JP2669598B2 - Plasma etching tools - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to plasma etching or reactive ion etching (RIE) of semiconductor wafers.
Reactive Ion Etching), and in particular, to an improved electrode structure for a plasma or RIE etcher.

[0002]

2. Description of the Related Art RIE and plasma etching techniques are widely used to etch products such as semiconductor wafers. These techniques basically involve exposing the wafer with a plasma to remove selected surface materials in selected areas, such as silicon dioxide on the semiconductor wafer surface. A polymeric material such as a photoresist is used as an etching mask to prevent unnecessary etching. If the etching is performed in a chemical or physical manner, the etching of the selected material can be very finely controlled because the etching process is limited.

[0003] Although the etching tools currently in use have been greatly improved to date and allow for more precise control of gas flow, pressure, temperature, overall electric field, and plasma formation, yet. Asymmetrical etching can occur during processing.

RIE or plasma etching occurs when ions are separated from the plasma and etched by the electric field present between the wafer, pedestal and plasma sheath, ie, the edge of the plasma cloud. Ions separated from the plasma travel along the electric field lines and collide with and react to selected exposed areas of the wafer surface. Ideally, these field lines should be perpendicular to the entire surface of the wafer. However, the edges of the wafers and pedestals in industrially used equipment, and the wafer retaining clips used in some equipment, can be distorted or changed in the direction of the electric field lines between the plasma sheath, wafer, pedestal and clip. Trigger. Wafer and pedestal distortion exacerbates electric field and plasma sheath distortion. Thus, the pedestal design may further bend the electric field near the edge of the wafer.
Such changes in the electric field affect the ions that are separated from the plasma and that are being etched, acting at an acute or obtuse angle to the surface of the wafer. The non-perpendicular ion projection angle results in asymmetrical etching of the wafer. Such asymmetric etching is particularly severe around the wafer due to the high level plasma sheath and field line distortion caused by the edge of the wafer and pedestal.

[0005] To date, many attempts have been made to solve the problem of non-uniformity. Some of these attempts include using quartz spacers to separate the wafer from the cathode, curving the surface of the wafer, changing the flow of plasma gas, and using flat anodes with large areas. The wafer pedestal may change in various directions with respect to the physical position of the wafer on the cathode when it is operated. The device itself has also been modified by removing the use of large flat power distribution boards of the prior art and replacing it with a centrally located hexagonal post on which the wafer is mounted essentially vertically.

[0006] The above solution has improved the symmetry of the overall etch, but until the present invention did not achieve a symmetrical etch on the entire surface of the wafer.

[0007] As the demand for higher density semiconductor devices increases, if the surface etched holes are not at all symmetrical, the surface will render the device imperfect.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a plasma plasma by making the electric field lines between the plasma sheath and the wafer essentially vertical over the entire wafer surface to symmetrically etch over the entire wafer surface. It is to improve the symmetry of etching in an etching apparatus.

Another object of the present invention is to provide an arrangement that ensures that the etching of all features in all regions of the wafer surface is etched symmetrically regardless of the location of the region on the wafer. That is.

[0010]

SUMMARY OF THE INVENTION In a batch type etching tool, an insulating ring for suppressing an edge effect of an electric field line is provided along an edge of a cylindrical pedestal on which each wafer is placed, so that a surface of the wafer is provided. Symmetric etching can be obtained in any region, and the asymmetric defect in the prior art can be eliminated. The main constitution of the present invention is as follows. A means for establishing a plasma etching atmosphere in a reaction chamber including a pair of cathode and anode electrodes disposed in opposing relation, and a bottom surface fixedly spaced above said one electrode for mounting a wafer; A plurality of substantially cylindrical, low-height pedestals having a surface to be mated, and a plurality of substantially annular insulators fitted around the periphery of each of the pedestals and extending a predetermined height beyond the surfaces; Sex ring,
A plasma etching tool, wherein each of the rings comprises a substantially annular edge portion circumscribing the pedestal at a height reaching the surface of the pedestal and a diameter slightly less than an outer diameter of the pedestal. Is formed of a substantially annular wall portion having a small inner diameter that overhangs the inner wall of the edge portion to shield the edge of the pedestal and project from the pedestal surface, the height and inner diameter of the wall portion Means that the plasma atmosphere and all electric field lines between the wafers are substantially perpendicular to the wafer surface,
And the dimensions are such that the etched features formed on any region of the wafer surface by ions free from the plasma atmosphere are substantially symmetric about an axis perpendicular to the wafer surface at the center point of the features. A plasma etching tool characterized by that.

