JP2003031633A - Apparatus and method for evaluating silicon wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and a method for evaluation which enable to evaluate electrical characteristics of a wafer accurately without being influenced by an insulation film on a rear face even if no treatment is applied to the rear face when evaluating electrical characteristics such as withstanding pressure of an oxide film of a wafer having an insulation film such as a CVD oxide film on the rear face, by a mercury probe method. SOLUTION: The apparatus for evaluating a silicon wafer by a mercury probe method comprises at least a mercury probe, a wafer chuck for holding the rear face of a wafer, and a ring for contact connected to the wafer chuck. The ring for contact has such a structure that it is brought into contact with a peripheral part of the surface and/or an edge part of the silicon wafer when the silicon wafer is held by the wafer chuck. At least a part of the ring for contact which is brought into contact with the peripheral part of the surface and/or the edge part of the silicon wafer is formed of a conductor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for evaluating a silicon wafer, and in particular, it accurately evaluates the electrical characteristics such as the breakdown voltage of an oxide film of a wafer by a mercury probe method of bringing a mercury probe into contact with a gate oxide film. It is related to the technology.

[0002]

2. Description of the Related Art In recent years, as MOS-LSIs have been promoted to be highly integrated and miniaturized, there has been an increasing demand for thinned and highly reliable gate oxide films. To evaluate the reliability of this oxide film, TZDB (Time Z
ero Dielectric Breakdown: oxide film breakdown voltage evaluation, TDDB (Time Depende)
nt Dielectric Breakdown (dielectric breakdown characteristics over time) evaluation is generally used.

Generally, the breakdown voltage of an oxide film and the evaluation of dielectric breakdown characteristics with time are performed by using polycrystalline silicon deposited on a silicon wafer as an electrode. Figure 1
FIG. 3 is a cross-sectional explanatory diagram when evaluating the oxide film breakdown voltage using polycrystalline silicon as an electrode. First, a silicon wafer 1 obtained by the CZ method or the like is subjected to a thermal oxidation treatment to form an insulating film (gate oxide film) 2, and polycrystalline silicon is deposited on the formed gate oxide film by the CVD method or the like. After that, photolithography and etching of polycrystalline silicon are performed to fabricate a MOS capacitor having polycrystalline silicon as the electrode 3. The silicon wafer on which the MOS capacitor is formed is held on the wafer chuck 5 so that the back surface of the wafer 1 and the wafer chuck 5 are held.
, And the wafer chuck 5 is connected to the ground. By applying an electrical stress from the measuring probe 4 to the silicon wafer thus connected, the oxide film breakdown voltage can be evaluated.

However, when the oxide film breakdown voltage characteristics are evaluated using polycrystalline silicon as an electrode, it is necessary to deposit the polycrystalline silicon and perform the photolithography process and the etching process as described above. It takes time to evaluate the withstand voltage characteristics of the oxide film, and also has a drawback that the facility cost is burdened.

In order to solve such a problem, a mercury probe method has been developed for evaluating the breakdown voltage of an oxide film using mercury as an electrode. FIG. 2 shows a cross-sectional explanatory diagram when the oxide film breakdown voltage is evaluated by the mercury probe method. The mercury probe method is a method of using a mercury electrode in which mercury 6 is placed in a holder 7 for holding mercury such as glass or resin, instead of polycrystalline silicon which is usually used as an electrode. The electrical characteristics such as the breakdown voltage of the oxide film can be evaluated by contacting with and applying an electrical stress.
The evaluation of the breakdown voltage of the oxide film by the mercury probe method also uses so-called wafer back surface contact in which the wafer 1 is held on the wafer chuck 5 and the wafer chuck 5 and the back surface of the wafer 1 are brought into contact with each other. As described above, by using the mercury probe as the electrode, it is possible to easily evaluate the oxide film breakdown voltage characteristic in a shorter time than in the case of using polycrystalline silicon.

