JPH03200348A - Life time measurement of semiconductor - Google Patents

Abstract

PURPOSE:To shorten measurement time of generated life time without the loss of measurement accuracy by previously estimating balancing capacity at inversion voltage by a capacity-voltage measurement and completing a measurement at the time the balancing capacity is attained by a capacity-time measurement. CONSTITUTION:A C meter 1 for measuring capacity by application of voltage, a central processing unit CPU2, and a printer 3 are connected with each other through a data-address bus 4. Further, a sample 5 of a MOS semiconductor wafer is connected to the C meter 1, whereby capacity C of a semiconductor 5 is measured as a function of voltage V as well as the capacity C of the semiconductor 5 is measured as a function of time t. Balancing capacity at inversion voltage is previously estimated, and upon a C-t measurement the measurement is interrupted before the balancing capacity is attained and after the elapse of arbitrary time since the initiation of the measurement. Upon a self-analysis thereafter the balancing capacity is substituted to measure generated life time. Hereby, measurement time of the generated life time can be shortened without losing measurement accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for measuring generation lifetime using the MOS C-method, and is intended to shorten the measurement time.

(Prior Art) Conventionally, as a method of measuring the generation lifetime of a Si-type semiconductor substrate, a method (MOSC-method) has been used in which a MOS diode is formed and the transient response of the capacitance is used.

This C- method measures the transient change in capacitance C caused by switching the applied voltage from the accumulation state to the inversion state, and after measuring the transient change in C until the capacitance C reaches the equilibrium capacitance Cfin, the vertical axis shows - d/d t(Cox/C)" is plotted (Selbst plot) with (Cfin/C-1) on the horizontal axis. The generation lifetime is determined from the slope m of the straight line. Cox is the oxide film capacitance.

(Problem to be Solved by the Invention) However, in the C- method described above, transient changes in C must be monitored until the capacitance C reaches the equilibrium capacitance Cfin at the inversion voltage, and it takes a long time to measure. There is a problem that needs to be addressed.

Therefore, an object of the present invention is to provide a lifetime measuring method that can reduce the time required to measure the generation lifetime by the C- method as much as possible, and maintain the same level of accuracy.

(Means for Solving the Problems) The lifetime measuring method of the present invention is a method of measuring the lifetime C- of a MOS type semiconductor using the C-v method (capacitance-voltage method) in advance. Find the equilibrium capacitance Cfin at the inversion voltage, and when measuring C-, the capacitance Cfin
The measurement is interrupted after an arbitrary period of time has elapsed from the start of the measurement before reaching fin, and the generation lifetime is measured by substituting the capacitance Cfin during the subsequent Zelbst analysis.

(Function) To explain the present invention and the conventional measurement method using FIG. 4, for example, in the case of a P-type Si semiconductor, the applied voltage changes from -5 volts (accumulation region) to ), and the subsequent capacity recovery process is measured as a time change (Fig. 4 (1)). Such a conventional method requires a long time of 1000 seconds or more for each measurement.

On the other hand, in the case of the present invention, the C-v method is used [Fig. 4 (
2)), change the voltage from minus 5 volts to plus 5 volts in the dark
When swept in volts, the capacitance C changes as shown. At +5 volts, the equilibrium capacitance Cfi in the bright state
It focuses on the point where n is reached in a short time, and this capacitance Cf
By substituting in into a predetermined conditional expression together with the measured value of C-, the generation lifetime of the semiconductor is determined.

(Example) Embodiments of the present invention will be described below based on the drawings.

Figure 1 shows the outline of the measuring device, in which 1 is a C meter (
2 is a central processing unit CPtT, 3 is a printer, and these are connected to each other by a data and address bus 4. Further, a sample 5 of a MOSfi semiconductor wafer is connected to the C meter 1, and the configuration is such that the capacitance of the semiconductor 5 can be measured as a function of voltage, and the capacitance of the semiconductor 5 can be measured as a function of time.

