JPH04275874A - Double face lap grinding method used with electrolytic dressing - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to the field of grinding and polishing of hard and brittle materials using electrolytic dressing, and in particular,
The present invention relates to a double-sided lap grinding method using electrolytic dressing that can simultaneously process both sides of a silicon wafer used as a semiconductor substrate.

0002

2. Description of the Related Art Silicon wafers used as substrates for semiconductor devices are manufactured through many processing steps. The processing process consists of cutting a silicon single crystal rod into wafer shapes and then removing the thickness, size, shape, surface texture, mirror surface, etc. by mechanical polishing (lapping) or the like. Furthermore, in the device process, in order to prevent contamination of the device surface during high-temperature heat treatment, mechanical roughening treatment of several to tens of micrometers is performed on the back surface of the device during wafer processing in order to trap heavy metals in crystal distortion. . Finally, the device is finished by polishing using free abrasive grains to obtain good surface roughness, mirror finish, and dimensional accuracy. Processing of silicon wafers thus requires an extremely large number of steps and time.

Conventionally, for lapping and polishing, a double-sided lapping apparatus shown in FIG. 5 has been developed which can simultaneously process both sides of several wafers. The double-sided lapping device shown in the figure holds a workpiece 53 between large ring-shaped upper and lower lapping surface plates 51 and 52 that rotate coaxially, and a workpiece 53 is sandwiched between the upper and lower surface plates and the workpiece 54 and 55. A machining fluid containing abrasive grains is infiltrated, and pressure from an upper surface plate is applied from above to lap polish both surfaces. The workpiece 53 is held by a work holder (or carrier) 56 that holds it, and is configured to simultaneously process multiple workpieces while making planetary motion by the work holder and a gear 57 that drives it. .

0004

[Problems to be Solved by the Invention] However, in the above-mentioned conventional double-sided lapping device, free abrasive grains must be uniformly supplied to the processing surface, and even if they are supplied, the machining efficiency will be reduced due to rolling of the abrasive grains. Limitations have been pointed out. Furthermore, since free abrasive grains of around #1200 (average abrasive grain diameter of approximately 12 μm) are used to increase removal efficiency, the brittle mode of the abrasive grains is easily removed by pressure, and the desired machined surface roughness can be obtained. Unable to do so.
Many steps and batch processing are required.

In the conventional processing method as described above, processing efficiency is improved by processing ten or more wafers at the same time, but there is a yield limit in the removal processing of hard and brittle materials, and furthermore, there are Too many processing steps are necessary, such as the need for processing steps to change the surface properties of the surface, mirror finishing of the surface by final polishing, etc., and there is also the need for desorption, transportation, fixing, and contamination during each step. Preventive equipment is also needed. In other words, the conventional method has many problems such as productivity, automation, yield, and quality control.

Therefore, the present invention utilizes the known electrolytic in-process dressing (Electrolytic Inpr dressing).
ocess Dressing: Below, Elid
Say. ) By adopting the grinding method (Japanese Unexamined Patent Publication No. 1-188266) in the silicon wafer processing process, the purpose is to simplify the conventional processing process and improve overall productivity. In other words, the present invention applies a removal processing method using Elid grinding to both sides of a silicon wafer, and also changes the surface properties of the front and back surfaces in-process.
Furthermore, through high-efficiency removal processing, the above-mentioned wrapping,
This provides a method that can perform back surface damage processing and polishing all at once.

[0007]

Means for Solving the Problems The above problems are solved by employing the following method according to the present invention. That is, a conductive lower whetstone and an upper whetstone are provided that rotate horizontally around a rotation axis, and the rotation axes of the lower whetstone and the upper whetstone are shifted so that the grindstone surfaces of the respective grindstones are aligned. an electrode is provided on the outside of the superimposed portion and close to the grinding wheel surface of each of the grinding wheels, a conductive liquid is supplied between the grinding wheel and the electrode, and an electric current is applied between the grinding wheel and the electrode. The workpiece is held by a holder disposed in the gap between the overlapping parts and sandwiched between the opposed grindstones, and the grindstone surface of each grindstone is electrolytically dressed while the workpiece is This can be achieved by using a double-sided lap grinding method using electrolytic dressing, which is characterized by grinding both sides.

