JPH11204464A - Manufacture of wafer having high flatness - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer having excellent flatness on the surface and back sides, by calculating the shape of the surface and back sides of the wafer on the basis of optical interference fringes obtained from the surface and back sides of the wafer, and removing a portion to be worked, protruding from a reference surface, on the surface and back sides by plasma etching. SOLUTION: From shape measurement data of the surface and back sides of a wafer obtained by an optical measuring device, total quantities of etching of the surface side and the back side are calculated. Then, the side having the greater total quantity of etching is assumed as being the back side B and is etched at a high rate using a high-power plasma etching device. It is also possible to etch the back side B at a large scan pitch within such a range that the standard of the glossiness of the back side is met. Therefore, a portion to be worked C is quickly removed by etching. On the other hand, on the surface side A having the smaller quantity of removal, a portion to be worked D is removed by etching with a making power which does not cause any damage. Thus, a product wafer having high flatness both on the surface side A and on the back side B is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a wafer having a surface close to an ideal plane, in which even a waviness component is removed.

[0002]

2. Description of the Related Art A semiconductor wafer cut from an ingot is subjected to lapping, polishing and other processes.
It is etched to flatten with high precision. Since the etching at this time is required to remove a limited area by a predetermined amount, plasma-assisted chemical etching is employed. The etching amount is determined on the basis of the flatness of the wafer obtained from optical interference fringes or by scanning both surfaces of the wafer with a displacement sensor. In a method using optical interference fringes, as disclosed in Japanese Patent Application Laid-Open No. 1-143906, the flatness of a wafer is calculated from an optical lens serving as a reference plane and interference fringes formed by the wafer. In the method of scanning both sides of a wafer with a displacement sensor, Japanese Patent Publication No. 5-771
As disclosed in Japanese Patent Publication No. 79, the thickness variation of the wafer is calculated based on the displacement signals obtained from the two capacitive displacement sensors arranged on both sides of the wafer, and the back side is calculated. The flatness of the wafer is determined by converting it to an ideal plane.

[0003]

However, in either case, the thickness deviation, which is the displacement of the other surface assuming that one surface is an ideal plane, is treated as flatness, and the removal amount by etching is calculated from the flatness. ing. That is, the wafer is etched with a target of a product having a small thickness deviation. Therefore, undulations and inclinations of the wafer that do not have a thickness deviation are treated as not to be measured, and are not removed by etching. Using the thickness deviation as an index is partly due to the fact that the wafer to be measured for flatness is flattened by a suction force when the wafer is suction-held by a vacuum chuck or the like. However, in the case of wafers used for semiconductor devices, on which demands for higher integration and ultra-miniaturization are becoming stronger, the influence of deformation due to suction force on device fabrication and breakage cannot be ignored. For this reason, a wafer having high flatness on both the front and back surfaces is desired, but a method of manufacturing such a high flatness wafer has not been proposed so far.

The present inventors have proposed in Japanese Patent Application No. 9-154023 an optical shape measuring instrument for determining the shape and flatness of both front and back surfaces of a wafer from optical interference fringes on both surfaces of the wafer. In this apparatus, the wafer is vertically held via an edge portion without being suction-held, and two optical measuring devices are arranged on both sides of the wafer to face each other. Then, the shape and flatness of both front and back surfaces are calculated from the optical interference fringes obtained by both optical measuring devices. The present invention focuses on the fact that the optical shape measuring device proposed earlier is effective for measuring the shape of the front and back surfaces of the wafer, and determines the amount removed by etching according to the obtained shape of the front and back surfaces for each of the front and back surfaces. Thereby, an object is to obtain a wafer having excellent flatness on both front and back surfaces.

