EP0916450A1 - Method and apparatus for polishing semiconductor wafers - Google Patents

Abstract

During polishing the semiconductor disk (5) slides over at least two radial zones with different temperatures on the polishing tray (4). Means are provided which allow the radial width, temperature and number of such zones to be specified before polishing of the semiconductor disks. The claimed apparatus is characterized in that the polishing tray incorporates a system of concentric annular chambers (Z1, Z2, ...) for flow of a medium whose temperature is adjustable.

Description

The invention relates to a method for polishing Semiconductor wafers with at least one side at least a semiconductor wafer against one covered with a polishing cloth Polishing plate is pressed and polished, the Semiconductor wafer and the polishing plate a relative movement To run. The invention also relates to a device which is suitable for performing the method.

The planarization of a semiconductor wafer using a chemo-mechanical Polishing is an important processing step in the process flow for the production of a flat, defect-free and smooth semiconductor wafer. This polishing step provides the final form in many production processes and thus decisively determining the surface properties Step before reusing the semiconductor wafer as raw material for the production of electrical, electronic and microelectronic components. Objectives of Polishing processes are particularly high Flatness and parallelism of the two disc sides, the removal pretreatment of damaged surface layers ("damage removal") and the reduction of the microroughness of the Semiconductor wafer.

Commonly used are single-sided and double-sided polishing processes used. When polishing a group of several semiconductor wafers ("single side batch polishing") the semiconductor wafers with one side on the front a carrier plate mounted by between the side and the carrier plate has a positive and non-positive connection, for example by adhesion, gluing, kitten or vacuum application, will be produced. As a rule, the semiconductor wafers mounted on the carrier plate so that it is a Form a pattern of concentric rings. After assembly the free sides of the disc are fed with a polishing agent against a polishing plate over which a polishing cloth is stretched is pressed with a certain polishing force and polished. The carrier plate and the polishing plate are thereby usually rotated at different speeds. The necessary polishing force is provided by a pressure stamp hereinafter referred to as "polishing head" transfer the back of the carrier plate. A variety of used polishing machines are designed so that they over have several polishing pots and accordingly several carrier plates be able to record.

With double side polishing (DSP) the front and back are polished simultaneously by several semiconductor wafers between two covered with polishing cloths, upper and lower polishing plates. Here the semiconductor wafers lie in thin guide cages ("wafer carrier"), which are referred to as rotor disks and in a similar form when lapping semiconductor wafers be used. Double-sided polishing processes and devices are always for the treatment of groups of semiconductor wafers designed ("batch polishing").

Several factors make it difficult to achieve the desired flatness and parallelism of the semiconductor wafers, subsequently sought Called geometry. Polished semiconductor wafers often have pages that are not parallel to each other but in cross-section the shape of a wedge take in.

The shape of the wedge can be described with the term linear thickness variation describe. The linear thickness variation is the largest measured difference in thickness between two measuring points, the on the same diameter symmetrical to the center of the semiconductor wafer lie. The measuring points are usually symmetrical on a circle that is a distance of, for example 6 mm from the edge of the wafer of the semiconductor wafer. Is the edge the semiconductor wafer, which faces the edge of the carrier plate, thicker (thinner) than the edge of the pane, towards the center of the carrier plate shows, one speaks of a positive (negative) linear Wedging.

Another measure of the wedge shape of semiconductor wafers is the so-called TTV value (TTV = total thickness variation). This value gives the difference between the thickest and the thinnest point on the semiconductor wafer.

A wedge of a semiconductor wafer caused by the polish is ultimately the result of an uneven Material removal. It can arise if the carrier plate radially deformed during polishing by its own weight or a certain radial wedge, due to the manufacturing process Has. Sometimes there is also wear and tear of the polishing cloth cause that the disc geometry deteriorated in the course of several polishing runs. A certain one Basic wedge results even when used ideally level Carrier plates because of the kinematic conditions in the Single disc polishing, which is an inhomogeneous material removal promote.

