JPH04186147A - Sensing method for foreign matter on semiconductor wafer - Google Patents

Abstract

PURPOSE:To sense defect of wafer in an early stage by judging the degree of cleanliness in the washing process for semiconductor wafer by means of in-line measurement. CONSTITUTION:A semiconductor wafer 1 is inserted between electrodes 2, 3 and placed on the former 2, and either the wafer is put in contact with the latter 3 or a space is provided. Externally, for example from a frequency response device 4, a high frequency voltage is impressed to the gap between these two electrodes 2, 3. Therein the wafer 1 and impurities have different electric resistances and capacitances, and therefore, their components are separately measured by varying the frequency of the impressed voltage. This electric resistance is proportioned to the thickness of impurities and is in inverted proportion to the area, while the capacitance is in inverted proportion to the length and is proportioned to the area. Accordingly changes in the thickness and area of the impurities become apparent as changes in the electric resistance and the capacitance, which are thus measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a mechanism for detecting foreign matter on a wafer after washing with water in a semiconductor wafer manufacturing process.

[Conventional technology]

In semiconductor wafer manufacturing, an oxide film is formed on a silicon wafer and impurities are doped to obtain a semiconductor. In this step, various oxidation steps are completed, but in between, a cleaning step is performed to remove impurities. Ultrapure water of high purity is used for cleaning, taking into consideration the types of impurities. This can be accomplished by immersing a cassette 1- of a large number of wafers in an ultrapure water bath, or by spraying ultrapure water onto the cassette.

On the other hand, the quality of defects in manufactured semiconductor wafers is related to the presence of impurities in the oxide film or residual foreign matter in the 1-wrench (clean) portion. In order to inspect defective products, voltage is applied to defects mainly caused by short circuits between circuits, and withstand voltage measurements are taken until dielectric breakdown occurs.

On the other hand, watermark method (flatermark) is used to determine whether impurities remain on the wafer.
A method called ``is being considered. Originally, it was used to determine the purity of washing water, but the presence or absence of residue on the element 2 is determined by drying and its surface using an optical microscope.

No conventional method has been established, and in particular, no evaluation technology has been developed to determine the presence or absence of impurities in the washing and drying processes on the spot.

[Problem to be solved by the invention]

With conventional techniques, it has not been possible to semi-determine the presence or absence of impurities in semiconductor wafers during the manufacturing process.

An object of the present invention is to provide a determination device that determines impurities on a wafer after cleaning and drying steps.

[Means to solve the problem]

To achieve the above object, the present invention utilizes the difference in electrical properties between a semiconductor wafer and an impurity. That is, the semiconductor wafer and the impurity have different electrical resistance and capacitance, and the presence of the impurity is determined by separately measuring these components. Differential measurements can be made by changing the frequency of the applied voltage.

Regarding the measurement method, a semiconductor wafer is inserted between two pairs of electrodes (main electrode and counter electrode), an element is placed on one of the electrodes, and the other electrode is contacted or a space is provided.
A voltage is applied between both electrodes.

Voltage is applied to the sample wafer, contact resistance section, and insulating plate section.

It involves the part where the air layers are lined up in series, and measures the electrical resistance and capacitance of the sample electrode between these parts. Further, impurities in the sample electrode are measured as changes in resistance and capacitance of the sample electrode.

[Effect]

When impurities exist in the semiconductor wafer as points or planes, the electrical resistance R and capacitance C based on the components are R-ρ-- (1) ρ: Specific resistance Q: Length A: Area ε: Relative dielectric constant In formulas (1) and (2), R increases as the thickness of the impurity increases and is inversely proportional to the area. On the other hand, C is inversely proportional to Q and proportional to A.

Therefore, changes in the thickness and area of impurities appear as changes in R and C, respectively.

In order to increase these R and C changes, it is conceivable to place an insulator or the like before and after the wafer sample.

〔Example〕

In carrying out the present invention, the basic configuration is shown in FIG. A semiconductor wafer 1 is placed between two electrodes 2 and 3, and a voltage is externally applied between them from a frequency response device 4. A shielding body 5 made of a metal material may be installed at the electrode portion to block stray capacitance from the outside world, and this shielding body 5 and the frequency response device 4 are grounded.

