Device, and Method of Manufacture, for use in Mechanically Cleaning Nanoscale Debris from a Sample Surface

Abstract

A mechanical method of removing nanoscale debris from a sample surface using an atomic force microscope (AFM) probe. The probe is shaped to include an edge that provides shovel-type action on the debris as the probe is moved laterally to the sample surface. Advantageously, the probe is able to lift the debris without damaging the debris for more efficient cleaning of the surface. The edge is preferably made by focused ion beam (FIB) milling the diamond apex of the tip.

Claims

1. A mechanical device for removing nanoscale debris from a sample surface comprising: a surface configured to contact a bottom portion of the debris and lift the debris when moved laterally to the sample surface.

2. The device of claim 1, wherein the mechanical device is an AFM probe having a tip, and the surface defines part of the tip.

3. The device of claim 2, wherein the tip is a diamond tip and the surface defines a notch formed between proximal and distal ends of the tip.

4. The device of claim 1, wherein the notch is formed by focus ion beam (FIB) milling.

5. The device of claim 1, wherein the sample surface is a surface of a lithography mask used in semiconductor fabrication.

6. An AFM having a probe according claim 1.

7. A method of cleaning nanoscale debris from a sample surface, the method comprising: a mechanical device including a surface configured to contact a bottom portion of the debris and lift the debris when moved laterally to the sample surface.

8. The method of claim 7, wherein the mechanical device is an AFM probe having a tip, and the surface defines part of the tip.

9. The method of claim 8, further comprising moving the tip in a vector having both lateral and vertical components resulting in scooping of the debris from the sample surface.

10. The method of claim 8, further comprising: engaging the tip to the surface; and providing relative lateral motion between the surface and the tip so that the surface secures the debris against the tip and lifts the debris.

11. The method of claim 10, further comprising AFM imaging the sample surface prior to the engaging step to identify the debris.

12. The method of claim 8, further comprising providing relative orthogonal motion between the probe and the sample so as to lift the debris with the tip to a predetermined height.

13. A method of manufacturing a device to clean nanoscale debris from a sample surface, the method comprising: providing a probe including a diamond tip; and modifying the tip such that when the probe is moved laterally to the sample surface and interacts with the nanoscale debris the modified tip contacts a bottom portion of the debris so as to provide an upward force to the debris.

14. The method of claim 13, wherein the tip has a first and second ends, and wherein modifying step comprises cutting a notch in a surface of the tip between the first and second ends.

15. The method of claim 14, wherein, prior to being modified, the tip is generally conical in shape.

16. The method of claim 14, wherein the modifying step includes focused ion beam (FIB) milling the tip.

17. An AFM probe made according to the method of claim 13.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] A preferred exemplary embodiment of the invention is illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which:

[0028] FIG. 1 is a schematic illustration of a Prior Art atomic force microscope;

[0029] FIG. 2 is a schematic side elevational view of a standard pyramidal-shaped AFM probe tip being used in a Prior Art method to clean a sample surface of debris;

[0030] FIG. 3 is a schematic side elevational view of a Prior Art AFM probe having a pyramidal-shaped tip made of diamond;

[0031] FIG. 4 is a schematic side elevational view of a probe, starting as the prior art probe of FIG. 3, then focused ion beam (FIB) milled according to a preferred embodiment;

[0032] FIG. 5 is a schematic side elevational view of a probe similar to FIG. 2, but using the probe of FIG. 4 to illustrate the force exerted on debris during a lifting operation of the preferred embodiments;

[0033] FIG. 6 is a flow chart of a method for cleaning a surface of nanoscale debris using the probe shown in FIG. 4, according to a preferred embodiment; and

[0034] FIG. 7A-7E are a series of schematic side elevational views illustrating the removal of debris from a sample surface, according to a method of the preferred embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Referring initially to FIG. 3, a probe 60 is shown having a cantilever 62 and a pyramidal-shaped tip 64 typically used in an AFM, similar to that shown in FIG. 2. Tip 64 may be made of diamond. Starting with this probe, a probe 70 of a preferred embodiments includes a cantilever 72 supporting a tip 74 shaped to have a surface defining a notch 76 and to have a blunt distal end 78, as shown in FIG. 4. The surface is the outer surface of tip 74 in FIG. 4, but could be an inner surface or even a side surface. Blunt distal end 78 is not as sharp as a typical AFM tip used to image sub-nanometer features of samples, but it is sufficient to image the surface and provide a map of the debris prior to cleaning, as described further below in connection with the corresponding method.

[0036] In the preferred embodiments, focused ion beam (FIB) milling is used to form the surface so it is configured to lift debris as relative lateral motion is provided by the AFM scanner. As shown in FIG. 4, notch 76 of probe 70 is bordered at its bottom edge by an upper surface 80 of a wedge-shaped “blade.” When viewed in profile, this blade has a relatively planar lower surface 78 forming the blunt bottom of the tip and an upper surface 80 that slopes upwardly moving more inward to the body of the tip or to the rear in FIG. 4. In this embodiment, the notch is bordered at its upper edge by a tip surface 82 that slopes downwardly moving more inward to the body of the tip or to the rear in FIG. 4 The notch thus generally takes on the shape of a sideways “v”. The resultant modified tip is able to “shovel” or scoop up and carry away debris. As the AFM provides relative motion during the cleaning process, the debris may adhere and/or wedge in notch 76.