EP-4033 A1 proposes intermediate layers made of soft elastic bodies between the polishing pot and the back insert the carrier plate, thereby the carrier plate is deliberately curved a little radially symmetrically. In order to can be prevented to a certain extent from the semiconductor wafers be wedge-polished. However, this procedure is cannot be automated and prone to errors, since its success is largely from the experience and care of the operators depends on the width of the liners must select and insert. But even if there are no mistakes made, the wedge of the polished semiconductor wafers remains above a certain limit.

The present invention solves the problem in polishing of semiconductor wafers an improved uniformity of the To achieve polishing removal, so that in particular the wedge the polished semiconductor wafers is low.

The invention relates to a method for polishing Semiconductor wafers with at least one side at least a semiconductor wafer against one covered with a polishing cloth Polishing plate is pressed and polished, the Semiconductor wafer and the polishing plate a relative movement execute, characterized in that the semiconductor wafer at least two areas on the polishing plate during polishing sweeps that have certain radial widths and have different temperatures, and tempering agents are provided in the polishing plate, with the aid of which the number, the radial latitudes and the temperatures of the areas before Polishing the semiconductor wafers can be determined.

The invention further relates to a device for Implementation of the procedure, which is characterized by a Chamber system made of concentric in the polishing plate arranged annular chambers through which a tempering medium flows that a certain, adjustable in each annular chamber Temperature.

Investigations by the inventors have shown that polishing occurs a radially convex temperature profile on the polishing plate, this is partly responsible for the wedge shape of polished semiconductor wafers is. The temperature profile causes an inhomogeneous Material removal through the use of the above elastic intermediate layers (e.g. when using ceramic carrier plates that are practically not arched may) or not sufficient (when using carrier plates less rigid material) can be compensated. Such compensation is provided by the present invention possible because of the creation of tempered areas specified a radial temperature profile of the polishing plate that decisively determines the material removal. The invention allowed to polish the wedge shape of semiconductor wafers set within comparatively wide limits. By the invention can produce semiconductor wafers, which are specifically positive or negative wedge. Primarily However, the invention is used for kinematic influences and influences of the carrier plate or the polishing cloth, which too Wedges would lead to compensate and for example an extension of the service life of the polishing cloth to reach.

The invention can be used both for one-sided polishing (one and Multi-disc polish), as well as for double-sided polish become. The invention is illustrated below using the example multi-disc single-side polishing (single-side batch polishing) explained in more detail.

According to the invention it is ensured that the semiconductor wafers at least two areas during polishing paint over the polishing plate, which is caused by temperature control in the Polishing pads are kept at certain temperatures. The Areas are preferably laid out in concentric rings, taking temperatures from at least two of the ranges differentiate. The number, the radial latitudes and the temperatures the areas are determined before a polishing run. Not excluded is the temperature at which the areas be held during a polishing run change.

Due to influences of the polishing kinematics, the use not completely flat carrier plates and an inhomogeneous one The polishing cloth wears during polishing Semiconductor wafers on a conventional polishing plate are not homogeneous Temperature before. The temperature often increases from the edge r / 2 of the polishing plate (r is the radius of the polishing plate) and drops to the center of the polishing plate, making a radial convex temperature profile results. By the establishment from areas on the polishing plate, from areas in the polishing plate housed temperature control agents at certain temperatures can be maintained, a homogenization of the temperature profile can be achieved. To avoid training a radially convex temperature profile should be at least two tempered areas can be set up on the polishing plate. For example, three areas in the shape are suitable concentric rings, the outer and the inner on one higher temperature than the middle range. This creates heat in the center area of the polishing plate arises during the polishing of semiconductor wafers, dissipated via the temperature control. The outer and inner ring and thus preserve the parts of the polishing plate near the edge additional thermal energy, so that overall a flatter radial temperature profile results. Basically, by the invention of any polishing process radial temperature profile are made uniform.

