CN117420072A - Objective lens focal plane positioning method and device and semiconductor detection equipment - Google Patents

Abstract

The invention discloses an objective focal plane positioning method, an objective focal plane positioning device and semiconductor detection equipment, wherein the method comprises the following steps: adjusting the distance between the objective lens and the sample to be measured so that the distance is larger than the working distance of the objective lens; controlling the driving mechanism to cut the light path switching device into a light path of a Kohler illumination system for providing illumination so as to form an image which is convenient for positioning the focal plane of the objective lens on the focal plane of the objective lens; adjusting the distance between the objective lens and the sample to be measured, so that the distance is shortened according to the first step length until the camera detects a blurred image for positioning the focal plane of the objective lens; and fine-adjusting the distance between the objective lens and the sample to be measured by taking the second stepping length as a unit until the camera detects a clear image for positioning the focal plane of the objective lens, wherein the surface of the sample to be measured is positioned at the focal plane position of the objective lens, and moving the light path switching device out of the light path of the Kohler illumination system through the driving mechanism. The device can improve the focal plane positioning speed and safety of the objective lens with high multiplying power, high numerical aperture and short working distance.

Description

Objective lens focal plane positioning method, device and semiconductor testing equipment

Technical field

The invention relates to the field of microscopic imaging, and in particular to an objective lens focal plane positioning method, device and semiconductor detection equipment.

Background technique

In the field of defect detection, in order to image the wafer clearly, the focal plane must be prepared first for wafers of unknown thickness, that is, the relative position origin of the automatic focusing system must be set. During the automated wafer inspection process, the autofocus system always uses the origin as the basis for judging whether the objective lens and the wafer are out of focus. When the wafer surface undulates away from the origin (or focal plane), the autofocus system will drive the objective lens or wafer The axial movement of the stage brings the wafer into focus, thereby realizing automated inspection of the wafer.

Before automated wafer inspection, positioning the focal plane of the objective lens is a critical step. Generally, low-magnification objectives such as 1X/2X/5X have a large field of view, a large depth of focus, and a large dynamic range of autofocus (nearly several millimeters). You can directly use the origin value previously saved by the autofocus system to automatically find the focus of the objective lens. noodle. For objectives with high magnification, high numerical aperture, and short working distance, their focal depth is small and the dynamic range of autofocus is small (only a few microns). Autofocus often cannot directly find the focal plane of the objective lens. Even when automatically searching, there is a possibility of causing motor errors. The movement causes the objective lens to hit the wafer, and the focal plane can only be found manually. However, due to the small field of view of this type of objective lens, when the uniform area of the wafer happens to be within the field of view of the objective lens, when the objective lens is moved up and down, a uniform grayscale response is always maintained in the camera field of view, and it is impossible to determine whether the wafer is on the focal plane. Moving the objective lens downward too much also risks hitting the wafer. This method of finding the focal plane based on the clarity of the wafer image has low adaptability and poor safety.

There is also a solution to the above problem using a focusing and leveling sensor. For example, by setting an aperture or a light shield in the light source system to project onto the substrate, and then detecting the characteristics of the moiré fringe to determine whether the height and tilt of the substrate are at the appropriate level. Position, the implementation of this solution requires the use of focusing and leveling sensors and the applicable scene is limited. In short, for the focal plane positioning of objective lenses with high magnification, high numerical aperture, and short working distance, the current methods are limited, and a new method needs to be conceived to determine the optimal focal plane of the objective lens.

Contents of the invention

In order to solve the problems of difficulty in positioning the focal plane of high magnification, high numerical aperture, and short working distance objective lenses, low adaptability, and poor safety, the present invention provides a method and device that can quickly locate the focal plane of an objective lens. , short working distance objective lens, which can facilitate workers to quickly find and locate the focal plane, and has the characteristics of high safety and strong adaptability.

In order to achieve the above object, the present invention provides a method for positioning the focal plane of an objective lens, which includes the following steps:

Adjust the distance between the objective lens and the sample to be measured so that the distance is greater than the working distance of the objective lens;

The driving mechanism is controlled to cut the light path switching device into the light path of the Kohler illumination system used to provide illumination, so as to form an image on the focal surface of the objective lens that is convenient for positioning the focal surface of the objective lens;

Adjust the distance between the objective lens and the sample to be measured so that the distance is shortened according to the first step until the camera detects a blurred image used to locate the focal plane of the objective lens;

Fine-tune the distance between the objective lens and the sample to be measured in units of the second step length until the camera detects a clear image used to locate the focal plane of the objective lens. At this time, the surface of the sample to be measured is at the focal plane of the objective lens. The drive mechanism will The light path switching device moves out of the light path of the Kohler lighting system.

