P. 1439). In addition, a similar technique is disclosed in Patent Document 5 (Japanese Patent Laid-Open No. 9-148207).

In such a technique for bonding semiconductor devices to increase the density of elements and increase the operation speed, alignment (alignment) between the bonded semiconductor devices is one of the important techniques. Conventional techniques of this type include a method in which two surfaces of a semiconductor device to be bonded are observed at the same time (for example, by using a two-field camera and a two-field microscope) to align the positions, and two surfaces to be bonded together Can be observed separately at two points separated by a fixed interval, and the positions are aligned by calculating the positional relationship between them. In the method of observing two surfaces at the same time, it is important to observe with the distance between the two surfaces as narrow as possible. For example, Patent Document 6 (Japanese Patent Laid-Open No. 10-163253) discloses an improved technique in this respect. In addition, in order to observe the two surfaces separately at two different points and relate the positions, the measurement accuracy of the distance between the two points and the accuracy of the observation system itself are important. For example, Japanese Patent Laid-Open No. 4-206534 No.) discloses an improved technique of this point.
[Patent Document 1] JP 2001-257307 [Patent Document 2] JP 2002-050735 [Patent Document 3] JP 2000-349228 [Patent Document 4] JP 2000-208702 [Patent Document 5] Kaihei 9-148207 [Patent Document 6] JP-A-10-163253 [Patent Document 7] JP-A-4-206534 [Non-Patent Document 1] Lindner et al .: 2002 Electronic Component and Technology Conference P.M. 1439

  However, with conventional methods, if the wafer diameter increases to 8 inches or 12 inches, adjusting the alignment accuracy to the submicron on the entire wafer surface is insufficient for position measurement accuracy and alignment device drive accuracy. It has become clear that it is impossible.

  The present invention has been made to solve such problems, and an object of the present invention is to provide an overlaying method for bonding two wafers with submicron positional accuracy and an apparatus therefor.

In the present invention, the following means are used to achieve the above object.
A method of superimposing first and second wafers having a plurality of semiconductor devices,
A first wafer fixing step of fixing the first wafer to a first holder having a plurality of fiducial marks in the periphery;
A first measuring step of measuring a positional relationship between the alignment mark on the first wafer and the reference mark;
A second wafer fixing step of fixing the second wafer to a second holder;
A second holder fixing step of fixing the second holder holding the second wafer to a second table movable in the X and Y directions;
Measuring a position coordinate in a reference coordinate system of an alignment mark on the second wafer held by the second holder;
A first holder fixing step of fixing the first holder holding the first wafer to a first table;
A third measuring step of measuring a position coordinate of the reference mark in the reference coordinate system;
Based on the positional coordinates of the reference mark measured in the third measuring step and the positional relationship measured in the first measuring step, the alignment mark on the first wafer in the reference coordinate system A position coordinate determination step for obtaining a position coordinate;
A position adjustment step of adjusting the overlapping position of the first and second wafers based on the results of the position coordinate determination step and the second measurement step;
A proximity step of moving the first and second holders relatively in the Z direction to bring the first and second wafers close together;
An overlapping method, comprising: an overlap fixing step of overlappingly fixing the first and second holders in a state where the first and second wafers are in contact with each other.

In this way, one wafer is positioned at the reference coordinates based on the measurement values of the plurality of alignment marks, and the other wafer is also aligned with the reference coordinate system through the plurality of reference marks based on the positional relationship with the plurality of alignment marks. Therefore, two wafers can be superimposed with high accuracy.
In the present invention, in the first and second measurement steps in the above method, the positional relationship or the position coordinates may be measured by an interferometric method. When the amount of movement of the table is measured by the interferometry method, the position coordinates of the table can be measured with high accuracy. As a result, the measurement accuracy of the position coordinates of the alignment mark is improved, and the overlay accuracy is improved by an order of magnitude as compared with the measurement using other means, for example, a linear scale. In particular, when measuring a long distance, the difference in accuracy becomes significant.

  In the present invention, at least one of the alignment marks on the first wafer or the alignment mark on the second wafer is provided for alignment during the manufacture of the semiconductor device, and the alignment mark used is used. Sometimes. When a semiconductor device is formed on a wafer in a so-called pre-process, an alignment mark is provided on the wafer in order to ensure the overlay accuracy between the layers. In the process of superimposing wafers having semiconductor devices, the use of this alignment mark eliminates the need for a process of engraving the mark again, thereby eliminating the manufacturing cost and time.

