JP2869112B2 - Method for manufacturing semiconductor device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to wet etching of a semiconductor.

[Conventional technology]

As for the etching of semiconductors, there are a dry method and a wet method, and a dry method having excellent controllability of etching is widely used. However, wet etching is used in compound semiconductors such as GaAs, whose element characteristics vary greatly due to damage caused by dry etching. Among the compound semiconductor elements, those requiring the highest etching accuracy are a GaAs field effect transistor (hereinafter abbreviated as FET) and a high mobility field effect transistor (hereinafter abbreviated as HEMT).

Hereinafter, a conventional method of manufacturing a semiconductor device will be described with reference to the drawings, taking a GaAs FET as an example.

FIG. 5 is a sectional view showing the structure of a GaAs FET, and FIG.
FIG. 2 is a cross-sectional view of a GaAs FET showing a step of forming the concave structure shown in FIG. In the figure, (1) is a source electrode, (2) is a drain electrode, (3) is a gate electrode, (4) is an operation layer, and (5) is a concave structure (hereinafter, referred to as an etching layer) in which the operation layer (4) is removed. (Referred to as recess structure), (6) is a buffer layer, (7) is Ga
As a semi-insulating substrate, (8) is a resist. In GaAs FETs, in order to reduce the parasitic resistance and improve the reverse breakdown voltage, the operation layer (4) of the gate electrode (3) formed between the source electrode (1) and the drain electrode (2) Adopts a recess structure (5). The channel current of the GaAs FET in the recess structure (5) is equal to the etching depth t for forming the recess structure (5) from the initial operation layer d.
And the thickness a of the operating layer (4) immediately below the gate electrode (3). The performance and yield of GaAs FETs are mainly determined by the channel current. In other words, controlling a to a desired value accurately and with good reproducibility is to equate the performance and yield of GaAs FET. As shown in FIG. 6, a normal recess structure (5) is formed by forming a source electrode (1) and a drain electrode (2), patterning the recess structure (5) with a resist (8), and exposing the same. Recessed structure (6)
Is etched several times using a wet etchant, a channel current between the source electrode (1) and the drain electrode (2) is measured for each etching, and a desired current value (thickness a) is corrected while correcting the etching time. ) Is determined.

[Problems to be solved by the invention]

Since the conventional semiconductor device manufacturing method is performed as described above, the etching time is determined by experience,
Also, even at a constant etching composition and etching temperature, the limit is ± 10% of the desired value due to the variation of the surface condition of the operating layer and the variation of stopping etching by washing. That is, in order to improve the performance variation and reproducibility of the GaAs FET, it is important to improve the accuracy of wet etching when forming the recess structure, and there is a problem that a high level of skill is required.

The present invention has been made in order to solve the above-described problems, and uses an etchant that etches a semiconductor only when light is irradiated, and detects the amount of etching by a current flowing between the semiconductor and the etchant. It is intended to improve the etching accuracy of a semiconductor.

[Means for solving the problem]

The method for manufacturing a semiconductor device according to the present invention includes the steps of: contacting a part of the surface of the doping layer disposed on the surface of the semiconductor layer with an etchant that selectively etches the semiconductor in response to light irradiation; Is etched while monitoring the photocurrent flowing through the semiconductor layer and the etchant, and is determined based on the relationship between the etching depth and the photocurrent of the etching by the light irradiation using the etchant and the doping profile determined in advance. The method includes a step of stopping light irradiation with a photocurrent value corresponding to a predetermined remaining thickness of the doping layer.

Further, the doping layer is an operation layer of the field-effect transistor, and the surface of the operation layer is irradiated with light to form a gate recess.

Still further, the semiconductor layer is formed of a compound semiconductor.

