JPS62143899A - Impurity diffusion apparatus - Google Patents

Abstract

PURPOSE:To form a thin diffusion layer having high concentration, by supplying a gas containing an element to be diffused, steam and O2 to the surface of a semiconductor substrate in a high-temperature diffusion chamber and diffusing a thermal reaction product into the semiconductor. CONSTITUTION:For example, three semiconductor substrates 7a-7c such as silicon wafers are placed on a specimen table 5 in a diffusion chamber 2 made of quartz glass at the circumference and placed in an impurity diffusion apparatus 1 and are heated at 800-900 deg.C in a diffusion furnace 3. Separately, water heated in a bubbler 4 is bubbled with N2 gas supplied to the bubbler through a valve 4b to obtain steam. An aqueous solution of phosphorus oxychloride is bubbled in a bubbler 5 with N2 gas supplied through a valve 5b and generated phosphorus oxychloride vapor is delivered through a pipe 8. The steam and the phosphorus oxychloride vapor are supplied to the diffusion chamber 2 together with O gas supplied via a valve 9b and N2 gas supplied via a valve 9a as a carrier gas. Phosphorus oxychloride is made to react with O2 to form P2O5 and Cl2. SiO2 is produced on the surface of wafers 7a-7c by the reaction of OH<-> of steam and Si and the reaction of O2 and Si and is converted to a eutectic crystal with P2O5 to form a phosphorus silicate glass film 10. Phosphorus is further diffused and segregated to form a thin diffusion layer 11 having high concentration.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an impurity diffusion device for forming an impurity diffusion layer such as phosphorus on a semiconductor substrate such as a silicon wafer.

[Traditional technique]

Semiconductor i! such as LSI! In order to create a product circuit, phosphorus (P) and boron (B) are applied to a silicon wafer etc. through a mask.
An impurity expansion technique is required to implant the impurity. Conventionally, a diffusion chamber heated to a high temperature in a heating furnace is used for this impurity diffusion (injection), and this is done by forming a glass film containing a diffusion element on the surface of a silicon wafer, etc. placed inside this diffusion chamber. It is. That is, a liquid compound containing an element to be diffused into a silicon wafer and oxygen are introduced together with a carrier gas into a diffusion chamber kept at a high temperature, and a glass film containing the element is formed on the surface of the silicon wafer. For example, when forming a phosphorus (P) diffusion layer on a silicon wafer, phosphorus acid chloride (Pocks), which is a liquid compound of phosphorus (P), is pumped into a diffusion chamber and PSG (Pocks) is deposited on the surface of the silicon wafer. Forms a phosphorus/silicate glass) layer. PS formed on a silicon wafer in this way
G is caused by the fact that phosphorus (P) ions in PSG diffuse into the silicon wafer over time, and phosphorus (P) ions in the silicon wafer
) forms a diffused N-type layer. This method of forming a diffusion layer is similarly carried out for other elements of Groups (1) and (2) of the Periodic Table of Elements.

[Problems with conventional technology]

In the conventional impurity diffusion device as described above, the impurity is diffused by creating an oxygen atmosphere in the diffusion chamber, so that only a very thin glass film (PSG film) is formed on the silicon substrate. Therefore, the total amount of impurities diffused into the silicon substrate from this glass film is small. therefore,
In order to form a highly concentrated diffusion layer on a silicon substrate, a long diffusion process is required. However, in this case, the N-type diffusion layer inevitably became wider, and it was not possible to form a diffusion layer with a high concentration and a shallow junction. This impairs the degree of integration of semiconductors and hinders the production of small ICs.

[Purpose of the invention]

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the above-mentioned conventional drawbacks and to provide an impurity diffusion device capable of forming a highly concentrated and shallow diffusion layer in a semiconductor.

[Key points of the invention]

In order to achieve the above object, the present invention supplies moisture when forming a diffusion layer, forms a glass film containing a large amount of impurities, and gradually diffuses the impurities in this glass film onto a silicon substrate. As a result, the concentration of impurities diffused onto the silicon substrate becomes dense, and the main idea is to perform shallow diffusion.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic diagram of the impurity diffusion device of this embodiment. In the figure, an impurity diffusion device 1 includes a diffusion chamber 2, a diffusion furnace 3 provided on the outer peripheral surface of the diffusion chamber 2, bubblers (saturators) 4 and 5, and the like.