  In the present invention, three or more alignment mark positions are measured in at least one of the first measurement process and the second measurement process, and in the position adjustment process, an optimization process is performed to perform overlay. The position may be adjusted. In a pre-process for manufacturing a semiconductor device, the semiconductor device forming surface generally generates stress along with processing, and the forming surface is distorted. Therefore, for example, when only two alignment mark positions are measured and overlapped with each other, the joint portions of the semiconductor devices formed on the two wafers may not overlap correctly. Even if a slight misalignment occurs between the positions of the two alignment marks, the entire alignment mark may be correctly joined as a whole. For this purpose, the alignment position is optimized while viewing the overall position coordinates. The actual optimization method will be described later.

  In the present invention, in the wafer fixing step, the first holder and the second holder may be any one of a vacuum adsorption force, a magnetic force, an electrostatic force, a mechanical fixing force, and an adhesive force of a polymer resin, or these It may be fixed by overlapping. The first and second holders sandwiching the overlapped wafers need to be fixed to each other in order to transport them to the next process. In addition to the magnetic force and electrostatic force that are easy to control electrically, the vacuum adsorption force Is available. These forces are also used to hold the wafer in the holder, and the piping and mechanism system need not be specifically designed. In addition, when a mechanical fixing force is used, conveyance to the next process becomes easy. Furthermore, the adhesive force can be used more simply, and the conveyance to the next process becomes easy as in the mechanical fixing method.

  In the present invention, a baseline measurement step of measuring a distance between measurement means used in the third measurement step as necessary may be performed. As a result, even if the baseline length (distance between the measuring means) varies due to thermal factors or temporal factors, it is possible to prevent an error in measuring the measurement position of the reference mark.

  In the present invention, the first or second holder is positioned within a predetermined position range of the reference coordinate system in at least one of the first measurement process, the second measurement process, and the third measurement process. The rough alignment process may be performed. The wafer is provided with an orientation flat and a notch, and these are used as a guide to roughly align and fix the first table and the second table. As a result, alignment marks and reference marks can be placed in the field of view of the measuring means, and the process time can be shortened by shortening the measurement time and the table driving mechanism can be simplified by shortening the distance to which the table should move. .

  In the present invention, the displacement of the second table in the X and Y directions is measured by an interferometric method during the proximity step, and the displacement of the second table in the X and Y directions is based on the measurement result. The first and second wafers may be brought close to each other while preventing this. After aligning the wafers to be overlapped with each other, the wafers are brought close to each other. In this proximity process, the wafer position coordinates may change. In such a case, during the process in which the wafer is close, the movement in the direction in which the wafer moves and the direction in which the wafer moves perpendicularly is measured, and the positional accuracy of the wafer is corrected based on the result, thereby ensuring overlay accuracy. .

In the present invention, in order to achieve the above object, the following apparatus is provided.
An apparatus for superimposing first and second wafers having a plurality of semiconductor devices,
A first table holding a first holder;
A second table holding a second holder;
A relative movement mechanism that relatively moves the first table and the second table in directions of Z and θz,
A second driving device for moving the second table in the X and Y directions;
Distance measuring means for measuring the amount of movement of the second table;
A reference microscope for measuring a mark on the second table and an alignment mark position on the wafer held on the table;
It is a superposition device having a plurality of measurement microscopes for measuring a plurality of reference mark positions on a holder held on a first table.

This apparatus is particularly suitable for the superposition method described above, and can perform a series of steps.
In the present invention, the measurement accuracy is also increased by using an interferometer as the measurement apparatus. As described above, the measurement of the moving distance by the interferometer is remarkably superior to other measuring means in measuring accuracy.

In the present invention, the second driving device may have a gas bearing. Since the gas bearing can drive the table without contact, it has excellent mechanical stability and positioning accuracy.
In the present invention, an air cylinder may be used for the second drive device. Unlike other electromagnetic drive mechanisms, the air cylinder does not need to move electromagnets or permanent magnets, can be quantified as a whole, and can respond to acceleration / deceleration at high speed.

  In the present invention, the amount of movement of the second table is set to be approximately the same as or larger than the diameter of the wafers to be superimposed. In some cases, the alignment marks on the wafer may be arranged at the edges of each other across the center. In this case, it may be convenient to make the movement amount of the table larger than the diameter of the wafer in order to make it possible to measure the item mark. Correspondingly, the measurement range of the measurement system for measuring the movement amount is also made longer than the diameter of the wafer.