[Action]

The method of manufacturing a semiconductor device according to the present invention includes the step of contacting a part of the surface of the doping layer disposed on the surface of the semiconductor layer with an etchant that selectively etches the semiconductor in response to light irradiation, Etching while monitoring the photocurrent flowing through the substrate, and a photocurrent value corresponding to a predetermined residual thickness of the doping layer determined based on a relationship between a photocurrent and an etching depth of etching by light irradiation determined in advance and a doping profile. The semiconductor is etched by a chemical reaction between the holes and the etchant generated when the semiconductor is irradiated with light, and the hole concentration and the semiconductor resistance (film thickness / carrier concentration) ), And the change in the current allows the thickness of the semiconductor to be detected under a constant light irradiation amount, It can be obtained a relationship between the etching depth and the photocurrent. Further, in addition to the relationship between the etching depth and the photocurrent, a doping profile on the surface of the semiconductor layer is also determined in advance, and based on the photocurrent value corresponding to the predetermined remaining thickness of the doping layer, the predetermined reproducibility of the semiconductor layer is determined. Can be controlled. Further, the residual thickness of the doping layer at the time of etching can be set according to the value of the carrier concentration of the doping profile.

Further, the doping layer is an operation layer of a field-effect transistor, and a gate recess is formed by irradiating the surface of the operation layer with light, and the thickness of the channel layer depends on the value of the carrier concentration in the doping profile. It is possible to control the predetermined etching amount of the gate recess with good reproducibility.

Furthermore, since the semiconductor layer is formed of a compound semiconductor, it is possible to perform etching for obtaining stable element characteristics.

〔Example〕

One embodiment of a method of manufacturing a semiconductor device according to the present invention will be described below with reference to a GaAs FET as an example.

1 and 4 are schematic sectional views of an etching apparatus for a GaAs wafer. FIG. 1 shows a step of performing doping profile measurement by a CV method at the same time as etching by light irradiation, and FIG. The following steps are shown. Second
FIG. 3 is a graph showing the relationship between the photocurrent measured in the step of FIG. 1 and the depth from the surface of the active layer. FIG. 3 is the relationship between the carrier concentration measured in the step of FIG. 1 and the depth from the surface of the active layer. FIG. In the figure, (9) is a GaAs wafer, (10)
Is etchant, (11) sealing, (12) sapphire window, (13) carbon electrode, (14) electrode on wafer, (15) ammeter, (16) platinum electrode, (17) cell , (18) is a wafer holder and (19) is light.

 Next, a manufacturing method will be described.

KOH, Tiron and the like are known as etchants for etching GaAs only when irradiated with light. First,
As shown in the figure, a part of the GaAs wafer (9) is brought into contact with the etchant (10) via the sealing (11), and the energy larger than the band gap energy of GaAs is passed through the sapphire (12) to the GaAs wafer (9). Irradiate with light (19). At this time, DG bias is applied between the carbon electrode (13) in the etchant (10) and the electrode (14) on the wafer,
Measure the current during etching with an ammeter (15). At the same time, an AC bias is applied between the platinum electrode (16) in the etchant (10) and the electrode (14) on the wafer, and the capacitance-voltage (C-V) between the GaAs wafer (9) and the etchant (10) is increased. 3) A measurement is performed to determine a relationship (doping profile) between the thickness of the active layer (4) on the GaAs wafer (9) and the carrier concentration from the CV characteristics.

According to the above measurement, when it is desired to set the thickness a of the recess structure (5) after the etching to 1000 °, when the photocurrent is reduced to 82% (147.5 / 180) from the start of the etching, the light (19) at the point A in FIG. It becomes clear that the irradiation of the laser beam should be stopped.

Next, the GaAs wafer (9) measured as shown in FIG. 3 is patterned with a resist (8) so as to expose only the recess structure (5), and the electrode (14) portion on the wafer is removed.
The entire surface of the GaAs wafer (9) is brought into contact with the etchant (10) and irradiated with light (19). When the photocurrent reaches 82% of the start of etching, the light (19) is stopped and the GaAs wafer (9) is washed with water. And complete the etching.

The actual measured value of the channel current between the source electrode (1) and the drain electrode (2), which is determined by the variation in the etching, can be reduced to ± 5% for the entire 2-inch wafer, which is less than half the conventional value. Also, the conventional manufacturing method requires a high skill that the setting of the etching time is determined by the degree of change (decrease) of the channel current due to the previous etching, whereas the manufacturing method according to the present invention uses only the photocurrent value. Since it is sufficient to detect and stop the photocurrent, the reproducibility can be greatly improved from the conventional ± 15% to ± 5%.

