Title of Invention

"A DEVICE FOR MONITORING ION BEAM ETCHING PROCESS"

Abstract

A device for monitoring ion beam etching process characterized by an electrically isolated annular metallic aperture plate (1) placed at electrical virtual ground such as herein descrived, an ion detector(2) being movably fixed concentrically with the said aperture, a holder for placing a sample(3) being provided between the said annular metallic aperture plate(l) and the said ion detector(2) so as to allow an ion beam to impinge onto the area of the sample to be etched and effect absorption of secondary electron emission(4) by the said annular metallic aperture plate(l), the said annular metallic aperture plate(l) being connected to a current meter(5) for measuring the said secondary electron emission(4), the output of the said current meter(5) being connected to the input of a process controller(7), the output of the said ion beam detector(2) being also connected through a current meter(6) to the input of the said process controller(7), the output of the said process controller(7) being connected to power supply(8) of known ion beam source(9).

Full Text

The invention relates to a device for monitoring ion beam etching process. The present invention particularly relates to a device for monitoring and controlling by terminating at an appropriate level, the process of etching of materials by sputtering from energetic ion beam of any gases, in particular with argon ions in a vacuum chamber for the preparation of electron microscopy specimens, such as electron transparent cross-section specimens for the study of their microstructure. For examining the microstructure of various materials which may be metals, alloys, composites, semiconductors, ceramics or semiconductor devices by transmission electron microscopy, (hereinafter referred to as TEM), the sample thickness has to be less than the required thickness for electron beam transparency. This thickness may be around 100 nm for most commercial TEMs operating at 200-300 KeV range. The sample may be thinned to the required thickness by conventionally known methods of chemical or electrochemical etching. However, in many situations such as when the material or part of it is chemically resistant or has the tendency to etch in a selective manner in the chemical etching procedure, ion beam etching technique is preferred, to avoid inclusion of artifacts in the microstructure. With advancement of nano technology novel device structures based on multilayers of semiconductors dielectrics and magnetic materials with thickness of individual layers of nanometer range are being synthesized and investigated. Given the fact that these structures have high etching selectivity, much improved knowledge of the etching process and accurate control of etching seguence has become almost imperative, me knowledge that the device or interface region wnich is needed to be examined is being located at the etching area and the evaluation of the specimen has been thinned to the adequate level to enable TEM examination of sub micrometer or nanometer scale device or periodic structures is critical to the ion beam etching technique, in absence of such procedures, the ion beam etching technique shall need very cumbersome trial and error methods, which may require time to time examination of the sample under the TEM and transfer back to the etching system if the ion beam thinning has not been adequate. Such repeated transfer and etching sequences lead to inaccuracies in the microstructure or material analysis such as needed for Energy Dispersive Electron Spectroscopy (EDX )or Elelctron Energy Loss bpectroscopy (EELS), as well as at times lead to complete destruction ot the specimen. in order to obtain thin large electron beam transparent areas around the perforation for adequate microstructure determination, the perforation has to be just adequate. Over etching results in a larger hole formation and consequent loss of specimen. This establishes a technical precondition for specimen preparation for structural examination and analysis. Thus, a key parameter in ion beam etching procedure is knowledge of etch rates of the sample through a monitoring system and termination of the etching process precisely at the time when micro-hole perforation condition has been obtained during the etching process Reference may be made to a conventional method and process of an ion beam etching as described in a review article 'ion milling of Materials Science Specimens for Electron Microscopy" by D G. Howit, published in Journal of Electron Microscopy Techniques 1, 405 (1984). in the conventional ion beam etching method, the etching process is initiated when energetic ions or neutrals of select gases such as Ar, N. bombard the target surface, transfer the momentum to tne surface atoms of the target material which is then sputtered out. Continuous bombardment results in the thinning of the target material and perforation or formation of a micro-hole. Etching rate and process of etching is essentially controlled by the