  The present invention may further include a first interferometer that measures the amount of movement of the first table. When superimposing, the table holding the wafer may be displaced due to thermal deformation or aging of the entire apparatus, so this means can accurately measure the displacement of the table to compensate for the displacement. .

In the present invention, there may be a calculation means for optimizing the overlapping position.
The alignment marks of the two overlapping wafers are changed in position due to processing at the time of manufacture even if the design positions are the same. In this case, optimization processing is performed to align the two alignment mark positions so that the entire wafer is properly aligned, and the two wafers are superimposed. As a result, it is possible to realize an appropriate overlay for the entire wafer.

  By using the present invention, it is possible to accurately overlap wafers on which semiconductor devices are formed. In particular, even if there is a surface deformation in the manufacturing process of the semiconductor device, the most appropriate overlapping position can be determined, and the overlapping is realized so that there is no influence of the deformation.

It is a figure which shows the structural member and example of arrangement | positioning of the wafer superposition apparatus of this invention. It is a figure which shows the reference | standard coordinate system in this invention. It is a figure which shows the state which hold | maintained the wafer to the holder of this invention. It is a figure which shows the process of measuring the position of the alignment mark of a wafer and the reference mark of a holder in this invention. It is a figure which shows the reference mark detection process on a wafer by the microscope for a measurement in this invention. It is a conceptual diagram of the proximity | contact process of this invention. It is a figure explaining the member which fixes a holder of this invention. It is a figure which shows the example of the member which fixes a holder mutually mechanically of this invention. It is a figure which shows the process of calibrating the positional relationship of the reference | standard microscope and the measurement microscope in this invention. It is a figure which shows the example of the table of this invention, and a drive device. It is a figure which shows the example of the air cylinder suitable for this invention. It is a figure which shows the flowchart of the wafer superimposition method of this invention.

FIG. 1 is a conceptual diagram of an apparatus configuration showing a state in which members used in the overlaying method of the present invention are held in the overlaying apparatus of the present invention.
In the figure, the first wafer 1 is fixed to the first holder 3, the second wafer 2 is fixed to the second holder 4, and the holders 3 and 4 are respectively attached to the first table 5 and the second table 6. The held state is shown.

Each wafer has a surface opposite to the superposed surface held by each holder by well-known vacuum suction or electrostatic suction. In the figure, a suction hole and suction device for vacuum suction, and an electrode for electrostatic suction are shown. The power supply unit is omitted. The holder holding surface of the first table 5 and the holder holding surface of the second table 6 face each other, and when the holder holding the wafer is fixed, the overlapping surfaces of the wafers face each other. Although the first table 5 is coupled to the first drive device 10, the function of this device has design freedom. For example, there may be provided a “function for moving the first and second tables (wafers) in the directions of relative Z and θz” according to claim 9 and a function for finely moving the first holder. In some cases, the device may not be necessary. The second table 6 is moved in at least the X and Y directions by the second driving device 9, and the movement amount of the second table 6 is measured by a distance measuring device, for example, an interferometer 11.
As described above, the “function for moving the first and second tables (wafers) in the directions of relative Z and θz” according to claim 9 may be incorporated in the second driving device 9. . An alignment mark is formed on the first and second wafers, and a reference mark 22 is formed on the holder. The positions of these marks are observed when the wafer is aligned. The reference microscope 7 and the measurement microscope 8 are arranged as an observation device for that purpose, and the positional relationship between the reference microscope 7 and the measurement microscope 8 is in a predetermined arrangement. Has been made. The reference microscope 7 is adjusted so that the reference mark and the alignment mark become the object surface of the optical system of the microscope when the second table 4 is located at a predetermined height position. The reference mark 22 of the first holder 3 held on the first table 5 is observed from the back surface of the holder, and when the holder is held, the reference mark 22 becomes an object surface of the optical system of the microscope. Has been adjusted. In this configuration, when the stacked wafers are further stacked, since the thickness of the second wafer 2 is different, it may be necessary to adjust the height of the reference mark 22 of the second holder 2. . For this reason, a piezo element (not shown) is provided, and adjustment in the height direction is performed as necessary.

