JPH03185849A - Method of c-v measurement - Google Patents

Abstract

PURPOSE:To perform C-V measurement without guard ring under a condition close to the condition with an actual device by performing the C-V measurement after the surface of an insulating film on the peripheral of an electrode is scored. CONSTITUTION:When the surface of an SiO2 insulating film 2 on the periphery of a gate electrode 3 is scored 5, the lateral expansion of a depletion layer formed in the semiconductor substrate 1 at the lower section of the electrode 3 can be suppressed similarly to the case where a guard ring 4 is formed around the electrode 3 and a voltage is applied across the ring. Therefore, when C-V measurement is performed on MOS capacitors after the surface of the film 2 is scored 5, the measurement can be performed without guard ring similarly as if a guard ring is used, and thus, the C-V measurement can be performed under a condition close to the condition with an actual device. It is considered that a change takes place in the surface charge of the film 2 and the lateral expansion of a depletion layer formed in the n-type Si substrate at the lower part of the electrode 3 is suppressed, when the surface of the film 2 is scored 5.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the relationship between capacitance (C) and voltage (V) of a MOS capacitor.
This invention relates to a C-① measurement method suitable for use in measuring characteristics.

[Summary of the invention]

The present invention provides a method for measuring C-■ of a semiconductor device in which an electrode is formed on a semiconductor substrate via an insulating film, in which the C-■ measurement is performed after damaging the surface of the insulating film around the electrode. By doing so, it is possible to perform C-■ measurements under conditions closer to those of the actual device without using a guard ring.

[Conventional technology]

The C-■ characteristic of a MOS capacitor has a great influence on the characteristics of a MOSFET, and its measurement is
This is important in achieving improved ET performance.

6 and 7 show MOS capacitors used in conventional CV measurement methods. Here, Figure 7 is the 6th
It is a sectional view taken along the line ■-■ in the figure. Figures 6 and 7
As shown in the figure, in this conventional MOS capacitor, for example, a Si
, a film 102 is formed, and a circular gate electrode 103 is formed from aluminum (AI) on the SiO□ film 10. Further, a guard ring 104 made of A1 is formed on the Sing film 10 around the gate electrode 103 and close to the gate electrode 103. Here, the diameter of the gate electrode 103 is, for example, 200 am.
The distance between the gate electrode 103 and the guard ring 104 is, for example, 2 μm.

When actually performing C-■ measurements using the MOS capacitors shown in FIGS. 6 and 7, the capacitance of the MOS capacitor is measured while applying a voltage to the gate electrode 103. Gate electrode 10 on guard ring 104
3, a voltage comparable to the maximum voltage applied to the gate electrode 103 is applied to the n-type Si substrate 1, and thereby
This suppresses the spread of the depletion layer formed in 01 in the lateral direction (direction parallel to the substrate surface). When no voltage is applied to the guard ring 104 in this way, especially when the humidity of the measurement environment is high, the SiO
□An effect similar to when the area of the gate electrode 103 becomes larger due to the spread of charges on the surface of wA 102 occurs, so that the shape of the C-v curve at high frequencies changes from that of C at low frequencies.
- ■ The shape becomes close to the shape of a curve.

Here, the C-■ characteristic at high frequency of an ideal MOS capacitor will be explained with reference to FIG.
It is assumed that the semiconductor substrate in this MOS capacitor is of n-type. Moreover, the vertical axis in FIG. 8 is the capacitance C of the MOS capacitor normalized by the capacitance Cox of the oxide film, and the horizontal axis is the voltage V applied to the gate electrode. In Figure 8,
When the voltage applied to the gate electrode is positive, majority carriers (electrons in this case) are accumulated in the n-type semiconductor substrate near the interface with the oxide film. When the voltage changes negative, the majority carriers become n
It flows away from the surface of the type semiconductor substrate into the interior of the substrate, changing from an accumulation state to a depletion state.

When the voltage applied to the gate electrode changes further to the negative side, an inversion layer is formed in the n-type semiconductor substrate near the interface with the oxide film. After this, the charge no longer contributes to depletion, so the decrease in C due to the spread of the depletion layer in the depth direction stops, and C takes a constant value Csin.

