JPH0476918A - Etching of epitaxially grown layer in wafer surface - Google Patents

Abstract

PURPOSE:To improve yield through uniformization of the film thickness of an epitaxial grown layer by spouting the etchant while an etchant-spouting nozzle is moved from a vicinity of the center of the epitaxially grown layer of an existing wafer to its outer periphery. CONSTITUTION:With a wafer 1 spun, pure water is spouted to a vicinity of the spin center of the wafer 1 from the nozzle 3a of a pure water spouter 3 controlled to drive by a microcomputer and the like, thereby improving the wettability of the wafer surface to the etchant. In the case of using an etchant with concentration much decreased, it is switched to pure water after spouting over a fixed period of time. The etchant is then spouted to a vicinity of the spin center of the wafer 1 from the nozzle 4a of an etchant spouter 4, and a spout point of the etchant is moved to the outer periphery of the wafer 1 on the basis of conditions predetermined from experiment or others. At this time, pure water keeps on spouting to the spin center from the device. This process can uniformize the film thickness of the epitaxially grown layer of an existing wafer and improve yield.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an etching method for uniformizing the thickness of an epitaxially grown layer formed on the surface of an existing wafer.

(Prior art) Conventionally, in order to manufacture FETs (field effect transistors), wafers were purchased from semiconductor substrate manufacturers, etc., and FETs were manufactured by forming source electrodes, train electrodes, or gates on the surface of the existing wafers. are doing.

(Problem to be Solved by the Invention) However, when manufacturing FETs, the epitaxial growth layer of the wafer is used as an active layer, so the thickness distribution of the epitaxial growth layer directly influences I dss (channel saturation current). Become. For example, φ
In the case of a 2-inch GaAs wafer, the thickness distribution of the epitaxial growth layer is about 2%, but if the thickness of the epitaxial growth layer is 0°4 μm, the thickness distribution is (maximum thickness -
The minimum film thickness) is approximately 80A.

Therefore, if the existing wafer is used as is, as in the past, this film thickness distribution will become the distribution of the channel layer of the FET, and the I dss distribution will deteriorate significantly. For example, as shown in FIG. 2, I dss is 30 at the center of the wafer.
It is approximately mA, but increases as it approaches the wafer edge, reaching approximately 200 mA near the edge.

Since the range of I dss required for a FET is limited depending on the use of the FET, if the uniformity of I dss within the wafer surface is poor, the number of FET elements that can be obtained from a unit wafer will decrease. Yield decreases.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention has a method of discharging the etching solution while moving a nozzle that discharges the etching solution from near the center of the epitaxial growth layer of the existing wafer toward the outer periphery. did.

(Function) The film thickness of the epitaxially grown layer of an existing wafer becomes thicker as it approaches the outer periphery, but the closer it is to the outer periphery, the longer it is exposed to the etching solution, and as a result, the thickness of the epitaxially grown layer becomes uniform.

(Example) Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a conceptual diagram of an apparatus used to carry out the method of the present invention.

To make the thickness of the epitaxially grown layer of an existing wafer uniform, for example, the surface of the existing wafer can be wet-etched so as to eliminate the thickness distribution of the epitaxially grown layer. In this wet etching, etching solution is discharged onto the surface of the wafer while rotating the wafer around a point within its surface, and at this time, the center of rotation of the wafer is set at I ds.
The thickness of the epitaxially grown layer can be made uniform by setting the center point of the s distribution and moving the discharge point of the etching solution from the center of rotation toward the outer circumference at a predetermined speed.

To explain this in detail with reference to FIG. 1, the wafer 1
Estimate the center position of the epitaxially grown layer thickness distribution,
Shaft 2 of the spinner device that connects this position to a vacuum pump, etc.
Then, the wafer 1 is placed on the upper end of the shaft 2 and sucked through a suction hole opened at the upper end of the shaft 2.

Then, the wafer 1 is rotated at a high speed of, for example, 5000 rpm/min, and pure water (or etching liquid with a very low concentration) is applied to the rotation center of the wafer 1 from the nozzle 3a of the pure discharge device 3, which is driven and controlled by a microcomputer or the like. The etching liquid is discharged nearby to improve the wettability of the surface of the wafer 1 with respect to the etching liquid. When using an etching solution with a very low concentration, it is discharged for a certain period of time and then switched to pure water.

Thereafter, the etching liquid is discharged from the nozzle 4a of the etching liquid discharging device 4, which is controlled by a microcomputer, near the rotation center of the wafer 1, and the etching liquid discharge point is set on the wafer 1 based on conditions determined in advance through experiments. move it toward the outer circumference. At this time, the pure water discharging device 3 continues discharging pure water to the rotation center.

When the etching liquid discharge point reaches the outer circumference of the wafer 1, the etching liquid discharge device 4 stops discharging the etching liquid, and then the deionized water discharge device 3 stops discharging pure water to the rotation center for a predetermined period of time. After continuing, the discharge of pure water is also stopped, and the rotation of the wafer 1 continues for a while, and after draining, the rotation is stopped.

By doing this, the exposure time to the etching solution increases as the wafer 1 is exposed to the etching solution longer and deeper as it goes from the center of rotation (the center of the thickness distribution of the epitaxially grown layer) to the outer periphery. Uniform layer thickness distribution.

After performing such treatment to make the thickness of the epitaxially grown layer uniform, an FET is manufactured.

(Effects of the Invention) As explained above, according to the present invention, it is possible to homogenize the film thickness of the epitaxial growth layer of an existing wafer. The distribution is narrower, increasing yield when FETs with a specific range of I dss are required.

[Brief explanation of drawings]

Figure 1 is a conceptual diagram of the apparatus used to carry out the method of the present invention;
The figure is an explanatory diagram showing the distribution of I dss when FETs are manufactured using existing wafers as they are. DESCRIPTION OF SYMBOLS 1... Wafer, 2... Spinner shaft, 3... Pure water discharge device, 3a... Pure water discharge nozzle, 4... Etching liquid discharge device, 4a... Etching liquid discharge nozzle. Patent applicant: Victor Japan Co., Ltd. Agent Patent attorney 2 1) Part: Patent attorney Koyama Tow bar 2 Spinner shaft 3, pure water discharging device 3a...Pure water discharging nozzle 4 Etching liquid discharging device 4a...Etching liquid discharge nozzle 1 Fig. 2

Claims (2)

[Claims] (1) The center of distribution of the epitaxial growth layer formed on the surface of the wafer is aligned with the center of rotation by the spinner, and the wafer is rotated, and the etching solution is discharged while moving the nozzle from near the center of rotation to the outer periphery of the rotating wafer. A method for etching an epitaxially grown layer on a wafer surface, characterized in that: (2) The method for etching an epitaxially grown layer on the surface of a wafer according to claim 1, wherein the etching is performed while discharging pure water near the center of rotation of the rotating wafer.