  Although not essential to the present invention, a reference coordinate system (X, Y) with the reference microscope 7 as the origin and the moving direction of the table 6 as the X and Y axes is used in order to determine the position of the wafer or the like to be superimposed. Is set. Therefore, the position of the measuring microscope 8 has a predetermined coordinate value in the reference coordinate system. When two wafers are overlapped, the origin and the rotation angle are matched, so that at least two alignment marks are required. See FIG.

  The operation of the superposition apparatus will be described below, and the superposition method of the present invention will be described.

First, the positional relationship between the reference mark 22 on the first holder 3 and the first wafer 1 held by the holder is obtained.
As shown in FIG. 3, one wafer 1 to be superimposed is fixed to a first holder 3 having a plurality of reference marks 22 in the peripheral portion by well-known vacuum suction or electrostatic suction. The first holder 3 is held on the second table 6 and the reference mark 22 of the holder 3 is detected by the reference microscope 7 as shown in FIG. Next, as shown in FIG. 4B, the second drive device 9 moves the second table 6 to detect the alignment mark 23 on the first wafer 1. At this time, the movement amount of the second table 6 is detected by the movement amount measuring means, for example, the interferometer 11, and the positional relationship between the reference mark 22 and the alignment mark 23 is obtained.

In the present apparatus, the moving range of the second table 6 is set to be equal to or larger than the diameter of the wafer to be overlaid so that the above measurement can be performed.
In this embodiment, the positional relationship between the alignment mark 23 on the wafer 1 fixed to the holder 1 and the reference mark 22 on the holder is obtained by using the superimposing apparatus according to the present invention. For example, measurement may be performed using a light wave coordinate measuring device or the like.

  Furthermore, in the present invention, the alignment mark formed on the wafer at the time of manufacturing the semiconductor device is used as the alignment mark on the wafer at the time of superposition, thereby reducing the cost by omitting the step of providing a new mark. Has also been done.

Next, the position coordinate of the alignment mark of the second wafer 2 is measured in the reference coordinate system.
The second wafer 2 is held on the second holder 4 in the same manner as the first wafer is held on the first holder. The first wafer 1 and the first holder 3 whose positional relationship is determined are removed from the second table 4, and the second holder 4 holding the second wafer 2 is fixed to the second table 6. The second driving device 9 is operated to sequentially move the alignment marks on the second wafer 2 into the field of view of the reference microscope 7 and the amount of movement is measured by a distance measuring device, for example, an interferometer 11. Thereby, the positional relationship between the optical axis of the reference microscope 7 and each alignment mark is obtained. (Same operation as in FIG. 4B.) As a result, the position of the alignment mark on the second wafer 2 in the reference coordinate system is determined.

  When the coordinates of the alignment mark of the second wafer 2 are obtained, the first holder 3 that holds the first wafer 1 is fixed to the first table 5, and the reference coordinate system of the alignment mark of the first wafer 1 is used. Find the position coordinates. The procedure is described below.

  As shown in FIG. 5, coarse adjustment is performed in advance so that the reference mark 22 of the holder 3 enters the field of view of the measuring microscope 8 whose coordinate position in the reference coordinate system is known, and the reference mark 22 is observed. According to claim 7 of the present invention, “the holder is positioned within a predetermined position range of the reference coordinate system” means that “the alignment mark on the wafer held by the holder is in the field of view of the measuring microscope or on the holder. This means that the fiducial mark is positioned so that it falls within the field of view of the fiducial microscope and the measuring microscope. For this rough adjustment, position adjustment based on the orientation flat or notch of the wafer is performed. As a specific method, for example, the technique disclosed in Japanese Patent Laid-Open No. 9-283604 by Tsuda-Hikima can be used. However, even with this rough adjustment, the reference mark 22 may not be within the observation field of the measurement microscope 8. For this purpose, the first drive device includes a drive mechanism for moving the first table 5 by a small amount. If the reference mark 22 does not fall within the observation field of view of the measuring microscope 8, the position of the first table 5 is adjusted. This drive mechanism can be configured using, for example, a piezo element. For example, it can be configured by the technique disclosed in Japanese Patent Application Laid-Open No. 2002-359170 by Tanaka.