[0037] Turning to FIG. 5, tip 74 of the probe of the preferred embodiments is shown as it cleans a surface 90 of debris 92. In comparison to the interaction between probe tip 52 and debris 56 in FIG. 2, in this case, the debris 92 is scooped up as bottom 80 of notch 76 of the tip surface engages the bottom of the debris particle 92. The arrow shown indicates the force on the defect/debris is essentially upward in contrast to a similar operation with a conventional AFM tip in which the force pushes the defect down when the two encounter each other (FIG. 2), possibly smashing the debris to pieces. When the shovel probe 70 of the preferred embodiments exerts lateral forces it engages the defect/debris, and the tip provides a lifting force. The lifting force not only can preserve the defect 92 as a whole piece, but also move the defect into the notch within the tip, improving removal efficiency.

[0038] FIG. 6 illustrates a method 100 according to the preferred embodiments. A pre-repair topographic image of the debris and surrounding area is collected using the probe shown in FIG. 4, and location of the debris to be removed is identified in the pre-repair image in Step 102. To clean the sample surface, after AFM start-up, an engage routine is initiated in Step 104. This brings the planar bottom surface of the probe tip into careful contact with the sample surface. Next, the AFM method, in Step 106, provides relative lateral motion to move the tip towards the defect. As the relative motion continues, forces exerted on the debris by the blade of the probe tip exerts a lift up force on the defect, and then loosens the defect and starts to lift it in Step 108. The relative motion is continued (forward along the scan trajectory) so the tip, and more particularly, the notch, lifts the defect in Step 110, and secures the defect in Step 112.

[0039] More particularly, the vector direction for debris removal is determined and set in the pre-repair image through a graphical user interface (GUI) linked to the repair control. This vector direction is positioned relative to all other surface features so as to avoid any incidental interaction with surface features other than the debris to be removed. There are usually several parallel vectors in a repair area for any debris removal action.

[0040] A location marker is placed in the pre-repair image to define the leading-edge location in the path of the repair vector associated with the debris to be removed using the control GUI. The primary vector direction is typically parallel to the XY plane of the sample surface and provides relative lateral (X-Y) motion until the leading-edge location trigger is reached during the repair vector move.

[0041] After reaching the leading-edge trigger location, the repair vector direction changes to orthogonal to the sample XY plane, and provides motion so that the probe moves in Z up away from the XY plane of the sample surface, preferably to a predetermined height. After this upward motion is completed, the repair vector direction returns to parallel with the XY sample plane and continues to complete the requested length of the repair vector if any distance remains after the leading-edge trigger placement.

[0042] The AFM then lifts, for example, the probe and returns to the start location for the next repair vector defined is the series of repair vector moves.

[0043] This process is illustrated in more detail in FIGS. 7A-7E. In FIG. 7A, in a system in which the AFM moves the probe laterally and orthogonally to the sample surface, the tip is brought down to the sample surface. The tip is then moved forward towards the debris (FIG. 7B). Then, after engaging the debris, the tip is moved further forward to provide a lift up force to the defect due to engagement of the debris with the wedge shaped blade on the tip, as shown in FIG. 7C). This lifting force loosens the debris. Next, in FIG. 7D, the tip is lifted. This applies an upward force to the debris, lifting the debris up off the sample surface. When the tip is moved forward again, the debris is secured in the notch. As shown in FIG. 7E, the AFM is operated to lift the defect up so the debris can be discarded by tip cleaning, post debris collection.

[0044] In summary, the shovel probe is engaged with the surface of the sample at an appropriate height. The probe is then pushed towards the pre-identified defects, with the opening concaved ends moving towards the defect(s). When the shovel tip pushes the defect, the force on the defect is upward. This keeps the defect a whole piece and loosens the defect's attachment with the surface. Due to the forward force, the defect has a larger chance to move towards the concaved portion of the shovel tip.

[0045] Then the shovel tip is then lifted upward to hold the defect off the surface. And in the last step, the shovel tip moves forward to secure the defect.

[0046] Note that in the focused ion beam (FIB) process, the energy level of the Ga+ beam (ion current) was optimized to mill the notch. In particular, the energy is preferably adjusted to maintain the integrity of the tip material (diamond) while still providing milling efficiency. Well-defined milling masks are used to suppress stray ion beam energy to achieve accurate final diamond tip geometry. The sample (diamond tip) was mounted on a proper sample holder and tilted at certain angles to accommodate the ion milling process. For example, the sample holder may be designed to match the 13° use angle when installed in an AFM, and thereafter adjusted according the milling process employed. Notably, what has been presented here is a preferred geometry, but note that any number of blade shapes could be created using known techniques.

[0047] Although the best mode contemplated by the inventors of carrying out the present invention is disclosed above, practice of the present invention is not limited thereto. It will be manifest that various additions, modifications and rearrangements of the features of the present invention may be made without deviating from the spirit and scope of the underlying inventive concept.