In actual C-■ measurements at high frequencies, the voltage rises so quickly that the formation of the inversion layer cannot follow the voltage.
As shown by the broken line curve in FIG. 8, C decreases to a value smaller than Csin.

This state is a deep depletion state. Like this Cwh i
C, which has decreased to a value smaller than a, becomes C when the voltage is held.
sine, and when the voltage decreases thereafter, the curve shown by the solid line in FIG. 8 is traced in the opposite direction to that when the voltage increases.

[Problem to be solved by the invention]

As mentioned above, in the conventional C-■ measurement method, the sixth
As shown in the figure and FIG. 7, this gate electrode 103 is attached to a guard ring 104 formed around the gate electrode 103.
By applying a voltage comparable to the maximum voltage applied to the n-type Si substrate 10 in the lower part of the gate electrode 103.
This suppresses the lateral spread of the depletion layer formed in 1. However, such a situation is different from the situation in an actual device, and the distribution shape of the depletion layer is considered to be different from the actual depletion layer. Also, guard ring 10
In devices without an equivalent of 4, it is virtually impossible to perform CV measurements without being affected by surface charges.

Therefore, an object of the present invention is to provide a C-■ measurement method that does not use a guard ring and can perform C-■ measurement under conditions closer to those of an actual device.

[Means to solve the problem]

As a result of various experiments, the inventor of the present invention has determined that by damaging the surface of the Si0g film around the gate electrode of a MOS capacitor, a guard ring is formed around the gate electrode, and a voltage is applied to this guard ring. We found that similar effects can be obtained when The mechanism behind this phenomenon is currently being elucidated, but Sing M! Damage to the surface of the n-type S causes some change in its surface charge, resulting in n-type S
This is thought to be due to the fact that the lateral spread of the depletion layer formed in the i-substrate is suppressed.

The present invention has been devised based on the above studies by the inventor.

That is, in order to achieve the above object, the present invention provides a method for measuring C-■ of a semiconductor device in which an electrode (3) is formed on a semiconductor substrate (1) via an insulating film (2).
The C-■ measurement is carried out after damaging (5) the surface of the insulating film (2) in the peripheral area of (3).

[Effect]

According to the C-① measurement method of the present invention, which is performed at the bottom of the tank as described above, damage (
5), the semiconductor substrate (1) in the lower part of the electrode (3) can be
Lateral expansion of the depletion layer formed therein can be suppressed. Therefore, by performing C-■ measurement after damaging (5) the surface of the insulating film (2) around the electrode (3) in this way, it is possible to measure the C-■ measurement without using a guard ring. The C-■ measurement of the MOS capacitor can be carried out under the same conditions as in the case of the present invention. As a result, C-■ measurement can be performed under conditions closer to those of the actual device without using a guard ring.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view of a MOS capacitor used in the C-■ measuring method according to this embodiment, and FIG.
It is a sectional view taken along the line ■-■ in the figure.

As shown in FIGS. 1 and 2, C-
(2) In the MOS capacitor used in the measurement method, for example, a SiO□ film 2 is formed on, for example, an n-type St substrate 1, and a circular gate electrode 3 made of, for example, AI is formed on this Sing film 2. This gate electrode 3
The diameter is, for example, about 200 μm. Further, a guard ring 4 is formed on the Sin film 2 around the gate electrode 3 in close proximity to the gate electrode 3, for example, from AI. The distance between the guard ring 4 and the gate electrode 3 is, for example, about 2 μm. Although the guard ring 4 is not actually necessary, it is formed here for the purpose of comparison with a conventional MOS capacitor for C-① measurement that uses a guard ring.

In this embodiment, the gate electrode 3 and the guard ring 4 are
A damaged layer 5 is formed on the surface of the Sing film 2 in the portion between. In other words, the Si around the gate electrode 3
A damaged layer 5 is formed on the surface of the NG film 2.

FIG. 3 shows an example of C--characteristics measured using the MOS capacitor according to this embodiment. However, the specific resistance of the n-type Si substrate 1 is 0.8 to 1.

