JP4185893B2 - Wafer grip fingers to minimize distortion - Google Patents

Description

<Related applications>
This application is a continuation-in-part of US application 09 / 674,814, referred to as a wafer grip finger, filed on Nov. 6, 2000. This application claims the priority of US Provisional Application 60 / 483,426, called Wafer Grip Finger, which minimizes the distortion of the application filed on June 27, 2003.
<Declaration on research and development supported by the federal government>
None

<Background of the invention>
The present invention generally relates to an apparatus and method for measuring the shape of a semiconductor wafer, and more particularly to an apparatus and method for measuring the shape of a semiconductor wafer with improved accuracy.

  In the manufacture of semiconductor devices, the shape of a semiconductor wafer is typically measured to determine whether the wafer meets a predetermined standard or standard. Such standards relate to various wafer shape parameters such as flatness, bow, warp, etc. If it is determined that the semiconductor wafer does not meet a predetermined wafer shape standard, the wafer may be considered unusable and is therefore discarded.

  For example, when testing and / or measuring a wafer during semiconductor manufacturing, the semiconductor wafer may be held in a horizontal or vertical position by a wafer handling device. Such wafers are often held in a horizontal position to reduce wafer sag due to gravity and to reduce wafer contamination by minimizing horizontal surfaces to which molecules in the outside air can float. To do. However, if the semiconductor wafer is excessively warped or distorted, the results obtained from the wafer test and measurement may not be accurate. In addition, such excessive bowing or warping of a semiconductor wafer may cause undesirable stress on thin film layers that may have previously settled on the wafer surface.

  Not only is there a possibility of excessive bow and warp in a semiconductor wafer, the wafer handling device itself may exacerbate the wafer bow and warp. For example, conventional wafer handling devices typically include a wafer gripping finger having a V-shaped groove configured to hold a wafer edge. Wafer grip finger grooves are typically made of the non-contaminating material polyetheretherketone (PEEK) used in various applications in the semiconductor industry. Wafer grip finger grooves may distort the shape of the wafer, since V-shaped grooves may over-constrain the wafer and cause an indeterminate load on the groove / wafer contact surface. For example, if the semiconductor wafer is held in a vertical position by a V-shaped groove, torque may be generated and the wafer may be twisted, which increases the error in wafer shape measurement. Furthermore, measurement errors induced by such loads are often a function of the original shape of the wafer being measured. For this reason, it is difficult, if not impossible, to separate the load induced error from the measured wafer shape parameters.

  Accordingly, it is desirable to have an apparatus and method within a wafer test or metrology station that minimizes any distortion in the wafer shape and accurately places and holds the semiconductor wafer. Such a device would place the wafer in a wafer test and measurement station so that the wafer fits within the area of the measurement device over the range of wafer shape parameters. It would also be desirable to have an apparatus and method for holding a wafer in a wafer test and measurement station so that not only wafer distortion is minimized, but also a reliable wafer grip force can be generated.

<Simple summary of invention>
In accordance with the present invention, a semiconductor wafer shape measurement apparatus and method that minimizes distortion of the wafer being measured is disclosed. In one embodiment, the apparatus includes a plurality of wafer grip fingers configured to hold the semiconductor wafer in place during wafer testing and measurement. Each wafer grip finger includes a groove configured to contact the edge of the wafer. The groove and wafer edge each have a radius of curvature, and the radius of curvature of the groove to ensure that the wafer gripping finger contacts only one point, a patch or a section of the groove. Is larger than that of the wafer edge. In a preferred embodiment, the contact point, subregion or area is located in the central region of the groove. Further, each wafer grip finger preferably includes a stainless steel blank having a substantially horseshoe-shaped recess at a central location at one end thereof. Each wafer grip finger further includes a compliant, non-contaminating material disposed in the recess protruding from the entire length of the steel blank end. In the preferred embodiment, the compatible non-staining material is polyetheretherketone (PEEK). The groove is formed in the portion of PEEK protruding from the steel blank. Since the PEEK is located along the entire length of the end of the steel blank and fills the centrally located recess, the PEEK first protrudes from the steel blank at a central position by a first predetermined distance; Next, a second predetermined distance protrudes from the steel blank on both sides of the recess. Here, the first predetermined distance is larger than the second predetermined distance.