In addition, regarding the SL semiconductor substrate and the produced MOS diode used in the above lifetime measurement example, the specifications, heat treatment conditions, and electrode production conditions shown in the attached table were used.

Attached Table (blank below) Next, the procedure for measuring the generation lifetime of MO5 type semiconductor using this method will be shown. First, the dopant concentration (Nsub) and Cfin of silicon are measured by the C-v method.

Then, the transient change in the capacitance C caused by switching the applied voltage from the accumulation state to the inversion state is measured using the C- method. The transient change in capacitance C is expressed by the following equation.

(-d/dt)(Cox/C)”m(2nicox/N
5ub-EoxEsi)S.

+(2niCox/N5ub-Cfin)・(1/τ
g) ・[(Cfin/c)-11...(1) However, Cox: oxide film capacitance, ni: intrinsic carrier concentration Eox: oxide film dielectric constant, Esi: dielectric constant τg of St
; Minority rear life time, So; Surface generation speed When measuring the transient change in the above capacitance C, stop the measurement before the capacitance C reaches Cfin, and
Substitute fin into equations (1) and (2), and plot (-d/dt
)・(Cox/C)2 on the horizontal axis [(Cfin/C)−
11 and plot it (Zerbst plot). If the slope at that time is m, then the generation lifetime can be calculated using the following equation.

? r2m-' (ni/N5ub) ・(Cox/C
f in) ...(2) However, if the time until the measurement stop is too short, τg cannot be measured accurately.
It is preferable to stop the measurement when C reaches a capacity of about 80% of Cfin.

As a result of the tests conducted by the inventor, the results shown in FIGS. 2 and 3 were obtained. Figure 2 shows the transient change in capacitance by the MOS C- method (Figure 2(a)).

(b), (C), (d)”) and Serbst plot (
Figures 2(e), (f), (g), and (h)) are shown, and Figures 2(b) to (d) show the cases in which Figures 2(a) and (e) are based on the conventional method. ).

(f) to (h) show cases in which the method of the present invention is used.

Figure 3(a) shows the correlation between the measurement time and generation lifetime in the conventional method and the method of the present invention, and Figure 3(b) shows the Ce (capacity at the end of measurement) in both methods. It shows the correlation between /Cfin and occurrence lifetime.

In addition, in FIGS. 3(f) to 3(h), the left and right dashed lines indicate the calculation range of the slope.

From this result, according to this method, C/Cfin = 0.8
It has become clear that by measuring transient changes in capacitance up to a certain level, generation lifetime can be measured with accuracy comparable to that of conventional methods and in about 60% of the time.

(Effect of the invention) As explained above, according to the present invention, C-■
If the balanced capacitance Cfin at the inversion voltage is determined by measurement, if C- is measured and the measurement is finished when the capacitance reaches approximately 80% of Cfin, the measurement accuracy will not be compromised.
This has the effect of making it possible to shorten the time required to measure the occurrence lifetime.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of the measuring device, Figure 2 (a) to (d)
(e) to (f) A diagram showing the relationship between capacitance transient change and Selbst plot, Figure 3 (a) is a correlation diagram between measurement time and generation lifetime, and Figure 3 (b) is Ce/Cfin.
Figure 4 shows the relationship between C- and occurrence lifetime.
FIG. 2 is an explanatory diagram of the v method. 4...MOS type semiconductor wafer τg...lifetime

Claims (2)

[Claims] (1) MOSC-t Si type semiconductor substrate lifetime
In this method, the equilibrium capacitance Cfin at the reversal voltage is determined in advance by the CV method, and when measuring C-t, the capacitance Cfin is measured before the capacitance Cfin is reached and after an arbitrary period of time has elapsed from the start of the measurement. 1. A semiconductor lifetime measuring method, characterized in that measurement is interrupted and the capacitance Cfin is substituted during subsequent Selpst analysis to determine generation lifetime. (2) When approximately 80% of the capacity Cfin is reached,
2. A semiconductor lifetime measuring method according to claim 1, wherein measurement by the C-t method is interrupted.