FR2677291A1 - PRESSURE CONTROL POLISHING MACHINE. - Google Patents

Abstract

The machine of the invention comprises a bracket (50) supporting an electromagnet (56), an articulated arm (70) with a sample support head (86) and a pressure sensor (62). Application to the production of magnetic writing and reading heads.

Description

DESCRIPTION

POLISHING MACHINE

PRESSURE CHECK

  The present invention relates to a polishing machine with pressure control.

  The invention finds particular application in the polishing of internal microelectronic components.

  rigged in semiconductor wafers (in silicon for example) IT can be, in particular, magnetic heads

  writing and reading ticks. Methods for producing such heads are described in numerous documents and in particular

  in US-A-4,837,924 and US-A-4,333,229 The first document relates to heads with a structure called "horizon-

  tale "-car formed of a stack of layers deposited on the upper face of a semiconductor wafer- and the second to heads with a structure called" vertical "20 -car formed of layers deposited on the edge of such a wafer- .

  The micro-machining carried out on such wafers consists, in the first case, in leveling (or "planarizing") and in polishing various intermediate sub-assemblies obtained during the production process, in defining an air gap and in bringing the whole of the head in the general plane of the substrate, also called the flight plan. In the second case, the purpose of micro-machining is to define an air gap and to adjust the shape of the flight pads. Although possibly applicable to the production of heads of the second category (vertical heads), the machine object of this

  invention is above all intended for polishing a set

  wheat or sub-assemblies corresponding to the first category (horizontal heads), because it is in this case

  that Technological problems are the most difficult.

  FIG. 1 shows, by way of example of a polishing piece, a magnetic writing and reading head in a horizontal structure. The assembly represented corresponds to, The last stage of production, just before polishing f ina L This assembly comprises a substrate of Si Licium 10 in which L a box has been etched, a magnetic circuit 12 of iron-nickel alloy, a double coil 14 of copper, a layer of Si Lice 16 3 to 6 pm thick, a non-magnetic spacer 18 in if Lice of l Vm of thickness approximately and two pieces

  in. Upper 20 nickel-iron bars The polishing plane

  final sage is marked in broken lines and referenced 22. The material removal relates to the pole pieces 20 and to the protrusions 23 in silica In order not to alter the magnetic circuit, this removal must not reduce the thickness of the uniform layer silica larger than 0.3 µm The final polishing plan

  defines the flight plan for the head.

  Two such heads are generally placed side by side on two parallel strips known as "skis",

  defining two flight plans, in a general structure

catamaran ride.

  Polishing, which consists of removing material in very small quantities, is a well-known operation. It is encountered in metallography, optics and microelectronics. One or the other of the two following techniques is used: diamond tool: this is a machining in which a semi-continuous or continuous "chip" is formed by two relative combined movements between the tool and the workpiece (a feed movement and a cut movement) ; lapping and polishing: this is a more or less fine abrasion (or work hardening) and controlled from the surface by friction on very varied discs which are non-abrasive by nature, on which an abrasive is applied in paste or in aqueous solution ; a variant consists in placing, on a rotary polishing plate, a disc of abrasive film and in spraying the latter during polishing with a liquid to cool the part and avoid fouling, these integrated comps

  Polishing of semiconductor wafers

  However, a very large number of microcomponents poses particular problems: firstly, the wafer is deformed and deformable, moreover, the running-in must simultaneously affect several materials of very different hardnesses: silica, alumina, alumina / carbide alloy titanium, iron / nickel alloy, the parts to be lapped have very small surfaces compared to the silicon wafer, finally, it involves machining, in their thickness, layers deposited on a p Laquette, and generally, i L must in. Simultaneously read 600 outgrowths corresponding to 600 magnetic heads, exceeding

  of a few microns, and this with a precision

  nanometer order, without decreasing the thickness of the thin layer that covers

  The wafer of more than 200 to 300 nm.

  Known polishing machines do not meet all of these requirements.

  reasons for this inability is that the pressure exerted on the workpiece is not controlled with 1.0 enough precision throughout the polishing.