This significant improvement can be made in etching tools by providing a pedestal supporting each wafer with a uniquely designed ring. Each hoop or collar is made of a selected height or diameter from a selected insulating or dielectric material to modify the plasma sheath and change the direction of the electric field lines at the end of the pedestal, as detailed below. , Formed to a thickness. Such modification eliminates or significantly reduces non-perpendicular field lines at or near the edge of the wafer, and thus specifically controls the direction of ions that separate from the plasma and etch.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The present invention addresses the problem of asymmetry in the prior art by providing a ring or collar having an internal diameter, height, thickness, shape designed to eliminate the electromagnetic field distortions present in conventional devices. The problem is solved by installing a wafer on each pedestal. By essentially eliminating such strains, an essentially uniform plasma sheath across the entire surface of the wafer being etched is achieved,
As a result, the direction of the ions separated from the plasma and colliding with the surface of the wafer becomes appropriate, which enables more precise and uniform etching.

[0013] Today, wafer products are generally etched in batches. FIG. 1 is a schematic diagram of the inside of a batch type plasma etching apparatus commonly used in the semiconductor industry. Commercially available such devices include Applied Materials' Model 8310. The apparatus is a low pressure, batch type wafer reactive ion etching tool. As shown here, the device has a pressure chamber 10 typically made of stainless steel or other suitable metal. Inside this chamber 10 is a cylindrical anode electrode 12, and in the center is a hexagonal cathode 14 having a plurality of tapered pedestals 18 vertically aligned on each side. The wafer 16 to be etched is
Placed on tapered pedestal 18. The anode and cathode are connected to a suitable radio frequency (RF) power supply 17.
Suitable etching gas, suitable source (not shown)
To the chamber 10 through the tube 15. When the chamber is filled with such gas at a suitable pressure and power is applied from the RF source 17, a plasma is formed. If necessary, gas is withdrawn from chamber 10 through outlet tube 19 which connects to a vacuum pump (not shown). As noted above, such devices are widely used and commercially available in the semiconductor industry and, therefore, will not be discussed in detail herein with respect to their features and methods of use.

2 and 3 are enlarged views of the pedestal 18 and the wafer 16 mounted thereon. FIG.
FIG. 3 is a diagram of the surface of the pedestal 18 to which the wafer 16 is fixed. In current Applied Materials equipment, the wafer is secured by a plurality of S-shaped retaining clips 20. Other plasma etchers may use different retention methods. FIG. 3 shows the pedestal 18,
3 is a side cross-sectional view of the wafer 16, plasma sheath 22, and electric field lines 24 between the sheath and the pedestal and the wafer. FIG. From FIG. 3, the lower part 18a of the pedestal 18 is the upper part 18
b, it can be seen that the surface of the pedestal is at an angle to the central cathode 14. This sloping surface 18c of the pedestal 18 is required for the handling methods currently used to place and remove wafers from the pedestal. Since the pedestal surface 18c is inclined with respect to the vertical surface of the cathode 14, the distortion of the plasma sheath and the refraction of the electric field are further aggravated. The effect occurs around the entire pedestal and varies with the material of the pedestal. Clip 2
When 0 is used to hold the wafer on the pedestal, the electric field lines can be slightly distorted around it. However, the strain around the clip is so small that it does not affect the symmetry of adjacent features etched on the surface of the wafer.

As shown in FIG. 3, the edges of the pedestal cause the plasma sheath to distort near the edges of the wafer and pedestal, deflecting the angle of the electric field lines 24 with respect to the surface of the wafer 16 and making it non-vertical. The effect of this strain extends 25 mm away from the edge of the wafer. As shown here, the angle of the electric field lines 24 becomes less and less vertical as one approaches the edge of the wafer and the edge of the pedestal. These non-perpendicular field lines are shown at 24a. As the ions separated from the plasma as described above travel along the electric field lines, the electric field lines that are not perpendicular to the surface of the wafer make the etched features, such as holes or openings, on the surface of the wafer asymmetric. On a 125 mm diameter wafer, this may affect 40% of the chips produced on this wafer.

