KR20010086495A - Wet etch apparatus by measuring the concentration of silicate in phosphoric acid - Google Patents

Abstract

PURPOSE: A wet etching apparatus using the density measure of silicate in a phosphate solution is provided to control uniformly the amount of etching by measuring the density of silicate and by adjusting the processing time according to the density. CONSTITUTION: A phosphate solution is filled in a bath(1) in which a wafer is wet-etched. A process controller(2) controls the overall process. A phosphate solution-supplying unit(5, 5') connects to the bath(1) and supplies water or phosphate. A temperature controller(6) controls the temperature of the phosphate solution. A phosphate densitometer(4) is mounted on the bath(1) to measure the density of the phosphate solution. A silicate densitometer(3) measures the density of silicate to control the process time in every batch.

Description

WET ETCH APPARATUS BY MEASURING THE CONCENTRATION OF SILICATE IN PHOSPHORIC ACID}

The present invention relates to a wet etch process (wet etch process) used in the pattern process, in detail, the nitride film (Si ₃ N ₄ ) of the wafer surface using phosphoric acid (H ₃ PO ₄ ) during the process of manufacturing a semiconductor device. It relates to a wet etching process for removing the crystals.

Etching is a process of selectively removing grown, deposited, and deposited thin films under a photoresist through a photo process using gas or chemicals. Etching includes dry etching and wet etching. Dry etching can be used to generate a plasma using gas to enable fine pattern processing and isotropic etching. On the other hand, wet etching is a method using a chemical such as H ₂ SO ₄ , H ₃ PO ₄ , H ₂ O ₂ , HF, HCl, NH ₄ OH and the like is used for relatively fine work than dry, and anisotropic etching There is a characteristic. Wet etching cannot be used in units smaller than 3 μm, and there are disadvantages such as chemical hazards and explosion hazards, but it is widely used for etching processes in the field because of its low price, high reliability, and good selectivity. have.

Wet etching is used to etch Si, SiO 2, Si ₃ N ₄ , Al, and phosphoric acid (H ₃ PO ₄ ) is used as a chemical to etch the nitride film (Si ₃ N ₄ ). The nitride film is mainly used as a mask or an insulating film for selective oxidation of silicon, and a process in which the nitride film is used includes LOCOS (Local Oxidation of Silicon), PBL (Poly Buffered LOCOS), and STI (ShallowTrench Isolation). have. An important factor influencing the etch rate of the phosphate solution on the nitride film is the temperature and concentration of the phosphate solution. Therefore, in order to create stable process conditions, the temperature and concentration of the phosphate solution are controlled by a process controller.

However, byproducts of silicate are inevitably generated in the process of etching the nitride film using a phosphoric acid solution. Therefore, repeated application of the same phosphate solution to multiple batches adversely affects the accumulation of silicates, which reduces the etch rate of the phosphate solution to the nitride film. In order to prevent this, conventionally, a method of vaporizing silicate using HF is used. The addition of HF causes another problem that causes the problem of worsening the selectivity of SiO ₂ and Si ₃ N ₄ in the phosphoric acid solution. Have

It is an object of the present invention to solve the problem that the etching rate of the phosphoric acid solution is reduced by the silicate accumulated as described above.

1 is a block diagram of a wet etching apparatus of the present invention

Figure 2 is a graph showing the silicate cumulative amount and etch rate change of the conventional wet etching apparatus

3 is a graph showing the change in the etching rate of the present invention.

* Explanation of symbols for main parts of the drawings

1: bath

2: process controller

3: silicate densitometer

4: Phosphate densitometer

5, 5 ': phosphoric acid (H ₃ PO ₄ ) solution supply

6: temperature controller

7: wafers

In order to achieve the above object, the present invention is configured to measure and monitor the concentration of silicate during wet etching, and to control the etching amount by adjusting the processing time according to the concentration.

1 is a block diagram of a wet etching apparatus of the present invention. Referring to FIG. 1, the wet etching apparatus of the present invention includes a bath (1) containing phosphoric acid solution and wet etching the wafer, and a process controller (2) for controlling the entire process. And a phosphoric acid solution supply unit (5, 5 ') connected to the bath to supply water or phosphoric acid, and a temperature controller (6) for constantly adjusting the temperature of the phosphoric acid solution. In addition, a phosphate densitometer (4) mounted on the bath to measure the concentration of the phosphate solution, and a silicate concentration meter (silicate) for measuring the concentration of silicate in each batch to control the process time (process time) densitometer).

FIG. 2 illustrates silicate accumulated when etching multiple batches by applying the same process time using a conventional wet etching apparatus, and a change in etching rate accordingly. As shown in Figure 2a, the amount of silicate accumulated in the same phosphate solution increases linearly with the number of processes. Figure 2b also shows that the etch rate decreases as the amount of silicate accumulates. As shown, this correlation is also approximately linear.

Therefore, in the present invention, the etching amount is controlled by the process time by using the relationship that the etching rate decreases as the silicate concentration increases. Equation (1) is applied to an embodiment of the present invention and is a calculation formula for predicting an appropriate process time.

(One)

Here, what each symbol means is as follows.

t: process time

T: total etching depth

E ₀ : Etch rate when silicate concentration is zero

C _si : silicate concentration in phosphate solution

K: coefficient between silicate concentration and etch rate

In Eq. (1), the etch rate correlation coefficient is an empirical figure obtained to reflect the relationship between the etch rate reduction and the silicate concentration of the nitride film due to the silicate accumulation during the wet etching through various batches. As can be seen from the equation, increasing the silicate concentration decreases the denominator of the calculation, which increases the processing time. Therefore, even if the etching rate is reduced by the repeated process it is possible to control the constant amount of etching because it increases the process time to reflect this. The method of calculating the process time may be the same as in Equation (1), and other types of calculations (exponential function, logarithmic function, etc.) may be used to reflect the decrease in etch rate.

3 is a graph showing how the etching rate of the nitride film changes when the present invention is applied to various batches. By adjusting the wet process time to reflect the concentration of silicate, which affects the etching rate, the etching rate can be maintained even if silicate accumulates as shown in the figure.

As described above, when the present invention is applied to the wet etching process, the etching amount can be maintained. Keeping the etching amount uniform can improve the quality of the wafer processed in the wet etching apparatus. In addition, the use of HF, which adversely affects the selection cost, can be eliminated, thus reducing the cost of silicate removal.

Claims (3)

In the wet etching apparatus for selectively removing the thin film of the wafer to manufacture a semiconductor, Bass; A solution supply part connected to the bath to replenish a solution; A densitometer mounted to the bath, And a process control device for adjusting the process time according to the measured concentration by receiving the data measured by the densitometer. The method of claim 1, The solution supplied to the bath is a phosphate solution and the concentration meter is a wet etching apparatus, characterized in that the silicate concentration meter. The method of claim 2, A temperature control device for maintaining a solution temperature of the bath; Including a phosphate concentration meter mounted to the bath, Wet etching apparatus characterized in that the process control device controls the temperature and concentration of the phosphate solution.