JPH10339711A - Inspection equipment for semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a secondary electric image having good image quality with high reproducibility by splitting an electron beam and performing the scanning simultaneously on a same path such that one split electron beam follows up the other split electron beam thereby controlling the charge up quantity precisely. SOLUTION: An electron beam 2 emitted from an electron gun 1 is passed through a deflection coil 3 and split into two through a biprism comprising a potential applicable thin wire 4 and a ground electrode 5. Two split electron beams 2 passes through an electron lens system 6 and a scanning coil 7 and reaches a sample 8 under sufficiently converged state. Secondary electrons or reflected electrons generated from the part of the sample 8 irradiated with the electron beam are detected by a secondary electron detector 10. A secondary electron image is acquired through simultaneous scanning where the other split electron beam follows up one split electron beam to scan a specified part on the sample 8. According to the arrangement, the secondary electron image of a semiconductor wafer can be acquired under best charge-up state with high reproducibility resulting in a highly reliable defect inspection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection apparatus technology for a semiconductor device, and particularly to an observation of a shape including a poorly conductive material on a large sample such as a defect inspection of a circuit pattern formed on a semiconductor wafer. The present invention relates to a preferable electron beam inspection apparatus for semiconductor devices.

[0002]

2. Description of the Related Art In general, in manufacturing a semiconductor integrated circuit device, a circuit pattern is formed on a semiconductor wafer by a deposition process of a conductive material or a poorly conductive material, a lithography process, an etching process, or the like. Since the quality of a circuit pattern formed on a semiconductor wafer has a great effect on productivity such as the production yield of a semiconductor integrated circuit device, the circuit pattern on such a semiconductor wafer is often used in the process of manufacturing a semiconductor integrated circuit device. Has been conventionally performed.

With today's high integration of semiconductor integrated circuit devices, circuit patterns formed on semiconductor wafers are rapidly becoming finer. For this reason, there has been proposed a method of using a scanning electron microscope having higher resolution than a conventionally used optical inspection device as a circuit pattern inspection unit.

As a related technique, for example, Japanese Patent Application Laid-Open No. 5-258703 discloses a method of inspecting a pattern formed on an X-ray mask or a conductive substrate equivalent thereto by using a scanning electron microscope and its method. A system is disclosed.

Further, Japanese Patent Publication No. 6-16407 discloses that a semiconductor wafer is continuously moved in a predetermined direction and converges in each of a plurality of divided areas set in an inspection area on the semiconductor wafer. There is disclosed means for scanning an electron beam and inspecting a circuit pattern at a high speed by using an obtained accurate secondary electron image without distortion.

Further, Japanese Patent Application Laid-Open No. 63-218803 discloses that the irradiation time of an electron beam on a semiconductor wafer at the time of image acquisition is precisely controlled so that the influence of charge-up and gradation drift of the semiconductor wafer on image quality can be reduced. Means for reducing and improving the reliability and sensitivity of secondary electron images used for inspection are disclosed. A mechanism for splitting an electron beam emitted from an electron source into two is described, for example, in Japanese Patent Application Laid-Open No. Hei 6-333529.

[0007]

Generally, a circuit pattern on a semiconductor wafer is composed of a complex combination of a conductive material and a poorly conductive material. When such a circuit pattern is irradiated with an electron beam, electric charges accumulate in the poorly conductive material portion (charge up). For this reason, the image quality of the secondary electron image fluctuates depending on the charge accumulation amount, and there is a problem that a reproducible secondary electron image cannot be obtained.

Here, the image quality of the secondary electron image is not always the best when there is no charge-up, but is often the best when there is an appropriate charge-up. Therefore, in order to acquire a secondary electron image with good image quality with good reproducibility, it is necessary to control the charge-up state with high accuracy. As means for this, for example, a method of precisely controlling the irradiation time of an electron beam as described in Japanese Patent Application Laid-Open No. 63-218803 is known. It is practically difficult to precisely control the electron beam, and it is generally difficult to control the charge-up only by controlling the electron beam irradiation time. As a practical means for obtaining a reproducible secondary electron image, It was inadequate.

An object of the present invention is to provide a means for acquiring a secondary electron image in a state in which the amount of charge-up is precisely controlled, thereby obtaining a secondary electron image with good image quality with good reproducibility. Is to make it possible.