A further improvement of the present invention is that the first step length is 1/30 to 1/10 of the working distance of the objective lens.

A further improvement of the present invention is that the second step length is 1/4 to 1 of the focal depth of the objective lens.

A further improvement of the present invention is that the light path switching device is a lens, and the position and optical parameters of the lens are such that when the lens cuts into the parallel light path of the Kohler lighting system, the Kohler lighting system switches to critical lighting. , and causes the light source image to be projected on the objective lens focal surface of the objective lens focal surface positioning device.

A further improvement of the present invention is that the optical path switching device is an aperture diaphragm. When the aperture diaphragm cuts into the pupil plane of the Kohler illumination system, a clear aperture is formed on the focal plane of the objective lens conjugate with the pupil plane. Aperture pattern.

A further improvement of the present invention is that the aperture diaphragm is provided with a single aperture or an aperture array formed by multiple apertures, and the shape of the apertures is a round hole or a rectangular hole.

The invention also provides an objective lens focal plane positioning device for performing the above objective lens focal plane positioning method, which includes:

Kohler Lighting Systems for lighting;

The driving mechanism is used to drive the light path switching device to cut into the Kohler lighting system during the positioning process of the objective lens focal plane; when the driving mechanism drives the light path switching device to cut into the Kohler lighting system, the light path switching device causes the objective lens focal plane to be formed to facilitate positioning. The image of the focal plane of the objective lens.

A further improvement of the present invention is that it includes a beam splitter, and the light emitted by the Kohler illumination system is reflected by the beam splitter and then passes through the objective lens to illuminate the surface of the sample to be measured; the objective lens has a corresponding tube lens and a camera, and The light reflected by the sample passes through the objective lens, beam splitter, and tube lens in sequence, and enters the camera.

A further improvement of the present invention is that it also includes a spacing adjustment mechanism that drives the relative movement between the sample to be measured and the objective lens.

The present invention also provides a semiconductor testing equipment, which includes the above-mentioned objective lens focal plane positioning device.

The solution provided by the invention has the following technical effects:

1. Improved the speed and safety of positioning the focal plane of the objective lens for high magnification, high numerical aperture, and short working distance objectives;

2. Strong adaptability, applicable to different wafer morphologies;

3. The operation is simple and clear, making it easy for staff to quickly grasp the operating procedures and key operating points, which can effectively improve production efficiency.

Description of the drawings

Figure 1 is a schematic diagram of an objective lens focal plane positioning device in one embodiment of the present invention;

Figure 2 is a schematic diagram of an objective lens focal plane positioning device in another embodiment of the invention;

Figure 3 is the pattern of Aperture used in the invention.

Detailed ways

The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, as long as there is no conflict, the following embodiments and the features in the embodiments can be combined with each other.

It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, so the illustrations only show the components related to the present invention and are not based on the number, shape and number of components during actual implementation. Dimension drawing, in actual implementation, the type, quantity and proportion of each component can be arbitrarily changed, and the component layout type may also be more complex.

While some exemplary embodiments of the invention have been described for purposes of illustration, it is to be understood that the invention may be practiced otherwise than specifically shown in the drawings.

Embodiment 1: As shown in Figure 1, this embodiment provides an objective lens focal plane positioning device, which includes: a Kohler illumination system 10 for providing illumination, and a light path switching device for driving the light path switching device during positioning of the objective lens focal plane. The driving mechanism of the Kohler lighting system 10. The Kohler illumination system 10 mainly includes a condenser lens group 13, a condenser lens group 14 and an optical path switching device. The principle of positioning the focal plane of the objective lens in this embodiment is to achieve the positioning of the focal plane of the objective lens by switching between Kohler illumination and critical illumination. Critical illumination projects the image of the light source 16 directly onto the focal plane of the objective lens. When the sample (wafer) to be tested is at the focal plane of the objective lens, the camera will observe the light source image (this image is used to position the focal plane of the objective lens). By switching Kohler illumination to critical illumination and adjusting the height of the objective lens or stage to clearly image the light source, the wafer is in focus. specific:

In this embodiment, the light path switching device is the lens 11. When the driving mechanism drives the lens 11 to cut into the parallel light path of the Kohler lighting system, the cutting position of the light path switching device is located at the pupil of the Kohler lighting system; when the light path switching device is the lens 11, the lens The focal length of 11 is equal to the distance from the pupil position to the focal position of the condenser lens group 14, so that the light beam passing through the lens 11 is converged to the focus F of the condenser lens group 14 of the Kohler illumination system, which completes the switch from Kohler illumination to critical illumination. In this case, the clear light source image is projected on the objective lens focal surface of the objective lens focal surface positioning device to facilitate positioning of the objective lens focal surface.