nature of ions (atomic mass and charge). Thus, in the techniques of prior art, the monitoring of the etching process have been indirectly rendered by monitoring of the ion current. . The measurement of ion current and more precisely spatial aistnoution of ion current has been disclosed in a US Patent; 4,626, 209 by wittkower in 1966, which uses measurement of ion beam through various apertures by a Faraday cup. in this patent disclosures the measurement of ion current is performed to monitor and control the ion beam divergence only and not the process of etching itself. Another method of measurement has oeen disclosed in a US patent 5,475,231 by M Cook et.ai. in 1995. in this patent disclosure, the current at an aperture piate due to irradiation or interception of the ions from the ion source is used to provide an indication of the ion beam performance. This aperture current has been used to control the ion beam divergence. Neither of these patents utilizes the aperture piate to capture any secondary electron emission for any process control or monitoring of the etching process of the specimen. Further this is aiso evidenced by the fact that a -ve voitage is applied to the aperture piate. The use of -ve voitage is to trap more and more of ions and restrict the divergence of the etching ion beam. Another method of prior art disclosed in a paper published in J. vac. Sci Technoi. Vol. Bii, page 531 of 1993, describes ion bean etching by Focused ion Beam (FiB) and monitoring of the progress of the etching such as thickness of the film, by observing secondary or reflecting electrons generated, in this disclosure use has been made of an independent additional electron source. This electron source is used in conjunction with the FiB and provides an electron beam at the target to be etched an monitored during the etch process. The process monitoring is done by measuring the secondary electrons and the reflected electrons so generated from the target. The use of additional electron source in the machine complicates the measurement process and aiso does not guarantee the actual ion etching process aesired to be monitored. An improved method, mainly of use with FiB etching technique has been disclosed in an US patent number 5,656,811 of 1997. This patent describes the use of a iignt oeam to monitor the process wnich is more economical than the electron beam. However tne use of light beam ism advantageous only when it is required to create a hole through the sample All these methods are extremely complex and involve use of scanning electron microscope ( SEM) and offer considerable difficulty in terms of spatially integrating the etching and monitoring system involving electron nun control ier ana ion beam source. in a US patent no. 5,966,264 of 1999, use of scanning electron microscope for imaging the etching process for insitu and precise monitoring of the etching stage and for locating the device of interest in the region of etching has been described. This patent describes the use of electron beam aiong with detector to register the electrons transmitted through the specimen during the etching process, which provides the status of etching, it aiso describes a known control device having a process controller to shut off ion source for terminating the etching process being carried out by ion sources. The said patent uses an independent electron beam of the SEM for imaging the etching stages and subseguent stopping of the process. This therefore is cumbersome technigue as it needs an independent electron beam for the imaging of the etched sample and subseguent control of the process. Among the eguipment and systems of prior art which are commercially available for ion beam thinning/etching, various approaches have been employed for exact knowledge of the etching process for controlling the etching thickness. Among the commercially available systems, DuoMiii System model 600 DIP or 600 TMP from Gatan INC USA, the ion beam etching eguipments have used laser light beam as a mean to terminate the ion beam etching process. The laser light aligned with the milling beam gets transmitted through the specimen once the hole appears on the specimen. This upon failing onto a light sensitive resistor dives a sianai wnicn is usea to snut off the ion beam the said commercial system is thus useful only in such situations where a tnrougn noie is needed. The ion beam etching system RES 010 from BAL-TEC uses the detection of charged particles by means of a Faraday cage aione for which a special specimen holder is provided. This system severely restricts the rotation of sample in relation to the impinging ion beam. This essentially means that the system earn be used whenever a preferential etching is required for a specific application or a study. Another equipment of the prior art is commercially manufactured by M/S Atom Tech Limited. The series 700 ion beam thinning module uses manual control for the termination of the etching process based on detection of through light from a lamp from the perforated hole on the sample