The number of areas, their radial latitude and the temperatures, on which they are held are before polishing of the semiconductor wafers. As the basis for the determination can data from an analysis of the geometry previously polished Semiconductor wafers are used, for example the linear thickness variation determined for these semiconductor wafers. Measurement data of the radial temperature profile can also form the basis of the polishing plate during a previous one Polishing run were determined.

The functional relationship between that after a polish too expected geometry of the semiconductor wafers and the one to be determined Number, width and temperatures of the areas on the The polishing plate is expediently carried out by routine experimentation determined. In such experiments, the number is radial Systematic changes in width and temperature of the areas and the effects on the geometry of the polished semiconductor wafers examined.

After completing such experiments, the polishing process can be started be automated easily. A host computer receives as input data the radial temperature profile, which during a previous polishing run or data on the geometry (for example on the wedge shape) of semiconductor wafers, which polished on a previous polishing run were and is based on the empirically found connection those to achieve a desired one Disc geometry necessary parameters (number, radial width and temperature of the areas).

The invention is described in more detail below with reference to figures. In Figure 1 is a preferred embodiment of the claimed device shown schematically. The figure shows a vertical section through the device in side view. In Figure 2 is a horizontal section through the polishing plate the device shown in plan view. In the figures 3a, 3b and 4a, 4b is shown schematically as the Geometry of semiconductor wafers through the application of the invention can be influenced. Below is only on characteristics pointed out that necessary to illustrate the invention are. Similar features are used in the figures pointed out the same reference numerals.

First, reference is made to FIG. 1. In the shown Embodiment is a single side polishing machine with several polishing pots, one of which can be seen is. The polishing pot 1 presses a carrier plate 2 with a polishing force K against a polishing plate covered with a polishing cloth 3 4. The carrier plate is, for example, vacuum suction held on the polishing pot. The semiconductor wafers 5 are on the front of the carrier plate facing the polishing cloth 3 2 fixed. During the polishing, both the Carrier plate as well as the polishing plate with a certain Speed and direction of rotation. Essential characteristic of the Device are in the polishing plate in concentric Orbital ring chambers through which a tempering medium flows. There are five annular chambers Z1 in the polishing plate shown provided up to Z5. Each annulus becomes independent of one others from a temperature control medium, for example water, flows through, the tempering medium in each annular chamber has certain temperature and the temperatures are different could be. The temperature control medium is through flow lines VZ1 to VZ5 pumped into the respective ring chambers and leaves this again through return lines RZ1 to RZ5. The Flow and return lines run through a rotating union 6, which is attached to the underside of the polishing plate 4. For the sake of clarity, the supply and return lines are shown interrupted. The temperature control medium is from a thermostat 7 at a desired temperature held. The thermostat is operated by one Control computer 8 controlled, the target temperatures SZ1 to SZ5 specifies for the temperature control medium in the annular chambers Z1 to Z5. The master computer in turn accesses a data store 9 back, stored in the measurement data of previous polishing runs and automatically calculates the Target temperatures.

The temperature control medium holds a certain one in each annular chamber Temperature upright, so that on the polishing plate radially symmetrical Areas with a characteristic temperature arise that sweep over the semiconductor wafers during polishing. The The number of available areas depends on the number of the provided ring chambers. The radial widths of the areas are of the chosen radial widths of the annular chambers and depending on the temperature of the temperature control medium flows through the annular chambers.

In Figure 2 is a horizontal section through the polishing plate the device shown in Figure 1 in plan view. If the temperature of the temperature control medium in each ring chamber Z1 to Z5 of the temperatures of the tempering medium in the rest Differentiates annular chambers, produce the annular chambers the polishing plate corresponds to the number of annular chambers Number of annular areas. These areas are on a Temperature maintained, which is essentially the temperature of the Temperature control medium in the associated ring chamber corresponds. The Number of areas is correspondingly lower when the temperature of the temperature control medium in two or more neighboring ones Annular chambers is the same. Is the temperature of the temperature control medium the same in two adjacent ring chambers, results from this an area on the polishing plate whose radial width is approximately the sum of the radial widths of these annular chambers corresponds. 2 to 5 annular chambers are preferred provided. The radial widths of the annular chambers are preferably 25 to 120% of the diameter of the to be polished Semiconductor wafers.