There are several possible methods for placing a semiconductor wafer sample between electrodes. The installation method is shown in Figure 2. In (a), a sample 1 is placed on the electrode 2 and is spaced apart from the counter electrode 3. In this case, the resistance and capacitance between the electrodes is composed of the sample and the air phase in the space. In (b), the insert material 4 is placed in the air phase of (a), and the sample and the insulating material 4 form an electrical component. In (c), inserts 4 and 5 are inserted before and after the sample. In this case, it consists of a sample and two inserts. The electrical circuit between these electrodes includes the contact resistance between each material itself and at the same time. Regarding insert materials,
It is selected based on the electrical characteristics of the deposits on the sample. If the electrical resistance is high, a highly conductive material is used, and if the resistance is low, an insulating material is used. The shape of the insert material must have the same surface condition on the front and back sides.

On the other hand, during measurement, the spacing between the electrodes 2 and 3 is kept constant to eliminate errors caused by the shape from the reference characteristic values.

<Example 1> The results of actual measurements are shown in FIG. The sample was a 50φ silicon element (thickness: 0.8 mm) covered with a film of about 0.3 μm on the front and back sides of 5jOj.

On the other hand, in the case of a contaminated element, the contaminated part is located at the center of the wafer with a diameter of 15 mm.
It is formed into a cylindrical shape. The components are estimated to be metal oxides. Regarding the measurement method, a sample was placed between both electrodes 2 and 3, and polystyrene plates of 50φ x 0.5t were inserted in the front and back. The electrode spacing was maintained at 1 and 8 null. Measurements were made with a voltage of 0.5μ, a response from frequency fIKHz to 10MHz, and an impedance of 1
z1 and capacitance C are displayed. As a result, 1z1 and C exhibit responses with the same tendency for both the wafer and the contaminated wafer.

That is, IZI decreases in proportion to frequency f,
C shows a large value in the low and high frequency ranges. The contaminated wafer has a larger value 121 and a smaller C than the new wafer. This characteristic means that the resistance of the deposits on the wafer is high and the dielectric constant of the deposits, which appears as capacitance, is also high.

<Example 2> FIG. 4 shows the measurement results when the configuration between the electrodes was changed for the same sample as in Example 1. In contrast to Example 1, one polystyrene plate was inserted between the wafer and the lower electrode. ” Some of them are spaced at intervals of Q, 5 +++m.

The measured values are almost the same as in Example 1, but the IZ of the contaminated element
The difference in l and C from the new wafer is smaller. This means that among the electrical characteristics of the cavity at the top of the element, the electrical resistance is smaller than that of the polystyrene plate.

From the above two embodiments, there is a difference in electrical resistance and capacitance between wafers with deposits and clean wafers. Factors that influence the difference include the component and amount9 distribution of the deposit, and the shape related to the thickness and the like. The frequency dependence is directly expressed in the capacitance C of the component, and is also expressed in the impedance IZI. Therefore 121
The presence or absence of deposits can be determined from the frequency profiles of and C.

〔Effect of the invention〕

According to the present invention, since the degree of cleaning in a semiconductor wafer cleaning process can be determined from in-line measurement, defects in the wafer can be detected at an early stage.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an apparatus for determining deposits on a semiconductor wafer according to an embodiment of the present invention, FIG. 2 is a sectional view of a sample and an electrode in the detection mechanism, and FIGS. 3 and 4. FIG. 2 is an explanatory diagram of a measurement example for determination according to the present invention. 1... Semiconductor wafer, 2... Electrode, 3... Electrode, 4
Frequency responder.

Claims (1)

[Claims] 1. In a mechanism for detecting foreign substances on an oxide film of a wafer in a semiconductor wafer manufacturing process, a wafer is placed between two pairs of electrodes, and a high frequency voltage is applied between the electrodes. 1. A method for detecting foreign matter on a semiconductor wafer, the method comprising determining the presence of a foreign matter by measuring AC impedance of the semiconductor wafer and comparing it with the impedance of a wafer free of foreign matter. 2. A method for detecting foreign matter on a semiconductor wafer according to claim 1, wherein the wafer of the object to be measured is fixed in contact with both electrodes, or is placed on one electrode with a gap provided therebetween. 3. A method for detecting foreign matter on a semiconductor wafer according to claim 2, wherein both or one of the electrodes is coated with an insulating material. 4. A method for detecting foreign matter on a semiconductor wafer according to claim 1, wherein the applied alternating current wave has a voltage of 10 mV or more and sweeps a constant frequency or frequency in a frequency range of 1 KHz or more.