JPS63174330A - Scanning electronic microscope for observing semiconductor wafer - Google Patents

Abstract

PURPOSE:To determine on which wafer and on which pellet of the wafer a defective element is present and which is the defective element of the pellet, by knowing a relation between a coordinate system representing a position of the wafer table and a coordinate system provided on the wafer or pellet. CONSTITUTION:Information on a position of an LSI pellet on a wafer and information on a position of a memory cell on the pellet are read from a storing device 5 for storing positional information of pellet and memory cell. A wafer table 1-1 is moved so that the center of the wafer is put on the center of visual field. X- and Y- coordinates (xs) and (ys) of the wafer table detected when a defective memory cell is viewed at the center of the view field are read from a device 3 for detecting amount of movement of the wafer table and relative coordinates from the center of the wafer are calculated therefrom. A device 4 for determining position of a defective element determines, based on the positional information of the memory cell, to which pellet and to which bit that defective memory cell belongs.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a scanning electron microscope for observing semiconductors, and particularly to a scanning electron microscope suitable for observing ultrafine products such as 256KSRAM and IMDRAM.

[Conventional technology]

One effective method for detecting defects in semiconductor products is visual inspection using a microscope. Conventionally, metallurgical microscopes have been used for this visual inspection, but as semiconductor products become smaller, devices with higher resolution have become necessary. Therefore, in recent years, scanning electron microscopes, which have a resolution nearly 100 times that of metallurgical microscopes, have come to be used for visual inspection.

In order to analyze semiconductor defects, it is essential to know where the defective elements detected by SEM are located on the wafer or pellet. For example, defective oxide film thickness often occurs due to uneven oxidation temperature distribution on the wafer, so it is effective to investigate the position of the defective location on the wafer in the analysis. Furthermore, for defective elements detected by SEM, the results of electrical inspection and visual inspection are often compared; in this case, it is necessary to check the position of the defective element on the pellet.

Incidentally, while the dimensions of a wafer or pellet are on the order of millimeters, the dimensions of elements are on the order of microns.

For this reason, if you adjust the magnification so that the entire image of the wafer or pellet is visible in the field of view, you will not be able to detect defective elements, and conversely, if you increase the magnification so that the entire image of the wafer or pellet is visible in the field of view, you will not be able to detect which element on which wafer you are observing. I don't know if there is.

Conventionally, the method of ``fixing the defective element at the center of the field of view of the SEM, reducing the magnification, and examining where the center is on the wafer or pellet'' was used to identify the defective element being observed on the wafer or pellet. I knew where it was in the throat.

[Problem that the invention seeks to solve]

In the conventional method described above, in order to determine the location of the defective element on the wafer or pellet, there are three steps: 1. Align the defective element with the center of the field of view, 2. Decrease the magnification, 2. Observers must manually observe the location of the object. This is it.

It is not possible to grasp the distribution of defective elements on a wafer or to compare electrical and visual inspection results in real time. For this reason, it is difficult to quickly perform failure analysis using SEM.

An object of the present invention is to solve the above problems and improve the usability of the SEM.

[Means for solving problems]

The above objective is achieved by the following means.

■Method for storing position information Each LS on the wafer for each two types
I. Means for storing the position of the pellet and the position of each element on the pellet.

■Method for determining the position of a defective element 2 Based on the position information stored in the above (■) and the position of the sample stage when the defective element is photographed at the center of the field of view, determine which element of which pellet on the wafer the defective element is. A means of determining whether

[Effect]

The position of each LSI pellet on the wafer and the position of each element on the pellet can be easily determined from the design data. Therefore, by knowing the correspondence between the coordinate system indicating the position of the sample stage and the coordinate system provided on the wafer or pellet, it is possible to determine which element of which pellet on the wafer the defective element is.

The present invention achieves the following objects by the means described above.

(1) The position of each LSI pellet is expressed on the wafer in a coordinate system set in advance, and is stored by means (2). Also,
The position of each element is expressed on the pellet in a coordinate system set in advance, and is stored by the means (2).

(2) The origin of the coordinate system indicating the position of the sample stage is set at a predetermined point on the wafer, and the correspondence between this coordinate system and the wafer coordinate system or the pellet coordinate system is calculated by the means (2). Furthermore, based on this correspondence and the position of the sample stage when the defective element was observed, which Belen is the defective element? It is determined in which element the occurrence occurred.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows an overall configuration diagram of an embodiment of the present invention.

