JP4356246B2 - Sample surface detection method in hardness tester - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sample surface detection method for detecting the contact of an indenter with a sample surface in a hardness tester for measuring the hardness of a material surface such as a semiconductor or steel, or a thin film formed on the surface of these materials. About. In particular, the present invention relates to a sample surface detection method in a hardness tester that measures the surface hardness from the amount of indentation and the force applied to the indenter at the time of pushing an indenter with a sharp tip.
[0002]
[Prior art]
In a hardness testing machine that measures the hardness of the sample surface from the amount of the indenter pushed into the sample surface, generally, a mechanism that applies force to drive the indenter up and down and push it into the sample, and the indenter is pushed into the sample. A mechanism is provided for measuring the quantity, ie the displacement of the indenter. A load means using an electromagnetic coil or the like is used for driving the indenter, and a displacement measuring means such as a differential transformer or a laser displacement meter is used as a displacement measuring mechanism. The sample stage on which the sample is placed is composed of a triaxial drive mechanism, and includes a mechanism that moves back and forth and left and right to perform planar positioning and a mechanism that moves up and down to bring the sample surface closer to the indenter.
[0003]
In such a hardness tester, the amount of indentation is measured by measuring the distance the indenter has moved toward the sample from the point when the indenter tip touches the sample surface. This is necessary and this is called detection of the sample surface. Usually, an appropriate space is required below the indenter for setting the sample. Therefore, a relatively large distance is provided between the indenter and the sample surface before the measurement is started. In order to detect the sample surface from this state, in the conventional hardness tester, the sample stage on which the sample is placed is continuously raised, and the position where the sample surface is in contact with the indenter and the indenter is displaced is detected. The surface of the sample is used. Alternatively, the surface detection point is a position where the indenter is continuously lowered and the tip of the indenter comes into contact with the sample surface and the descending speed of the indenter changes.
[0004]
In order to detect contact between the sample surface and the indenter, the position of the indenter is continuously monitored, and when the sample is driven while the indenter is stationary, the time when the position of the indenter changes is the time of surface detection. And When moving the indenter at a constant speed with the sample stationary, the moving speed of the indenter is monitored by taking a differential value with respect to the time of the indenter position, and the time when the moving speed changes is set as the time of surface detection. .
[0005]
[Problems to be solved by the invention]
In the method of detecting the surface by raising the sample stage, it is difficult to accurately detect the surface because the position resolution of the sample stage is rough and there is vibration of the motor used for driving. Since the sample stage needs to move a relatively large distance, and the sample stage itself is large and heavy, a mechanism for converting the rotation of the motor into a linear motion by a screw or a gear is generally employed. For this reason, it is generally difficult to increase the position resolution and reduce the vibration associated with driving.
[0006]
In addition, in the method of detecting the surface by lowering the indenter, the position resolution is generally good and the detection accuracy is improved. However, the height of the sample is positioned so that the lowering stroke is short and the sample enters the lowering range in advance. It is necessary to keep. For driving the indenter, a mechanism for generating a force by applying an electric current to an electromagnetic coil placed in a stationary magnetic field is adopted, but this generally has a high position resolution but a short moving stroke. For this reason, the method of detecting the surface by lowering the indenter requires positioning so that the sample surface falls within a predetermined height range, which takes time and effort.
[0007]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a surface detection method in a hardness tester that improves detection accuracy while saving the operator's trouble.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a hardness tester for measuring the hardness of a sample surface from the amount of the indentation and the force applied to the indenter at that time by pushing the indenter into the sample surface. In the sample surface detection method for detecting contact with the surface, detecting whether the indenter contacts the sample surface while driving the indenter within a predetermined distance so as to approach the sample from the origin position, and within the predetermined distance When the indenter does not contact the sample surface, the step of returning the indenter to the origin position and driving the sample closer to the indenter by the predetermined distance; and when the indenter contacts the sample surface within the predetermined distance Storing the indenter driving distance to the contact position, returning the indenter to the origin position, and bringing the sample closer to the indenter by a distance slightly shorter than the indenter driving distance; Characterized in that it comprises a step of cormorants driving.
[0009]
In the sample surface detection method of the present invention, the indenter is brought close to the sample within a predetermined range where the indenter can be driven, and if there is no sample surface within the range, the indenter is retracted to the original position and only within the predetermined range. Move the sample closer to the indenter. By repeating this, when the indenter is driven, the indenter can contact the sample surface to detect the sample surface. Therefore, the surface detection is equivalent to performing the indentation by driving the indenter with the sample stationary, so that the accuracy of the surface detection is improved.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an example of a hardness tester for implementing the method of the present invention.