This asymmetry is more clearly illustrated by FIGS. FIGS. 4 and 5 show holes 2 etched into the surface of a semiconductor wafer using conventional equipment.
It is a scanning electron microscope (SEM) photograph of No. 1. FIG. 4 shows hole 21
FIG. 5 is a plan view of the same hole 21. This hole 21 was made in the surface of the semiconductor wafer 16 by a series of photoresist and etching processes. The effect of the asymmetry on the axis 23 (FIG. 4) extending perpendicularly from the center of the bottom of the hole 21 is shown in FIG.
It is particularly remarkable on the left side 21a of the hole 21 in.
From these figures, with respect to the line drawn perpendicular to the surface of the wafer, the wall on the left side of the hole forms a greater angle than the wall on the right side,
Therefore, it can be seen that the holes are asymmetric. This asymmetry becomes more severe as the etching process is repeated.

FIG. 6 is a side sectional view of the pedestal 28 with the wafer 26 mounted thereon. This pedestal 28
Comprises a unique ring 30 of the present invention. The annulus 30 shown in more detail in FIG. 8 is formed of an insulating or dielectric material such as ceramic or plastic.

The ring 30 has a thicker lower edge 32 and a thinner, tubular upper wall 34. Edge 3 at the bottom
2 is tapered along its diameter as shown in FIG. 9 to accommodate the taper of the pedestal that the rim surrounds as shown in FIG. When the retaining clip is used, the annulus 30 further comprises a plurality of grooves 33 adjacent the clip 20 on the circumference of the rim.

In designing the annulus, the wall height is selected so that the plasma sheath is uniform over the entire surface of the wafer. If the wall is too high, for example about 6 centimeters, the plasma sheath will be distorted as if it were without a loop and the loop effect will be lost. The wall thickness should be as small as possible while maintaining the mechanical strength of the material used. Therefore, plastic materials such as ceramics, due to their plastic properties, inevitably have thicker walls than machined plastics. Further, the inner diameter (also referred to as the inner diameter) of the wall should be selected such that the distance (ie, the difference in radius) from the inner wall of the wall to the outer periphery of the wafer is in the range of 20 millimeters to 2.5 millimeters. In other words, the internal diameter of the wall should be greater than the diameter of the wafer by 40 to 5 millimeters. For large dimensions where the inside diameter of the wall exceeds this upper limit, a wall is not necessary. The reason is,
This is because the distortion of the electric field lines due to the edge effect on the pedestal does not reach the wafer since the wafer is located at the center away from the outer periphery of the pedestal by the large dimension. On the other hand, if the inner diameter of the wall becomes smaller than the lower limit, the electric field lines will be distorted near the outer periphery of the wafer. Further, in the case of such a narrow interval, the etching gas tends to be insufficiently supplied in the vicinity of the outer periphery of the wafer, which makes uniform etching difficult.

The wheels used to achieve the results described in the preferred embodiment of the present invention were formed from LEXAN ™ polycarbonate plastic sold by General Electric. The ring 30 used in the Applied Materials Model 8310 has an inner diameter of the rim 32 of 14.70 cm, an inner diameter of the wall 34 extending upwards of 14.45 cm, and a pedestal surface 1.
The height above 8b is 1.78 cm and the thickness is 0.508 cm. It should be noted that the inner diameter of the wall 34 is smaller than the inner diameter of the lower rim and covers the inner surface of the lower rim 32 and covers the edge of the pedestal 28. The groove 33 is
It is 1.70 cm high and 2.54 cm wide, and the top of the groove ends at the border between the rim and the wall. These grooves 33 allow free movement of the retaining clip 20 which is opened for inserting, placing and removing the wafer on the surface of the pedestal. Note that if other devices are used that do not use retaining clips, these holes are not needed. 1
When used with a 25 mm wafer, the annulus 30 changes the electric field such that all electric field lines 36 on the entire wafer surface are essentially perpendicular to the wafer surface as shown in FIG.