In the figure, a device 1 is the main body of a scanning electron microscope (SEM), and includes an electron gun, a converging lens, an objective lens, a polarizing coil, a secondary electron detector, and an amplifier. Device H is a sample stage, device 2 is a sample stage drive device, device 3 is a sample stage movement detection device, device 5 is a storage device for the position of each LSI pellet on the wafer and the position of each element on the pellet, and device 4 is a device for storing the position of each LSI pellet on the wafer and the position of each element on the pellet. ,
This device determines which element of which pellet the defective element is based on the sample stage position input from the apparatus 3 and the position information input from the apparatus 5.

In this embodiment, a case will be considered in which the location of a defective memory cell is determined for a memory IC.

The main data stored in the device 5 is the LS on the wafer.
One relates to the position of the I pellet, and the other relates to the position of each memory cell on the pellet.

The former specifically refers to the wafer radius and pellet dimensions.

These include the relative positional relationship between the wafer center and the pellet position. On the other hand, the latter includes the memory cell dimensions, the relative positional relationship between the pellet outer periphery and each memory cell, and the like.

The device 4 determines to which bit of which pellet a defective memory cell on the wafer corresponds, according to the flowchart shown in FIG. The procedure will be explained below.

201: Pellet, memory cell position information import device 5
Information regarding the position of the LSI pellet on the wafer is acquired from the wafer. That is, the X direction dimension AL of the pellet shown in FIG.
X l y direction dimension Ly, pellet i (i=1.2・
Relative X coordinate of the lower left corner point of ) from the wafer center X□,
Information about the location of the memory cell on the pellet is taken in to the 0th order, such as the y-coordinate yP1. That is, the X-direction dimension Mx p of the memory cell shown in FIG. 4, the y-direction dimension My,
Relative X coordinate X1 of the lower left corner point of memory cell j (j=1+2...) from the lower left corner point of the pellet.

For example, the y coordinate is y1.

202: Zero point adjustment of sample stand position coordinates Move the sample stand and align the center point of the wafer with the center of the field of view. The sample stage position coordinates are converted so that the X coordinate of the sample stage and the X coordinate at this time become zero. That is, assuming that the actual value of the sample stage position is Xo, 7s, the sample position at the center of the wafer is "Sow yso," and the coordinate values after conversion are Xs, Ys, the following equation is established.

203: From the sample stage position import device 3, take in the X-direction coordinate Xs and the y-direction coordinate 'is of the sample stage when the defective memory cell is imaged at the center of the field of view, and use the above equation (1) to calculate the position from the wafer center. relative coordinates
S.

Calculate Ys.

204: Relative coordinates Xs, Ys of the defective memory cell calculated in defective memory cell position determination 203
Then, based on the pellet and memory cell position information taken in step 201, it is determined which bit of which pellet the defective memory cell is.

For example, in FIG. 3, xpi<Xs<Xpi+Lx
If y pi < Y s <'/ pi + L, it is determined that the defective memory cell shown in the center of the field of view is generated in pellet i.

Furthermore, in Fig. 4, x, kuXs−z, turtle<X
a a + M x and Vwaa<Ys ypt
If <y1+M y, it is determined that the defective memory cell is the fifth bit.

By repeating steps 203 and 204 among the processing steps described above, the positions of a plurality of defective elements generated on the same wafer can be determined.

〔Effect of the invention〕

According to the present invention, it is possible to easily determine in which element of which pellet on a wafer a defective element detected by SEM occurs. Therefore, the usability of the SEM for semiconductor observation is dramatically improved, and there is an effect of speeding up failure analysis.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram of an embodiment of the present invention, Fig. 2 is a processing flow for determining the position of a defective element, Fig. 3 is an explanatory diagram of pellet position information on a wafer, and Fig. 4 is a memory on the pellet. An explanatory diagram of cell location information is shown. 1st Old 3rd Entrance 4th B

Claims (1)

[Claims] 1. Scanning electron microscope
onMicroscope (SEM) has a function to memorize the position of each LSI pellet on the wafer and the position of each element on the pellet, and based on this position information and the position of the sample stage, it is possible to identify the element in the center of the field of view. A scanning electron microscope for observing semiconductor wafers, which is equipped with a function to determine which element of which pellet is on a wafer.