[0005]

In order to achieve the object, the manufacturing method of the present invention calculates the shape of both the front and back surfaces of a wafer based on optical interference fringes obtained from both the front and back surfaces of a vertically held wafer, and obtains a reference and a reference value. It is characterized in that the processed parts on both the front and back surfaces which are raised from the front surface are removed by plasma etching. When a wafer whose front surface or back surface is not predetermined is etched, the side where a large number of processed parts to be removed is used as the back surface, and high-power plasma is irradiated. When etching the back surface, if the back surface side is plasma-etched at a scan pitch larger than that of the front side, the processing speed is increased.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An apparatus for measuring the shape of both front and back surfaces of a wafer 1 holds an edge portion of a wafer 1 in a vertical direction by appropriate means, for example, as shown in FIG. By holding the wafer 1 vertically, the wafer 1 is released from restraint by a holding means such as a vacuum chuck, and measurement in a free state becomes possible. Further, since the wafer 1 is held via the edge portion, an unmeasurable region due to the holding means does not occur. Optical measurement systems 10 and 20 are provided on both sides of the wafer 1.
Is arranged. The optical measurement systems 10 and 20 include a light emitting device 11 and
The measurement light beams 12 and 22 emitted from 21 are reflected by the half mirror 1
Are sent to collimator lenses 14 and 24 via 3, 23,
The reference plane lenses 15 and 25 are transmitted as parallel beams, and the front and back surfaces of the wafer 1 are irradiated. Measuring light 12,
22 is reflected on both the front and back surfaces of the wafer 1, but a part of the reference plane lens 15,
It is also reflected on 25 reference planes.

The measuring beams 12, 22 reflected on the front and back surfaces of the wafer 1 and the reference planes of the reference plane lenses 15, 25 pass through the reference plane lenses 15, 25 and the collimator lenses 14, 24 along the reverse path. Half mirrors 13, 23
And is taken into the light receivers 16 and 26. The measurement light beams 12 and 22 reflected on the front and back surfaces of the wafer 1 have different optical path differences from the measurement light beam reflected on the reference surfaces of the reference plane lenses 15 and 25. Since the optical path difference reflects the surface shape of the wafer 1 in this manner, the surface shape and the back surface shape of the wafer 1 can be determined from the observed interference fringes.

The light-emitting devices 11, 21 and the light-receiving devices 16, 26
Are connected to computing units 17 and 27. Arithmetic unit 17,
27 includes monitors 18 and 28, and the optical lens 1
Two interference fringes respectively formed by 5, 25 and both surfaces of the wafer 1 are simultaneously captured. The calculators 17 and 27 calculate and record the shapes of the front and rear surfaces of the wafer 1 from the captured interference fringes. In addition, the flatness of the wafer 1 is calculated and recorded from one interference pattern based on one surface shape. Alternatively, a thickness gauge (not shown) is arranged at equal intervals in the circumferential direction of the wafer 1, and the wafer 1 directly measured by the thickness gauge is used.
The shape of both the front and back surfaces of the wafer 1 is calculated from the optical interference fringes based on the thickness of the wafer 1. When the surface of the wafer whose shape is to be measured is relatively rough, an oblique incidence method using a triangular prism instead of the reference plane lenses 15 and 25 can be employed. In this case, an optical system as shown in FIG. That is, the light emitted from the light emitters 31 and 41 is spread into a predetermined light flux by the convex lenses 32 and 42 and the like, and the measurement light converted into the parallel light flux by the collimator lenses 33 and 43 enters the triangular prisms 34 and 44. Triangular prisms 34, 44
Is arranged such that the reference bottom surface is opposed to both the front and back surfaces of the wafer 1.

A part of the measuring light incident on the triangular prisms 34 and 44 passes through the triangular prisms 34 and 44 and is reflected on the front and back surfaces of the wafer 1, and the rest is reflected on the triangular prisms 34 and 4.
4 is reflected by the reference bottom surface. Therefore, an optical path difference corresponding to the flatness of each of the front and back surfaces of the wafer 1 is generated between the measurement light reflected on the front and back surfaces of the wafer 1 and the measurement light reflected on the reference bottom surfaces of the triangular prisms 34 and 44. According to this optical path difference, optical interference fringes are generated as in the case of FIG. The optical interference fringes are projected on screens 35 and 45 and are transmitted through lenses 36 and 46 to television cameras 37 and 47.
Are formed on the imaging surface of the arithmetic units 38 and 48 as video signals.
Is input to The computing units 38 and 48 analyze the video signal to calculate the surface shape of the wafer 1 and record it, and display it on the monitors 39 and 49 as appropriate.