As a result, the central region of the groove that contacts the wafer edge is more suitable than the groove portion on each side of the central region, thereby reducing the distortion of the semiconductor wafer when contacting the wafer edge. Further, since the groove portions on both sides of the central region are harder than the central region of the groove, the plurality of wafer grip fingers can hold the semiconductor wafer with high accuracy.
Other features, functions, and aspects of the present invention will be apparent from the detailed description of the invention set forth below.

<Detailed Description of the Invention>
No. 09 / 674,814 filed Nov. 6, 2000 (Wafer Grip Finger) is incorporated herein by reference. No. 60 / 483,426 filed Jun. 27, 2003 (grip fingers that minimize distortion) is incorporated herein by reference.

  Disclosed is a semiconductor shape measuring apparatus and method for minimizing distortion of a wafer to be measured. The apparatus and method disclosed herein employs a plurality of wafer grip fingers to hold a test semiconductor wafer, each wafer grip finger having a single point, a patch, or a section of the central portion. One groove is in contact with one end of the wafer. The grooves are more conformable in the central area but stiffer at the end areas on either side of the central area, so that the plurality of wafer grip fingers can hold the wafer with increased accuracy while reducing distortion. .

  FIG. 1 depicts a wafer 12 typically made of a semiconductor material such as silicon. The wafer 12 is supported by three wafer grip fingers 14, 16, 18. Prior art wafer grip fingers 14, 16, 18 are shown in FIGS. 2a-2c. As shown in FIGS. 2 a-2 c, the finger has a body 20 having a groove 24 for holding the wafer 12 in a region 22 at one end thereof. As shown in FIG. 2b, the groove 24 contacts the wafer 12 at two points 26 and 28 that are physically separated. By using three fingers, six contact points will hold the wafer, but at any one of these points excessive wafer constraints may occur that force, torque, or stress cannot be accurately controlled. is there. The force may occur in a direction deviating from the wafer plane. As a result, the wafer may experience deformation forces and torques that can cause dimensional measurement errors.

  3a-3c depict a wafer grip finger 32 having a curved groove 34 with a radius of curvature that is greater than that of the edge of the wafer. The wafer contacts only at a central point. The contacts may be small areas or areas of finite size. Contact limited to a single point or area minimizes the deformation force on the wafer and improves measurement accuracy.

  For example, the wafer gripping fingers 32 have grooves coated with Teflon or other suitable low friction material to mitigate friction-induced forces, particularly those that deviate from the wafer plane. May be. The finger itself may be made of such a material.

  FIG. 4 depicts the contact patch 36 and groove 34 of the wafer in more detail. As shown in FIG. 4, since all the force applied to the wafer is within the plane of the wafer, the force that deforms the wafer hardly occurs or is equal to zero. If a V-shaped groove as shown in FIGS. 2a-2c is used, the contact stress deviates from the plane of the wafer, causing a force to deform the wafer.

Figure 5 is a graph showing the effect of the song in the radii on opposite shearing the plane force of the groove, the curvature of the wafer edge radius (i.e., r _e) are shown over a range of more than twice from. As shown in FIG. 5, when the radius of curvature of the groove is increased, the shear deformation force is substantially reduced.

  FIG. 6a shows another embodiment of an apparatus 100 for holding a semiconductor wafer 104 according to the present invention. In the illustrated embodiment, the wafer holding device 100 includes a plurality of wafer grip fingers 102 that can be operated to hold a wafer 104 such as a silicon wafer in a position selected from a horizontal position to a vertical position. As shown in FIG. 6a, the wafer holding device 100 uses three wafer grip fingers 102 to hold the wafer 104 in a substantially vertical position. The wafer holding device 100 may be a part of a wafer transport handle, a supporting fixture for holding the wafer 104 on a wafer test / measurement station, or other suitable for handling semiconductor wafers. Any device or system can be used. For example, the wafer holding device 100 may be part of a suitable dimension measuring machine manufactured by ADE Corporation of Westwood, Massachusetts.

6b is a side view of one of the plurality of wafer grip fingers 102 of FIG. 6a. As shown in Figure 6b, the wafer gripping finger 102 includes a predetermined radius of curvature is r _f, substantially groove 101 having a circular cross-section. Furthermore, the edge of the semiconductor wafer 104 has a predetermined radius of curvature r _e. In the preferred embodiment, the radius of curvature r _f of the groove 101 is greater than the radius of curvature r _e of the edge of the wafer 104. As a result, the wafer gripping finger 102 contacts the wafer edge substantially at only one point, a small area, or only one area 103 of the groove 101, and induces a reduction in the amount of twist and torque on the wafer 104 during loading. .

