JPH01175226A - Measurement of epitaxial layer thickness - Google Patents

Abstract

PURPOSE:To measure a layer thickness on the basis of a stepped height by a method wherein, after a thermoplastic substance has been coated on the surface of an uppermost layer of two or more epitaxial layers excluding a prescribed region and the two or more epitaxial layers are exposed to be stepped shape by repeating a selective etching operation and a heating operation. CONSTITUTION:An InGaAs lower-part epitaxial layer 2 and InP upper-part epitaxial layer 3 are grown one after another on an InP substrate 1; a thermoplastic substance 6 is coated, e.g., on the wax surface excluding a region 5. Only the upper-part epitaxial layer 3 is etched selectively by using HCl; this assembly is heated; the thermoplastic substance 6 flows sown to the exposed lower-part epitaxial layer 2. Then, this assembly is etched selectively by using an etchant of HF+HNO3 which is suitable for InGaAs. A part to be etched is only a part to which the thermoplastic substance 6 has not been applied. The lower-part epitaxial layer 2 and the upper-part epitaxial layer 3 are exposed in a stepped shape; each stepped height can be measured with a thickness gauge using a probe.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for measuring the epitaxial layer thickness of a multilayer structure, the present invention provides a method for measuring the epitaxial layer thickness that reduces the fracture area of the wafer, improves the measurement accuracy, and further improves the workability. A first step of applying a thermoplastic material to the top layer surface of a plurality of epitaxially grown epilayers except for a desired region, and applying an epitaxial layer through the desired region. a second step in which the top layer of the layer is selectively etched to expose the surface of the epitaxial layer of the next layer; and a third step in which the applied thermoplastic is heated and flows to the exposed surface of the epitaxial layer of the next layer. and a fourth step of selectively etching the exposed epitaxial layer of the next layer, and repeating the third and fourth steps for successive epitaxial layers to step all the epitaxial layers. Finally, the thickness of each epitaxial layer is measured from the height of each step of the staircase.

[Industrial application field]

The present invention relates to a method for measuring epitaxial layer thickness, and more particularly, to a method for measuring the thickness of each epitaxial layer on a multilayered epitaxial wafer. Concerning a method for measuring layer thickness.

-a. In order to manufacture semiconductor devices, various device processes are required.
GaAs IC using a compound semiconductor such as As as a substrate
In order to fabricate an active layer having sufficient electron mobility, an active layer or the like must be formed on the crystal surface of the substrate by some means.

One of the methods is to provide an active layer to the required depth on the substrate surface by ion implantation + annealing.
Another method is to epitaxially grow a necessary active layer on a substrate. Particularly, in the latter method, various epitaxial crystal growth techniques have been developed and put into practical use in response to the increasing performance and variety of target semiconductor devices.

[Conventional technology]

For example, taking liquid phase epitaxy as an example of epitaxial growth technology, liquid phase epitaxy involves making a metal with a low melting point into a liquid, using it as a solvent, and dissolving the raw material of the semiconductor to be grown in it at high temperature. This is an epitaxy method that takes advantage of the fact that semiconductors precipitate on the substrate as the saturation level decreases when the substrate is cooled. Such liquid phase epitaxy requires crystallization to occur in near thermal equilibrium and stoichiometric composition (stoichiometric composition).
c Comp.

5iLion) has relatively high structural integrity due to its non-slip properties.

By the way, it is desirable that the epitaxial thickness formed on a single wafer be uniform over the entire wafer surface, but some errors in epitaxial thickness may occur due to variations in in-plane temperature distribution, etc. This may result in so-called defective areas in which the product cannot be obtained.

Therefore, by sampling an arbitrary part on the wafer and randomly measuring the epitaxial thickness of this part, we can obtain a representative value for the entire upper bar surface and manufacture devices while avoiding defective parts of the epitaxial thickness. things are done.

In particular, in LEDs, LDs, and light-receiving devices using m-v group compounds, it is common practice to create a p-n junction in an epitaxially grown epitaxial layer by diffusion, so diffusion can be precisely controlled. In order to do this, it is necessary to precisely measure the thickness of the epitaxial layer.