As described above, when flatness is obtained by using two interference fringes obtained from both the front and back surfaces of the wafer 1, a measurement result can be obtained in an extremely short time as compared with a conventional method using a displacement sensor. In addition, since not only the flatness but also the front surface shape and the back surface shape of the wafer 1 are measured, it is also possible to determine waviness and warpage without thickness fluctuation. In the present invention, the etching removal amount is determined according to the flatness, undulation, warpage, and the like detected in this manner. For example, in the case of etching a wafer 1 for which which surface is to be the front surface or the back surface is not predetermined, from the shape measurement data of the front and back surfaces of the wafer 1 obtained by the optical measuring device of FIG. 1 or FIG. And the total etching amount on the back surface is calculated. Then, as shown in FIG. 3, a surface having a large total etching amount is defined as a back surface B, and high-speed etching is performed using a high-power plasma etching apparatus (a). The back surface B can be etched at a large scan pitch within a range that satisfies the specification of the back surface glossiness. Therefore, the processed portion C is quickly removed by etching (b). On the other hand, the surface A with a small removal amount
, The workpiece D is removed by etching with a power that does not cause damage. In this way, a product wafer having high flatness on both the front surface A and the back surface B is obtained (c).

When etching the wafer 1 having a fixed front and back surface, the back surface B is etched at a high scan pitch with a large scan pitch using a high-power plasma etching apparatus. The surface A is etched under normal conditions. As the plasma etching apparatus, an apparatus previously proposed by the present inventors in Japanese Patent Application No. 9-58878 is used. In this plasma etching apparatus, as shown in FIG. 4, an edge portion of a wafer 1 to be processed is gripped by a holder 51, the wafer 1 is held vertically, and set in a reaction chamber 50. A gas supply pipe 52 penetrating the reaction chamber 50 extends to a position facing the front or back surface of the wafer 1 so as to feed the etching gas 53 toward both the front and back surfaces of the wafer 1.

A waveguide 55 extending from a magnetron 54 surrounds the gas supply pipe 52 so that the etching gas 53 passing through the gas supply pipe 52 is turned into plasma by microwave excitation. The radical species 56 generated by the plasma are supplied from the gas supply pipe 52 to the front surface or the back surface of the wafer 1 and used for etching the wafer 1. Since there is no problem even if the back surface of the wafer 1 is slightly damaged, the processed portion C can be removed with a large plasma output. Therefore, not only the processing efficiency is improved, but also a gettering effect of capturing impurities such as metal that adversely affects the device manufacturing process at the damaged portion is obtained.

When removing the workpiece D from the surface of the wafer 1, ordinary etching conditions are employed. The removal of the workpieces C, D may be performed in either two steps of removing the workpiece D after removing the workpiece C, or in one step of removing the workpieces C, D simultaneously. . Alternatively, instead of the gas supply pipes 52 opposed to both sides of the wafer 1 shown in FIG. 4, the gas supply pipes 52 are arranged on one side of the wafer 1 and the wafer 1 is turned over to process both the front and back sides. The holder 51 is provided with a mechanism for, for example, gripping the edges of the wafer 1 at equal intervals in the circumferential direction and rotating and / or moving the wafer 1 so as to expose the processed portion C or D of the wafer 1 to the radical species 56. ing. In this way, the advantage of etching using microwave-excited plasma that does not require the wafer 1 to be placed on
And the exposed portion C or D of the wafer 1 is exposed to the radical species 56 sent out from the gas supply pipe 52, whereby both the front and back surfaces of the wafer 1 can be processed to a high flatness.

