Ion beam angle calibration and emittance measurement system for ribbon beams

An ion beam angle calibration and emittance measurement system, comprising a plate comprising an elongated slit therein, wherein the elongated slit positioned at a rotation center of the plate and configured to allow a first beam portion to pass therethrough. A beam current detector located downstream of the plate, wherein the beam current detector comprises a slit therein configured to permit a second beam portion of the first beam portion to pass therethrough, wherein the beam current detector is configured to measure a first beam current associated with the first beam portion. A beam angle detector is located downstream of the beam current detector and configured to detect a second beam current associated with the second beam portion. The plate, the current beam detector and the beam angle detector are configured to collectively rotate about the rotation center of the plate.

FIELD OF THE INVENTION

The present invention relates generally to ion implantation systems for implanting ions into a workpiece, and more specifically to an ion beam angle calibration and emittance measurement system for ion and ribbon beams.

BACKGROUND OF THE INVENTION

Beam angle control during ion beam implantation has emerged as one of the critical parameters possibly second only to dose control. Implantation that takes place through apertures in masks with high aspect ratios (i.e., depth vs. width) is sensitive to the angle of incidence of the ions impinging on the workpiece surface. It is important that the angular distribution of ions be as symmetrical as possible in order to produce uniform dose into all desired areas of the workpiece. Obtaining uniform angles of incidence dictate that the angular distribution of the ion beams be accurately measured and controlled. Additionally, it is desired that ion beam emittance in both the x and y directions be measured at the plane of the workpiece. Knowing the emittance of the ion beam at the plane of measurement allows one to predict the ion beam envelope at any point in the free drift region.

Ion beam intensity is a measure of the number of particles per unit time at a given location of the ion beam cross section. The ion beam emittance is a measure of the angular spread of the beam at that location.

It is desirable to know the ion beam intensity and ion beam emittance across the extent of the ion beam. If doping problems occur, the intensity and emittance profile of the beam can be used for diagnosing those problems. Additionally, this information is useful when tuning the ion beam to assure consistency between successive workpiece doping cycles.

It is desirable that ion beam profile information be readily available on an essentially “real time” basis so that technicians monitoring ion implanter performance can make adjustments based upon the ion beam profile. Rapid updating of beam profile information allows those adjustments to be made and the effect the adjustments have on the beam profile to be studied and re-evaluated.

Thus, it is desirable to provide a system for improved ion beam angle calibration and emittance measurement.

SUMMARY OF THE INVENTION

The present invention overcomes the limitations of the prior art by providing a system for significantly improving the ion beam angle calibration and emittance measurement system for ion beams.

In one embodiment of the present invention is an ion beam angle calibration and emittance measurement system. The system comprising a plate comprising an elongated slit therein, wherein the elongated slit positioned at a rotation center of the plate and configured to allow a first beam portion to pass therethrough. A beam current detector located downstream of the plate, wherein the beam current detector comprises a slit therein configured to permit a second beam portion of the first beam portion to pass therethrough, wherein the beam current detector is configured to measure a first beam current associated with the first beam portion. A beam angle detector is located downstream of the beam current detector and configured to detect a second beam current associated with the second beam portion wherein the plate, the current beam detector and the beam angle detector are configured to collectively rotate about the rotation center of the plate.

In another embodiment of the present invention is an ion beam angle calibration and emittance measurement system. The system comprises a beam current detecting system comprising a housing with a face comprising an elongated slit on the face having a long dimension greater than a selected workpiece diameter, the elongation slit is configured as a rotation center of the housing. An electrostatic suppressor is located downstream of the elongated slit, wherein a profile Faraday cup with a rear slit is located downstream of the electrostatic suppressor configured to measure beam profiles in a first direction and in a second direction that is orthogonal to the first direction. An angle Faraday cup is located downstream of the rear slit configured to obtain an angular distribution of the ion beam in the first direction and in the second direction. A first fraction of an ion beam is admitted into the profile Faraday cup after passing through a protection plate slit and the front elongation slit. A second fraction of an ion beam is admitted into the angle Faraday cup.

In yet another embodiment of the present invention a system for measuring and calibrating a workpiece surface plane with respect to an ion beam plane, comprising a sensor assembly with a sensor head plane. The sensor assembly comprises a housing with a face having an elongated slit with an electrostatic suppressor downstream of the slit. A profile Faraday cup upstream of the electrostatic suppressor is configured to measure beam profiles in the x and y axes. The profile Faraday cup has a rear slit which allows a portion of the ion beam to pass though the rear slit into the angle Faraday cup. The sensor head plane and the measurement plane are coincident and ion beam emittance is measured along the sensor head plane.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed generally toward improving ion beam angle calibration and emittance measurement systems for ion beams. Accordingly, the present invention will now be described with reference to the drawings, wherein like reference numerals may be used to refer to like elements throughout. It should be understood that the description of these aspects are merely illustrative and that they should not be interpreted in a limiting sense. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be evident to one skilled in the art, however, that the present invention may be practiced without these specific details.

