WO2003098683A1

WO2003098683A1 - System for aligning wafers and for reading micro bar-codes and marks on chips using laser

Info

Publication number: WO2003098683A1
Application number: PCT/ES2003/000207
Authority: WO
Inventors: Manuel Lozano Fantoba; Carles PERELLÓ GARCÍA; Xavier Enrich Sard; Joaquín SANTANDER VALLEJO
Original assignee: Consejo Superior De Investigaciones Científicas
Priority date: 2002-05-16
Filing date: 2003-05-09
Publication date: 2003-11-27
Also published as: ES2195786B1; ES2195786A1; AU2003236212A1

Abstract

The invention relates to a system for reading micra-sized marks on semiconductor wafers, which can be connected to wafer measurement test stations. The aforementioned micra-sized marks can be bar-codes containing information or special marks for the alignment of the axes of the chips on the wafer in relation to the axes of movement X and Y of the station. The invention consists of a laser reading system of the type used in CD players, which enables micrometer resolution. The reading system is stationary while the wafer moves by means of motors in the test station. The advantages of the invention lie in the simplicity of the system which can be connected to any existing test station and which is, therefore, very cheap. In addition, said system can be used to read micro bar-codes containing the relevant information of each chip.

Description

TITLE

SHAFT ALIGNMENT AND READING SYSTEM

BAR AND BRAND MICROCODES IN CHIPS WITH LASER.

SECTOR OF THE TECHNIQUE

The invention is directed to the microelectronic technology sector. And more specifically to the section of electrical characterization of integrated circuits in wafer.

When you have finished manufacturing a wafer, it is necessary to proceed to its electrical characterization. For this, the wafer is placed in a system called a tip table, which holds the wafer by means of a vacuum on a metal support and metal tips make electrical contact with the manufactured circuits, allowing its test. The metal support has an X-Y movement that allows the movement of one chip to another. It also has a Z movement, which allows the tips to make electrical contact or to be located at a certain distance from the wafer, in this way X-Y displacement is possible.

When placing a wafer for the first time on the support it is necessary to align the XY directions of the chips with the XY directions of movement of the support, so that when moving the wafer according to the axes of the tip table, we always move from a chip to another and not diagonally. This alignment can be done manually or automatically. One of the objects of this patent is to perform the alignment automatically.

Wafers may contain information recorded on them. These marks are usually made by laser marking and are for the entire wafer. Another object of this patent is to allow reading microscopic size marks, such as bar codes, on the wafer. These brands can be global for the entire wafer or individual for each chip. The marks to read do not have to be limited to barcodes. It is possible to use the system to read marks made with the metal reading tips, in small metal rectangles intended for this purpose, manufactured on the chips. STATE OF THE TECHNIQUE

The system currently used for aligning and reading wafer marks is based on an optical microscope, an image acquisition system and computer image processing. Since microscopes and image acquisition plates are very expensive elements, the systems on the market have a very high cost.

There is no known article on the use of a laser system for bar microcode reading and wafer alignment. Bar microcodes are a new concept and there are no systems for reading.

With respect to patents, the database of Esp @ cenet, of the Spanish Patent and Trademark Office (http://es.espacenet.com/), has been searched. The related patents found are listed below, although none of them refers to an invention similar to that described herein.

As barcode readers, the only reference that appears with the barcode and wafer search (barcode AND reader) is as follows:

Bar code recipe selection system using workstation controllers. Patent number US5432702, date: 11-7-1995, author: Barnett Gerald W. This system reads bar codes associated with silicon wafers to determine the process to be performed on the mentioned wafers. The barcode is not microscopic in size, the type of reader is not specified, and what protects is the system of reading a barcode to select a process. It does not serve for alignment.

As an alignment system, a reference appears in the search for the terms laser, wafer and test table (AND wafer AND prober laser):

Wafer prober. Patent number: US4864227, date: 5-9-1989, author: Mitsuya Sato. This system uses a laser beam to proceed with the alignment, but not of the wafer, but of the metal needles that are used to establish electrical contact between it and the measuring equipment. It is not the same as the invention described herein.

DESCRIPTION OF THE INVENTION - Brief description of the invention.

The invention consists of a system for reading marks of the size of microns in semiconductor wafers, adaptable to test stations measuring wafers. These marks can be bar codes containing information or special marks for the alignment of the axes of the chips in the wafer with respect to the axes of movement X and Y of the test station. This pre-alignment is a necessary step before you can start mapping (measuring all wafer chips) and it must be done either manually by a trained operator or by an automatic system. But all automatic commercial systems are based on video cameras with image recognition system, which are very expensive.

The novelty of this system is that it is based on a laser reader system used in CD players and allows micrometer resolution. The reading system is fixed and it is the wafer, thanks to the engines of the test station, who moves. The main advantages are its simplicity, which can be adapted to any existing test station and is very cheap. It also allows the reading of bar microcodes, containing relevant information of each chip.

- Detailed description of the invention. The system object of this invention is designed to be incorporated into a table of measuring tips of wafers, as shown in Figure 1. On said table of tips is placed the reading system composed of a laser diode and a photodiode, together with its optical system, shown in figure 2. This subsystem should be placed on one side where it does not interfere with the measuring tips, but is above the area covered by the wafer. It is mounted on a micrometer screw to adjust its position on the Z axis depending on the thickness of the wafer. A system with a micromotor could also be used to make the position adjustment automatic. The marks that have to be put on the wafer can be made on any type of material as long as they present a sufficient contrast with the environment. In the field of microelectronics, the most common is to use the level of metallization, on silicon oxide, although it is not limited to this choice.