6 and 7, the plasma sheath 38 modified by the annulus 30 according to the present invention will be further described. FIG. 7 shows in particular how the electric field lines 36 between the sheath 38 and the pedestal 28 in contact with the ring 30 are modified by the ring 30 of the present invention in the region of the edge of the wafer. In FIG. 7, the wheel 30 and in particular the upper wall 34
Alters the plasma sheath 38, i.e., by preventing the sheath from bending downward at the end of the pedestal, thereby making the sheath 38 essentially flat over the entire wafer surface. The annulus 30 is thus essentially a plasma sheath 38 by the end of the pedestal.
And the effect on the electric field lines 36 is eliminated. Modifying the effect of the edge of the pedestal causes the electric field lines 36 at the edge of the wafer to be oriented essentially perpendicular to the surface of the wafer. This occurs because the annulus 30 effectively eliminates the effects of the pedestal edge and forces the plasma sheath to remain essentially flat over the entire wafer surface. Since the diameter of the wafer is smaller than the diameter of the pedestal, there is a slight height difference between the sheath and the surface of the pedestal, and the plasma sheath has a ring 30.
Before it begins to rise along the wall 34 of the vehicle.
However, this descent does not significantly affect the symmetry of the features formed on the surface of the wafer. As described above, as ions separated from the plasma travel along the electric field lines, any ions following the non-perpendicular electric field lines 36 are kept away from the edge of the wafer and do not cause asymmetry of features etched at the surface of the wafer.

Symmetrical feature, namely the inventive ring 3
The holes formed using 0 in the surface of the semiconductor wafer are shown in FIGS. 10 and 11, which are photographs of holes 40 etched in the surface of the semiconductor wafer 26. FIG. 10 is a sectional view of the hole, and FIG. 11 is a plan view of the same hole. This hole was etched in the same region of the semiconductor wafer by performing exactly the same process that was performed to create the asymmetrical hole 21 shown in FIGS. 4 and 5. FIG.
And in comparison with the axis 23 extending perpendicularly to the surface of the wafer from the center of the hole in FIG. 11, the effect of the annulus 30 eliminating the asymmetry is clear. Thus, it is clear that all walls are at the same angle with respect to a line drawn perpendicular to the surface of the wafer.

Although the preferred embodiment has been described with reference to etching holes in the surface of the wafer, the present invention is suitable for leaving other features that exit from the surface of the component or are recessed from the surface of the component. It should be noted that it can also be used to etch the surface of various components. Using the present invention, the features thus formed have walls that are at the same angle to an axis that is drawn perpendicular to the surface of the part.

Therefore, the present invention is directed to plasma or RIE.
It is disclosed that the use of the annulus 30 in an etcher results in a symmetrical etching of features on the surface of the part or in the part, regardless of the location in the etcher or the location of the feature on the part surface.

This is accomplished by eliminating the strain of the plasma sheath in the annulus so that the annulus 30 makes the plasma sheath uniform with respect to the part surface.

Although the present invention has been described for use in a batch type etcher, the present invention also includes single wafer
It is understood that it can also be used in an etching device or an etching device with a pedestal of different mechanical construction. In such other environments, the wheel 30
It is preferred that the lower rim 32 of the is adapted to the mechanical configuration of the pedestal and that the wall 34 overlap the edge of the pedestal.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that other changes may be made without departing from the spirit and scope of the invention.

[0028]

Since the present invention is constructed as described above, the electric field lines between the plasma sheath and the wafer are essentially vertical over the entire wafer surface, and the etching over the entire surface of the wafer is symmetric. be able to.

[Brief description of the drawings]

FIG. 1 is a schematic view of an entire etching apparatus that can efficiently use the present invention.

FIG. 2 is a plan view of a wafer holding pedestal used in the apparatus of FIG. 1 with the wafer secured by clips.

FIG. 3 is a cross-sectional view of the wafer support pedestal used in the apparatus of FIG. 1 with a plasma sheath surrounding the pedestal and electric field lines extending between the sheath and the wafer.

FIG. 4 is a photomicrograph of holes etched in the surface of a wafer when the wafer is placed in the pedestal shown in FIGS. 2 and 3.

FIG. 5 is a micrograph of the etched hole of FIG.