The conventional epi FEH measurement method is as follows: (1) After the epi wafer is cleaved, the cleavage plane is exposed to light and then immersed in a felsian solution for stain etching. Methods include visually measuring the resulting step in the epitaxial layer, and (n) selectively etching a desired region using a mask to expose a cross section of the epitaxial layer to be measured.

[Problem that the invention seeks to solve]

However, in such conventional epitaxial thickness measurement methods, in the case of (1), there is a large measurement error due to visual inspection, and there is a tendency for other epitaxial layers to be slightly etched in the thickness direction due to stain etching. However, there are problems in that the measurement accuracy is only about 0.1 μm, and in addition, since cleavage occurs, it is necessary to avoid the area near the center of the epitaxial wafer, making it difficult to obtain the required epitaxial limit value at the center of the wafer. There was a problem that there was no.

In the case of (■), it is possible to measure the epitaxial thickness at a desired position on the wafer, but for multiple epitaxial layers, it is necessary to change the location for each layer and provide a mask several times, increasing the number of sampling points. There were problems in that the area of destruction was large and workability was poor because a mask was required for each layer.

The present invention was made in view of these problems, and
The purpose of this invention is to realize a method for measuring epitaxial NrFJ that reduces the fracture area of a wafer, improves measurement accuracy, and improves workability.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a first step of applying a thermoplastic material to the surface of the uppermost layer of a plurality of epitaxially grown epitaxial layers except for a desired region; a second step in which the top layer of the epitaxial layer is selectively etched to expose the surface of the next epitaxial layer; and a third step in which the applied thermoplastic material is heated and flows to the exposed surface of the next epitaxial layer. and a fourth step of selectively etching the exposed epitaxial layer of the next layer, and repeating the third and fourth steps for successive epitaxial layers until all the epitaxial layers are etched. is exposed in a stepwise manner, and finally, the thickness of each epitaxial layer is measured from the height of each step of the step.

[For production]

In the present invention, after applying a thermoplastic material such as wax to the top layer surface of a plurality of epitaxial layers except for a predetermined area, the plurality of epitaxial layers are exposed in a stepped manner by simply repeating selective etching and heating. The thickness of each epitaxial layer is measured from each step height of the staircase.

Therefore, the destruction area of the wafer is limited to only the etched area of the top layer, and the measurement accuracy is relatively high (for example, when using the alpha step method described later).
An accuracy of 0.01 p m) is obtained. Furthermore, since the thermoplastic material only needs to be applied once regardless of the number of epitaxial layers, workability is improved.

〔Example〕

Hereinafter, the present invention will be explained based on the drawings.

FIGS. 1(a) to 1(e) are process diagrams showing one embodiment of the epitaxial layer thickness measurement method according to the present invention,
This is an example applied to an epitaxial wafer having two epitaxial layers.

The present embodiment will be described below in accordance with the process order.

First, a thermoplastic material 6 is epitaxially grown on the epitaxial wafer 4 in which a lower epitaxial layer N2 made of InGaAs and an upper epitaxial layer 3 made of InP are sequentially epitaxially grown on a substrate 1 made of InP, except for a desired region 5. Apply to the surface of layer 3. The thermoplastic substance 6 softens at a predetermined temperature or higher,
Moreover, any material may be used as long as it does not chemically change with the various etchants described below, and for example, so-called wax such as wax may be used. Alternatively, a resist may be used as long as it has a softening point.

In step 1°゛ b), an etchant suitable for InP (for example, HCI) is applied.
The upper epitaxial layer N3 is selectively etched using a etchant to expose the surface of the lower epitaxial layer 2. At this time, the lower epi layer 2 is
Since it is not compatible with the etchant used for the upper epitaxial layer 3,
There will be no etching.

Step 1 of 1C) Thereafter, the epi wafer 4 is dried and heated to flow the thermoplastic material M6 to the surface of the lower epi N2. That is, the purpose of heating at this time is to make the thermoplastic substance 6 flow, and therefore, the heating temperature may be set based on the softening point of the thermoplastic substance 6.