[0008]

[Operation] The present invention can be achieved by providing a structure in which the known grinding method by Elid grinding can be applied to both sides of a workpiece. For example, by attaching another device equipped with a rotational drive mechanism to the table of a general-purpose grinding machine and shifting the rotational axis of the grinding machine and the rotational axis of the rotational drive unit on the table, a disc-shaped cast iron Fiber-bond diamond grinding wheels (hereinafter referred to as CIFB-D grinding wheels) are attached respectively, and each grinding wheel is set as a + pole, and the electrode installed close to each grinding wheel is set as a - pole, and weak conductivity is established between each of the grinding wheels and each electrode. By applying a pulsed DC current from the power supply and electrolytically dressing each grinding wheel while supplying abrasive grinding fluid while ensuring the protrusion of the abrasive grains, it is possible to perform high-removal grinding of various hard and brittle materials. Even mirror polishing can be easily performed. It is preferable for the rotation direction of each grindstone to be relatively reverse rotation, but
Rotation in the same direction is also possible depending on the amount of cut. To change the surface roughness of the front and back surfaces, it is sufficient to change the grain size of the upper and lower whetstones, and when using whetstones with different grain sizes for the inner and outer peripheries, by sliding the upper whetstone,
High removal and mirror finishing can be performed efficiently. Since the cutting is generally performed by lowering the upper grinding wheel, it is preferable that the holder of the workpiece be placed close to the lower grinding wheel and gripped by an external device.

[0009]

EXAMPLES Examples of the present invention will be described in detail below. FIG. 1 is a conceptual diagram for implementing Elid double-sided lap grinding of the present invention. The lower whetstone 11 and the upper whetstone 12 are
The grindstone surfaces 13 and 13' are arranged oppositely so that they are overlapped,
A work holder 15 for semi-fixing the workpiece 14 is fixed to the opposing overlapping portion in close proximity to the lower grindstone 11 by an external fixture (not shown). On the other hand, attachments (FIG. 3) each consisting of an electrode 16 and a power supply section 17 for electrolytically dressing the upper and lower grindstones are provided on the outside of the overlapping portion. Elid
The power supply 18 supplies a pulse current to each attachment, and a switch S1 switches the electrolysis mode of each grindstone.
, S2, and S3 are provided, and the current supplied between the grinding wheel and the electrodes via the grinding fluid supplied from the weakly conductive grinding fluid (coolant) supply port 19 is switched at any time, and each grinding wheel is electrolytically dressed. to ensure the protrusion of the abrasive grains.

FIG. 2 is a conceptual diagram of the upper and lower grindstones viewed from the grindstone surface side, showing the state in which the electrolytic attachment is attached. Also, Figure 3 is similar to Figures 1 and 2.
3 is a conceptual diagram showing the structure of the attachment shown in the figure.
The power supply section 17 is supported by a spring 33 so as to be in pressure contact with the grindstone via the power supply section 2 . Similarly, the electrode 16 made of a copper material is supported via an insulating rod 32' extending from a support plate 31 and a reinforcing plate 34, and is insulated from the power supply section. The table below shows the specifications of the system used to implement the invention described above.

[0011]

[Table 1]

A self-made rotary table was used to drive the lower CIFB-D grindstone, and the grinding machine shown in the table was used to drive the upper CIFB-D grindstone and cut into the workpiece. A self-made rotary table was installed with the rotation axis of the grinding machine shifted by 90 mm between the rotation axis of the lower grinding wheel, and a CIFB-D grinding wheel and an electrolytic attachment (Fig. 3) were attached to each rotation axis. . The coolant is a water-soluble grinding fluid diluted with tap water, and the grindstone has a common outer diameter of φ200m
A CIFB-D grindstone disk with a diameter of 77.5 mm and a width of 77.5 mm was used, and the inner circumference #4000/outer circumference #30000 was used on the upper side, and the inner circumference #1200/outer circumference #4000 was used on the lower side. The workpieces were made of cemented carbide (WC), silicon carbide (SiC), and alumina with a diameter of 47/44 mm and a thickness of 6.5 mm, and experiments were mainly conducted on changes in machining conditions, vertical load, and machined surface roughness. .