  The object of the present invention is precisely to remedy this drawback. To this end, the invention proposes a machine which, first of all, and like all polishing machines, comprises: a polishing plate, a means capable of maintaining a sample ,

  face to be polished opposite the polishing plate

wise,

  means for exerting an application force

  tion of the face to po Read on the set

  polishing and for moving transversa-

  Lement the sample to be polished relative to the polishing plate, this machine being characterized by the fact that the means for exerting the force and depositing the sample L Lon and the polishing plate relative to each other are improved to allow very fine control of the applied force. In a servo variant, the machine of the invention allows the sample to be applied to

  the polishing plate with a pressure equal to a set value.

  way, the features and any advantages of the invention will appear better in light

  of the description which follows This description

  relates to exemplary embodiments given by way of explanation and in no way limitative and refers to the appended drawings, in which: FIG. 1, already described, shows an example of a polishing piece corresponding to a magnetic writing and reading head, FIG. 2 shows the general structure -10 of a read po machine according to the invention, FIGS. 3 a and 3 b show in detail L a machine according to the invention with

  its means to exert controlled pressure

  Lée on the support head and to move this head, Figure 4 shows four positions of

  these different means and illustrates the main

  eg installation of the support head with pressure control,

  Figure 5 shows an intermediate subset

  diary in the realization of a magnetic head

  writing and reading tick, FIG. 6 shows the profile of this sub-assembly before and after polishing,

  figure 7 shows the magnetic head

  born, figure 8 shows the profile of this head

before and after polishing.

  In the example which will be described, the sample

  lon is assumed to be held by a support piece disposed above the polishing plate In this case, the

  force is applied to the sample through-

  re of the support head and the polishing plate is fixed But the invention applies equally well to a machine where the L Lon sample to be polished would be located below the polishing tool on a sample support table , the polishing tool being held by the support head on which pressure is exerted. The machine shown in FIG. 2 schematically comprises: a fixed polishing plate 30, means 34 for exerting a force F on the support head 32 in order to apply the sample 44 to be polished on the plate

  polishing 30 and to move transversely

  Lement the support head 32 relative to the fixed plate 30, this means can

understand an eccentric 37.

  The invention relates essentially to the means represented schematically by the block 34.

  The machine shown in FIGS. 3 a (side view) and 3 b (end view) comprises a rigid pole 50 sliding on vertical columns 52 and 54 An electromagnet 56 is powered by means 58 This electromagnet is fixed to one end of the stem 50, and is provided with a movable axial rod 25 60 This rod is equipped with a pressure sensor

  62 having an outlet 64 connected to a pressure display means 65 and to the supply means 58.

  In a variant with pressure control

  pressure sensor 62 (or the display means

  ) is connected to a comparator 67 also receiving a setpoint signal from a generator 69.

  The comparator output delivers an error signal equal to the difference, in magnitude and in sign, between the pressure measured by the sensor and the set pressure The Electromagnet 56 is then controlled

  so that the error signal is canceled.

  An arm 70 is mounted oscillating around two horizontal axes 72-74 integral with the bracket

  A spindle 80 supports, at its lower part, an adjustable eccentric 82 provided with a means 84 for hooking

  chage of the sample support head 86 This pin is equipped, at its upper part, with a stop 90.10 for example a ball stop The pin 80 is fixed at the end of the arm, under the electromagnet 56 La axial rod 60 of this electromagnet and its sensor

  pressure 62 come to bear on the stop 90.

  A motor 91 is arranged at the other end of the arm 70 and forms a counterweight A balancing mass

  92, adjustable in position, is arranged near the motor 91 and is able to balance the arm 70 in posi-

  tion of the latter.20 A means 93 for transmitting movement, for example a toothed belt, is arranged between the motor 91 and the eccentric 82 to control the rotation of the eccentric 82. Means 94, 95, for example cylinders,

  are provided to move the stem vertically and all the means attached to it, along the columns

  nes vertical 52, 54 until bringing the sample near the polishing plate 30.

  Figure 4 provides a better understanding of how this machine works.

  At rest, the gallows is at the top stop; the swing arm is then slightly tilted

  born (figure a); the ball stop is supported on the rod of the electromagnet; the pressure display 65

indicates substantially zero.

  The sample holder 86 is hooked to the eccentric; the swinging arm 70 swings down;

  we find the equilibrium position (sensor at zero) 5 by moving the balancing mass 92 (FIG. b).

  The stem descends along axes 52-54 and is locked in the low position by the jacks (figure c). In this configuration, the oscillating arm 70 is always inclined very slightly upwards and the sample support is approximately one millimeter from the abrasive plane 30. The electromagnet 56 is then supplied with an adjustable and stable continuous voltage, up to the sample comes into contact with the polishing plane Then the load is increased to the desired force value (figure d) The polishing can then be carried out by controlling the motor 91. This device makes it possible to adjust and to control the polishing pressure from an almost zero value up to a maximum value fixed by the electromagnet

chosen from 0 to 100 kg for example.