[0011]
An indenter 1 in which a diamond whose tip is sharpened in a predetermined shape is embedded in the tip is held by a leaf spring 2 and moves only in the vertical direction. The indenter 1 is driven by an electromagnetic actuator 3, and the amount of displacement in the vertical direction is measured by a displacement meter 4. The vertical position and driving force of the electromagnetic actuator 3 are controlled by controlling the magnitude of the current flowing through the coil constituting the electromagnetic actuator 3 with the control device 7. Below the indenter 1 is a sample stage 5 that is moved up and down by a motor. The sample 6 whose hardness is to be measured is placed on the sample stage 5 and faces the tip of the indenter 1. The control device 7 is also electrically connected to the displacement meter 4 and the sample stage 5, and controls each of them to take in data.
[0012]
Further, the control device 7 includes means for storing measurement data and calculation means, and calculates the hardness of the sample surface based on the indentation depth of the indenter with respect to the sample surface and the test force loaded at that time. The measured results are stored in a storage device such as an internal hard disk, displayed on a display device as a graph or numerical value, and output to a printer or the like. The control device 7 can be configured to have a computer and its peripheral device as a main body and an interface for hardware control.
[0013]
The hardware configuration shown in FIG. 1 will be supplementarily described. The electromagnetic actuator 3 includes a coil wound in an outer donut shape and an inner coil. A constant current is passed through the outer coil to generate a stationary magnetic field, and the force generated by controlling the current passed through the inner coil is controlled. The static magnetic field may be generated by a permanent magnet. The displacement meter 4 is constituted by a differential transformer. Here, the differential transformer is composed of an outer coil and a magnetic core disposed therein, and the relative movement distance between the coil and the magnetic core is measured by detecting that the impedance of the coil changes depending on its relative position. To do. As the displacement meter, a laser displacement meter or any other device capable of measuring a minute displacement can be employed. The method of holding the indenter is not limited to the leaf spring 2, and a balance mechanism or the like can be used. The sample stage 5 is a three-axis XYZ stage, and can be driven not only in the height direction but also on a plane.
[0014]
In the following description, as an example, the movable range (maximum stroke) of the electromagnetic actuator 3 is 100 μm, the resolution of the displacement meter 4 is 1 nm, the vertical position resolution of the sample stage 5 is 1 μm, and the movable range (maximum stroke) is 20 mm. To do.
[0015]
FIG. 2 shows a schematic diagram of surface detection, and FIG. 3 shows a flowchart of the surface detection procedure. Hereinafter, the surface detection method of the present invention will be described along the flowchart of FIG. 3 with reference to FIG. Each step of the flowchart is denoted as S1 to S14.
[0016]
Before the surface detection operation, the sample stage 5 is lowered downward enough to place the sample (S1). The position of the sample stage 5 may be the lowest position in the movable range, but it is sufficient if there is a space for placing the sample on the sample stage even if it is not the lowest position. The indenter 1 is not driven, that is, is located at the origin (S2). The sample 6 is placed on the sample stage 5 and is disposed directly below the indenter 1.
[0017]
When the surface detection is started, first, a gradually increasing current is supplied to the coil of the electromagnetic actuator 3 to apply a driving force increasing at a constant speed to the indenter 1, so that the indenter 1 is moved to a leaf spring as shown in FIG. It descends at a constant speed according to the spring constant of 2. The descending stroke is set to a predetermined distance M (in this embodiment, for example, the maximum movable range is 100 μm). When the indenter 1 touches the sample surface, the descending speed of the indenter 1 changes, so the differential value of the output of the displacement meter 4 changes. Therefore, the surface can be detected by monitoring the output of the displacement meter 4. is there. While the indenter 1 is lowered (S3), it is monitored whether or not the tip of the indenter has touched the sample surface (S4), and if it has not touched the sample surface, it is determined whether or not it has moved by a predetermined distance M (S5). If the stroke range M has not been reached, the indenter descends (S3), and if it has reached, the indenter 1 is returned to the origin and the sample stage 5 is the same as the stroke range M of the indenter, as shown in FIG. Raise by 100 μm. This is repeated until it is determined that the indenter 1 has touched the sample surface in step S4.