The device of this embodiment also includes a beam splitter 20. The light emitted by the Kohler illumination system 10 is reflected by the beam splitter 20 and then passes through the objective lens 30 to illuminate the surface of the sample 40 to be measured. The objective lens 30 has a corresponding tube lens 50 and a camera 60 . The light reflected by the sample 40 to be measured passes through the objective lens 30 , the beam splitter 20 , and the tube lens 50 in order, and enters the camera 60 . When the light source image is projected on the objective lens focal plane of the objective lens focal plane positioning device and the objective lens focal plane is located on the surface of the sample 40 (wafer) to be tested, a clear light source image can be detected by the camera 60 .

In this embodiment, the driving mechanism includes a motor 15. The motor 15 is connected to the lens 11 through a transmission mechanism to drive the lens 11 to cut into or out of the optical path. In addition, this embodiment also includes a spacing adjustment mechanism that drives the relative movement between the sample to be tested 40 and the objective lens. In this embodiment, the sample to be tested 40 is stationary, and the spacing adjustment mechanism drives the objective lens 30, the beam splitter 20, the tube lens 50, the camera 60, The Kohler illumination system 10 moves synchronously to adjust the distance between the sample 40 to be measured and the objective lens 30 . The spacing adjustment mechanism is powered by the motor 31.

This embodiment also provides an objective lens focal plane positioning method for the above-mentioned objective lens focal plane positioning device. This method performs objective lens focal plane positioning when a wafer of unknown thickness is used as a sample to be tested, and includes the following steps:

(1) Adjust the distance between the objective lens 30 and the sample to be measured 40 so that the distance is greater than the working distance of the objective lens;

(2) Adjust the power of the light source 16 of the Kohler lighting system 10 so that the response of the camera 60 reaches 4.4% to 5.5% (at this time, the response is all system stray light);

(3) Control the driving mechanism to cut the light path switching device (lens 11) into the light path of the Kohler lighting system 10;

(4) Adjust the distance between the objective lens 30 and the sample to be measured 40 so that the distance is shortened according to the first step length until the camera 60 detects the blurred light source image; the first step length is 1/30 of the working distance of the objective lens ~1/10;

(5) Fine-tune the distance between the objective lens 30 and the sample to be measured 40 in units of the second step length until the camera 60 detects a clear light source image. At this time, the surface of the sample to be measured 40 is at the focal plane of the objective lens. By driving The mechanism moves the light path switching device out of the light path of the Kohler lighting system 10 . Set the origin of automatic focus and complete the focal plane positioning.

Since the light source filament has a known pattern and high contrast, it is very convenient for the staff to determine whether the direction of movement of the objective lens is correct (the overall gray scale of the camera becomes stronger and the contrast gradually increases), and to quickly determine whether the objective lens has found the focal plane (the light source filament is clear Imaging), this process is basically not affected by the actual wafer topography.

An embodiment of the present invention also provides a semiconductor testing equipment, which includes the above-mentioned objective lens focal plane positioning device, and adopts the above-mentioned objective lens focal plane positioning method to perform focal plane positioning.

Embodiment 2: As shown in Figure 2, the main difference between this embodiment and Embodiment 1 is that the optical path switching device is different. In this embodiment, the optical path switching device is an aperture diaphragm 12 (Aperture). The principle is: in the Kohler illumination system, the pupil surface of the illumination system is conjugate to the focal surface of the objective lens, and an aperture diaphragm 12 of a specific shape is set at the pupil surface. If and only when the wafer is in the focal plane, the camera 60 The shape of the aperture stop 12 will be observed. By adjusting the Z-axis height of the objective lens 30 or the height of the wafer stage (that is, adjusting the distance between the sample to be measured and the objective lens), the aperture diaphragm 12 is imaged clearly, that is, the wafer is in focus.

As shown in Figure 3, the aperture diaphragm is provided with a single hole or an array of holes formed by multiple holes, and the shape of the holes is a round hole or a rectangular hole.