After the 1 d process, an etchant suitable for InGaAs (for example,
Using HF+HNO:l), the exposed lower epi layer 2
Select and etch. At this time, since the thermoplastic substance 6 has flowed into the surface of the lower epitaxial layer 2, the etched portion is only the part to which the thermoplastic substance 6 is not adhered, and the etched portion is removed from the previous step (FIG. 1(b)). The area is narrower than the etched area (ie, region 5) of the upper epitaxial layer 3 etched in step 1.

Therefore, after removing the thermoplastic material 6, the lower epi layer 2 and the upper epi layer 1! i3 is exposed in a stepped manner.

The lower epi layer 2 and upper epi layer N3 exposed in this way
Although not shown, the epitaxial thickness is measured in the final step.

That is, the epitaxial thickness is measured, for example, by tracing the unevenness with a thickness gauge using a needle (generally, there seems to be no fixed name, and here we use the alpha step method for convenience). Each step height of the lower epitaxial layer 2 and the upper epitaxial layer 3 is measured with extremely high accuracy (accuracy of about 0.01 μm), which is a feature of the alpha step method.

Note that the measurement method is of course not limited to the method described above, and is limited to any method that can measure the height of each stepped step and with an accuracy equal to or higher than the above. It's not a thing.

As described above, in this embodiment, after coating the thermoplastic substance 6 on the surface of the upper epi layer 3 of the uppermost layer of the epi wafer 4, the lower epi layer 3 can be etched by simply repeating selective etching and heating.
and the upper epitaxial layer 3 can be exposed in a stepwise manner,
The thickness of each layer can be precisely measured using, for example, the alpha step method, which has relatively high accuracy.

Therefore, the area of failure is limited to the portion to which the thermoplastic substance 6 is not applied to the surface of the upper epitaxial layer 3, and the area of failure can be minimized. As a result, measurement can be carried out at any arbitrary position within the 4 planes of the epitaxial wafer.

In addition, the etchant is used for the lower epi layer 2 and the upper epi layer 3.
Since the epitaxial layer is adapted to the etching process, epitaxial layers other than those desired are not etched, and the exposed step shape accurately represents the thickness of each epitaxial layer. Furthermore, since the highly accurate alpha step method can be used, the measurement accuracy is high, and specifically, it is possible to expect a 10 times improvement in accuracy compared to the conventional stain etching method.

Further, after applying the thermoplastic material 6, selective etching and heating can be simply repeated, so that workability is significantly improved.

Although this embodiment shows an example in which the present invention is applied to two epitaxial layers, it goes without saying that the present invention can also be applied to a multilayer structure having two or more layers.

〔Effect of the invention〕

According to the present invention, a plurality of epitaxial layers can be exposed in a stepwise manner simply by applying a thermoplastic substance to the top layer surface of a plurality of epitaxial layers except for a predetermined area, and then repeating selective etching and heating. Can be done.

Therefore, the area of destruction of the wafer can be limited to the etched area of the uppermost layer, and measurement accuracy can be improved by using, for example, the alpha step method. Furthermore, since the thermoplastic material can be applied only once regardless of the number of epitaxial layers, workability can be improved.

[Brief explanation of the drawing]

FIGS. 1(a) to 1(e) are process diagrams showing an embodiment of the epitaxial layer thickness measuring method according to the present invention. 5... Area, 6... Thermoplastic material. Patent applicant: Fujitsu Limited. 'l of one embodiment: jth 2: lower epi layer 3: upper epi layer 5: region 6: thermoplastic t process diagram

Claims (1)

[Claims] A first step of applying a thermoplastic substance to the top layer surface of a plurality of epitaxially grown epitaxial layers except for a desired region, and applying a thermoplastic substance to the top layer of the epitaxial layer through the desired region. a second step in which the surface of the epitaxial layer of the next layer is selectively etched; a third step is to heat the applied thermoplastic material and flow it to the exposed surface of the next epitaxial layer; and a fourth step of selectively etching the epitaxial layer of the next layer, and repeating the third and fourth steps for the epitaxial layer of the next layer to expose all the epitaxial layers in a stepwise manner. , Finally, a method for measuring epitaxial layer thickness, characterized by performing a step of measuring the thickness of each epitaxial layer from each step height of the stairs.