Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L22/00—Testing or measuring during manufacture or treatment; Reliability measurements, i.e. testing of parts without further processing to modify the parts as such; Structural arrangements therefor
  • H01L22/10—Measuring as part of the manufacturing process
  • H01L22/14—Measuring as part of the manufacturing process for electrical parameters, e.g. resistance, deep-levels, CV, diffusions by electrical means

Definitions

• the present invention generally relates to semiconductor engineering and can be used for controlling a doping profile in semiconductors.
• the method of [5] by which semiconductor characteristics in an MlS- structure can be determined is based on measurement of capacity-voltage characteristics of the MlS-structure. Traps being present in the insulator are taken into account by numerical solution of an inverse problem, thereby lowering depth resolution due to regularization effects.
• It comprises the positioning of a sample in an electrolyte, the measurement of high frequency differential capacitance at a given change of electrode potential and fixed temperature, and the determination of dopant concentration by measured values of high frequency differential capacitance in the range of potentials corresponding to the charge carrier depletion of the near- surface volume in the semiconductor.
• the present invention proposes a method as claimed in claim 1.
• the present invention proposes a method for determining the concentration profile of a dopant in semiconductors, comprising the steps of placing a sample in an electrolyte, measuring the high frequency differential capacitance at a given variation of electrode potential and fixed temperature, and determining the dopant concentration based on the measured values of high frequency differential capacitance in the range of the potentials corresponding to the charge carrier depletion of the near-surface volume in the semiconductor.
• the dependency of the polarization current of the semiconductor on the electrode potential is measured, and based on this dependency, the value of potential drop in the electrolyte is determined in accordance with the measured dependencies of differential capacitance on the electrode potential taking into account the value of potential drop in the electrolyte the concentration profile of the dopant in the near-surface volume of the semiconductor.
• the present method for determining the concentration profile of a dopant is thus based on HF CV characteristics measurement.
• the advantage of the present method is the high accuracy of determination of the surface potential value by measuring the quasi-steady state and dynamic capacity-voltage characteristics, allowing substantially enhanced reliability of the determination of dopant distribution and the maximum profiling depth by taking into account (and excluding) the influence of the electronic states being localized close to the sample surface (surface states).
• the technical result of the invention is thus an enhanced measurement reliability and expansion of the range of depths of the near-surface layer of the sample in which the dopant concentration is determined.
• the above-mentioned known method [18] for determining the concentration profile of dopants in semiconductors consists in the positioning of the sample in an electrolyte, measuring the high frequency differential capacitance at a given variation of electrode potential and fixed temperature, and determining the dopant concentration in accordance with the measured values of high frequency differential capacitance in the range of potentials corresponding to the charge carrier depletion of the near-surface volume in the semiconductor, whereas in accordance with the invention the dependency of the polarization current of the semiconductor on the electrode potential is measured, by which dependency the value of the potential drop in the electrolyte is determined, and based on the measured dependencies of differential capacitance on the electrode potential by taking into account the value of the drop of potential in the electrolyte, the profile of dopant concentration in the near-surface volume of the semiconductor can be determined.
• the operating range of electrode potentials can be selected as follows: in the anode region - the potential at which a sharp increase of current due to the dissolution reaction of the near-surface layer of the semiconductor begins, in the cathode region - the potential at which the semiconductor-electrolyte barrier is electrically disrupted. Thereby the electrode potential, the high frequency differential capacitance of the semiconductor- electrolyte system, and the polarization current are measured.
• the method further comprises the measurement of the differential capacitance in the range of potentials corresponding to charge carrier degeneracy in the near-surface volume of the semiconductor.
• the advantage of this embodiment is the further enhanced accuracy and reliability at dopant concentrations of N>10 18 cm "3 .
• the measurement of the dependencies of high frequency differential capacitance and polarization current on the electrode potential, electrochemical stripping, and calculation of the dopant concentration profile are repeated several times before the desired depth of dopant concentration determination is reached, and the electrochemical stripping of the semiconductor is effected by switching on the polarization current while illuminating the sample surface and electrolyte stirring in a mode eliminating the diffusion barrier for chemical reactions in progress.
• the expansion of the range of depths of the near-surface layer of the sample in which the dopant concentration is determined is carried out by multiply repeating measurements of HF CV characteristics and electrochemical stripping in the area of the near-surface layer of the sample. This procedure allows to determine dopant concentration in any depth. The further enhancement of measurement reliability is achieved by subtraction of the surface state capacitance from the results of HF CV characteristics measurements.
• Fig. 1 is a graph showing the measured dependencies of the differential capacitance of the semiconductor-electrolyte system on the electrode potential.
• Fig. 2 is a graph showing the dependency of the polarization current on the electrode potential being used for calculating the value of the potential drop in the electrolyte.
• Fig. 3 in accordance with the measured dependency of polarization current I on the electrode potential V e , the dependencies l 4/5 on V e are built in the cathode region of potentials.
• Fig. 4 presents the results of the present method (see Example 1) as a dependency of dopant concentration on depth in the form of a continuous curve.
• the theoretical dependency of dopant concentration on depth for a sample of this type is shown as the dashed curve.
• Fig. 5 presents the corresponding results of the sample of Example 2.
