JPH01169347A - Evaluation of conductive type layer characteristic - Google Patents

Abstract

PURPOSE:To measure an electric characteristic of an shallow ion injection layer, by using a heat wave measurement with an Ar ion laser as excitation light and an He-Ne laser as probe light. CONSTITUTION:A Schottky electrode is formed on a wafer the same in heat wave signal distribution 11 as a GaAs substrate in which an Si ion is injected at an acceleration voltage 150keV and at a dose of 3.5X10<12>/cm<3>. A peak carrier density (Np)12 obtained by the measurement of voltage and current is compared with a carrier (Ns)14 at a peak position (Xp)13 with a depth of 2mum. From the results, a better correspondence is obtained between the heat wave signal distribution 11 and the Np 12 thereby enabling the evaluation of a conductive type layer characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a method for evaluating conductivity type layers in which a means for detecting electrical characteristics is improved.

(Prior Art) In manufacturing a semiconductor device, it is well known that a layer of a predetermined conductivity type is formed by ion-implanting impurities into a semiconductor substrate. For example, when forming a GaAs substrate integrated circuit, ions are generally implanted into a semi-insulating GaAs substrate to form an active layer, or ions are implanted to form highly concentrated impurity layers in the source and drain regions. There is. In order to use this ion implantation method to form high-speed, highly integrated devices with high yield, there is an increasing demand for improved controllability of the ion implantation process.

Especially GaAs field effect transistors (MESFETs)
is its figure of merit, transconductance (ga+)
There has been a tendency to make the ion implantation layer shallower in order to increase the

Conventionally, there has been no suitable method for evaluating a deep conductive layer formed under such ion implantation conditions of 80 KeV or less. For example, when measuring resistance using the four-terminal needle method after implanting ions into a Si substrate, the measurement terminal exhibits Schottky characteristics instead of ohmic characteristics for semi-insulating substrates, resulting in large errors in measured values. Accompany. Furthermore, although the voltage-current measurement method (C-V measurement) can directly observe the conductive layer, it cannot measure the profile of impurities implanted at less than 80 meters due to the influence of zero bias.

On the other hand, there is a thermal wave measurement method as a method for non-contact measurement of an ion-implanted layer after ion implantation. This method uses an Ar ion laser as an excitation light source and observes the distribution of heat waves and plasma waves generated on a semiconductor surface using a He--Ne laser beam as a probe beam. Although this method does not require an annealing process and is effective as a fast feedback method, it is generally difficult to obtain information about the implant depth direction. From the above, it was not clear whether the thermal wave measurement method could be used to evaluate shallow ion-implanted layers.

(Problems to be Solved by the Invention) As described above, the electrical characteristics of a shallow impurity layer cannot be sufficiently evaluated using the conventional evaluation method for a conductivity type layer.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for evaluating conductivity type layer characteristics that can accurately evaluate the electrical characteristics of a shallow impurity layer.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention uses a thermal wave measurement method using an Ar laser as an excitation light and a He-Ne laser as a probe light. It is characterized by measuring the electrical characteristics of the ion-implanted layer.

(Function) Using an Ar ion laser as excitation light on a semiconductor substrate, a He-
The thermal wave signal intensity measured using a Ne laser as a probe light is correlated with the peak carrier concentration by a linear function. Therefore, the electrical characteristics of the conductivity type layer determined by the peak carrier concentration can be approximately expressed by the thermal wave signal intensity.

In particular, the electrical characteristics of a conductive type layer into which impurities are implanted at an accelerating voltage of 60 KeV or less are well approximated by the thermal wave signal intensity.

(Example) The details of the present invention will be explained using examples.

Hereinafter, as an example of the present invention, a case will be described in which a threshold value determined by the electrical characteristics of a conductive type layer of a GaAs Schottky gate field effect transistor (MESFET) is measured.

FIG. 1 is a diagram showing the results of measuring heat waves by irradiating a wafer with laser light. St ion acceleration voltage 15
0 KeV, dose m 3.5X 10'/c
A Schottky electrode was formed on the same wafer as the thermal wave signal distribution 11 of the GaAs substrate implanted at j, and the peak carrier concentration (Np) 12 obtained by the CVel constant had a peak position (Xp) 13 and a depth of 2 μm. Carrier concentration (Ns)
14 are compared respectively. From these results, it can be seen that the thermal wave signal distribution 11 and Np12 show good correspondence. From this, FIG. 2 plots the relationship between the thermal wave signal distribution 11 (thermal wave signal unit, TWV) and Np12, and shows linearity.