In the above embodiment, the case of manufacturing a GaAs FET has been described, but it goes without saying that the present invention can be applied to a HEMT and a heterojunction device in addition to the FET. Furthermore, the same effects as in the above embodiment can be obtained even when the present invention is applied not only to GaAs but also to other compound semiconductors, Si, or the like.

〔The invention's effect〕

As described above, according to the present invention, a part of the surface of the doping layer disposed on the surface of the semiconductor layer is brought into contact with the etchant for selectively etching the semiconductor in response to light irradiation, and the etchant and the semiconductor layer Etching while monitoring the photocurrent flowing through the substrate, and a photocurrent value corresponding to a predetermined residual thickness of the doping layer determined based on a relationship between a photocurrent and an etching depth of etching by light irradiation determined in advance and a doping profile. The method includes a step of stopping the light irradiation, the amount of etching can be controlled by a photocurrent value corresponding to a predetermined residual thickness of the doping layer, and the residual depth of the doping layer can be controlled by the value of the carrier concentration of the doping profile. Semiconductor device having a predetermined residual thickness of the doping layer can be formed with good reproducibility, and Residual thickness of Doping layer can be obtained with good reproducibility by a simple method of a semiconductor device which greatly affects the electrical characteristics of the semiconductor device.

Further, the doping layer is an operation layer of the field effect transistor, and a gate recess is formed by irradiating light to the surface of the operation layer. Etching of the gate recess is performed by a photocurrent value corresponding to the thickness of the channel layer. The amount can be controlled, and a field-effect transistor with a uniform thickness of the channel layer can be formed. As a result, a field-effect transistor with a uniform channel current and uniform electric characteristics can be obtained with high yield.

Further, since the semiconductor layer is formed of a compound semiconductor, etching for obtaining stable element characteristics can be performed, and a compound semiconductor device can be obtained with a simple method with good reproducibility.

[Brief description of the drawings]

1 and 4 are schematic cross-sectional views of an apparatus for etching a GaAs wafer according to an embodiment of the method of manufacturing a semiconductor device according to the present invention. FIG.
FIG. 4 shows the steps after the step shown in FIG. 1, and FIG. 2 shows the photocurrent measured in the step of FIG. 1 and the depth from the surface of the active layer. FIG. 3 is a graph showing the relationship between the carrier concentration measured in the process of FIG. 1 and the depth from the surface of the active layer, FIG. 5 is a cross-sectional view showing the structure of a conventional GaAs FET, FIG. 6 is a GaAs F showing a process of forming the recess structure shown in FIG.
It is sectional drawing of ET. In the figure, (9) is a GaAs wafer, (10) is an etchant, (11) is a ceiling, (12) is a sapphire window, (1)
3) is a carbon electrode, (14) is an electrode on a wafer, (15)
Is an ammeter, (16) is a platinum electrode, (17) is a cell, (18) is a wafer holder, and (19) is light. In the drawings, the same reference numerals indicate the same or corresponding parts.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) H01L 21/306-21/3063 H01L 21/308 H01L 21/465-21/467 H01L 29/80

Claims (3)

(57) [Claims] A part of a surface of a doping layer provided on a surface of a semiconductor layer is brought into contact with an etchant for selectively etching a semiconductor in response to light irradiation, and the surface of the doping layer is irradiated with light. Etching while monitoring the photocurrent flowing through the etchant and the semiconductor layer, and the relationship between the etching depth and the photocurrent of the etching by light irradiation using the etchant previously determined and the doping layer determined based on the doping profile. A method for manufacturing a semiconductor device, comprising a step of stopping light irradiation with a photocurrent value corresponding to a predetermined residual thickness. 2. The method according to claim 1, wherein the doping layer is an operation layer of the field-effect transistor, and a gate recess is formed by irradiating a surface of the operation layer with light. . 3. The method according to claim 1, wherein the semiconductor layer is formed of a compound semiconductor.