The annular chambers can deviate from the illustration in Fig. 2 also be structured in itself (for example meandering). The specification of a certain radial temperature profile the polishing plate by providing areas with a certain temperature can also be considered other than described above can be achieved, for example by the integration of heating and cooling elements in the polishing plate. These can be done inductively or through a likewise in the polishing plate housed power supply are operated.

FIGS. 3a, 3b and 4a, 4b show schematically like the geometry of semiconductor wafers through the application the invention can be influenced. The figures reflect that Result of exemplary embodiments.

After a polishing run in a device according to FIG Preserved semiconductor wafers with positive taper. While during the polishing run, tempering medium flowed through the ring chambers, which is tempered in the annular chambers Z1 to Z5 as follows was: Z1 = 30 ° C, Z2 = 30 ° C, Z3 = 40 ° C, Z4 = 30 ° C and Z5 = 30 ° C (Fig. 3a). By changing the temperatures in the annular chambers (Z1 = 40 ° C, Z2 = 40 ° C, Z3 = 30 ° C, Z4 = 40 ° C and Z5 = 40 ° C) were able to a subsequent polishing run with nearly semiconductor wafers plane-parallel sides can be obtained (Fig. 3b).

After a polishing run in a device according to FIG Preserved semiconductor wafers with negative wedge. While during the polishing run, tempering medium flowed through the ring chambers, which is tempered in the annular chambers Z1 to Z5 as follows was: Z1 = 30 ° C, Z2 = 30 ° C, Z3 = 40 ° C, Z4 = 30 ° C and Z5 = 30 ° C (Fig. 4a). By changing the temperatures in the annular chambers (Z1 = 20 ° C, Z2 = 20 ° C, Z3 = 50 ° C, Z4 = 20 ° C and Z5 = 20 ° C) were able to a subsequent polishing run around semiconductor wafers with almost plane-parallel sides can be obtained (Fig. 4b).

Claims (10)

Method for polishing semiconductor wafers, in which at least one side against at least one semiconductor wafer pressed a polishing plate covered with a polishing cloth and is polished, the semiconductor wafer and the polishing plate perform a relative movement, characterized in that that the semiconductor wafer at least during polishing swept over two areas on the polishing plate that determined have radial latitudes and different temperatures and temperature control agents are provided in the polishing plate, with their help the number, the radial latitudes and the temperatures the areas before polishing the wafers be determined. A method according to claim 1, characterized in that the Areas in plan view of the polishing plate concentric rings form. Method according to claim 1 or claim 2, characterized in that that the number, the radial latitudes and the temperatures of areas depending on the result of one Measurement performed during a previous polishing run the radial temperature profile of the polishing plate become. Method according to claim 1 or claim 2, characterized in that that the number, the radial latitudes and the temperatures of areas depending on the result of one Analysis of the geometry of previously polished semiconductor wafers be determined. Method according to one of claims 1 to 4, characterized in that that the number, the radial latitudes and the temperatures of the areas computer-aided and automatically determined become. Method according to one of claims 1 to 5, characterized in that that the temperatures of the areas during polishing to be changed. Method according to one of claims 1 to 6, characterized in that that the polishing is selected from a group of Polishing process, the one-sided polishing, the double-sided polishing, the single-disc polish and the multi-disc polish includes. Device for polishing semiconductor wafers, with at least a polishing plate that is covered with a polishing cloth is characterized by a concentric chamber system housed in the polishing plate arranged annular chambers through which a tempering medium flows that a certain, adjustable in each annular chamber Temperature. Device according to claim 8, characterized by a Master computer based on transmitted process data the temperature of the temperature control medium in each ring chamber controls. Device according to claim 8 or claim 9, characterized in that that each annular chamber has a radial width of 25 has up to 120% of the diameter of the semiconductor wafers.

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