Vol. 8 No. 2 1991 25

THE RIGAKU JOURNAL VOL. 8 / NO. 2 / 1991

10” TOPOGRAPHY IMAGING SYSTEM

1. Introduction X-ray topography permits direct observation of the im-

age of a strain or lattice defect in single crystals. As such, this technique has been used particularly as a tool to evaluate the crystalline properties of single crystal material in the semi- conductor industry. Compared with the etching method, elec-tron microscopy, etc., X-ray topography has the advantage of non-destructive observation allowing the inspection of LSIs in each stage of their manufacturing process. Thus, the X-ray topographic technique (as a method to assess process im-provement) has contributed to the enhancement of process yields.

The progress of semiconductor technologies is notewor-thy. With the recent advancement toward larger diameter silicon wafers and larger scale integration, it is now expected that a process for 0.5 µm line width and 8" diameter wafers will be viable by the fall of 1991. Thus, assessing crystalline properties by X-ray topography is becoming more and more important.

Introduced here is a topography imaging system for 10"

wafers. The system has been developed specifically to meet the latest demand in the semiconductor industry.

2. Features & Functions First a very important feature of this system is its capa-

bility of doing topography on wafers up to 10" diameter. This satisfies both present and future needs of the industry. This technology to deal with large dia. wafers has been realized for the first time by the introduction of a curved incident slit (Japanese patent No. 135740).

Secondly, the system feature the ease of operation en-abled by automation with an X-ray TV camera and computer. So far, the operation of the existing X-ray topographic sys-tems has called for considerable skills and knowledge of X-ray crystallography. Now, this new system has resolved such difficulties.

Another feature is the use of a powerful X-ray generator (model RU-300, RU-500 or RU-1000) that has substantially reduced the exposure time. This has eliminated the drawback of X-ray topography of taking a long time to get the result and thus hampering efficient inspection. In particular, the TV

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system using an X-ray TV camera and video frame memory takes only two minutes or so for integration and synthesis. An X-ray topograph can be displayed on the video monitor within 10 minutes including the time required for crystal setting and orientation adjustment. Moreover, the picture quality is sufficiently good for the observation of a slip and a vortical distribution of precipitation. The use of X-ray film

may be unnecessary depending on the purpose of the meas-urement. The result can be recorded and stored on Polaroid film or floppy disk.

The function of the system is described referring to Fig. 1. X-rays generated by a powerful X-ray source pass through the incident slit and impinge on the sample, forming a long and narrow belt- shape irradiated area.

Vol. 8 No. 2 1991 27

(b) Photography with X-ray film

Fig 2 X-ray topograph of 8” wafer.

Diffraction takes place from the entire irradiated area on the sample when the rotation φ in the sample plane and the X-ray incidence angle ω are properly adjusted. The diffracted X-rays are projected on a fluorescent screen. A slit is ar-ranged between the sample and the fluorescent screen. It is set in such a way as to prevent the direct X-rays from bathing the screen, allowing only the diffracted X-rays to pass through.

A diffracted X-ray image which is incident on the fluo-rescent screen is converted to a visible ray image and is pho-tographed with a high-sensitivity TV camera located rear-ward. Under this condition, a slender belt-shape X-ray image can be observed on the video monitor. Along with the sample and the fluorescent screen, a TV camera is mounted on a scanning stage, a mechanism for parallel movement to scan the sample from one end to the other at a constant speed. Concurrently, the integration and synthesis of the X-ray im-age are made with the video frame memory so that the dif-fracted X-ray image of the whole sample can be displayed and observed on the video monitor.

Since this method offers the entire view of a large-dia. wafer at a glance, it allows observation of a strain image as well as a distribution of precipitation covering a broad area. They hitherto tended to be unnoticed by the direct method that uses a PbO vidicon (where the imaging area is as small as 9 x 12 mm2).

Topography using X-ray film is conducted by installing a film cassette to the front side of the fluorescent screen. Fig. 2 shows X-ray topographs of a 8" wafer taken on the video and on the X-ray film. A dislocation network due to heat treatment is seen over the entire area of the wafer.

Remote-controlled, automatic operation of the whole system can be made by personal computer control. For a curved crystal, topography of its whole area can be made by ABAC (Automatic Bragg Angle Control) through the ω angle control.

The 10" topograph imaging system has been developed as an improved model based on Rigaku's past experience of manufacturing more than ten topographic systems for 8" use. The 10" system features operational productivity and rapidity in serving as a practical evaluation unit for the semiconductor device manufacturing process.

3. Specifications

3.1 Configuration (1) Topographic goniometer 1 set (2) TV camera system 1 set

(X-ray TV camera, frame memory, TV signal processor, 12" monitor)

(3) Microcomputer system 1 set (4) Stand 1 set (5) X-ray generator 1 set

A powerful X-ray generator is needed such as the model RU-500 with a normal, point focus.

3.2 Detailed Specifications

(1) Topographic goniometer

a) Topographic method: Lang method (dedicated to the transmission method)

b) Topograph observation system: Observation of TV synthesized traverse topograph taken with TV camera and frame memory. Observation by X-ray film recording

c) X-ray source-to-sample distance: 1400 mm

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d) Sample-to-film distance: 10-80 mm e) X-ray beam center height: From the stand top; 700±10 mm f) ω rotation:

Allows manual coarse setting and clamping at the angular position of Si(111)- (440) reflections with MoKα. After clamping, remote-controlled rotation can be made by stepping motor driving over the 5° range.

g) Scanning stage: Scanning range ±130 mm, stepping motor driving

h) Sample holder: Can hold wafer crystal of 10" dia. in max. Intrapla-nar rotation 360°, stepping motor driving

i) 3rd slit arm: Holds 3rd slit and allows coaxial rotation with the w axis. Allows setting for Si(111)- (440) rotation with MoKα. Manual.

j) Slit system 1st slit:

2, 3, 5 mm wide fixed slits. Another slit for zero setting.

2nd slit: For width limitation. MoKα Si(111), (220), (400), (333), (440) curved slits. Another slit for zero setting. 10 µm, 30 µm straight slits for section topography. 5", 6", 8" for height limitation.

3rd slit: Slit width. Independent movement by stepping motor. Distance from sample: 0-70 mm, variable, manual (rack & pinion). Movement in slit whole width direction: ±10 mm, manual.

k) Film cassette: For 10". Dry plate frames for 8", 6", 5" provided. Installable to the front of TV camera fluorescent screen hood. 2 sets.

l) X-ray-proof path:

X-ray-proof drum for X-ray beam from the X-ray source.

(2) TV camera system a) Method: Indirect method b) Fluorescent screen:

GRENEX HR-8, approx. 260mm dia. c) TV camera:

High-sensitivity TV camera using SIT tube. Syn-chronization: EIA.

d) Field of vision: 6 to 11", variable To make focusing, a screen for focusing is to be in-stalled in place of fluorescent screen.

e) Monitor: With 12" video monitor

f) Frame monitor: Digital frame memory Memory size: 640 x 512 x 16 bits

(3) Microcomputer a) Microcomputer: PC-9801 (NEC) b) Printer: PC-PR101GS (NEC) c) Control and data processing:

Manual operation of each axis Curvature measure-ment TV synthesis Topography of traverse topograph and section to-pograph.

(4) Radiation Safety An X-ray-proof X-ray chamber should be prepared by the user to accommodate the X-ray generator and the topographic goniometer. If such an X-ray chamber is unavailable, then consultation may be made between the user and Rigaku to provide an adequate radiation shield.

(5) Other Depending on the type of the X-ray generator to be combined, the shutter section may need to be modi-fied.