  In the preferred embodiment, each wafer grip finger 102 contacts the edge of the semiconductor wafer 104 substantially in the central region of the groove 101 so that all of the forces that the plurality of wafer grip fingers 102 exert on the wafer 104 are applied. It is guaranteed to be within the plane of 104. Such stresses that fall within the plane of the wafer 104 essentially cannot deform the wafer 104. As a result, one or more conventional measurement probes 110 (see, eg, probes 1 and 2 in FIG. 6b) can be employed to reduce measurement errors induced during loading while maintaining flatness, bows, warps, etc. The wafer shape parameters such as can be measured.

  FIG. 7 is a detailed view of one of the wafer grip fingers 102 (see also FIG. 6a). In the illustrated embodiment, the wafer grip finger 102 includes a solid member 102a and a compatible non-contaminating material 202 disposed on the solid member 102a having a curved groove 101 formed therein. For example, the solid member 102a can be a metal blank made of stainless steel or other suitable material. Further, the compatible non-staining material 202 can be polyethyl ether ketone (PEEK) or other suitable material. Still further, the PEEK material 202 may be placed on the metal blank 102 a by molding or other suitable manufacturing process to form the groove 101 in the PEEK material 202. The preferred embodiment employs an injection mold process to ensure that all wafer grip fingers 102 contained within the wafer holding device 100 are substantially identical. As shown in FIG. 7, the PEEK 202 protrudes from the end of the metal blank 102a by a first predetermined distance 206 at the center of the groove 101 and by a second predetermined distance 208 at opposite ends of the groove 101. To do. Here, the distance 206 is larger than the distance 208.

  Accordingly, the central region of the groove 101 is more suitable than the opposite end portions of the groove 101 because the thickness is increased at the central position of the PEEK material 202 as indicated by the predetermined distance 206. Further, as indicated by the predetermined distance 208, the PEEK material 202 has a small thickness at the end position, so that the end portion of the groove 101 is stronger than the central region of the groove 101.

  Since each wafer grip finger 102 contacts the edge of the semiconductor wafer 104 in a more suitable central region of the groove 101 (see FIG. 6a), wafer deformation and wear are reduced. In addition, since the groove 101 is stronger on both sides of the central region, particularly at the end of the groove, the plurality of wafer grip fingers 102 can hold and arrange the wafer with high accuracy. It is worth noting that reducing the thickness of the PEEK material 202 in the end region of the groove 101 increases the structural strength of the wafer gripping finger 102.

FIG. 8 shows a simulation of stress concentration in the wafer gripping finger 102 when holding the semiconductor wafer 104 for test or measurement (see also FIG. 6a). For example, simulation of such stress concentrations within a wafer grip finger can be determined using ANSYS ^™ finite element analysis software or other suitable software analysis tool. The stress concentration simulation of the multiple zones depicted in FIG. 8 corresponds to a loading stress on the wafer of about 3.5 kg by the wafer gripping finger, which causes a deflection of about 25 nm in the conformal central region, as indicated at 302 Become. The stress concentration is highest in the central region 302 of the groove and gradually decreases from the central region 302 of the groove toward the end portion as indicated by reference numeral 304.

FIG. 10 is a detailed view of the stainless steel blank 102a contained within the wafer grip finger 102 (see also FIG. 6a). In the illustrated embodiment, the steel blank 102a includes substantially horseshoe-shaped depressions 504 formed in opposing surfaces of the steel blank 102a. As shown in FIG. 10, a plurality of holes 502 are formed in the recessed portion 504 through the steel blank 102a. As a result, when the PEEK material 202 is placed in the recess 504 of the steel blank 102a, the PEEK material 202 flows through the plurality of holes 502 and joins the steel blank 102a. In this way, a substantially closed frame PEEK material is formed on the steel blank 102a with better structural adhesion. The steel blank 102a further includes a recess 206a that allows accumulation of the PEEK material 202 near the central region of the groove 101 where the wafer gripping finger 102 contacts the wafer (see FIG. 7). For example, the appropriate dimensions of the recess 206a can be determined to achieve a predetermined thickness 206 (see FIG. 7) of the PEEK material 202 based on a predetermined stress applied to the wafer by the wafer gripping fingers. In the preferred embodiment, the indentations 504 and indentations 206a formed in the steel blank 102a have a plurality of circular corners 506 that serve to reduce the strength of stress concentrations in the PEEK material 202 (see FIG. 7) (see FIG. 10), thereby preventing premature failure of the wafer grip fingers. FIGS. 9 and 11 are solutions of a simulation of stress concentration in the wafer gripping finger 102 when holding the semiconductor wafer for testing and measurement. As described above with reference to FIG. 8, simulation of stress concentration in such wafer grip fingers is determined using ANSYS ^™ finite element analysis software or other suitable software analysis tools. As shown by the black shading in FIG. 9, the strength of the stress concentration in the PEEK material 202 is in the region adjacent to the rounded corner of the depression 504 (see reference numerals 402 and 404) and the rounded corner of the depression 206a. It is attenuated in the adjacent region (see reference numeral 406).