The Sing film 2 had a thickness of 260 Ω, and the gate electrode 3 and guard ring 4 were formed by patterning a 1 μm thick AI film formed by vapor deposition using wet etching. The damaged layer 5 was formed by forming the gate electrode 3 and the guard ring 4 on the Sing film 2 and then performing ashing using oxygen (0□) plasma. Here, ashing by this 02 plasma is performed at a substrate temperature of 50
The ashing was carried out under the following conditions: °C, power consumption of 1000 W, and ashing time of 40 minutes. On the other hand, for comparison, a conventional MOS capacitor having the same structure as the MOS capacitor according to this embodiment except that the damage layer 5 is not formed is separately prepared, and this MOS for C-v measurement is used. C-■ measurements were carried out for the case where a voltage of 15cm was applied to the guard ring 4 of the capacitor and the case where no voltage was applied. The results are shown in Figures 4 and 5, respectively.
The measurement frequencies of the C-■ characteristics shown in FIGS. 4 and 5 are all IMHz.

As shown in FIG.
A MOS capacitor in which the damage layer 5 is not formed on the surface of the film 2 exhibits high frequency C-■ characteristics similar to those shown in FIG. 8 when a voltage of -5V is applied to the guard ring 4, and when the voltage is held You can see that C has returned to C,,7. On the other hand, as shown in FIG. 5, when no voltage is applied to the guard ring 4, a depletion layer is formed in the n-type Si substrate 1 under the gate electrode 3 when the voltage is maintained as described above. The value of C becomes abnormally large due to the spread in the horizontal direction. Therefore, it is difficult to determine the value of C,50.

On the other hand, as shown in FIG. 3, in the case of the MOS capacitor according to this embodiment, although no voltage is applied to the guard ring 4, the same C-■ as shown in FIG. characteristics have been obtained.

As described above, according to this embodiment, after the damage layer 5 is formed on the surface of the Sin film 2 and the Sin film 2 around the gate electrode 3, the C
-■ Since the measurement is being carried out, even though no voltage is applied to the guard ring 4, that is, even without actually using the guard ring 4, the n
It is possible to prevent the depletion layer formed on the type Si substrate 1 from spreading in the lateral direction. As a result, C-■ measurement can be performed under conditions closer to the actual device, such as when there is no equivalent to the guard ring 4.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications can be made based on the technical idea of the present invention.

For example, in the above embodiment, the damaged layer 5 is formed by ashing using Ot plasma, but the damaged layer 5 can also be formed by a method other than this ashing. Further, this damaged layer 5 only needs to be formed on at least the 5tO2 film 2 in the peripheral area of the gate electrode 3. Furthermore, as already mentioned, the guard ring 4 formed on the surface of the 5iC)z film 2 around the gate electrode 3 is essentially unnecessary and can be omitted.

In addition, in the above-mentioned embodiment, the case where the present invention is applied to the C-■ measurement of a MOS capacitor using an n-type Si substrate 1 is explained, but the
It goes without saying that the present invention can be applied to C-■ measurement of an S capacitor.

〔Effect of the invention〕

As described above, according to the present invention, the C-■ measurement is performed after damaging the surface of the insulating film in the peripheral area of the electrode. The lateral spread of the formed depletion layer can be suppressed,
As a result, C-■ measurement can be performed under conditions closer to those of the actual device without using a guard ring.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a MOS capacitor used in the C-■ measurement method according to an embodiment of the present invention, FIG. 2 is a sectional view taken along line n-'n in FIG. 1, and FIG. C- measured by the C-V measurement method according to an embodiment of the present invention
■A graph showing an example of the characteristics, Figures 4 and 5 are graphs showing an example of the C-V characteristics measured when voltage is applied to the guard ring and when no voltage is applied to the guard ring, respectively. The figure is a plan view showing a MOS capacitor used in the conventional C-■ measurement method, Figure 7 is a cross-sectional view taken along the line ■-■ in Figure 6, and Figure 8 is a theoretical curve of C-■ characteristics. This is a graph showing. Explanation of main symbols in the drawings: n-type Si substrate, : 5iOt film, : gate electrode, : guard ring, : damaged layer.

Claims (1)

[Claims] In a CV measurement method for a semiconductor device in which an electrode is formed on a semiconductor substrate via an insulating film, the CV measurement method is provided after damaging the surface of the insulating film in the peripheral area of the electrode. A C-V characterized in that it performs measurement.
Measuring method.