DE10054165B4 - A method of separating a plurality of slices from a workpiece - Google Patents

Abstract

A method of separating a plurality of disks from a workpiece with a wire saw, wherein the workpiece travels through a wire wire of saw wire which is alternately moved forward and backward at a certain speed in the direction of a plane defined by the wire gate, the forward movement and the rearward movement each in an acceleration phase .DELTA.t ₁ , a holding phase .DELTA.t ₂ and a deceleration phase .DELTA.t _{3 are} divided, characterized in that the ratios .DELTA.t ₂ / .DELTA.t ₁ and .DELTA.t ₂ / At _{3 are} limited to a value of less than 0.5.

Description

The present invention is particularly suitable for the production of semiconductor wafers. It relates to a method for separating a plurality of disks from a workpiece with a wire saw, wherein the workpiece travels through a wire wire of saw wire, which is alternately moved forward and backward at a certain speed in the direction of a plane defined by the wire gate, wherein the forward movement in an acceleration phase .DELTA.t ₁ , a holding phase .DELTA.t ₂ and a deceleration phase .DELTA.t ₃ is divided.

The Production of a semiconductor wafer requires a series of process steps, depending on from the properties exhibited by the finished semiconductor wafer should, if necessary, added or omitted individual steps or the Changed sequence of steps can be. A single crystal of semiconductor material is usually after the Czochralski method (Cz method) or zone melting (FZ method) produced. The single crystal is cut to length and ground round and optionally with one or more orientation features provided for the identification of the crystal axes. Then he will with a wire saw or an inner hole saw divided into semiconductor wafers. Wire saws are with rollers equipped, are grooved into the depending on the required pane thickness grooves. In these grooves, a finite wire is guided so that a wire gate (wire web) is formed, which is formed by adjacent wire sections becomes. The ones to be sawn workpieces be against the moving saw wire pressed, which is sprayed with a cutting suspension. By the rubbing or lapping Movement of the wire sections, semiconductor material is removed, depending on the width of the wire gate and the distance of the wire sections to each other generates a certain number of semiconductor wafers simultaneously becomes.

you speaks of an oscillating or pilgrim stepping method when the Movement of saw wire into a forward and a backward motion subdivided is. In DE-19828420 A1 the oscillating operating mode is described in more detail. When using such a method in the usual Ways emerging semiconductor wafers have surfaces a wavy structure. The ripple can be measured and she is over it out already by visual inspection. Such a thing pronounced Ripple is for many Applications disturbing. The object of the present invention was to provide a corresponding method specify the discs, the surfaces of which a much lower Have waviness.

The invention relates to a method for separating a plurality of slices of a workpiece with a wire saw, in which the workpiece passes through a wire gate of saw wire, which is moved at a certain speed in the direction of a plane defined by the wire gate alternately forward and backward, wherein the forward movement and the backward movement are each subdivided into an acceleration phase Δt ₁ , a holding phase Δt ₂ and a braking phase Δt ₃ , characterized in that the ratios Δt ₂ / Δt ₁ and Δt ₂ / Δt _{3 are set} to a value less than 0 5 are limited.

The values Δt ₁ and Δt ₃ may be the same or in pairs for the forward movement and the backward movement in pairs.

The invention will be explained in more detail below with reference to figures. The figures are diagrams that characterize the time course of the wire movement. 1 describes the wire movement in a method that can be attributed to the prior art. 2 describes the wire movement in a method according to the invention. In the 3 and 4 in each case a section of the surface structure of two semiconductor wafers is shown.

The in 1 shown speed trajectory is formed trapezoidal, wherein between the acceleration phases .DELTA.t ₁ and the braking phases .DELTA.t ₃ longer holding phases .DELTA.t _{2 are provided} at a nominal speed _Vnenn . The holding phase Δt ₂ is always longer during the forward movement of the saw wire than during the backward movement, whereby the saw wire has a forward effective velocity V _eff .

According to the invention, the cycle time t _cycle , as it is in 2 is shown, greatly shortened by shorter holding phases .DELTA.t _{2 are} provided in comparison to the acceleration phases .DELTA.t ₁ and braking phases .DELTA.t ₃ . The waviness of the semiconductor wafers produced will be so low in particular that it is no longer visually recognizable when the movement of the saw wire is slowed down as soon as possible after reaching the rated speed and vice versa. In fact, such so-called "as cut" discs are visually indistinguishable from a lapped semiconductor wafer. The ratios Δt ₂ / Δt ₁ and Δt ₂ / Δt _{3 are} preferably limited to a value of less than 0.5, more preferably less than 0.4. The cycle times t _cycle are preferably 10 to 15 s, especially before zugt 12 s. Typical examples of acceleration phase, deceleration phase and holding phase are Δt ₁ = 3.33 s, Δt ₃ = 3.33 s and Δt ₂ = 1.3 s. Furthermore, it is particularly preferred if the number of cycles performed (Δt _1vor + Δt _2vor + Δt _3vor + Δt _1rück + Δt _2rück + Δt _3rück ) is at least 5 cycles per 200 micron sawn distance, the indices forward and backward for the forward - and the backward movement stand. The invention is preferably used for the production of semiconductor wafers made of silicon.

Example:

Single crystals of silicon were cut by means of a wire saw into semiconductor wafers. In the 3 and 4 a section of the surface structure of two of the semiconductor wafers is shown. While the surface of the semiconductor wafer in 3 according to a method according to 1 produced, has significant traces of waviness, such tracks are in the semiconductor wafer in 4 , which was prepared according to the invention, does not exist.

Claims (5)

A method of separating a plurality of disks from a workpiece with a wire saw, wherein the workpiece travels through a wire wire of saw wire which is alternately moved forward and backward at a certain speed in the direction of a plane defined by the wire gate, the forward movement and the rearward movement each in an acceleration phase .DELTA.t ₁ , a holding phase .DELTA.t ₂ and a deceleration phase .DELTA.t _{3 are} divided, characterized in that the ratios .DELTA.t ₂ / .DELTA.t ₁ and .DELTA.t ₂ / At _{3 are} limited to a value of less than 0.5. Method according to Claim 1, characterized in that the speed is changed linearly in the acceleration phase Δt ₁ and in the deceleration phase Δt ₃ . Method according to Claim 1 or Claim 2, characterized in that the values Δt ₁ and Δt ₃ for the forward movement and the return movement are equal in pairs. Method according to Claim 1 or Claim 2, characterized in that the values Δt ₁ and Δt ₃ for the forward movement and the return movement are pairwise different. Method according to one of claims 1 to 4, characterized in that the holding phase .DELTA.t ₂ lasts during the forward movement of the saw wire longer than during the backward movement of the saw wire.