• Fig. 6 dopant concentration profiles obtained for the sample of Example 3 by taking into account surface state calculation by the continuous curve. The profile obtained without surface state calculation is shown by the dashed curve.
• the prepared sample is placed into an electrochemical cell in which also metal (platinum) or glass-graphite electrodes are placed for polarization of the sample, capacitance measurement, and potential measurement.
• the cell is filled with an electrolyte.
• Electrolyte stirring is advantageously done by a pump being connected to the cell, the pump working in a closed loop.
• the rate of electrolyte supply is chosen so that during measurement of volt-ampere characteristic no hysteresis effect is present, thereby proving that there is no diffusion limitation to the ongoing electrochemical reactions.
• the working range of the electrode potentials can be selected as follows: In the anode region the potential at which a sharp increase of current due to the dissolution reaction of the near-surface layer of the semiconductor begins, and in the cathode region the potential of electrical disruption of the semiconductor-electrolyte barrier.
• the variation of polarization voltage is effected in a way that the measuring electrode potential changes linearly with respect to time. Thereby are measured the electrode potential, the high frequency differential capacitance of the semiconductor-electrolyte system, and the polarization current.
• the capacitance of the semiconductor-electrolyte system is preferably measured by the high-frequency pulse method at a pulse length of 0.8 - 1 ⁇ s.
• the capacitance value is obtained by integrating the signal over pulse series.
• the number of pulses in a series (Ni) is selected so that the relation between the value of the confidence interval for an average signal value and the average signal value does not exceed 0.1%.
• the scan speed with respect to the electrode potential is determined as
• the polarization current is measured by the voltage drop value at a known standard resistor which is connected in series with the polarization electrode.
• the dependency / 4/s on V e is built.
• the linear regression of the obtained dependency is calculated, and the electrode potential V e0 at which the regression line cuts the abscissa axis is found.
• This value of the electrode potential corresponds to the value of the surface potential being equal to the edge of the conductivity band (for n-type material, or the edge of the valence band for p- type material).
• the width of the band gap of the semiconductor is determined by reference data. Knowing the difference between the values of electrode potential and surface potential, the measured dependencies of the differential capacitance on the electrode potential are replotted to dependencies of the differential capacitance on the surface potential.
• ⁇ o is the electric constant
• ⁇ sc is the inductive capacity of the semiconductor
• e is the electron charge
• S is the semiconductor-electrolyte contact surface area
• the calculation is thereby carried out in the range of potentials corresponding to charge carrier degeneracy in the near-surface region of the semiconductor.
• the electrochemical stripping of the semiconductor near-surface layer can be carried out under anode polarization.
• the potential of the polarization electrode is fixed, this potential being equal to the stationary potential (i.e. to the potential at which the polarization current is equal to zero), the capacitometer is switched off, and the polarization-current meter is switched on.
• the illumination works with light with a wave length of less than hc/E g , where h is the Planck constant, c is the light speed, and E 9 is the width of the band gap of the semiconductor, the light being focussed by means of an optical system to a homogenous spot on the sample surface.
• h the Planck constant
• c the light speed
• E 9 the width of the band gap of the semiconductor
• the dissolution depth increment is selected to not exceed D max which is calculated by the formula:
• Ad - ⁇ ⁇ ZSN A where the sum is taken over the registered values of the polarization current (I n ), ⁇ is the time interval between the current measurements, Z is the average ion valence of the semiconductor in the dissolution reaction, A is the molecular ion weight of the semiconductor, N A is the Avogadro constant, and p is the volume density of the semiconductor.
• Example 1 Some embodiments of the present method and the results achievable therewith are illustrated below in Examples 1 to 3.
• Example 1 Some embodiments of the present method and the results achievable therewith are illustrated below in Examples 1 to 3.
• n-Si phosphorus-doped n-type silicon 7.5 Ohm * cm
• the rated depth of doping profile is 600 nm.
• Measurements were carried out in an aqueous solution of KCl (1 mol/l).
• Electrochemical stripping was carried out in an aqueous solution of HF (0.05 mol/l) + NH 3 F (20g/l). During dissolution, a voltage of 6.5 V was applied to the sample, the electrolyte feed rate was 0.5 l/min.
• Illumination was carried out by a system built by an incandescent lamp having a power of 250W and a focusing objective.
• n-Si (phosphorus-doped n-type silicon 5 Ohm * cm), with an epitaxial layer n + (0.5 Ohm*cm) having a rated thickness of 100 nm. Measurement was carried out under the same conditions and by using the same electrolytes as in Example 1.
• the values of dopant concentration in the epitaxial layer region and in the sample volume differ from the rated ones by not more than 15%.
• the epitaxial layer depth differs from the rated one by 20 nm.
• Fig. 6 dopant concentration profiles obtained for the present sample.
• the profile obtained by taking into account surface state calculation according to the present method is shown in Fig. 6 by the continuous curve.
• the profile obtained without surface state calculation is shown by the dashed curve. This example demonstrates the enhancement of reliability of the dopant concentration profile determination taking into account the influence of surface states.
• the examples confirm that the present method allows to achieve the above technical object, consisting in the enhancement of reliability of measurements and expansion of the range of depths of the near-surface layer of the sample in which dopant concentration is determined, and also in a significant increase of accuracy of the determination of the concentration profile of a dopant and an expansion of the range of values of dopant concentration to be measured by obtaining any depth of profile determination rated in advance, thereby without dependency on the semiconductor doping level and ultimate disruption voltage of the semiconductor-electrolyte interface.

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• 2009
  • 2009-03-30 RU RU2009112263/09A patent/RU2393584C1/ru active
• 2010
  • 2010-03-30 WO PCT/IB2010/000729 patent/WO2010113021A1/en active Application Filing

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