  In the measuring microscope 8, an index having a fixed relationship with the optical axis is disposed in the field of view (actually, the index is disposed at a position conjugate with the image plane of the microscope). When observed, the positional relationship between the reference mark 22 and the optical axis of the measuring microscope 8 is obtained. As described above, since the position coordinate in the reference coordinate system of the measurement microscope is known, the position coordinate of the reference mark 22 in the reference coordinate system is determined from the position of the reference mark 22 with respect to the optical axis of the measurement microscope 8. The positional relationship between the alignment mark 23 and the reference mark 22 on the wafer 1 has been measured in the first measurement step. Accordingly, the position coordinates of the alignment mark 23 of the wafer 1 in the reference coordinate system are determined via the position map of the reference mark 22 in the reference coordinate system.

  Once the alignment mark coordinates on the first wafer 1 and the alignment mark coordinates on the second wafer are determined, the overlapping positions of the first and second wafers are then adjusted. The method will be described below. The overlapping position adjustment is performed using the second driving device 9 and the relative movement mechanism. For example, when the relative movement mechanism is incorporated in the first driving device 10, the second driving device 9 is used to translate the second wafer, and the first driving device 10 is used for the first driving. Rotate the wafer.

従って、２つのアライメントマークの位置座標を用いることにより、上式より移動量（Ｔｘ、Ｔｙ）及びθの値が定まる。このＴｘ、Ｔｙ、θを用いて駆動装置６及び相対移動機構を働かせると、第１のウェハ１、第２のウェハ２を互いに重ねあわせる位置が調整されたことになる。 At this time, the parallel movement amount to be translated and the rotation amount to be rotated are calculated as follows.
When the amount of movement of the second wafer is (Tx, Ty) and the amount of rotation is θ, the measured alignment mark position coordinates (Xm, Ym) and the converted position coordinates (Xc, Yc) There is the following relational expression between them.
<Equation 1>

Therefore, by using the position coordinates of the two alignment marks, the movement amounts (Tx, Ty) and θ are determined from the above formula. When the driving device 6 and the relative movement mechanism are operated using the Tx, Ty, and θ, the position where the first wafer 1 and the second wafer 2 are overlapped with each other is adjusted.

  By the way, in general, an in-plane deformation of the circuit surface of the wafer is caused by a pre-process of wafer processing. When wafers having such deformations are overlapped with high accuracy, three or more alignment marks on the wafer are prepared, and the wafers that are deformed with respect to each other are overlapped with each other so as to achieve the highest accuracy. Optimize the positional relationship. An example of optimization is shown below.

次に、第１のウェハ上のアライメントマークの、基準座標系での位置座標を（Ｄｘｉ，Ｄｙｉ）とし、最小自乗法によりθ、Ｔｘ、Ｔｙを求める。即ち、関数Ｆ（θ、Ｔｘ、Ｔｙ） ＝ Σ（（Ｄｘｉ−Ｍｘｉ）^２ ＋ （Ｄｙｉ−Ｍｙｉ）^２）が最小値になるようにθ、Ｔｘ、Ｔｙを定める。 The position coordinate of the alignment mark measured on the second wafer in the reference coordinate system is (Axi, Ayi). i are prepared for the number of alignment marks. When the wafer is rotated and translated, the coordinates (Mxi, Myi) after conversion of the alignment marks are as follows, as described above.
<Equation 2>

Next, the position coordinate of the alignment mark on the first wafer in the reference coordinate system is (Dxi, Dyi), and θ, Tx, Ty are obtained by the method of least squares. That is, θ, Tx, and Ty are determined so that the function F (θ, Tx, Ty) = Σ ((Dxi−Mxi) ² + (Dyi−Myi) ² ) becomes the minimum value.

  This apparatus incorporates an optimization calculation means as a part of the control function so as to perform the above-described optimal calculation. For example, a programmed DSP is incorporated in the control system 30.

In the above description, when determining the overlay position between the wafers, the optimization process is performed based on the positional relationship between the alignment marks on the two wafers. The position and orientation of each wafer, that is, the optimum values of Tx, Ty, and θ, may be determined in advance in the system. In this case, the position of the alignment mark may be different between the two wafers.
When the positional relationship between the first and second wafers is determined, the two wafers are brought close to each other by the second driving device 9. At this time, the fluctuation in the XY plane of the moving second table 6 is measured by the interferometer 11 and is brought close to the second driving device 9 while applying feedback so that it is within a predetermined deviation range. See FIG. However, when the wafer interval is sufficiently narrow and the positional deviation between the wafers is small due to proximity, it is not necessary to observe the in-plane variation.