This embodiment also provides an objective lens focal plane positioning method for the above-mentioned objective lens focal plane positioning device. This method performs objective lens focal plane positioning when a wafer of unknown thickness is used as a sample to be tested, and includes the following steps:

(1) Adjust the distance between the objective lens 30 and the sample to be measured 40 so that the distance is greater than the working distance of the objective lens;

(2) Adjust the power of the light source 16 of the Kohler lighting system 10 so that the response of the camera 60 reaches 4.4% to 5.5% (at this time, the response is all system stray light);

(3) Control the driving mechanism to cut the light path switching device (aperture diaphragm 12) into the light path of the Kohler lighting system 10;

(4) Adjust the distance between the objective lens 30 and the sample to be measured 40 so that the distance is shortened according to the first step length until the camera 60 detects the blurred light source image; the first step length is 1/30 of the working distance of the objective lens ~1/10;

(5) Fine-tune the distance between the objective lens 30 and the sample to be measured 40 in units of the second step length until the camera 60 detects a clear light source image. At this time, the surface of the sample to be measured 40 is at the focal plane of the objective lens. By driving The mechanism moves the light path switching device out of the light path of the Kohler lighting system 10 . Set the origin of automatic focus and complete the focal plane positioning.

Since the aperture diaphragm pattern is a known designed pattern and has a high contrast (the light-passing part is 100% transparent and the blocking part is 100% light-blocking), it is very convenient for the staff to judge whether the direction of movement of the objective lens is correct (the overall gray scale of the camera becomes stronger, The contrast gradually becomes larger), and it is quickly determined whether the objective lens has found the focal plane (the aperture diaphragm is clearly imaged). This process is basically not affected by the actual shape of the wafer. (a) and (b) in Figure 3 are both designed aperture diaphragm patterns.

The above embodiments only illustrate the principles and effects of the present invention, but are not intended to limit the present invention. Anyone familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed in the present invention shall still be covered by the claims of the present invention.

Claims (10)

1. A method for positioning the focal plane of an objective lens, characterized in that it includes the following steps: Adjust the distance between the objective lens and the sample to be measured so that the distance is greater than the working distance of the objective lens; The driving mechanism is controlled to cut the light path switching device into the light path of the Kohler illumination system used to provide illumination, so as to form an image on the focal surface of the objective lens that is convenient for positioning the focal surface of the objective lens; Adjust the distance between the objective lens and the sample to be measured so that the distance is shortened according to the first step until the camera detects a blurred image used to locate the focal plane of the objective lens; Fine-tune the distance between the objective lens and the sample to be measured in units of the second step length until the camera detects a clear image used to locate the focal plane of the objective lens. At this time, the surface of the sample to be measured is at the focal plane of the objective lens. The drive mechanism will The light path switching device moves out of the light path of the Kohler lighting system. 2. The method for positioning the focal plane of an objective lens according to claim 1, wherein the first step length is 1/30 to 1/10 of the working distance of the objective lens. 3. The objective lens focal plane positioning method according to claim 1, characterized in that the second step length is 1/4 to 1 of the focal depth of the objective lens. 4. The objective lens focal plane positioning method according to claim 1, characterized in that: the optical path switching device is a lens, and the position and optical parameters of the lens are satisfied when the lens cuts into the parallel optical path of the Kohler illumination system. At this time, the Kohler illumination system is switched to critical illumination, and the light source image is projected on the objective lens focal plane of the objective lens focal plane positioning device. 5. The objective lens focal plane positioning method according to claim 1, characterized in that: the optical path switching device is an aperture diaphragm, and when the aperture diaphragm cuts into the pupil plane of the Kohler illumination system, it is in contact with the The conjugate objective focal plane of the pupil plane forms a clear aperture stop pattern. 6. The objective lens focal plane positioning method according to claim 5, wherein the aperture diaphragm is provided with a single aperture or an aperture array formed by multiple apertures, and the shape of the apertures is a round hole or a rectangular hole. 7. An objective lens focal plane positioning device, used to perform the objective lens focal plane positioning method according to any one of claims 1 to 6, characterized in that it includes: Kohler Lighting Systems for lighting; The driving mechanism is used to drive the light path switching device to cut into the Kohler lighting system during the positioning process of the objective lens focal plane; when the driving mechanism drives the light path switching device to cut into the Kohler lighting system, the light path switching device causes the objective lens focal plane to be formed to facilitate positioning. The image of the focal plane of the objective lens. 8. The objective lens focal plane positioning device according to claim 1, characterized in that it includes a beam splitter, and the light emitted by the Kohler illumination system is reflected by the beam splitter and then passes through the objective lens to illuminate the surface of the sample to be measured; The objective lens has a corresponding tube lens and a camera, and the light reflected by the sample to be measured passes through the objective lens, beam splitter, and tube lens in sequence, and enters the camera. 9. The objective lens focal plane positioning device according to claim 1, further comprising a spacing adjustment mechanism that drives the sample to be measured and the objective lens to move relative to each other. 10. Semiconductor testing equipment, characterized by comprising the objective lens focal plane positioning device according to any one of claims 7 to 9.