6 is a cross-sectional view of a wafer-holding pedestal used in the apparatus of FIG. 1 with the addition of a wheel according to the present invention.

7 is a partial enlarged view of FIG. 6 showing how the electric field lines and the plasma sheath are modified by attaching the ring according to the invention to the pedestal.

FIG. 8 is an isometric view of a ring according to the present invention.

FIG. 9 is a sectional view of a hoop according to the invention showing how the hoop tapers to accommodate the pedestal of the device used.

10 is a photomicrograph of a hole etched in the surface of a wafer when a pedestal used in the etching apparatus of FIG. 1 is fitted with a ring according to the present invention as shown in FIGS. 6 and 7; is there.

FIG. 11 is a micrograph of the etched hole of FIG.

[Explanation of symbols]

 10 Pressure Chamber 12 Anode 14 Cathode 16, 26 Wafer 17 High Frequency Power Supply 18, 28 Pedestal 20 Holding Clip 22, 38 Plasma Sheath 24, 36 Electric Field Line 30 Wheel 32 Edge 33 Groove 34 Wall

 ───────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Eric Andre Bryn France 75014 Paris-Louis-Louis-Morard 8 (72) Inventor Timothy Edward Neari United States 05452 Vermont Essex Junction Margaret Street 34 (72) Inventor Sylvia Rose Label Toesle B United States 05403 South Burlington Spare Street, Vermont 112 (72) Inventor Arthur Clifford Winslow United States 05452 Essex Junction Clover Drive, Vermont 48 (56) References JP-A-2-220435 (JP, A) JP 1-118224 (JP, A) JP-A-62-30327 (JP, A)

Claims (9)