However, for example, device latches
P / p used as a measure against up ⁺Epitaxial
Wafer (p-type low resistivity substrate with normal p-type resistivity)
Wafers with a epitaxial layer) are epitaxial
Wafer to prevent auto-doping during growth.
A CVD oxide film is formed on the back surface of the. Like this on the back
Wafer with insulating film such as oxide film
When evaluating the pressure characteristics, the wafer backside
In the method using tact, the backside insulation film is used as a resistor.
I was unable to make accurate measurements.

Therefore, when the oxide film breakdown voltage characteristics are evaluated using polycrystalline silicon as an electrode, since the polycrystalline silicon is directly deposited on the wafer surface, the wafer surface is protected by using, for example, a photoresist, After that, back surface treatment can be performed by etching only the oxide film on the back surface of the wafer with hydrofluoric acid or the like. Thereby, the oxide film on the back surface can be removed and the breakdown voltage characteristics of the gate oxide film on the front surface can be accurately evaluated.

On the other hand, when a mercury probe is used as the electrode, if the same treatment as described above is performed for protecting the surface after forming the gate oxide film, the gate oxide film contacting with the mercury electrode is covered with a protective film such as a photoresist. However, the back surface treatment of the wafer could not be performed because the film quality of the gate oxide film was adversely affected.

Therefore, when a wafer having an insulating film on its back surface is evaluated by the mercury probe method, the mercury electrode contacting from the upper side has a double structure as shown in FIG. That is, the electrode 11 corresponding to the polycrystalline silicon electrode is formed in the center part, and the ring-shaped mercury electrode 12 is arranged around the center electrode to serve as the ground side corresponding to the back surface of the wafer.

However, when the mercury electrode has a double structure in this way, the size of the mercury electrode portion becomes large, and the measurement points overlap at the time of multipoint measurement within the wafer surface, making accurate evaluation impossible. It was Moreover, this double structure
The mercury electrode, which is important in the mercury probe method, must be newly prepared from a single structure in which mercury is merely contained in a holder for holding mercury such as a normal capillary (capillary) to a double structure. Besides the parts, it was necessary to reconstruct the whole measurement system so that the electric wiring and the like were suitable for the double structure.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to prevent breakdown voltage of an oxide film on a wafer having an insulating film such as a CVD oxide film on the back surface by a mercury probe method. To provide an evaluation device and an evaluation method capable of accurately evaluating the electrical characteristics of a wafer without being affected by the insulating film on the back surface even when the back surface treatment is not performed when evaluating the electrical characteristics such as is there.

[0012]

In order to achieve the above object, according to the present invention, there is provided an apparatus for evaluating a silicon wafer by a mercury probe method, comprising a wafer chuck for holding at least a mercury probe and a back surface of the wafer, and the wafer chuck. A contact ring connected to the chuck, wherein the contact ring has a structure in contact with a peripheral portion and / or edge portion of the surface of the silicon wafer when the silicon wafer is held on the wafer chuck, and at least the ring. An apparatus for evaluating a silicon wafer is provided in which the material of the peripheral portion of the silicon wafer surface and / or the contact portion with the edge portion is a conductor (claim 1).

As described above, when a silicon wafer is evaluated by the mercury probe method, a contact ring having a contact portion with the surface peripheral portion and / or edge portion of the silicon wafer is provided in the evaluation device, and the contact portion of the contact ring is provided. Even if an insulating film such as a CVD oxide film is present on the back surface of the silicon wafer by using the evaluation device using the material of as a conductor, the oxide film withstand voltage of the silicon wafer can be accurately measured without being affected by the insulating film. Electrical characteristics can be evaluated.

At this time, it is preferable that the conductor portion of the contact ring is electrically connected to the detector and used as the ground side (claim 2). In this way, if the contact ring is electrically connected to the detector and is used as the ground side, it can be measured without applying the insulating film existing on the back surface of the wafer when the electric stress is applied. Wafers can be evaluated accurately without being affected by.