  The preferred thicknesses 206 and 208 of the PEEK material 202 (see FIG. 7) can be determined based on the predetermined stress that the wafer gripping finger 102 applies to the semiconductor wafer (see FIG. 6a). For example, a suitable thickness 208 for the PEEK material 202 may be determined to be approximately 0.8 mm. FIG. 11 shows a simulation of stress concentration in the wafer gripping finger 102 when holding the wafer, where the PEEK material thickness 208 is about half of the exemplary thickness of 0.8 mm, ie, about 0.4 mm. is there. The area of the plurality of stress concentration simulations depicted in FIG. 11 corresponds to a load force of about 2 kg applied to the wafer by the wafer gripping finger 102.

  The stress concentration is highest in the central region 602 of the groove and decreases at the end portion of the groove, as indicated by reference numeral 604. Furthermore, in this illustrated example, indications of the steel blank 102a (see FIG. 10) due to non-optimal PEEK thickness 208 are observed, as indicated by reference numeral 606. For example, the PEEK material in the central area 602 of the groove may deform across the steel blank portion 606 and may cause undesirable wafer deformation and / or contamination. However, if the PEEK material thickness 208 is about twice the exemplary preferred thickness of 0.8 mm, ie, about 1.6 mm, the wafer will still remain even if wafer deformation, contamination, and wear are reduced. Unstable when held by gripping fingers. Accordingly, the thickness of the PEEK material employed in the wafer gripping finger 102 may be optimized based at least in part on the loading conditions of the wafer and the requirements of the dimension measuring machine.

  The wafer grip finger 102 (see FIG. 6a) of the present disclosure can be used when the semiconductor wafer to be measured is to be accurately held with low deformation and high loading accuracy. Wafer contamination is minimized by reducing the contact area between the individual wafer grip fingers and the wafer edge and by selecting the material used to form the finger grooves. Furthermore, since the radius of curvature of the groove of the finger is larger than that of the wafer edge, the twist and deformation of the wafer are reduced. The curved grooves of the wafer grip fingers, preferably made of molded PEEK material, improve the manufacturability, reliability and loading accuracy of the wafer grip fingers.

  Those of ordinary skill in the art can make changes and changes to the wafer grip fingers that minimize the deformation described above without departing from the inventive concepts disclosed herein. Accordingly, the invention should not be viewed as limited except by the scope and spirit of the appended claims.

The present invention is fully understood in connection with the following detailed description in conjunction with the drawings. Those drawings are:
A perspective view of a semiconductor wafer held by a plurality of wafer gripping fingers; Illustration of prior art wafer grip fingers Illustration of prior art wafer grip fingers Illustration of prior art wafer grip fingers 1 is a view of a wafer gripping finger having a curved groove for contacting the edge of the semiconductor wafer of FIG. 1 is a view of a wafer gripping finger having a curved groove for contacting the edge of the semiconductor wafer of FIG. 1 is a view of a wafer gripping finger having a curved groove for contacting the edge of the semiconductor wafer of FIG. Explanatory drawing of consideration when designing wafer grip finger according to the present invention Explanatory drawing of consideration when designing wafer grip finger according to the present invention A perspective view of an apparatus for holding a semiconductor wafer according to the present invention; A side view of a wafer gripping finger used to hold a semiconductor wafer when testing or measuring, included in the apparatus of FIG. 6a; A perspective view of the wafer gripping finger of FIG. 6b; Drawing depicting simulated stress concentration in the wafer gripping finger of FIG. 6b when the semiconductor wafer is held for testing or measurement. Drawing depicting simulated stress concentration in the wafer gripping finger of FIG. 6b when the semiconductor wafer is held for testing or measurement. A perspective view of the stainless steel blank contained within the wafer gripping finger of FIG. 6b. FIG. 6b is a drawing simulating stress concentration in the wafer gripping finger of FIG. 6b when a representative thickness of PEEK material is employed in the wafer gripping finger.