by means of an optical microscope. Again in this unit only such situations can be used where a through hoie is needed. it is common to ail the commercially available systems to use optical stereozoom microscopy with magnification factor of 100 for alignment of ion beam and observe the etching process. A significant disadvantage of the available commercial systems is that they do not offer any method to monitor the progress of the etching of the specimen. Oniy the ion current measured at the ion source or over the sample provides an indication of the characteristics of the bombarding ions, which are responsible for etching thus providing indirect means of assessment. More often than not, this could aiso be misleading as the ion current at sample (specimen current may be modified by cnarge puiio up. beam spreaoing etc thus at best it provides only a quick information that ion beam is striking the target and the etching is actuaiiy being initiated , which is cieariy inadequate. Another deficiency of the ion beam etching systems of the prior art is their inability to control the etching at the near perforation stage of the etching process. Over etching in the final stages of the perforation results in destruction of thin electron transparent regions containing the microstructure in information of cross section of the specimen. The optical means of detection of final stages of the etching process is inadequate and inaccurate for determination of the exact etching process and its termination by actuating the ion source cut off process. The sensitivity of optical and electronic methods which have been used in the systems of the prior art is not adequate for determination of end point of etching process on time for preparation of cross sectional specimens for TEM. in the prior art mentioned above few of the ion etch process monitoring system use ex situ method of determining the end point of the etching process by repeatedly taking out the sample for examination by Scanning Electron Microscope or high resolution optical microscopes, in a few case laser light is used which is useful only when a through hoie is desired to be created, in many a situation in materials analysis or preparation, it is not desirable to have a through hoie made by continued ion etching process . in such a situation it is sufficient to have a very thin section of the etched sample and not a hoie. in such a situation, neither the ex situ method nor the laser beam method of monitoring of ion etch process is useful. These problems are circumvented by me svstem of the oresent invention of monitoring and auto terminating the ion etching process by use of measurement of secondary electron emission by the ion impingement on the sample. The auto termination of the process being achieved by using the transmitted ion signal as detected by an ion detector like Faraday cage and feeding the signal to the ion source power supply. The main object of the present invention is to provide a device for monitoring ion beam etching process which obviates the drawbacks mentioned above. Another object of the preset invention is to provide a system for monitoring the process of ion beam etching of any sample from any ion source and terminate the process of etching as the required stage of sample perforation is attained corresponding to extended and optimum region of sample which are thinned to the desired level of electron transparency for cross sectional investigation in a transmission electron microscope. Yet another objective of the present invention is to provide a more accurate method based on secondary electron emission in place of the available methods of prior art based on ion beam current measurements to determine the rate and degree of etching of the samples during the process of ion beam etching by bombardment from an ion source without obstructing or interfering with the etching process. Still another objective of the present invention is to provide a control device, which is coupled to an ion source which automatically stops the ion beam source and hence the etching when a pre set level of transmitted ion current wnich is an accordance with the degree of etching is attained thereby Enhancing the precision control and reproducibility of specimen preparation process. In the drawing accompanying the specification. Fig 1 shows the block diagram of the device of present invention wherein. (1) is an annular metallic aperture piate; (2) is an ion detector; (3) is a sample to be etched; (4) is the secondary electron emission emanating from the sample (3); (5), (6) are current meters; (7) is a Process controller; (8) is power supply; and (9) is an ion Beam Source. Accordingly the present provides a device for monitoring ion beam etching process characterized by an electrically isolated annular metallic aperture plate (1) placed at electrical virtual ground such as herein descrived, an ion detector(2) being movably fixed concentrically with the said aperture, a holder for placing a sample(3) being provided between the said annular metallic aperture