Referring now to the figures, in accordance with one exemplary aspect of the present invention,FIG. 1illustrates an exemplary ion implantation system100, wherein the ion implantation system is operable to scan a workpiece102(e.g., a semiconductor substrate or workpiece) relative to an ion beam104, thereby implanting ions into the workpiece102. As stated above, various aspects of the present invention may be implemented in association with any type of ion implantation apparatus, including, but not limited, to the exemplary system100ofFIG. 1. The exemplary ion implantation system100comprises a terminal106, a beamline assembly108, and an end station110that generally forms/contains a process chamber112, wherein the ion beam104is generally directed at the workpiece102positioned at a workpiece location114. An ion source116in the terminal106is powered by a power supply118to provide an extracted ion beam104(e.g., an undifferentiated ion beam) to the beamline assembly108, wherein the ion source116comprises one or more extraction electrodes122to extract ions from the source116and thereby to direct the extracted ion beam104toward the beamline assembly108.

The beamline assembly108, for example, comprises a beamguide124having an entrance126proximate to the source116and an exit128proximate to the end station110. The beamguide124, for example, comprises a mass analyzer130(e.g., a mass analysis magnet) that receives the extracted ion beam104and creates a dipole magnetic field to pass only ions of appropriate energy-to-mass ratio or range thereof through a resolving aperture132to the workpiece102. The ions that pass through the mass analyzer130and exit the resolving aperture132generally define a mass analyzed or desired ion beam134having ions of the desired energy-to-mass ratio or range thereof. Various beam forming and shaping structures (not shown) associated with the beamline assembly108may be further provided to maintain and bound the ion beam104when the ion beam is transported along a desired beam path136to the workpiece102.

In one example the desired ion beam134is directed to the workpiece102, wherein the workpiece102is generally positioned via a workpiece scanning system138associated with the end station110. The end station110illustrated inFIG. 1, for example, may comprise a “serial” type end station that provides a mechanical scanning of the workpiece within the evacuated process chamber112, in which the workpiece102(e.g., a semiconductor workpiece, display panel, or other workpiece) is mechanically translated through the beam path136in one or more directions via a workpiece scanning system138. According to one exemplary aspect of the present invention, the ion implantation system100provides the desired ion beam134(e.g., also referred to as a “spot beam” or “pencil beam”) as being generally stationary, wherein the workpiece scanning system138generally translates the workpiece102in two generally orthogonal axes with respect to the stationary ion beam. A beam current detecting system140can be located between the resolving aperture132and the workpiece102. It should be noted, however, that for example, ribbon beams and batch or other type end stations may alternatively be employed, and fall within the scope of the present invention. For example, the system100may comprise an electrostatic beam scanning system (not shown) operable to scan the ion beam104along one or more scan planes relative to the workpiece102. Accordingly, the present invention contemplates any scanned or non-scanned ion beams104as falling within the scope of the present invention. According to one exemplary aspect of the invention, the ion implantation system100may comprise the ion implantation system and scanning apparatus described in commonly-owned U.S. Pat. No. 7,135,691 filed Apr. 5, 2005, the contents of which are hereby incorporated by reference. The ion implantation system100may also comprise other systems such as the Optima HD Scan System manufactured by Axcelis Technologies of Beverly, Mass.

Illustrated inFIG. 2is a simplified cross sectional view of a beam current detecting system200. The emittance profiler Faraday beam current detecting system200comprises a housing230, a profile Faraday cup202, a resolving slit204, e.g., approximately 0.88 mm wide by 185 mm long, located in front of the profile Faraday cup202(e.g., Graphite). A protection shield224can be placed in front of an initial ion beam201in the beam current detecting system200with a shield resolving slit226to limit the ions of an ion beam214striking the housing face220of the beam current detecting system200. A first beam portion213is admitted into the profile Faraday cup202which measures a first beam current. The beam214passes therethrough the slit204and a suppressor212to form a first ion beam portion213. The profile Faraday cup202located downstream of the slit204and the profile Faraday cup202comprises a slit208therein that permits a second beam portion215of the first beam portion213to pass therethrough. The profile Faraday cup202is configured to measure a first beam current associated with the first beam portion213. An angle Faraday cup206is located downstream of the profile Faraday cup202and configured to detect a second beam current associated with the second beam portion215. The housing face220, the profile Faraday cup202and the angle Faraday cup206are configured to collectively rotate about the rotation center of the housing face220.