Claims (10)

A plurality of wafer gripping fingers (102) configured to hold the semiconductor wafer (104) in place, the wafer having an edge, each wafer gripping finger having a rectangular solid member (102a) The solid member includes a free end including an edge having a first straight portion, a second straight portion, and a horseshoe-shaped portion provided between the first and second straight portions; The horseshoe shape forms a depression at the free end of the rectangular solid member,
Each wafer gripping finger further includes a compatible non-contaminating material (202), the compatible non-contaminating material being a first portion provided on each of the first and second straight portions of the free end edge. , And a second portion provided in the horseshoe-shaped portion of the free end edge to fill the recess at the free end of the solid member, provided on each of the first and second straight portions of the free end edge Each first portion of the compatible non-contaminating material has a first predetermined thickness (208) and a second portion of the compatible non-contaminating material that fills the depression at the free end of the solid member. The portion has a second predetermined thickness (206);
The compatible non-contaminating material has a groove (101) formed across the first and second straight portions of the free end edge of the solid member across the recess at the free end of the solid member ;
The groove is provided opposite to the central region (302) provided opposite to the recess at the free end of the solid member and the first and second straight portions of the free end edge of the solid member. An end portion (304), and a central region of the groove is configured to contact the wafer edge;
The second predetermined thickness of the compatible non-contaminating material is greater than the first predetermined thickness of the compatible non-contaminating material, and the central region of the groove contacting the wafer edge is from each end portion of the groove, More adaptable, which reduces wafer deformation and wear,
Semiconductor wafer handling equipment. Has a circular curve cross section the groove has a Jo Tokoro radius of curvature (r _f),
The apparatus of claim 1. The central region of the groove is configured to contact the wafer at one point (103),
The apparatus of claim 1. The solid member of each wafer grip finger is made of metal,
The apparatus of claim 1. The non-contaminating material of each wafer grip finger is made of polyethyl ether ketone (PEEK),
The apparatus of claim 1. The semiconductor wafer (104) is held in place by a plurality of wafer gripping fingers (102), and the wafer has an edge,
Each wafer grip finger includes a rectangular solid member (102a) that includes a first straight portion, a second straight portion, and a horseshoe-shaped portion provided between the first and second straight portions. A free end including an edge having a horseshoe shape of the free end edge forming a depression at the free end of the rectangular solid member;
Each wafer grip finger further includes a compatible non-contaminating material (202), the compatible non-contaminating material comprising a first portion provided on each of the first and second straight portions of the free end edge; And a second portion provided in the horseshoe-shaped portion of the free end edge to fill the recess at the free end of the solid member, the second portion provided on each of the first and second straight portions of the free end edge Each first portion of the compatible non-contaminating material has a first predetermined thickness (208), and the second portion of the compatible non-contaminating material filling the depression at the free end of the solid member is the first portion. Two predetermined thicknesses (206);
The compatible non-contaminating material has a groove (101) formed across the first and second straight portions of the free end edge of the solid member across the recess at the free end of the solid member;
The groove is provided opposite to the central region (302) provided opposite to the depression at the free end of the solid member and the first and second straight portions of the free end edge of the solid member. And a central region of the groove is configured to contact the wafer edge;
The second predetermined thickness of the compatible non-contaminating material is greater than the first predetermined thickness of the compatible non-contaminating material, and the central region of the groove in contact with the wafer edge is more from each end portion of the groove. Having steps to adapt and thereby reduce wafer deformation and wear,
A method of handling semiconductor wafers. Has a circular curve cross section the groove has a Jo Tokoro radius of curvature (r _f),
The method of claim 6. Further comprising contacting the wafer at a point (103) in a central area of the groove,
The method of claim 6. The solid member of each wafer grip finger is made of metal,
The method of claim 6. The non-contaminating material of each wafer grip finger is made of polyethyl ether ketone (PEEK),
The method of claim 6.

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