[0014]

EXAMPLE A flatness of a wafer having an average thickness of 725 .mu.m, which was cut out from a single crystal silicon ingot having a diameter of 200 mm and polished on both sides, was measured using a shape measuring instrument having the equipment configuration shown in FIG. When the cross-sectional shape of the front surface of the wafer was calculated based on the interference fringes obtained from the front and back surfaces of the wafer, the height varied on the front surface and the back surface as shown in FIG. When the protrusions were calculated on the basis of the level of the height of 0 μm on the front side and the back side, the volume of the front side protrusion was 1
5 mm ³ , and the volume of the rear-side protuberance was 30 mm ³ .
The wafer 1 having protrusions on both front and back surfaces was set in the reaction chamber 50 shown in FIG. 4, and the protrusions were removed from both front and back surfaces by plasma etching.

In removing the rear-side protuberance, the etching gas SF ₆ is excited by a microwave having a frequency of 2.45 GHz and a power of 1 KW to generate plasma, and radical species 56 generated by the plasma are supplied to the gas supply. The wafer 1 was supplied via a tube 52 to a wafer 1 placed in a reaction chamber 50 at a vacuum degree of 5 Torr. The distance between the opening of the gas supply pipe 52 and the back surface of the wafer 1 was set to 5 mm, and the opening diameter of the gas supply pipe 52 was set to 10 mm. During etching,
The wafer 1 was moved at a scan pitch of 10 mm so that the ridge was exposed to the radical species 56. Except for moving the wafer 1 at a scan pitch of 8 mm, the same conditions as those on the back surface side are used to excite the etching gas SF ₆ with a microwave of a frequency of 2.45 GHz and a power of 400 W to generate plasma, with respect to the front side protrusion. Plasma etched underneath. When the surface shape of the etched wafer 1 was measured again by the shape measuring instrument shown in FIG. 1, it was found that the wafer 1 had an extremely high flatness in which the protrusions were 2 μm or less on both the front and back surfaces.

[0016]

As described above, in the present invention, the shape of the front and back surfaces of a wafer is measured, and the front and back surfaces of the wafer are selectively etched based on the obtained surface shape and back surface shape. Both are processed into wafers with high flatness. In the wafer thus obtained, various functional layers are formed on the surface having a high flatness, so that a highly reliable semiconductor device can be formed. Also, even when the back side is sucked by a vacuum chuck or the like when various processes are performed in a later process,
There is no deformation that adversely affects the device to be built.

[Brief description of the drawings]

Fig. 1 A shape measuring instrument that measures the shape of both sides of a wafer using a reference plane lens

Fig. 2 A shape measuring device that measures the shape of both sides of a wafer using a triangular prism.

FIG. 3 shows the shape of the front and back surfaces of a wafer obtained by a shape measuring instrument (a), a wafer from which a processed part on the back side is removed (b), and a wafer from which a processed part on the front side is removed (c)

FIG. 4 is a plasma etching apparatus used in an embodiment of the present invention.

FIG. 5 shows the shape of both sides of the wafer measured in the example.

[Explanation of symbols]

1: Wafer 10, 20: Optical measurement system 11, 21: Light emitting device 1
2, 22: measuring light 13, 23: half mirror 14, 24: collimator lens 15, 25: reference plane lens 16, 2
6: light receiver 17, 27: arithmetic unit 18, 28: monitor 31, 41: light emitter 32, 42: convex lens 3
3, 43: Collimator lens 34, 44: Triangular prism 35, 45: Screen 36, 46: Lens 37, 47: Television camera 38, 48: Computer 39, 49: Monitor 50: Reaction chamber 51: Holder 52: Gas Supply pipe 53: Etching gas 54: Magnetron 55: Waveguide 56: Radical species A: Front surface B: Back surface C: Back side processed part D: Back side processed part

Claims (3)

[Claims] 1. The shape of both front and back surfaces of a wafer is calculated based on optical interference fringes obtained from both front and back surfaces of a vertically held wafer, and processed portions of both front and back surfaces which are raised from a reference surface are subjected to plasma etching. A method for manufacturing a wafer having a high flatness, characterized by removing. 2. The method for manufacturing a wafer having high flatness according to claim 1, wherein a side having a large number of portions to be removed is set as a back surface, and high-power plasma is irradiated. 3. The method for manufacturing a wafer having high flatness according to claim 1, wherein plasma etching is performed on the rear surface side at a scan pitch larger than that on the front surface side.