[0018]
In step S4, when the indenter 1 touches the sample surface and the output differential value of the displacement meter 4 changes, it is determined that the sample surface has been detected. The displacement amount (falling distance) A from the origin of the indenter 1 at this time is stored (S8), and the indenter 1 is once returned to the origin (S9). Thereafter, a distance smaller than the stored displacement amount A by a slight amount α is obtained, and the sample stage 5 is raised by that distance (= A−α) (S10). For example, if the indenter 1 touches the surface when the indenter 1 is lowered by 60 μm as shown in FIG. 2C, α is set to 2 μm, the indenter 1 is returned to the origin, and then the sample is shown as shown in FIG. Raise the stage by 58 μm. Thereafter, the surface is detected while lowering the indenter 1 again (S11) (S12), and if the surface is not detected, the indenter descending (S11) is continued, and if the surface is detected, the descending of the indenter 1 is stopped (S13). ). Since the surface detection is completed, the hardness measurement is subsequently executed (S14).
[0019]
Since the hardness measurement step S14 is the same as that of the conventional apparatus, it will be briefly described. After detecting the sample surface, an electric current is applied by the electromagnetic actuator 3 so that a predetermined force is applied to the indenter, and the indenter 1 is pushed into the sample. The amount by which the indenter 1 enters the sample 6 is measured by the displacement meter 4. From the final test force F and the indentation depth D, the hardness H of the sample surface is obtained by the following equation.
H = K · F / D ²
Here, K is a coefficient determined by the shape of the indenter tip.
[0020]
The method for detecting the sample surface will be further described with reference to FIG. When a current that gradually increases is supplied to the coil of the electromagnetic actuator 3 to control the indenter 1 to apply a driving force that increases at a constant speed, the indenter 1 descends at a constant speed according to the spring constant of the leaf spring 2. That is, as shown in FIG. 4A, before the indenter tip touches the sample surface, the descending amount of the indenter increases linearly with time. Assuming that the time point when the tip of the indenter 1 touches the sample surface is T1, the descending amount deviates from the straight line because the indenter receives a drag force from the sample at T1. When the descending amount is differentiated with respect to time and drawn as a graph of descending speed, it is as shown in FIG. The descending speed is a constant value until T1, but after T1, the descending speed decreases at a substantially constant rate. It is assumed that the surface is detected by specifying the time T1 when the descending speed starts to decrease from a constant value.
[0021]
In the above example, the sample stage has a vertically movable range of 20 mm, but the resolution is only 1 μm. Therefore, when the surface detection is performed by driving the sample stage, the surface detection can be performed only in increments of 1 μm. On the other hand, the resolution of the indenter position measurement is 1 nm, which is very good. However, since the driving range of the indenter is only 100 μm, if surface detection is to be performed by lowering the indenter, the sample surface must be within 100 μm from the tip of the indenter in advance. It is very difficult to perform this manually as in the conventional method. In contrast, according to the method of the present invention, the surface of the sample automatically enters the movable range of the indenter, so that the operator is not burdened and accurate surface detection can be performed without failure.
[0022]
Note that the reason why the indenter is returned to the origin in step S9 after the surface is detected in step S4 in the above example is to ensure a sufficient driveable range when the indenter is pushed into the sample. Further, the value of α is arbitrary, but it is desirable that the value be about 1/100 to 1/10 of the movable range of the indenter.
[0023]
【The invention's effect】
According to the method of the present invention, it is possible to deal with samples of various heights by using a sample stage having a low resolution but a wide driving range, and the work for setting the sample can be facilitated. On the other hand, the sample surface can be detected with high accuracy by using an indenter driving unit and a measuring unit with good position resolution. That is, since the method of the present invention can perform highly accurate surface detection while improving operability, it can be applied to extremely thin thin film samples or hardness measurement performed using a minute force, resulting in highly accurate hardness measurement. It can be performed.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a hardness tester to which a method of the present invention is applied.
FIG. 2 is a diagram conceptually showing a sample surface detection method.
FIG. 3 is a flowchart showing a sample surface detection procedure;
FIG. 4 is a diagram for explaining a point in time of sample surface detection.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Indenter 2 ... Leaf spring 3 ... Electromagnetic actuator 4 ... Displacement meter 5 ... Sample stage 6 ... Sample 7 ... Control apparatus

Claims (1)

In a hardness tester that measures the hardness of a sample surface from the amount of the indenter pressed into the sample surface and the force applied to the indenter at that time, in a sample surface detection method for detecting that the indenter has contacted the sample surface A step of detecting whether the indenter is in contact with the sample surface while driving the indenter within a predetermined distance so as to approach the sample from the origin position, and the indenter when the indenter does not contact the sample surface within the predetermined distance. To return the origin to the origin position, and to drive the sample closer to the indenter by the predetermined distance, and to store the driving distance of the indenter to the contact position when the indenter contacts the sample surface within the predetermined distance. And a step of driving the sample closer to the indenter by a distance slightly shorter than the driving distance of the indenter while returning the indenter to the origin position. Sample surface detection method in tester.

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