plate(l) and the said ion detector(2) so as to allow an ion beam to impinge onto the area of the sample to be etched and effect absorption of secondary electron emission(4) by the said annular metallic aperture plate(l), the said annular metallic aperture plate(l) being connected to a current meter(5) for measuring the said secondary electron emission(4), the output of the said current meter(5) being connected to the input of a process control ler(7), the output of the said ion beam detector(2) being also connected through a current meter(6) to the input of the said process controller(7), the output of the said process controller(7) being connected to power supply(8) of known ion beam source(9). In an embodiment of the present invention, the annular metallic aperture plate may be of a material having low sputtering yield such as aluminium, steel. In another embodiment of the present invention, the annular metallic aperture plate may be maintained at virtual ground by applying a positive potential in the range of 50 to 100 Volts with respect to ground. In still another embodiment of the present invention, the ion detector used may be such as a p/n junction diode, Faraday cage. The device, according to the present invention, comprises of an electrically isolated annular metallic aperture plate (1) parallel to the surface of the specimen on the side of incident ion beam for monitoring the etching rates and an ion detector (2), which could be a Faraday cage or a semiconductor solid state detector mounted axially in the direction of the ion beams for registering the transmitted ions through the specimen being etched. The annular metallic aperture plate the ample to be etched and the ion detector are mounted on a specially designed sample holder. This sample holder simultaneously allows centering and rotation of the specimen and changing the angle at which the ion beam is incidence over the sample for etching. Sample holder containing the specimen is reciprocated at desired angle with respect to ion beam without altering the relative position of annular metallic aperture plate in front and detector at the rear.. The suitably biased annular metallic aperture plate measures me secondary electron current arising from tne ton Deam bombardment resulting in sputtering of the specimen material and provides a method to monitor the etching process, which gives an indication to the operator to make necessary adjustments if needed thus carrying out the ion beam milling/etching process in an optimum manner, in another feature of the present invention, the rear mounted Faraday cage or solid state detector is coupied to a current meter (6), which measures the ion current, compares it with a pre-set ion current vaiue corresponding to a state of thinned specimen arrived by ion etching and provides a trigger to shut off the high voltage supply of the ion source automatically terminating the etching process in a highly sensitive way and thus avoiding over etching of specimens, for example the state in which a larger hole is formed in the specimen. To describe the present invention as shown in to Fig. 1, an ion source (9) of any type is used in etching . This is so mounted in a hexagonal block to allow impingement of accelerated ions through a well-directed ion beam of high energies onto a sample (3) mounted on a sample holder. The ion beam, on impact on the sample (3) removes the surface layers of material from the ion impinging region of the sample by well known scientific principle of sputtering. Prolonged irradiation by ion beam results in layer by layer sputter etching of material from the surface resulting in thinning of the sample in that region and eventually perforation. in the methods of prior art, the ion current at the source beam or at the sample is measured to estimate the etch rates, instead of relying on these being unreuable ana inaccurate metnoa of measunna the etcn rate, in tne oresent invention secondary electron current (4) is measured, for monitoring the rate of etching of the sample due to energetic ion bombardment. In the present invention, for this purpose, an electrically isolated conducting annular metallic aperture plate (1) is employed which is mounted in close proximity of the sample (3). The other part of the system involves measurement of the current. In an embodiment of present invention, the aperture plate is a metallic disc preferably made of aluminum or stainless steel metal sheet of the thickness 1 mm and diameter 8mm.. The inner diameter of annular metallic aperture plate is sufficiently large so as not to intercept the main ion beam from the source. To maintain the function of the annular metallic aperture plate, it is equally desirable that the diameter of inner open aperture is not excessively large, preferably as close as that of the size of the sample being etched. In the present invention, the is typically diameter is 4 mm. Different size of the aperture plate may be needed if the ion beam is more divergent, ion source to sample distance is large or sample size is more. The