(57) [Claims] A means for establishing a plasma etching atmosphere in a reaction chamber including a pair of cathode and anode electrodes disposed in opposing relation; a bottom surface fixedly spaced above said one electrode; A plurality of substantially columnar, low-height pedestals having a surface on which a wafer is to be mounted; substantially a plurality of pedestals fitted around the pedestals and extending a predetermined height beyond the surfaces; A plasma etching tool comprising: a plurality of annular insulating rings; each ring circumscribing the pedestal at a height reaching the surface of the pedestal. And having an inner diameter slightly smaller than the outer diameter of the pedestal, projecting in an overhanging manner at the top of the inner wall of the rim to shield the edge of the pedestal, and A substantially annular insulating wall portion extending from the surface, wherein the height and inner diameter of the wall portion are such that the plasma atmosphere and all electric field lines between the wafers are substantially perpendicular to the wafer surface. And the size of the etched shape formed on any region of the wafer surface by ions free from the plasma atmosphere is substantially symmetric about an axis perpendicular to the wafer surface at the center point of the shape. A plasma etching tool that is characterized by: 2. A means for establishing a plasma etching atmosphere in a reaction chamber including a pair of cathode and anode electrodes disposed in opposing relation, a bottom surface being fixedly spaced above said one electrode; A plurality of substantially columnar, low-height pedestals having a slanted surface on which a wafer is to be mounted, fitted on the outer periphery of each of the pedestals, and extending a predetermined height beyond the surfaces; A plasma etching tool comprising: a plurality of substantially annular insulating rings; each ring circumscribing the pedestal at a height reaching the surface of the pedestal. Having a slightly smaller inner diameter than the outer diameter of the pedestal and overhanging at the top of the inner wall of the pedestal so as to shield the edge of the pedestal and the edge of the pedestal. A substantially annular insulative wall portion extending from the top surface of the minute portion, the inner diameter of said wall portion having a dimension greater than the diameter of the wafer by 5 to 40 millimeters. The height and inner diameter of the wall portion is such that all field lines between the plasma atmosphere and the wafer are substantially perpendicular to the wafer tilt surface, and any area of the wafer tilt surface due to ions free from the plasma atmosphere. A plasma etching tool characterized in that the etching features formed thereon are dimensioned such that they are substantially symmetrical about an axis perpendicular to the wafer tilt surface at the center point of the features. 3. The plasma etching tool according to claim 1, wherein the surface of the pedestal comprises a surface inclined from a horizontal plane. 4. When using the pedestal designed to mount a semiconductor wafer having a diameter of 125 millimeters, the height of the highest position of the wall portion is 17.8 millimeters, and the height of the wall portion and the edge are increased. 3. The method of claim 2, wherein the difference in inner diameter between the parts is selected to be 2.5 millimeters.
Or the plasma etching tool described in 3). 5. The interface between the rim portion and the wall portion of the loop forms a substantially annular interface which is inclined at the same angle as the inclined surface of the pedestal. Or the plasma etching tool described in 3). 6. Each of the pedestals has a plurality of retaining clips on its surface for retaining an outer periphery of each wafer, while a plurality of retaining clips are provided at positions where the inner wall surface of the wall portion of the loop is aligned with the retaining clips. Claim 2 or 3 which has a groove
Plasma etching tool described in. 7. A means for establishing a plasma etching atmosphere within a reaction chamber including a pair of cathode and anode electrodes disposed in opposing relation, and a bottom surface fixedly spaced above said one electrode; An apparatus for adjusting an electric field for use in a plasma etching tool including a plurality of substantially cylindrical, low-height pedestals having a surface on which a wafer is to be mounted, the apparatus comprising: Providing a plurality of substantially annular insulating rings that fit around the perimeter and extend a predetermined height beyond the surface, wherein each of the rings circumscribes the pedestal at a height that reaches the surface of the pedestal; A substantially annular insulating rim portion having an inner diameter sized to be millimeters smaller than the outer diameter of the pedestal, and an outer peripheral edge of the wafer at the top of an inner wall of the rim portion. Et al. 2.5 millimeters to 2
A substantially annular shape that overhangs from the edge toward the outer periphery of the wafer to an outer position separated by a distance of 0 millimeter to shield the pedestal surface including the edge and extends from the top surface of the edge portion. The height and the inner diameter of the wall portion are free from the plasma atmosphere, with the electric field lines between the plasma atmosphere and the wafer being substantially vertical over the entire surface of the wafer. Electric field adjustment, characterized in that the etching shape formed on any area of the wafer surface by the ions of the above is selected to be substantially symmetrical about an axis perpendicular to the wafer surface at the center of the shape. apparatus. 8. A means for establishing a plasma etching atmosphere in a reaction chamber including a pair of cathode and anode electrodes disposed in opposing relation, and a bottom surface fixedly mounted on said one electrode; An apparatus for adjusting an electric field for use in a plasma etching tool comprising a plurality of substantially cylindrical, low-height pedestals having an inclined surface on which a wafer is to be mounted, the apparatus comprising: Providing a plurality of substantially annular insulating rings that fit around the periphery of each pedestal and extend a predetermined height beyond the surface, wherein each ring has a height that reaches the surface of the pedestal; A substantially annular insulating edge portion circumscribing the pedestal, and an overhanging shape protruding at the top of the inner wall of the edge portion having an inner diameter slightly smaller than the outer diameter of the pedestal, and A substantially annular insulative wall portion that shields an edge of a destal and extends from a top surface of the rim portion, wherein an interface between the rim portion and the wall portion of the loop is An electric field conditioning device, characterized in that it forms a substantially annular boundary surface which is inclined at the same angle as said inclined surface of the pedestal. 9. A means for establishing a plasma etching atmosphere in a reaction chamber including a pair of cathode and anode electrodes disposed in opposing relation, and a bottom surface fixedly spaced above said one electrode; An apparatus for adjusting an electric field for use in a plasma etching tool comprising a plurality of substantially cylindrical, low-height pedestals having a wafer retaining clip near a perimeter of a surface, the apparatus comprising: Providing a plurality of substantially annular insulative rings that fit around the periphery of the pedestal and extend a predetermined height beyond the surface, wherein each of the rings has a height that reaches the surface of the pedestal. A substantially annular insulating rim portion circumscribing, and an inner diameter slightly smaller than the outer diameter of the pedestal, overhanging at the top of the inner wall of the rim portion; The retaining clip at the inner wall surface of the wall portion of the annulus, wherein the retaining clip comprises a substantially annular insulated wall portion extending out and shielding the edge of the pedestal and extending from a top surface of the rim portion. An electric field adjusting device, wherein a plurality of grooves are provided at matching positions.