Further, in this case, it is preferable that the contact ring is detachable from the wafer chuck. As described above, by making the contact ring detachable from the wafer chuck, the wafer can be easily transferred and the work efficiency can be improved. Further, by making it detachable, a conventional wafer chuck or the like can be basically used as it is.

Furthermore, it is preferable that the contact ring can be divided (claim 4). By thus dividing the contact ring, even if there is a contact on the wafer surface, the wafer can be transferred easily without being affected.

Further, the evaluation method of the present invention is a method for evaluating a silicon wafer by a mercury probe method, in which a contact ring in which a contact portion with a peripheral portion of the silicon wafer surface and / or an edge portion is a conductor is provided, Evaluating the oxide film breakdown voltage of the silicon wafer by connecting the output part of the tester to the mercury electrode of the mercury probe and electrically connecting the conductor part of the contact ring to the detector and using it as the ground side. The method for evaluating a silicon wafer is characterized by (claim 5).

As described above, when the oxide film withstand voltage characteristic of a silicon wafer is evaluated by the mercury probe method, a contact ring having a conductor at the contact portion with the peripheral portion of the silicon wafer surface and / or the edge portion is provided, and a tester is provided. Is connected to the mercury electrode of the mercury probe, and the conductor portion of the contact ring is electrically connected to the detector to be used as the ground side.
Even if an insulating film such as a VD oxide film is present, the oxide film breakdown voltage of the silicon wafer can be accurately evaluated without being affected by the insulating film.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below, but the present invention is not limited thereto. The present inventors, when evaluating the oxide film breakdown voltage characteristics of a wafer using the mercury probe method, even if the wafer has an insulating film such as a CVD oxide film on the back surface, it is possible to use mercury without interposing the insulating film on the back surface. The inventors have found that if the electrical stress applied from the electrodes can be detected by a detector, the electrical characteristics such as the oxide film withstand voltage can be accurately evaluated, and the present invention has been completed.

That is, a conventionally used evaluation device for oxide film withstand voltage and the like is provided with a contact ring connected to a wafer chuck, and the contact ring holds the silicon wafer when the silicon wafer is held on the wafer chuck. As long as it has a structure in contact with the peripheral portion of the front surface and / or the edge portion, and at least the material of the contact portion is a conductor, the peripheral portion of the front surface of the wafer and It becomes possible to connect from the edge part to the ground side via the contact ring. Therefore, the oxide film breakdown voltage and the like can be accurately evaluated without being affected by the insulating film on the back surface of the wafer.

Here, the silicon wafer evaluation apparatus and method using the mercury probe method according to the present invention will be specifically described with reference to FIG. As shown in FIG. 4, first, the silicon wafer 1 having the gate oxide film 2 formed thereon is held on the wafer chuck 5, and then the contact ring 8 is formed so as to cover up to about 5 mm of the surface of the silicon wafer 1. Is connected to the wafer chuck 5.
The contact ring 8 is brought into contact not only with the peripheral portion of the wafer surface but also with the edge portion of the wafer. Then mercury 6
The mercury electrode placed in the holder 7 for holding mercury is brought into contact with the gate oxide film 2. The electrical stress is applied from the output part 9 of the tester to the gate oxide film 2 through the mercury electrode of the mercury probe.
Applied to. Since the CVD oxide film is not deposited on the peripheral portion and the edge portion of the silicon wafer 1 and only the thin gate oxide film is formed, and the surface shape of the edge portion is fine unevenness, the peripheral portion of the silicon wafer is Alternatively, the edge portion and the contact ring 8 can be electrically connected.

At this time, the material of the contact ring 8, at least the material of the peripheral portion of the surface of the wafer and / or the contact portion with the edge portion is a conductor, and the conductor portion of the contact ring 8 is connected via a wafer chuck. By electrically connecting with the detector 10, it can be used as the ground side. As a result, the oxide film breakdown voltage characteristic of the gate oxide film 2 can be evaluated without being affected by the CVD oxide film on the back surface of the wafer. In this case, of course, the entire contact ring may be made of a conductor, and it is more preferable to use the same material as that of the wafer chuck for conductivity.

