Browse Prior Art Database

Inspecting Impurity Concentration in Semiconductors

IP.com Disclosure Number: IPCOM000085758D
Original Publication Date: 1976-May-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 43K

Publishing Venue

IBM

Related People

Yun, BH: AUTHOR

Abstract

It is desirable to be able to inspect the impurity concentration of the semiconductor portion of a metal-insulator semiconductor (MIS) system 2 (Fig. 1), which is comprised of a metal gate plate 4, an insulator portion 6, and a semiconductor portion 8.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

Inspecting Impurity Concentration in Semiconductors

It is desirable to be able to inspect the impurity concentration of the semiconductor portion of a metal-insulator semiconductor (MIS) system 2 (Fig.
1), which is comprised of a metal gate plate 4, an insulator portion 6, and a semiconductor portion 8.

A ramp voltage V(g)(t) is applied, at time t=0, to the gate plate 4 of the MIS 2, causing a current J(t) to flow in the external circuit of Fig. 2. Thus, the output voltage V(1)(t) of the operational amplifier 10 is proportional to Integral/t/(o) Jdt. V(1)(t) is AC coupled to the output of a unity-gain buffer 11, for the purpose of suppressing any leakage associated with the measurement system.

The output of the buffers, V(o)(t), is given by:

(Image Omitted)

where Q(s)(t) is the charge/cm/2/ in the semiconductor portion 8, and C(o) the oxide capacitance/cm/2/. The measurement must be made, however, under the condition that the collective contribution from conduction current in the insulator 6, thermal generation of carriers and change in surface-state charge in the semiconductor 8 is small in comparison to Q(s)(t). The surface potential Phi(s) is: Phi(s)(t) = V(g)(t) + V(o)(t), (2) and is proportional to the first moment of the charge distribution rho(x,t) in the semiconductor 8, where x is a distance into the semiconductor 8 and is zero at the semiconductor-insulator 6 interface. The substrate bias V(s) should also be adjusted, so that absolute valueQ(S)
(0)absolute value<<absolute valueQ (t)absolute value.

Combining Eqs. 1 & 2 leads to an expression for the centroid x of the depleted impurity distribution rho (x,t), i.e.: V(g) (t) over 1 + x'(t) + V(o) (t) = 0 (3) and, x'(t) =(x(t)/x(o)) . (Epsilon(ox)/Epsilon(s)), where x(o) is the insulator 6 thickness, and epsilon(ox)/epsilon(s) is the permittivity of the insulator 6 to that of the semiconductor 8. For a preselected value of x', there is only one unique pair of V(g) and V(o), say V(g)(t(o)) and V(o)(t(o)), which will satisfy Eq. 3.

Consider the following example. Let x(o) = 500 Angstroms, epsilon(ox)/epsioln(s) = 1/3, and the the expected centroid of 7 depleted impurity distribution (ion implanted, for example) be about 2000 Angstrom deep into the semiconductor 8. Thus, setting x = 2000 Angstroms, it can be...