[0010]

In order to solve the above-mentioned problems, the present invention focuses on the cause of the deterioration of the reproducibility of a secondary electron image when charge-up occurs. In most cases, the charge generated on the surface by electron beam irradiation does not maintain the state immediately after generation for a long time, but relaxes on various time scales according to the generation and surrounding electrical and topological conditions. Go. For this reason, the charge-up state changes from moment to moment, and the change is irregularly different at each location of the sample.

The above is the main cause of the deterioration of the reproducibility of the secondary electron image when the charge-up occurs. In order to prevent such a cause from affecting the image quality of the secondary electron image, If a charge-up occurs, a secondary electron image may be promptly obtained before the charge-up occurs. For this purpose, an electron beam for acquiring a secondary electron image may be scanned immediately after irradiation with an electron beam for causing charge-up. However, for example, when two sets of electron optical systems are used for this purpose, the device becomes large and complicated, and more complicated control is required, and it is inevitable that operation and maintenance become difficult.

The present invention solves the above problem by generating two electron beams in the same electron optical system and irradiating them on a semiconductor wafer to be inspected while controlling them under predetermined conditions. Is given.

In order to realize this, according to the present invention, a mechanism for dividing an electron beam emitted from an electron source into two is provided in an electron optical system, and each of these two electron beams is used for charge-up. And is used for secondary electron detection. As a mechanism for dividing the electron beam emitted from the electron source into two, a biprism for an electron beam including a conductive thin wire and a ground electrode may be used. This biprism is installed in the electron optical system so that the thin wire crosses the electron beam path, and by applying a potential to the thin wire in this state, electron beams passing on both sides of the thin wire can be deflected in opposite directions. it can. The deflection amount of both electron beams can be easily changed by changing the potential applied to the fine wire.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a device configuration according to an embodiment of the present invention. In FIG. 1, an electron beam 2 emitted from an electron gun 1 composed of an electron source, an extraction electrode, an accelerating electrode, etc., passes through a deflection coil 3 and then is formed of a thin wire 4 to which a potential can be applied and a biprism comprising a ground electrode 5. Is divided into two. The two split electron beams 2 pass through the electron lens system 6 and the scanning coil 7 and reach the semiconductor wafer as the sample 8 in a sufficiently converged state. The sample 8 is set on a movable stage 9, and in this state, a retarding voltage can be applied by a mechanism not shown in the drawing. Secondary electrons or reflected electrons generated from the portion of the sample 8 irradiated with the electron beam 2 are reflected by the secondary electron detector 1.
0 is detected.

In FIG. 1, the deflection coil 3 is driven by a deflection coil driving device 11 and has a function of deflecting the electron beam 2 by a predetermined amount. Further, the potential applied to the thin wire 4 which is a component of the biprism is controlled by the potential control device 12, whereby the amount of separation of the component of the electron beam 2 split on both sides of the thin wire 4 is adjusted. Then, the electron lens system 6 is controlled by the lens control device 13, and the convergence state and the dividing direction of the two divided electron beams 2 when reaching the sample 8 are optimally controlled.

Further, the scanning coil 7 is connected to the scanning control device 1.
4, which has a function of scanning the electron beam 2 one-dimensionally or two-dimensionally at a predetermined speed and width.
The retarding voltage applied to the sample 8 is controlled by the retarding control device 15 and plays a role of adjusting the energy of the electron beam 2 when reaching the sample 8 to a predetermined value. And the stage 9 is the stage driving device 1
6 is driven and controlled by the position of the sample 8 prior to observation,
Adjustment of the direction and, if necessary, that is, when the scanning of the electron beam 2 by the scanning coil 7 is one-dimensional, enables the sample 8 to be continuously moved in one direction during observation. Further, the signal from the secondary electron detector 10 undergoes processing including A / D conversion in the signal processing device 17.

In FIG. 1, a control unit 18 integrally controls a deflection coil control unit 11, a potential control unit 12, a lens control unit 13, a scanning control unit 14, a retarding control unit 15, and a stage drive unit 16. Then, a secondary electron image is generated under predetermined conditions based on data from the signal processing device 17 and sent to the automatic defect determination / storage / display device 19. Then, the defect automatic judgment / storage / display device 19 automatically detects the defect of the circuit pattern on the semiconductor wafer as the sample 8 from the secondary electron image, stores the defect, and stores it in FIG. Are displayed on the omitted display unit.