annular metallic aperture plate is held in a close proximity of the sample. In the design of the present system, the distance is kept at around 2 mm. This distance could be varied and may be in the range of 2-5 mm. The optimum choice is dependent on the nature of the sample, more specifically the samples with high or low rates of etching. The secondary electron emission is measured by means of a conductor connected to the annular metallic aperture plate . The conductor is connected to input terminal of an operation amplifier ana tne electrical signal may be monitored by a voitmeter, which reads the annular aperture piate voitage which is proportional to the current drawn by the aperture piate. in the present invention the measured current at the electrically isolated aperture piate is used to monitor the rate of sputtering of the surface layers of the sample by ion beam bombardment. The current at the annular metaiiic aperture piate emanates from the secondary electrons emitted form the sample as the energetic ions impinge on it. The number flux of secondary electrons is proportional to the energy of incident ions and sputtering yield of the sampie surface being etched. The annular metaiiic aperture piate is held eiectricaiiy isolated from the other system components such as sampie holder, ion source and vacuum chamber housing the etching contraption. However, the annular aperture plate is maintained at virtual ground by maintaining a smaii +ve potential in the range of 50 to 100 volts with respect to ground. During ion sputter etching process, the emitted secondary electrons strike the aperture piate and produce an electron current. The piate current is measured using a current meter atter amplification by an operation amplifier. Since under conventional conditions, annular aperture piate current may have contribution from directly impinging and scattered ions or stray electrons in the system, some error could creep into monitoring of the etching rates as a result. Positively biased annular aperture metaiiic piate wouid repel ions and attract secondary electrons emitted from the sampie surface undergoing sputter etcnina. This ennances tne sensitivitv of tne monitonng tne rates sputter erching. in yet another feature of the invention, the positive potential at the annular metaiiic aperture piate is used for optimizing the signal intensity and sensitivity of the etching process monitoring. Measuring the change in the current drawn by the annular metaiiic aperture plate, we can derive knowledge of the true etching rates of the sample. The annular metaiiic aperture piate current being proportional to the secondary electron emitted from the sample during etching is first calibrated for this purpose. The increase in ion beam energy by increasing the magnitude of the high voltage at the ion source causes a corresponding increase in the secondary electron current at the annular metaiiic aperture piate, indicative of higher etching rates, in another situation when the ion beam energy is beiow the sputtering threshold for the etching of the particular sample the annular aperture piate current is zero or negligibly small. increasing the plasma current of the ion source, which increases the ion beam flux aiso increases the etching rate. There is a corresponding increase in the secondary electron emission current. Thus, increasing the ion beam flux or Deam energy causes a change in the sample etch rate ana a corresponding change in secondary electron emission current. Observing this current it can be decided if the appropriate conditions of the ion beam source e.g. ion flux, gas flow rate and acceleration high voltage have been achieved and thereby achieve optimum or desired etching rates of the sample. Uniike the monitoring technique used in the prior art, which rely on ion beam source parameter, the monitoring system descned in tne present invention being indeoendent or ion Deam source operation provide considerable flexibility of operation and aiso provide an accurate knowledge of the sample etch rate. The method of monitoring the etching rate of samples by ion beam bombardment described herein, could aiso be used in other situations as weii and with other equipment's not intended to prepare specimen for cross sectional TEM as an objective as in this patent. The scope of this patent is thus not limited to the example of application described herein. in the device described in this invention, the detector current which arise due to ions transmitted through the sample is used to obtain the information on the degree of thinness of the sample. The ions from ion beam, which are etching the sample begin to get transmitted through the sample at a state of thinness of the sample which is thin enough to aiiow transmission of ions, but is prior to the state of perforation of the sample. Most of the optical techniques of the prior art depend upon transmission of light being detected when a hole is formed on the sample, instead, the method described in the present invention detects the degree of thinness of the