In the chamber 2, on a sample stage 6, there are three semiconductor wafers, for example, silicon wafers (hereinafter referred to as Si wafers) 7a, 7b, and T.
c is placed at f2. These Si wafers 7a to 7c are
It is made of high-purity silicon single crystal formed by a pulling method (CZ method) or the like. Further, this diffusion chamber 2 is heated to 800° C. to 900° C. during the diffusion process by a diffusion furnace 3 provided around the outer periphery of the diffusion chamber 2.

On the other hand, bubblers 4 and 5 are valves 4a% and 5a
It is connected to the diffusion chamber 2 via a pipe (delivery pipe) 8. Water (H2O) is placed in the bubbler 4, and a solution of phosphorus acid chloride (POCl2) 5 is placed in the bubbler 5. The water in the bubbler 4 is heated by a heater (not shown), and water vapor is sent out by passing nitrogen gas through the bubbler 4 via the valve 4b. Further, the phosphorus acid chloride 5 has a high vapor pressure, and the phosphorus acid chloride gas is sent out by passing nitrogen gas through the solution of the phosphorus acid chloride 5 through the valve 5b.

The water vapor sent out from the bubbler 4 in this manner is sent to the pipe 8 via the valve 4a.

In addition, the phosphorus acid chloride sent out from the bubbler 5 is
a to the pipe 8. Furthermore, the water vapor and phosphorus acid chloride sent to the pipe 8 are sent to the diffusion chamber 2 by nitrogen gas (carrier gas) sent to the pipe 8 via the valve 9a.

Further, at this time, oxygen (02) is also sent out from the pipe 8 to the diffusion chamber 2 via the pulp 9b.

In the impurity diffusion device of this embodiment configured as described above, an operation is performed in which phosphorus oxychloride sent to the diffusion chamber 2, water vapor and oxygen spreads phosphorus onto the Si wafers 7a to 7C (1)k. This will be explained below.

Figures 2 fa) to (d) are process diagrams showing this process,
The process will be explained below according to this process diagram.

First, the diffusion chamber 2 in which the Si wafers 7a to 7c (indicated by 7a representing 7a to 7C in the figure) is installed is heated by the diffusion furnace 3, and acid chloride is released from the bubblers 4 and 5 as described above. Supplies phosphorus and water vapor. Further, the valve 9b is opened to supply oxygen to the diffusion chamber 2. In this way, when the inside of the diffusion chamber 2 is maintained at 800°C to 900°C and each of the above-mentioned gases is introduced into the diffusion chamber 2, the phosphorus acid chloride and oxygen introduced into the diffusion chamber 2 are A chemical reaction occurs between the two, as shown in the same figure (81
The state shown in the figure changes to the state shown in bl. In other words, phosphorus acid chloride (POC63) and oxygen (02) react to produce phosphorus pentoxide (P20!,) and chlorine (Ci22).
) is generated.

In addition, part of the water vapor in the diffusion chamber 2 is dissociated into H+ and OH-, and the OH- group reacts with silicon (Si), causing S
Silicon dioxide (hereinafter referred to as silicon oxide) (SiO2) is generated on the surface of the i-wafer 7a (20H-+5i-3i
O? +H2↑). At this time, the oxygen in the diffusion chamber 2 is also S
It reacts with i-Uni/X7a to produce silicon oxide (Si02), but since the OH- group in the diffusion chamber 2 is more active than oxygen, most of the silicon oxide (SiO2) is produced by the former reaction. , and its production speed is also fast.

Therefore, the amount produced is much larger than that in the case of oxygen alone.

The silicon oxide (Si02) produced in this way,
The aforementioned phosphorus pentoxide (P2O3) becomes a eutectic state, and as shown in the same figure (C), Si5. / psc on the surface of 7a
<phosphorus/silicate glass) film 10 is formed.