The electrostatic suppressor212prevents electrons from crossing the suppressor plane allowing only the energetic beam ions to pass throughwith which in turn results in an accurate measurement of the ion beam charge by the Faraday system200profile Faraday cup202. The approximately 0.88 mm wide by 160 mm long rear resolving slit208is formed in the profile Faraday cup202and an angle Faraday cup206is located downstream of the profile Faraday cup202. The sum of the current sampled by the profile Faraday cup202and the angle Faraday cup206divided by the 0.88 mm aperture width is the one dimensional dose rate dI/dx or dI/dy. In general the fraction of the total beam flux admitted through the housing slit204is much greater than the total beam flux admitted through the profile Faraday cup slit208. The axial distance between the surface of the first resolving slit204and the rear slit208is 40 mm resulting in an angular uncertainty of 2×0.88/40 or 44 mrad or +/−1.26 degrees. This measure is the resolution of the collimating apertures but does not limit the differential resolution of the system while the Faraday system200is being swept through smaller angular increments. The resulting measurement is the convolution of the +/−1.26 degree window with the angular distribution function of the ion beam. Although there may be no necessity to deconvolute the measurement, there are well known techniques by those of skill in the art that may be applied to do so.

A controller240can be utilized to determine the ion beam emittance and angle as a function of the wobble angle, the first beam current and the second beam current for various locations in a plane or a 3D space. The controller240can be used to utilize these measurements to tune the ion beam. In other words, the ion beam profile information can be readily available on essentially a “real time” basis so that technicians monitoring the ion implanter performance can make adjustments based upon the ion beam profile. Rapid updating of beam profile information allows those adjustments to be made and the effect the adjustments have on the beam profile to be studied and re-evaluated.

It should be appreciated that one of skill in the art could fabricate the beam current detecting system200without the housing230. In other words, the system200can comprise a plate with an elongated slit, wherein the elongated slit positioned at the rotation center of the plate. Both the profile and the angle Faraday cups can be replaced by any type of beam current detectors known by those of skill in the art. The plate, the current beam detector and the beam angle detector can be configured to collectively rotate about the rotation center of the plate.

The beam current detecting system may be used with systems such as the Optima HD Scan System manufactured by Axcelis Technologies, for example, the system pictorially shown inFIG. 1.

The beam current detecting system200illustrated inFIG. 2can be mounted to a robotic arm system, a linear drive system, and the like, wherein, for example, a robotic arm (not shown) causes the beam current detecting system200to move in a rectilinear or scanning motion in a first direction (scanning motion) orthogonal to the slit204. A rotating motion216can be done simultaneously with the scanning motion at a much faster rate to produce many angular scan passes per rectilinear scan pass. The first beam portion213is admitted into the profile Faraday cup202, as illustrated. The second beam portion admitted into the angle Faraday cup206can be sampled at a 1000 samples per second simultaneously with motor positions producing a 4×10,000 sample array of beam intensity vs. motor position in a 10 second measurement period. The array contains angle Faraday cup readings vs. angle, and profile Faraday cup readings vs. scan position. It should be appreciated by one of skill in the art that various other sampling rates, measurement periods, dimensions, etc., can be utilized and not depart from the scope of the present invention, nor limit the invention in any way.

In one embodiment, the beam current detecting system200shown inFIG. 2is attached to a robotic arm302of a robotic arm system300shown inFIGS. 3 and 4. The robotic arm system300is a special purpose robot that utilizes, for example, three motors to effect the motion of a slit204in both x and y directions. The drive arm stepper motor304shown inFIG. 3moves the drive arm306between three positions, park position500(FIG. 5), x-scan ready position600(FIG. 6), and y-scan ready position1000(FIG. 10). The scan stepper motor308(FIG. 4) sweeps the beam current detecting system200across the ion beam302while a DC servo wobble axis motor312with a wobble drive crank313rotates the beam current detecting system200through plus and minus 12 degrees many times back and forth per sweep. The wobble axis of rotation is about the center of the housing slit204. An optical encoder can be attached to each tilt axis314,316and318(i.e., x, y and z) to accurately determine the position of the beam current detecting system200. The beam current detecting system tilt stage can provide continuous scanning up to 3 Hz with an angular accuracy of 0.05 degrees or better.