sample before the microhoie perforation stage had occurred. This results in highly reproduclble and reliable preparation of cross sectional specimens tor electron microscopy. The current at the detector begins to appear as soon as the thickness of the sample during the process of etching by ion bombardment approaches the state when the energetic ions are transmitted through the sample. The maanitude or tne aetector current is mverseiv proportionai to tne tnicmess or tne etched sample, i he increase in ion detector current indicates the increasing number of ions transmitted through the sample thereby relating to its reducing thickness. This provide a way for taking a decision about the etching process in situ with the ion beam etching as to whether the specimen has reached a stage of electron transparency sufficient for examination of microstructure in TEM or whether or not the etching process ought io be continued or terminated. The detector current is usually of sufficient magnitude, typically 10-100 µA in case of Faraday cage detector. This renders the ion beam etching of the sample to be carried out in a most accurate and reproducible way without resorting to empirical and repeated procedures that are done in the methods of prior art. in an example of use of this method of present invention, the point of termination of ion etching of sample when the microhoie perforation stage is reached is accurately determined by a sudden increase in detector current corresponding to high density of ion flux transmitted through the perforation. For effecting auto termination of the etching process, the output of the ion detector is connected to a control device in a way that allows automatic switching off of the high voltage applied to the ion source for producing the ion beam when a pre-set level of the detector current corresponding to a sample thickness for electron transparency or just state of perforation has reached.. The detector current is first converted to a voltage signal by resistance array, which selects the voltage range. This signal forms an input for the processor where the signal is compared with the preset level. The control unit activates a relay connected to the hian voltaae power SUDDIV used to operate the ion source. I ne actuation ot relay turns off the ion source that terminates the etching process, This automatic cut off takes away the discretion on the part of the operator. The automatic cut off as soon as the ion detector registered a pre-determined current ievei is highly sensitive as it has the ability to interrupt the ion beam etching process before the perforation (hole formation) even takes place. The device, according to present invention therefore, allows monitoring and controlling of the etching process in an accurate and most systematic manner to the desired thickness of the sample after etching and also termination of the etching process at the precise time in situ with the ion beam etching in a manner which is quite independent of the ion beam etching parameters. The varied angle of etching permits lateral thinning (polishing etching) of samples which are more suitable for cross section microscopy. The novelty of the present invention lies in simultaneous monitoring and termination of ion beam etching process by using the inventive step of measuring of secondary electron emission from a metallic disc placed adjacent to the sample being etched. in the following examples an embodiment of an ion source and a sample holder with annular metallic aperture plate and an ion detector is used . The entire combination is housed in a conventional vacuum system comprising a combination of diffusion pump and mechanical pump. Alternatively the vacuum system may also be pumped by turbo molecular pump. The following examples are given by way of illustration only and should not be construed to limit the scooe ot the invention. Example-1 Etchinq Rate Monitoring A Cu-Be foil of 25 micron thickness was taken and fixed on the sample holder behind the annular metaiiic aperture plate. The ion source was Died with Ar gas for the generation of ion beam. The flow was kept at 2 sccm. The voltage of the ion source was set to give an ion beam of 5.OKeV energy. At this energy there was no secondary electron current measured at the annular metallic aperture plate thereby indicating that the etching threshold for the sample had not reached. Example-2 A Cu-Be foil of 25 micron thickness was taken and fixed on the sample holder behind the annular metallic aperture plate. The ion source was bled with Ar gas for the generation of ion beam. The flow was kept at 2 sccm The voltage of the in source was set to give an ion beam of 5.5KeV energy. At this energy a secondary electron was current measured to be 6 microamperes at the annular metallic aperture plate thereby indicating that the etching threshold for the sample had reached and therefore the etching process initiated. Example-3 A Cu-Be foil of 25 micron thickness was taken and fixed on the sample holder behind the annular metallic aperture plate. The