Here, the function of the biprism composed of the deflection coil 3 and the thin wire 4 and the ground electrode 5 in FIG. 1 will be described in more detail with reference to FIG. In FIG. 2, a deflection coil 3 is arranged to deflect the electron beam 2 in a direction perpendicular to the thin wire 4. The thin wire 4 is placed in the path of the electron beam 2, but the deflection coil 3 deflects the electron beam 2 to change the division ratio (current ratio) of the electron beam 2 passing on both sides of the thin wire 4. Can be. In FIG. 2, the electron beam 2
Are referred to as a precharge beam 20 and a main beam 21, respectively, and the split ratio of both beams is a: 1−1.
a. As described above, a can be arbitrarily changed by deflecting the electron beam 2 in the direction perpendicular to the thin wire 4 by the deflection coil 3.

Next, a method of defect inspection according to the embodiment of the present invention described with reference to FIGS. 1 and 2 will be described. In the present invention, a condition is set such that the distance between the precharge beam 20 and the main beam 21 is kept constant and the above-mentioned a is kept constant, and that the main beam 21 passes immediately after the portion where the precharge beam 20 has passed. Scan simultaneously while keeping. Such scanning can be easily realized by adjusting the relative direction between the precharge beam 20 and the main beam 21 by adjusting the lens system 6. Further, even when the precharge beam 20 and the main beam 21 are two-dimensionally scanned, the precharge beam 20 and the main beam 21
Is one-dimensionally scanned, and it is needless to say that both can be realized even when the stage 9 is continuously moved in a direction perpendicular to the scanning direction.

Next, a secondary electron signal obtained when the precharge beam 20 and the main beam 21 are simultaneously scanned under the above conditions will be described. The intensity of a signal obtained from the amount of secondary electrons generated when an electron beam having a unit current amount is irradiated on a place X in the sample 8 is represented by Inc (X) and Ic (X).
And Here, Inc (X) is the signal intensity when the location X is not charged up, and Ic (X) is the location X
Is the signal intensity in the charged-up state immediately after the electron beam has passed. When the precharge beam 20 and the main beam 21 are scanned as described above, the main beam 21
Pass through the same location immediately after the precharge beam 20 has passed. Therefore, the total signal intensity Itotal (X) when the main beam 21 irradiates the place X in the sample 8 is given by the following equation.
Becomes

[0021]

Itotal (X) = a · Inc (X + D) + (1−a) · Ic (X) (1) where D is the precharge beam 20 and the main beam 21
Are the intervals on the sample 8. Generally, the amount of charge-up required to obtain the best secondary electron image is small. Therefore, in many cases, a should be sufficiently smaller than 1. In such a case, the above equation is approximately
From Equation 2, it can be considered that the total signal intensity is the signal intensity that gives the best secondary electron image, and a highly reliable defect inspection can be performed.

[0022]

## EQU2 ## It goes without saying that even when the sample 8 is a semiconductor wafer on which a circuit pattern is formed, secondary electrons can be obtained based on the above approximate expression. In this case, it is possible to obtain a more accurate secondary electron image utilizing the characteristics of the sample 8, which will be described below.

When the target semiconductor wafer is a DRAM manufacturing process, the circuit pattern is composed of a group of memory cells 22 of the same shape arranged regularly as schematically shown in FIG. When such a periodic pattern inspection is performed, it is preferable that the interval D between the precharge beam 20 and the main beam 21 coincides with the period T in the pattern scanning direction. It is desirable that the period T be as short as possible. For this purpose, it is effective to previously match the scanning direction with the pattern direction. Such adjustment of the direction can be easily performed by driving the stage 9 by the stage driving device 16 in FIG. By performing the above adjustment, as shown schematically in FIG. 3, the precharge beam 20 and the main beam 21 are always applied to an equivalent part of the adjacent memory cell 22.

In such a case, the total signal strength is given by Equation 3 where D = T in Equation 1, but since the circuit pattern repeats with a period T, Equation 4 holds, and Equation 3 becomes Equation 5
Becomes

[0025]

Itotal (X) = a · Inc (X + T) + (1−a) · Ic (X) (3)

[0026]

Inc (X + T) = Inc (X) (4)

[0027]

## EQU00005 ## Ital (X) = a.Inc (X) + (1-a) .Ic (X) (5) In this case, the total signal strength Itotal (X) is not equal to Although the secondary electron signal is included, the obtained secondary electron image is similar to the image obtained only from the secondary electrons generated from the place X regardless of the size of a.

