Method of modifying a sample surface layer from a microscopic sample

Abstract

A method of modifying a sample surface layer in the vacuum chamber of a particle-optical apparatus, the method performed in vacuum, the method comprising: Providing the microscopic sample attached to a manipulator, Providing a first liquid at a first (controlled) temperature, Dipping the sample in the first liquid, thereby causing a sample surface modification, Removing the sample from the first liquid, Providing a second liquid at a second (controlled) temperature, Dipping the sample in the second liquid, and Removing the sample from the second liquid. This enables the wet processing of a sample in-situ, thereby enhancing speed and/or avoiding subsequent alteration/contamination of the sample, such as oxidation, etc. The method is particularly useful for etching a lamella after machining the lamella with a (gallium) FIB to remove the surface layer where gallium implantation occurred, or where the crystal lattice is disturbed.

Claims

1. Method of modifying a sample surface layer from a sample in a particle-optical apparatus, the method performed in vacuum, the method comprising: providing the sample attached to a manipulator, providing a first liquid at a first temperature, the first liquid including an etchant; dipping the sample in the first liquid in a vacuum chamber of the particle-optical apparatus, thereby causing the sample surface layer to be etched, removing the sample from the first liquid using the manipulator, providing a second liquid, different from the first liquid, at a second temperature, the second liquid including a rinsing solution comprising ethanol or water, the second liquid being matched to the first liquid; dipping the sample in the second liquid in the vacuum chamber to rinse the sample, and removing the sample from the second liquid in which the sample is a semiconductor lamella having gallium implantation and causing the sample surface layer to be etched includes etching less than 50 nm from the lamella surface to remove the implanted gallium.

2. The method of claim 1 in which the sample is attached to the manipulator by forming a weld using beam induced deposition, the beam induced deposition induced by a laser beam, an electron beam or an ion beam.

3. The method of claim 1 in which the sample has a dimension of less than 10 m in any direction and the first liquid and the second liquid are deposited as droplets with a volume of less than 1 picoliter.

4. The method of claim 1 in which the step of providing the sample attached to a manipulator comprises the steps of: providing a work piece, attaching the sample to the manipulator, and excising the sample from the work piece using a focused ion beam in the vacuum chamber.

5. The method of claim 1 in which dipping the sample in the first liquid in a vacuum chamber of the particle-optical apparatus thereby causing the sample surface layer to be etched includes electro-chemical etching, said electro-chemical etching using a non-virtual cathode.

6. The method of claim 5 in which the thickness of the removed sample surface layer is less than 10 nm.

7. The method of claim 1 in which the sample is rinsed repeatedly.

8. The method of claim 1 in which the two liquids are provided on one surface, the manipulator movable with respect to said surface.

9. The method of any claim 1 in which the liquids are applied using a first liquid insertion system and a second liquid insertion system.

10. The method of claim 1 in which the second temperature is different from the first temperature.

11. The method of claim 10 in which the rate of evaporation of the first liquid and the second liquid is controlled by controlling the temperatures of the first liquid and the second liquid.

12. The method of claim 1 in which dipping the sample in the first liquid in a vacuum chamber of the particle-optical apparatus, thereby causing the sample surface layer to be etched comprises controlling the amount of etching by controlling the submerging time, the first liquid concentration, or the first liquid temperature.

13. The method of claim 1 in which the etchant comprises KOH, HClO4, butoxyethanol, NaOH, or H3PO4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is now elucidated using figures, in which identical numerals indicate corresponding figures. To that end:

(2) FIG. 1 schematically shows a SEM according to the invention,

(3) FIG. 2 schematically shows a detail of a SEM according to the invention,

(4) FIG. 3 schematically shows a detail of an alternative arrangement of a SEM according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(5) FIG. 1 schematically shows a SEM according to the invention.

(6) A SEM column 100 is mounted on a evacuable sample chamber 130. The SEM column comprises an electron emitter 102 producing a beam of energetic electrons 104 with a selectable energy of between 0.2 to 30 keV (note: higher and lower energies are known to be used). This beam of electrons is manipulated by lenses 106A, 106B, 106C and deflected by deflectors 108A, 108B. Lenses and deflectors may be electrostatic or magnetic in nature, and the number of lenses and deflectors may vary. The beam is passed through apertures in diaphragms (not shown), thereby limiting the diameter of the beam as well as limiting the influx of gas into the vacuum of the SEM column.

(7) The beam of electrons exiting the SEM column is directed to the sample stage 112 of the SEM. The stage is typically capable of translation in three directions and tilting round two or three axis. Before inspecting the sample the sample 120, attached to the distal end 118 of a manipulator 116, is dipped in a droplet of a first liquid 122. The droplet of first liquid is obtained out of liquid injector 110A. Likewise a droplet of a second liquid can be obtained out of liquid injector 110B.

(8) After dipping the sample in the first and the second liquid the sample is transported to the position where the beam of electrons intersects the stage. When the beam hits the sample, secondary electrons are emitted, to be detected by, for example, an Everhart-Thornley detector 114, thus enabling inspection of the sample.