  After confirming contact between the wafers based on an output value of a load cell (not shown), the holders 3 and 4 are fixed while the wafers 1 and 2 are held in contact. A member used for this purpose is shown in FIG. In FIG. 7, reference numeral 42 denotes a connecting portion for connecting two holders, which is a bellows. The connection end portion 43 made of a rubber material is pressed against the other holder surface and exhausted from the exhaust hole 41 to fix the two holders. The connection in FIG. 7 may be other than vacuum suction, and an electrode may be arranged at the connection end to perform electrostatic suction, or an electromagnet may be arranged to use magnetic force suction. Further, a polymer resin having a temporary adhesive force may be fixed through the middle. Furthermore, the mechanical fixing force may be used in the configuration as shown in FIG. FIG. 8A shows the first holder 3 and has a notch 82. Although the number of the notches 82 is one in the drawing, a plurality of, for example, three in the periphery are provided. FIG. 8B shows a fixing mechanism on the second holder 4. This mechanism includes a T-shaped member 84, a rotary receiver 85 that rotatably holds the member, and a rubber tube 83 that is wound around the axis of the T-shaped member and fixed to the upper surface of the T-shaped member. Yes. When the two holders holding the wafer come close to each other, the T-shaped member of the second holder is rotated and inserted into the notch portion 82 of the first holder. Here, when air is introduced from the introduction pipe 86, the rubber pipe expands and pressurizes the first holder 3. When the pressure reaches an appropriate value, the introduction tube is separated from the air insertion mechanism and can be transferred while holding the two wafers. This mechanism can be achieved by using, for example, a bicycle air pressure holding mechanism.

The method for aligning two wafers and superimposing them and the configuration of the apparatus used therefor have been described above, but operations related to apparatus maintenance will be further described.
In the position coordinate determination step of the first wafer 1 described above, the positions of the reference microscope 7 and the measurement microscope 8 in the reference coordinate system are known and the coordinates are determined. However, the coordinates may change due to thermal causes or temporal causes. In the present invention, in order to cope with such a case, a calibration process as described below is provided as necessary.

  First, as shown in FIG. 9A, the fiducial mark 21 on the second table 6 is placed in the visual field by the reference microscope 7. Next, as shown in FIGS. 9B and 9C, the second table 6 is moved to place the previous fiducial mark 21 in the field of view of the measuring microscope 8. At this time, the positional relationship between the reference microscope 7 and the measuring microscope 8 can be calibrated by measuring the movement amount of the second table 6 by the interferometer 11. At this time, since the object planes of the reference microscope 7 and the measuring microscope 8 are not the same on the Z axis, after observing the fiducial mark 21 with the reference microscope 7, the second table 6 is slightly moved to the Z axis. Move in the direction (upward) and observe.

Based on FIG. 10, a preferred second table 6 of the present invention and a second driving device 9 which is a driving device thereof will be described.
The 2nd table 6 is hold | maintained with respect to the base | substrate 92 by the support body 91 via the air bearing. That is, an air bearing is disposed on the lower surface of the holding body 91 facing the base, and the second table 6 is held without contact with the base. The second table 6 is attached to the second driving device 9. The second drive device 9 has a drive guide 93 fixed to the base 92 and a slider 94 guided by this guide. Furthermore, a second guide 95 fixed on the slider 94 and a second slider 96 guided by the second guide 95 are provided, and the second table 6 is attached to the second slider 96. The sliders 94 and 96 are driven by an air cylinder. A specific configuration example is shown in FIG. In FIG. 11, 121 is a slider and 111 is a guide. The slider is moved with respect to the guide by controlling the pressure of P1 and P2 with the pressure receiving plate 116 interposed therebetween.

In the above description, the superposition method and apparatus of the present invention should be understood, but a flowchart of the superposition method is described for confirmation.
As described above, in the present process, S1 and S2 do not need to use the apparatus of the present invention, and the order may be anywhere before S6.

  It is a remarkable industrial trend to effectively increase the density of elements by stacking semiconductor devices. This lamination requires alignment between wafers, and there is a need for a more accurate method and apparatus for that purpose. Therefore, the present invention is an inevitable technique in the semiconductor industry.