Further, in this case, it is preferable that the contact ring is detachable from the wafer chuck. When the contact ring has a contact portion with the peripheral portion of the surface of the silicon wafer, as shown in FIG. 5, the contact ring is detachable from the wafer chuck, so that the conventional wafer chuck is used as it is. It is possible to easily transfer the silicon wafer to the evaluation device.

At this time, if the contact ring 8 can be divided as shown in FIG. 6, the contact ring can be easily attached to and detached from the wafer chuck. When evaluating a large-diameter silicon wafer, the equipment such as a contact ring will be expanded, but a contact ring that can be attached and detached and divided as in the present invention is easy to increase the diameter of a wafer. Can correspond to.

On the other hand, if a wafer chuck of a type that sandwiches the wafer from the left and right is used, the contact ring does not necessarily have to be removable. With this method, it is possible to transfer the wafer easily and efficiently while the contact ring is still connected to the wafer chuck, but it is necessary to newly manufacture the wafer chuck.

In the above description, the contact ring has a contact portion with the peripheral portion of the surface and the edge portion of the silicon wafer, but the contact ring does not contact the peripheral portion of the surface of the silicon wafer, that is, The structure may be such that it only contacts the edge portion of the wafer. In this case, since the contact ring is in contact with the edge of the wafer, conduction is obtained, but the wafer can be easily transferred without removing the contact ring while it is still connected to the wafer chuck. Has the advantage that it can proceed more efficiently.

[0027]

EXAMPLES The present invention will be described more specifically below by showing Examples and Comparative Examples, but the present invention is not limited to these. (Example) As a sample, a silicon wafer having a diameter of 200 mm, a P-type (boron-doped), and a CVD oxide film with a film thickness of 300 nm on the back surface was prepared. This silicon wafer was subjected to a thermal oxidation treatment in a dry atmosphere at 900 ° C. for about 100 minutes to form a 25 nm gate oxide film.

The obtained silicon wafer was held on a wafer chuck (see FIG. 5a), and then a contact ring covering up to 5 mm around the surface of the silicon wafer was connected to the wafer chuck (see FIG. 5b)). This time,
The contact ring was made of gold-plated ceramics, and the resistance when current flows through the contact ring was negligible. After that, the mercury electrode 13 was brought into contact with the gate oxide film of the wafer, and the breakdown voltage of the oxide film was evaluated by the mercury probe method (see FIG. 5c). The measurement condition is that the voltage is applied in the negative direction with respect to the wafer, that is, in the range of 0 to -40 V on the accumulation side, the current value flowing at that time is measured by the detector, and the wafer current (Ig) -voltage (Vg ) The characteristics were evaluated. The result is shown in FIG. 7. After the measurement, the contact ring was removed from the wafer chuck so that the wafer could be taken out of the apparatus (see FIG. 5d)).

(Comparative Example 1) As a sample, a silicon wafer similar to that of the example except that there is no CVD oxide film on the back surface of the wafer was prepared.
The thermal oxidation treatment was carried out for about 100 minutes in the dry atmosphere to form a 25 nm gate oxide film. The obtained silicon wafer was held on a wafer chuck, and the oxide film breakdown voltage characteristics were evaluated under the same conditions as in the examples by the mercury probe method without using a contact ring. The result is shown in FIG.

(Comparative Example 2) As a sample, the same silicon wafer as in the example having a CVD oxide film with a film thickness of 300 nm on the back surface of the wafer was prepared, and this silicon wafer was dried in a dry atmosphere at 900 ° C. for about 100 minutes. A thermal oxidation process was performed to form a 25 nm gate oxide film. The obtained silicon wafer was held on a wafer chuck, and the oxide film breakdown voltage characteristics were evaluated under the same conditions as in the examples by the mercury probe method without using a contact ring. The result is shown in FIG.