ion source was bled with Ar gas for the generation of ion beam. The flow was kept at 1.0 sccm. This increased the ptasma current of the ton source, to about 1 mA at 5.5 KeV potential applied to ion source. The current at the annular metallic aperture plate increased to 11 microamperes. This, indicates that the increase in the ion beam flux also increased the etching rate, Example-4 A Cu-Be foil of 25 micron thickness was taken and fixed on the sample holder behind the annular metallic aperture plate. The ion source was bled with Ar gas for the generation of ion beam. The flow was kept at 1.0 scm. A positive potential 60 volts was applied to the annular metallic aperture plate and the ion beam energy of 6.0 KeV was set. Under these conditions the secondary electron current at the annular metallic aperture plate was measured to be 20 microamperes. Therefore the application of the positive voltage at the metallic aperture plate helps in the ability to monitor the etching process due to increased secondary electron emission current and therefore easy control over the process. . Example-5 Etching Process Termination A Cu-Be foil of 25 micron thickness was taken and fixed on the sample holder behind the annular metallic aperture plate . The ion source was bled with Ar gas for the generation of ion beam. The flow was kept at 1.0 sccm. A positive potential 60 volts was applied to the annular metallic aperture plate and the ion beam energy of 6.0 KeV was set. The etching was continued till a current was detected at the Faraday Cage ion detector kept behind the sample along the ion etch axis. The process was terminated at an ion current of 15 microamperes which gave a thickness of the foil to be 0.3 microns in the area etched by tne ion Deam . Tnere was no hole formed by the ton Deam. Example-6 A Cu-6e foil of 25 micron thickness was taken and fixed on the sample holder behind the annuiar metallic aperture piate. The ion source was bied with Ar gas for the generation of ion beam. The flow was Kept at 1 .0 sccm. A positive potential 60 voits was applied to the annuiar metallic aperture piate and the ion Deam energy of 6.0 KeV was set. The etching was continued tiii a current was detected at the Faraday Cage ion detector kept behind the sample along the ion etcn axis. The process was terminated at an ion current of 80, microamperes. After the etching process was completed the sample was removed and it was observed that a hoie was made due to prolonged etching . The hole diameter was measured to be 10 microns. This way, Dy suitable combination of the secondary electron emission current value and the ion beam current through the sample as measured by the ion detector behina tne sample , one can easily prepare a sample with or without a hoie. The main advantages of the present invention are: 1, The monitoring and auto termination can be done for ion beam etching of sample mounted in any direction with respect to the ion beam. 2. The ion monitor and terminator system can be retrofitted to any available ion beam etching system We Claim: 1. A device for monitoring ion beam etching process characterized by an electrically isolated annular metallic aperture plate (1) placed at electrical virtual ground such as herein descrived, an ion detector(2) being movably fixed concentrically with the said aperture, a holder for placing a sample(3) being provided between the said annular metallic aperture plate(l) and the said ion detector(2) so as to allow an ion beam to impinge onto the area of the sample to be etched and effect absorption of secondary electron emission(4) by the said annular metallic aperture plate(l), the said annular metallic aperture plate(l) being connected to a current meter(5) for measuring the said secondary electron emission(4), the output of the said current meter(5) being connected to the input of a process controller(7), the output of the said ion beam detector(2) being also connected through a current meter(6) to the input of the said process controller(7), the output of the said process controller(7) being connected to power supply(8) of known ion beam source(9). 2. A device as claimed in claim 1, wherein the annular metallic aperture plate is made of a material having low sputtering yield such as aluminum, steel. 3. A device as claimed in claims 1-2wherein the annular metallic aperture plate is maintained at virtual ground by applying a positive potential in the range of 50 to 100 volts with respect to ground. 4. A device as claimed in claims 1-3, wherein the ion detector used is such as a p/n type junction diode, Faraday cage. 5. A device for monitoring ion beam etching process substantially as herein described with reference to the examples and drawing accompanying this specification.

Documents:

208-del-2001-abstract.pdf

208-del-2001-claims.pdf

208-del-2001-correspondence-others.pdf

208-del-2001-correspondence-po.pdf

208-del-2001-description (complete).pdf

208-del-2001-drawings.pdf

208-del-2001-form-1.pdf

208-del-2001-form-19.pdf

208-del-2001-form-2.pdf

208-del-2001-form-3.pdf