Further, even if a is not small enough to satisfy Equation 2, if it is small to some extent, the main part of the total signal intensity Itotal (X) will be at the best charge-up state at location X. The signal Ic (X) is occupied, and a secondary electron image in the best charge-up state is obtained effectively. Therefore, the reliability of the defect inspection is improved as compared with the case where the approximate expression (2) is used.

The present invention is not limited to the embodiment described here.
The electron beam 2 is divided into two so that the electron beam 2 reaches the sample 8 at a desired current ratio and at a desired interval, and further passes through a specific place on the sample 8 immediately after one of them passes through the other. As long as it is possible to simultaneously scan and acquire a secondary electron image as described above, it goes without saying that this can be carried out without impairing the essence of the present invention, regardless of the means and device configuration therefor. .

[0030]

As described above, according to the present invention, a secondary electron image of a semiconductor wafer as a sample can be obtained with good reproducibility in the best charge-up state. It can be carried out. Moreover, since the precharge for realizing the best charge-up state is performed simultaneously with the acquisition of the secondary electron image, high inspection efficiency can be achieved. Further, since the mechanism for performing the precharge has a configuration that can be easily incorporated into a standard electron optical system, the apparatus does not increase in size.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an inspection apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of functions of an electron biprism used in one embodiment of the present invention.

FIG. 3 is a plan view of the inspection object for explaining the operation and functions of the embodiment of the present invention.

[Explanation of symbols]

1. Electron gun, 2. Electron beam, 3. Deflection coil, 4. Fine wire,
5 ground electrode, 6 electron lens system, 7 scanning coil, 8
... sample, 9 ... stage, 10 ... secondary electron detector, 11 ...
Deflection coil driving device, 12: electric potential control device, 13: lens control device, 14: scanning control device, 15: retarding control device, 16: stage driving device, 17: signal processing device, 18: control device, 19: defect Automatic judgment / storage / display device, 20: precharge beam, 21: main beam,
22 memory cells.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hisaya Murakoshi 1-280 Higashi-Koigakubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. Within the Central Research Laboratory (72) Inventor Masaki Hasegawa 1-280 Higashi Koikekubo, Kokubunji City, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (72) Inventor ▲ Taka ▼ Atsuko Fuji 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Inside Central Research Laboratory, Hitachi, Ltd.

Claims (4)

[Claims] 1. An electron gun, an electron optical system for converging an electron beam emitted from the electron gun and irradiating the electron beam on a sample, a scanning mechanism for scanning the converged electron beam in an observation area of the sample, and the sample A detection mechanism for detecting electrons emitted from the convergent electron beam irradiation portion, and a scanning mechanism for controlling the scanning mechanism to generate a scanned image of a signal from the detection mechanism or a signal obtained by performing a predetermined operation on the signal. In the inspection apparatus for a semiconductor device, comprising a scanning image generating mechanism and a mechanism for performing a defect inspection of a pattern formed on the sample based on the scanning image, the electron beam is divided into two at a predetermined current ratio. A mechanism for splitting the split electron beam into a desired condition for setting a relative splitting direction of the split electron beam upon arrival at the sample so that one of the split electron beams tracks the other; On the same route Inspection apparatus for a semiconductor device and generates the scanned image by scanning at. 2. An apparatus for inspecting a semiconductor device according to claim 1, further comprising a mechanism for setting an interval between said divided electron beams upon arrival at said sample to a desired condition, wherein said pattern is formed on said sample. When the whole or a part has a periodic pattern that repeats the same structure periodically, the interval between the divided electron beams at the time of arrival at the sample is maintained while being matched with the period of the periodic pattern. An inspection device for a semiconductor device, which generates a scanned image. 3. The semiconductor device inspection apparatus according to claim 2, further comprising a retarding voltage applying mechanism for applying a retarding voltage to the sample. 4. A semiconductor device inspection apparatus according to claim 3, further comprising a moving mechanism capable of continuously moving said sample in one direction, wherein said moving mechanism is used in combination with said scanning mechanism. An inspection apparatus for a semiconductor device, wherein a scanning image is formed by scanning the divided electron beam in one direction and continuously moving the sample in a direction perpendicular thereto.