The marks are detected by a difference in the light collected by an array of photodiodes that comes from a laser diode and that is reflected on the wafer surface. The system can operate in ambient light, although the contrast is reduced.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1. Tip table for measuring wafers with the built-in barcode reader. The tip table consists of a fixed system (1). A support (2) moves in a motorized manner on the X and Y axes. This support has a moving part along the Z axis (3). On this support the wafer is fixed with circuits (4). This wafer is the one that contains the circuits to be measured, along with the bar microcodes and alignment marks. We also have metal tips (5) that are the ones that make the electrical contact and a microscope (6). On one side, but in a position such that the support (2) together with the wafer (4) can move under it, is the system object of this invention composed of a micrometric screw with movement in the Z axis (7) and the laser diode and photodiode system (8).

Figure 2. Bar code reading system and other marks on the wafers. It consists of laser diode (1), control photodiode (2), laser diode lenses (3), diffraction network (4), cylindrical lens (5), polarized prism (6), photodiode matrix (7), lens collimation (8), quarter wave polarized filter (9), objective (11). The reading surface is represented in (12) and the vertical and lateral movement of the focus in (13).

Figure 3. Profile view (1) and plan view (2) of the photodiode matrix (7) of Figure 2. A, B, C, D, E and F are the six photodiodes. Figure 4. Detail of the three-ray focusing and positioning system, achieved by the prism (6) and the cylindrical lens (5) of Figure 2, using the six photodiode matrix of Figure 3. A, B, C, D, E and F are the six photodiodes.

Figure 5. Focus circuit of the laser diode. It consists of oscillator circuit (1), counter circuit (2), 8 or 12 bit bus (3), digital-analog converter circuit (4), reference voltage or threshold (5), comparator circuit (6), matrix of photodiodes (7), laser emitting diode (8) and focusing coils (9) that controls the movement on the Z axis of the focusing lenses. In (10) the wafer is represented with the marks to be read.

Figure 6. Schematic of the circular crown used to find the origin of the wafer. P is the point, arbitrary, when you begin to read the marks on the wafer, Δx is the distraction traveled from when you enter the crown until you leave it, R is the radius of the crown.

Figure 7. Scheme of the way in which the turn to be corrected in the wafer is calculated. (xι, yι) is the center of the first crown, (x ₂ , y ₂ ) is the center of the second crown and γ is the angle rotated.

EXAMPLE OF EMBODIMENT OF THE INVENTION.

The system consists of an external laser reader, which is placed on the tip table and a control electronics, which is connected to the external laser reader and to a computer through an appropriate interface.

The external laser reader (8) of figure 1, is fastened by a micrometric screw, (7) of figure 1, in an area of the tip table, to allow vertical adjustment of the initial position, which will depend on the thickness of the wafers. The laser reader is a standard reader used in CD reading equipment.

The external reader is connected to an interface as shown in figure 5. The necessary signals are the outputs of the photodiode array, the polarization of the diode laser and polarization of the focus coils on the one hand and the connection to the computer by the desired port on the other.

Several different actions are distinguished in the operation of the system: find the origin, align the wafer and read the bar codes,

Find the origin

Once the wafer is placed on the tip table it is necessary to find the reference of the same with respect to the laser beam. For this, a circular crown-shaped motif with a small circle in the center is used, as shown in Figure 6, which must be visibly engraved on the wafer, a task that is performed simultaneously with the process of microelectronic manufacturing

The algorithm of finding the center of the motif, and therefore, the coordinate reference of the wafer, is as follows: i) Place the laser beam in any area near the outside of the circular crown, ii) Move the beam of horizontal way until the crown is detected. Fix the origin momentarily at this point. iii) Move the wafer so that the beam follows the horizontal to the other end of the crown. iv) Calculate the distance traveled and apply the following formula:

Ax

Δy =, R ^a -

where,

Δx = distance traveled.

R = external radius of the circular crown.

v) Move the beam a distance Δy on the y axis and a distance Δx / 2 on the x axis. Align the wafer

Once the wafer is located on the tip table, it is necessary to align it angularly so that the x and y axes of movement of the table coincide with the x and y axes of the wafer.

For automatic alignment, two circular crowns are used, such as the algorithm of finding the origin, separated by a distance c, as shown in Figure 7. Both centers are located with the previous algorithm and the angle they form is calculated directly.

Barcode reading

The bar code reading is limited to moving the wafer under the laser reader and measuring the width of the light and dark areas, later this information is transformed into the sequence of bars of different widths and the written text is decoded . The system can work with any type of barcode.

Claims

REINVINDICATIONS

1.- Bar code reader system for tip tables for the characterization of microelectronic wafers formed by a laser reader reader used in compact disc players and an electronic computer interface that attaches to conventional tip tables.

2. Application of apparatus according to claim 1 to find the origin of the wafer on the tip table.

3. Application of the apparatus according to claim 1 to find the angle that the wafer is rotated and to be able to properly align it with the axes of movement of the tip table.