R. Schmitt

Electron-beam MCM testing and probing

IC probing with electron beams is already common practice for design verification and failure analysis. E-beams can also be applied to substrate testing offering flexibility for further MCM developments. A new electron beam MCM substrate tester has been developed and installed in the Siemens-Nixdorf fabrication line. It provides a spot size of below 25 /spl mu/m to probe pads in a 30 cm/spl times/30 cm field without mechanical movement and without electrical contact. The tester is automated for fabrication environment and ease of operation. More than one hundred substrates have already been tested on the system while not missing any defect. Diagnostic methods using electron beams can be transferred from IC to MCM application, However, conventional e-beam probe stations cannot handle the size of an MCM substrate. Therefore, a new system was developed allowing the beam to probe an area of 100 mm/spl times/80 mm. >

The limits of high-speed e-beam testing

Abstract The development of new types of very high-speed integrated circuits, such as those based on GaAs, makes extremely high demands on electron beam measuring technology. The limits of this measurement method for the time, voltage and spatial resolution were theoretically investigated. It is found that these parameters are mutually dependent on each other and that improvements in the time resolution can be made only at the expense of the voltage or spatial resolution. The theory allows specific optimization of the electron beam measuring devices inclusive of their electron-optical properties. An experimental system was realized for high speed measurements on GaAs devices. Electron pulse widths of 15 ps were experimentally attained with measuring probes of 0.5 μm diameter and an effective noise voltage of 30 mV. This device was used to investigate various components in the GHz range.

E-beam testing of high speed electronic devices

Abstract Electron beam testing techniques are successfully applied to failure analysis and time-resolved voltage measurements on conventional integrated circuits. These techniques, however, offer a time resolution of about 1 ns which does not meet the requirements of the high-speed devices presently being developed by the electronics industry. Our current work, which is discussed in this paper, aims at an improvement of time resolution along with a reduction of probe size to serve future needs. The theoretical limits of e-beam testing are discussed. Assuming realistic conditions for the performance of the electron optics, a system with 40 ps time resolution and 0.5 μm spatial resolution should theoretically allow a voltage resolution of 0.4 mV. So far, our experimental test system allows only 30 mV to be resolved under these conditions. The practical results already allow useful applications, but leave room for further improvements.

Investigations and measurements of the dynamic performance of high-speed ADCs

Investigations concerning the origin of the aperture jitter in a 4-b parallel analog-to-digital converter (ADC) implemented in a 0.5- mu m GaAs FET technology have been undertaken. On-chip electron-beam measurements of the comparator clock distribution show a deviation of 20 ps between the comparators. Simulation considering process variations shows similar results. To overcome these problems, a GaAs 5-b, 1-Gsamples ADC with on-chip track-and-hold circuitry (T&H) has been developed. A complete DC and AC characterization of the ADC using a histogram test, fast Fourier transform test, sine wave curve-fitting test and beat frequency test up to 1.3 GHz was performed. The measurement set-up consisted of a 4-GHz sine wave generator, a 10-GHz pulse generator, an 8-b wide 700-MHz digital acquisition system for data recording, and a PC. By using the T&H in front of the parallel ADC, 4.6 effective number of bits (ENOB) has been achieved at 1-GHz input signal compared to 3.7 ENOB without T&H. A comparison of the different test methods and results is given.<<ETX>>

Application of high-speed electron-beam testing in solid-state electronics

Abstract A high-speed electron-beam tester was developed to measure signals inside integrated high-frequency circuits, in particular those on a GaAs basis. This paper describes the current stage of development. Using electron beam pulses down to only 7 ps makes the tester capable of measurements at frequencies of approx. 60 GHz. Simultaneously a probe diameter of 0.5 μm and a noise voltage at the system output of 2 mV/√Hz are achieved at 2.2 keV acceleration voltage and 1 GHz pulse repetition rate. To meet practical demands a wafer prober was designed extending the application of the tester to on-wafer measurements. A GaAs 1k SRAM is used by way of example to demonstrate the possibilities for practical applications. Extending into the ps range, the high temporal resolution of the tester leads to a detailed comparison between calculated and measured signals. While allowing verifacation of the parameters used for simulation, this also yields useful hints on measures for redesigning the circuit.