1, 2, ... Wafers 3, 4 ... Holders 5, 6 ... Table 7 ... Reference microscope 8 ... Measuring microscope 9, 10 ... .. Driving device 11... Distance measuring means 21... Fiducial mark 22 .. Reference mark 23... Alignment mark 30. ... Exhaust port 42 ... Connector 43 ... Connector end 82 ... Notch 83 ... Rubber tube 84 ... T-shaped member 85 ······················································································································ Bases 93 and 95 ··· ··· Guide 121 ··· Slider 116 ··· Pressure plate

Claims (15)

A method of superimposing first and second wafers having a plurality of semiconductor devices,
A first wafer fixing step of fixing the first wafer to a first holder having a plurality of fiducial marks in the periphery;
A first measuring step of measuring a positional relationship between the alignment mark on the first wafer and the reference mark;
A second wafer fixing step of fixing the second wafer to a second holder;
A second holder fixing step of fixing the second holder holding the second wafer to a second table movable in the X and Y directions;
Measuring a position coordinate in a reference coordinate system of an alignment mark on the second wafer held by the second holder;
A first holder fixing step of fixing the first holder holding the first wafer to a first table;
A third measuring step of measuring a position coordinate of the reference mark in the reference coordinate system;
Based on the positional coordinates of the reference mark measured in the third measuring step and the positional relationship measured in the first measuring step, the alignment mark on the first wafer in the reference coordinate system A position coordinate determination step for obtaining a position coordinate;
A position adjustment step of adjusting the overlapping position of the first and second wafers based on the results of the position coordinate determination step and the second measurement step;
A proximity step of moving the first and second holders relatively in the Z direction to bring the first and second wafers close together;
An overlapping method, comprising: an overlapping fixing step of overlappingly fixing the first and second holders in a state where the first and second wafers are in contact with each other. The superposition method according to claim 1,
In the first measurement step or the second measurement step,
An overlay method, wherein the positional relationship or position coordinates are measured by an interferometric method. The superposition method according to claim 1 or 2,
Of the alignment marks on the first wafer or the alignment mark on the second wafer, at least one of the alignment marks is an alignment mark that is provided and used for alignment when the semiconductor device is manufactured. How to superimpose.   4. The overlay method according to claim 1, wherein the positions of three or more alignment marks are measured in at least one of the first measurement step and the second measurement step, and A superimposing method comprising adjusting an overlapping position by performing an optimization process in a position adjusting step.   5. The superposition method according to claim 1, wherein in the wafer fixing step, the first holder and the second holder are made to have a vacuum adsorption force, a magnetic force, an electrostatic force, a mechanical fixing force, A method of superposition, characterized in that the superposition is performed by any one of the adhesive forces of polymer resins or a combination thereof. The superposition method according to any one of claims 1 to 5,
An overlaying method comprising a baseline measuring step of measuring a distance between measuring means used in the third measuring step as necessary. The superposition method according to any one of claims 1 to 6,
In at least one of the first measurement step, the second measurement step, and the third measurement step,
An overlaying method comprising a rough alignment step of positioning the first or second holder within a predetermined position range of a reference coordinate system. The superposition method according to any one of claims 1 to 7,
During the approaching step, the displacement of the second table in the X and Y directions is measured by interferometry, and the second table is prevented from being displaced in the X and Y directions based on the measurement result. A method for superimposing the first and second wafers. A superposition apparatus for superposing first and second wafers having a plurality of semiconductor devices,
A first table holding a first holder;
A second table holding a second holder;
A relative movement mechanism that relatively moves the first table and the second table in directions of Z and θz,
A second driving device for moving the second table in the X and Y directions;
Measuring means for measuring the amount of movement of the second table;
A reference microscope for measuring a mark on the second table and an alignment mark position on the wafer held on the table;
A superposition apparatus comprising a plurality of measurement microscopes for measuring a plurality of reference mark positions on a holder held by a first table The superposition device according to claim 9,
An overlay apparatus, comprising: an interferometer as measurement means for measuring the movement amount of the second table. The superposition device according to claim 9 or 10,
The superposing device, wherein the second driving device has a gas bearing. The superposition device according to any one of claims 9 to 11,
The superposing apparatus, wherein the second driving device has an air cylinder. The superposition device according to any one of claims 9 to 12,
An overlay apparatus, wherein the movement amount of the second table is equal to or larger than a diameter of a wafer to be superimposed. The superposition device according to any one of claims 9 to 13,
The overlay apparatus further comprising a first interferometer for measuring a moving amount of the first table. The superposition device according to any one of claims 9 to 14,
A superposition apparatus comprising arithmetic means for optimizing the superposition position.

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