  The machine which has just been described can advantageously be combined with the provisions provided for in four other patent applications filed by the present Applicant, on the same day as the filing of the present application, and which are entitled respectively: "Polishing machine with improved platelet support head ",

  "Process for producing a polishing tool

  wise and tool obtained by this process ",

  "Microabra- sheet polishing machine

  stretched sive "," Table polishing machine

improved sample holder ".

  With the polishing machine which has just been described, equipped with an improved wafer support head, according to the first of these requests and a microabrasive sheet stretched over the polishing plate, according to the third of these requests, The Applicant has obtained remarkable results which are illustrated in FIGS. 5 to 8.10 FIG. 5 shows, in section, a sub-assembly corresponding to a magnetic writing and reading head in a horizontal structure, of the kind which has already been mentioned about FIG. 1 The sub-assembly of FIG. 5 essentially comprises a silicon substrate 100, two edges of the casing 102 in Si Lice, two vertical studs 104 in iron-nickel. This involves polishing this subset according to a plan 106

  before continuing the operations of forming the upper pole piece.

  Before polishing, the profile of the sub-assembly is shown in part a of Figure 6. On the abscissa, the entire recorded interval measures 1.2 mm (the units indicated are therefore in micrometers). On the ordinate, the units are in hundreds of nanometers. We can clearly see, on this statement, the two edges of the box and, in the center, the two vertical studs in fernickel. 30 After polishing, the profile has the shape of part b of La figure 6 The entire measured interval measures 4 mm (which means that the reading covers the entire "ski" carrying the head) On the ordinate, the scale is in tens of 35 nanometers The residual overshoot in the natural curvature L The "ski" is less than or equal to 30 nm (this

  curvature being a fraction of the deformation of the substrate).

  FIG. 7 shows the head after the operations for forming the non-magnetic spacer 110 and

  upper pole pieces 112 made of nickel-plated iron. Reliefs 114 appear in the center of the head. The final Lan of po Lissage is referenced 116.

  On part a of figure 8, we see the profi L of this sub-assembly before running in. The units

  are the same as for FIG. 6 a: 1.2 mm for the entire axis of the abscissa and hundreds of 15 nanometers on the ordinate The three peaks corresponding to the three reliefs of the pole pieces are clearly visible.

  wheat. Part b of Figure 8 shows the re Survey after polishing On the abscissa, The units are still in micrometers and on the ordinate, in tens of nanometers No residual overshoot is detected, we

  only measures the natural curvature L Le of the skate (this curvature being a fraction of the deformation of the substrate).

1 1

Claims (4)

  1 polishing machine comprising: a smoothing plate (30), a means (32) able to hold polishing samples (44), face to be polished opposite the polishing plate (30), means (34) ) to exert an application force of the surface to be polished on the polishing plate (30) and to move the sample to be polished transversely relative to the fixed polishing plate ( 30),   this machine being characterized by the fact that said means for exerting the application force and for   move the sample relative to the polishing plate   wise include: a rigid bracket (50) sliding on vertical columns (52, 54), an electromagnet (56) and its supply means (58), the electromagnet being fixed to one end of the bracket (50), this electromagnet being provided with a movable axial rod (60), this rod being equipped with a pressure sensor (62) having an outlet (64) connected to the supply means (58) of the electromagnet (56), an arm (70) mounted oscillating around two horizontal axes (72-74) integral with the bracket (50), a spindle (80) supporting, at its lower part, an adjustable eccentric (82) provided with a means (84 ) hanging a   support head and equipped at its upper part   re, with a stop (90), this pin (80) being fixed to one end of the arm, under the electromagnet (56) fixed to the bracket (50), the axial rod (60) thereof and its pressure sensor (62) coming to bear on the stop (90) of the spindle (80), a motor (91) disposed at the other end of the arm (70) and forming a counterweight, a balancing mass (92) adjustable in position and arranged near the motor (91) capable of balancing the arm (70) in a substantially horizontal position, a means (93) for transmitting movement between the motor (91) and the eccentric (82) for controlling the rotation of the eccentric (82) supported by the spindle (80),   means (94-95) for dep Vertical lacing-   The bracket and all the means attached to it along the vertical columns (52, 54) until bringing the sample (86) into contact with the polishing plate ( 30).   2 Machine according to claim 1, character-   laughed at by the fact that it comprises a comparator (67) with two inputs connected respectively to the pressure sensor (62) and to a setpoint generator (69),   and to an output connected to the supply circuit (58) of the electromagnet (56).   3 Machine according to claim 1, character-   laughed at by the fact that the support head supports the sample   polishing pin, the polishing plate being located under the support head.   4 Machine according to claim 1, character-   laughed at by the fact that the support head supports the p Smoothing slat, the Lon sample to be smoothed being located under the support head.