It should be appreciated by one of skill in the art that the robotic arm system300that moves the beam current detecting system200can be any electromechanical system e.g., a linear actuated system, a belt/motor driven system, etc. The system can scan the beam current detecting system200in the horizontal or vertical direction at approximately 10 seconds per scan or faster. The system can park the robotic arm system300in less than one second to move the system300out of the way of the ion beam302.FIGS. 7,8and9illustrate the robotic arm system300as the beam current detecting system200is swept in a scanning motion in a first direction (e.g., horizontally) fully left600of the 180 mm maximum beam diameter602, for example, in the horizontal scan center position800continuously to the horizontal scan fully right position900of the beam diameter602.FIGS. 10,11and12illustrate the robotic arm system300as the beam current detecting system200is swept in a scanning motion, for example, in a second direction, that is orthogonal to the first direction, (e.g., vertically) to a fully up position1000, through the vertical scan center position1100of the workpiece diameter602continuously to the vertical scan fully down position1200of the beam diameter602.

The x x′ or y y′ emittance is the two dimensional phase space diagram describing the ion beam intensity I(x,x′)and I(y,y′). When plotted in an x-y topographical format the x axis usually has units of millimeters or meters while the y axis has angular units of milliradians or radians. The intensity distribution is represented as contours of equal intensity, similar to the elevation contours in a topographical map. The choice of contour intervals may be defined as a 2-D histogram containing a fraction of the total beam or it may be a contour interval of intensity fraction. Technically it should be an interval enclosing a fraction of the total beam. The typical shape of an emittance plot is an ellipse. This is due to the nature of the plot as it represents an ensemble or collection of particles traveling together at roughly the same velocity (vz) having components of transverse velocity (vx, and vy) assigned to each particle. The tangents of the transverse angles are represented by the vertical axis of the emittance plot while their spatial locations x or y are represented by the horizontal axis.

Referring toFIG. 3again, for example, the beam current detecting system200at the top of the drive arm306is swept in an arc through the ion beam214while the beam current detecting system200is rotated many times about the wobble axis314utilizing a DC servo wobble axis motor312producing simultaneous scans of both angle and position.

The beam current detecting system200, illustrated inFIGS. 3-10admits the portion of the ion beam214selected by the housing slit204and the angle Faraday cup slit210depending on the spatial and angular position of the beam current detecting system200and its given position and orientation as a function of time. While the beam current detecting system200is being moved, the beam current is sampled by the profile Faraday cup202and the angle Faraday cup210along with the angle and position of the Faraday assembly, for example. The sample rate is of the order of 1000 hertz enabling a large high resolution array of beam intensity vs position and angle. The resulting data array D(i,j)has i rows, and j, columns. For an x emittance scan D(i,1)is the x position column containing the center of the first resolving slit204, D(i,2)is the column containing the angles of the plane of the slit204, D(i,3)is the column containing the beam current samples made by the profile Faraday cup202, and D(i,4)is the column containing the beam current samples made by the angle Faraday cup210. The information contained in the data array D(i,j) is manipulated and presented as follows in order to fully realize the utility of this invention.

First, the plot of beam current dI/dx vs x is created by first calculating the numerical value of dI/dx for each data point and then plotting the resulting values against the corresponding x locations. If we assume the slot width of the first slit204is S then equation 1 below represents the value of dI/dx for each sample of beam current.

[ⅆIⅆx]i=Di,3+Di,4S(Eq.⁢1)
The x interval between samples is:
Δxi=Di,2−Di-1,2(Eq. 2)
The total beam current approximated between samples is:

Δ⁢⁢Ii=Δ⁢⁢xi⁡[ⅆIⅆx]i(Eq.⁢3)
The total current contained in the beam being measured is:

Three of the data columns in the data array Di,j contain the information required for emittance measurement and plots. The columns Di,1, Di,2, and Di,4contain the x position, x′ angle, and current samples from angle Faraday cup210. A new array Dk,lis generated with k corresponding to x position, l corresponding to x′ angle, and the values from Di,4. The beam emittance plot is done by producing a 2 dimensional contour plot of beam intensity vs x and x′. The current samples contained in the matrix Dk,lare normalized using the total current from equation 4 as follows:

wherein K is a normalization factor used to normalize the sum of the angle Faraday cup plus the sampled current in the angle Faraday cup. The factor K is necessary to add dimensions to the values dI/dx′ and dI/dy′ and is well known by those of skill in the art.

The normalized current (Inorm) from the angle Faraday210samples is:

The mapping of the one dimensional profiles1400, (dI/dx vs x) and (dI/dx′ vs x′) is illustrated inFIG. 14and two dimensional profiles1500inFIG. 15. The data summed across each row of Dk,lis plotted against the x position corresponding to the row to produce the plot of (dI/dx vs x). The data summed across each column is plotted against the x′ angle corresponding to the column to produce the plot of (dI/dx′ vs x′). These types of profiles are well known by those of skill in the art.