In this case, generally G a A s M E S F E
The value voltage (V th) of T is v −V−-! ;1-Nd2(1) th bl 2ε It can be approximated. Here, "bl is the bit-in potential 9・q is the electron charge, ε is the dielectric constant of the semiconductor, and N is the carrier concentration d is the depth of ε. Therefore, the change in vth (Δ
v1h) is △Vth~-i [ΔNd2+N△(d2)]
(2) must be satisfied, and in order to satisfy this condition, the ion implantation condition is preferably 60 KeV or less.

From the above, a calibration straight line was established to show the relationship between the dose amount during ion implantation, the thermal wave signal intensity, and the threshold voltage (FIG. 3).

As shown above, from the thermal wave signal intensity of the wafer measured immediately after ion implantation, using Figure 3, we can determine the G after heat treatment.
It is possible to predict a threshold value for a A s M E S F E T .

FIG. 4 shows a GaAsME S F formed using a calibration straight line obtained from a thermal wave measurement method according to an embodiment of the present invention.
FIG. 3 is a diagram showing cross-sectional views of ET in the order of steps.

First, Si ions 43 are implanted into a semi-insulating GaAs substrate 41 from above a resist mask 42 at an acceleration voltage of 50 KeV and a dose of 2 x 10 '''/cjl:r to form an n-type operating layer 44. Immediately after injection,
A thermal wave signal was measured by a thermal wave measurement method using an Ar ion laser as excitation light and a He-Ne laser as probe light. The heat wave signal intensity at this time was 87.50 heat wave signal units. The threshold value of GaAs MESFET at this time is
It is estimated from a calibration straight line between the heat wave signal intensity and the threshold voltage of the GaAs MESFET that has been set in advance, and will be +50 mV.

As a result, G
The threshold voltage of the aAs MESFET can be predicted, and if it deviates from the calibration straight line at this point, it is possible to perform additional SL ion implantation (FIG. 4(a)).

Next, tungsten nitride (WNx) was used as the gate metal.
5a is deposited over the entire surface of the wafer by reactive sputtering. Thereafter, a resist is applied to the entire surface and patterned to form a mask 46 (FIG. 41(b)).

Furthermore, etching is performed using RIE using the mask 461 to form a gate electrode 45b (FIG. 4(C)).

Then, after removing the mask 46, photoresist is applied to the entire surface again and patterned, and a mask 47 is formed.
form. Si ions are accelerated onto the substrate 41 from above the mask 47 and the gate electrode 45b at a voltage of 180 KeV.
Implantation is performed at a dose of ff13 x 1013/cJ.

In this state, capless annealing is performed at a temperature of 800° C. for 1 hour and 15 minutes using AsH3 as an atmosphere to activate the impurities and form n'' GaAs source and drain regions 49 (Fig. 4(d) )).

Finally, AuG e is deposited on the source and drain regions 49.
An ohmic electrode 51 made of /N i /A u is formed by alloying at 400° C. for 2 minutes to complete the semiconductor device. Since it is possible to predict the threshold after annealing immediately after the ion implantation process of the active layer using thermal wave measurement, it is possible to form a MESFET with an accurate threshold by performing ion implantation again. can do. Therefore,
A device having a conductivity type layer formed through such an ion implantation process can be formed with good controllability. In addition, the present invention
It can be used not only for measuring the threshold value of SFET but also for electrical measurement of shallow conductivity type layers. For example, it can be applied to measuring the resistance value of a shallow resistor formed by ion implantation.

[Effects of the Invention] According to the configuration of the present invention, it is possible to provide a conductivity type layer characteristic evaluation method that can measure the electrical characteristics of a shallow conductivity type layer.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing measurement results according to an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between thermal wave signal intensity and peak carrier concentration, and FIG. 3 is a diagram showing the relationship between dose amount and thermal wave signal intensity. FIG. 4 is a diagram showing the formation of an apparatus using heat wave measurement results according to an embodiment of the present invention. 11... Heat wave signal distribution 12... Peak carrier concentration (Np) 41... Semi-insulating GaAs substrate 42... Photoresist mask 44... N-type GaAs active layer 45b... Gate electrode 46... Photoresist mask 49... N-type GaAs source and drain region 50... Insulating film 51... Source and drain electrode

Claims (4)

[Claims] (1) Measuring the electrical characteristics of a shallow conductivity type layer formed by ion-implanting impurities into a semiconductor substrate using a thermal wave measurement method using an Ar ion laser as excitation light and a He-Ne laser as probe light. Evaluation method of characteristic conductivity type layer characteristics. (2) The method for evaluating conductivity type layer characteristics according to claim 1, wherein the semiconductor substrate is a semi-insulating GaAs substrate. (3) The method for evaluating conductivity type layer characteristics according to claim 1, wherein the conductivity type layer is a channel region of a Schottky gate field effect transistor. (4) The method for evaluating conductivity type layer characteristics according to claim 1, wherein the conductive layer has a low antibody content.