From the above measurement, the current-voltage characteristic of the silicon wafer having the CVD oxide film on the back surface was measured by the evaluation method of the present invention (FIG. 7).
It was found that the result is almost the same as that of the silicon wafer having no D oxide film (FIG. 8). On the other hand, when the silicon wafer having the CVD oxide film on the back surface was measured by the conventional method, it was found that the current did not flow unless a higher voltage was applied due to the effect of the CVD oxide film on the back surface.

The present invention is not limited to the above embodiment. The above-described embodiment is merely an example, and it has substantially the same configuration as the technical idea described in the scope of claims of the present invention, and has the same operational effect.
Anything is included in the technical scope of the present invention.

[0033]

As described above, according to the present invention,
Even for a silicon wafer having an insulating film such as a CVD oxide film on the back surface, by providing a contact ring, the electrical characteristics such as the breakdown voltage of the oxide film can be evaluated by the mercury probe method without performing special back surface treatment. You can

[Brief description of drawings]

FIG. 1 is an explanatory cross-sectional view when evaluating an oxide film breakdown voltage using polycrystalline silicon as an electrode.

FIG. 2 is a cross-sectional explanatory view when an oxide film breakdown voltage is evaluated by a mercury probe method.

FIG. 3 is an explanatory cross-sectional view when an oxide film breakdown voltage is evaluated by a mercury probe method with a mercury electrode having a double structure.

FIG. 4 is a cross-sectional explanatory view when evaluating an oxide film breakdown voltage according to the present invention.

FIG. 5 is a cross-sectional view showing attachment / detachment of a contact ring when performing measurement.

FIG. 6 is a plan view showing a contact ring that can be divided.

FIG. 7 is a graph showing current-voltage characteristics of a wafer with a back oxide film measured by the method of the present invention.

FIG. 8 is a graph showing current-voltage characteristics of a wafer without a backside CVD oxide film measured by a conventional method.

FIG. 9 is a graph showing current-voltage characteristics of a wafer with a backside CVD oxide film measured by a conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Silicon wafer, 2 ... Gate oxide film, 3 ... Polycrystalline silicon electrode, 4 ... Measurement probe, 5 ... Wafer chuck, 6 ... Mercury, 7 ... Holder for holding mercury, 8
... contact ring 9 ... output part, 10 ... detector 11 ... mercury electrode (center electrode), 12 ... mercury electrode (peripheral electrode) 13 ... mercury electrode.

Claims (5)

[Claims] 1. An apparatus for evaluating a silicon wafer by a mercury probe method, comprising: a wafer chuck that holds at least a mercury probe and a back surface of the wafer; and a contact ring connected to the wafer chuck, the contact ring being made of silicon. When the wafer is held on the wafer chuck, the peripheral portion of the surface of the silicon wafer and / or
An apparatus for evaluating a silicon wafer, which has a structure of contacting an edge portion, and at least a material of a peripheral portion of the surface of the silicon wafer of the ring and / or a contact portion with the edge portion is a conductor. 2. The silicon wafer evaluation apparatus according to claim 1, wherein the conductor portion of the contact ring is electrically connected to a detector and used as a ground side. 3. The contact ring can be attached to and detached from a wafer chuck.
Alternatively, the silicon wafer evaluation apparatus according to claim 2. 4. The silicon wafer evaluation apparatus according to claim 1, wherein the contact ring is separable. 5. A method for evaluating a silicon wafer by a mercury probe method, comprising: providing a contact ring having a conductor at a contact portion with a peripheral portion and / or an edge portion of the surface of the silicon wafer, wherein a mercury probe is used as an output portion of a tester. Of the silicon wafer characterized by evaluating the oxide film breakdown voltage of the silicon wafer by connecting to the mercury electrode, and electrically connecting the conductor part of the contact ring to the detector and using it as the ground side. Evaluation methods.