Furthermore, inside the PSG film 1 formed in this way)
The IJ7(P) component is Sitsus)'X1a is 800"
Since it is heated to 0 to 900°C, it gradually diffuses (penetrates) into the Si wafer 7a, as shown in the figure (dl).

Of course, phosphorus (P) is diffused within 3i Ueno\7a (
In the meantime, a new reaction caused the aforementioned silicon oxide (SiO
2) and phosphorus pentoxide (P2O3) is being produced, and new PSGSiO1 is successively formed. For this reason, the surface of 3i j-/\7a gradually becomes silicon oxide (
(SiOz). When silicon containing phosphorus (P) changes into molecules of silicon oxide (Si02), phosphorus (P)
Due to the effect that phosphorus (P) tends to exist in silicon rather than in silicon oxide (SiO2), the so-called segregation effect of phosphorus (P), the phosphorus (P) concentration in the diffusion layer 11 near silicon oxide (SiO2) increases. On the other hand, phosphorus in silicon (
The diffusion rate of P) is slow in the low concentration region, that is, in the deep region of the diffusion layer 11. Therefore, in this embodiment, in which the rate of silicon oxide (Si02) production is increased by supplying water vapor to the diffusion chamber 2, the diffusion layer 11 can be formed as a shallow and highly concentrated layer.

The above explanation has been made using Si wafers 7b and 7c as a representative, but phosphorus (P) is diffused in the same way in other Si wafers 7b and 7c, and the shallowness of the diffusion layer 11 and the high concentration of N The mold expansion 1'dz'fN is uniformly formed.

In addition, although a solution of phosphorus acid chloride was used in this example, solutions of phosphorus trichloride (PCJ3), phosphorus tribromide (PBr3), etc., in addition to phosphorus acid chloride, may be placed in the nozzle 5. It may be configured such that phosphorus pentoxide (P2O3) is generated by reacting with oxygen in the diffusion chamber 2, and phosphorus (P) is diffused into the Si wafers 7a to 7C.

In addition, instead of putting water into the bubbler 4, hydrogen gas (I2) and a large amount of oxygen gas (02) are supplied into the diffusion chamber 2, and ○H- groups (ions-water vapor) are generated in the diffusion chamber 2. may be generated and reacted with the Si wafers 7a to 7C. By performing the cleaning in this manner, an N-type diffusion layer 11 having a more uniform concentration than that described above is formed on the Si wafers 7a to 7.
It can be formed on C.

In this example, the sample placed on the sample stage 6 is a single crystal S.
It goes without saying that although the i-wafers 7a to 7C are used, the process can also be carried out in the same manner even on a silicon substrate in the middle of semiconductor fabrication.

In addition, in this embodiment, phosphorus (P) is added to the Si wafers 7a to 7C.
However, not only phosphorus (P) but also tribromide (BB)
A solution of r3) is placed in the bubbler 5 and reacted with oxygen in the diffusion chamber 2 to generate boron pentoxide (B205) and boron (B205).
) may be diffused into the Si wafers 7a to 7c.

〔Effect of the invention〕

As explained in detail above, according to the present invention, when forming a diffusion layer on a silicon substrate, the diffusion layer is formed in a diffusion chamber containing water vapor, so a shallow diffusion layer with high concentration can be formed. The degree of integration of IC can be improved.

Further, the PSG film formed at the same time can also be used as a protective film for the diffusion layer.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of the impurity expansion device of this embodiment, and Figure 2
Figures (a) to (dl) are process diagrams for diffusing phosphorus into a silicon wafer using the impurity diffusion device of this embodiment. 1. Impurity diffusion device, 2. Diffusion chamber, 3. Diffusion furnace, 4. 5... Bubbler, 4a, 4b, 5a, 5b, 9a,
9b...Valve, 6...Sample stand, 7a-7C...Silicon wafer, 8...Vibe, 10...PSG film, 11...N type diffusion eyebrow. Patent applicant Casio Computer Co., Ltd. Figure 1

Claims (1)

[Claims] A high-temperature diffusion chamber in which a semiconductor substrate is installed, a means for supplying a gas containing an element to be diffused into the semiconductor substrate, a means for supplying oxygen, and a means for supplying moisture to the diffusion chamber. An impurity diffusion device characterized by: