DE102006058819A1 - Separating method for multiple disks of workpiece, involves fixing pre-wearing bar on opposite side of peripheral area of workpiece, which is guided from saw wire into workpiece by wire gate - Google Patents

Abstract

The method involves fixing a pre-wearing bar on the opposite side of the peripheral area of the workpiece, which is guided from the saw wire into the workpiece by the wire gate. The pre-wearing bar is removed, and is dimensioned such that the total wire length of the adjacent wire gate coils, used by saw of the workpiece, is required for chipping the cross section of the pre-wearing bar.

Description

The The invention relates to a method for separating a plurality of Slices of a workpiece by means of a wire saw.

Wire saws are for example, a variety of semiconductor wafers, solar wafers and to separate other crystal wafers from a crystal piece in one operation.

In US 5,771,876 is the principle of operation of such a wire saw described.

Own wire saws a wire gate made of a saw wire is formed, which to two or more Drahtführungs- or pulleys is wound.

Of the saw wire can be covered with a cutting surface.

at Use of wire saws with sawdust without firmly bound cutting grain is cutting grain in the form of a Suspension ("slurry") during the Abtrennvorganges supplied.

At the Separation process penetrates the workpiece mounted on a table, the wire gate, in which the saw wire arranged in the form of parallel adjacent wire sections is. The penetration of the wire gate is provided with a feed device the table causes the workpiece against the wire gate or the wire gate against the workpiece leads.

Usually is the workpiece on its peripheral surface with a saw bar connected to the saw wire after cutting the workpiece cuts.

The saw strip For example, it may be a graphite strip adhered to the peripheral surface of the workpiece or is puttied. The workpiece with the saw bar finally becomes puttied on the table.

The separated slices remain like the teeth of one after separation Comb on the saw bar fixed and can taken out of the wire saw become. Later becomes the remaining saw bar detached from the slices.

at the described method according to stand The technique occurs in a part of the separated discs increased total Thickness variances (TTV, "total thickness variation ") on. In the prior art, causes for this were not known, accordingly also no approaches to the solution this problem.

Therefore The object of the invention was to provide a method for separating to provide a plurality of slices of a workpiece, wherein different thickness variations of the separated discs avoided become.

The The object of the invention is achieved by a method of separating a plurality of slices from a workpiece, which is a longitudinal axis and a peripheral surface having the over one, on the peripheral surface the workpiece applied, saw strip mounted on a table workpiece by a perpendicular to longitudinal axis directed relative movement between the table and the wire gate a wire saw by means of a feed device by that of a multiple over pulleys wound sawdust led formed wire gate is, characterized in that on the opposite of the saw bar Side of the peripheral surface of the workpiece a Vorverschleißleiste is fixed before the penetration of the saw wire of the wire gate through the workpiece led this wire gate and is machined and which is dimensioned so that for cutting the Cross section of the pre-wear bar at least the entire wire length the following when sawing of the workpiece used wire gate windings is needed.

at the workpiece it is preferably a cylindrical single crystal made of silicon.

The However, method is also for sawing non-cylindrical crystal blocks suitable, the one peripheral surface include, so z. B. of crystal blocks, which is a square or rectangular cross-section.

When Workpiece material are semiconductor materials such. As silicon, germanium, gallium arsenide suitable. It may also be polycrystalline material.

Of the saw wire preferably comes from a spool and is repeated several times (eg 300-400 times) wrapped around pulleys so that a wire gate arises with the corresponding many cuts can be made on a workpiece. At the Output of the wire gate is the used wire preferably wound up on another spool.

Of the Wire performs preferably cyclic forward and backward movements: He runs for example, 300 m forward and again 240 m backwards, so effectively about 60 m per cycle forward.

The Method works in the same way also in wire sawing processes where the wire is only moved in one direction.

The workpiece is over a saw bar mounted on a table and is perpendicular from above in the wire gate introduced.

The Feed or feed rate of the table is preferably dependent on set from the table position.

The amounts the forward and backward movements can also be dependent vary from the table position.

The Inventors have recognized in the invention that the stand The technique observed different thickness variance in particular at the wire outlet side kerfs occurs. Wire outlet side in this context means Sägespalte in the area of the saw wire receiving coil. The wire gate is known from several times formed saw wire wound around pulleys, the saw wire usually unwound from a dispensing spool and finally from a receiving spool is wound up again.

The observed different thickness variance in the wire exit side Area hangs together with that at the beginning of the cut (with freshly equipped machine) the entire gate is made of unworn wire, in this Area but in the course of the cut only wire arrives, the already in all previous crevasses Has done cutting work and is thinner due to wire wear than at the beginning of the cut. A disc between these wire outlet side kerfs becomes correspondingly thinner in the incision area than later of the cut.

in the first wire inlet side sawing comes so while the entire sawing process always new unworn wire from a wire spool. In all others sawing gaps comes from a certain incision depth T (n) only wire, the at all previous crevasses has already done machining, so already worn accordingly is. This incision depth T (n) is different in each kerf and grows with increasing Sägespaltnummer n. The thickness of the wire and thus the cutting width change So for the rear crevices over the Cutting position. The resulting slices of higher sawtooth numbers are correspondingly thinner in the area of the incision than later of the cut.

According to the invention this is by attaching a Vorverschleißleiste on the wire gate facing side of the peripheral surface of the to be scored workpiece prevented. As a result, the wire is vorverschlissen so that when cutting into the workpiece only wire on the gate which already has cutting work in all previous crevices has done. This results in each sawing gap throughout the sawing process only wire one at least with respect to the individual crevices consistent wire size to the workpiece. This is the thickness variance in particular in the wire outlet side Area separated slices compared to the prior art improved.

A according to the invention introduction of the workpiece from the top to the saw gate, at the bottom of the workpiece attached pre-wear bar serves to pre-wear the wire defined, so that at incision into the workpiece only wire is still on the gate, which all previous ones sawing gaps already happened in the pre-wear bar Has. This will change the thickness of the wire in the pre-wear bar relocated. The thickness variance of the discs with higher Sägespaltnummern is, in the feed direction measured, reduced accordingly.

The Dimensioning of the pre-wear bar is preferably in dependence on the ratio of wire wear in the pre-scuff material relative to the wire wear in the Workpiece material, from the number of cuts within the workpiece, from the dimensions of the Wire gate as well as from the for the process available standing wire length selected.

Preferably will also an effective speed of the saw wire adjusted so that the wire is homogeneous over his length wears. This ensures that from the incision depth T (n) only still wire of constant wire thickness arrives at Sägespaltnummer n.

In the alternating process (forward and backward movement of the saw wire), the wire moves forward at the beginning of a cycle during the period Δt _ν by a distance Δx _ν and then immediately afterwards by a distance Δx _r in the period Δt _r . Within a cycle time of Δt _z = Δt _ν + Δt _r , it therefore returns a path of Δx _z = Δx _ν - Δx _r (cf. 2 ).

, die durch entsprechende Wahl der Vor- und Rückwärtsbewegungen gegeben ist.Thus applies to the effective speed of the saw wire

, which is given by appropriate choice of forward and backward movements.

For non-alternating processes, the effective speed of the saw wire corresponds to the wire speed (in one direction, eg, just before) Windwärts).

The Table feed profile is stored in the sawing recipe. This is done by setting the desired delivery speed dependent on from the table position y.

A machined volume Z of a sawing gap is given by the average cutting width D and the area of the workpiece swept by the wire. For a circular cylindrical workpiece, for example: Z = D · 2πR 2

gegeben ist.At a given table position y <R, the wire has only reached a part of the surface to be swept, namely a circle portion of the height h = y + R and an incision length through

given is.

wobei l(y) die Eingriffslänge des Drahtes im Werkstück bei Tischposition y bezeichnet.For the swept area of the workpiece as a function of the table position, the following applies:

where l (y) denotes the engagement length of the wire in the workpiece at table position y.

The cutting rate ż, ie the removal per unit time, depending on the table position is:

Of the Wear of the saw wire is characterized by wire abrasion and a corresponding change in diameter.

Generally applies to the wear α at a wire position x:

in this connection f is a function that is preferably all relevant to wear Describes factors at a table position.

Preferably should α (x) constant, independent of x.

Therefore, the following relationship is preferred for the effective speed of the saw wire:

Preferably This condition becomes an optimized one for each table position effective wire speed determined.

The Determination of the optimum effective wire speeds takes place preferably in that the wear of the saw wire and its dependencies of sawing parameters be determined.

Preferably, the wear of the wire is proportional to the machined volume. The wear of the wire is therefore proportional to the swept surface (the cutting width is constant for each individual cut):

Preferably exists between the effective speed of the saw wire and the product of incision length and feed rate a proportional relationship.

to inventive control the effective wire speed is preferably one each Forward and backward profile the wire movement set.

To determine the optimum dimensioning of the preliminary wear bar, the procedure is preferably as follows:
The relative wear of the wire in the workpiece (eg, silicon), in the saw bar (eg, coal) and in the pre-wear bar (preferably carbon or glass) is taken into account by means of correction factors, which are preferably determined experimentally.

The correction factor for the pre-wear bar γ _V is given as the ratio of the wire length l _V required for machining the pre-scuff material to the wire length l _W required for cutting an equally sized piece of workpiece material with equal wear of the wire.

If, for example, you need about twice the amount of wire for the cutting of glass with the same wire wear as for cutting an equal-sized silicon cross-section, then γ _V = 2. Similarly, the correction factor γ _K for the saw bar is obtained.

The pre-wear bar is preferably dimensioned so that at least the entire used gate length L _G = NL _{0 is} required for machining the effective Vorverschleißquerschnitts A _V (L ₀ denotes the length of a Gatterumschlingung). The total wire length used does not necessarily correspond to the total wire length of the gate.

Example 1:

In the case of a gate of 310 mm width and 310 mm height guided over 4 deflection rollers with radius r = 50 mm, a winding or looping L ₀ = 4 × 310 mm + 2 πr = 1.27 m long. For example, if the gate density is 1 gate loop / mm, N = 200 gate turns are engaged in a workpiece of 200 mm in length. In this case, the used wire length L _G = NL ₀ = 254 m.

For the effective cross section of the pre-wear bar, the following condition is preferably selected:

Where L is the wire length for the entire cut. A corresponds to the area swept by the saw wire and consists essentially of the cross sections of the pre-wear bar, workpiece and saw bar. A _V is the cross section of the preliminary wear bar, A _{T is} the cross section of the preliminary wear bar at workpiece height. A _W corresponds to the cross section of the workpiece, A _{K is} the cross section of the sawn part of the saw bar (see. 3 ).

The cross-sections A _V , A _T and A _K are effective cross-sectional areas, ie the real cross-sectional areas changed by the factors γ _V and γ _K.

Thus, for the effective cross section of the pre-wear bar, it is preferable to have a condition:

In this case, the cross section A _T "wasted surface", it should be kept as small as possible in the context of technical constraints (adhesive surface, "soft transition" of Vorverschleißleiste into the workpiece, etc.).

Preferably, therefore (for A _T ≈ 0):

in the The subject matter of the invention is illustrated below with reference to figures.

1 schematically shows a crystal piece with wire gate, wire inlet, outlet and crevices.

2 shows wire back and wire backward movement as well as the effective movement of the saw wire in an alternating process.

3 schematically shows a workpiece cross section with saw bar and Vorverschleißleiste.

1 shows a piece of crystal 1 and a freshly armored wire gate and a wire gate in the stationary state. Shown are wire inlet, wire outlet and crevasses. In the state of the art, the wire has a significantly smaller thickness in the stationary state in the area of the wire outlet side kerfs than in the case of freshly prepared gates, which is related to the fact that the saw wire arriving in this area has already carried out cutting work in all previous kerfs. In the prior art, this leads to significantly poorer total thickness variances (TTV) of the slices cut off in the area of the wire outlet.

2 shows the forward and backward movement of the saw wire in the form of the temporal change of the wire position. It also shows the effective wire movement that results from these cyclic forward and backward movements. The acceleration phases were not displayed for the sake of simplicity

In 3 shows the cross section of a crystal piece with radius R, on which a saw bar and a Vorverschleißleiste invention are attached. The position of the table on which the crystal piece is attached by means of the saw bar is also indicated. The workpiece is introduced in the illustration shown down in a wire gate. Schematically illustrated are also the cross sections of the workpiece and the saw bar, the effective cross section of the pre-wear bar A _V , the height h and the cross section of the pre-wear bar A _T in workpiece height.

Example 2:

For a circular cylindrical workpiece with radius R = 150 mm and 200 mm length, a saw bar with 170 mm width and a cutting end 5 mm above the workpiece (cf. 3 ) results in a workpiece cross section of A _W = π · R ² ≈ 70700 mm ² and a cross section of the machined saw bar of A _K ≈ 2290 mm ² . If this workpiece is to be sawn with the gate dimensions given in Example 1 with a wire of total length L = 60 km, then the minimum wear of the pre-wear bar should be selected as:

If γ _V = 1, a pre-wear bar with a width of 30 mm and a height of 12 mm is suitable. For a correspondingly difficult to machine material with γ _V = 2, a pre-wear bar with a height of 6 mm is already suitable.

Claims (6)

A method of separating a plurality of disks from a workpiece having a longitudinal axis and a peripheral surface, the workpiece being mounted on a table via a saw bar mounted on the peripheral surface of the workpiece by a relative movement between the table and the wire gate directed perpendicular to the longitudinal axis a wire saw is guided by means of a feed device through the formed by a multiple wound over guide rollers saw wire wire gate, characterized in that on the side opposite the saw bar side of the peripheral surface of the workpiece a Vorverschleißleiste is attached, before the penetration of the saw wire of the wire gate in the workpiece is guided by this wire gate and machined and which is dimensioned so that for cutting the cross section of the Vorverschleißleiste least the entire wire length of the subsequently used in the sawing of the workpiece Drahtgatterwic needed. A method according to claim 1, characterized in that the wire length of the used wire gate windings is given by L _G = NL ₀ , where L ₀ corresponds to the length of a single wire gate winding and N corresponds to the number of wire gate windings engaged during sawing of the workpiece. Method according to one of claims 1 or 2, characterized that the pre-wear bar is dimensioned so that the relative proportion of its cross section on the whole, swept by the saw wire Area, which is the cross section of the Vorverschleißleiste, the cross section of workpiece and the cross section of a sawn Part of the saw bar at least the relative proportion of the length of one Wire gate winding on the entire wire length corresponds. Method according to one of claims 1 to 3, characterized that saw wire moving at an effective speed and this effective Speed of saw wire dependent on from a nick length of the saw wire into the workpiece is determined. Method according to claim 4, characterized in that that the effective speed of the saw wire is adjusted so that between effective wire speed and the product of table feed speed and incision length proportional relationship exists. Method according to claim 4, characterized in that that the effective speed of the saw wire is adjusted so that the wire wear over the total used wire length is constant.