[0013] After suitably truing the upper and lower parts of the CIFB-D grindstone disc, sharpening was performed separately for about 30 minutes. Truing is Eli using CIFB-D cup whetstone.
d-truing etc. were applied. The workpiece is held in a sample holder, and the Elid conditions are: no-load voltage E0 = 90V, maximum setting current Ip = 24A, pulse width τon = 12μs/τ
The upper and lower grindstones were simultaneously electrolytically dressed by setting off to 3 μs. Although the rotation directions of the upper and lower grindstones were relatively reversed, no significant difference was observed even in the same direction as a preliminary experiment. First, the upper grindstone cut into the surface of the workpiece by step feeding by a predetermined amount, then sparked out for a predetermined time, and finally the upper grindstone was retracted to complete one process. Through experiments under the above conditions, grinding wheel peripheral speed VL=
100m/min, cutting speed fd=6μm/min
, When the total cutting depth DT = 80 μm per cut, the spark-out effect is the best, the amount of uncut material is small, and Eli
It was found that with the continuous characteristics of the d effect, there was no change in the maximum load after the second time, and stable Elid grinding could be performed.

FIGS. 4(A), 4(B), and 4(C) show examples of finished surface roughness according to each grain size of cemented carbide. In the case of cemented carbide, RMax 100 nm for #1200 (A), #400
0(B) had a mirror finish with an RMax of 50 nm, and #30000(C) had a mirror finish with an RMax of around 15 nm, and good mirror polishing was also achieved when using a finer submicron grindstone. The above examples are results obtained using cemented carbide, silicon carbide, and alumina as samples, which are materials with hardness and brittleness equivalent to silicon, and it can be confirmed that the present invention can be applied to grinding of silicon wafers. Ta.

[0015]

Effects of the Invention According to the present invention, the El
Since ID grinding can be performed on both sides of the workpiece at the same time, great effects can be achieved especially when applied to double-sided processing of silicon wafers made of semiconductor materials that require double-sided processing. In other words, the removal processing efficiency, processing surface roughness, control of surface roughness of the front and back surfaces, and reduction of processing surface damage required for silicon wafers are improved all at once, and in addition, the conventional three steps of lapping → back surface damage → polishing are improved. It becomes possible to automate the process as a leaf processing method. Furthermore, the mirror finishing efficiency of silicon wafers can be processed in about 2 to 3 minutes per silicon wafer.

[0016]

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of the double-sided lap grinding method using electrolytic dressing of the present invention.

FIG. 2 is a conceptual diagram showing how upper and lower grindstones and electrolytic attachments are attached.

FIG. 3 is a conceptual diagram showing the structure of an electrolytic attachment.

FIG. 4 is a surface roughness pattern diagram obtained by implementing the present invention with each particle size.

FIG. 5 is a sectional view showing the structure of a conventional double-sided wrapping device.

[Explanation of symbols]

11 Lower whetstone 12 Upper whetstone 13, 13' Grinding wheel surface 14, 53 Workpiece 15, 56 Work holder 16 Electrode 17 Power supply section 18 Elid power supply 19 Coolant supply port S1, S2, S3 switch 31 Support plate 32, 32' insulation rod 33 Spring 34 Reinforcement plate 51, 52 Lap surface plate 54, 55 Gap 57 Gear

Claims (1)

[Claims] 1. A conductive lower grindstone and an upper grindstone that rotate horizontally around a rotation axis, and the rotation axes of the lower grindstone and the upper grindstone are shifted so that the grindstone surfaces of the respective grindstones are overlapped. electrodes are provided on the outside of the overlapping portion and close to the grinding wheel surface of each of the grinding wheels, and a conductive liquid is supplied between the grinding wheels and the electrodes, and the contact between the grinding wheels and the electrodes is A current is supplied between the two, and the workpiece is held by a holder disposed in the gap between the overlapping parts and sandwiched between the opposed grinding wheels, thereby electrolytically dressing the grinding surface of each grinding wheel and applying the coating. A double-sided lap grinding method using electrolytic dressing, which is characterized by grinding both sides of the workpiece.