Non-invasive waveform measurements of IC-internal GHz signals in A ps time scale

Abstract Electron beam testing has recently started to gain importance in GHz integrated-circuit characterization. It competes in this application with several other techniques. The advantages of the e-beam technique are: 1) its flexibility of device operation - pulses, logic signals or sine waves can be input to the device under test and may be changed in frequency between dc and several GHz, 2) its non-loading probe does not affect the function of the device under test, 3) its capability for probing lines below 1 μm. Currently an effective sampling-gate width of 8 ps is achieved, including the influence of pulse duration, timing jitter and transit time effect of secondary electrons. The system bandwidth is therefore approximately 80 GHz. Signal propagation delays of less than 3.5 ps can be resolved. The noise amplitude is 2 mV/√Hz at a 1GHz pulse repetition rate. This allows typical waveforms to be measured within several seconds.

Electron-beam testing of flat panel display substrates

Abstract A contactless electron-beam AM LCD-substrate test for in-process application has been developed, which includes a short-open test of control lines and pixels, and offers methods for a characterization of the active elements (including TFTs, MIMs and diodes). The technique uses e-beam input to the active elements by charging of pixel electrodes at a speed of more than 10 6 pixels (1 colour VGA plate) per minute. Detection of line defects, pixel shorts as well as variations in the active element performance are demonstrated. These test sequences do not require any external signals supplied to the matrix. In a real operation with control signals supplied e.g. to the shorting bars, internal matrix and driver signals can be probed for diagnostic purposes. These measurements are contactless and non-loading.

Electron-beam substrate testing approaches 25 cm × 25 cm

Abstract Miniaturization in electronics packaging technology require the development of new testing methods. Electron beam techniques have already demonstrated their applicability to the testing of multichip module substrates. Broad application of this technique requires a large scanfield in order to gain flexibility in the size of substrates. The electron optics for beam deflection over an area of 25 cm × 25 cm are being developed. Beam focusing and fast positioning have been experimentally realized. An e-beam spot size of 25 μm is attained in any position within the field at a beam current of 140 nA. The settling time of the beam on a 100 μm pad is 30 μs in the worst case.

Contactless testing of multi-chip modules

Abstract IC probing with electron beams is already common practice for design verification and failure analysis. These diagnostic methods can be transferred from IC to MCM application. However, conventional e-beam probe stations cannot handle the size of an MCM substrate. Therefore, a new system was developed allowing the beam to probe an area of 100 mm × 80 mm. E-beams can also be applied to the testing of substrates offering flexibility for further MCM developments. A new electron beam MCM substrate tester has been developed and installed in the Siemens-Nixdorf fabrication line. It provides a spot size of below 25 μm to probe pads in a 30 cm × 30 cm field without mechanical movement and without electrical contact. The tester is automated for fabrication environment and ease of operation. More than hundred substrates have already been tested on the system while not missing any defect.

Specifications for sampling techniques in the time domain definition and measurement

Abstract Sampling-techniques are used by instruments such as sampling-oscilloscopes or electron-beam testers for measuring voltage waveforms [1,2]. In this paper definitions and measurement procedures are proposed to compare the temporal resolution of different methods and instruments [3,4,5] under practical conditions. The main aspects are phase-stability, rise-time resolution, and cut-off frequency. Whereas the limits for defining time intervals depend on the stability of the time base and phase control, both rise time resolution and cut-off frequency are additionally determined by the sampling gate width. Gate width, switching characteristics of the gate and the phase stability of the trigger control together will result in an effective width and shape of the sampling gate. The measured waveform of a signal is the result of the convolution of this effective sampling gate with the original waveform.