(9) To control the evaporation rate of the liquids a Peltier heater/cooler 124 is attached to the stage. Cooling a liquid, ultimately freezing it, lowers the vapour pressure of a liquid, and thus its evaporation rate (in vacuum).

(10) A controller 126 controls the column (including deflectors), acts as signal/image processor for the signal from detector 114, and controls the manipulator, liquid injectors and vacuum pumps (the latter not shown).

(11) It is noted that a liquid injection system is known to the skilled person and commercially available from e.g. Kleindiek Nanotechnik GmbH, Reutlingen, Germany, see http://www.nanotechnik.com/mis-em.html [-4-]. Other injectors may be based on modified gas injection systems (GISses) or on injectors using techniques derived from inkjet printers (for example using piezo-expellers as discussed in U.S. Pat. No. 8,919,902 assigned to Ricoh Company Ltd. [-5-], or thermal bubble expellers as discussed in U.S. Pat. No. 8,919,938 assigned to Hewlett Packard Development Company L.P. [-6-]) or based on electro-spraying from a needle.

(12) It is further noted that, although the above example only mentions an electron beam, likewise apparatuses producing charged particle beam comprising ions are known. The ions can be formed by, for example, a gas discharge source, a liquid metal ion source. The ions can be positive or negative charged ions, and can be multiply charged or single charged ions. Also charged clusters can be generated.

(13) FIG. 2 schematically shows a detail of a SEM according to the invention.

(14) FIG. 2 schematically shows an enlarged view of the area where the liquid droplets are formed. Sample 120 on distal end 118 is seen to be dipped in the liquid droplet 122A. This can be achieved by moving the sample manipulator 116 and the stage 112 with respect to each other, i.e., by moving either the manipulator or the stage. The temperature of the first droplet 122A is regulated by heater 124, and need not be identical to the temperature of the second droplet 122B. The volume of the droplets can be regulated by the supply of the liquid via liquid injection systems 110A and 110B, respectively, the temperature of the droplets, and the composition of the residual gasses in the vacuum surrounding the droplets.

(15) As clear to the skilled artisan the speed of modification of the sample surface is a function of the composition of the liquid (concentration of materials, etc.), the temperature and the period of time the sample is dipped in the liquid. Also movement of the sample within the droplet (thereby influencing the concentration of chemicals near the surface of the sample while the sample is immersed in the droplet) influences the process speed. This can advantageously be used by using e.g. (ultra)sonic excitation of the droplet (e.g. by placing the droplet on a resonating piezo-actuator or, as an alternative, form the extremity of the manipulator to which the sample is attached as a vibrating extremity, or place the whole manipulator on an (ultra)sonic excitator). Also the stage can be equipped to move the liquid.

(16) FIG. 3 schematically shows a detail of another embodiment.

(17) FIG. 3 shows an embodiment where no droplets are used, but instead small containers 300A, 300B are used. To avoid continuous evaporation these containers can be closed by lids 302A, 302B, movable by actuators (not shows). The actuators of these lids may employ piezo-actuators, or other means. Also quick temperature control may be used to avoid evaporation when the liquid is not in use.

(18) The size (diameter) of the containers should be sufficiently large that the sample can be dipped in the containers.

(19) It is noted that, in the case that the surface of the liquid is sufficiently removed from the surface of the sample stage 112, a higher temperature of the liquids can be combined with a low temperature of the channels, leading to a reduced evaporation rate, as the vapour condenses on the walls of the channels.

(20) The skilled artisan will recognize that more than two liquids can be used, and that also before, in-between or after dipping the sample in the liquids the sample may be inspected, exposed to gas, exposed to for example BID (beam induced deposition, using either an ion beam, electron beam or a laser beam), exposed to a plasma, etc.

(21) The method enables the wet processing of a sample in-situ, thereby enhancing speed (as the sample need not be taken out of the vacuum chamber) and/or avoiding subsequent alteration/contamination of the sample, such as oxidation, etc.

(22) The method is particularly useful for etching a lamella after machining the lamella with a (gallium) FIB to remove the surface layer where gallium implantation took place, or where the crystal lattice is disturbed.

CITED LITERATURE

(23) [-1-] S J Randolph et al., Capsule-free fluid delivery and beam-induced electrodeposition in a scanning electron microscope, RSC Adv., 2013, p 20016-23. [-2-] U.S. Pat. No. 5,270,552 assigned to Hitachi. [-3-] J. Mayer et al., TEM Sample Preparation and FIB-Induced Damage, MRS BULLETIN, Vol. 32 (May 2007), p. 400-407. [-4-] http://www.nanotechnik.com/mis-em.html [-5-] U.S. Pat. No. 8,919,902 assigned to Ricoh Company Ltd. [-6-] U.S. Pat. No. 8,919,938 assigned to Hewlett Packard Development Company L.P.